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Sheahan Diamond Literature Technical Reference Compilation 2017


The Sheahan Diamond Literature Reference Compilation
The Sheahan Diamond Literature Reference Compilation is compiled by Patricia Sheahan who publishes on a monthly basis a list of new scientific articles related to diamonds as well as media coverage and corporate announcementscalled the Sheahan Diamond Literature Service that is distributed as a free pdf to a list of followers. Pat has kindly agreed to allow her work to be made available as an online digital resource at Kaiser Research Online so that a broader community interested in diamonds and related geology can benefit. The references are for personal use information purposes only; when available a link is provided to an online location where the full article can be accessed or purchased directly. Reproduction of this compilation in part or in whole without permission from the Sheahan Diamond Literature Service is strictly prohibited. Return to Diamond Resource Center
Sheahan Diamond Literature Reference Compilation - Scientific Articles by Author for all years
A-An Ao+ B-Bd Be-Bk Bl-Bq Br+ C-Cg Ch-Ck Cl+ D-Dd De-Dn Do+ E F-Fn Fo+ G-Gh Gi-Gq Gr+ H-Hd He-Hn Ho+ I J K-Kg Kh-Kn Ko-Kq Kr+ L-Lh
Li+ M-Maq Mar-Mc Md-Mn Mo+ N O P-Pd Pe-Pn Po+ Q R-Rh Ri-Rn Ro+ S-Sd Se-Sh Si-Sm Sn-Ss St+ T-Th Ti+ U V W-Wg Wh+ X Y Z
Sheahan Diamond Literature Reference Compilation - Media/Corporate References by Name for all years
A B C D-Diam Diamonds Diamr+ E F G H I J K L M N O P Q R S T U V W X Y Z
Tips for Users
Posted/Published Reference CodesThe SDLRC provides 3 types of references identified in the reference code. DS for scientific article, DM for a media article, and DC for a corporate announcement. Consider DS0512-0001. The DS stands for "diamond scientific". 05 stands for 2005, the year the reference was posted. 12 represents the month the reference was posted. For all years prior to 2015 the default month is 12. -0001 is the reference's identifier and it does not mean anything. The number below the refence code, ie 2015, is the year the article was published. Note that the posted year may sometimes be later than the published year.
Sort OrderReferences are sorted by the "author" name and when the reference was posted to the compilation.
Most RecentIf the reference code is highlighted yellow, the reference was made available through the most recent monthly compilation of new literature. Use this to check out new references. When new references are posted, we make it our priority to track down an online link and obtain an abstract. With regard to older references, tracking down an abstract and an online link is a work in progress.
Link to external location of article: If the title has a link, it means we have found a location online where you can either retrieve the full article free, or purchase access to it. The Sheahan Diamond Literature Service is not a technical article procurement service; if you want a restricted article, you must deal directly with the vendor who controls the copyright to the article.
Searching this page for a specific term or authorIn your Firefox browser click Edit in the menu bar and then Find. In the Find box that shows up at the bottom of the web page enter your search term. Firefox will highlight all occurrences. This is particularly helpful when the author you are seeking was not the lead author by whom the compilation is sorted.
Sending or sharing a referenceThe left column (Posted/Published) has an embedded hyperlink for each reference. In Firefox, if you right click on it, you can obtain the link url for that reference's location within the page, which you can copy and paste into an email or any other document. You can also use the "share this link" option to tweet, facebook etc the link.
Monthly Sheahan Diamond Newsletters for 2017
January 2017 May 2017 September 2017
February 2017 June 2017 October 2017
March 2017 July 2017 November 2017
April 2017 August 2017 December 2017
2017 Technical Reference Compilation
Posted/
Published
AuthorTitleSourceRegionKeywords
DS201712-2667
2018
Abdelsalam, G., Atekwana, E., Elsenbeck, J., Jones, A.G., Chikambwe, E.Imaging Precambrian lithospheric structure in Zambia using electromagnetic methods.Gondwana Research, Vol. 54, pp. 38-49.Africa, Zambia, Malawigeophysics

Abstract: The Precambrian geology of eastern Zambia and Malawi is highly complex due to multiple episodes of rifting and collision, particularly during the formation of Greater Gondwana as a product of the Neoproterozoic Pan-African Orogeny. The lithospheric structure and extent of known Precambrian tectonic entities of the region are poorly known as there have been to date few detailed geophysical studies to probe them. Herein, we present results from electromagnetic lithospheric imaging across Zambia into southern Malawi using the magnetotelluric method complemented by high-resolution aeromagnetic data of the upper crust in order to explore the extent and geometry of Precambrian structures in the region. We focus particularly on determining the extent of subcontinental lithospheric mantle (SCLM) beneath the Archean-Paleoproterozoic cratonic Bangweulu Block and the Mesoproterozoic-Neoproterozoic Irumide and Southern Irumide Orogenic Belts. We also focus on imaging the boundaries between these tectonic entities, particularly the boundary between the Irumide and Southern Irumide Belts. The thickest and most resistive lithosphere is found beneath the Bangweulu Block, as anticipated for stable cratonic lithosphere. Whereas the lithospheric thickness estimates beneath the Irumide Belt match those determined for other orogenic belts, the Southern Irumide Belt lithosphere is substantially thicker similar to that of the Bangweulu Block to the north. We interpret the thicker lithosphere beneath the Southern Irumide Belt as due to preservation of a cratonic nucleus (the pre-Mesoproterozoic Niassa Craton). A conductive mantle discontinuity is observed between the Irumide and Southern Irumide Belts directly beneath the Mwembeshi Shear Zone. We interpret this discontinuity as modified SCLM relating to a major suture zone. The lithospheric geometries determined from our study reveal tectonic features inferred from surficial studies and provide important details for the tectonothermal history of the region.
DS201707-1298
2017
Abers, G.A., van Keken, P.E., Hacker, B.R.The cold and relatively dry nature of mantle forearcs in subduction zones.Nature Geoscience, Vol. 10, pp. 333-337.Mantlesubduction

Abstract: Some of Earth's coldest mantle is found in subduction zones at the tip of the mantle wedge that lies between the subducting and overriding plates. This forearc mantle is isolated from the flow of hot material beneath the volcanic arc, and so is inferred to reach temperatures no more than 600 to 800 °C - conditions at which hydrous mantle minerals should be stable. The forearc mantle could therefore constitute a significant reservoir for water if sufficient water is released from the subducting slab into the mantle wedge. Such a reservoir could hydrate the plate interface and has been invoked to aid the genesis of megathrust earthquakes and slow slip events. Our synthesis of results from thermal models that simulate the conditions for subduction zones globally, however, indicates that dehydration of subducting plates is too slow over the life span of a typical subduction zone to hydrate the forearc mantle. Hot subduction zones, where slabs dehydrate rapidly, are an exception. The hottest, most buoyant forearcs are most likely to survive plate collisions and be exhumed to the surface, so probably dominate the metamorphic rock record. Analysis of global seismic data confirms the generally dry nature of mantle forearcs. We conclude that many subduction zones probably liberate insufficient water to hydrate the shallower plate boundary where great earthquakes and slow slip events nucleate. Thus, we suggest that it is solid-state processes and not hydration that leads to weakening of the plate interface in cold subduction zones.
DS201708-1588
2017
Abersteiner, A.Significance of halogens ( F, Cl) in kimberlite melts: insights from mineralogy and melt inclusions in the Roger pipe ( Ekati, Canada).11th. International Kimberlite Conference, PosterCanada, Northwest Territoriesdeposit - Roger

Abstract: The abundance and distribution of halogens (F, Cl) are rarely recorded in kimberlites and therefore their petrogenetic significance is poorly constrained. Halogens are usually present in kimberlite rocks in the structure of phlogopite and apatite, but their original concentrations are never fully retained due to the effects of alteration. To provide new constraints on the origin and evolution of halogens in kimberlites and their melts, we present a detailed study of the petrography and geochemistry of the late-Cretaceous Group-I (or archetypal) Roger kimberlite (Ekati cluster, Canada). The studied samples contain abundant anhedral-to-euhedral olivine which is set in a crystalline groundmass of monticellite, phlogopite, apatite, spinel (i.e. magnesian ulvöspinel-magnetite (MUM), Mg-magnetite, pleonaste, Cr-spinel), and perovskite along with abundant secondary alteration phases (i.e. serpentine, garnet (andradite-schlorlomite), amakinite ((Fe2 +, Mg, Mn)(OH)2), calcite). The Roger kimberlite is characterised by the highest recorded F-content (up to 2688 ppm) of the Ekati cluster kimberlites, which is reflected by the preservation of F-rich phases, where bultfonteinite (Ca4(Si2O7)(F, OH)2) and fluorite commonly replace olivine. In order to examine the composition and evolution of the kimberlite melt prior to post-magmatic processes, we studied melt inclusions in olivine, Cr-spinel, monticellite and apatite. Primary multiphase melt inclusions in Cr-spinel, monticellite and apatite and secondary inclusions in olivine are shown to contain a diversity of daughter phases and compositions that are dominated by alkali/alkali-earth (Na, K, Ba, Sr)-enriched Ca-Mg-carbonates ± F, Na-K-chlorides and sulphates, phosphates ± REE, spinel, silicates (e.g. olivine, phlogopite, (clino)humite), and sulphides. Although alkali/alkali-earth- and halogen-bearing phases are abundant in melt inclusions, they are generally absent from the kimberlite groundmass, most likely due to ubiquitous effects of syn- and/or post-magmatic alteration (i.e. serpentinisation). Comparisons between halogens and other trace elements of similar compatibility (i.e. F/Nd and Cl/U) in the Roger kimberlite and their respective estimated primitive mantle abundances show that halogens should be a more significant component in kimberlites than typically measured. We propose that fluorine in the Roger kimberlite was magmatic and was redistributed during hydrothermal alteration by Ca-bearing serpentinising fluids to produce the observed bultfonteinite/fluorite assemblages. Based the compositions and daughter mineral assemblages in primary melt inclusions and reconstructed halogen abundances, we suggest that Cr-spinel, monticellite and apatite crystallised from a variably differentiated Si-P-Cl-F-bearing carbonate melt that was enriched in alkalis/alkali-earths and highly incompatible trace elements.
DS201708-1589
2017
Abersteiner, A.Monticellite in Group 1 kimberlites: implications for evolution of partial melts and post-emplacement CO2 degassing.11th. International Kimberlite Conference, PosterTechnologymonticellite

Abstract: Monticellite is a magmatic and/or deuteric mineral that is often present, but widely varying in concentrations in Group-I (or archetypal) kimberlites. To provide new constraints on the petrogenesis of monticellite and its potential significance to kimberlite melt evolution, we examine the petrography and geochemistry of the minimally altered hypabyssal monticellite-rich Leslie (Canada) and Pipe 1 (Finland) kimberlites. In these kimberlites, monticellite (Mtc) is abundant (25–45 vol%) and can be classified into two distinct morphological types: discrete and intergrown groundmass grains (Mtc-I), and replacement of olivine (Mtc-II). Monticellite in group-I kimberlites: Implications for evolution of parental melts and post-emplacement CO 2 degassing (PDF Download Available). Available from: https://www.researchgate.net/publication/318032868_Monticellite_in_group-I_kimberlites_Implications_for_evolution_of_parental_melts_and_post-emplacement_CO_2_degassing [accessed Aug 10, 2017].
DS201707-1299
2017
Abersteiner, A., Giuliani, A., Kamenetsky, V.S., Phillips, D.Petrographic and melt inclusion constraints on the petrogenesis of a magmaclast from the Venetia kimberlite cluster, South Africa.Chemical Geology, Vol. 455, pp. 331-341.Africa, South Africadeposit - Venetia

Abstract: Kimberlitic magmaclasts are discrete ovoid magmatic fragments that formed prior to emplacement from disrupted kimberlite magma. To provide new constraints on the origin and evolution of the kimberlite melts, we document the mineralogy and petrography of a magmaclast recovered from one of the ca. 520 Ma Venetia kimberlites, South Africa. The sample (BI9883) has a sub-spherical shape and consists of a ~ 10 mm diameter central olivine macrocryst, surrounded by porphyritic kimberlite. The kimberlitic material consists of concentrically aligned, altered olivine phenocrysts, set in a crystalline groundmass of calcite, chromite, perovskite, phlogopite, apatite, ilmenite, titanite, sulphides, rutile and magnetite along with abundant alteration phases (i.e. serpentine, talc and secondary calcite). These features are typical of archetypal hypabyssal kimberlites. We examined primary fluid/melt inclusions in chromite, perovskite and apatite containing a diversity of daughter phases. Chromite and perovskite host polycrystalline inclusions containing abundant alkali-carbonates (i.e. enriched in K, Na, Ba, Sr), phosphates, Na-K chlorides, sulphides and equal to lesser quantities of olivine, phlogopite and pleonaste. In contrast, apatite hosts polycrystalline assemblages with abundant alkali-carbonates and Na-K chlorides and lesser amounts of olivine, monticellite and phlogopite. Numerous solid inclusions of shortite (Na2Ca2(CO3)3), Na-Sr-carbonates and apatite occur in groundmass calcite along with fluid inclusions containing daughter crystals of Na-carbonates and Na-chlorides. The primary inclusions in chromite, perovskite and apatite are considered to represent remnants of fluid(s)/melt(s) trapped during crystallisation of the host minerals, whereas the fluid inclusions in calcite are probably secondary in origin. The component proportions of these primary fluid/melt inclusions were estimated in an effort to constrain the composition of the evolving kimberlite melt. These estimates suggest melt evolution from a silicate-carbonate kimberlite melt that became increasingly enriched in carbonates, phosphates, alkalis and chlorides, in response to the fractional crystallisation of constituent minerals (i.e. olivine to apatite). The concentric alignment of crystals around the olivine kernel and ovoid shape of the magmaclast can be ascribed to the low viscosity of the kimberlite melt and rapid rotation whilst in a liquid or partial crystalline state, or to progressive layer-by-layer growth of the magmaclast. Although the mineralogy of our sample is similar to hypabyssal kimberlites worldwide, it differs from hypabyssal kimberlite units in the main Venetia pipes, which contain monticellite-phlogopite rich assemblages and segregationary matrix textures. Therefore magmaclast BI9883 probably originated from a batch of magma distinct from those that produced known hypabyssal units within the Venetia kimberlite cluster.
DS201708-1563
2017
Abersteiner, A., Kamanetsky, V.S., Kamenetsky, M., Goemann, K., Ehrig, K., Rodemann, T.Significance of halogens ( F, Cl) in kimberlite melts: insights from mineralogy and melt inclusions in the Roger pipe ( Ekati, Canada).Chemical Geology, in press available, 16p.Canada, Northwest Territoriesdeposit, Roger, Ekati

Abstract: The abundance and distribution of halogens (F, Cl) are rarely recorded in kimberlites and therefore their petrogenetic significance is poorly constrained. Halogens are usually present in kimberlite rocks in the structure of phlogopite and apatite, but their original concentrations are never fully retained due to the effects of alteration. To provide new constraints on the origin and evolution of halogens in kimberlites and their melts, we present a detailed study of the petrography and geochemistry of the late-Cretaceous Group-I (or archetypal) Roger kimberlite (Ekati cluster, Canada). The studied samples contain abundant anhedral-to-euhedral olivine which is set in a crystalline groundmass of monticellite, phlogopite, apatite, spinel (i.e. magnesian ulvöspinel-magnetite (MUM), Mg-magnetite, pleonaste, Cr-spinel), and perovskite along with abundant secondary alteration phases (i.e. serpentine, garnet (andradite-schlorlomite), amakinite ((Fe2 +, Mg, Mn)(OH)2), calcite). The Roger kimberlite is characterised by the highest recorded F-content (up to 2688 ppm) of the Ekati cluster kimberlites, which is reflected by the preservation of F-rich phases, where bultfonteinite (Ca4(Si2O7)(F, OH)2) and fluorite commonly replace olivine. In order to examine the composition and evolution of the kimberlite melt prior to post-magmatic processes, we studied melt inclusions in olivine, Cr-spinel, monticellite and apatite. Primary multiphase melt inclusions in Cr-spinel, monticellite and apatite and secondary inclusions in olivine are shown to contain a diversity of daughter phases and compositions that are dominated by alkali/alkali-earth (Na, K, Ba, Sr)-enriched Ca-Mg-carbonates ± F, Na-K-chlorides and sulphates, phosphates ± REE, spinel, silicates (e.g. olivine, phlogopite, (clino)humite), and sulphides. Although alkali/alkali-earth- and halogen-bearing phases are abundant in melt inclusions, they are generally absent from the kimberlite groundmass, most likely due to ubiquitous effects of syn- and/or post-magmatic alteration (i.e. serpentinisation). Comparisons between halogens and other trace elements of similar compatibility (i.e. F/Nd and Cl/U) in the Roger kimberlite and their respective estimated primitive mantle abundances show that halogens should be a more significant component in kimberlites than typically measured. We propose that fluorine in the Roger kimberlite was magmatic and was redistributed during hydrothermal alteration by Ca-bearing serpentinising fluids to produce the observed bultfonteinite/fluorite assemblages. Based the compositions and daughter mineral assemblages in primary melt inclusions and reconstructed halogen abundances, we suggest that Cr-spinel, monticellite and apatite crystallised from a variably differentiated Si-P-Cl-F-bearing carbonate melt that was enriched in alkalis/alkali-earths and highly incompatible trace elements
DS201708-1564
2017
Abersteiner, A., Kamanetsky, V.S., Pearson, D.G., Kamenetsky, M., Ehrig, K., Goemann, K., Rodemann, T.Monticellite in group I kimberlites: implications for evolution of parallel melts and post emplacement CO2 degassing. Leslie, Pipe 1Chemical Geology, in press available, 54p.Canada, Northwest Territories, Europe, Finlanddeposit, Leslie

Abstract: Monticellite is a magmatic and/or deuteric mineral that is often present, but widely varying in concentrations in Group-I (or archetypal) kimberlites. To provide new constraints on the petrogenesis of monticellite and its potential significance to kimberlite melt evolution, we examine the petrography and geochemistry of the minimally altered hypabyssal monticellite-rich Leslie (Canada) and Pipe 1 (Finland) kimberlites. In these kimberlites, monticellite (Mtc) is abundant (25–45 vol%) and can be classified into two distinct morphological types: discrete and intergrown groundmass grains (Mtc-I), and replacement of olivine (Mtc-II). Monticellite in group-I kimberlites: Implications for evolution of parental melts and post-emplacement CO 2 degassing (PDF Download Available).
DS201709-1949
2017
Abritis, A., McCook, A.Cash bonuses for peer reviewed papers go global. Overview citing Chin a excessive payments.Retraction Watch, Aug. 10, 3p.Global, Chinaresearch papers

Abstract: China is well known for the generous bonuses it pays scientists who land a peer-reviewed publication in a prestigious research journal. But scientists in many countries are reaping similar bounties. After spotting a discussion on a scholarship listserv about the topic, we dug further to find official documents on such payments from institutions named in the thread. Searching the internet using key terms such as “publishing cash incentives” and “schemes cash publishing” widened our net. We relied mostly on online documents in English, so we surely missed some policies. The numbers in the graphic below represent the maximum amounts we uncovered at a particular institution in a specific country. Even under those constraints, we documented publishing incentives from all corners of the globe, including at a number of U.S. institutions. Awards are primarily cash; some are as small as the $10 that Oakwood University in Huntsville, Alabama, bestows on authors when their papers are cited in the literature. Some institutions designate payments for faculty members, whereas others reward student authors.
DS201707-1300
2017
Ackerman, L., Magna, T., Rapprich, V., Upadhyay, D., Kratky, O., Cejkova, B., Erban, V., Kochergina, Y.V., Hrstka, T.Contrasting petrogenesis of spatially related carbonatites from Samalpatti and Sevattur, Tamil Nadu, India.Lithos, Vol. 284-285, pp. 257-275.Indiacarbonatite - Samalpatti, Sevattur

Abstract: Two Neoproterozoic carbonatite suites of spatially related carbonatites and associated silicate alkaline rocks from Sevattur and Samalpatti, south India, have been investigated in terms of petrography, chemistry and radiogenic–stable isotopic compositions in order to provide further constraints on their genesis. The cumulative evidence indicates that the Sevattur suite is derived from an enriched mantle source without significant post-emplacement modifications through crustal contamination and hydrothermal overprint. The stable (C, O) isotopic compositions confirm mantle origin of Sevattur carbonatites with only a modest difference to Paleoproterozoic Hogenakal carbonatite, emplaced in the same tectonic setting. On the contrary, multiple processes have shaped the petrography, chemistry and isotopic systematics of the Samalpatti suite. These include pre-emplacement interaction with the ambient crustal materials with more pronounced signatures of such a process in silicocarbonatites. Calc-silicate marbles present in the Samalpatti area could represent a possible evolved end member due to the inability of common silicate rocks (pyroxenites, granites, diorites) to comply with radiogenic isotopic constraints. In addition, Samalpatti carbonatites show a range of C–O isotopic compositions, and ?13CV-PDB values between + 1.8 and + 4.1‰ found for a sub-suite of Samalpatti carbonatites belong to the highest values ever reported for magmatic carbonates. These heavy C–O isotopic signatures in Samalpatti carbonatites could be indicative of massive hydrothermal interaction with carbonated fluids. Unusual high-Cr silicocarbonatites, discovered at Samalpatti, seek their origin in the reaction of pyroxenites with enriched mantle-derived alkali-CO2-rich melts, as also evidenced by mantle-like O isotopic compositions. Field and petrographic observations as well as isotopic constraints must, however, be combined with the complex chemistry of incompatible trace elements as indicated from their non-uniform systematics in carbonatites and their individual fractions. We emphasise that, beside common carriers of REE like apatite, other phases may be important for incompatible element budgets, such as mckelveyite–(Nd) and kosmochlor, found in these carbonatites. Future targeted studies, including in-situ techniques, could help further constrain temporal and petrologic conditions of formation of Sevattur and Samalpatti carbonatite bodies.
DS201710-2209
2017
Ackerman, L., Slama, J., Haluzova, E., Magna, T., Rapprich, V., Kochergin, Y., Upadhyay, D.Hafnium isotope systematics of carbonatites and alkaline silicate rocks from south and west India.Goldschmidt Conference, 1p. AbstractIndiadeposit - Amba Dongar
DS201711-2497
2017
Adam, C., Caddick, M.J., King, S.D.Pyroxenite causes fat plumes and stagnant slabs.Geophysical Research Letters, DOI: 10.1003/ 2017GL072943Mantleplumes

Abstract: Conventional wisdom holds that there is a change in the pattern of mantle convection between 410 and at 660 km, where structural transformations convert olivine into its high-pressure polymorphs. In this regard, recent tomographic studies have been a complete surprise, revealing (i) rapid broadening of slow seismic anomalies beneath hotspots from hundreds of kilometers wide at shallow depths to 2000-3000 km wide deeper than ~800 km, and (ii) fast seismic anomalies associated with subducted lithosphere that appear to flounder at 800-1000 km. It is difficult to reconcile these observations with the conventional view of a mantle that experiences limited mineralogical change below 660 km. Here we propose that plumes and slabs contain significant proportions of lithologies that experience an entirely different suite of mineral reactions, demonstrating that both subducted basalt and pyroxenite upwelling in plumes experience substantial changes in mineralogy and thus physical properties at ~800 km depth. We show the importance of this for mantle rheology and dynamics and how it can explain hitherto puzzling mantle tomographic results.
DS201701-0001
2016
Adhikary, D., Sahoo, R.K., Maurya, N.Petrography and geochemistry of new finding alkaline lamprophyre dyke in eastern margin of the eastern Dharwar craton, near Khammam, Telangana India.Acta Geologica Sinica, Vol. 90, 1, p. 197. abstractIndiaLamprophyre
DS201708-1590
2017
Agashev, A.Geochemistry of eclogite xenoliths from kimberlite pipe Udachnaya: section of Archean oceanic crust sampled?11th. International Kimberlite Conference, OralRussia, Siberiadeposit - Udachnaya

Abstract: A suite of 17 unique big (1 to 20 kg) and fresh ecligite xenoliths from Udachnaya kimberlite pipe have been studied for their whole-rock and minerals major and trace elements composition.Whole rock major elements composition of the Udachnaya eclogite xenoliths suite have a great variability in their MgO contents (9-19Wt%). Based on major elements composition Udachnaya eclogites can be subdivided in two subsets, high magnesian (Mg# 68.8-81.9) and low magnesian (Mg# 56.8-59). High variations also shown by Al2O3 and Na2O concentrations and high Mg# samples tend to contain less of those oxides then low Mg# samples with some exceptions. Two eclogitic groups are clearly different in style of inter-elements correlations. FeO and CaO contents are positively correlate with MgO in low Mg# group of eclogites but negatively in high Mg# group. The same relations present between Al2O3 contents of eclogite group with their Mg#. Compared to present day MORB composition eclogite samples have similar contents of most of elements with some depletion in TiO2 and P2O5 and enrichment in MgO and K2O. The variability of these elements concentrations can be related to melt extraction while elevated K2O can indicate late metasomatic enrichment. In terms of trace elements composition Udachnaya eclogites are enriched over PM but comparable to that of MORB composition, except significant enrichment in LILE elements (Rb, Ba, K, Sr). The records of both subduction related processes and mantle metasomatism could be find in geochemical features of these rocks. Most of the eclogites show positive Eu anomaly which is direct evidence of plagioclase accumulation in eglogites protolith. Variation of La/Yb ratio (1-11), in majority of samples are the range 2-4 indicates different degrees of samples metasomatic enrichment in LREE. Udachnaya eclogites have range of Sm/Nd ratio from 0.25 to 0.5 (MORB is 0.32) which positive covariates with Nd content. This trend could not be a result of melt extraction nor metasomatic enrichment rather it could reflect heterogeneity of oceanic crust composition and/or mixing with peridotite component during subduction.
DS201708-1591
2017
Agashev, A.Geochemistry of Mirny field kimberlites, Siberia.11th. International Kimberlite Conference, PosterRussia, Siberiadeposit - Mirny
DS201705-0806
2017
Agrosi, G., Tempesta, G., Mele, D., Allegretta, I., Teranzo, R., Nestola, F.Multi analytical approach for non-destructuve analyses of a diamond from Udachnaya and its trapped inclusions: the first report of (fe, Ni) 1+xS machinawite sulphide in diamonds.European Geosciences Union General Assembly 2017, Vienna April 23-28, 1p. 5374 AbstractRussiaDeposit - Udachnaya

Abstract: The study of diamonds and the mineral inclusions trapped in them is of great interest for Earth science, since they can provide insight about deep mantle conditions and its evolution. The conventional techniques commonly used are destructive and thus do not allow the employment of different methods used simultaneously to obtain integrated and complementary results. Significant information about the growth conditions of diamonds and their inclusions still trapped within them can be preferably obtained by in situ investigation. In this study, we propose a multi-analytical approach, using a set of non-destructive techniques with conventional sources, to investigate one diamond from Udachnaya kimberlite (Siberia, Russia). The combined use of micro-X-ray Tomography, micro-X-ray Fluorescence, X-Ray Powder Diffraction and micro-Raman spectroscopy, allowed us to determine the spatial distribution of the inclusions, their chemical and mineralogical composition and, finally, the paragenetic suite, totally preserving the diamond host. The sample was also studied by means of X-ray Diffraction Topography to characterize the structural defects and to obtain genetic information about the growth history of the diamond. The combination of the different data provided a sort of «mapping» of a diamond. The X-Ray Topographic images show that the sample investigated exhibits plastic deformation. Actually, one set of {111} slip lamellae, corresponding to polysynthetic twinning, affect the whole sample. The tomographic images reveal that the primary inclusions, not observable optically, show a poly-faceted shape corresponding to an assemblage of tiny crystals. The chemical data display that the trapped minerals are mono-sulphides of Fe, Ni. The diagrams obtained by the X-Ray diffraction reveal that the inclusions mainly consist of an assemblage of tiny crystals of pentlandite and pyrrothite. Nevertheless, a thorough analysis of the diffraction data suggests the presence of another mono-sulphide of Fe,Ni: mackinawite. Raman spectra taken on these inclusions confirm, for the first time, the presence of this metastable phase as inclusion in diamond. The genetic implications of these results are discussed.
DS201712-2668
2017
Agrosi, G., Tempesta, G., Mele, D., Allegretta, I., Terzano, R., Shirery, S.B., Pearson, G.D., Nestola, F.Non-destructive, multi-method, internal analysis of multiple inclusions in a single diamond: first occurrence of mackinawite ( Fe,Ni)1+xSAmerican Mineralogist, Vol. 102, pp. 2235-2243.Russia, Siberiadeposit - Udachnaya

Abstract: A single gem lithospheric diamond with five sulfide inclusions from the Udachnaya kimberlite (Siberia, Russia) has been analyzed non-destructively to track the growth conditions of the diamond. Sulfides are the most abundant mineral inclusions in many lithospheric diamond crystals and are the most favorable minerals to date diamond crystals by Re-Os isotope systematics. Our investigation used non-destructive, micro-techniques, combining X-ray tomography, X-ray fluorescence, X-ray powder diffraction, and Raman spectroscopy. This approach allowed us to determine the spatial distribution of the inclusions, their chemical and mineralogical composition on the microscale, and, finally, the paragenetic association, leaving the diamond host completely unaffected. The sample was also studied by X-ray diffraction topography to characterize the structural defects of the diamond and to obtain genetic information about its growth history. The X-ray topographic images show that the sample investigated exhibits plastic deformation. One set of {111} slip lamellae, corresponding to polysynthetic twinning, affects the entire sample. Chemical data on the inclusions still trapped within the diamond show they are monosulfide solid solutions of Fe, Ni and indicate a peridotitic paragenesis. Micro-X-ray diffraction reveals that the inclusions mainly consist of a polycrystalline aggregate of pentlandite and pyrrothite. A thorough analysis of the Raman data suggests the presence of a further Fe, Ni sulfide, never reported so far in diamonds: mackinawite. The total absence of any oxides in the sulfide assemblage clearly indicates that mackinawite is not simply a “late” alteration of pyrrhotite and pentlandite due to secondary oxidizing fluids entering diamond fractures after the diamond transport to the surface. Instead, it is likely formed as a low-temperature phase that grew in a closed system within the diamond host. It is possible that mackinawite is a more common phase in sulfide assemblages within diamond crystals than has previously been presumed, and that the percentage of mackinawite within a given sulfide assemblage could vary from diamond to diamond and from locality to locality.
DS201712-2669
2017
Agrosi, G., Tempestra, G., Della Ventura, G., Guidi, M., Hutchison, M., Nimis, P., Nestola, F.Non-destructive in situ study of plastic deformations in diamonds: x-ray diffraction topography and micro-FTIR mapping of two super deep diamond crystals from Sao Luiz ( Juina, Brazil).Crystals, Vol. 7, #233South America, Brazildeposit - Juina

Abstract: Diamonds from Juina, Brazil, are well-known examples of superdeep diamond crystals formed under sublithospheric conditions and evidence would indicate their origins lie as deep as the Earth's mantle transition zone and the Lower Mantle. Detailed characterization of these minerals and of inclusions trapped within them may thus provide precious minero-petrogenetic information on their growth history in these inaccessible environments. With the aim of studying non-destructively the structural defects in the entire crystalline volume, two diamond samples from this locality, labelled JUc4 and BZ270, respectively, were studied in transmission mode by means of X-ray Diffraction Topography (XRDT) and micro Fourier Transform InfraRed Spectroscopy (µFTIR). The combined use of these methods shows a good fit between the mapping of spatial distribution of extended defects observed on the topographic images and the µFTIR maps corresponding to the concentration of N and H point defects. The results obtained show that both samples are affected by plastic deformation. In particular, BZ270 shows a lower content of nitrogen and higher deformation, and actually consists of different, slightly misoriented grains that contain sub-grains with a rounded-elongated shape. These features are commonly associated with deformation processes by solid-state diffusion creep under high pressure and high temperature.
DS201704-0615
2017
Agrusta, R., Goes, S., van Hunen, J.Subducting slab transition zone interaction: stagnation, penetration and mode switches.Earth and Planetary Science Letters, Vol. 464, pp. 10-23.MantleSubduction

Abstract: Seismic tomography shows that subducting slabs can either sink straight into the lower mantle, or lie down in the mantle transition zone. Moreover, some slabs seem to have changed mode from stagnation to penetration or vice versa. We investigate the dynamic controls on these modes and particularly the transition between them using 2D self-consistent thermo-mechanical subduction models. Our models confirm that the ability of the trench to move is key for slab flattening in the transition zone. Over a wide range of plausible Clapeyron slopes and viscosity jumps at the base of the transition zone, hot young slabs (25 Myr in our models) are most likely to penetrate, while cold old slabs (150 Myr) drive more trench motion and tend to stagnate. Several mechanisms are able to induce penetrating slabs to stagnate: ageing of the subducting plate, decreasing upper plate forcing, and increasing Clapeyron slope (e.g. due to the arrival of a more hydrated slab). Getting stagnating slabs to penetrate is more difficult. It can be accomplished by an instantaneous change in the forcing of the upper plate from free to motionless, or a sudden decrease in the Clapeyron slope. A rapid change in plate age at the trench from old to young cannot easily induce penetration. On Earth, ageing of the subducting plate (with accompanying upper plate rifting) may be the most common mechanism for causing slab stagnation, while strong changes in upper plate forcing appear required for triggering slab penetration.
DS201706-1061
2017
Albekov, A.Yu., Chemyshov, N.M., Ryborak, M.V., Kuznetsov, V.S., Sainikova, E.B., Kholin, V.M.U-Pb isotopic age of apatite bearing carbonatites in the Kursk Block, Voronezh crystalline massif ( Central Russia).Doklady Earth Sciences, Vol. 473, 1, pp. 271-272.Russiacarbonatite

Abstract: In the central part of the European part of Russia in the southeastern part of the Kursk tectonic block, some deposits and occurrences of apatite genetically related to the alkaline-carbonatite complex have been revealed. The results of U-Pb analysis of titanite provided the first confident age estimate of silicate-carbonate (phoscorite) rocks in the Dubravin alkaline-ultramafic-carbonatite massif: they formed no later than 2080 ±13 Ma, which indicates their crystallization in the pre-Oskol time during the final stage of the Early Paleoproterozoic (post-Kursk time) stabilization phase of the Kursk block of Sarmatia (about 2.3-2.1 Ga).
DS201706-1062
2017
Albers, G.A., van Keken, P.E., Hacker, B.R.The cold and relatively dry nature of mantle forearcs in subduction zones.Nature Geoscience, Vol. 10, 5, pp. 333-337.Mantlesubduction

Abstract: Some of Earth's coldest mantle is found in subduction zones at the tip of the mantle wedge that lies between the subducting and overriding plates. This forearc mantle is isolated from the flow of hot material beneath the volcanic arc, and so is inferred to reach temperatures no more than 600 to 800 °C — conditions at which hydrous mantle minerals should be stable. The forearc mantle could therefore constitute a significant reservoir for water if sufficient water is released from the subducting slab into the mantle wedge. Such a reservoir could hydrate the plate interface and has been invoked to aid the genesis of megathrust earthquakes and slow slip events. Our synthesis of results from thermal models that simulate the conditions for subduction zones globally, however, indicates that dehydration of subducting plates is too slow over the life span of a typical subduction zone to hydrate the forearc mantle. Hot subduction zones, where slabs dehydrate rapidly, are an exception. The hottest, most buoyant forearcs are most likely to survive plate collisions and be exhumed to the surface, so probably dominate the metamorphic rock record. Analysis of global seismic data confirms the generally dry nature of mantle forearcs. We conclude that many subduction zones probably liberate insufficient water to hydrate the shallower plate boundary where great earthquakes and slow slip events nucleate. Thus, we suggest that it is solid-state processes and not hydration that leads to weakening of the plate interface in cold subduction zones.
DS201707-1301
2017
Alexander, C.M.O'D., Cody, G.D., De Gregorio, B.T., Nittler, L.R., Stroud, R.M.The nature, origin and modification of insoluable organic matter in chondrites, the major source of Earth's C and N.Chemie der Erde, Vol. 77, pp. 227-256.Mantlemeteorites

Abstract: All chondrites accreted ?3.5 wt.% C in their matrices, the bulk of which was in a macromolecular solvent and acid insoluble organic material (IOM). Similar material to IOM is found in interplanetary dust particles (IDPs) and comets. The IOM accounts for almost all of the C and N in chondrites, and a significant fraction of the H. Chondrites and, to a lesser extent, comets were probably the major sources of volatiles for the Earth and the other terrestrial planets. Hence, IOM was both the major source of Earth’s volatiles and a potential source of complex prebiotic molecules. Large enrichments in D and 15N, relative to the bulk solar isotopic compositions, suggest that IOM or its precursors formed in very cold, radiation-rich environments. Whether these environments were in the interstellar medium (ISM) or the outer Solar System is unresolved. Nevertheless, the elemental and isotopic compositions and functional group chemistry of IOM provide important clues to the origin(s) of organic matter in protoplanetary disks. IOM is modified relatively easily by thermal and aqueous processes, so that it can also be used to constrain the conditions in the solar nebula prior to chondrite accretion and the conditions in the chondrite parent bodies after accretion. Here we review what is known about the abundances, compositions and physical nature of IOM in the most primitive chondrites. We also discuss how the IOM has been modified by thermal metamorphism and aqueous alteration in the chondrite parent bodies, and how these changes may be used both as petrologic indicators of the intensity of parent body processing and as tools for classification. Finally, we critically assess the various proposed mechanisms for the formation of IOM in the ISM or Solar System.
DS201709-1950
2017
Alifirova, T.A., Pokhilenko, L.N., Taylor, L.A.Evolution of garnet clinopyroxenites from a margin of Siberian craton in major and rare element viewpoint.Goldschmidt Conference, abstract 1p.Russia, Siberiadeposit - Obnazhennaya

Abstract: Clinopyroxenite mantle xenoliths from Obnazhënnaya kimberlite pipe, NE part of Siberian craton (Russia), preserve porphyroclastic clinopyroxene with no less than two generations of garnet and orthopyroxene lamellae, sometimes together with rutile. Their crystallographic relationships are consistent with an origin by solid-state exsolution. According to reintegrated major-element chemistry and datasets for natural systems the homogeneous high-Al clinopyroxenes were previously in equilibrium within a T range of ~1400– 1500 ºC at a minimum P of 2 GPa. Ca and Al variations in a clinopyroxene assume exsolution to take place during a cooling accompanied by a compression. According to Al contents the growth of orthopyroxene lamellae in the rocks is continued down to ~850 ºC and 2.7 GPa. The xenoliths matrix assemblage of Cpx+Grt±Opx marks strain-induced recrystallization where the exsolution features in recrystallized minerals are absent. Later re-equilibration of the mineral assemblage occurred at 790–810 ºC and 3.0–3.2 GPa in the cratonic mantle prior to the removal of rocks by kimberlite melts; the reactions were controlled by the diffusion of Ca and Al in a pyroxene structure. It was noted that Sr in clinopyroxenes (284–556 ppm) increases from core to rim together with V (149–226 ppm) and Ca, opposite to Al content higher in the center of Cpx porphyroclasts. A positive Eu anomaly is significant both in clinopyroxenes and garnets (Eu/Eu* = 1.5–1.8 and 1.3–2.0, respectively). Substitution of Al for Si in the pyroxene tetrahedral sites has allowed charging balance for the substitution of additional trivalent REE into the pyroxene M2 site [1]. The process has affected to the Sr2+, Sm3+ and V3+ contents and Eu2+/Eu3+ relations responsible for the presence of Eu anomaly in a pyroxene. The work was supported by the grant of the President of the Russian Federation MK-2231.2017.5. The study with LAT was funded by NSF grant EAR-1144337.
DS201703-0396
2017
Almeida, V.V., Janasi, V.A., Heaman, L.M., Shaulis, B.J., Hollanda, M.H.B.M., Renne, P.R.Contemporaneous alkaline and tholeiitic magmatism in the Ponta Grossa Arch, Parana Etendeka magmatic province: constraints from U-Pb zircon baddeleyite and 40Ar/39Ar phlogopite dating of the Jose Fernandes gabbro and mafic dykes.Journal of Volcanology and Geothermal Research, in press available 11p.South America, BrazilAlkaline rocks

Abstract: We report the first high-precision ID-TIMS U-Pb baddeleyite/zircon and 40Ar/39Ar step-heating phlogopite age data for diabase and lamprophyre dykes and a mafic intrusion (José Fernandes Gabbro) located within the Ponta Grossa Arch, Brazil, in order to constrain the temporal evolution between Early Cretaceous tholeiitic and alkaline magmatism of the Paraná-Etendeka Magmatic Province. U-Pb dates from chemically abraded zircon data yielded the best estimate for the emplacement ages of a high Ti-P-Sr basaltic dyke (133.9 ± 0.2 Ma), a dyke with basaltic andesite composition (133.4 ± 0.2 Ma) and the José Fernandes Gabbro (134.5 ± 0.1 Ma). A 40Ar/39Ar phlogopite step-heating age of 133.7 ± 0.1 Ma from a lamprophyre dyke is identical within error to the U-Pb age of the diabase dykes, indicating that tholeiitic and alkaline magmatism were coeval in the Ponta Grossa Arch. Although nearly all analysed fractions are concordant and show low analytical uncertainties (± 0.3-0.9 Ma for baddeleyite; 0.1-0.4 Ma for zircon; 2?), Pb loss is observed in all baddeleyite fractions and in some initial zircon fractions not submitted to the most extreme chemical abrasion treatment. The resulting age spread may reflect intense and continued magmatic activity in the Ponta Grossa Arch.
DS201707-1302
2017
Almqvist, B.S.G., Mainprice, D.Seismic properties and anisotropy of the continental crust: predictions based on mineral texture and rock microstructure.Reviews of Geophysics, in press available 43p.Mantlegeophysics - seismics

Abstract: Progress in seismic methodology and ambitious large-scale seismic projects are enabling high-resolution imaging of the continental crust. The ability to constrain interpretations of crustal seismic data is based on laboratory measurements on rock samples and calculations of seismic properties. Seismic velocity calculations and their directional dependence are based on the rock micro fabric, which consists of mineral aggregate properties including crystallographic preferred orientation (CPO), grain shape and distribution, grain boundary distribution, and misorientation within grains. Single mineral elastic constants and density are crucial for predicting seismic velocities, preferably at conditions that span the crust. However, high temperature and pressure properties are not as common as elastic constants at standard temperature and pressure (STP) at atmospheric conditions. Continental crust has a very diverse mineralogy, however a select number appear to dominate seismic properties because of their high volume fraction contribution. Calculations of micro fabric-based seismic properties and anisotropy are performed with averaging methods that in their simplest form takes into account the CPO and modal mineral composition. More complex methods can take into account other microstructural characteristics, including the grain shape and distribution of mineral grains, and cracks and pores. A challenge for the geophysics and rock physics communities is the separation of intrinsic factors affecting seismic anisotropy, due to properties of crystals within a rock and apparent sources due to extrinsic factors like cracks, fractures and alteration. This is of particular importance when trying to deduce the state of crustal composition and deformation from seismic parameters.
DS201704-0616
2017
Almqvist. B.S.G., Mainprice, D.Seismic properties and anisotropy of the continental crust: predictions based on mineral texture and rock microstructure.Reviews of Geophysics, in press availableMantleGeophysics - seismic

Abstract: Progress in seismic methodology and ambitious large-scale seismic projects are enabling high-resolution imaging of the continental crust. The ability to constrain interpretations of crustal seismic data is based on laboratory measurements on rock samples and calculations of seismic properties. Seismic velocity calculations and their directional dependence are based on the rock micro fabric, which consists of mineral aggregate properties including crystallographic preferred orientation (CPO), grain shape and distribution, grain boundary distribution, and misorientation within grains. Single mineral elastic constants and density are crucial for predicting seismic velocities, preferably at conditions that span the crust. However, high temperature and pressure properties are not as common as elastic constants at standard temperature and pressure (STP) at atmospheric conditions. Continental crust has a very diverse mineralogy, however a select number appear to dominate seismic properties because of their high volume fraction contribution. Calculations of micro fabric-based seismic properties and anisotropy are performed with averaging methods that in their simplest form takes into account the CPO and modal mineral composition. More complex methods can take into account other microstructural characteristics, including the grain shape and distribution of mineral grains, and cracks and pores. A challenge for the geophysics and rock physics communities is the separation of intrinsic factors affecting seismic anisotropy, due to properties of crystals within a rock and apparent sources due to extrinsic factors like cracks, fractures and alteration. This is of particular importance when trying to deduce the state of crustal composition and deformation from seismic parameters.
DS201712-2670
2017
Alty, R.Diavik diamond mines - 2016 Socio-economic Monitoring Agreement performance.45th. Annual Yellowknife Geoscience Forum, p. 2 abstractCanada, Northwest Territoriesdeposit - Diavik

Abstract: At Diavik, sustainable development is integrated into everything we do. Our operations provide benefits and opportunities for local communities, businesses, and governments. We work with all our stakeholders to deliver substantial and lasting benefits. The Diavik sustainable development report, is a requirement under the Diavik socio-economic monitoring agreement (SEMA). Through this report information on annual training, employment, business benefits, and community initiatives are available to the public. During this session of the Geoscience discussion, we will be sharing the Diavik Diamond mine performance under the SEMA up to and including December 2016.
DS201705-0807
2017
Alvaro, M., Angel, R., Nimis, P., Milani, S., Harris, J., Nestola, F.Orientation relationship between diamond and magnesiochromite inclusions.European Geosciences Union General Assembly 2017, Vienna April 23-28, 1p. 12200 AbstractRussiaDeposit - Udachnaya

Abstract: The correct determination of the relative crystallographic orientations of single crystals has many applications. When single crystals undergo phase transitions, especially at high pressures, the relative orientations of the two phases yields insights into transition mechanisms (Dobson et al 2013). On the other hand, determination of the crystallographic orientations of minerals included in diamonds can provide insights into the mechanisms of their entrapment and the timing of their formation relative to the host diamond (e.g. Nestola et al. 2014, Milani et al. 2016). The reported occurrence of non-trivial orientations for some minerals in diamonds, suggesting an epitaxial relationship, has long been considered to reflect contemporaneous growth of the diamond and the inclusion (e.g. syngenesis). Correct interpretation of such orientations requires (i) a statistically significant crystallographic data set for single and multiple inclusions in a large number of diamonds, and (ii) a robust data-processing method, capable of removing ambiguities derived from the high symmetry of the diamond and the inclusion. We have developed a software to perform such processing (OrientXplot, Angel et al. 2015), starting from crystallographic orientation matrixes obtained by X-ray diffractometry or EBSD data. Previous studies of inclusions in lithospheric diamonds, by single-crystal X-ray diffraction and EBSD, indicate a wide variety in the orientations of different inclusion phases with respect to their diamond host (Futergendler & Frank-Kamenetsky 1961; Frank-Kamenetsky 1964; Wiggers de Vries et al. 2011; Nestola et al. 2014, Milani et al. 2016). For example, olivine inclusions in lithospheric diamonds from Udachnaya do not show any preferred orientations with respect to their diamond hosts, but multiple inclusions in a single diamond often show very similar orientations within few degrees. In the present work on magnesiochromite inclusions in diamonds from Udachnaya, there is a partial orientation between inclusion and host. A (111) plane of each inclusion is sub-parallel to a {111} plane of their diamond host, but with random orientations of the magnesiochromite [100], [010] and [001] relative to the diamond. In one case, where a single inclusion comprised a magnesiochromite-olivine touching pair, the magnesiochromite was oriented as noted above and the olivine showed a random orientation. The implications of these observations for the mechanisms of diamond growth will be explored and the results will be compared and combined with previous work.
DS201707-1303
2017
Ames, D.E., Kjarsgaard, I.M., McDonald, A.M., Good, D.J.Insights into the extreme PGE enrichment of the W Horizon, Marathon Cu-Pd deposit, Coldwell alkaline complex, Canada: platinum group mineralogy, compositions and genetic implications.Ore Geology Reviews, in press availableCanada, Ontarioalkaline - Coldwell Complex

Abstract: The W Horizon, Marathon Cu-Pd deposit in the Mesoproterozoic Midcontinent rift is one of the highest grade PGE repositories in magmatic ore deposits world-wide. The textural relationships and compositions of diverse platinum-group mineral (PGM) and sulfide assemblages in the extremely enriched ores (>100 ppm Pd-Pt-Au over 2 m) of the W Horizon have been investigated in mineral concentrates with ?10,000 PGM grains and in situ using scanning electron microprobe and microprobe analyses. Here we show, from ore samples with concentrations up to 23.1 Pd ppm, 8.9 Pt ppm, 1.4 Au ppm and 0.73 Rh ppm, the diversity of minerals (n = 52) including several significant unknown minerals and three new mineral species marathonite (Pd25Ge9; McDonald et al., 2016), palladogermanide (Pd2Ge; IMA 2016-086, McDonald et al., 2017), kravtsovite (PdAg2S, IMA No 2016-092, Vymazalová et al., 2017). The PGM are distributed as PG-, sulfides (52 vol%), -arsenides (34 vol%), -intermetallics of Au-Ag-Pd-Cu and Pd-Ge(10 vol%) and -bismuthides and tellurides (4 vol%). The discovery of abundant (>330 grains) large unknown sulfide minerals with Rh allows us to present analyses three significant potentially new minerals (WUK-1, WUK-2, WUK-3) that are all clearly enriched in Rh (averaging 4.2, 8.5 and 28.21 wt% Rh respectively). Several examples of paragenetic sequences and mineral chemical changes for enrichment of Cu, Pd and Rh with time are revealed in the PGM and base-metal sulfides. We suggest this enhanced metal enrichment formed in response to increasing fO2 causing the oxidation of Fe2+ to Fe3+ and to a lesser extent, S. Phase relations in the Ag-Pd-S, Rh-Ni-Fe-S, Pd-Ge, Au-Pd-Cu-Ag, Pd-Ag-Te systems help constrain the crystallization temperatures of the majority of ore minerals in the W Horizon at ?500 °C or moderate to high subsolidus temperatures (400–600 °C). Local transport by aqueous fluids becomes evident as minerals recrystallize down to <300 °C. The PGE-enriched W Horizon ores exhibit a complex post-magmatic history dominated by the effects of oxidation during cooling of a Cu-PGE enriched magma source from a deep reservoir.
DS201712-2671
2017
AmiraAmira Roadmap. Excellent documentation of their 15 year extensive compilation.amirainternational.com, amirainternational .com /WEB/sites/ P1162A/ Documents/ FinalDocuments/ Roadmap Documents Index.aspAustraliamineral project analyses
DS201701-0002
2016
An, Y., Huang, J-X., Griffin, W.L., Liu, C., Huang, F.Isotopic composition of Mg and Fe in garnet peridotites from the Kaapvaal and Siberian cratons.Geochimica et Cosmochimica Acta, in press available 45p.Africa, RussiaGeochronology

Abstract: We present Mg and Fe isotopic data for whole rocks and separated minerals (olivine, clinopyroxene, orthopyroxene, garnet, and phlogopite) of garnet peridotites that equilibrated at depths of 134-186 km beneath the Kaapvaal and Siberian cratons. There is no clear difference in ?26Mg and ?56Fe of garnet peridotites from these two cratons. ?26Mg of whole rocks varies from ?0.243‰ to ?0.204‰ with an average of ?0.225 ± 0.037‰ (2?, n = 19), and ?56Fe from ?0.038‰ to 0.060‰ with an average of ?0.003 ± 0.068‰ (2?, n = 19). Both values are indistinguishable from the fertile upper mantle, indicating that there is no significant Mg-Fe isotopic difference between the shallow and deep upper mantle. The garnet peridotites from ancient cratons show ?26Mg similar to komatiites and basalts, further suggesting that there is no obvious Mg isotopic fractionation during different degrees of partial melting of deep mantle peridotites and komatiite formation. The precision of the Mg and Fe isotope data (?±0.05‰ for ?26Mg and ?56Fe, 2?) allows us to distinguish inter-mineral isotopic fractionations. Olivines are in equilibrium with opx in terms of Mg and Fe isotopes. Garnets have the lowest ?26Mg and ?56Fe among the coexisting mantle minerals, suggesting the dominant control of crystal structure on the Mg-Fe isotopic compositions of garnets. Elemental compositions and mineralogy suggest that clinopyroxene and garnet were produced by later metasomatic processes as they are not in chemical equilibrium with olivine or orthopyroxene. This is consistent with the isotopic disequilibrium of Mg and Fe isotopes between orthopyroxene/olivine and garnet/clinopyroxene. Combined with one sample showing slightly heavy ?26Mg and much lighter ?56Fe, these disequilibrium features in the garnet peridotites reveal kinetic isotopic fractionation due to Fe-Mg inter-diffusion during reaction between peridotites and percolating melts in the Kaapvaal craton.
DS201702-0192
2017
An, Y., Huang, J-X., Griffin, W.L., Liu, C., Huang, F.Isotopic composition of Mg and Fe in garnet peridotites from the Kaapvaal and Siberian cratons.Geochimica et Cosmochimica Acta, Vol. 200, pp. 167-185.Africa, South Africa, RussiaMetasomatism

Abstract: We present Mg and Fe isotopic data for whole rocks and separated minerals (olivine, clinopyroxene, orthopyroxene, garnet, and phlogopite) of garnet peridotites that equilibrated at depths of 134-186 km beneath the Kaapvaal and Siberian cratons. There is no clear difference in ?26Mg and ?56Fe of garnet peridotites from these two cratons. ?26Mg of whole rocks varies from ?0.243 to ?0.204 with an average of ?0.225 ± 0.037 (2?, n = 19), and ?56Fe from ?0.038‰ o 0.060 with an average of ?0.003 ± 0.068 (2?, n = 19). Both values are indistinguishable from the fertile upper mantle, indicating that there is no significant Mg-Fe isotopic difference between the shallow and deep upper mantle. The garnet peridotites from ancient cratons show ?26Mg similar to komatiites and basalts, further suggesting that there is no obvious Mg isotopic fractionation during different degrees of partial melting of deep mantle peridotites and komatiite formation. The precision of the Mg and Fe isotope data (±0.05 for ?26Mg and ?56Fe, 2?) allows us to distinguish inter-mineral isotopic fractionations. Olivines are in equilibrium with opx in terms of Mg and Fe isotopes. Garnets have the lowest ?26Mg and ?56Fe among the coexisting mantle minerals, suggesting the dominant control of crystal structure on the Mg-Fe isotopic compositions of garnets. Elemental compositions and mineralogy suggest that clinopyroxene and garnet were produced by later metasomatic processes as they are not in chemical equilibrium with olivine or orthopyroxene. This is consistent with the isotopic disequilibrium of Mg and Fe isotopes between orthopyroxene/olivine and garnet/clinopyroxene. Combined with one sample showing slightly heavy ?26Mg and much lighter ?56Fe, these disequilibrium features in the garnet peridotites reveal kinetic isotopic fractionation due to Fe-Mg inter-diffusion during reaction between peridotites and percolating melts in the Kaapvaal craton.
DS201704-0617
2017
An, Y., Huang, J-X., Griffin, W.L.,Liu, C., Huang, F.Isotopic composition of Mg and Fe in garnet peridotites from the Kaapvaal and Siberian cratons.Geochimica et Cosmochimica Acta, Vol. 200, pp. 167-185.Africa, South Africa, RussiaCraton, Peridotite

Abstract: We present Mg and Fe isotopic data for whole rocks and separated minerals (olivine, clinopyroxene, orthopyroxene, garnet, and phlogopite) of garnet peridotites that equilibrated at depths of 134-186 km beneath the Kaapvaal and Siberian cratons. There is no clear difference in ?26Mg and ?56Fe of garnet peridotites from these two cratons. ?26Mg of whole rocks varies from ?0.243‰ to ?0.204‰ with an average of ?0.225 ± 0.037‰ (2?, n = 19), and ?56Fe from ?0.038‰ 0.060 with an average of ?0.003 ± 0.068‰ (2?, n = 19). Both values are indistinguishable from the fertile upper mantle, indicating that there is no significant Mg-Fe isotopic difference between the shallow and deep upper mantle. The garnet peridotites from ancient cratons show ?26Mg similar to komatiites and basalts, further suggesting that there is no obvious Mg isotopic fractionation during different degrees of partial melting of deep mantle peridotites and komatiite formation. The precision of the Mg and Fe isotope data (?±0.05‰ for ?26Mg and ?56Fe, 2?) allows us to distinguish inter-mineral isotopic fractionations. Olivines are in equilibrium with opx in terms of Mg and Fe isotopes. Garnets have the lowest ?26Mg and ?56Fe among the coexisting mantle minerals, suggesting the dominant control of crystal structure on the Mg-Fe isotopic compositions of garnets. Elemental compositions and mineralogy suggest that clinopyroxene and garnet were produced by later metasomatic processes as they are not in chemical equilibrium with olivine or orthopyroxene. This is consistent with the isotopic disequilibrium of Mg and Fe isotopes between orthopyroxene/olivine and garnet/clinopyroxene. Combined with one sample showing slightly heavy ?26Mg and much lighter ?56Fe, these disequilibrium features in the garnet peridotites reveal kinetic isotopic fractionation due to Fe-Mg inter-diffusion during reaction between peridotites and percolating melts in the Kaapvaal craton.
DS201709-1951
2017
Andersen, A.K., Clark, J.G., Larson, P.B., Donovan, J.J.REE fractionation, mineral speciation, and supergene enrichment of the Bear Lodge carbonatites, Wyoming, USA.Ore Geology Reviews, Vol. 89, pp. 780-807.United States, Wyomingcarbonatite - Bear Lodge

Abstract: The Eocene (ca. 55–38 Ma) Bear Lodge alkaline complex in the northern Black Hills region of northeastern Wyoming (USA) is host to stockwork-style carbonatite dikes and veins with high concentrations of rare earth elements (e.g., La: 4140–21000 ppm, Ce: 9220–35800 ppm, Nd: 4800–13900 ppm). The central carbonatite dike swarm is characterized by zones of variable REE content, with peripheral zones enriched in HREE including yttrium. The principle REE-bearing phases in unoxidized carbonatite are ancylite and carbocernaite, with subordinate monazite, fluorapatite, burbankite, and Ca-REE fluorocarbonates. In oxidized carbonatite, REE are hosted primarily by Ca-REE fluorocarbonates (bastnäsite, parisite, synchysite, and mixed varieties), with lesser REE phosphates (rhabdophane and monazite), fluorapatite, and cerianite. REE abundances were substantially upgraded (e.g., La: 54500–66800 ppm, Ce: 11500–92100 ppm, Nd: 4740–31200 ppm) in carbonatite that was altered by oxidizing hydrothermal and supergene processes. Vertical, near surface increases in REE concentrations correlate with replacement of REE(±Sr,Ca,Na,Ba) carbonate minerals by Ca-REE fluorocarbonate minerals, dissolution of matrix calcite, development of Fe- and Mn-rich gossan, crystallization of cerianite and accompanying negative Ce anomalies in secondary fluorocarbonates and phosphates, and increasing ?18O values. These vertical changes demonstrate the importance of oxidizing meteoric water during the most recent modifications to the carbonatite stockwork. Scanning electron microscopy, energy dispersive spectroscopy, and electron probe microanalysis were used to investigate variations in mineral chemistry controlling the lateral complex-wide geochemical heterogeneity. HREE-enrichment in some peripheral zones can be attributed to an increase in the abundance of secondary REE phosphates (rhabdophane group, monazite, and fluorapatite), while HREE-enrichment in other zones is a result of HREE substitution in the otherwise LREE-selective fluorocarbonate minerals. Microprobe analyses show that HREE substitution is most pronounced in Ca-rich fluorocarbonates (parisite, synchysite, and mixed syntaxial varieties). Peripheral, late-stage HREE-enrichment is attributed to: 1) fractionation during early crystallization of LREE selective minerals, such as ancylite, carbocernaite, and Ca-REE fluorocarbonates in the central Bull Hill dike swarm, 2) REE liberated during breakdown of primary calcite and apatite with higher HREE/LREE ratios, and 3) differential transport of REE in fluids with higher PO43?/CO32? and F?/CO32? ratios, leading to phosphate and pseudomorphic fluorocarbonate mineralization. Supergene weathering processes were important at the stratigraphically highest peripheral REE occurrence, which consists of fine, acicular monazite, jarosite, rutile/pseudorutile, barite, and plumbopyrochlore, an assemblage mineralogically similar to carbonatite laterites in tropical regions.
DS201707-1304
2017
Andersen, T., Elburg, M., Erambert, M.The miaskitic to agpaitic transition in peralkaline nepheline syenite ( white foyaite) from the Pelanesberg complex, South Africa.Chemical Geology, Vol. 455, pp. 166-181.Africa, South Africaalkaline rocks

Abstract: The Mesoproterozoic Pilanesberg Complex, South Africa, is built up by several distinct, ring-shaped intrusions of syenite and peralkaline nepheline syenite. A mildly peralkaline ((Na + K) / Al = 1.04–1.09), medium-to coarse grained nepheline syenite makes up the outermost ring in the southwestern part of the complex (“Matooster type white foyaite”). In this rock, mafic silicate minerals (amphibole, biotite, aegirine) and Ti-bearing minerals (ilmenite, astrophyllite, aenigmatite, lorenzenite, bafertisite, jinshajiangite) are interstitial to feldspar and nepheline, and define a series of mineral assemblages reflecting a change from a miaskitic crystallization regime (with Na-Ca amphibole, titanite and ilmenite) to increasingly agpaitic conditions (with arfvedsonite, aegirine, astrophyllite, aenigmatite, lorenzenite). The main driving force behind the evolution was an increase in peralkalinity of the trapped liquid, mainly by adcumulus growth of alkali feldspar and nepheline, which in the later stages of evolution was combined with increases in oxygen fugacity and water activity. Unlike in most other agpaitic rock complexes, Zr remained compatible in aegirine (and to some extent in amphibole) almost to the end of the process, when a hydrous zirconium silicate mineral (hilairite) crystallized as the only mineral in the rock having essential zirconium. The presence of minerals such as hilairite, bafertisite, jinshajiangite and a Na-REE-Sr rich apatite group mineral (fluorcaphite ?) in the latest assemblages suggests that the last remaining interstitial melt or fluid approached a hyperagpaitic composition. The isolated melt pockets in the Pilanesberg white foyaite follow a pattern of evolution that can be seen as a miniature analogue of the fractional crystallization processes controlling magma evolution in large, alkaline igneous rock complexes.
DS201710-2210
2017
Anderson, K.R., Poland, M.P.Abundant carbon in the mantle beneath Hawaii.Nature Geoscience, Vol. 10, 9, pp. 704-708.United States, Hawaiicarbon

Abstract: Estimates of carbon concentrations in Earth’s mantle vary over more than an order of magnitude, hindering our ability to understand mantle structure and mineralogy, partial melting, and the carbon cycle. CO2 concentrations in mantle-derived magmas supplying hotspot ocean island volcanoes yield our most direct constraints on mantle carbon, but are extensively modified by degassing during ascent. Here we show that undegassed magmatic and mantle carbon concentrations may be estimated in a Bayesian framework using diverse geologic information at an ocean island volcano. Our CO2 concentration estimates do not rely upon complex degassing models, geochemical tracer elements, assumed magma supply rates, or rare undegassed rock samples. Rather, we couple volcanic CO2 emission rates with probabilistic magma supply rates, which are obtained indirectly from magma storage and eruption rates. We estimate that the CO2 content of mantle-derived magma supplying Hawai‘i’s active volcanoes is 0.97?0.19+0.25 wt% -roughly 40% higher than previously believed-and is supplied from a mantle source region with a carbon concentration of 263?62+81?ppm. Our results suggest that mantle plumes and ocean island basalts are carbon-rich. Our data also shed light on helium isotope abundances, CO2/Nb ratios, and may imply higher CO2 emission rates from ocean island volcanoes.
DS201711-2498
2017
Anderson, S.D.Preliminary geology of the diamond occurrence at southern Knee Lake, Oxford Lake-Knee Lake greenstone belt, Manitoba ( NTS 53L15).Manitoba Geological Survey, Open File OF2017-3, 34p. PdfCanada, Manitobageochemistry
DS201711-2499
2017
Andrault, D., Bolfan-Casanova, N., Bouhifd, M.A., Boujibar, A., Garbarino, G., Manthilake, G., Mezouar, M., Monteux, J., Parisiades, P., Pesce, G.Toward a coherent model for the melting behaviour of the deep Earth's mantle.Physics of the Earth and Planetary Interiors, Vol. 265, pp. 67-81.Mantlemelting

Abstract: Knowledge of melting properties is critical to predict the nature and the fate of melts produced in the deep mantle. Early in the Earth’s history, melting properties controlled the magma ocean crystallization, which potentially induced chemical segregation in distinct reservoirs. Today, partial melting most probably occurs in the lowermost mantle as well as at mid upper-mantle depths, which control important aspects of mantle dynamics, including some types of volcanism. Unfortunately, despite major experimental and theoretical efforts, major controversies remain about several aspects of mantle melting. For example, the liquidus of the mantle was reported (for peridotitic or chondritic-type composition) with a temperature difference of ?1000 K at high mantle depths. Also, the Fe partitioning coefficient (DFeBg/melt) between bridgmanite (Bg, the major lower mantle mineral) and a melt was reported between ?0.1 and ?0.5, for a mantle depth of ?2000 km. Until now, these uncertainties had prevented the construction of a coherent picture of the melting behavior of the deep mantle. In this article, we perform a critical review of previous works and develop a coherent, semi-quantitative, model. We first address the melting curve of Bg with the help of original experimental measurements, which yields a constraint on the volume change upon melting (?Vm). Secondly, we apply a basic thermodynamical approach to discuss the melting behavior of mineralogical assemblages made of fractions of Bg, CaSiO3-perovskite and (Mg,Fe)O-ferropericlase. Our analysis yields quantitative constraints on the SiO2-content in the pseudo-eutectic melt and the degree of partial melting (F) as a function of pressure, temperature and mantle composition; For examples, we find that F could be more than 40% at the solidus temperature, except if the presence of volatile elements induces incipient melting. We then discuss the melt buoyancy in a partial molten lower mantle as a function of pressure, F and DFeBg/melt. In the lower mantle, density inversions (i.e. sinking melts) appear to be restricted to low F values and highest mantle pressures. The coherent melting model has direct geophysical implications: (i) in the early Earth, the magma ocean crystallization could not occur for a core temperature higher than ?5400 K at the core-mantle boundary (CMB). This temperature corresponds to the melting of pure Bg at 135 GPa. For a mantle composition more realistic than pure Bg, the right CMB temperature for magma ocean crystallization could have been as low as ?4400 K. (ii) There are converging arguments for the formation of a relatively homogeneous mantle after magma ocean crystallization. In particular, we predict the bulk crystallization of a relatively large mantle fraction, when the temperature becomes lower than the pseudo-eutectic temperature. Some chemical segregation could still be possible as a result of some Bg segregation in the lowermost mantle during the first stage of the magma ocean crystallization, and due to a much later descent of very low F, Fe-enriched, melts toward the CMB. (iii) The descent of such melts could still take place today. There formation should to be related to incipient mantle melting due to the presence of volatile elements. Even though, these melts can only be denser than the mantle (at high mantle depths) if the controversial value of DFeBg/melt is indeed as low as suggested by some experimental studies. This type of melts could contribute to produce ultra-low seismic velocity anomalies in the lowermost mantle.
DS201709-1952
2017
Angel, R.J., Alvaro, M., Nestola, F.40 years of mineral elasticity: a critical review and a new parameterisation of equations of state for mantle olivines and diamond inclusions.Physics and Chemistry of Minerals, in press available, 19p.Technologydiamond inclusions

Abstract: Elasticity is a key property of materials, not only for predicting volumes and densities of minerals at the pressures and temperatures in the interior of the Earth, but also because it is a major factor in the energetics of structural phase transitions, surface energies, and defects within minerals. Over the 40 years of publication of Physics and Chemistry of Minerals, great progress has been made in the accuracy and precision of the measurements of both volumes and elastic tensors of minerals and in the pressures and temperatures at which the measurements are made. As an illustration of the state of the art, all available single-crystal data that constrain the elastic properties and pressure–volume–temperature equation of state (EoS) of mantle-composition olivine are reviewed. Single-crystal elasticity measurements clearly distinguish the Reuss and Voigt bulk moduli of olivine at all conditions. The consistency of volume and bulk modulus data is tested by fitting them simultaneously. Data collected at ambient pressure and data collected at ambient temperature up to 15 GPa are consistent with a Mie–Grünesien–Debye thermal-pressure EoS in combination with a third-order Birch–Murnaghan (BM) compressional EoS, the parameter V0 = 43.89 cm3 mol?1, isothermal Reuss bulk modulus KTR,0=126.3(2) GPaKTR,0=126.3(2) GPa, K?TR,0=4.54(6)KTR,0?=4.54(6), a Debye temperature ?D=644(9)K?D=644(9)K, and a Grüneisen parameter ?0 = 1.044(4), whose volume dependence is described by q = 1.9(2). High-pressure softening of the bulk modulus at room temperature, relative to this EoS, can be fit with a fourth-order BM EoS. However, recent high-P, T Brillouin measurements are incompatible with these EoS and the intrinsic physics implied by it, especially that (?K?TR?T)P>0(?KTR??T)P>0. We introduce a new parameterisation for isothermal-type EoS that scales both the Reuss isothermal bulk modulus and its pressure derivative at temperature by the volume, KTR(T,P=0)=KTR,0[V0V(T)]?TKTR(T,P=0)=KTR,0[V0V(T)]?T and K?TR(T,P=0)=K?TR,0[V(T)V0]??KTR?(T,P=0)=KTR,0?[V(T)V0]??, to ensure thermodynamic correctness at low temperatures. This allows the elastic softening implied by the high-P, T Brillouin data for mantle olivine to be fit simultaneously and consistently with the same bulk moduli and pressure derivatives (at room temperature) as the MGD EoS, and with the additional parameters of ?V0 = 2.666(9) × 10?5 K?1, ?E=484(6)?E=484(6), ?T?T = 5.77(8), and ???? = ?3.5(1.1). The effects of the differences between the two EoS on the calculated density, volume, and elastic properties of olivine at mantle conditions and on the calculation of entrapment conditions of olivine inclusions in diamonds are discussed, and approaches to resolve the current uncertainties are proposed.
DS201712-2672
2017
Angel, R.J., Mazzucchelli, M.L., Alvaro, M., Nestola, F.EosFit-Pinc: a simple GUI for host inclusion elastic thermobarometry.American Mineralogist, Vol. 102, pp. 1957-1960.Technologygeobarometry

Abstract: Elastic geothermobarometry is a method of determining metamorphic conditions from the excess pressures exhibited by mineral inclusions trapped inside host minerals. An exact solution to the problem of combining non-linear Equations of State (EoS) with the elastic relaxation problem for elastically isotropic spherical host-inclusion systems without any approximations of linear elasticity is presented. The solution is encoded into a Windows GUI program EosFit-Pinc. The program performs host-inclusion calculations for spherical inclusions in elastically isotropic systems with full P-V-T EoS for both phases, with a wide variety of EoS types. The EoS values of any minerals can be loaded into the program for calculations. EosFit-Pinc calculates the isomeke of possible entrapment conditions from the pressure of an inclusion measured when the host is at any external pressure and temperature (including room conditions), and it can calculate final inclusion pressures from known entrapment conditions. It also calculates isomekes and isochors of the two phases.
DS201712-2673
2016
Angel, R.J., Milani, S., Alvaro, M., Nestola, F.High quality structures at high pressure? Insights from inclusions in diamonds.Zeitschrfit fur Kristallographie, Vol. 231, pp. 467-473.Technologydiamond inclusions

Abstract: We describe the experimental protocols necessary to measure the crystal structures of minerals trapped within diamonds by single-crystal X-ray diffraction to the same quality as obtained from minerals studied at ambient conditions. The results show that corrections for X-ray absorption in complex cases can be made with good precision. Comparison of the refined structure of a single-crystal olivine inclusion inside a diamond with the structure of a similar olivine held in a high-pressure diamond-anvil cell shows that data resolution, not the correction for absorption effects, is the dominant factor in influencing the quality of structures determined at high pressures by single-crystal X-ray diffraction.
DS201708-1592
2017
Anzolini, C.Depth of formation of super deep diamonds.11th. International Kimberlite Conference, PosterMantleUHP

Abstract: “Super-deep” diamonds are thought to crystallize between 300 and 800 km depth because some of the inclusions trapped within them are considered to be the products of retrograde transformation from lower mantle or transition zone precursors. In particular, single inclusion CaSiO3-walstromite is believed to derive from CaSiO3-perovskite, although its real depth of origin has never been proven. Our aim is therefore to determine for the first time the pressure of formation of the diamond-CaSiO3-walstromite pair by “single-inclusion elastic barometry” and to determine whether CaSiO3-walstromite derives from CaSiO3-perovskite or not. We investigated several single phases and assemblages of Ca-silicate inclusions still trapped in a diamond coming from Juina (Brazil) by in-situ analyses (single-crystal X-ray diffraction and micro-Raman spectroscopy) and we obtained a minimum entrapment pressure of ~ 5.7 GPa (? 180 km) at 1500 K. However, the observed coexistence of CaSiO3-walstromite, larnite (?-Ca2SiO4) and CaSi2O5-titanite in one multiphase inclusion within the same diamond indicates that the sample investigated is sub-lithospheric with entrapment pressure between ~ 9.5 and ~ 11.5 GPa at 1500 K, based on experimentally-determined phase equilibria. In addition, thermodynamic calculations suggested that, within a diamond, single inclusions of CaSiO3-walstromite cannot derive from CaSiO3-perovskite, unless the diamond around the inclusion expands by ~ 30% in volume.
DS201704-0618
2017
Aramastsev, A.A., Vesolovskiy, R.V., Travin, A.V., Yudin, D.S.Paleozoic tholeiitic magmatism of the Kola Peninsula: spatial distribution, age, and relation to alkaline magmatism.Petrology, Vol. 25, 1, pp. 42-65.Russia, Kola PeninsulaMagmatism - alkaline

Abstract: This paper focuses on the occurrences of tholeiitic magmatism in the northeastern Fennoscandian shield. It was found that numerous dolerite dikes of the Pechenga, Barents Sea, and Eastern Kola swarms were formed 380-390 Ma ago, i.e., directly before the main stage of the Paleozoic alkaline magmatism of the Kola province. The isotope geochemical characteristics of the dolerites suggest that their primary melts were derived from the mantle under the conditions of the spinel lherzolite facies. The depleted mantle material from which the tholeiites were derived shows no evidence for metasomatism and enrichment in high fieldstrength and rare earth elements, whereas melanephelinite melts postdating the tholeiites were generated in an enriched source. It was shown that the relatively short stage of mantle metasomatism directly after the emplacement of tholeiitic magmas was accompanied by significant mantle fertilization. In contrast to other large igneous provinces, where pulsed intrusion of large volumes of tholeiitic magmas coinciding or alternating with phases of alkaline magmatism was documented, the Kola province is characterized by systematic evolution of the Paleozoic plume-lithosphere process with monotonous deepening of the level of magma generation, development of mantle metasomatism and accompanying fertilization of mantle materials, and systematic changes in the composition of melts reaching the surface.
DS201709-1953
2017
Arcay, D.Modeling the interplate domain in thermo-mechanical simulations of subduction: critical effects of resolution and rheology, and consequences on wet mantle melting.Physics of the Earth and Planetary Interiors, Vol. 269, 1, pp. 112-132.Mantlesubduction

Abstract: The present study aims at better deciphering the different mechanisms involved in the functioning of the subduction interplate. A 2D thermo-mechanical model is used to simulate a subduction channel, made of oceanic crust, free to evolve. Convergence at constant rate is imposed under a 100 km thick upper plate. Pseudo-brittle and non-Newtonian behaviours are modelled. The influence of the subduction channel strength, parameterized by the difference in activation energy between crust and mantle (?Ea) is investigated to examine in detail the variations in depth of the subduction plane down-dip extent, zcoup . First, simulations show that numerical resolution may be responsible for an artificial and significant shallowing of zcoup if the weak crustal layer is not correctly resolved. Second, if the age of the subducting plate is 100 Myr, subduction occurs for any ?Ea . The stiffer the crust is, that is, the lower ?Ea is, the shallower zcoup is (60 km depth if ?Ea = 20 kJ/mol) and the hotter the fore-arc base is. Conversely, imposing a very weak subduction channel (?Ea > 135 J/mol) leads there to an extreme mantle wedge cooling and inhibits mantle melting in wet conditions. Partial kinematic coupling at the fore-arc base occurs if ?Ea = 145 kJ/mol. If the incoming plate is 20 Myr old, subduction can occur under the conditions that the crust is either stiff and denser than the mantle, or weak and buoyant. In the latter condition, cold crust plumes rise from the subduction channel and ascend through the upper lithosphere, triggering (1) partial kinematic coupling under the fore-arc, (2) fore-arc lithosphere cooling, and (3) partial or complete hindrance of wet mantle melting. zcoup then ranges from 50 to more than 250 km depth and is time-dependent if crust plumes form. Finally, subduction plane dynamics is intimately linked to the regime of subduction-induced corner flow. Two different intervals of ?Ea are underlined: 80-120 kJ/mol to reproduce the range of slab surface temperature inferred from geothermometry, and 10-40 kJ/mol to reproduce the shallow hot mantle wedge core inferred from conditions of last equilibration of near-primary arc magmas and seismic tomographies. Therefore, an extra process controlling mantle wedge dynamics is needed to satisfy simultaneously the aforementioned observations. A mantle viscosity reduction, by a factor 4-20, caused by metasomatism in the mantle wedge is proposed. From these results, I conclude that the subduction channel down-dip extent, zcoup , should depend on the subduction setting, to be consistent with the observed variability of sub-arc depths of the subducting plate surface.
DS201709-1954
2017
Armistead, S.E., Collins, A.S., Payne, J.L., Foden, J.D., De Waele, B., Shaji, E., Santosh, M.A re-evaluation of the Kumta Suture in western peninsular India and its extension into Madagascar,Journal of Asian Earth Sciences, in press available, 47p.India, Africa, Madagascartectonis

Abstract: It has long been recognised that Madagascar was contiguous with India until the Late Cretaceous. However, the timing and nature of the amalgamation of these two regions remain highly contentious as is the location of Madagascar against India in Gondwana. Here we address these issues with new U-Pb and Lu-Hf zircon data from five metasedimentary samples from the Karwar Block of India and new Lu-Hf data from eight previously dated igneous rocks from central Madagascar and the Antongil-Masora domains of eastern Madagascar. New U-Pb data from Karwar-region detrital zircon grains yield two dominant age peaks at c. 3100 Ma and c. 2500 Ma. The c. 3100 Ma population has relatively juvenile ?Hf(t) values that trend toward an evolved signature at c. 2500 Ma. The c. 2500 Ma population shows a wide range of ?Hf(t) values reflecting mixing of an evolved source with a juvenile source at that time. These data, and the new Lu-Hf data from Madagascar, are compared with our new compilation of over 7000 U-Pb and 1000 Lu-Hf analyses from Madagascar and India. We have used multidimensional scaling to assess similarities in these data in a statistically robust way. We propose that the Karwar Block of western peninsular India is an extension of the western Dharwar Craton and not part of the Antananarivo Domain of Madagascar as has been suggested in some models. Based on ?Hf(t) signatures we also suggest that India (and the Antongil-Masora domains of Madagascar) were palaeogeographically isolated from central Madagascar (the Antananarivo Domain) during the Palaeoproterozoic. This supports a model where central Madagascar and India amalgamated during the Neoproterozoic along the Betsimisaraka Suture.
DS201708-1593
2017
Armstrong, J.Karowe diamond mine: a world class source of exceptional diamonds.11th. International Kimberlite Conference, OralAfrica, Botswanadeposit - Karowe

Abstract: The Karowe mine, owned and operated by Lucara Diamond Corporation, located in the Republic of Botswana, achieved commercial diamond production in July 2012. The AK06 kimberlite discovered in 1969 is the ore source at Karowe. The AK06 kimberlite within the Orapa Kimberlite Field is a roughly north-south elongate kimberlite body with a near surface expression of approximately 3.3 ha and a maximum area of approximately 7 ha at approximately 120 m below surface. The body comprises three geologically distinct, coalescing pipes that taper with depth. These pipes are referred to as the North Lobe, Centre Lobe, and South Lobe. The AK6 kimberlite is an opaque-mineral-rich monticellite kimberlite, texturally classified primarily as fragmental volcaniclastic kimberlite with lesser macrocrystic hypabyssal facies kimberlite of the Group 1 variety. The nature of the kimberlite differs between each lobe with distinctions apparent in the textural characteristics. The South Lobe is considered to be distinctly different from the North and Centre Lobes that are similar to each other in terms of their geological characteristics. The North and Centre Lobes exhibit internal textural complexity whereas the bulk of the South Lobe is more massive and internally homogeneous. The South Lobe forms the majority of the resource and displays the coarsest diamond size distribution of the three lobes. In three years of production, Karowe has established a continuing production of high value diamonds including coloured diamonds. In March 2013 a 239 ct gem quality diamond was recovered which was the first in a continuing population of large high value Type IIa diamonds recovered from the Centre Lobe, and more importantly the South Lobe, of the Karowe mine. Large diamonds, 50 ct in size, are spatially distributed horizontally and vertically within the South Lobe. Since commissioning to mid-December 2015, approximately 1.5 Mct have been produced and specials (diamonds greater than 10.8 ct in weight) represent circa 4.6% by weight of all diamond production. Life of Mine average stone size for the specials is 29.6 ct/stone. In 2015, a plant optimization project was completed to modify the process plant to treat harder kimberlite at depth and improve the recovery of exceptional diamonds via bulk sorters for primary run of mine large diamond recovery. In November 2015, the Karowe mine recovered an 813 ct stone and the world’s second largest gem quality diamond in over 100 years weighing 1,111 ct
DS201710-2211
2017
Armstrong, J.P., Gababotse, J.Karowe diamond mine.11th International Kimberlite Field Trip Guide, Sept. 19p. PdfAfrica, Botswanadeposit - Karowe
DS201708-1594
2017
Arndt, N.Formation of dunite xenoliths in kimberlites and allikites, petrographic and mineral compositions from a deformed xenolith in the Majuagaa kimberlite dike, Greenland.11th. International Kimberlite Conference, PosterEurope, Greenlanddeposit - Majuagaa
DS201712-2674
2017
Arndt, N.T., Fontbote, L., Hedenquist, J.W., Kesler, S.E., Thompson, J. F.H., Wood, D.G.Future Global and Mineral Resources.geochemicalperspectives.org, Vol. 6, 1, April, 187p. Pdf 28 MBGlobalgeochemistry

Abstract: Some scientists and journalists, and many members of the general public, have been led to believe that the world is rapidly running out of the metals on which our modern society is based. Advocates of the peak metal concept have predicted for many decades that increasing consumption will soon lead to exhaustion of mineral resources. Yet, despite ever-increasing production and consumption, supplies of minerals have continued to meet the needs of industry and society, and lifetimes of reserves remain similar to what they were 30-40 years ago. In this volume, we discuss the reasons for this apparent paradox using our broad experience and expertise on both academic and industrial sides of the minerals sector. Many misconceptions arise from flawed estimates of the size of global mineral resources which stem from a lack of understanding of the critical difference between reserves and resources. Some authors use quoted reserves – the amount of metal proven to exist and to be economic for mining at present – when predicting imminent shortages. Resources – the amount that may be accessible in the upper few kilometres of the crust – are far larger.Over the last 150 years, improved technologies, economies of scale and increased efficiency have combined to reduce costs hence allowing lower-grade ore to be mined economically. The net result is that the long-term inflation-adjusted price of most metals has decreased more or less in parallel with increasing production, a second apparent paradox that frequently is not well understood. Using copper as the principal example and other metals as appropriate, we summarise the latest research on ore deposits and the activities of the minerals industry. Following a description of the numerous geological processes that form ore deposits, we outline the scientific methods used by the minerals industry to explore for new deposits. We also discuss how resources are mined and how minerals are processed, as well as recent efforts to reduce related environmental impacts. Economic and societal factors influence supply, and these are as important as the actual presence of a resource. Finally, we discuss the critical roles that geoscientists will play in assuring continued supplies of minerals. These include the development of new concepts and techniques that will assist the discovery, mining, processing, remediation, and management of mineral resources. It is essential that researchers help to educate the general public about the need for continued exploration to find new resources to meet growth in world living standards. We demonstrate that global resources of copper, and probably of most other metals, are much larger than most currently available estimates, especially if increasing efficiencies and higher prices allow lower-grade ores to be mined. These observations indicate that supplies of important mineral commodities will remain adequate for the foreseeable future.
DS201705-0808
2017
Ashchepkov, I., Ntaflos, T., Logvinova, A., Vladykin, N., Ivanov, A., Spetsius, Z., Stegnitsky, Y., Kostrovitsky, S., Salikhov, R., Makovchuk, I., Shmarov, G., Karpenko, M., Downes, H., Madvedev, N.Evolution of the mantle sections beneath the kimberlite pipes example of Yakutia.European Geosciences Union General Assembly 2017, Vienna April 23-28, 1p. 6337 AbstractRussia, YakutiaDeposit - Sytykanskaya, Dalnyaya, Aykhal, Zarya, Komosomolskaya, Zarnitsa, Udachnaya

Abstract: The PTX diagrams for the separate phases in Sytykanskaya (Ashchepkov et al., 2016) Dalnyaya (Ashchepkov et al., 2017), pipes shows that the PK show the relatively simple P-X trends and geotherms and shows more contrast and simple layering. The PK contain most abundant material from the root of the magma generation they are dunitic veins as the magma feeders represented by the megacrysts. New results for the Aykhal, Zarya and Komsomolskaya pipes in Alake field and Zarnitsa and Udachnaya pipes in Daldyn field show that evolution is accompanied by the developing of metasomatites and branching and veining of the wall rock peridotites . In Aykhal pipe in PK the Gar- dunites prevail, the xenoliths from the dark ABK "Rebus" contain Cr-Ti - rich garnets and ilmenites, more abundant compared with the grey carbonited breccia Nearly the same features were found for Yubileinaya pipe. The example of Komsomolskya pipes show that the ABK contain more eclogitic xenolith than PK. The developing of the magma channel shown in satellite Chukukskaya and Structurnaya pipe was followed by the separation of some parts of the magmatic feeders and crystallization of abundant Gar megacrysts near o the walls blocking the peridotites from the magma feeder. This drastically decrease diamond grade of pipes. Such blocking seems to be the common features for the latest breccias. In Zarnitsa pipe, the dark PK and ABK also contain fresh xenoliths but not only dunites but also sheared and metasomatic varieties and eclogites. Most of dark ABK in Yakutia contain the intergrowth of ilmenites with brown Ti- Cpx showing joint evolution trends. The late breccia contains completely altered peridotite xenoliths mainly of dunite- harzburgite type. The comparison of the trace elements of the coexisting minerals in megacryst show that they were derived from the protokimberlites but are not in complete equilibrium as well as other megacrystalline phases. Ilmenites show inflections of the trace element patterns of most Ilmenites but more regular for the Cpx and Garnets revealing the sub parallel patterns elevating LREE with the rising TRE. But commonly these are not continuous sequances because they developed in the pulsing moving systems like beneath Zarnitsa. The minerals from the feeders like dunites also show the inflected or S-type REE patterns. From the earlier to later phases the TRE compositions became more evolved reflecting the evolution of protokimberlites. The wall rocks also often show the interaction with the more evolved melts and sometimes "cut" spectrums due to the dissolution some phases and repeated melting events So we could suggest the joint evolution of the mantle column protokimberlites and megacrysts composition and type of kimberlites with the diamond grade. The mantle lithospheric base captured by the PK. The developing and rising protokimbelrites was followed by the crystallization of the diamonds in the gradient in FO2 zone in wall rocks due to reductions of C -bearing fluids and carbonatites (> 1 QMF) on peridotites ((< -2 -5 QMF). The most intensive reactions are near the graphite - diamond boundary where protokimberlites are breaking and where most framesites are forming.
DS201703-0397
2017
Ashwal, L.D., Wiedenbeck, M., Torsvik, T.H.Archean zircons in Miocene oceanic hotspot rocks establish ancient continental crust beneath Mauritius.Nature Communications, Jan. 31, doi 10:1038/ncomms1048Africa, MauritiusHot spots

Abstract: A fragment of continental crust has been postulated to underlie the young plume-related lavas of the Indian Ocean island of Mauritius based on the recovery of Proterozoic zircons from basaltic beach sands. Here we document the first U-Pb zircon ages recovered directly from 5.7?Ma Mauritian trachytic rocks. We identified concordant Archaean xenocrystic zircons ranging in age between 2.5 and 3.0?Ga within a trachyte plug that crosscuts Older Series plume-related basalts of Mauritius. Our results demonstrate the existence of ancient continental crust beneath Mauritius; based on the entire spectrum of U-Pb ages for old Mauritian zircons, we demonstrate that this ancient crust is of central-east Madagascar affinity, which is presently located ?700?km west of Mauritius. This makes possible a detailed reconstruction of Mauritius and other Mauritian continental fragments, which once formed part of the ancient nucleus of Madagascar and southern India.
DS201711-2500
2017
Asthana, D., Kumar, S., Kumar Vind, A., Zehra, F., Kumar, H., Pophare, A.M.Geochemical fingerprinting of ~ 2.5 Ga forearc-arc-backarc related magmatic suites in the Bastar Craton, central India.Journal of Asian Earth Sciences, in press available, 17p.Indiageodynamics

Abstract: The Pitepani volcanic suite of the Dongargarh Supergroup, central India comprises of a calc-alkaline suite and a tholeiitic suite, respectively. The rare earth element (REE) patterns, mantle normalized plots and relict clinopyroxene chemistry of the Pitepani calc-alkaline suite are akin to high-Mg andesites (HMA) and reveal remarkable similarity to the Cenozoic Setouchi HMA from Japan. The Pitepani HMAs are geochemically correlated with similar rocks in the Kotri-Dongargarh mobile belt (KDMB) and in the mafic dykes of the Bastar Craton. The rationale behind lithogeochemical correlations are that sanukitic HMAs represent fore-arc volcanism over a very limited period of time, under abnormally high temperature conditions and are excellent regional and tectonic time markers. Furthermore, the tholeiitic suites that are temporally and spatially associated with the HMAs in the KDMB and in the mafic dykes of the Bastar Craton are classified into: (a) a continental back-arc suite that are depleted in incompatible elements, and (b) a continental arc suite that are more depleted in incompatible elements, respectively. The HMA suite, the continental back-arc and continental arc suites are lithogeochemically correlated in the KDMB and in the mafic dykes of the Bastar Craton. The three geochemically distinct Neoarchaean magmatic suites are temporally and spatially related to each other and to an active continental margin. The identification of three active continental margin magmatic suites for the first time, provides a robust conceptual framework to unravel the Neoarchaean geodynamic evolution of the Bastar Craton. We propose an active continental margin along the Neoarchaen KDMB with eastward subduction coupled with slab roll back or preferably, ridge-subduction along the Central Indian Tectonic Zone (CITZ) to account for the three distinct magmatic suites and the Neoarchean geodynamic evolution of the Bastar Craton.
DS201708-1595
2017
Aulbach, S.Re-Os isotope systematics of sulphide inclusions in diamonds from Victor ( Superior craton) document mobilization of volatiles and Os during Rodinia break up.11th. International Kimberlite Conference, PosterCanada, Ontario, Attawapiskatdeposit - Victor
DS201709-1955
2017
Aulbach, S.Evidence for a cool and depleted Archean convecting mantle: some implications eclogite kimberlites.Goldschmidt Conference, abstract 1p.Mantleeclogites

Abstract: Mantle potential temperature (TP) and composition are crucial parameters that regulate terrestrial dynamics and geochemical cycles, ranging from controls on the peridotite solidus and consequent geochemical differentiation, to plate stiffness conducive to the operation of plate tectonics, and the recycling efficiency of volatiles in subduction zones. Earth’s mantle has been cooling, but there is little agreement on the rate at which this proceeded. It is also unclear whether the Archaean ambient mantle was similar to, or more or less depleted than that giving rise to modern MORB. Since the ambient convecting mantle is most reliably sampled at spreading ridges, ancient kimberlite-borne eclogite xenoliths with low-pressure oceanic crustal protoliths, together with orogenic eclogites and (meta)basalts from allochtonous greenstone belts, may be used to constrain some characteristics of the convecting mantle sources from which their protoliths were ultimately derived. Carefully screened eclogite suites up to 3 Ga in age have TiO2-REE relationships consistent with fractionation of olivine±plagioclase during formation of picritic protoliths from a melt that separated from a garnet-free peridotite source, implying intersection of the solidus at ?3.0 GPa. Low melt fractions (F<0.25), calculated from samples with the least fractionated protoliths using the batch melting equation, further argue against deep intersection of the mantle solidus. This is contingent on correctly identifying the mantle source (C0) as depleted, which is supported by depleted initial 176Hf/177Hf in 2.9 to 2.6 Ga orogenic eclogite suites. Inversion of melt fractions for temperature suggests moderately elevated TP of ~1420-1470º C, significantly lower than some estimates for the ambient convecting mantle at that time. If these results are accurate, the unusual degree of melt depletion experienced by cratonic lithospheric mantle (F = 0.3-0.5) underpinning Earth’s oldest continental cores requires formation at excess TP and/or from fertile mantle which sustains longer melting columns and higher melt productivity, either during plume-ridge interactions or plume subcretion. This matches increasing evidence that ancient continental crust formed by melting at the base of oceanic plateau-like enriched oceanic crust. A moderate Mesoarchaean TP also argues for early plate strengthening that would support plate tectonics and topography.
DS201710-2212
2017
Aulbach, S., Jacob, D.E., Cartigny, P., Stern, R.A., Simonetti, S.S., Womer, G., Viljoen, K.S.Eclogite xenoliths from Orapa: Ocean crust recycling, mantle metasomatism and carbon cycling at the western Zimbabwe craton margin.Geochimica et Cosmochinica Acta, Vol. 213, pp. 574-592.Africa, Botswanadeposit - Orapa

Abstract: Major- and trace-element compositions of garnet and clinopyroxene, as well as 87Sr/86Sr in clinopyroxene and ?18O in garnet in eclogite and pyroxenite xenoliths from Orapa, at the western margin of the Zimbabwe craton (central Botswana), were investigated in order to trace their origin and evolution in the mantle lithosphere. Two groups of eclogites are distinguished with respect to 87Sr/86Sr: One with moderate ratios (0.7026-0.7046) and another with 87Sr/86Sr >0.7048 to 0.7091. In the former group, heavy ?18O attests to low-temperature alteration on the ocean floor, while 87Sr/86Sr correlates with indices of low-pressure igneous processes (Eu/Eu?, Mg#, Sr/Y). This suggests relatively undisturbed long-term ingrowth of 87Sr at near-igneous Rb/Sr after metamorphism, despite the exposed craton margin setting. The high-87Sr/86Sr group has mainly mantle-like ?18O and is suggested to have interacted with a small-volume melt derived from an aged phlogopite-rich metasome. The overlap of diamondiferous and graphite-bearing eclogites and pyroxenites over a pressure interval of ?3.2 to 4.9 GPa is interpreted as reflecting a mantle parcel beneath Orapa that has moved out of the diamond stability field, due to a change in geotherm and/or decompression. Diamondiferous eclogites record lower median 87Sr/86Sr (0.7039) than graphite-bearing samples (0.7064) and carbon-free samples (0.7051), suggesting that interaction with the - possibly oxidising - metasome-derived melt caused carbon removal in some eclogites, while catalysing the conversion of diamond to graphite in others. This highlights the role of small-volume melts in modulating the lithospheric carbon cycle. Compared to diamondiferous eclogites, eclogitic inclusions in diamonds are restricted to high FeO and low SiO2, CaO and Na2O contents, they record higher equilibrium temperatures and garnets have mostly mantle-like O isotopic composition. We suggest that this signature was imparted by a sublithospheric melt with contributions from a clinopyroxene-rich source, possibly related to the ca. 2.0 Ga Bushveld event.
DS201709-1956
2017
Aulbach, S., Jacob, D.E., Cartigny, P., Stern, R.A., Simonetti, S.S., Worner, G., Viljoen, K.S.Eclogite xenoliths from Orapa: ocean crust recycling, mantle metasomatism and carbon cycling at the western Zimbabwe craton margin.Geochimica et Cosmochimica Acta, Vol. 213, pp. 574-592.Africa, Botswanadeposit - Orapa

Abstract: Major- and trace-element compositions of garnet and clinopyroxene, as well as 87Sr/86Sr in clinopyroxene and ?18O in garnet in eclogite and pyroxenite xenoliths from Orapa, at the western margin of the Zimbabwe craton (central Botswana), were investigated in order to trace their origin and evolution in the mantle lithosphere. Two groups of eclogites are distinguished with respect to 87Sr/86Sr: One with moderate ratios (0.7026-0.7046) and another with 87Sr/86Sr >0.7048 to 0.7091. In the former group, heavy ?18O attests to low-temperature alteration on the ocean floor, while 87Sr/86Sr correlates with indices of low-pressure igneous processes (Eu/Eu?, Mg#, Sr/Y). This suggests relatively undisturbed long-term ingrowth of 87Sr at near-igneous Rb/Sr after metamorphism, despite the exposed craton margin setting. The high-87Sr/86Sr group has mainly mantle-like ?18O and is suggested to have interacted with a small-volume melt derived from an aged phlogopite-rich metasome. The overlap of diamondiferous and graphite-bearing eclogites and pyroxenites over a pressure interval of ?3.2 to 4.9 GPa is interpreted as reflecting a mantle parcel beneath Orapa that has moved out of the diamond stability field, due to a change in geotherm and/or decompression. Diamondiferous eclogites record lower median 87Sr/86Sr (0.7039) than graphite-bearing samples (0.7064) and carbon-free samples (0.7051), suggesting that interaction with the - possibly oxidising - metasome-derived melt caused carbon removal in some eclogites, while catalysing the conversion of diamond to graphite in others. This highlights the role of small-volume melts in modulating the lithospheric carbon cycle. Compared to diamondiferous eclogites, eclogitic inclusions in diamonds are restricted to high FeO and low SiO2, CaO and Na2O contents, they record higher equilibrium temperatures and garnets have mostly mantle-like O isotopic composition. We suggest that this signature was imparted by a sublithospheric melt with contributions from a clinopyroxene-rich source, possibly related to the ca. 2.0 Ga Bushveld event.
DS201709-1957
2017
Aulbach, S., Woodland, A.B., Vasileyev, P., Galvez, M.E., Viljoen, K.S.Effects of low pressure igneous processes and subduction on Fe3/Fe and redox state of mantle eclogites from Lace ( Kaapvaal craton).Earth and Planetary Science Letters, Vol. 474, pp. 283-295.Africa, South Africadeposit - Lace

Abstract: Reconstructing the redox state of the mantle is critical in discussing the evolution of atmospheric composition through time. Kimberlite-borne mantle eclogite xenoliths, commonly interpreted as representing former oceanic crust, may record the chemical and physical state of Archaean and Proterozoic convecting mantle sources that generated their magmatic protoliths. However, their message is generally obscured by a range of primary (igneous differentiation) and secondary processes (seawater alteration, metamorphism, metasomatism). Here, we report the Fe3+/?Fe ratio and ?18 O in garnet from in a suite of well-characterised mantle eclogite and pyroxenite xenoliths hosted in the Lace kimberlite (Kaapvaal craton), which originated as ca. 3 Ga-old ocean floor. Fe3+/?Fe in garnet (0.01 to 0.063, median 0.02; n = 16) shows a negative correlation with jadeite content in clinopyroxene, suggesting increased partitioning of Fe3+ into clinopyroxene in the presence of monovalent cations with which it can form coupled substitutions. Jadeite-corrected Fe3+/?Fe in garnet shows a broad negative trend with Eu*, consistent with incompatible behaviour of Fe3+ during olivine-plagioclase accumulation in the protoliths. This trend is partially obscured by increasing Fe3+ partitioning into garnet along a conductive cratonic geotherm. In contrast, NMORB-normalised Nd/Yb - a proxy of partial melt loss from subducting oceanic crust (<1) and metasomatism by LREE-enriched liquids (>1) - shows no obvious correlation with Fe3+/?Fe, nor does garnet ?18OVSMOW (5.14 to 6.21‰) point to significant seawater alteration. Median bulk-rock Fe3+/?Fe is roughly estimated at 0.025. This observation agrees with V/Sc systematics, which collectively point to a reduced Archaean convecting mantle source to the igneous protoliths of these eclogites compared to the modern MORB source. Oxygen fugacites (fO2) relative to the fayalite-magnetite-quartz buffer (FMQ) range from ?log ? fO2 = FMQ-1.3 to FMQ-4.6. At those reducing conditions, the solubility of carbon in the fluids released by dehydration is higher than in fluids closer to FMQ. The implication is that Archean processes of C transport and deposition would have differed from those known in modern-style subduction zones, and diamond would have formed from methane-rich fluids. In addition, such reducing material could drive redox melting or freezing upon deep recycling and migration of CH4-bearing fluids into the ambient mantle.
DS201704-0619
2017
Baker, D.R., Sofonio, K.A metasomatic mechanism for the formation of Earth's earliest evolved crust.Earth and Planetary Science Letters, Vol. 463, pp. 48-55.MantleMetasomatism

Abstract: Following giant impacts the early Hadean Earth was shrouded in a steam atmosphere for durations on the order of 1 Ma. In order to investigate the potential of this atmosphere to fractionate major elements between various silicate reservoirs and influence a planet's geochemical evolution, we performed experiments simulating the interaction of a post-giant-impact steam atmosphere with a bulk silicate Earth (BSE) composition. Our experiments indicate that the composition of the solute in a water-rich atmosphere at 10 MPa and ?727?°C is remarkably similar to that of Earth's modern continental crust and would constitute up to 10% of the solution mass. This solute composition is similar to solute compositions previously measured at higher pressures, but distinct from those of near-solidus peridotite melts. Mass balance calculations based upon the hypothesis that Earth's initial water concentration was similar to that in CI carbonaceous chondrites, and that degassing and metasomatism produced the BSE, indicate that metasomatism could produce from 10 to 300% of the mass of the modern crust. If instead the amount of metasomatism is estimated by the difference between the water concentration in the BSE and in the depleted upper mantle, then a mass of up to approximately 4% of the current crust could be produced by metasomatism. Using results of earlier research we find that the solute is expected to have a smaller Sm/Nd ratio than the residual BSE, and if the solute was formed early in Earth's history its Nd isotopic signatures would be highly enriched. Although we cannot be certain that the metasomatic process created a significant fraction of Earth's crust in the early Hadean, our research indicates that it has the potential to form crustal nuclei and possibly was responsible for the production of incompatible-element enriched reservoirs in the early Earth, as seen in the isotopic signatures of Archean rocks.
DS201704-0620
2017
Ballmer, M.D., Houser, C., Hernlund, J.W., Wentzcovitch, R.M., Hirose, K.Persistence of strong silica enriched domains in the Earth's lower mantle.Nature Geoscience, Vol. 10, 3, pp. 236-240.MantleGeophysics - seismic

Abstract: The composition of the lower mantle—comprising 56% of Earth’s volume—remains poorly constrained. Among the major elements, Mg/Si ratios ranging from ~0.9-1.1, such as in rocky Solar-System building blocks (or chondrites), to ~1.2-1.3, such as in upper-mantle rocks (or pyrolite), have been proposed. Geophysical evidence for subducted lithosphere deep in the mantle has been interpreted in terms of efficient mixing, and thus homogenous Mg/Si across most of the mantle. However, previous models did not consider the effects of variable Mg/Si on the viscosity and mixing efficiency of lower-mantle rocks. Here, we use geodynamic models to show that large-scale heterogeneity associated with a 20-fold change in viscosity, such as due to the dominance of intrinsically strong (Mg, Fe)SiO3-bridgmanite in low-Mg/Si domains, is sufficient to prevent efficient mantle mixing, even on large scales. Models predict that intrinsically strong domains stabilize mantle convection patterns, and coherently persist at depths of about 1,000-2,200?km up to the present-day, separated by relatively narrow up-/downwelling conduits of pyrolitic material. The stable manifestation of such bridgmanite-enriched ancient mantle structures (BEAMS) may reconcile the geographical fixity of deep-rooted mantle upwelling centres, and geophysical changes in seismic-tomography patterns, radial viscosity, rising plumes and sinking slabs near 1,000?km depth. Moreover, these ancient structures may provide a reservoir to host primordial geochemical signatures.
DS201702-0193
2016
Ballmer, M.D., Schumacher, L., Lekic, V., Thomas, C., Ito, G.Compositional layering with the large slow shear wave velocity provinces in the lower mantle.Geochemistry, Geophysics, Geosystems: G3, Vol. 17, 2, pp. 5056-5077.MantleGeophysics - seismics

Abstract: The large low shear-wave velocity provinces (LLSVP) are thermochemical anomalies in the deep Earth's mantle, thousands of km wide and ?1800 km high. This study explores the hypothesis that the LLSVPs are compositionally subdivided into two domains: a primordial bottom domain near the core-mantle boundary and a basaltic shallow domain that extends from 1100 to 2300 km depth. This hypothesis reconciles published observations in that it predicts that the two domains have different physical properties (bulk-sound versus shear-wave speed versus density anomalies), the transition in seismic velocities separating them is abrupt, and both domains remain seismically distinct from the ambient mantle. We here report underside reflections from the top of the LLSVP shallow domain, supporting a compositional origin. By exploring a suite of two-dimensional geodynamic models, we constrain the conditions under which well-separated "double-layered" piles with realistic geometry can persist for billions of years. Results show that long-term separation requires density differences of ?100 kg/m3 between LLSVP materials, providing a constraint for origin and composition. The models further predict short-lived "secondary" plumelets to rise from LLSVP roofs and to entrain basaltic material that has evolved in the lower mantle. Long-lived, vigorous "primary" plumes instead rise from LLSVP margins and entrain a mix of materials, including small fractions of primordial material. These predictions are consistent with the locations of hot spots relative to LLSVPs, and address the geochemical and geochronological record of (oceanic) hot spot volcanism. The study of large-scale heterogeneity within LLSVPs has important implications for our understanding of the evolution and composition of the mantle.
DS201708-1596
2017
Banas, A.Can microdiamonds be used to predict the distribution of large Type II a macrodiamonds? A case study of Letseng mine.11th. International Kimberlite Conference, PosterAfrica, Lesothodeposit - Letseng
DS201708-1597
2017
Banas, A.Yellow and white diamonds from the Qilalugaq kimberlites: two generations of diamond growth.11th. International Kimberlite Conference, PosterCanada, Nunavutdeposit - Qilalugaq
DS201709-1958
2017
Bannerjee, A., et al.Significant variation in stable Ca isotopic composition of global carbonatites: role of mantle mineralogy and subducted carbonate. Goldschmidt Conference, abstract 1p.Indiacarbonatite, Ambadongar

Abstract: Stable calcium isotopic composition (44/40Ca) of silicate rock standards show limited variability [c.f., 1] although, fractionation between co-exiting ortho- and clino-pyroxenes have been reported [2]. Variability in 44/40Ca in Hawaiian shield stage tholeiites have been interpreted as evidence of subducted ancient marine carbonates, with very low 44/40Ca, into the Hawaiian plume [3]. Carbonatites are unique mantlederived carbonate-bearing igneous rocks with limited spatial but wide temporal occurrences. Few available measurements (n=5) of 44/40Ca in whole rock and leached carbonatites show a 0.2 ‰ range but broadly overlapping values with mantle-derived silicate rocks from different tectonic settings [1,4]. However, boron isotopic composition of global carbonatites suggest the contribution of subducted crustal component to the mantle source of relatively young carbonatites (<300 Ma old) [5], a signature which should potentially be traceable using Ca isotopes. We report 44/40Ca of global carbonatites ranging in age from Proterozoic to recent. The samples were analyzed using a 43Ca- 48Ca double spike on a Thermo Fischer Triton Plus Thermal Ionization Mass Spectrometer (TIMS) at IISc. 44/40Ca in the carbonatites (n = 11) range from 0.47 - 0.97 ‰ (w.r.t. SRM 915a). Our external reproducibility, estimated from multiple analyses of NIST standards SRM 915a, SRM 915b and seawater (NASS6), is better than 0.1 ‰ (2SD). 44/40Ca of the ~65 Ma old Ambadongar carbonatites of India, associated with eruption of the Deccan Traps, show correlations with Nb/Yb, K/Rb as well as with Sr/Nb, Sr/Zr. These variations suggest the role of phlogopite versus amphibole in the mantle source as well as subducted carbonates in controlling the 44/40Ca of these carbonatites.
DS201708-1598
2017
Barnett, W.Kelvin and Faraday kimberlite emplacement geometries and implications for Subterranean magmatic processes.11th. International Kimberlite Conference, OralCanada, Northwest TerritoriesDeposit - Kelvin, Faraday

Abstract: The Kennady North Project kimberlites are located approximately 280 kilometers east-northeast of Yellowknife, in the Northwest Territories of Canada. The unusual geometry and extent of the kimberlite magmatic system is revealed by renewed exploration drilling activities by Kennady Diamonds since 2012. It has become clear that the system comprises multiple intrusive dykes within which several volcaniclastic bodies have developed, all within 11 kilometres of the Gahcho Kué kimberlite cluster and diamond mine. The detailed exploration of the entire system provides unique evidence for subterranean volcanic conduit growth processes that may have scientific and practical exploration benefits.
DS201710-2213
2017
Barnett, W.Kelvin and Faraday kimberlite emplacement geometries and implications for subterranean magmatic processes.Vancouver Kimberlite Cluster, Oct. 17, 1p. AbstractCanada, Northwest Territorieskimberlite emplacement
DS201712-2675
2017
Barnett, W., Stubley, M., Hrkac, C., Hetman, C.M., McCandless, T.Kelvin and Faraday kimberlite emplacement geometries and implications for subterranean magmatic processes.45th. Annual Yellowknife Geoscience Forum, p. 4 abstractCanada, Northwest Territoriesdeposit - Kelvin, Faraday

Abstract: The Kennady North Project kimberlites are located approximately 280 kilometers east-northeast of Yellowknife, in the Northwest Territories of Canada. The unusual geometry and extent of the kimberlite magmatic system is revealed by renewed exploration drilling activities by Kennady Diamonds since 2012. It has become clear that the system comprises multiple intrusive dykes within which several volcaniclastic bodies have developed, all within 11 kilometres of the Gahcho Kué kimberlite cluster and diamond mine. The detailed exploration of the entire system provides unique evidence for subterranean volcanic conduit growth processes that may have scientific and practical exploration benefits. The identified Kennady North Project volcaniclastic bodies are named Kelvin, Faraday 1, Faraday 2 and Faraday 3, and have complex geometries atypical of the more common subvertical kimberlite pipes. Rather, these pipe-like bodies are inclined between 12 and 30 degrees towards the northwest. Kelvin has sharp angular change in trend towards the north. On-going detailed petrographic studies have shown that the pipes contain layers of complex volcaniclastic units with variable volumes of xenolithic fragments, as well as coherent magmatic layers. The pipe textures include evidence for high energy magma and country rock fragmentation processes typically observed in open volcanic systems. The pipes have developed within a shallow 20 degree northwest dipping kimberlite dyke system. Detailed structural geology studies, using fault observations in oriented and unoriented drill core, have identified at least two important fault-fracture trends. The first fault-fracture system is parallel to the dyke segments, and likely related to the intrusion of the dykes and the regional stress tensor during emplacement. The second fault system is subvertical and north-south striking, parallel to the lithological layering within the metasedimentary country rock. The north-south faults match the contact geometry of the Kelvin pipe’s north-south limb exactly. The dykes have been 3-D modelled along with the pipes. Three possible renditions of the dykes have been created, based on different interpretations of dyke segment continuity. The renditions have been labelled “Optimistic”, “Realistic” and “Pessimistic”. The assumptions made have important implications for developing dyke-type mineral resources. The realistic dyke model defines dyke segments that intersect the Kelvin pipe, and those intersections match geometric trends and irregularities in the pipe shape. The coincidental geometries strongly imply that the pipe development interacted with a penecontemporaneous dyke system. The north-south faults also controlled the local trend of Kelvin pipe development, possibly by enhancing fluid permeability, alteration and brecciation along the faults, connecting from one shallow dipping dyke to the next above. Breccia bodies have been observed on similar dipping dykes at Snap Lake mine that intersect fault structures. We conclude that the pipe development geometry and process is governed by a combination of stress, structure and magmatic fluids, and speculate on the nature of the energy required for fragmentation and development of the pipe at some still unknown depth in the crust.
DS201707-1305
2017
Barron, L.M., Barron, B.J., Mernagh, T.P.Modelling the combination of birefringence retardations from strain envelopes around multiple inclusions in diamond. BingaraAustralian Journal of Earth Sciences, Vol. 64, 4, pp. 557-564.Australia, New South Walesdeposit - Bingara

Abstract: A paleo-alluvial 0.21 ct yellow diamond (L058) from Bingara (NSW) has three inclusions of coesite (two subequant crystals and one thin plate), each under more than 3.1 GPa internal pressure as measured by Raman spectroscopy. These inclusions cause overlapping birefringent retardation stress/strain haloes in the host diamond, visible under cross-polarised light. The complicated retardation pattern is quantified by mapping targeted retardation contours (170 nm, 270 nm and 380 nm) onto a photo of the diamond. A mathematical model of retardation is developed for each inclusion, and then the combined light retardations (CLR) are calculated using radial and tangential components with spherical and elliptical geometries. The CLR model reproduces most features of the measured data, but remaining differences may be due to local release of stress/strain by two short fractures radiating from one inclusion.
DS201710-2214
2017
Barry, P.H.Deep mantle: enriched carbon source detected.Nature Geoscience, Vol. 10, 9, pp. 625-627.United States, Hawaiicarbon

Abstract: Estimates of carbon in the deep mantle vary by more than an order of magnitude. Coupled volcanic CO2 emission data and magma supply rates reveal a carbon-rich mantle plume source region beneath Hawai'i with 40% more carbon than previous estimates.
DS201709-1959
2016
Basson, I.J., Creus, P.K., Anthonissen, C.J., Stoch, B., Ekkerd, J.Structural analysis and implicit 3D modelling of high grade host rocks to the Venetia kimberlite diatremes, central Zone, Limpopo belt, South AfricaJournal of Structural Geology, Vol. 86, pp. 47-61.Africa, South Africadeposit - Venetia

Abstract: The Beit Bridge Complex of the Central Zone (CZ) of the Limpopo Belt hosts the 519 ± 6 Ma Venetia kimberlite diatremes. Deformed shelf- or platform-type supracrustal sequences include the Mount Dowe, Malala Drift and Gumbu Groups, comprising quartzofeldspathic units, biotite-bearing gneiss, quartzite, metapelite, metacalcsilicate and ortho- and para-amphibolite. Previous studies define tectonometamorphic events at 3.3-3.1 Ga, 2.7-2.5 Ga and 2.04 Ga. Detailed structural mapping over 10 years highlights four deformation events at Venetia. Rules-based implicit 3D modelling in Leapfrog Geo™ provides an unprecedented insight into CZ ductile deformation and sheath folding. D1 juxtaposed gneisses against metasediments. D2 produced a pervasive axial planar foliation (S2) to isoclinal F2 folds. Sheared lithological contacts and S2 were refolded into regional, open, predominantly southward-verging, E-W trending F3 folds. Intrusion of a hornblendite protolith occurred at high angles to incipient S2. Constrictional-prolate D4 shows moderately NE-plunging azimuths defined by elongated hornblendite lenses, andalusite crystals in metapelite, crenulations in fuchsitic quartzite and sheath folding. D4 overlaps with a: 1) 2.03-2.01 Ga regional M3 metamorphic overprint; b) transpressional deformation at 2.2-1.9 Ga and c) 2.03 Ga transpressional, dextral shearing and thrusting around the CZ and d) formation of the Avoca, Bellavue and Baklykraal sheath folds and parallel lineations.
DS201709-1960
2017
Basu, S., et al.Subduction in Early Proterozoic mantle: implications from nitrogen in carbonatites and diamonds. JagersfonteinGoldschmidt Conference, abstract 1p.Africa, South Africa, Indiadeposit, Jagersfontein

Abstract: The nitrogen isotopic composition of mantle samples lie between -15 to -5 ‰ and, is different from subducted sediments that varies between +6 to +15 ‰. As a result, N can be an excellent tracer of a subducted component [e.g. 1]. We have studied N from Indian carbonatites of adjacent locations in Hogenakal (2700 Ma) and Sevattur (770 Ma) with established mantle origin. We have also studied two diamonds representative of the Witwatersrand basin (2900–2700 Ma) and Jagersfontein (1100-1700 Ma) belonging to the Kapvaal supergroup. Both India and the Kapvaal craton formed part of a supercontinent that persisted as coherent units until the breakup of Pangea. Comparing the N in these diamonds with the carbonatites will put constraints on differences in their sources and the role of subduction in their generation. The nitrogen isotopic composition of the carbonatites are comparable ranging between -3 to +13 ‰, although value as low as -22 ‰ is observed from an apatite from Hogenakal. The N contents vary from 130 to 6000 ppb. Of the diamonds, Jagersfontein have ?15N of +2.3 and +9.3 ‰, while those from the Witwatersrand basin are –2.3 and 0 ‰. Their nitrogen lie between 500-900 ppm. These results have important implications for their formation and sources.
DS201708-1565
2016
Bata, T., Parnell, J., Samaila, N.K., Haruna, A.I.Anomalous occurrence of Cretaceous placer deposits: a review. Earth and Atmospheric Sciences, Vol. 1, pp. 1-13.Mantlealluvials

Abstract: During the Cretaceous, the CO2 content of the global atmosphere drastically increased in response to volcanism associated with the disintegration of the former continents. This increase in the global atmospheric CO2 level subsequently led to a considerable rise in global temperatures. The interaction among the high levels of atmospheric CO2, extreme global warmth, and humidity witnessed in the Cretaceous implies extreme environmental conditions, which involved a possibly more acidic and chemically destructive atmosphere than at present; these conditions are believed to have favoured widespread deep weathering at that time. Economically important minerals were reworked from their primary sources during these Cretaceous weathering events. The extreme global warmth witnessed in the Cretaceous also caused the melting of most of the polar ice caps, resulting in the expansion of the volume of Cretaceous seawaters, which subsequently led to a significant rise in the global sea level. Extensive palaeo-seaways played a vital role in transporting and depositing the huge volume of sediments generated during the Cretaceous weathering events, which included economically important minerals (e.g., gold, diamond, and platinum). These mineral deposits are now preserved in Cretaceous sands as placer deposits. Three categories of Cretaceous placer deposits can be distinguished: those occurring in Cretaceous sands resting unconformably on the Precambrian basement, those occurring in Cretaceous sands resting unconformably on the Palaeozoic rocks, and those occurring in Cretaceous sands that unconformably overlay Mesozoic strata.
DS201701-0003
2016
Bataleva, Yu.V., Palyanov, Yu.N., Borzdov, Yu.M., Sobolev, N.V.Graphite and diamond formation via the interaction of iron carbide and Fe, Ni sulfide under mantle P-T parameters.Doklady Earth Sciences, Vol. 471, 1, pp. 1144-1148.TechnologyPetrology - experimental

Abstract: Experimental research in the Fe3C-(Fe,Ni)S system was carried out. The objective of the investigation was to model the reactions of carbide-sulfide interaction related to graphite (diamond) formation in reduced lithosphere mantle domains. T ? 1200°C is the formation temperature of the Ni-cohenite + graphite assemblage coexisting with two immiscible melts such as sulfide (Fe60-Ni3-S37)L and metal-sulfide (Fe71-Ni7-S21-C1)L containing dissolved carbon. T ? 1300°C is the generation temperature of a unified melt such as (Fe80-Ni6-S10-C4)L characterized by graphite crystallization and diamond growth. The extraction of carbide carbon during the interaction with the sulfide melt can be considered as one of the potential mechanisms of graphite and diamond formation in the reduced mantle.
DS201702-0194
2017
Beccaluva, L., Bianchini, G., Natali, C., Siena, F.The alkaline carbonatite complex of Jacupiranga ( Brazil): magma genesis.Gondwana Research, Vol. 44, pp. 157-177.South America, BrazilCarbonatite

Abstract: A comprehensive study including new field, petrological and geochemical data is reported on the Jacupiranga alkaline-carbonatite complex (133-131 Ma) which, together with other alkaline complexes, occurs in southern Brazil and is coeval with the Paraná CFB province. It consists of a shallow intrusion (ca. 65 km2) in the Precambrian crystalline basement, and can be subdivided in two main diachronous plutonic bodies: an older dunite-gabbro-syenite in the NW and a younger clinopyroxenite-ijolite (s.l.) in the SE, later injected by a carbonatitic core (ca. 1 km2). An integrated petrogenetic model, based on bulk rock major and trace element analyses, mineral chemistry and Sr-Nd-Pb-C isotopic data, suggests that the two silicate intrusions generated from different mantle-derived magmas that evolved at shallow level (2-3 km depth) in two zoned cup-shaped plutonic bodies growing incrementally from independent feeding systems. The first intrusion was generated by OIB-like alkaline to mildly alkaline parental basalts that initially led to the formation of a dunitic adcumulate core, discontinuously surrounded by gabbroic cumulates, in turn injected by subanular syenite intrusive and phonolite dykes. Nephelinitic (± melilite) melts - likely generated deep in the lithosphere at ? 3 GPa - were the parental magmas of the second intrusion and gave rise to large coarse-grained clinopyroxenite ad- to meso-cumulates, in turn surrounded, and partially cut, by semi-annular fine-layered melteigite-ijolite-urtite ortho-cumulates. The available isotopic data do not evidence genetic links between carbonatites and the associated silicate intrusions, thus favouring an independent source from the mantle. Moreover, it may be suggested that, unlike gabbro-syenites and carbonatites, mostly generated from lithospheric mantle sources, the parental magmas of the ijolite-clinopyroxenite intrusion also record the influence of sublithospheric (plume-related?) geochemical components.
DS201707-1306
2017
Bedard, J.H.Stagnant lids and mantle overturns: implications for Archean tectonics, magmagenesis, crustal growth, mantle evolution, and the start of plate tectonics.Geoscience Frontiers, in press available 12p.Mantlesubduction

Abstract: The lower plate is the dominant agent in modern convergent margins characterized by active subduction, as negatively buoyant oceanic lithosphere sinks into the asthenosphere under its own weight. This is a strong plate-driving force because the slab-pull force is transmitted through the stiff sub-oceanic lithospheric mantle. As geological and geochemical data seem inconsistent with the existence of modern-style ridges and arcs in the Archaean, a periodically-destabilized stagnant-lid crust system is proposed instead. Stagnant-lid intervals may correspond to periods of layered mantle convection where efficient cooling was restricted to the upper mantle, perturbing Earth's heat generation/loss balance, eventually triggering mantle overturns. Archaean basalts were derived from fertile mantle in overturn upwelling zones (OUZOs), which were larger and longer-lived than post-Archaean plumes. Early cratons/continents probably formed above OUZOs as large volumes of basalt and komatiite were delivered for protracted periods, allowing basal crustal cannibalism, garnetiferous crustal restite delamination, and coupled development of continental crust and sub-continental lithospheric mantle. Periodic mixing and rehomogenization during overturns retarded development of isotopically depleted MORB (mid-ocean ridge basalt) mantle. Only after the start of true subduction did sequestration of subducted slabs at the core-mantle boundary lead to the development of the depleted MORB mantle source. During Archaean mantle overturns, pre-existing continents located above OUZOs would be strongly reworked; whereas OUZO-distal continents would drift in response to mantle currents. The leading edge of drifting Archaean continents would be convergent margins characterized by terrane accretion, imbrication, subcretion and anatexis of unsubductable oceanic lithosphere. As Earth cooled and the background oceanic lithosphere became denser and stiffer, there would be an increasing probability that oceanic crustal segments could founder in an organized way, producing a gradual evolution of pre-subduction convergent margins into modern-style active subduction systems around 2.5 Ga. Plate tectonics today is constituted of: (1) a continental drift system that started in the Early Archaean, driven by deep mantle currents pressing against the Archaean-age sub-continental lithospheric mantle keels that underlie Archaean cratons; (2) a subduction-driven system that started near the end of the Archaean.
DS201711-2501
2015
Begg, G.C., Griffin, W.L., O'Reilly, S.Y., Natapov, L.Geoscience dat a integration: insights into mapping lithospheric architecture.ASEG-PESA 2015, 2 p. abstract Mantledata integration

Abstract: In order to develop a 4D understanding of the architecture of the entire lithosphere, it is necessary to embrace integration of multi-disciplinary, multi-scale data in a GIS environment. An holistic understanding has evolved whereby geologic, geochemical and geophysical signals are consistent with a subcontinental lithospheric mantle (SCLM) dominated by a mosaic of domains of Archean ancestry, variably overprinted by subsequent tectonothermal events. Pristine Archean SCLM is mostly highly depleted (high Mg#), low density, high velocity and highly resistive, and preserves intact Archean crust. There is a first order relationship between changes to these signals and the degree of tectonothermal overprint (by melts, fluids). Continental crust is comprised largely of reconstituted Archean components, variably diluted by juvenile addition, symptomatic of the various overprinting events. These events impart crustal fabrics and patterns dictated by SCLM architecture, influenced by the free surface and crust-mantle decoupling.
DS201709-1961
2017
Beland, C.M.J., William-Jones, A.E.The nature and origin of REE mineralization in the Ashram deposit, Eldor carbonatite complex, Quebec, CanadaGoldschmidt Conference, abstract 1p.Canada, Quebeccarbonatite, Eldor

Abstract: A growing number of studies have suggested that hydrothermal remobilization is crucial for the formation of carbonatite-hosted rare earth element (REE) deposits [1-3]. The Ashram REE deposit, hosted by the Paleoproterozoic Eldor Carbonatite Complex [4], is an example of a REE deposit formed mainly due to hydrothermal processes in magnesio- and ferro-carbonatite. The REE minerals in the Ashram deposit, monazite-(Ce), bastnäsite-(Ce), xenotime- (Y) and minor aeschynite-(Y), are secondary, and were precipitated from hydrothermal fluids. They occur mainly as disseminations, in breccia matrices and veins, and as vug fillings. Hydrothermal apatite and fluorite are also present in appreciable quantities in REE-mineralized zones. Monazite- (Ce) was the earliest REE mineral to form, and was followed by xenotime-(Y) and bastnäsite-(Ce). The compositions of the main REE minerals vary with location in the deposit, particularly in respect to their Nd2O3 and ThO2 contents. Two generations of monazite-(Ce) have been distinguished on the basis of their Nd content. Early, low-Nd monazite-(Ce) formed by replacing apatite through the substitution of 3REE3+ for 5Ca2+ + F- ; low-Nd apatite is LREE-enriched compared to apatite. In contrast, the later high-Nd generation, which has a chondrite-normalized REE profile almost perfectly parallel to that of the apatite, is interpreted to have formed by dissolving the Ca2+ and F- of the apatite and reconstituting the REE and phosphate as monazite-(Ce): Ca4.94REE0.060(PO4)3F = 0.060REEPO4 + F- + 4.94Ca2+ + 2.94PO4 3- Bastnäsite-(Ce) developed as a replacement of monazite- (Ce) through ligand exchange (F- and CO3 2- for PO4 3- ), while preserving the original REE chemistry. A combination of magmatic zone-refinement and hydrothermal remobilization, involving a chloride-bearing fluid, contributed to the formation of a carbonatite-hosted REE deposit.
DS201707-1307
2017
Bell, A.S., Shearer, C., Burger, P., Ren, M., Newville, M., Lanzirotti, A.Quantifying and correcting the effects of anisotropy in Xanes measurements of chromium valence in olivine: implications for a new olivine oxybarometer.American Mineralogist, Vol. 102, pp. 1165-1172.Technologyolivine

Abstract: Chromium valence ratios in igneous olivine may hold a wealth of redox information about the melts from which they crystallized. It has been experimentally shown that the Cr2+/?Cr of olivine varies systematically with fO2, therefore measurements of Cr valence in olivine could be employed as a quantitative oxybarometer. In situ synchrotron ?-XANES analyses of Cr valence ratios of individual olivine phenocrysts in thin section have the potential to unlock this stored magmatic redox information on a fine spatial scale. However, there are still obstacles to obtaining accurate XANES measurements of cation valence in crystalline materials, as the results from these measurements can be compromised by anisotropic absorption effects related to the crystallographic orientation of the sample. Improving the accuracy of XANES measurements of Cr valence ratios in olivine by calibrating an anisotropy correction is a vital step in developing Cr valence measurements in olivine as a rigorous oxybarometer. To accomplish this goal, we have used an integrated approach that combined experiments, electron backscatter diffraction analysis, and XANES measurements in olivine to systematically examine how orientation affects the resultant Cr K-edge XANES spectra and the Cr valence ratios that are calculated from them. The data set generated in this work was used to construct a model that mitigates the effects of anisotropy of the calculated Cr2+/?Cr values. The application of this correction procedure as a part of spectral processing improves the overall accuracy of the resultant Cr2+/?Cr values by nearly a factor of five. The increased accuracy of the XANES measured Cr valence ratios afforded by the anisotropy correction reduces the error on calculated fO2 values from approximately ±1.2 to ±0.25
DS201707-1308
2017
Bell, E.Ancient magma sources revealed. Nature Geoscience, Vol. 10, 6, pp. 397-398.Mantlemelting

Abstract: The composition of Earth's oldest crust is uncertain. Comparison of the most ancient mineral grains with more recent analogues suggests that formation of the earliest crust was heavily influenced by re-melting of igneous basement rocks.
DS201705-0809
2017
Benaouda, R., Holzheid, A., Schenk, V., Badra, L., Ennaciri, A.Magmatic evolution of the Jbel Boho alkaline complex in the Bou Azzer In lier ( Anti-Atlas/Morocco) and its relation to REE Mineralization.Journal of African Earth Sciences, Vol. 129, pp. 202-223.Africa, MoroccoAlkaline rocks

Abstract: The Jbel Boho complex (Anti-Atlas/Morocco) is an alkaline magmatic complex that was formed during the Precambrian-Cambrian transition, contemporaneous with the lower early Cambrian dolomite sequence. The complex consists of a volcanic sequence comprising basanites, trachyandesites, trachytes and rhyolites that is intruded by a syenitic pluton. Both the volcanic suite and the pluton are cut by later microsyenitic and rhyolitic dykes. Although all Jbel Boho magmas were probably ultimately derived from the same, intraplate or plume-like source, new geochemical evidence supports the concept of a minimum three principal magma generations having formed the complex. Whereas all volcanic rocks (first generation) are LREE enriched and appear to be formed by fractional crystallization of a mantle-derived magma, resulting in strong negative Eu anomalies in the more evolved rocks associated with low Zr/Hf and Nb/Ta values, the younger syenitic pluton displays almost no negative Eu anomaly and very high Zr/Hf and Nb/Ta. The syenite is considered to be formed by a second generation of melt and likely formed through partial melting of underplated mafic rocks. The syenitic pluton consists of two types of syenitic rocks; olivine syenite and quartz syenite. The presence of quartz and a strong positive Pb anomaly in the quartz syenite contrasts strongly with the negative Pb anomaly in the olivine syenite and suggests the latter results from crustal contamination of the former. The late dyke swarm (third generation of melt) comprises microsyenitic and subalkaline rhyolitic compositions. The strong decrease of the alkali elements, Zr/Hf and Nb/Ta and the high SiO2 contents in the rhyolitic dykes might be the result of mineral fractionation and addition of mineralizing fluids, allowing inter-element fractionation of even highly incompatible HFSE due to the presence of fluorine. The occurrence of fluorite in some volcanic rocks and the Ca-REE-F carbonate mineral synchysite in the dykes with very high LREE contents (Ce ?720 ppm found in one rhyolitic dyke) suggest the fluorine-rich nature of this system and the role played by addition of mineralizing fluids. The REE mineralization expressed as synchysite-(Ce) is detected in a subalkaline rhyolitic dyke (with ?LREE = 1750 ppm) associated with quartz, chlorite and occasionally with Fe-oxides. The synchysite mineralization is probably the result of REE transport by acidic hydrothermal fluids as chloride complex and their neutralization during fluid-rock interaction. The major tectonic change from compressive to extensional regime in the late Neoproterozoic induced the emplacement of voluminous volcaniclastic series of the Ediacran Ouarzazate Group. The alkaline, within-plate nature of the Jbel Boho igneous complex implies that this extensional setting continued during the early Cambrian.
DS201708-1566
2017
Bentham, H.L., Rost, S., Thorne, M.S.Fine scale structure of the mid-mantle characterised by global stacks of PP precursors.Earth and Planetary Science Letters, Vol. 472, pp. 164-173.Mantlegeophysics, seismic

Abstract: Subduction zones are likely a major source of compositional heterogeneities in the mantle, which may preserve a record of the subduction history and mantle convection processes. The fine-scale structure associated with mantle heterogeneities can be studied using the scattered seismic wavefield that arrives as coda to or as energy preceding many body wave arrivals. In this study we analyse precursors to PP by creating stacks recorded at globally distributed stations. We create stacks aligned on the PP arrival in 5° distance bins (with range 70–120°) from 600 earthquakes recorded at 193 stations stacking a total of 7320 seismic records. As the energy trailing the direct P arrival, the P coda, interferes with the PP precursors, we suppress the P coda by subtracting a best fitting exponential curve to this energy. The resultant stacks show that PP precursors related to scattering from heterogeneities in the mantle are present for all distances. Lateral variations are explored by producing two regional stacks across the Atlantic and Pacific hemispheres, but we find only negligible differences in the precursory signature between these two regions. The similarity of these two regions suggests that well mixed subducted material can survive at upper and mid-mantle depth. To describe the scattered wavefield in the mantle, we compare the global stacks to synthetic seismograms generated using a Monte Carlo phonon scattering technique. We propose a best-fitting layered heterogeneity model, BRT2017, characterised by a three layer mantle with a background heterogeneity strength (?=0.8%) and a depth-interval of increased heterogeneity strength (?=1%) between 1000 km and 1800 km. The scalelength of heterogeneity is found to be 8 km throughout the mantle. Since mantle heterogeneity of 8 km scale may be linked to subducted oceanic crust, the detection of increased heterogeneity at mid-mantle depths could be associated with stalled slabs due to increases in viscosity, supporting recent observations of mantle viscosity increases due to the iron spin transition at depths of ?1000 km.
DS201702-0195
2017
Beyer, C., Frost, D.J.The depth of sub-lithospheric diamond formation and the redistribution of carbon in the deep mantle.Earth and Planetary Science Letters, Vol. 461, pp. 30-39.MantleMajorite, geobarometry

Abstract: Most diamonds form in the Earth's lithosphere but a small proportion contain Si-rich majoritic garnet inclusions that indicate formation in the deeper mantle. The compositions of syngenetic garnet inclusions can potential yield information on both the depth and mantle lithology in which the diamonds formed. Pressure dependent changes in garnet compositions have been calibrated using the results of experiments conducted in a multi-anvil apparatus at pressures between 6 and 16 GPa and temperatures of 1000 to 1400?°C. Using the results of these experiments a barometer was formulated based on an empirical parameterisation of the two major majoritic substitutions, referred to as majorite (Maj ; Al3+=Mg2++Si4+Al3+=Mg2++Si4+), and Na-majorite (Na-Maj ; Mg2++Al3+=Na++Si4+Mg2++Al3+=Na++Si4+). Moreover, previously published experimental garnet compositions from basaltic, kimberlite, komatiite and peridotite bulk compositions were included in the calibration, which consequently covers pressures from 6 to 20 GPa and temperatures from 900 to 2100?°C. Experimental pressures are reproduced over these conditions with a standard deviation of 0.86 GPa. The barometer is used to determine equilibration pressures of approximately 500 reported garnet inclusions in diamonds from a range of localities. As the majority of these inclusions are proposed to be syngenetic this allows a detailed picture of diamond formation depths and associated source rocks to be established using inclusion chemistry. Geographic differences in diamond source rocks are mapped within the sub-lithospheric mantle to over 500 km depth. Continuous diamond formation occurs over this depth range within lithologies with eclogitic affinities but also in lithologies that appear transitional between eclogitic and peridotitic bulk compositions, with an affinity to pyroxenites. The geographic differences between eclogitic and pyroxenitic diamond source rocks are rationalised in terms of diamond formation within downwelling and upwelling regimes respectively. Macroscopic diamond formation in rocks with pyroxenite compositions are likely facilitated in the deep mantle by higher average oxidation states and low mineral H2OH2O solubility compared to the surrounding mantle, which aid the mobility of C-O-H volatile species. The apparent lack of inclusions with a peridotite affinity may result from generally low oxygen fugacities in such lithologies, which reduces carbon mobility, and the lack of a suitable oxidising agent to allow diamonds to form from CH4. This glimpse of deep carbon cycle processes implies that heterogeneities in the carbon content, redox state and chemical composition of the mantle may be strongly coupled.
DS201708-1599
2017
Bezzola, M.The geology and evaluation of the Kelvin kimberlite pipe, NWT, Canada.11th. International Kimberlite Conference, PosterCanada, Northwest Territoriesdeposit - Kelvin
DS201706-1063
2017
Bianchini, G., Bodinier, J-L., Braga, R., Wilson, M.Crust-mantle and lithosphere-Asthenosphere boundaries.Geological Society of America, SPE 526, 200p.Mantlebook
DS201708-1567
2017
Blanchini, G., Bodinier, J-L., Braga, R., Wilson, M.The crust mantle and lithosphere-asthenosphere boundaries: insights from xenoliths, orogenic deep sections, and geophysical studies. 2 Chapters citedGeological Society of London, book - cost approx. 43 lbsMantlexenoliths
DS201702-0196
2016
Blattler, C.L., Kump, L.R., Fischer, W.W., Paris, G., Kasbohm, J.J.Constraints on ocean carbonate chemistry and pco2 in the Archean and Paleoproterozoic.Nature Geoscience, Vol. 10, pp. 41-45.GlobalGeochemistry

Abstract: One of the great problems in the history of Earth’s climate is how to reconcile evidence for liquid water and habitable climates on early Earth with the Faint Young Sun predicted from stellar evolution models. Possible solutions include a wide range of atmospheric and oceanic chemistries, with large uncertainties in boundary conditions for the evolution and diversification of life and the role of the global carbon cycle in maintaining habitable climates. Increased atmospheric CO2 is a common component of many solutions, but its connection to the carbon chemistry of the ocean remains unknown. Here we present calcium isotope data spanning the period from 2.7 to 1.9 billion years ago from evaporitic sedimentary carbonates that can test this relationship. These data, from the Tumbiana Formation, the Campbellrand Platform and the Pethei Group, exhibit limited variability. Such limited variability occurs in marine environments with a high ratio of calcium to carbonate alkalinity. We are therefore able to rule out soda ocean conditions during this period of Earth history. We further interpret this and existing data to provide empirical constraints for carbonate chemistry of the ancient oceans and for the role of CO2 in compensating for the Faint Young Sun.
DS201708-1600
2017
Bloom, A.Density measurement within the context of the rock mass characterization program of the Kelvin and Faraday kimberlites and surrounding country rock in the Northwest Territories of Canada.11th. International Kimberlite Conference, PosterCanada, Northwest Territoriesdeposit - Kelvin, Faraday
DS201708-1601
2017
Bobrov, A.V.Sodium-bearing phases in the transition zone and uppermost lower mantle: experimental and natural data.11th. International Kimberlite Conference, PosterMantlemineralogy
DS201710-2215
2017
Bolhar, R., Hofman, A., Kemp, A.I.S., Whitehouse, M.J., Wind, S., Kamber, B.S.Juvenile crust formation in the Zimbabwean Craton deduced from the O-Hf isotopic record 3.8-3.1 Ga detrital zircons.Geochimica et Cosmochinica Acta, Vol. 215, pp. 432-446.Africa, Zimbabwecraton

Abstract: Hafnium and oxygen isotopic compositions measured in-situ on U-Pb dated zircon from Archaean sedimentary successions belonging to the 2.9–2.8 Ga Belingwean/Bulawayan groups and previously undated Sebakwian Group are used to characterize the crustal evolution of the Zimbabwe Craton prior to 3.0 Ga. Microstructural and compositional criteria were used to minimize effects arising from Pb loss due to metamorphic overprinting and interaction with low-temperature fluids. 207Pb/206Pb age spectra (concordance >90%) reveal prominent peaks at 3.8, 3.6, 3.5, and 3.35 Ga, corresponding to documented geological events, both globally and within the Zimbabwe Craton. Zircon ?18O values from +4 to +10‰ point to both derivation from magmas in equilibrium with mantle oxygen and the incorporation of material that had previously interacted with water in near-surface environments. In ?Hf-time space, 3.8–3.6 Ga grains define an array consistent with reworking of a mafic reservoir (176Lu/177Hf ?0.015) that separated from chondritic mantle at ?3.9 Ga. Crustal domains formed after 3.6 Ga depict a more complex evolution, involving contribution from chondritic mantle sources and, to a lesser extent, reworking of pre-existing crust. Protracted remelting was not accompanied by significant mantle depletion prior to 3.35 Ga. This implies that early crust production in the Zimbabwe Craton did not cause complementary enriched and depleted reservoirs that were tapped by later magmas, possibly because the volume of crust extracted and stabilised was too small to influence (asthenospheric) mantle isotopic evolution. Growth of continental crust through pulsed emplacement of juvenile (chondritic mantle-derived) melts, into and onto the existing cratonic nucleus, however, involved formation of complementary depleted subcontinental lithospheric mantle since the early Archaean, indicative of strongly coupled evolutionary histories of both reservoirs, with limited evidence for recycling and lateral accretion of arc-related crustal blocks until 3.35 Ga.
DS201702-0197
2017
Boniface, N.Crystal chemistry of pyrochlore from the Mesozoic PAnd a Hill carbonatite deposit, western Tanzania.Journal of African Earth Sciences, Vol. 126, pp. 33-44.Africa, TanzaniaDeposit - Panda Hill

Abstract: The Mesozoic Panda Hill carbonatite deposit in western Tanzania hosts pyrochlore, an ore and source of niobium. This study was conducted to establish the contents of radioactive elements (uranium and thorium) in pyrochlore along with the concentration of niobium in the ore. The pyrochlore is mainly hosted in sövite and is structurally controlled by NW-SE (SW dipping) or NE-SW (NW dipping) magmatic flow bands with dip angles of between 60° and 90°. Higher concentrations of pyrochlore are associated with magnetite, apatite and/or phlogopite rich flow bands. Electron microprobe analyses on single crystals of pyrochlore yield very low UO2 concentrations that range between 0 and 0.09 wt% (equivalent to 0 atoms per formula unit: a.p.f.u.) and ThO2 between 0.55 and 1.05 wt% (equivalent to 0.1 a.p.f.u.). The analyses reveal high concentrations of Nb2O5 (ranging between 57.13 and 65.50 wt%, equivalent to a.p.f.u. ranging between 1.33 and 1.43) and therefore the Panda Hill Nb-oxide is classified as pyrochlore sensu stricto. These data point to a non radioactive pyrochlore and a deposit rich in Nb at Panda Hill. The Panda Hill pyrochlore has low concentrations of REEs as displayed by La2O3 that range between 0.10 and 0.49 wt% (equivalent to a.p.f.u. ranging between 0 and 0.01) and Ce2O3 ranging between 0.86 and 1.80 wt% (equivalent to a.p.f.u. ranging between 0.02 and 0.03), Pr2O3 concentrations range between 0 and 0.23 wt% (equivalent to 0 a.p.f.u.), and Y2O3 is 0 wt% (equivalent to 0 a.p.f.u.). The abundance of the REEs in pyroclore at the Panda Hill Carbonatite deposit is of no economic significance.
DS201709-1962
2017
Borisova, A.Y., Zagrtdenov, N.R., Toplis, M.J., Bohrson, W.A., Nedelec, A., Safonov, O.G., Pokrovski, G.S., Ceileneer, G., Melnik, O.E., Bychkov, A.Y., Gurenko, A.A., Shscheka, S., Terehin, A., Polukeev, V.M., Varlamov, D.A., Gouy, S., De Parseval, P.Making Earth's continental crust from serpentinite and basalt. Goldschmidt Conference, abstract 1p.Mantleperidotites

Abstract: How the Earth's continental crust was formed in the Hadean eon is a subject of considerable debates [1-4]. For example, shallow hydrous peridotites [2,5], in particular the Hadean Earth's serpentinites [6], are potentially important ingredients in the creation of the continental ptoto-crust, but the mechanisms of this formation remain elusive. In this work, experiments to explore serpentinite-basalt interaction under conditions of the Hadean Earth were conducted. Kinetic runs lasting 0.5 to 48 hours at 0.2 to 1.0 GPa and 1250 to 1300°C reveal dehydration of serpentinite and release of a Si-Al-Na-K-rich aqueous fluid. For the first time, generation of heterogeneous hydrous silicic melts (56 to 67 wt% SiO2) in response to the fluid-assisted fertilisation and the subsequent partial melting of the dehydrated serpentinite has been discovered. The melts produced at 0.2 GPa have compositions similar to those of the bulk continental crust [2,3]. These new findings imply that the Earth's sialic proto-crust may be generated via fluid-assisted melting of serpentinized peridotite at shallow depths (?7 km) that do not require plate subduction during the Hadean eon. Shallow serpentinite dehydration and melting may be the principal physico-chemical processes affecting the earliest lithosphere. Making Earth's continental crust from serpentinite and basalt.
DS201705-0810
2016
Bornyakov, S.A., Salko, D.V.Instrumental deformation monitoring system and its trial in open pit diamond mine.Journal of Mining Science, Vol. 52, 2, pp. 388-393.RussiaDeposit - Nyurbisnskaya

Abstract: The designed automated system for pitwall deformation monitoring consists of an independent data recorder, strain sensors, AD converters, and front-end and back-end controls. Data are accumulated on server in on-line mode via cellular modem. The self-contained tools are supplied from accumulators recharged by solar batteries, which expands operational life of the system. The system has been trailed in an open pit mine at Nyurbinskaya kimberlite pipe in deformation monitoring of faults in the eastern pitwall and estimation of its stability.
DS201710-2216
2017
Bosshard-Stadlin, S.A., Mattsson, H.B., Stewart, C., Reusser, E.Leaching of lava and tephra from the Oldoinyo Lengai volcano ( Tanzania): remobilization of fluorine and other potentially toxic elements in surface waters of the Gregory Rift.Journal of Volcanology and Geothermal Research, Vol. 322, pp. 14-25.Africa, Tanzaniadeposit - Oldoinyo Lengai

Abstract: Volcanic ash leachate studies have been conducted on various volcanoes on Earth, but few have been done on African volcanoes until now. Tephra emissions may affect the environment and the health of people living in this area, and therefore we conducted a first tephra (ash and lapilli sized) leachate study on the Oldoinyo Lengai volcano, situated in northern Tanzania. The recent explosive eruption in 2007-2008 provided us with fresh samples from the first three weeks of the eruption which were used for this study. In addition, we also used a natrocarbonatitic sample from the activity prior to the explosive eruption, as the major activity at Oldoinyo Lengai is natrocarbonatitic. To compare the leaching process affecting the natrocarbonatitic lavas and the tephras from Oldoinyo Lengai, the 2006 natrocarbonatitic lava flow was resampled 5 years after the emplacement and compared to the initial, unaltered composition. Special interest was given to the element fluorine (F), since it is potentially toxic to both humans and animals. A daily intake of fluoride (F?) in drinking water of > 1.5 mg/l can lead to dental fluorosis, and higher concentrations lead to skeletal fluorosis. For this reason, a guideline value for fluoride in drinking water was set by the WHO (2011) to 1.5 mg/l. However, surface waters and groundwaters in the Gregory Rift have elevated fluoride levels of up to 9.12 mg/l, and as a consequence, an interim guideline value for Tanzania has been set at 8 mg/l. The total concentration of fluorine in the samples from the natrocarbonatitic lava flow is high (3.2 wt%), whereas we observed a significant decrease of the fluorine concentration (between 1.7 and 0.5 wt%) in the samples collected three days and three weeks after the onset of the explosive 2007-08 eruption. However, the total amount of water-extractable fluoride is lower in the natrocarbonatitic lavas (319 mg/l) than in the nephelinitic tephra (573-895 mg/l). This is due to the solubility of the different F-bearing minerals. In the natrocarbonatites, fluorine exists predominantly in fluorite (CaF2), and in the early tephra as Na-Mg bearing salts such as neighborite (NaMgF3) and sellaite (MgF2). All these three minerals have very low solubility in water (16-130 mg/l). The later nephelinitic tephras contain surface coating of villiaumite (NaF), which is highly soluble (42,200 mg/l) in water and can thus release the fluoride more readily upon contact with water. Although there is still the need for further data and a more precise study on this topic in Tanzania, we can already draw a first conclusion that the intake of water during or directly following the deposition of the tephra is not advisable and should be avoided, whereas the release of fluoride from the lava flow has less influence on the river waters.-
DS201707-1309
2017
Bouhifd, M.A., Clesi, V., Boujibar, A., Cartier, C., Hammouda, T., Boyet, M., Manthilake, G., Monteux, J., Andrault, D.Silicate melts during the Earth's core formation.Chemical Geology, Vol. 461, pp. 128-139.Mantlemelting

Abstract: Accretion from primordial material and its subsequent differentiation into a planet with core and mantle are fundamental problems in terrestrial and solar system. Many of the questions about the processes, although well developed as model scenarios over the last few decades, are still open and much debated. In the early Earth, during its formation and differentiation into rocky mantle and iron-rich core, it is likely that silicate melts played an important part in shaping the Earth's main reservoirs as we know them today. Here, we review several recent results in a deep magma ocean scenario that give tight constraints on the early evolution of our planet. These results include the behaviour of some siderophile elements (Ni and Fe), lithophile elements (Nb and Ta) and one volatile element (Helium) during Earth's core formation. We will also discuss the melting and crystallization of an early magma ocean, and the implications on the general feature of core-mantle separation and the depth of the magma ocean. The incorporation of Fe2 + and Fe3 + in bridgmanite during magma ocean crystallization is also discussed. All the examples presented here highlight the importance of the prevailing conditions during the earliest time of Earth's history in determining the composition and dynamic history of our planet.
DS201708-1602
2017
Bovkun, A.Features of diamond and its indicator minerals of kimberlites of the M.V. Lomonov deposit, Arkangelsk region, Russia.11th. International Kimberlite Conference, OralRussia, Archangeldeposit - Lomonov
DS201710-2217
2017
Bragagni, A., Luguet, A., Fonseca, R.O.C., Pearson, D.G.,Lorand, J-P., Nowell, G.M., Kjarsgaard, B.A.The geological record of base metal sulfides in the cratonic mantle: a microscale 187Os/188Os study of peridotite xenoliths from Somerset Island, Rae Craton ( Canada).Geochimica et Cosmochimia Acta, Vol. 216, pp. 264-285.Canada, Nunavut, Somerset IslandGeochronology

Abstract: We report detailed petrographic investigations along with 187Os/188Os data in Base Metal Sulfide (BMS) on four cratonic mantle xenoliths from Somerset Island (Rae Craton, Canada). The results shed light on the processes affecting the Re-Os systematics and provide time constraints on the formation and evolution of the cratonic lithospheric mantle beneath the Rae craton. When devoid of alteration, BMS grains mainly consist of pentlandite + pyrrhotite ± chalcopyrite. The relatively high BMS modal abundance of the four investigated xenoliths cannot be reconciled with the residual nature of these peridotites, but requires addition of metasomatic BMS. This is especially evident in the two peridotites with the highest bulk Pd/Ir and Pd/Pt. Metasomatic BMS likely formed during melt/fluid percolation in the Sub Continental Lithospheric Mantle (SCLM) as well as during infiltration of the host kimberlite magma, when djerfisherite crystallized around older Fe-Ni-sulfides. On the whole-rock scale, kimberlite metasomatism is visible in a subset of bulk xenoliths, which defines a Re-Os errorchron that dates the host magma emplacement. The 187Os/188Os measured in the twenty analysed BMS grains vary from 0.1084 to >0.17 and it shows no systematic variation depending on the sulfide mineralogical assemblage. The largest range in 187Os/188Os is observed in BMS grains from the two xenoliths with the highest Pd/Ir, Pd/Pt, and sulfide modal abundance. The whole-rock TRD ages of these two samples underestimate the melting age obtained from BMS, demonstrating that bulk Re-Os model ages from peridotites with clear evidence of metasomatism should be treated with caution. The TRD ages determined in BMS grains are clustered around 2.8-2.7, ?2.2 and ?1.9 Ga. The 2.8-2.7 Ga TRD ages document the main SCLM building event in the Rae craton, which is likely related to the formation of the local greenstone belts in a continental rift setting. The Paleoproterozoic TRD ages can be explained by addition of metasomatic BMS during (i) major lithospheric rifting at ?2.2 Ga and (ii) the Taltson-Thelon orogeny at ?1.9 Ga. The data suggest that even metasomatic BMS can inherit 187Os/188Os from their original mantle source. The lack of isotopic equilibration, even at the micro-scale, allowed the preservation of different populations of BMS grains with distinct 187Os/188Os, providing age information on multiple magmatic events that affected the SCLM.
DS201706-1064
2017
Bragagni, A., Luguet, A., Fonsecca, R.O.C., Pearson, D.G., Lorand, D.G., Nowell, G.M., Kjarsgaard, B.A.The geological record of base metal sulfides in the cratonic mantle: a microscale 187Os/188/Os study of peridotite xenoliths from Somerset Island, Rae craton,( Canada).Geochimica et Cosmochimica Acta, in press available 49p.Canada, Nunavut, Somerset Islandperidotite

Abstract: We report detailed petrographic investigations along with 187Os/188Os data in Base Metal Sulfide (BMS) on four cratonic mantle xenoliths from Somerset Island (Rae Craton, Canada). The results shed light on the processes affecting the Re-Os systematics and provide time constraints on the formation and evolution of the cratonic lithospheric mantle beneath the Rae craton. When devoid of alteration, BMS grains mainly consist of pentlandite + pyrrhotite ± chalcopyrite. The relatively high BMS modal abundance of the four investigated xenoliths cannot be reconciled with the residual nature of these peridotites, but requires addition of metasomatic BMS. This is especially evident in the two peridotites with the highest bulk Pd/Ir and Pd/Pt. Metasomatic BMS likely formed during melt/fluid percolation in the Sub Continental Lithospheric Mantle (SCLM) as well as during infiltration of the host kimberlite magma, when djerfisherite crystallized around older Fe-Ni-sulfides. On the whole-rock scale, kimberlite metasomatism is visible in a subset of bulk xenoliths, which defines a Re-Os errorchron that dates the host magma emplacement. The 187Os/188Os measured in the twenty analysed BMS grains vary from 0.1084 to >0.17 and it shows no systematic variation depending on the sulfide mineralogical assemblage. The largest range in 187Os/188Os is observed in BMS grains from the two xenoliths with the highest Pd/Ir, Pd/Pt, and sulfide modal abundance. The whole-rock TRD ages of these two samples underestimate the melting age obtained from BMS, demonstrating that bulk Re-Os model ages from peridotites with clear evidence of metasomatism should be treated with caution. The TRD ages determined in BMS grains are clustered around 2.8-2.7, ?2.2 and ?1.9 Ga. The 2.8-2.7 Ga TRD ages document the main SCLM building event in the Rae craton, which is likely related to the formation of the local greenstone belts in a continental rift setting. The Paleoproterozoic TRD ages can be explained by addition of metasomatic BMS during (i) major lithospheric rifting at ?2.2 Ga and (ii) the Taltson-Thelon orogeny at ?1.9 Ga. The data suggest that even metasomatic BMS can inherit 187Os/188Os from their original mantle source. The lack of isotopic equilibration, even at the micro-scale, allowed the preservation of different populations of BMS grains with distinct 187Os/188Os, providing age information on multiple magmatic events that affected the SCLM.
DS201708-1603
2017
Brett, C.Petrology of the White River Diamondiferous Paleoproterozoic intrusive rocks.11th. International Kimberlite Conference, PosterCanada, Ontariodeposit - White River
DS201708-1604
2017
Brey, G.The birth, growth and ageing of the Kaapvaal subcratonic mantle.11th. International Kimberlite Conference, OralAfrica, Southern AfricaSubduction, metasomatism
DS201709-1963
2017
Broadley, M.W., et al.Noble gases in diamond hosted fluid inclusions: sorting the deep from the dregs.Goldschmidt Conference, abstract 1p.Russia, Siberiadeposit, Nyurbinskaya

Abstract: Fluid inclusions trapped during diamond formation provide pristine information into the nature of mantle volatile sources. The majority of diamonds are formed at the base of the lithosphere, which due to its non-convective nature is able to retain geochemical heterogeneities introduced through interactions with the upper and lower mantle, crustal, and subduction related sources. In order to evaluate the origin of diamond forming fluids in the lithosphere, we present noble gas isotopic data from a suite of cubic, coated and cloudy diamond from the Nyurbinskaya Kimberlite, Siberia. Noble gas signatures extracted from fluid inclusions by crushing show two distinct volatile components present within the Siberian lithosphere. Cubic diamonds have average 3 He/4 He of 10 RA, whilst the 3 He/4 He of the coated and cloudy diamonds is the 6 RA. The Ne isotopic data is also different between the diamonds with 20Ne/22Ne in the cubic diamonds (10.7) consistently higher that the coated and cloudy diamonds, which are dominated by an atmospheric component. The 3 He/4 He in fluids trapped in the coated and cloudy diamonds are typical of samples from the lithospheric mantle. Fluids trapped in the cubic diamonds have higher 3 He/4 He than lithospheric and MORB mantle sources, but are similar to values reported from the Siberian Flood Basalts (SFB), which are derived from a lower mantle source. Ne isotopic data from the cubic diamond also suggests these diamonds contain a lower mantle volatile component. Noble gases in diamond hosted fluid inclusions have shown the Siberian lithosphere contains both lihtospheric and lower mantle volatile compponents. The coexistence of lithospheric and lower mantle volatiles within diamonds originating from the same kimberlite indicates the Siberian lithosphere must have had at least two periods of diamond growth from two distinct diamond forming fluids.
DS201707-1310
2017
Broom-Fendley, S., Brady, A.E., Horstwood, M.S.A., Woolley, A.R., Mtegha, J., Wall, F., Dawes, W., Gunn, G.Geology, geochemistry and geochronology of the Songwe Hill carbonatite, Malawi.Journal of African Earth Sciences, Vol. 134, pp. 10-23.Africa, Malawicarbonatite - Songwe Hill

Abstract: Songwe Hill, Malawi, is one of the least studied carbonatites but has now become particularly important as it hosts a relatively large rare earth deposit. The results of new mapping, petrography, geochemistry and geochronology indicate that the 0.8 km diameter Songwe Hill is distinct from the other Chilwa Alkaline Province carbonatites in that it intruded the side of the much larger (4 x 6 km) and slightly older (134.6 ± 4.4 Ma) Mauze nepheline syenite and then evolved through three different carbonatite compositions (C1–C3). Early C1 carbonatite is scarce and is composed of medium–coarse-grained calcite carbonatite containing zircons with a U–Pb age of 132.9 ± 6.7 Ma. It is similar to magmatic carbonatite in other carbonatite complexes at Chilwa Island and Tundulu in the Chilwa Alkaline Province and others worldwide. The fine-grained calcite carbonatite (C2) is the most abundant stage at Songwe Hill, followed by a more REE- and Sr-rich ferroan calcite carbonatite (C3). Both stages C2 and C3 display evidence of extensive (carbo)-hydrothermal overprinting that has produced apatite enriched in HREE (<2000 ppm Y) and, in C3, synchysite-(Ce). The final stages comprise HREE-rich apatite fluorite veins and Mn-Fe-rich veins. Widespread brecciation and incorporation of fenite into carbonatite, brittle fracturing, rounded clasts and a fenite carapace at the top of the hill indicate a shallow level of emplacement into the crust. This shallow intrusion level acted as a reservoir for multiple stages of carbonatite-derived fluid and HREE-enriched apatite mineralisation as well as LREE-enriched synchysite-(Ce). The close proximity and similar age of the large Mauze nepheline syenite suggests it may have acted as a heat source driving a hydrothermal system that has differentiated Songwe Hill from other Chilwa carbonatites.
DS201701-0004
2016
Broom-Fendley, S., Brady, A.E., Wall, F., Gunn, G., Dawes, W.REE minerals at the Songwe Hill carbonatite, Malawi: HREE enrichment in late stage apatite.Ore Geology Reviews, Vol. 81, pp. 23-41.Africa, MalawiCarbonatite

Abstract: Compared to all published data from carbonatites and granitoids, the fluorapatite compositions in the Songwe Hill carbonatite, determined by EPMA and LA ICP-MS, have the highest heavy (H)REE concentration of any carbonatite apatite described so far. A combination of this fluorapatite and the REE fluorocarbonates, synchysite-(Ce) and parisite-(Ce), which are the other principal REE bearing minerals at Songwe, gives a REE deposit with a high proportion of Nd and a higher proportion of HREE (Eu-Lu including Y) than most other carbonatites. Since Nd and HREE are currently the most sought REE for commercial applications, the conditions that give rise to this REE profile are particularly important to understand. Multiple apatite crystallisation stages have been differentiated texturally and geochemically at Songwe and fluorapatite is divided into five different types (Ap-0-4). While Ap-0 and Ap-1 are typical of apatite found in fenite and calcite-carbonatite, Ap-2, -3 and -4 are texturally atypical of apatite from carbonatite and are progressively HREE-enriched in later paragenetic stages. Ap-3 and Ap-4 exhibit anhedral, stringer-like textures and their REE distributions display an Y anomaly. These features attest to formation in a hydrothermal environment and fluid inclusion homogenisation temperatures indicate crystallisation occurred between 200-350 °C. Ap-3 crystallisation is succeeded by a light (L)REE mineral assemblage of synchysite-(Ce), strontianite and baryte. Finally, late-stage Ap-4 is associated with minor xenotime-(Y) mineralisation and HREE-enriched fluorite. Fluid inclusions in the fluorite constrain the minimum HREE mineralisation temperature to approximately 160 °C. A model is suggested where sub-solidus, carbonatite-derived, (carbo)-hydrothermal fluids remobilise and fractionate the REE. Chloride or fluoride complexes retain LREE in solution while rapid precipitation of apatite, owing to its low solubility, leads to destabilisation of HREE complexes and substitution into the apatite structure. The LREE are retained in solution, subsequently forming synchysite-(Ce). This model will be applicable to help guide exploration in other carbonatite complexes.
DS201709-1964
2017
Broom-Fendley, S., O'Neill, M., Wall, F.Are carbonate-fluorapatite rocks in carbonatite complexes the result of hydrothermal processes or weathering? Sokli, KovdorGoldschmidt Conference, abstract 1p.Europe, Finland, Russiacarbonatites, Sokli, Kovdor

Abstract: Carbonate-fluorapatite (also known as staffelite and/or francolite) can become a rock-forming mineral in the upper levels of some carbonatite complexes, such as at Sokli, Finland, and Kovdor, Russia. Carbonate-fluorapatite rocks are recognised as an important phosphate resource, but there is little consensus on their genesis. Two principal models are favoured: (1) a hydrothermal origin, from a late-stage, carbonatite-derived fluid or, (2) formation through supergene dissolution of carbonate and re-precipitation of apatite. In this contribution, we have investigated the texture and composition of different carbonate-fluorapatite generations (using cathodoluminescence microsopy and LA ICP MS) in order to evaluate the aforementioned formation mechanisms. Four carbonate-fluorapatite growth generations were identified: (1) primary apatite grains, with a rounded/euhedral habit and luminescing purple; (2) strongly luminescent epitactic rims on primary grains; (3) ‘aggregate’ apatite, forming a fine-grained groundmass, typically luminescing blue; (4) botryoidal growth zones, commonly luminescing blue, but in places green or non-luminescent. REE contents in secondary carbonate-fluorapatite generations (2–4) are markedly low, with some analyses below detection limit (typically <1 ppm). Furthermore, many of these analyses exhibit both positive and negative Ce anomalies, indicative of an oxidising environment. The low REE contents of the different carbonatefluorapatite generations indicates that negligible REE transfer occurred between different growth events, contrasting with hydrothermal apatite in other carbonatite complexes. Furthermore, the lack of any significant fractionation between subsequent carbonate-fluorapatite generations is interpreted as circumstantial evidence that these rocks did not form through hydrothermal alteration. This is compounded by the presence of a Ce anomaly, which is commonly interpreted as a weathering feature. While hydrothermal formation under different conditions, causing complete removal of the REE, cannot be ruled out, we conclude that the locations were, most-likely, formed in a supergene environment. Continued investigation of weathered carbonate-fluorapatite material from other localities is underway to assess this conclusion.
DS201712-2676
2017
Broom-Fendley, S., Wall, F., Spiro, B., Ullmann, C.V.Deducing the source and composition of rare earth mineralising fluids in carbonatites: insights from isotopic ( C,O,87Sr/86SR) dat a from Kangankunde, Malawi.Contributions to Mineralogy and Petrology, Vol. 172, 96Africa, Malawicarbonatite

Abstract: Carbonatites host some of the largest and highest grade rare earth element (REE) deposits but the composition and source of their REE-mineralising fluids remains enigmatic. Using C, O and 87Sr/86Sr isotope data together with major and trace element compositions for the REE-rich Kangankunde carbonatite (Malawi), we show that the commonly observed, dark brown, Fe-rich carbonatite that hosts REE minerals in many carbonatites is decoupled from the REE mineral assemblage. REE-rich ferroan dolomite carbonatites, containing 8-15 wt% REE2O3, comprise assemblages of monazite-(Ce), strontianite and baryte forming hexagonal pseudomorphs after probable burbankite. The 87Sr/86Sr values (0.70302-0.70307) affirm a carbonatitic origin for these pseudomorph-forming fluids. Carbon and oxygen isotope ratios of strontianite, representing the REE mineral assemblage, indicate equilibrium between these assemblages and a carbonatite-derived, deuteric fluid between 250 and 400 °C (?18O + 3 to + 5‰VSMOW and ?13C ? 3.5 to ? 3.2‰VPDB). In contrast, dolomite in the same samples has similar ?13C values but much higher ?18O, corresponding to increasing degrees of exchange with low-temperature fluids (< 125 °C), causing exsolution of Fe oxides resulting in the dark colour of these rocks. REE-rich quartz rocks, which occur outside of the intrusion, have similar ?18O and 87Sr/86Sr to those of the main complex, indicating both are carbonatite-derived and, locally, REE mineralisation can extend up to 1.5 km away from the intrusion. Early, REE-poor apatite-bearing dolomite carbonatite (beforsite: ?18O + 7.7 to + 10.3‰ and ?13C ?5.2 to ?6.0‰; 87Sr/86Sr 0.70296-0.70298) is not directly linked with the REE mineralisation.
DS201711-2502
2017
Brown, G.E., Hochella, M.F., Calas, G.Improving mitigation of the long term legacy of mining activities: nano and molecular level concepts and methods.Elements, Vol. 13, pp. 325-330.Globalresources

Abstract: Mining activities over several millennia have resulted in a legacy of environmental contamination that must be mitigated to minimize ecosystem damage and human health impacts. Designing effective remediation strategies for mining and processing wastes requires knowledge of nano- and molecular-scale speciation of contaminants. Here, we discuss how modern nano- and molecular-level concepts and methods can be used to improve risk assessment and future management of contaminants that result from mining activities, and we illustrate this approach using relevant case studies.
DS201709-1965
2017
Bruguier, O., Bosch, D., Caby, R., Vitale-Brovarone, A., Fernadez, L., Hammor, D., Laouar, R., Ouabadi, A., Abdallah, N., Mechanti, M.Age of UHP metamorphism in the Western Mediterranean: insight from rutile and minute zircon inclusions in a diamond bearing garnet megacryst ( Edough Massif, NE Algeria).Earth and Planetary Science Letters, Vol. 474, pp. 215-225.Africa, Algeriadiamond inclusions

Abstract: Diamond-bearing UHP metamorphic rocks witness for subduction of lithospheric slabs into the mantle and their return to shallow levels. In this study we present U-Pb and trace elements analyses of zircon and rutile inclusions from a diamond-bearing garnet megacryst collected in a mélange unit exposed on the northern margin of Africa (Edough Massif, NE Algeria). Large rutile crystals (up to 300 ?m in size) analyzed in situ provide a U-Pb age of 32.4 ± 3.3 Ma interpreted as dating the prograde to peak subduction stage of the mafic protolith. Trace element analyses of minute zircons (?30 ?m) indicate that they formed in equilibrium with the garnet megacryst at a temperature of 740-810 °C, most likely during HP retrograde metamorphism. U-Pb analyses provide a significantly younger age of 20.7 ± 2.3 Ma attributed to exhumation of the UHP units. This study allows bracketing the age of UHP metamorphism in the Western Mediterranean Orogen to the Oligocene/early Miocene, thus unambiguously relating UHP metamorphism to the Alpine history. Exhumation of these UHP units is coeval with the counterclockwise rotation of the Corsica-Sardinia block and most likely resulted from subduction rollback that was driven by slab pull.
DS201707-1311
2017
Buikin, A.I., Kogarko, L.N., Hopp, J., Trieloff, M.Light noble gas dat a in Guli massif carbonatites reveal the subcontinental lithospheric mantle as primary fluid source.Geochemistry International, Vol. 55, 5, pp. 457-464.Russiacarbonatite - Guli

Abstract: For better understanding of the fluid phase sources of carbonatites of Guli alkaline-ultrabasic intrusion (Maymecha-Kotuy complex) we have studied isotope composition of He and Ne in the carbonatites of different formation stages. The data definitely point to the subcontinental lithospheric mantle (SCLM) as a primary source of fluid phase of Guli carbonatites. The absence of plume signature in such a plume-like object (from petrological point of view) could be explained in terms that Guli carbonatites have been formed at the waning stage of plume magmatic activity with an essential input of SCLM components.
DS201708-1605
2017
Bulanova, G.Natural diamond growth conditions recorded by their internal structure.11th. International Kimberlite Conference, PosterTechnologydiamond morphology
DS201705-0811
2017
Bullock, E.Diamonds in the Sky.lithographie.org, No. 19, pp. 128-131.TechnologyBook - meteorites
DS201705-0812
2017
Bureau, H., Remusat, L., Esteve, I., Pinti, D., Cartigny, P.Isotopic characterization of diamond growth in fluids.European Geosciences Union General Assembly 2017, Vienna April 23-28, 1p. 19147 AbstractTechnologyDiamond inclusions

Abstract: Trapping inclusions in diamonds has been used as a diagnostic to constrain diamond growth media (e.g. Navon et al., 1994; Weiss et al., 2015) in the Earth's upper mantle. Experimental works now generate inclusion-bearing diamonds from seeds in mixtures of carbonates, graphite, and silicates in the presence of excess of pure water or saline fluids (H2O-NaCl) and investigate in more details the conditions of natural diamond growth (Bureau et al., 2012; 2016). Experiments were carried at conditions compatible with the Earth's geotherm between 6-7 GPa (1300-1675°C) in multi-anvil presses at the Bayerisches Geoinstitut, Bayreuth from a few hours two a few days. Results show that within the timescale of the experiments diamond growth occurs on seeds if water and alkali-bearing carbonates are present. We show that water promotes fast diamond growth, which is favorable to the formation of inclusions. Thin sections of a few diamond seeds containing exposed inclusions were prepared using a Focus Ion Beam (about 2 to 5 µm thickness). These sections were deposited on silicon wafers and gold coated for micron-scale determination of the delta 13C isotopic compositions using the NanoSIMS 50 installed at the Muséum National d'Histoire Naturelle, Paris. Carbon isotope measurement with NanoSIMS were calibrated against a natural Ia and a synthetic IIa diamond used for diamond anvil cells, whose compositions were determined by gas-source mass spectrometry at IPGP at 3.6±0.1‰ and -20.9±0.1‰, respectively (Pinti et al., 2016). All the starting materials used for the experiments were also characterized for their delta 13C by the same technique at GEOTOP, Montréal. The isotopic composition of the new diamond grown areas were measured close to the inclusions. They exhibit a different isotopic signature than that of the starting seeds (starting diamond composition: -29.6 to -30.4±1.4‰). The new diamond signatures are falling into the range of signatures of the starting carbonates used for the experiments (- 4.8±0.1 to -16.2±0.1‰) when they are far away from the composition of the starting graphite (-26.4±0.1‰). This shows that the carbon source for diamond growth must be the carbonates present either as CO32- ions dissolved in the melt or as carbon dioxide species CO2 in the aqueous fluid and that diamond growth occurred from carbonate reduction rather that from graphite dissolved in the melt. We suggest that the presence of small discrete or isolated volumes of water-carbonate-rich fluids are necessary to grow inclusion-bearing peridotitic, eclogitic, fibrous, cloudy and coated diamonds, and may also be involved in the growth of ultrahigh pressure metamorphic diamonds.
DS201709-1966
2017
Bureau, H., Remusat, L., Esteve, I., Pinti, L., Cartigny, P.The carbon source for lithospheric diamonds.Goldschmidt Conference, abstract 1p.Mantlecarbon

Abstract: Trapping inclusions in diamonds during growth experiments is used as a diagnostic to constrain natural diamond formation conditions in the Earth’s lithosphere. Isotopic signature of the new diamond grown areas close to those inclusions is also useful to identify the carbon source for the diamonds. In this study experiments were carried at conditions compatible with the Earth’s geotherm between 6-7 GPa (1300-1675°C) in multi-anvil presses from a few hours to a few days. Carbon-bearing starting materials are powders of carbonates and graphite. Results show that within the timescale of the experiments diamond growth occurs on preexisting seeds if water and alkali-bearing carbonates are present. The ?13C isotopic composition of the new diamond grown areas measured close to the inclusions show a different isotopic signature than that of the starting seeds (-29.6 to - 30.4±1.4‰). The new diamond carbon signatures are falling into the range of signatures of the starting carbonates used for the experiments (-4.8±0.1 to -16.2±0.1‰) but far away from the composition of the starting graphite (-26.4±0.1‰). This suggests that the carbon source for diamond growth at the conditions of the lithosphere must be the carbonates present either as CO3 2- ions dissolved in the melt or as carbon dioxide in the aqueous fluid. It is concluded that diamond growth occurred from carbonate reduction rather that from graphite dissolution in the melt.
DS201709-1967
2017
Burkhart, P.A., Alley, R.B., Thompson, L.G., Balog, J.D., Baukdauf, P.E., Baker, G.S.Savor the cryosphere.GSA Today, Vol. 27, pp. 4-11.Globalglaciers

Abstract: This article provides concise documentation of the ongoing retreat of glaciers, along with the implications that the ice loss presents, as well as suggestions for geoscience educators to better convey this story to both students and citizens. We present the retreat of glaciers—the loss of ice—as emblematic of the recent, rapid contraction of the cryosphere. Satellites are useful for assessing the loss of ice across regions with the passage of time. Ground-based glaciology, particularly through the study of ice cores, can record the history of environmental conditions present during the existence of a glacier. Repeat photography vividly displays the rapid retreat of glaciers that is characteristic across the planet. This loss of ice has implications to rising sea level, greater susceptibility to dryness in places where people rely upon rivers delivering melt water resources, and to the destruction of natural environmental archives that were held within the ice. Warming of the atmosphere due to rising concentrations of greenhouse gases released by the combustion of fossil fuels is causing this retreat. We highlight multimedia productions that are useful for teaching this story effectively. As geoscience educators, we attempt to present the best scholarship as accurately and eloquently as we can, to address the core challenge of conveying the magnitude of anthropogenic impacts, while also encouraging optimistic determination on the part of students, coupled to an increasingly informed citizenry. We assert that understanding human perturbation of nature, then choosing to engage in thoughtful science-based decision-making, is a wise choice. This topic comprised “Savor the Cryosphere,” a Pardee Keynote Symposium at the 2015 Annual Meeting in Baltimore, Maryland, USA, for which the GSA recorded supporting interviews and a webinar.
DS201708-1606
2017
Burness, S.The role of sulphur during partial melting of eclogite in the cratonic mantle: constraints from experiments and xenoliths.11th. International Kimberlite Conference, PosterMantleeclogite
DS201710-2218
2017
Burness, S., Smart, K.A., Stevens, G., Tappe, S., Sharp, Z.D., Gibbons, J.S-bearing metasomatism of mantle eclogites: constraints from the Kaapvaal craton and experiments.Goldschmidt Conference, 1p. AbstractAfrica, South Africadeposit - Roberts Victor, Jagersfontein
DS201708-1607
2017
Burnham, A.The nitrogen budget of subducted crust.11th. International Kimberlite Conference, PosterMantlenitrogen
DS201706-1065
2017
Burnham, A.D., Berry, A.J.Formation of Hadean granites by melting of igneous crust.Nature Geoscience, in press May 8 availableAustraliaJack Hills zircon

Abstract: The oldest known samples of Earth, with ages of up to 4.4?Gyr, are detrital zircon grains in meta-sedimentary rocks of the Jack Hills in Australia. These zircons offer insights into the magmas from which they crystallized, and, by implication, igneous activity and tectonics in the first 500 million years of Earth’s history, the Hadean eon. However, the compositions of these magmas and the relative contributions of igneous and sedimentary components to their sources have not yet been resolved. Here we compare the trace element concentrations of the Jack Hills zircons to those of zircons from the locality where igneous (I-) and sedimentary (S-) type granites were first distinguished. We show that the Hadean zircons crystallized predominantly from I-type magmas formed by melting of a reduced, garnet-bearing igneous crust. Further, we propose that both the phosphorus content of zircon and the ratio of phosphorus to rare earth elements can be used to distinguish between detrital zircon grains from I- and S-type sources. These elemental discriminants provide a new geochemical tool to assess the relative contributions of primeval magmatism and melting of recycled sediments to the continents over geological time.
DS201709-1968
2017
Bussweiler, Y., Poitras, S., Borovinskaya, O., Tanner, M., Pearson, G.Rapid multielemental analysis of garnet with LA-ICP-TOF-MS implications for diamond exploration studies.Goldschmidt Conference, abstract 1p.Canada, Northwest Territoriesdiamond potential

Abstract: Garnet arguably constitutes the most important mineral in diamond exploration studies; not only can the presence of mantle garnet in exploration samples point to kimberlite occurrences, but its minor and trace element composition can further be used to assess the “diamond potential” of a kimberlite. The content of Cr and Ca, especially, has been found to be a reliable tool to test whether garnets originate from within the diamond stability field in the mantle [1]. Trace element patterns can further indicate the mantle host rock of the garnets, for example, whether they originate from a depleted or ultra-depleted mantle section [2]. Routinely, two separate analytical methods are necessary to fully characterize the composition of garnet; major and minor elements are usually determined by electron probe micro-analysis (EPMA), whereas determination of trace elements requires the more sensitive method of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Here, we demonstrate rapid measurement of the entire suite of elements in garnet employing a new, commercially available timeof-flight (TOF) mass spectrometer, the icpTOF (TOFWERK AG, Thun, Switzerland), coupled to a fast wash-out laser ablation system (Teledyne Cetac Technologies Inc., Omaha, NE, USA). Using garnets from exploration samples taken from the Horn Plateau, Northwest Territories, Canada [3], we directly compare the icpTOF results to EPMA and LA-ICP-MS data. We examine whether the icpTOF can reliably characterize the garnets in Cr versus Ca space and at the same time reproduce their trace element patterns, thereby offering a cost effective method of analysis. The method of LA-ICP-TOF-MS, with its high speed of data acquisition and its ability to record the entire mass spectrum simultaneously, may have great benefits for (diamond) exploration studies. Moreover, the method can be used for fast, highresolution imaging, which is applicable to a wide range of geological materials and settings [4].
DS201708-1608
2017
Bussweiller, Y.Cr-rich megacrysts of clinopyroxene and garnet from Lac de Gras kimberlites, Slave craton, Canada - implications for the origin of clinopyroxenes and garnet in cratonic peridotites.11th. International Kimberlite Conference, OralCanada, Northwest Territoriesdeposit - Lac de Gras
DS201708-1609
2017
Bussweiller, Y.Evolution of calcite-bearing kimberlites by melt-rock reaction - evidence from polmineralic inclusions within clinopyroxene and garnet megacrysts from Lac de Gras kimberlites, Canada.11th. International Kimberlite Conference, PosterCanada, Northwest Territoriesdeposit - Lac de Gras

Abstract: Megacrystic (>1 cm) clinopyroxene (Cr-diopside) and garnet (Cr-pyrope) xenocrysts within kimberlites from Lac de Gras (Northwest Territories, Canada) contain fully crystallized melt inclusions. These `polymineralic inclusions' have previously been interpreted to form by necking down of melts at mantle depths. We present a detailed petrographical and geochemical investigation of polymineralic inclusions and their host crystals to better understand how they form and what they reveal about the evolution of kimberlite melt. Genetically, the megacrysts are mantle xenocrysts with peridotitic chemical signatures indicating an origin within the lithospheric mantle (for the Cr-diopsides studied here ~4.6 GPa, 1015 °C). Textural evidence for disequilibrium between the host crystals and their polymineralic inclusions (spongy rims in Cr-diopside, kelyphite in Cr-pyrope) is consistent with measured Sr isotopic disequilibrium. The preservation of disequilibrium establishes a temporal link to kimberlite eruption. In Cr-diopsides, polymineralic inclusions contain phlogopite, olivine, chromite, serpentine, and calcite. Abundant fluid inclusion trails surround the inclusions. In Cr-pyropes, the inclusions additionally contain Al-spinel, clinopyroxene, and dolomite. The major and trace element compositions of the inclusion phases are generally consistent with the early stages of kimberlite differentiation trends. Extensive chemical exchange between the host phases and the inclusions is indicated by enrichment of the inclusions in major components of the host crystals, such as Cr2O3 and Al2O3. This chemical evidence, along with phase equilibria constraints, supports the proposal that the inclusions within Cr-diopside record the decarbonation reaction: dolomitic melt + diopside ? forsterite + calcite + CO2, yielding the observed inclusion mineralogy and producing associated (CO2-rich) fluid inclusions. Our study of polymineralic inclusions in megacrysts provides clear mineralogical and chemical evidence for an origin of kimberlite that involves the reaction of high-pressure dolomitic melt with diopside-bearing mantle assemblages producing a lower-pressure melt that crystallizes a calcite-dominated assemblage in the crust.
DS201705-0813
2017
Butler, J.E., Feigelson, B.N.Laboratory-Grown Diamonds.lithographie.org, No. 19, pp. 114-127.TechnologyBook - synthetics
DS201712-2677
2017
Byerley, B.L., Kareem, K., Bao, H., Byerley, G.R.Early Earth mantle heterogeneity revealed by light oxygen isotopes of Archean komatiites.Nature Geoscience, Vol. 10, 11, pp. 871-875.Mantlegeochronology

Abstract: Geodynamic processes on early Earth, especially the interaction between the crust and deep mantle, are poorly constrained and subject to much debate. The rarity of fresh igneous materials more than 3 billion years old accounts for much of this uncertainty. Here we examine 3.27-billion-year-old komatiite lavas from Weltevreden Formation in the Barberton greenstone belt, which is part of the Kaapvaal Craton in Southern Africa. We show that primary magmatic compositions of olivine are well preserved in these lavas based on major and trace element systematics. These komatiitic lavas represent products of deep mantle plumes. Oxygen isotope compositions (?18O) of the fresh olivine measured by laser fluorination are consistently lighter (about 2‰) than those obtained from modern mantle-derived volcanic rocks. These results suggest a mantle source for the Weltevreden komatiites that is unlike the modern mantle and one that reflects mantle heterogeneity left over from a Hadean magma ocean. The anomalously light ?18O may have resulted from fractionation of deep magma ocean phases, as has been proposed to explain lithophile and siderophile isotope compositions of Archaean komatiites.
DS201708-1610
2017
Cairns, S.Revitalizing exploration in a key diamond district: a case study in the Northwest Territories, Canada.11th. International Kimberlite Conference, PosterCanada, Northwest Territoriesdeposit -
DS201711-2503
2017
Calas, G.Mineral Resources and Sustainable Development.Elements, Vol. 13, pp. 301-306.Globalresources, CSR

Abstract: Mineral resources have been used for millennia and are a key to society's development. With the growing importance of new technologies and the energy revolution, questions have arisen regarding the future availability of resources of metals and industrial minerals. As discovering large high-grade deposits has become increasingly rare, the concept of “sustainable development” will become viewed as essential to extract metals/minerals from new low-grade deposits. In addition to economic considerations, it is essential to reconcile mining activity with environmental protection and to allay the concerns of local populations. This issue of Elements highlights the progressive movement towards an active environmental and societal strategy for sustainably harnessing mineral resources.
DS201702-0198
2017
Campbell, I.H., Davies, D.R.Raising the continental crust.Earth and Planetary Science Letters, Vol. 460, pp. 112-122.MantleArchean - Boundary

Abstract: The changes that occur at the boundary between the Archean and Proterozoic eons are arguably the most fundamental to affect the evolution of Earth's continental crust. The principal component of Archean continental crust is Granite-Greenstone Terranes (GGTs), with granites always dominant. The greenstones consist of a lower sequence of submarine komatiites and basalts, which erupted onto a pre-existing Tonalite-Trondhjemite-Granodiorite (TTG) crust. These basaltic rocks pass upwards initially into evolved volcanic rocks, such as andesites and dacites and, subsequently, into reworked felsic pyroclastic material and immature sediments. This transition coincides with widespread emplacement of granitoids, which stabilised (cratonised) the continental crust. Proterozoic supra-crustal rocks, on the other hand, are dominated by extensive flat-lying platform sequences of mature sediments, which were deposited on stable cratonic basements, with basaltic rocks appreciably less abundant. The siliceous TTGs cannot be produced by direct melting of the mantle, with most hypotheses for their origin requiring them to be underlain by a complimentary dense amphibole-garnet-pyroxenite root, which we suggest acted as ballast to the early continents. Ubiquitous continental pillow basalts in Archean lower greenstone sequences require the early continental crust to have been sub-marine, whereas the appearance of abundant clastic sediments, at higher stratigraphic levels, shows that it had emerged above sea level by the time of sedimentation. We hypothesise that the production of komatiites and associated basalts, the rise of the continental crust, widespread melting of the continental crust, the onset of sedimentation and subsequent cratonisation form a continuum that is the direct result of removal of the continent's dense amphibole-garnet-pyroxenite roots, triggered at a regional scale by the arrival of a mantle plume at the base of the lithosphere. Our idealised calculations suggest that the removal of 40 km of the amphibole-garnet-pyroxenite root would have raised the average level of the continental crust by ?3 km. The emergence of the continental crust was an essential precursor to the rise of oxygen, which started some 200 Myr later.
DS201708-1657
2017
Campebll, D., Puumala, M., Eichenberg, D., Riemer, W., Wahl, R.Diamond field trip Marathon-White Ricer area. Guidebook, 15p. Pdf availableCanada, Ontarioguidebook
DS201711-2504
2017
Campione, M., Tumiati, S., Malaspina, N.Primary spinel + chlorite inclusions in mantle garnet formed at ultrahigh pressure. Maowu ultramafic complex.Geochemical Perspectives Letters, Vol. 4, pp. 19-23.ChinaUHP

Abstract: Multiphase inclusions represent microenvironments where the interaction between fluid and host mineral is preserved during the rock geological path. Under its peculiar chemical-physical constraints, the entrapped solute-rich fluid might follow a crystallisation mechanism which is not predictable through simple equilibrium arguments. In this letter, by the modelling of solid-solution equilibrium and the application of principles of mass conservation, we demonstrate that cavities in mantle garnet filled with slab-derived fluids can re-equilibrate to a pyrope + spinel + chlorite assemblage at the same high P-T of their formation. The basis of this occurrence is a dissolution-reprecipitation mechanism, triggered by a dilute, non-equilibrated slab fluid.
DS201709-1969
2017
Cangeloshi, D.A., et al.Influence of hydrothermal activity on the final REE mineralization at the Okorusu carbonatite complex, NamibiaGoldschmidt Conference, abstract 1p.Africa, Namibiacarbonatite, Okorusu

Abstract: Carbonatites are the primary source of LREE worldwide. Here we describe evidence from the Okorusu mine in NorthCentral Namibia, based on results from a suite of techniques including SEM-EDS and SEM-CL imaging, EPMA, LA-ICPMS on minerals and fluid inclusions, bulk rock chemistry and microthermometry. This provides indications of hydrothermal reworking in a carbonatite-related REE deposit. The Okorusu deposit is part of a ring complex consisting of syenites, nepheline syenites, and carbonatite with hydrothermal fluorite ore mineralisation formed principally by replacing carbonatite bodies. The primary carbonatites show a typical LREE enriched pattern. Primary REE mineralisation is contained in the magmatic phases apatite, pyrochlore and calcite. These phases have been partially broken down by hydrothermal activity. Most of the REE in the carbonatite samples now occur in secondary hydrothermal phases, mainly synchysite-(Ce). The REE occur also as synchysite-(Ce) in the hydrothermal fluorite but additionally they are incorporated into the fluorite structure resulting in cathodoluminescence zoning. Fluid inclusions are observed in both magmatic phases (apatite, calcite and clinopyroxene) and in hydrothermal phases (fluorite, calcite and quartz). The fluid inclusions associated with secondary REE mineralisation in fluorite consist of liquid-vapour inclusion with a constant liquid/bubble ratio and often a small daughter mineral. This suggests that the REE were transported by a relatively concentrated aqueous fluid. Fluid and melt inclusions hosted in the magmatic phases show a wider range in composition. The Okorusu carbonatite deposit shows primary and secondary features common to carbonatite deposits worldwide, and so the results reported here may be of wider significance.
DS201705-0814
2017
Carlson, R.W.Earth's building blocks. Nature, Vol. 541, pp. 468-470. Jan 25MantleMeteorites

Abstract: Earth grew by the accretion of meteoritic material. High-precision isotopic data reveal how the composition of this material changed over time, forcing revision of models of our planet's formation.
DS201711-2505
2017
Carreras, I.M.Minerales "exoticos" en chromititas ofioliticas de Tehuitzingo ( Estado de Puebla, Mexico)Thesis, Universitat de Barcelona *** SPA, 77p. PdfMexicochromites
DS201709-1970
2017
Caruso, M., Stagno, V.The Transition from carbonatitic to carbonate silicate magmas in carbonated elogitic rocks as function of pressure, temperature and oxygen fugacity.Goldschmidt Conference, abstract 1p.Mantlecarbonatite

Abstract: The deep carbon cycle and the origin of carbonatitic melts into the Earth’s mantle have been studied through the effect of CO2 on phase equilibria within carbonated eclogitic assemblage in the last decades. However the effect of temperature (T), pressure (P) and oxygen fugacity (fO2) on the melt composition remains unclear. This study aims to determine the melt composition of CO2-rich melts at fO2 buffered by the C/carbonate equilibrium as function of P and T. Experiments were performed using the Voggenreiter 840 t, Walker-type multi anvil press available at HP/HT Lab at National Institute of Geophysics and Volcanology (INGV) in Rome. The starting material employed for all the experiments is a mixture of synthetic omphacitic glass, quartz, dolomite and graphite representative of the Dolomite-CoesiteDiopside-Graphite buffering assemblage [DCDG; 1], doped with ilmenite and rutile and ~3 wt% iridium used as redox sensor to monitorate the oxygen fugacity during the experiment. The recovered quenched samples were polished for textural and chemical analysis of the mineral phases using Field emission scanning electron microscope and electron microprobe at the INGV. Preliminary results were combined with previous published data [2], and the determined fo2 compared with thermodynamic predictions. The obtained data show that at 800°C run product consists of a subsolidus mineral assemblage representative of the DCDG mineral assemblage. With increasing temperature, a carbonatitic melt forms with 1-5 wt% SiO2 at 900 °C, then evolves to a carbonate-silicate melt with 25 wt% SiO2 at 1100 °C, and to a silicate melt with ~32 wt% SiO2 at 1200 °C. Preliminary results demonstrate that magmas with compositions from carbonatitic to carbonate-silicate (hybrid) melts can form within less than 1 log unit of fO2 by redox melting of elemental carbon-bearing eclogite rocks.
DS201702-0199
2016
Castillo Clerici, A.M., Gomes, C.B., De Min, A., Comin-Chiaramonti, P.Heavy minerals in the sediments from Paraguay rivers as indicators for diamond occurrences. IN Port**Boletin del Museo Nacional de Historia Narural del Paraguay, Vol. 20, 2, pp. 188-204. pdf available in * PortSouth America, ParaguayGeochemistry - indicator minerals

Abstract: Many diamondiferous kimberlites in the Lac de Gras region of the Northwest Territories are concealed by glacial drift, rendering them challenging to detect by traditional exploration techniques that exploit residual surface chemistry. Much research has been aimed at the development of deep penetrating geochemical exploration technologies to increase the rate of discovery whilst reducing risk and exploration cost. However, results from a detailed study of soil geochemistry above the DO-18 kimberlite (Peregrine Diamonds) demonstrate the potential to apply conventional surface geochemical techniques coupled with surface material mapping and landscape evolution models to the evaluation of discrete targets. 50 soil samples from the oxidized upper B-horizon in a detailed grid crossing the concealed kimberlite were collected. Samples, screened to -180 microns, were analysed by multi-element ICP-MS following 4-acid, aqua-regia and deionized water extractions. Fp-XRF was utilised as an equivalent total method to evaluate its applicability. Sequential leach on selected samples was undertaken to understand the deportment of the elements of interest within the soils. Surficial mapping included soil type, topographic variation, landforms, environment and vegetation. This allows an assessment of surface controls on the geochemistry, in particular the generation of false anomalies from chemical traps such as swamps; and allows the generation of a landscape development model. Hydrocarbons, analysed using the SGH and Gore-sorber techniques, were evaluated to characterize the type and abundance of complex hydrocarbons above the kimberlite relative to above the host granitic gneiss. Geochemical data is subject to landform generation processes. The northern half of the grid comprises till with numerous frost boils. The southern half, at lower topography below a distinct break, is dominated by sand-rich material and fine clay. Results from the 4-acid and aqua regia extraction show a dispersion of Nb, Ni, Mg, Ce, Cr and Cs from directly above the northern part of the kimberlite to the edge of the sampling grid, approximately 500 metres to the northwest, following glacial dispersion. SGH-hydrocarbon results exhibit a similar pattern in light-alkyl benzenes. Fp-XRF data repeats the pattern in all elements except Mg, where the concentrations are too low for reliable detection. In the southern half of the grid, at a lower topographic level, geochemical responses are considerably more subtle. It is hypothesised that anomaly formation in the till followed standard glacial dispersion in the down ice trend. Material was entrained to the surface from deeper in the till, locally above the kimberlite, by frost boil action. The southern part of the area is considered to have been inundated with water, the remains of which comprise the current lake over the DO-27 kimberlite approximately 400m to the south. Sediments in this area are clay rich - comprising material deposited by the lake, or re-worked sandy material along the palaeo-lake margin and subsequent erosional channels. These later processes acted to further disperse, conceal and dilute the signal of the underlying body.
DS201708-1611
2017
Castillo Oliver, M.New constraints on the origin of carbonates in kimberlites using petrography, mineral chemistry and in situ stable isotope analysis.11th. International Kimberlite Conference, OralTechnologykimberlite -genesis
DS201708-1612
2017
Castillo Oliver, M.Metasomatism evolution of the SCLM beneath the Lunda Norte province ( NE Angola).11th. International Kimberlite Conference, PosterAfrica, Angolametasomatism
DS201711-2506
2017
Castillo-Oliver, M., Melgarejo, J.C., Gali, S., Pervov, V., Goncalves, A.O., Griffin, W.L., Pearson, N.J., O'Reilly, S.Y.Use and misuse of Mg- and Mn- rich ilmenite in diamond exploration: a petrographic and trace element approach. Congo-Kasai cratonLithos, Vol. 292-293, pp. 348-363.Africa, Angoladeposit - CAT115, Tchiuzo

Abstract: Magnesian ilmenite is a common kimberlite indicator mineral, although its use in diamond exploration is still controversial. Complex crystallisation and replacement processes have been invoked to explain the wide compositional and textural ranges of ilmenite found in kimberlites. This work aims to shed light on these processes, as well as their implications for diamond exploration. Petrographic studies were combined for the first time with both major- and trace-element analyses to characterise the ilmenite populations found in xenoliths and xenocrysts in two Angolan kimberlites (Congo-Kasai craton). A multi-stage model describes the evolution of ilmenite in these pipes involving: i) crystallisation of ferric and Mg-rich ilmenite either as metasomatic phases or as megacrysts, both in crustal and in metasomatised mantle domains; ii) kimberlite entrainment and xenolith disaggregation producing at least two populations of ilmenite nodules differing in composition; iii) interaction of both types with the kimberlitic magma during eruption, leading to widespread replacement by Mg-rich ilmenite along grain boundaries and fractures. This process produced similar major-element compositions in ilmenites regardless of their primary (i.e., pre-kimberlitic) origin, although the original enrichment in HFSE (Zr, Hf, Ta, Nb) observed in Fe3 +-rich xenocrysts is preserved. Finally (iv) formation of secondary Mn-ilmenite by interaction with a fluid of carbonatitic affinity or by infiltration of a late hydrothermal fluid, followed in some cases by subsolidus alteration in an oxidising environment. The complexities of ilmenite genesis may lead to misinterpretation of the diamond potential of a kimberlite during the exploration stage if textural and trace-element information is disregarded. Secondary Mg-enrichment of ilmenite xenocrysts is common and is unrelated to reducing conditions that could favour diamond formation/preservation in the mantle. Similarly, Mn-rich ilmenite should be disregarded as a diamond indicator mineral, unless textural studies can prove its primary origin.
DS201702-0200
2017
Cayer, E., Winterburn, P., Barrett, E.Direct detection of drift concealed kimberlites using surface geochemistry and Lands cape evolution in the Northwest Territories, Canada.Poster ( MDRU) presentation, 1p. Poster pdfCanada, Northwest TerritoriesGeochemistry

Abstract: Apatite-group phosphates are nearly ubiquitous in carbonatites, but our understanding of these minerals is inadequate, particularly in the areas of element partitioning and petrogenetic interpretation of their compositional variation among spatially associated rocks and within individual crystals. In the present work, the mode of occurrence, and major- and trace-element chemistry of apatite (sensu lato) from calcite and dolomite carbonatites, their associated cumulate rocks (including phoscorites) and hydrothermal parageneses were studied using a set of 80 samples from 50 localities worldwide. The majority of this set represents material for which no analytical data are available in the literature. Electron-microprobe and laser-ablation mass-spectrometry data (~ 600 and 400 analyses, respectively), accompanied by back-scattered-electron and cathodoluminescence images and Raman spectra, were used to identify the key compositional characteristics and zoning patterns of carbonatitic apatite. These data are placed in the context of phosphorus geochemistry in carbonatitic systems and carbonatite evolution, and compared to the models proposed by previous workers. The documented variations in apatite morphology and zoning represent a detailed record of a wide range of evolutionary processes, both magmatic and fluid-driven. The majority of igneous apatite from the examined rocks is Cl-poor fluorapatite or F-rich hydroxylapatite (? 0.3 apfu F) with 0.2-2.7 wt.% SrO, 0-4.5 wt.% LREE2O3, 0-0.8 wt.% Na2O, and low levels of other cations accommodated in the Ca site (up to 1000 ppm Mn, 2300 ppm Fe, 200 ppm Ba, 150 ppm Pb, 700 ppm Th and 150 ppm U), none of which show meaningful correlation with the host-rock type. Silicate, (SO4)2 ? and (VO4)3 ? anions, substituting for (PO4)3 ?, tend to occur in greater abundance in crystals from calcite carbonatites (up to 4.2 wt.% SiO2, 1.5 wt.% SO3 and 660 ppm V). Although (CO3)2 ? groups are very likely present in some samples, Raman micro-spectroscopy proved inconclusive for apatites with small P-site deficiencies and other substituent elements in this site. Indicator REE ratios sensitive to redox conditions (?Ce, ?Eu) and hydrothermal overprint (?Y) form a fairly tight cluster of values (0.8-1.3, 0.8-1.1 and 0.6-0.9, respectively) and may be used in combination with trace-element abundances for the development of geochemical exploration tools. Hydrothermal apatite forms in carbonatites as the product of replacement of primary apatite, or is deposited in fractures and interstices as euhedral crystals and aggregates associated with typical late-stage minerals (e.g., quartz and chlorite). Hydrothermal apatite is typically depleted in Sr, REE, Mn and Th, but enriched in F (up to 4.8 wt.%) relative to its igneous precursor, and also differs from the latter in at least some of key REE ratios [e.g., shows (La/Yb)cn ? 25, or a negative Ce anomaly]. The only significant exception is Sr(± REE,Na)-rich replacement zones and overgrowths on igneous apatite from some dolomite(-bearing) carbonatites. Their crystallization conditions and source fluid appear to be very different from the more common Sr-REE-depleted variety. Based on the new evidence presented in this work, trace-element partitioning between apatite and carbonatitic magmas, phosphate solubility in these magmas, and compositional variation of apatite-group minerals from spatially associated carbonatitic rocks are critically re-evaluated.
DS201710-2219
2017
Cerantola, V., Bykova, E., Kupenko, I., Merlini, M., Ismailova, L., McCammon, C., Bykov, M., Chumakov, A.I., Petitgirard, S., Kantor, I., Svityk, V., Jacobs, J., Hanfland, M., Mezouar, M., Prescher, C., Ruffer, R., Prakapenka, V.B., Duvbovinsky, L.How iron carbonates help form diamonds.Nature Communications, July 18 #15960Mantlecarbonate inclusions
DS201710-2220
2017
Cerpa, N.G., Wada, I., Wilson, C.R.Fluid migration in the mantle wedge: influence of mineral grain size and mantle compaction.Journal of Geophysical Research: Solid Earth, Vol. 122, 8, pp. 6247-6288.Mantlemineralogy

Abstract: Mineral grain size in the mantle affects fluid migration by controlling mantle permeability; the smaller the grain size, the less permeable the mantle is. Mantle shear viscosity also affects fluid migration by controlling compaction pressure; high mantle shear viscosity can act as a barrier to fluid flow. Here we investigate for the first time their combined effects on fluid migration in the mantle wedge of subduction zones over ranges of subduction parameters and patterns of fluid influx using a 2-D numerical fluid migration model. Our results show that fluids introduced into the mantle wedge beneath the forearc are first dragged downdip by the mantle flow due to small grain size (<1 mm) and high mantle shear viscosity that develop along the base of the mantle wedge. Increasing grain size with depth allows upward fluid migration out of the high shear viscosity layer at subarc depths. Fluids introduced into the mantle wedge at postarc depths migrate upward due to relatively large grain size in the deep mantle wedge, forming secondary fluid pathways behind the arc. Fluids that reach the shallow part of the mantle wedge spread trench-ward due to the combined effect of high mantle shear viscosity and advection by the inflowing mantle and eventually pond at 55-65 km depths. These results show that grain size and mantle shear viscosity together play an important role in focusing fluids beneath the arc.
DS201707-1312
2017
Cerva-Alves, T., Remus, M.V.D., Dani, N., Basei, M.A.S.Integrated field, mineralogical and geochemical characteristics of Cacapava do sul alvikite and beforsite intrusions: a new Ediacaran carbonatite complex in southernmost Brazil.Ore Geology Reviews, in press availableSouth America, Brazilcarbonatite

Abstract: The integrated evaluation of soil geochemistry, aerogammaspectrometry (eTh), geological and structural mapping associated with the description of boreholes and outcrops in the Caçapava do Sul region, southernmost Brazil, led to the discovery of two carbonatite bodies. They are located near the eastern and southeastern border of Caçapava do Sul Granite and intrude the Passo Feio Complex. The carbonatite system is composed of early pink-colored alvikite followed by late white beforsite dikes. The carbonatites are tabular bodies concordant with the deformed host rocks. Petrographic and scanning electron microscopy show that the alvikites are dominantly composed of calcite with subordinate apatite, magnetite, ilmenite, biotite, baddeleyite, zircon, rutile, pyrochlore-like and rare earth element minerals. Beforsite is composed of dolomite and has the same minor and accessory minerals as the alvikite. U-Pb zircon geochronology via laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was performed on a beforsite sample, yielding a 603.2 ± 4.5 Ma crystallization age. The carbonatite was emplaced an Ediacaran post-collisional environment with transpressive tectonism and volcanic activity marked by shoshonitic affinity.
DS201707-1313
2017
Chakhmouradian, A.R., Cooper, M.A., Reguir, E.P., Moore, M.A.Carbocernaite from Bear Lodge, Wyoming: crystal chemistry, paragenesis, and rare earth fractionation on a microscale.American Mineralogist, Vol. 102, pp. 1340-1352.United States, Wyoming, Colorado Plateaucarbonatite - Bear Lodge

Abstract: Zoned crystals of carbocernaite occur in hydrothermally reworked burbankite-fluorapatite-bearing calcite carbonatite at Bear Lodge, Wyoming. The mineral is paragenetically associated with pyrite, strontianite, barite, ancylite-(Ce), and late-stage calcite, and is interpreted to have precipitated from sulfate-bearing fluids derived from an external source and enriched in Na, Ca, Sr, Ba, and rare-earth elements (REE) through dissolution of the primary calcite and burbankite. The crystals of carbocernaite show a complex juxtaposition of core-rim, sectoral, and oscillatory zoning patterns arising from significant variations in the content of all major cations, which can be expressed by the empirical formula (Ca0.43–0.91Sr0.40–0.69REE0.18–0.59Na0.18–0.53Ba0–0.08)?1.96–2.00(CO3)2. Interelement correlations indicate that the examined crystals can be viewed as a solid solution between two hypothetical end-members, CaSr(CO3)2 and NaREE(CO3)2, with the most Na-REE-rich areas in pyramidal (morphologically speaking) growth sectors representing a probable new mineral species. Although the Bear Lodge carbocernaite is consistently enriched in light REE relative to heavy REE and Y (chondrite-normalized La/Er = 500–4200), the pyramidal sectors exhibit a greater degree of fractionation between these two groups of elements relative to their associated prismatic sectors. A sample approaching the solid-solution midline [(Ca0.57Na0.42)?0.99(Sr0.50REE0.47Ba0.01)?0.98(CO3)2] was studied by single-crystal X-ray diffraction and shown to have a monoclinic symmetry [space group P11m, a = 6.434(4), b = 7.266(5), c = 5.220(3) Å, ? = 89.979(17)°, Z = 2] as opposed to the orthorhombic symmetry (space group Pb21m) proposed in earlier studies. The symmetry reduction is due to partial cation order in sevenfold-coordinated sites occupied predominantly by Ca and Na, and in tenfold-coordinated sites hosting Sr, REE, and Ba. The ordering also causes splitting of carbonate vibrational modes at 690–740 and 1080–1100 cm?1 in Raman spectra. Using Raman micro-spectroscopy, carbocernaite can be readily distinguished from burbankite- and ancylite-group carbonates characterized by similar energy-dispersive spectra.
DS201702-0201
2017
Chakhmouradian, A.R., Rehuir, E.P., Zaitsev, A.N., Coueslan, C., Xu, C., Kynicky, J., Hamid Mumin, A., Yang, P.Apatite in carbonatitic rocks: compositional variation, zoning, element partitioning and petrogeneitic significance.Lithos, in press available, 138p.TechnologyCarbonatite

Abstract: The Late Cretaceous (ca. 100 Ma) diamondiferous Fort à la Corne (FALC) kimberlite field in the Saskatchewan (Sask) craton, Canada, is one of the largest known kimberlite fields on Earth comprising essentially pyroclastic kimberlites. Despite its discovery more than two decades ago, petrological, geochemical and petrogenetic aspects of the kimberlites in this field are largely unknown. We present here the first detailed petrological and geochemical data combined with reconnaissance Nd isotope data on drill-hole samples of five major kimberlite bodies. Petrography of the studied samples reveals that they are loosely packed, clast-supported and variably sorted, and characterised by the presence of juvenile lapilli, crystals of olivine, xenocrystal garnet (peridotitic as well as eclogitic paragenesis) and Mg-ilmenite. Interclast material is made of serpentine, phlogopite, spinel, carbonate, perovskite and rutile. The mineral compositions, whole-rock geochemistry and Nd isotopic composition (Nd: + 0.62 to ? 0.37) are indistinguishable from those known from archetypal hypabyssal kimberlites. Appreciably lower bulk-rock CaO (mostly < 5 wt%) and higher La/Sm ratios (12-15; resembling those of orangeites) are a characteristic feature of these rocks. Their geochemical composition excludes any effects of significant crustal and mantle contamination/assimilation. The fractionation trends displayed suggest a primary kimberlite melt composition indistinguishable from global estimates of primary kimberlite melt, and highlight the dominance of a kimberlite magma component in the pyroclastic variants. The lack of Nb-Ta-Ti anomalies precludes any significant role of subduction-related melts/fluids in the metasomatism of the FALC kimberlite mantle source region. Their incompatible trace elements (e.g., Nb/U) have OIB-type affinities whereas the Nd isotope composition indicates a near-chondritic to slightly depleted Nd isotope composition. The Neoproterozoic (~ 0.6-0.7 Ga) depleted mantle (TDM) Nd model ages coincide with the emplacement age (ca. 673 Ma) of the Amon kimberlite sills (Baffin Island, Rae craton, Canada) and have been related to upwelling protokimberlite melts during the break-up of the Rodinia supercontinent and its separation from Laurentia (North American cratonic shield). REE inversion modelling for the FALC kimberlites as well as for the Jericho (ca. 173 Ma) and Snap Lake (ca. 537 Ma) kimberlites from the neighbouring Slave craton, Canada, indicate all of their source regions to have been extensively depleted (~ 24%) before being subjected to metasomatic enrichment (1.3-2.2%) and subsequent small-degree partial melting. These findings are similar to those previously obtained on Mesozoic kimberlites (Kaapvaal craton, southern Africa) and Mesoproterozoic kimberlites (Dharwar craton, southern India). The striking similarity in the genesis of kimberlites emplaced over broad geological time and across different supercontinents of Laurentia, Gondwanaland and Rodinia, highlights the dominant petrogenetic role of the sub-continental lithosphere. The emplacement of the FALC kimberlites can be explained both by the extensive subduction system in western North America that was established at ca. 150 Ma as well as by far-field effects of the opening of the North Atlantic ocean during the Late Cretaceous.
DS201702-0202
2017
Chalapathi Rao, N.V., Lehmann, B., Belyatsky, B., Warnsloh, J.M.The Late Cretaceous Diamondiferous pyroclastic kimberlites from the Fort a La Corne (FALC) field, Saskatchewan craton, Canada: petrology, geochemistry and genesis.Gondwana Research, In press available 91p.Canada, SaskatchewanDeposit - Fort a La Corne

Abstract: The article gives new experimental data on spectral characteristics of photoluminescence of natural diamonds extracted from deep horizons of Mir and Internatsionalnaya Pipes, Republic of Sakha (Yakutia) depending on composition of basic and additional optically active structural defects in crystals and on temperature during spectrum recording, considering kinetics of luminescence. It is hypothesized on applicability of low-temperature effects to enhance efficiency of photoluminescence separation of diamond crystals.
DS201706-1066
2017
Chamberlain, K.R., Killian, T.M., Evans, D.A.D., Bleeker, W., Cousens, B.L.Wyoming on the run - toward final Paleoproterozoic assembly of Laurentia. Geology Forum Comment, April 1p.United Statescraton

Abstract: Paleoproterozoic suture zones mark the formation of supercontinent Nuna and provide a record of North America's assembly. Conspicuously young ages (ca. 1.715 Ga) associated with deformation in southeast Wyoming craton argue for a more protracted consolidation of Laurentia, long after peak metamorphism in the Trans-Hudson orogen. Using paleomagnetic data from the newly dated 1899 ± 5 Ma Sourdough mafic dike swarm (Wyoming craton), we compare the relative positions of Wyoming, Superior, and Slave cratons before, during, and after peak metamorphism in the Trans-Hudson orogen. With these constraints, we refine a collisional model for Laurentia that incorporates Wyoming craton after Superior and Slave cratons united, redefining the Paleoproterozoic sutures that bind southern Laurentia.
DS201705-0815
2017
Chandra Phani, P.R., Ningam, N., Prasad, K.R.Cr-diopsides from Lattavaram and Kalyanadurgam kimberlites, Anatapur district, Andhra Praseh, southern India: inferences from loam sampling.Department of Geophysics, University College of Science Osmania University, Hyderabad 500 007, March 16, 17, Role of Geophysics in Earth and Environmental studies: special emphasis on mineral exploration 1p. AbstractIndiaDeposit - Lattavaram, Kalyanadurgam
DS201705-0816
2017
Chandra Phani, R., Srinivas, M.Geochemistry of some calcretes in Nalgonda district: implications for target selection in kimberlite/lamproite exploration.National Seminar on Strategic trends and future perspectives in the development of natural resources of Telangana state, Kakatiya University, Abstract Volume, 1, March 30,31 pp. 18-19.India, TelanganaLamproites

Abstract: The authigenic carbonates which occur in arid and semi-arid regions of the world are commonly referred to as calcretes or caliche or kankar. These are pedogenic calcretes which occur in association with soil forming the residual regolith. Many rock types produce calcretes upon weathering and denudation, but calcrete derived from certain rocks acts as an exploration guide. Calcrete is a prominent sampling medium in countries like Australia and South Africa whereas it is not so popular in the Indian context. Kimberlites, being ultrapotassic in nature and owing to the enrichment of olivine, serpentine an calcite, often produce calcrete duricrust as a capping on the outcrops. The calcretes derived from kimberlites contain relict kimberlitic xenocrystic minerals like pyrope, ilmenite, Cr-diopside, pseudomorphs of olivine, phlogopite etc. unlike those derived from other rock types. The calcretes derived from granitoid rocks significantly contain minerals like chert, quartz, semi-weathered feldspar etc. Recently more than fifteen lamproites have been discovered at Vattikodu and Chintalapalli and one lamprophyre at Bayyaram of Telangana state, by the Geological Survey of India, unraveling new panorama that the state has a substantial potential for occurrence of more kimberlite clan rocks. Perhaps for the first time, an attempt has been made here to test the geochemical affinity of calcretes from various locations within Nalgonda district, which is endowed mostly with granitic terrain and Cuddapah sedeimentaries in the southern part. About sixteen samples have been collected from the in-situ regolith, spread in the granite-mafic dyke terrain, with an omission of calcretes occurring in transported black soil areas. The samples were geochemically analysed for major and trace elements for a preliminary study. The data has been compared with published geochemical data of lamproites of Ramadugu Field, to understand their geohchemical association. The calcretes are low in SiO2 (33.92-45.1wt %), high in K2O (1.07-2.21wt %) and CaO (0.78-13.61wt %). When compared to other major elements, MgO displays low concentration and K2O has a higher concentration than Na2O. The trace elements are found to be enriched in some of the samples collected in close vicinity of known lamproite occurrences. The samples show a high degree of chemical weathering, alteration and compositional variation indices. It is observed that enrichment of elements like Cr, Nb, Ni indicates, similar to parent kimberlite/lamproite rock, favourable targets for further ground exploration in virgin areas. In the present study, two samples, towards five kilometers southeast of Vattikodu Lamproite Field, possess higher Nb (>25ppm) concentration, which stand out as explorable targets for further ground investigations. Further field investigations such as geological mapping, pitting, petrography and geochemistry on these two locations are in progress to ascertain whether or not these two targets unveil new kimberlites/lamproites in the area.
DS201701-0005
2016
Chanturia, V.A., Bunin, I.Zh., Dvoichenkova, G.P., Kovalchuk, O.E.Low temperature effects to improve efficiency of photoluminescence separation of diamonds in kimberlite ore processing.Journal of Mining Science, Vol. 52, no. 2, pp. 332-340.Russia, YakutiaDeposit - Mir

Abstract: The article gives new experimental data on spectral characteristics of photoluminescence of natural diamonds extracted from deep horizons of Mir and Internatsionalnaya Pipes, Republic of Sakha (Yakutia) depending on composition of basic and additional optically active structural defects in crystals and on temperature during spectrum recording, considering kinetics of luminescence. It is hypothesized on applicability of low-temperature effects to enhance efficiency of photoluminescence separation of diamond crystals.
DS201702-0203
2016
Chanturia, V.A., Bunin, I.Zh., Dvoichenkova, G.P., Kovalchuk, O.E.Low temperature effects to improve effeciency of photoluminescence separation of diamonds in kimberlite ore processing.Journal of Mining Science, Vol. 52, 2, pp. 332-340.TechnologySpectroscopy

Abstract: The lithosphere beneath the Western Canada Sedimentary Basin has potentially undergone Precambrian subduction and collisional orogenesis, resulting in a complex network of crustal domains. To improve the understanding of its evolutionary history, we combine data from the USArray and three regional networks to invert for P-wave velocities of the upper mantle using finite-frequency tomography. Our model reveals distinct, vertically continuous high (> 1%) velocity perturbations at depths above 200 km beneath the Precambrian Buffalo Head Terrane, Hearne craton and Medicine Hat Block, which sharply contrasts with those beneath the Canadian Rockies (
DS201705-0817
2016
Chanturia, V.A., Dvoichenkova, G.P., Kovalchuk, O.E.Classification of mineral species on the surface of natural diamond crystals.Journal of Mining Science, Vol. 52, 3, pp. 535-540.RussiaDiamond morphology

Abstract: The analytical research has yielded differences in composition of mineral species on the surface of natural diamonds of hyperaltered kimberlites under conditions of diamond ore occurrence and processing. The classification of the mineral species is based on the mineral origin, properties and attachment on the diamond crystal surface.
DS201705-0818
2015
Chanturia, V.A., Dvoichenkova, G.P., Kovalchuk, O.E.Surface properties of diamonds recovered from metasomatically modified kimberlites duing processing.Journal of Mining Science, Vol. 51, 2, pp. 353-362.RussiaDiamond morphology
DS201705-0819
2015
Chanturia, V.A., Dvoichenkova, G.P., Kovalchuk, O.E., Timofeev, S.A.Surface composition and role of hydrophillic diamonds in foam seperation.Journal of Mining Science, Vol. 51, 6, pp. 1235-1241.RussiaDiamond morphology

Abstract: The article presents new test results on structural and chemical properties of mineral formations on the surface of natural hydrophilic diamonds using Raman, X-ray phase and Auger spectroscopy methods. Analysis of morphological features of nano formations involved scanning electron microscope Jeol-5610 and analyzer INCA. Based on the studies into phase composition of diamonds non-recovered in the circuit of kimberlite ore processing, two types of mineral formations are discovered on their surface: microformations as silicate nature globules less than 1 ?m in size and silicate nano films more than 5 nm thick. The tests detect also presence of layered talc silicates that make diamond surface hydrophilic.
DS201705-0820
2017
Chapman, J.Argyle Diamonds.lithographie.org, No. 19, pp. 104-109.AustraliaBook - Argyle
DS201705-0821
2017
Chauque, F.R., Cordani, U.G., Jamal, D.L., Onoe, A.T.The Zimbabwe Craton in Mozambique: a brief review of its geochronological pattern and its relation to the Mozambique Belt.Journal of African Earth Sciences, Vol. 129, pp. 366-379.Africa, MozambiqueCraton, Zimbabwe

Abstract: The eastern margin of the Zimbabwe Craton, along the Mozambique-Zimbabwe border, includes the oldest rocks of west-central Mozambique constituting a large terrain of granite-greenstone type dated between 3000 and 2500 Ma. These rocks consist mainly of gneisses and granitoid rocks of tonalitic-trondhjemitic-granodioritic composition belonging to the Mudzi Metamorphic Complex in the northern part and to the Mavonde Complex in the southern part. The latter is associated with a granite-greenstone terrain, which includes the eastern part of Mutare-Odzi-Manica greenstone belt. A volcano-sedimentary sequences cover, belonging to the apparently Mesoproterozoic and Paleoproterozoic Umkondo and Gairezi groups respectively was deposited along the eastern margin of the craton and is exposed in the territory of Mozambique. The Umkondo minimum age is marked by intrusive dolerite in Zimbabwe dated at 1100 Ma while for the Ghairezi it is still not well established. The Gairezi Group was subjected to progressive metamorphism of Pan-African age. At the margin of the Zimbabwe Craton, in its northern part, metasedimentary units occur representing a passive margin of Neoproterozoic age. They make up the Rushinga Group, which includes felsic metavolcanic rocks dated at ca.800 Ma. Granulites and medium- to high-grade paragneisses, and migmatites of the Chimoio, Macossa and Mungari Groups of Neoproterozoic metamorphic age, overly the ortho-metamorphic pre-existing rock of ca. 1100 Ma, which belongs to the Báruè Magmatic Arc. They characterize the N-S trend Mozambique Belt, which appears to the east of the craton tectonically juxtaposed on the Archean rocks. The maximum age of deposition of these rocks, indicated by U-Pb dating of detrital zircons, is ca. 700 Ma and their minimum age is limited by a few monzonitic Cambrian intrusions dated at ca. 500 Ma. The Neoproterozoic bimodal Guro Suite, dated at ca. 850 Ma and composed of felsic and mafic members characterizes the east-dipping outer rim of the craton margin in the north. The felsic member comprises the Serra Banguatere aplitic granite gneiss-migmatite and the mafic member consists of the Magasso metagabbro and mafic gneiss-migmatite. The geochemical signature and bimodality are all characteristics of anorogenic, A-type granites. The tectono-thermal effects of the Pan-African orogenic event, of approximately 500 Ma, are visible along the margin of the Zimbabwe Craton. Deformation and metamorphism are progressive from the craton towards the belt, from greenschist facies to granulite facies. The main suture in the study area shall be placed along the frontal thrusts of the Mungari and Macossa/Chimoio nappes of Neoproterozoic to Cambrian age. To the west of the suture the rejuvenated margin of the craton occurs, indicated by K-Ar dating. To the east, the Mozambique Belt occurs with its paragneisses of the Neoproterozoic overlaying the Mesoproterozoic granitoids of the Báruè magmatic arc.
DS201709-1971
2017
Chawla, D.S.Half of papers searched for online are free to read. Study PeerJ PreprintsNature, Aug. 10, 5p.Globalresearch papers

Abstract: Almost half of the scholarly papers that people attempt to access online are now freely and legally available, according to a huge study that tracked 100,000 online requests for journal papers in June. The work, published on 2 August in PeerJ Preprints1, examined reader data from a web-browser extension called Unpaywall, which trawls the Internet to find free-to-read versions of paywalled papers. The tool, which launched in April, was developed by two authors of the study, Jason Priem and Heather Piwowar, who co-founded the non-profit company Impactstory in Vancouver, Canada. It has been installed by more than 80,000 people worldwide and is used around 50,000 times a day, says Priem.
DS201712-2678
2017
Chebotarev, D.A., Doroshkevich, A.G., Sharygin, V.V., Yudin, D.S., Ponomarchuk, A.V., Sergeev, S.A.Geochronology of the Chuktukon carbonatite massif, Chadobets uplift ( Krasnoyarsk Territory).Russian Geology and Geophysics, Vol. 58, pp. 1222-1231.Russiacarbonatite

Abstract: We present results of U-Pb (SHRIMP II) and Ar-Ar geochronological study of the rocks of the Chuktukon massif, which is part of the Chadobets alkaline-carbonatite complex, and of the weathering crust developed after them. Perovskite from picrites and monazite from the weathering crust were dated by the U-Pb (SHRIMP II) method, and rippite from carbonatites, by the Ar-Ar method. Rippite has first been used as a geochronometer. The estimated ages (252 ± 12 and 231 ± 2.7 Ma) testify to two magmatism pulses close in time (within the estimation error) to the stages of alkaline magmatism in the Siberian Platform (250-245 and 238-234 Ma). These pulses characterize, most likely, the processes accompanying and completing the activity of the mantle superplume that formed the Siberian Igneous Province at 250-248 Ma. The monazite-estimated age (102.6 ± 2.9 Ma) reflects the time of formation of the ore-bearing weathering crust on the massif rocks.
DS201708-1613
2017
Cheen, Y., Lim, E., Sang, C.Complex zoning of olivine in archetypal kimberlite provides new insights into the evolution of kimberlite magmas.11th. International Kimberlite Conference, PosterTechnologyOlivine
DS201712-2679
2018
Chen, C., Hersh, G., Fischer, K.M., Andronicos, C.L., Pavlis, G.L., Hamburger, M.W., Marshak, S., Larson, T., Yang, X.Lithospheric discontinuities beneath the U.S. Midcontinent - signatures of Proterozoic terrane accretion and failed rifting.Earth and Planetary Science Letters, Vol. 481, pp. 223-235.United States, Illinois, Indiana, Kentuckygeophysics - seismics Reelfoot Rift

Abstract: Seismic discontinuities between the Moho and the inferred lithosphere-asthenosphere boundary (LAB) are known as mid-lithospheric discontinuities (MLDs) and have been ascribed to a variety of phenomena that are critical to understanding lithospheric growth and evolution. In this study, we used S-to-P converted waves recorded by the USArray Transportable Array and the OIINK (Ozarks-Illinois-Indiana-Kentucky) Flexible Array to investigate lithospheric structure beneath the central U.S. This region, a portion of North America's cratonic platform, provides an opportunity to explore how terrane accretion, cratonization, and subsequent rifting may have influenced lithospheric structure. The 3D common conversion point (CCP) volume produced by stacking back-projected Sp receiver functions reveals a general absence of negative converted phases at the depths of the LAB across much of the central U.S. This observation suggests a gradual velocity decrease between the lithosphere and asthenosphere. Within the lithosphere, the CCP stacks display negative arrivals at depths between 65 km and 125 km. We interpret these as MLDs resulting from the top of a layer of crystallized melts (sill-like igneous intrusions) or otherwise chemically modified lithosphere that is enriched in water and/or hydrous minerals. Chemical modification in this manner would cause a weak layer in the lithosphere that marks the MLDs. The depth and amplitude of negative MLD phases vary significantly both within and between the physiographic provinces of the midcontinent. Double, or overlapping, MLDs can be seen along Precambrian terrane boundaries and appear to result from stacked or imbricated lithospheric blocks. A prominent negative Sp phase can be clearly identified at 80 km depth within the Reelfoot Rift. This arrival aligns with the top of a zone of low shear-wave velocities, which suggests that it marks an unusually shallow seismic LAB for the midcontinent. This boundary would correspond to the top of a region of mechanically and chemically rejuvenated mantle that was likely emplaced during late Precambrian/early Cambrian rifting. These observations suggest that the lithospheric structure beneath the Reelfoot Rift may be an example of a global phenomenon in which MLDs act as weak zones that facilitate the removal of cratonic lithosphere that lies beneath.
DS201702-0204
2017
Chen, Y., Gu, Y.J., Hung, S-H.Finite frequency P-wave tomography of the western Canada sedimentary basin: implications for the lithospheric evolution in western Laurentia.Tectonophysics, Vol. 698, pp. 79-90.Canada, Alberta, SaskatchewanCraton, tomography
DS201709-1972
2017
Chepurov, A.A., Kosolobov, S.S., Shcheglov, D.V., Sonin, V.M., Chepurov, A.I., Latyshev, A.V.Nanosculptures on round surfaces of natural diamonds.Geology of Ore Deposits, Vol. 59, 3, pp. 256-264.Russiadeposit - Udachnaya -East

Abstract: The results of a study using scanning electron microscopy and atomic force microscopy comprising the micromorphology of the ditrigonal and trigonal layers on surfaces near the edges of octahedral diamond crystals from the Udachnaya-Eastern kimberlite pipe in Yakutia are presented. The studied surface sculptures are elongated parallel to the direction ?111? and have similar morphological features, characterized by a wavy profile across the lamination, the absence of flat areas at the micro- and nanolevel. It is proposed that both sculpture types were formed as a result of dissolution under natural conditions. This suggestion is corroborated by the revelation of negative trigons on the octahedral facets of the studied diamonds.
DS201707-1314
2016
Chetouani, K., Bodinier, J-L., Garrido, C.J., Marchesi, C., Amri, I., Targuisti, K.Spatial variability of pyroxenite layers in the Beni Bousera orogenic peridotite ( Morocco) and implications for their origin.Comptes Rendus Geoscience, Vol. 348, pp. 619-629.Africa, Moroccoperidotite

Abstract: The Beni Bousera peridotite contains a diversity of pyroxenite layers. Several studies have postulated that at least some of them represent elongated strips of oceanic lithosphere recycled in the convective mantle. Some pyroxenites were, however, ascribed to igneous crystal segregation or melt–rock reactions. To further constrain the origin of these rocks, we collected 171 samples throughout the massif and examined their variability in relation with the tectono-metamorphic domains. A major finding is that all facies showing clear evidence for a crustal origin are concentrated in a narrow corridor of mylonitized peridotites, along the contact with granulitic country rocks. These peculiar facies were most likely incorporated at the mantle–crust boundary during the orogenic events that culminated in the peridotite exhumation. The other pyroxenites derive from a distinct protolith that was ubiquitous in the massif before its exhumation. They were deeply modified by partial melting and melt–rock reactions associated with lithospheric thinning.
DS201708-1614
2017
Chinn, I.Stable isotope dat a and Ftir analyses of diamonds from the Orapa mine: a clear subduction signature.11th. International Kimberlite Conference, OralAfrica, Botswanadeposit - Orapa
DS201707-1315
2017
Chmyz, L., Amaud, N., Biondi, J.C., Azzone, R.G., Bosch, D., Ruberti, E.Ar-Ar ages, Sr-Nd isotope geochemistry and implications for the origin of the silicate rocks of the Jacupiranga ultramafic alkaline complex, Brazil.Journal of South American Earth Sciences, Vol. 77, pp. 286-309.South America, Brazilalkaline - Jacupiringa

Abstract: The Jacupiranga Complex is one of several Meso-Cenozoic alkaline intrusive complexes along the margins of the intracratonic Paraná Basin in southern Brazil. The complex encompasses a wide range of rock-types, including dunites, wehrlites, clinopyroxenites, melteigites-ijolites, feldspar-bearing rocks (diorites, syenites, and monzonites), lamprophyres and apatite-rich carbonatites. While carbonatites have been extensively investigated over the last decades, little attention has been paid to the silicate rocks. This study presents new geochonological and geochemical data on the Jacupiranga Complex, with particular emphasis on the silicate lithotypes. 40Ar/39Ar ages for different lithotypes range from 133.7 ± 0.5 Ma to 131.4 ± 0.5 Ma, while monzonite zircon analyzed by SHRIMP yields a U-Pb concordia age of 134.9 ± 1.3 Ma. These ages indicate a narrow time frame for the Jacupiranga Complex emplacement, contemporaneous with the Paraná Magmatic Province. Most of the Jacupiranga rocks are SiO2-undersaturated, except for a quartz-normative monzonite. Based on geochemical compositions, the Jacupiranga silicate lithotypes may be separated into two magma-evolution trends: (1) a strongly silica-undersaturated series, comprising part of the clinopyroxenites and the ijolitic rocks, probably related to nephelinite melts and (2) a mildly silica-undersaturated series, related to basanite parental magmas and comprising the feldspar-bearing rocks, phonolites, lamprophyres, and part of the clinopyroxenites. Dunites and wehrlites are characterized by olivine compositionally restricted to the Fo83-84 interval and concentrations of CaO (0.13–0.54 wt%) and NiO (0.19–0.33 wt%) consistent with derivation by fractional crystallization, although it is not clear whether these rocks belong to the nephelinite or basanite series. Lamprophyre dikes within the complex are considered as good representatives of the basanite parental magma. Compositions of calculated melts in equilibrium with diopside cores from clinopyroxenites are quite similar to those of the lamprophyres, suggesting that at least a part of the clinopyroxenites is related to the basanite series. Some feldspar-bearing rocks (i.e. meladiorite and monzonite) show petrographic features and geochemical and isotope compositions indicative of crustal assimilation, although this may be relegated to a local process. Relatively high CaO/Al2O3 and La/Zr and low Ti/Eu ratios from the lamprophyres and calculated melts in equilibrium with cumulus clinopyroxene point to a lithospheric mantle metasomatized by CO2-rich fluids, suggesting vein-plus-wall-rock melting mechanisms. The chemical differences among those liquids are thought to reflect both variable contributions of melting resulting from veins and variable clinopyroxene/garnet proportions of the source.
DS201708-1615
2017
Choi, E.Mineralogy, geochemistry, and petrogenesis of Paleoproterozoic alkaline magmas in the Yilgarn Craton, western Australia.11th. International Kimberlite Conference, PosterAustraliaalkaline rocks
DS201709-1973
2017
Choudhary, B.R., Xu, Y.G., Ernst, R.E., Pandit, D.Ti- rich garnet core in spinel in a kimberlite: evidence for metasomatic origin.Goldschmidt Conference, abstract 1p.Indiadeposit, P-5 Wajrakarur

Abstract: EPMA data are obtained from the P-5 kimberlite from the Wajrakarur field in the Eastern Dharwar craton of southern India (EDC). The studied sample consists of xenocrysts and xenoliths set in a variable grain size groundmass of olivine (with two textures: rounded-anhedral and subhedraleuhedral), phlogopite, perovskite, spinel, pyroxene, spinel and spinel containing Ti-garnet core. Ti-rich garnet associated with spinel is a rare occurrence in kimberlites. Two types of spinel have been identified (a) fine grained (<80 ?m) and compositionally non titaniferous, and (b) large macrocrysts (>100 ?m) having replacement cores having distinctly Ti-rich (TiO2 up to 28.51 wt %) compositions. Spinel is an abundant phase varying from <20 to >300 ?m in size, mostly subhedral to euhedral in shape. Pipe-5 has atolland necklace-textured spinels in addition to the euhedral groundmass spinels. Apart from individual grains in ground mass spinel there are also spinel intergrowths with perovskite (no apparent reaction texture observed), and sieve-like intergrowths. The composition of groundmass spinel is extensively used as petrogenetic indicator mineral (Roeder and Schulze 2008). Ti-garnets contain significant Ti (21.25-28.51wt.% TiO2), Ca (15.45-27.69 wt.% CaO), Fe (2.62-24.46 wt.% FeO) and low Cr (0.08-1.52 wt.% Cr2O3) and low Al (1.40-3.87 wt.% Al2O3). Ti- garnets and their paragenetic relationships to spinel are considered here as vital petrogenetic indicators of metasomatic fluids (Dongre et al., 2016; Cheng et al., 2014), and textural association with spinel shows that Ti-garnet formed when early crystallizing spinel interacted with residual melt during magma crystallization.
DS201710-2221
2017
Chowdbury, P., Gerya, T., Chakraborty, S.Emergence of silicic continents as the lower crust peels off on a hot plate tectonic Earth.Nature Geoscience, Vol. 10, 9, pp. 698-703.Mantleplumes

Abstract: The rock record and geochemical evidence indicate that continental recycling has been occurring since the early history of the Earth. The stabilization of felsic continents in place of Earth’s early mafic crust about 3.0 to 2.0 billion years ago, perhaps due to the initiation of plate tectonics, implies widespread destruction of mafic crust during this time interval. However, the physical mechanisms of such intense recycling on a hotter, (late) Archaean and presumably plate-tectonic Earth remain largely unknown. Here we use thermomechanical modelling to show that extensive recycling via lower crustal peeling-off (delamination but not eclogitic dripping) during continent-continent convergence was near ubiquitous during the late Archaean to early Proterozoic. We propose that such destruction of the early mafic crust, together with felsic magmatism, may have caused both the emergence of silicic continents and their subsequent isostatic rise, possibly above the sea level. Such changes in the continental character have been proposed to influence the Great Oxidation Event and, therefore, peeling-off plate tectonics could be the geodynamic trigger for this event. A transition to the slab break-off controlled syn-orogenic recycling occurred as the Earth aged and cooled, leading to reduced recycling and enhanced preservation of the continental crust of present-day composition.
DS201711-2507
2017
Chu, X., Ague, J.J., Podladchikov, Y.Y., Tian, M.Ultrafast eclogite formation via melting induced overpressure.Earth and Planetary Science Letters, Vol. 479, pp. 1-17.Mantleeclogite

Abstract: The conventional wisdom holds that metamorphic reactions take place at pressures near-lithostatic so that the thermodynamic pressure, reflected by the mineral assemblage, is directly correlated with depth. On the other hand, recent field-based observations and geodynamic simulations suggest that heterogeneous stress and significant pressure deviations above lithostatic (overpressure) can occur in Earth's crust. Here we show that eclogite, normally interpreted to form at great depths in subduction zones and Earth's mantle, may form at much shallower depths via local overpressure generated in crustal shear zones. The eclogites studied crop out as lenses hosted by felsic paragneiss in a sheared thrust slice and represent a local pressure and temperature anomaly in the Taconic orogenic belt, southern New England. Sharply-defined chemical zones in garnet, which record ?5 kbar pressure rise and fall accompanied by a temperature increase of 150-200?°C, demonstrate extremely short timescales of diffusion. This requires anomalously fast compression (?500 yrs) and decompression. We use coupled phase equilibria and garnet diffusion forward modeling to fit the observed garnet profiles and test the likely paths using a Monte Carlo-type approach, accounting for off-center sectioning of garnet. The simulation shows that a ?5 kbar pressure increase after the temperature peak is necessary to reproduce the garnet zoning. Remarkably, this post-peak-T compression (from 9 kbar to 14 kbar) lasted only ?500 yrs. If the compression was due to burial along a lithostatic pressure gradient, the descent speed would exceed 30 m?yr?1, defying any observed or modeled subduction rates. Local overpressure in response to partial melting in a confined volume (Vrijmoed et al., 2009) caused by transient shear heating can explain the ultra-fast compression without necessitating burial to great depth.
DS201702-0205
2017
Clements, B.The Canadian diamond business: 25 years and going strong.SEG Newsletter, No. 108, p. 1, 12-18.Canada, United StatesHistory - exploration, deposits
DS201705-0822
2017
Collins, A.T.Comment on the apparent anomalous reflectance of a Sumitomo synthetic diamond.Journal of Gemmology, Vol. 35, 5, p. 450.TechnologySynthetics
DS201703-0398
2017
Coltice, N., Gerault, M., Ulvrova, M.A mantle convection perspective on global tectonics. ReviewEarth Science Reviews, Vol. 165, pp. 120-150.MantleTectonics

Abstract: The concept of interplay between mantle convection and tectonics goes back to about a century ago, with the proposal that convection currents in the Earth’s mantle drive continental drift and deformation (Holmes, 1931). Since this time, plate tectonics theory has established itself as the fundamental framework to study surface deformation, with the remarkable ability to encompass geological and geophysical observations. Mantle convection modeling has progressed to the point that connections with plate tectonics can be made, pushing the idea that tectonics is a surface expression of the global dynamics of one single system: the mantle-lithosphere system. Here, we present our perspective, as modelers, on the dynamics behind global tectonics with a focus on the importance of self-organisation. We first present an overview of the links between mantle convection and tectonics at the present-day, examining observations such as kinematics, stress and deformation. Despite the numerous achievements of geodynamic studies, this section sheds light on the lack of self-organisation of the models used, which precludes investigations on feedbacks and evolution of the mantle-lithosphere system. Therefore, we review the modeling strategies, often focused on rheology, that aim at taking into account self-organisation. The fundamental objective is that plate-like behaviour emerges self-consistently in convection models. We then proceed with the presentation of studies of continental drift, seafloor spreading and plate tectonics in convection models allowing for feedbacks between surface tectonics and mantle dynamics. We discuss the approximation of the rheology of the lithosphere used in these models (pseudo-plastic rheology), for which empirical parameters differ from those obtained in experiments. In this section, we analyse in detail a state-of-the-art 3D spherical convection calculation, which exhibits fundamental tectonic features (continental drift, one-sided subduction, trench and ridge evolution, transform shear zones, small-scale convection, and plume tectonics). This example leads to a discussion where we try to answer the question: can mantle convection models transcend the limitations of plate tectonics theory?
DS201711-2508
2017
Coltice, N., Gerault, M., Ulvrova, M.A mantle convection perspective on global tectonics.Earth Science Reviews, Vol. 165, pp. 120-150.Mantletectonics

Abstract: The concept of interplay between mantle convection and tectonics goes back to about a century ago, with the proposal that convection currents in the Earth's mantle drive continental drift and deformation (Holmes, 1931). Since this time, plate tectonic theory has established itself as the fundamental framework to study surface deformation, with the remarkable ability to encompass geological and geophysical observations. Mantle convection modeling has progressed to the point where connections with plate tectonics can be made, pushing the idea that tectonics is a surface expression of the global dynamics of one single system: the mantle-lithosphere system. Here, we present our perspective, as modelers, on the dynamics behind global tectonics with a focus on the importance of self-organisation. We first present an overview of the links between mantle convection and tectonics at the present-day, examining observations such as kinematics, stress and deformation. Despite the numerous achievements of geodynamic studies, this section sheds light on the lack of self-organisation of the models used, which precludes investigations of the feedbacks and evolution of the mantle-lithosphere system. Therefore, we review the modeling strategies, often focused on rheology, that aim at taking into account self-organisation. The fundamental objective is that plate-like behaviour emerges self-consistently in convection models. We then proceed with the presentation of studies of continental drift, seafloor spreading and plate tectonics in convection models allowing for feedbacks between surface tectonics and mantle dynamics. We discuss the approximation of the rheology of the lithosphere used in these models (pseudo-plastic rheology), for which empirical parameters differ from those obtained in experiments. In this section, we analyse in detail a state-of-the-art 3-D spherical convection calculation, which exhibits fundamental tectonic features (continental drift, one-sided subduction, trench and ridge evolution, transform shear zones, small-scale convection, and plume tectonics). This example leads to a discussion where we try to answer the following question: can mantle convection models transcend the limitations of plate tectonic theory?
DS201701-0006
2016
Condamine, P., Medard, E., Devidal, J-L.Experimental melting of phlogopite peridotite in the garnet stability field.Contributions to Mineralogy and Petrology, Vol. 171, pp. 95-106.MantleMelting

Abstract: Melting experiments have been performed at 3 GPa, between 1150 and 1450 °C, on a phlogopite-peridotite source in the garnet stability field. We succeeded to extract and determine the melt compositions of both phlogopite-bearing lherzolite and harzburgite from low to high degrees of melting (? = 0.008-0.256). Accounting for the presence of small amounts of F in the mantle, we determined that phlogopite coexists with melt >150 °C above the solidus position (1150-1200 °C). Fluorine content of phlogopite continuously increases during partial melting from 0.2 to 0.9 wt% between 1000 and 1150 °C and 0.5 to 0.6 wt% between 1150 and 1300 °C at 1 and 3 GPa, respectively. The phlogopite continuous breakdown in the lherzolite follows the reaction: 0.59 phlogopite + 0.52 clinopyroxene + 0.18 garnet = 0.06 olivine + 0.23 orthopyroxene + 1.00 melt. In the phlogopite-harzburgite, the reaction is: 0.93 phlogopite + 0.46 garnet = 0.25 olivine + 0.14 orthopyroxene + 1.00 melt. Melts from phlogopite-peridotite sources at 3 GPa are silica-undersaturated and are foiditic to trachybasaltic in composition from very low (0.8 wt%) to high (25.6 wt%) degrees of melting. As observed at 1 GPa, the potassium content of primary mantle melts is buffered by the presence of phlogopite, but the buffering values are higher, from 6.0 to 8.0 wt% depending on the source fertility. We finally show that phlogopite garnet-peridotite melts are very close to the composition of the most primitive post-collisional lavas described worldwide.
DS201707-1316
2017
Condie, K., Arndt, N., Davaille, A., Puetz, S.J.Zircon age peaks: production or preservation of continental crust?Geosphere, Vol. 10, 6, pp. 397-398.Mantlegeochronology

Abstract: Zircon age peaks are commonly interpreted either as crustal production peaks or as selective preservation peaks of subduction-produced crust selectively preserved during continent-continent collision. We contribute to this ongoing debate, using the Nd isotopic compositions of felsic igneous rocks and their distribution during the accretionary and collisional phases of orogens. The proportion of juvenile input into the continental crust is estimated with a mixing model using arc-like mantle and reworked continental crust end members. Orogen length and duration proxies for juvenile crustal volume show that the amount of juvenile crust produced and preserved at zircon age peaks during the accretionary phase of orogens is ?3 times that preserved during the collisional phase of orogens. The fact that most juvenile crust is both produced and preserved during the accretionary phase of orogens does not require craton collisions for its preservation, thus favoring the interpretation of zircon age peaks as crustal production peaks. Most juvenile continental crust older than 600 Ma is produced and preserved before final supercontinent assembly and does not require supercontinent assembly for its preservation. Episodic destabilization of a compositionally heterogeneous layer at the base of the mantle may produce mantle plume events leading to enhanced subduction and crustal production. Our Nd isotope model for cumulative continental growth based on juvenile crust proxies for the past 2.5 b.y. suggests a step-like growth curve with rapid growth in accretionary orogens at the times of zircon age peaks.
DS201709-1974
2017
Condie, K., Shearer, C.K.Tracking the evolution of mantle sources with incompatible element ratios in stagnant-lid and plate-tectonic planets.Geochimica et Cosmochimica Acta, Vol. 213, pp. 47-62.Mantletectonics

Abstract: The distribution of high field strength incompatible element ratios Zr/Nb, Nb/Th, Th/Yb and Nb/Yb in terrestrial oceanic basalts prior to 2.7 Ga suggests the absence or near-absence of an enriched mantle reservoir. Instead, most oceanic basalts reflect a variably depleted mantle source similar in composition to primitive mantle. In contrast, basalts from hydrated mantle sources (like those associated with subduction) exist from 4 Ga onwards. The gradual appearance of enriched mantle between 2 and 3 Ga may reflect the onset and propagation of plate tectonics around the globe. Prior to 3 Ga, Earth may have been in a stagnant-lid regime with most basaltic magmas coming from a rather uniform, variably depleted mantle source or from a non-subduction hydrated mantle source. It was not until the extraction of continental crust and accompanying propagation of plate tectonics that “modern type” enriched and depleted mantle reservoirs developed. Consistent with the absence of plate tectonics on the Moon is the near absence of basalts derived from depleted (DM) and enriched (EM) mantle reservoirs as defined by the four incompatible element ratios of this study. An exception are Apollo 17 basalts, which may come from a mixed source with a composition similar to primitive mantle as one end member and a high-Nb component as the other end member. With exception of Th, which requires selective enrichment in at least parts of the martian mantle, most martian meteorites can be derived from sources similar to terrestrial primitive mantle or by mixing of enriched and depleted mantle end members produced during magma ocean crystallization. Earth, Mars and the Moon exhibit three very different planetary evolution paths. The mantle source regions for Mars and the Moon are ancient and have HFS element signatures of magma ocean crystallization well-preserved, and differences in these signatures reflect magma ocean crystallization under two distinct pressure regimes. In contrast, plate tectonics on Earth has destroyed most or all of the magma ocean crystallization geochemical record, or less likely, the terrestrial magma ocean may not have been strongly fractionated during crystallization. The rather uniform incompatible element ratio record in pre-2 Ga oceanic terrestrial basalts requires vigorous mixing of most of the mantle between magma ocean crystallization and about 4 Ga, the onset of the preserved greenstone record.
DS201703-0399
2017
Cook, T.Fingerprinting the source of fore-arc fluids.EOS Transaction of AGU, https://doi.org/10.1029/2017EO067201MantleSubduction
DS201706-1067
2017
Cook, T.An improved model of how magma moves through the crust.EOS Transaction of AGU, 98, available 2p.Mantlemagmatism

Abstract: Volcanic eruptions of basalt are fed by intrusions of magma, called dikes, which advance through Earth’s crust for a few hours or days before reaching the surface. Although many never make it that far, those that do can pose a serious threat to people and infrastructure, so forecasting when and where a dike will erupt is important to assessing volcanic hazards. However, the migration of magma below a volcano is complex, and its simulation is numerically demanding, meaning that efforts to model dike propagation have so far been limited to models that can quantify either a dike’s velocity or its trajectory but not both simultaneously. To overcome this limitation, Pinel et al. have developed a hybrid numerical model that quantifies both by dividing the simulations into two separate steps, one that calculates a two-dimensional trajectory and a second that runs a one-dimensional propagation model along that path. The results indicate that the migration of magma is heavily influenced by surface loading—the addition or removal of weight on Earth’s surface—such as that caused by the construction of a volcano or its partial removal via a massive landslide or caldera eruption. The team confirmed previous research that showed that increasing surface load attracts magma while also reducing its velocity, whereas unloading diverts much of the magma. To test their approach, the team applied their model to a lateral eruption that occurred on Italy’s Mount Etna in July 2001. The eruption was fed by two dikes, including one that in its final stages clearly slowed down and bent toward the west while still 1-2 kilometers below the surface. The results showed that the two-step model was capable of simulating that dike’s velocity and trajectory and thus offers a new means of constraining the local stress field, which partially controls these properties. In the future, report the authors, more complex versions of this model that incorporate information on local topography and magmatic properties could be integrated with real-time geophysical data to improve forecasts of when and where a propagating dike could erupt at the surface.
DS201701-0007
2017
Cooper, C.M., Miller, M.S., Moresi, L.The structural evolution of the deep continental lithosphere.Tectonophysics, Vol. 695, pp. 100-121.GlobalCraton, plate tectonics

Abstract: Continental lithosphere houses the oldest and thickest regions of the Earth's surface. Locked within this deep and ancient rock record lies invaluable information about the dynamics that has shaped and continue to shape the planet. Much of that history has been dominated by the forces of plate tectonics which has repeatedly assembled super continents together and torn them apart - the Wilson Cycle. While the younger regions of continental lithosphere have been subject to deformation driven by plate tectonics, it is less clear whether the ancient, stable cores formed and evolved from similar processes. New insight into continental formation and evolution has come from remarkable views of deeper lithospheric structure using enhanced seismic imaging techniques and the increase in large volumes of broadband data. Some of the most compelling observations are that the continental lithosphere has a broad range in thicknesses (< 100 to > 300 km), has complex internal structure, and that the thickest portion appears to be riddled with seismic discontinuities at depths between ~ 80 and ~ 130 km. These internal structural features have been interpreted as remnants of lithospheric formation during Earth's early history. If they are remnants, then we can attempt to investigate the structure present in the deep lithosphere to piece together information about early Earth dynamics much as is done closer to the surface. This would help delineate between the differing models describing the dynamics of craton formation, particularly whether they formed in the era of modern plate tectonics, a transitional mobile-lid tectonic regime, or are the last fragments of an early, stagnant-lid planet. Our review paper (re)introduces readers to the conceptual definitions of the lithosphere and the complex nature of the upper boundary layer, then moves on to discuss techniques and recent seismological observations of the continental lithosphere. We then review geodynamic models and hypotheses for the formation of the continental lithosphere through time and implications for the formation and preservation of deep structure. These are contrasted with the dynamical picture of modern day continental growth during lateral accretion of juvenile crust with reference to examples from the Australian Tasmanides and the Alaskan accretionary margin.
DS201702-0206
2017
Cooper, C.M., Miller, M.S., Moresi, L.The structural evolution of the deep continental lithosphere.Tectonophysics, Vol. 695, pp. 100-121.MantleCraton, Geophysics - seismics

Abstract: Continental lithosphere houses the oldest and thickest regions of the Earth's surface. Locked within this deep and ancient rock record lies invaluable information about the dynamics that has shaped and continue to shape the planet. Much of that history has been dominated by the forces of plate tectonics which has repeatedly assembled super continents together and torn them apart - the Wilson Cycle. While the younger regions of continental lithosphere have been subject to deformation driven by plate tectonics, it is less clear whether the ancient, stable cores formed and evolved from similar processes. New insight into continental formation and evolution has come from remarkable views of deeper lithospheric structure using enhanced seismic imaging techniques and the increase in large volumes of broadband data. Some of the most compelling observations are that the continental lithosphere has a broad range in thicknesses (< 100 to > 300 km), has complex internal structure, and that the thickest portion appears to be riddled with seismic discontinuities at depths between ~ 80 and ~ 130 km. These internal structural features have been interpreted as remnants of lithospheric formation during Earth's early history. If they are remnants, then we can attempt to investigate the structure present in the deep lithosphere to piece together information about early Earth dynamics much as is done closer to the surface. This would help delineate between the differing models describing the dynamics of craton formation, particularly whether they formed in the era of modern plate tectonics, a transitional mobile-lid tectonic regime, or are the last fragments of an early, stagnant-lid planet. Our review paper (re)introduces readers to the conceptual definitions of the lithosphere and the complex nature of the upper boundary layer, then moves on to discuss techniques and recent seismological observations of the continental lithosphere. We then review geodynamic models and hypotheses for the formation of the continental lithosphere through time and implications for the formation and preservation of deep structure. These are contrasted with the dynamical picture of modern day continental growth during lateral accretion of juvenile crust with reference to examples from the Australian Tasmanides and the Alaskan accretionary margin.
DS201704-0621
2017
Cooper, K.M.What does magma reservoir look like? The "crystal-eye" view.Elements, Vol. 13, 1, pp. 23-28.MantleMagmatism

Abstract: Crystals within volcanic rocks contain records of the changing chemical and thermal conditions within the magma reservoirs in which they resided before eruption. Observations from these crystal records place fundamental constraints on the processes operating within the reservoirs. Data from volcanic crystals are in accord with recent conceptual models of magma reservoirs being composed dominantly of crystal mushes, with small volumes and/or small fractions of melt present. The implication is that magma reservoirs have differing modes of behavior: magmas are stored over the long term in largely crystalline, quiescent, conditions, punctuated by brief episodes of intense activity during the decades to centuries immediately prior to an eruption.
DS201712-2680
2017
Cordani, U.G.O craton do sao francisco e as faixas brasilianas: meio seculo de avancos.Conference paper, 10p. PdfSouth America, Brazilcraton - Sao Francisco
DS201706-1068
2017
Cordier, C., Sauzeat, L., Arndt, N.T., Boullier, A-M., Batanova, V., Barou, F.Quantitative modelling of the apparent decoupling of Mg# and Ni in kimberlitic olivine margins: comment on Cordier et al. by A.Moore.Journal of Petrology, Vol. 58, pp. 1-3.Europe, Greenlanddeposit - Kangamiut

Abstract: Moore proposes in his Comment (Moore, 2017) that marginal zones in olivine grains in kimberlites (Fig. 1a) are produced by crystallization from kimberlite melt. He suggests that the chemical zones observed in these marginal zones (inner transition zones and outer margins, illustrated in his fig. 1) result from abrupt changes in distribution coefficients during crystallization. He proposes that the transition zones, characterized by variable Fo at constant and high Ni contents, are produced by crystallization with high KdFe-Mg (= 0•45) and low DNi (= 4) whereas the margins, characterized by a sharp drop in Ni content at nearly constant Fo (Fig. 1b), are produced by crystallization with higher DNi owing to a sudden change in physical conditions of crystallization (P,…
DS201710-2222
2017
Craddock, W.H., Blondes, M.S., DeVera, C.A., Hunt, A.G.Mantle and crustal gases of the Colorado Plateau: geochemistry, sources, and migration pathways.Geochimica et Cosmochinica Acta, Vol. 213, pp. 346-374.United States, Coloradovolatiles

Abstract: The Colorado Plateau hosts several large accumulations of naturally occurring, non-hydrocarbon gases, including CO2, N2, and the noble gases, making it a good field location to study the fluxes of these gases within the crust and to the atmosphere. In this study, we present a compilation of 1252 published gas-composition measurements. The data reveal at least three natural gas associations in the field area, which are dominated by hydrocarbons, CO2, and N2 + He + Ar, respectively. Most gas accumulations of the region exhibit compositions that are intermediate between the three end members. The first non-hydrocarbon gas association is characterized by very high-purity CO2, in excess of 75 mol% (hereafter, %). Many of these high-purity CO2 fields have recently been well described and interpreted as magmatic in origin. The second non-hydrocarbon gas association is less well described on the Colorado Plateau. It exhibits He concentrations on the order of 1-10%, and centered log ratio biplots show that He occurs proportionally to both N2 and Ar. Overall ratios of N2 to He to Ar are ?100:10:1 and correlation in concentrations of these gases suggests that they have been sourced from the same reservoir and/or by a common process. To complement the analysis of the gas-composition data, stable isotope and noble-gas isotope measurements are compiled or newly reported from 11 representative fields (previously published data from 4 fields and new data from 7 fields). Gas sampled from the Harley Dome gas field in Utah contains nearly pure N2 + He + Ar. The various compositional and stable and noble gas isotopic data for this gas indicate that noble gas molecule/isotope ratios are near crustal radiogenic production values and also suggest a crustal N2 source. Across the field area, most of the high-purity N2 + He + Ar gas accumulations are associated with the mapped surface trace of structures or sutures in the Precambrian basement and are often accumulated in lower parts of the overlying Phanerozoic sedimentary cover. The high-purity gas association mostly occurs in areas interior to the plateau that are characterized by a narrow range of elevated, moderate heat flow values (53-74 mW/m2) in the ancient (1.8-1.6 Ga) basement terranes of the region. Collectively, the geochemical and geological data suggest that (1) the N2 + He + Ar gas association is sourced from a crustal reservoir, (2) the gas association migrates preferentially along structures in the Precambrian basement, and (3) the sourcing process relates to heating of the crust. Prospecting for noble-gas accumulations may target areas with elevated Cenozoic heat flow, ancient crust, and deep crustal structures that focus gas migration. High-purity CO2 gas may also migrate through regional basement structures, however, there is not always a clear spatial association. Rather, CO2 accumulations are more clearly associated with zones of high heat flow (>63 mW/m2) that sit above hot upper mantle and are proximal to Cenozoic volcanic rocks near the plateau margins. These observations are consistent with previous interpretations of a magmatic gas source, which were based on geochemical measurements.
DS201712-2681
2018
Creus, P.K., Basson, I.J., Stoch, B., Mogorosi, O., Gabanakgosi, K., Ramsden, F., Gaegopolwe, P.Structural analysis and implicit 3D modelling of Jwaneng mine: insights into deformation of the Transvaal Supergroup in SE Botswana.Journal of African Earth Sciences, Vol. 137, pp. 9-21.Africa, Botswanadeposit - Jwaneng

Abstract: Country rock at Jwaneng Diamond Mine provides a rare insight into the deformational history of the Transvaal Supergroup in southern Botswana. The ca. 235 Ma kimberlite diatremes intruded into late Archaean to Early Proterozoic, mixed, siliciclastic-carbonate sediments, that were subjected to at least three deformational events. The first deformational event (D1), caused by NW-SE directed compression, is responsible for NE-trending, open folds (F1) with associated diverging, fanning, axial planar cleavage. The second deformational event (D2) is probably progressive, involving a clockwise rotation of the principal stress to NE-SW trends. Early D2, which was N-S directed, involved left-lateral, oblique shearing along cleavage planes that developed around F1 folds, along with the development of antithetic structures. Progressive clockwise rotation of far-field forces saw the development of NW-trending folds (F2) and its associated, weak, axial planar cleavage. D3 is an extensional event in which normal faulting, along pre-existing cleavage planes, created a series of rhomboid-shaped, fault-bounded blocks. Normal faults, which bound these blocks, are the dominant structures at Jwaneng Mine. Combined with block rotation and NW-dipping bedding, a horst-like structure on the northwestern limb of a broad, gentle, NE-trending anticline is indicated. The early compressional and subsequent extensional events are consistent throughout the Jwaneng-Ramotswa-Lobatse-Thabazimbi area, suggesting that a large area records the same fault geometry and, consequently, deformational history. It is proposed that Jwaneng Mine is at or near the northernmost limit of the initial, northwards-directed compressional event.
DS201709-1975
2017
Crosby, J., Mikhail, S., Stuart, F., Abernethy, F.Tracing volatiles in Earth's mantle using He-C-N isotopes in garnet bearing diamondites.Goldschmidt Conference, abstract 1p.Mantlediamondites

Abstract: The origin of diamond-forming carbon in the Earth is unclear [1-3]; sources include subducted organic sediment and primordial mantle carbon. For example, some diamonds contain eclogitic silicate + sufide inclusions and have depleted ?13C (-10 to -30‰), enriched ?15N (+3 to +35‰) values, consistent with subducted crustal material [2-3]. However, some diamonds show mantle-like ?15N (<-5‰) and depleted ?13C values (-10 to -30‰ ) which have been cited as evidence of enstatite chondrite-like primordial C-N sources [1]. The helium isotope composition of mantle rocks are powerful tracers,of Earth’s volatile history because primordial 3He is not recycled back into the mantle. However, there are few He isotope studies of diamond fluids. The 3He/4He of garnetbearing diamondites from the Orapa mine (Botswana) range from 0.1 to 3 Ra [4-5], consistent with a recycled origin. However, our recent work has identified a suite of diamondites with 3He/4He = 0.06 to 8.2 Ra which correlates negatively with ?13C, suggesting that the subduction-related C is associated with mantle 3He/4He ratios. To unravel this complexity we are combining He, C and N isotope analyses in polycrystalline diamond from garnetbearing diamondites from the Orapa mine. These data will also be used to assess the extent to which carbon and nitrogen isotopes are decoupled during diamond-formation [3].
DS201708-1616
2017
Czas, J.Diamond brecciation and annealing accompanying major metasomatism in eclogite xenoliths from the Sask craton, Canada.11th. International Kimberlite Conference, OralCanada, Saskatchewanmetasomatism
DS201709-1976
2017
Czupponi, G., Magna, T., Benk, Z., Rapprich, V., Ott, U.Noble gases in Indian carbonatites.Goldschmidt Conference, abstract 1p.Indiacarbonatites

Abstract: We have studied noble gases in carbonates and apatites from three carbonatites of South India, namely Hogenakal (2400 Ma), Sevattur (770 Ma) and Khambamettuu (523 Ma) by vacuum crushing. Apatite has also been analysed by pyrolysis. Vacuum crushing mostly releases the trapped gas components. The ratios 21Ne/20Ne, 22Ne/20Ne and 40Ar/36Ar increase with progressive crushing due to preservation of different composition gases in smaller inclusions released in later steps. This heterogeneity of isotopic composition of fluid inclusions is a consequence of the involvement of magmas carrying different noble gas signatures. The inclusions with lower ratios suggest the presence of a subducted atmospheric component, while the higher 21Ne/20Ne, 22Ne/20Ne and 40Ar/36Ar can be attributed to the presence of an enriched lithospheric mantle component. In addition, very minor trapped gases from less degassed, deeper mantle may also be present but overprinted by lithospheric and/or nucleogenic components. We propose that these carbonatites were generated only in an advanced stage of magmatism when this lithospheric component overwhelmed any contribution from the deeper mantle source. The lithospheric mantle underwent enrichment during an ancient subduction process through mantle metasomatism manifested in nucleogenic/radiogenic isotopic ratios of 21Ne/20Ne, 22Ne/20Ne and 40Ar/36Ar. The apatites analysed by pyrolysis clearly show nucleogenic 21Ne from 18O(?,n) reaction. We have demonstrated the potential of using U,Th–21Ne systematics as a thermo-chronometer in conjunction with the established U,Th–4He and U–136Xe clocks. While for Hogenakal, the U,Th–21Ne age of 845 ± 127 Ma is in agreement with the age of emplacement of other adjacent younger carbonatites, syenites and alkali granites, for the Sevattur apatite (738 ± 111 Ma) it indicates the crystallisation age.
DS201708-1617
2017
Dai, L-Q.Geochemical evidence for carbonated metasomatite as the mantle source of Cenozoic alkali basalts in western Qinling, Cjina.11th. International Kimberlite Conference, PosterChinametasomatism
DS201707-1317
2017
Dal Zilio, L., Faccenda, M., Capitanio, F.The role of deep subduction in supercontinental breakup.Tectonophysics, in press availableMantlesubduction

Abstract: The breakup of continents and their subsequent drifting plays a crucial role in the Earth's periodic plate aggregation and dispersal cycles. While continental aggregation is considered the result of oceanic closure during subduction, what drives sustained divergence in the following stages remains poorly understood. In this study, thermo-mechanical numerical experiments illustrate the single contribution of subduction and coupled mantle flow to the rifting and drifting of continents. We quantify the drag exerted by subduction-induced mantle flow along the basal surface of continental plates, comparing models of lithospheric slab stagnation above the upper-lower mantle boundary with those where slabs penetrate into the lower mantle. When subduction is upper-mantle confined, divergent basal tractions localise at distances comparable to the effective upper mantle thickness (~ 500 km), causing the opening of a marginal basin. Instead, subduction of lithosphere in the lower mantle reorganises the flow into a much wider cell localising extensional stresses at greater distances from the trench (~ 3000 km). Sub-continental tractions are higher and more sustained over longer time periods in this case, and progressively increase as the slab sinks deeper. Although relatively low, basal-shear stresses when integrated over large plates, generate tension forces that may exceed the strength of the continental lithosphere, eventually leading to breakup and opening of a distal basin. The models illustrate the emergence of a similar mechanism, which results in the formation of back-arc basins above upper-mantle confined subduction, and scales to much larger distances for deeper subduction. Examples include the Atlantic Ocean formation and drifting of the South and North American plates during the Mesozoic-Cenozoic Farallon plate subduction.
DS201708-1568
2017
Dalrymple, W., Anand, A.Koh-i-Noor. Historyexpressbookshop.co.uk, book - cost approx. 17 lbsIndiadiamond notable, Koh-i-noor

Abstract: The first comprehensive and authoritative history of the Koh-i Noor, arguably the most celebrated and mythologised jewel in the world. On 29 March 1849, the ten-year-old Maharajah of the Punjab was ushered into the magnificent Mirrored Hall at the centre of the great Fort in Lahore. There, in a public ceremony, the frightened but dignified child handed over to the British East India Company in a formal Act of Submission to Queen Victoria not only swathes of the richest land in India, but also arguably the single most valuable object in the subcontinent: the celebrated Koh-i Noor diamond.
DS201710-2223
2017
Danelian, T., Jolivet, M., Ionov, D.Insights into the geology and paleontology of Siberia from French-Siberian collaboration in the Earth Sciences.Bulletin de la Societe Geologique de France *eng, Vol. 188, 1-2, 7p.Russia, Siberiadeposit - Udachnaya
DS201708-1618
2017
Daniels, L.The magnitude of termites to the future of kimberlite exploration in Botswana.11th. International Kimberlite Conference, OralAfrica, Botswanatermites
DS201709-1977
2016
Danoczi, J., Creighton, S.Microdiamond analysis - a method for estimating the size frequency distribution of the macrodiamonds.South African Institute of Mining and Metallurgy, Vol. 116, 8, pp. 737-745.Technologymicrodiamond

Abstract: Estimating the size frequency distribution of the macrodiamonds on a new deposit is important for both economic reasons and for the design of the processing plant. Millions of dollars can be lost due to incorrectly sized comminution circuits. This report analyses an alternative methodology for macrodiamond grade estimation using the cumulative results from small parcels of microdiamonds and plotting them on a log-log scale. The method was first evaluated mathematically for diamond populations to assess the confidence for data extrapolation. Macrodiamond size distributions and grades were predicted using microdiamond data from three kimberlites, and the actual macrodiamond grades compared to the the predicted grades. The predicted grades were found to replicate the actual grades closely, showing that a high degree of confidence can be ascribed to the results from this method of analysis. This analysis can be used both for resource estimates and for predicting the diamond size distribution information needed for designing a new operation.
DS201708-1619
2017
Davies, G.The genesis and evolution of subcontinental lithospheric mantle beneath Botswana and N South Africa.11th. International Kimberlite Conference, OralAfrica, Botswana, South Africatectonics
DS201708-1620
2017
Davies, G.Genesis of diamond inclusions: an integrated cathodluminescence ( Cl) and electron backscatter diffraction ( EBSD) study on eclogitic and peridotitic inclusions and their diamond host.11th. International Kimberlite Conference, PosterTechnologyluminescence

Abstract: Diamond inclusions are potentially fundamental to understanding the formation conditions of diamond and the volatile cycles in the deep mantle. In order to fully understand the implications of the compositional information recorded by inclusions it is vital to know whether the inclusions are proto-, syn-, or epigenetic and the extent to which they have equilibrated with diamond forming fluids. In previous studies, the widespread assumption was made that the majority of diamond inclusions are syngenetic, based upon observation of cubo-octahedral morphology imposed on the inclusions. Recent work has reported the crystallographic relationship between inclusions and the host diamond to be highly complex and the lack of crystallographic relationships between inclusions and diamonds has led some to question the significance of imposed cubo-octahedral morphology. This study presents an integrated EBSD and CL study of 9 diamonds containing 20 pyropes, 2 diopsides, 1 forsterite and 1 rutile from the Jwaneng and Letlhakane kimberlite clusters, Botswana. A new method was developed to analyze the crystallographic orientation of the host diamond and the inclusions with EBSD. Diamonds plates were sequentially polished to expose inclusions at different levels in the diamond. CL imaging at different depths was performed in order to produce a 3D view of diamond growth zones around the inclusions. Standard diamond polishing techniques proved too aggressive for silicate inclusions as they were damaged to such a degree that EBSD measurements on the inclusions were impossible. The inclusions were milled with a Ga+ focused ion beam (FIB) at a 12° angle to clean the surface for EBSD measurements. Of the 24 inclusions, 9 have an imposed cubo-octahedral morphology. Of these inclusions, 6 have faces orientated parallel to diamond growth zones and/or appear to have nucleated on a diamond growth surface, implying syngenesis. In contrast, other diamonds record resorption events such that inclusions now cut diamond growth zones. In most cases, the growth zonation around inclusions is not well defined due to CL haloes but some inclusions clearly disrupt diamond growth. Crystallographic orientations of diamond and the inclusions, determined using EBSD, revealed that each inclusion has a homogeneous orientation and record no compositional zonation. The diamonds also showed no angular deviations despite many having multiple growth and resorption zones; implying epitaxial growth of diamond. Crystallographic alignment between diamond and inclusions was not recorded for the principle planes and limited to 3 possible coincidences on minor planes from the 24 inclusions studied. The CL data show no evidence of syngenesis for these 3 inclusions. Analyses of two diamonds with inclusion clusters in different growth zones, 400 µm apart, revealed the same chemical composition and orientation, potentially implying they originated from an original larger inclusion. Combined EBSD and CL data suggest that there is no direct orientational correlation (epitaxial growth) between silicate inclusions and the host diamond, even when the mineral phases are of the same symmetry group. The presentation will provide a detailed evaluation of the genesis of individual inclusions.
DS201712-2682
2017
Davies, R., Davies, A.W.Where have all the garnets gone - Lena West paleo-climate.45th. Annual Yellowknife Geoscience Forum, p. 93 abstract posterCanada, Northwest Territoriesdeposit - Lena West
DS201702-0207
2017
Davy, A.The Murowa kimberlites, Zimbabwe.PDAC 2017, March 6, 1p. AbstractAfrica, ZimbabweDeposit - Murowa
DS201708-1621
2017
Davy, A.The diamond size/frequency and size/quality distribution in the Argyle AK1 lamproite.11th. International Kimberlite Conference, OralAustraliadeposit - Argyle
DS201702-0208
2017
Day, J.M.D., Walker, R.J., Warren, J.M.186Os-187Os and highly siderophile element abundance systematics of the mantle revealed by abyssal peridotites and Os rich alloys.Geochimica et Cosmochimica Acta, Vol. 200, pp. 232-254.MantlePeridotite

Abstract: Abyssal peridotites are oceanic mantle fragments that were recently processed through ridges and represent residues of both modern and ancient melting. To constrain the nature and timing of melt depletion processes, and the composition of the mantle, we report high-precision Os isotope data for abyssal peridotites from three ocean basins, as well as for Os-rich alloys, primarily from Mesozoic ophiolites. These data are complemented by whole-rock highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, Re), trace- and major-element abundances for the abyssal peridotites, which are from the Southwest Indian (SWIR), Central Indian (CIR), Mid-Atlantic (MAR) and Gakkel Ridges. The results reveal a limited role for melt refertilization or secondary alteration processes in modifying abyssal peridotite HSE compositions. The abyssal peridotites examined have experienced variable melt depletion (2% to >16%), which occurred >0.5 Ga ago for some samples. Abyssal peridotites typically exhibit low Pd/Ir and, combined with high-degrees of estimated total melt extraction, imply that they were relatively refractory residues prior to incorporation into their present ridge setting. Recent partial melting processes and mid-ocean ridge basalt (MORB) generation therefore played a limited role in the chemical evolution of their precursor mantle domains. The results confirm that many abyssal peridotites are not simple residues of recent MORB source melting, having a more complex and long-lived depletion history. Peridotites from the Gakkel Ridge, SWIR, CIR and MAR indicate that the depleted MORB mantle has 186Os/188Os of 0.1198356 ± 21 (2SD). The Phanerozoic Os-rich alloys yield an average 186Os/188Os within uncertainty of abyssal peridotites (0.1198361 ± 20). Melt depletion trends defined between Os isotopes and melt extraction indices (e.g., Al2O3) allow an estimate of the primitive mantle (PM) composition, using only abyssal peridotites. This yields 187Os/188Os (0.1292 ± 25), and 186Os/188Os of 0.1198388 ± 29, both of which are within uncertainty of previous primitive mantle estimates. The 186Os/188Os composition of the PM is less radiogenic than for some plume-related lavas, with the latter requiring sources with high long-term time-integrated Pt/Os. Estimates of primitive mantle HSE concentrations using abyssal peridotites define chondritic Pd/Ir, which differs from previous supra-chondritic estimates for Pd/Ir based on peridotites from a range of tectonic settings. By contrast, estimates of PM yield supra-chondritic Ru/Ir. The cause of enhanced Ru in the mantle remains enigmatic, but may reflect variable partitioning behavior of Ru at high pressure and temperature.
DS201708-1622
2017
De Bruin, D.The mineral chemistry of the megacryst suite from the Schuller and Premier kimberlites.11th. International Kimberlite Conference, PosterAfrica, South Africadeposit - Schuller, Premier
DS201708-1623
2017
de Klerk, W.Geochemical and petrographical study of megacrysts and mantle xenoliths from Gemsbok Hollow and Gruendorn kimberlites in the Warmbad kimberlite Province, South Africa11th. International Kimberlite Conference, PosterAfrica, South Africadeposit - Warmbad
DS201702-0209
2017
De Oliveira, I.L., Brod, J.A., Cordeiro, P.F.O., Dantas, E.L., Mancini, L.H.Insights into the Late stage differentiation processes of the Cat alao I Carbonatite complex in Brazil: new Sr-Nd and C-O isotopic dat a in minerals from niobium ores.Lithos, In press available, 44p.South America, BrazilDeposit - Catalao I

Abstract: The Late Cretaceous Catalão I carbonatite complex consists of ultramafic silicate rocks, phoscorites, nelsonites and carbonatites. The latest stages of the evolution of the complex are characterized by several nelsonite (magnetite-apatite rock) and carbonatite dykes, plugs and veins crosscutting earlier alkaline rocks. The interaction between the latter and late-stage carbonatites and/or carbo-hydrothermal fluids, converted the original dunites and bebedourites to metasomatic phlogopitites. Late-stage nelsonites (N1), pseudonelsonites (N2) and various types of dolomite carbonatites (DC) including norsethite-, magnesite- and/or monazite-bearing varieties show significant whole-rock Nd and Sr isotopic variations. To elucidate whether magmatic or metasomatic processes, or both, were responsible for these isotope variations we characterized the Nd and Sr isotope compositions of major mineral phases (i.e. apatite, dolomite, norsethite, pyrochlore and tetraferriphlogopite) in these late-stage rocks. Mineral isotope data recorded the same differences observed between N1 and N2 whole-rocks with N2 minerals showing more enriched isotopic signatures than minerals from N1. Sr isotopic disequilibrium among minerals from N2 pseudonelsonites and spatially related dolomite carbonatite pockets implies formation from batches of carbonate melts with distinct isotopic compositions. A detailed investigation of Nd and Sr isotopes from whole-rocks and minerals suggests that the most evolved rocks of the Catalão I complex probably derive from two different evolution paths. We propose that an earlier magmatic trend (path A) could be explained by several batches of immiscible and/or residual melts derived from carbonated-silicate parental magma (e.g. phlogopite picrite) contaminated with continental crust to a variable extent, in an AFCLI-like process. A second trend (path B) comprises highly variable 143Nd/144Ndi at nearly constant 87Sr/86Sri coupled with high ?18O in carbonates. This is interpreted here as the result of the interaction of previously-formed dolomite carbonatites with carbo-hydrothermal fluids.
DS201711-2509
2017
De Villiers, J.P.R.How to sustain mineral resources: beneficiation and mineral engineering opportunities.Elements, Vol. 13, pp. 307-312.Globalresources, CSR

Abstract: The sustainability of a mineral resource depends, among other aspects, on what the mineral in question will be used for, price fluctuations, future resource requirements, and downstream manufacturing. A balance must be struck between the long-term commitment of developing a mineral deposit against the short-term threats of a changing commercial and social environment. Long-term resource sustainability is dependent both on increased efficiency, which improves profitability, and on revitalizing marginal mines. This is illustrated through breakthroughs in the processing of low-grade copper and refractory gold ores, as well as nickel laterite ores. Retreatment of mine wastes and tailings can also increase the sustainability of mining activity. Ongoing research and development is also helping to sustain mineral resource exploitation.
DS201708-1624
2017
De Wit, M.Prospecting history leading to the discovery of Botswana's diamond mines: from artifacts to Lesedi La Rona.11th. International Kimberlite Conference, OralAfrica, BotswanaHistory
DS201707-1318
2016
De Wit, M.C.J.Early Permian diamond bearing proximal eskers in the Lichtenburg/Ventersdorp area of the north west province, South Africa.South African Journal of Geology, Vol. 119, 4, pp. 585-606.Africa, South Africadeposit - Lichtenburg Ventersdorp

Abstract: Diamond-bearing gravels of the Lichtenburg-Ventersdorp area of the North West Province are associated with north-south orientated sinuous ‘runs’ that occur almost entirely on a flat erosional surface of the Malmani dolomites (Transvaal Supergroup) at some 1,500 m elevation. East to west, this dolomite plain measures 150 km, and north-south it is on average 40 km wide. This unconformity, which first developed before the Pretoria Group sedimentation over a period of at least 80 Myr, is marked by siliceous breccias (palaeo-karst infill) and conglomerates (reworked breccias). It was exhumed in pre-Karoo and post-Gondwana times. Glacial pavements and remnants of thin Lower Karoo sediments are also found on this polyphase surface. The gravels that make up these ‘runs’ and sinkholes directly or indirectly linked to these runs, are coarse-grained, very poorly-sorted, and are best described as diamictites. The ‘runs’ are narrow, elongated, generally positive ridges that meander across the dolomite surface and are up to 30 km long and between 80 to 300 m wide. They have always been regarded as post-Cretaceous drainage features linked to southward-flowing river systems. Diamonds were discovered in these ‘runs’ and they have produced some 12 million carats. However, no Cainozoic fossils or artefacts have ever been found in almost 90 years of mining. From new field evidence, geomorphological studies, age dating from inclusions in diamond and zircon and clay analyses, it is proposed that these coarse-grained runs represent proximal palaeoeskers of the last deglaciation of the Dwyka continental ice sheet, that are preserved on this ancient ‘palimpsest’ surface. The age of the deposit is constrained by two populations of agate within the diamictites that are linked to two separate volcanic units of the Pretoria Group. In addition, the youngest crustal zircon ages from the gravels are 1 Ba, but mantle zircons from Lichtenburg suggest that these have been derived from Cambrian age kimberlites. Analysis of inclusions in diamond support a Neoproterozoic to Cambrian source for the diamonds, so the absence of diamonds from Mesozoic kimberlites and Cainozoic fossils within the gravels support the conclusion that the runs are of Karoo age.
DS201702-0210
2017
Deibe, D., Amor, M., Doallo, R., Miranda, M., Cordero, M.GVLiDAR: an interactive web-based visualization frameowrk to support geospatial measures on lidar data.International Journal of Remote Sensing, Vol. 38, 3, pp. 827-849.TechnologyLIDAR

Abstract: In recent years lidar technology has experienced a noticeable increase in its relevance and usage in a number of scientific fields. Therefore, software capable of handling lidar data becomes a key point in those fields. In this article, we present GPU-based viewer lidar (GVLiDAR), a novel web framework for visualization and geospatial measurement of lidar data point sets. The design of the framework is focused on achieving three key objectives: performance in terms of real-time interaction, functionality, and online availability for the lidar datasets. All lidar files are pre-processed and stored in a lossless data structure, which minimizes transfer requirements and offers an on-demand lidar data web framework.
DS201705-0823
2017
Delaunay, A., Fritsch, E.A zoned type 1aB/IIa diamond of probable 'Superdeep' origin.Journal of Gemmology, Vol. 35, 5, pp. 397-399.TechnologyDiamond morphology
DS201708-1625
2017
Delgaty, J.Ontario's newest kimberlite cluster - the Pagwachuan cluster.11th. International Kimberlite Conference, PosterCanada, Ontariodeposit - Pagawachuan
DS201712-2683
2017
Deng, M., Xu, C., Song, W., Tang, H., Liu, Y., Zang, Q., Zhou, Y., Feng, M., Wei, C.REE mineralization in the Bayan Obo deposit, China: evidence from mineral paragenesis.Ore Geology Reviews, in press available, 10p.Chinadeposit - Bayan Obo

Abstract: Preliminary mineralogical and geochemical studies have been carried out on dolomite marble drill cores from the Bayan Obo REE deposit in China. Three types of apatites and four types of monazites have been identified based on textural features: Type 1 apatite occurs as grains with minor monazite (Type 1 monazite) on its border; Type 2 apatite veinlet shows clusters of assemblages with abundant bastnäsite and parisite at the rim; Type 3 apatite has a linear array associated with fluorite and bastnäsite veinlets. Type 2 monazite occurs as clusters intergrowing with parisite and fluorite. Type 3 and 4 monazites occur as polymineralic (fluorite and bastnäsite) and monomineralic veinlets, respectively. These four types of monazites have similar LREE composition but variable Y content (Y2O3 ranging from below determination limits to 0.7?wt%). The three types of apatites also show different REE content and distribution patterns, ranging from high REE abundance (?REE?+?Y: 27243-251789?ppm) and strong LREE enrichment [(La/Yb)CN ?101] in Type 1, less LREE enrichment [(La/Yb)CN ?8] in Type 2 to relatively low REE abundance (?REE?+?Y: 4323-11175?ppm) but high REE fractionation [(La/Yb)CN ?58] in Type 3. The primary apatite has high Sr (5461-6892?ppm) and REE content, implying a carbonatite origin. The late-stage apatites (Types 2 and 3) show different Sr and REE abundances. Significant differences in their Sr composition (6189?±?573, 6041?±?549 and 3492?±?802 for Types 1-3 samples, respectively) and Y/Ho ratio (20.9?±?0.11, 19.5?±?0.17 and 17.4?±?0.37, respectively) indicate that the three types of apatites may have crystallized from different metasomatic fluids. Multi-stage metasomatism resulted in remobilization and redeposition of primary REE minerals to form the Bayan Obo REE deposit.
DS201709-1978
2017
Deng, X., Qui, Z., Wang, Q., Zhang, Y.Kyanite inclusions in eclogitic macrodiamond from Hunan placer diamond deposit.Goldschmidt Conference, abstract 1p.Chinadeposit, Hunan
DS201704-0622
2017
Deschamps, F.Geodynamics: surviving mantle convection.Nature Geoscience, Vol. 10, 3, p. 161.MantleGeophysics - seismic

Abstract: Hints from seismic tomography and geochemistry indicate that Earth's mantle is heterogeneous at large scale. Numerical simulations of mantle convection show that, if it started enriched in silicates, the lower mantle may remain unmixed today.
DS201710-2224
2017
d'Eyrames, E., Thomassot, E., Kitayama, Y., Golovin, A., Korsakov, A., Ionov, D.A mantle origin for sulfates in the unusual "salty" Udachnaya-East kimberlite from sulfur abundances, speciation and their relationship with groundmass carbonates.Bulletin de la Societe Geologique de France *eng, Vol. 188, 1-2, 8p.Russia, Siberiadeposit - Udachnaya-East

Abstract: The Udachnaya-East pipe in Yakutia in Siberia hosts a unique dry (serpentine-free) body of hypabyssal kimberlite (<0.64wt% H2O), associated with a less dry type of kimberlite and a serpentinized kimberlitic breccia. The dry kimberlite is anomalously rich in salts (Na2O and Cl both up to 6wt%) whereas the slightly less dry and the breccia kimberlite are salt free. Yet the Udachnaya kimberlite is a group-I kimberlite, as is the archetypical kimberlite from Kimberley, South Africa. Samples were studied from the three different types of kimberlite (dry-salty, n=8, non-salty, n=5 and breccia, n=3) regarding their mineralogy, geochemistry, and more specifically their sulfur content. Our results show the salty kimberlite is unprecedentedly rich in sulfur (0.13-0.57wt%) compared to the non-salty kimberlite (0.04-0.12wt%) and the breccia (0.29-0.33wt%). In the salty kimberlite, most of the sulfur is present as sulfates (up to 97% of Stotal) and is disseminated throughout the groundmass in close association with Na-K-bearing carbonates. Sulfates occur within the crystal structure of these Na-K-bearing carbonates as the replacement of (CO3) by (SO3) groups, or as Na- and K-rich sulfates (e.g. aphtitalite, (K,Na)3Na(SO4)2). The associated sulfides are djerfisherite; also Na- and K-rich species. The close association of sulfates and carbonates in these S-rich alkaline rocks suggests that the sulfates crystallized from a mantle-derived magma, a case that has strong implication for the oxygen fugacity of kimberlite magmatism and more generally for the global S budget of the mantle.
DS201708-1626
2017
D'Haenens-Johansson, U.The 812 carat pure type IaB Constellation diamond from Karowe - part of an even larger rough?11th. International Kimberlite Conference, PosterAfrica, Botswanadeposit - Karowe
DS201708-1627
2017
Diering, M.Generation of 3D kimberlite pipe models for resource classification and mine planning dat a sources, procedures and guidelines.11th. International Kimberlite Conference, OralTechnologymodels
DS201701-0008
2016
Ding, S., Dasgupta, R.The fate of sulfide during decompression melting of peridotite - implications for sulfur inventory of the MORB source depleted upper mantle.Earth and Planetary Science Letters, Vol. 459, pp. 183-195.MantlePeridotite

Abstract: Magmatism at mid ocean ridges is one of the main pathways of S outflux from deep Earth to the surface reservoirs and is a critical step in the global sulfur cycle, yet our understanding of the behavior of sulfide during decompression melting of the upper mantle is incomplete. In order to constrain the sulfur budget of the mantle and reconcile the sulfur and chalcophile element budget of mantle partial melts parental to primitive mid-ocean ridge basalts (MORBs), here we developed a model to describe the behavior of sulfide and Cu during decompression melting by combining the pMELTS thermodynamic model and empirical sulfur contents at sulfide concentration (SCSS) models, taking into account the effect of the presence of Ni and Cu in sulfides on SCSS of mantle-derived melts. Calculation of SCSS along melting adiabat at mantle potential temperature of 1380?°C with variable initial S content in the mantle indicates that the complete consumption or partial survival of sulfide in the melting residue depends on initial S content and degree of melting. Primitive MORBs (Mg# > 60) with S and Cu mostly concentrated in 800-1000 ppm and 80-120 ppm are likely mixture of sulfide undersaturated high degree melts and sulfide saturated low degree melts derived from depleted peridotite containing 100-200 ppm S. Model calculations to capture the effects of variable mantle potential temperatures (1280-1420?°C) indicate that for a given abundance of sulfide in the mantle, hotter mantle consumes sulfide more efficiently than colder mantle owing to the effect of temperature in enhancing sulfide solubility in silicate melt, and higher mantle temperature stabilizing partial melt with higher FeO?FeO? and lower SiO2 and Al2O3, all of which generally enhance sulfide solubility. However, sulfide can still be exhausted by ?10-15%?10-15% melting with bulk S of 100-150 ppm in the mantle when TPTP is as low as 1300?°C. We also show that although variation of View the MathML sourceDCuperidotite/melt and initial Cu in the mantle can all affect the Cu concentration of primitive MORBs, 100-200 ppm S in the MORB source mantle can satisfy both S and Cu geochemistry of partial melts parental to ocean floor basalts.
DS201709-1979
2017
Djeddi, A., Parat, F., Ouzegane, K., Bodinier, J.L.Ree enrichment in apatite Britholite exsolutions in carbonatite in Quezal terrane, Hoggar, South Algeria.Goldschmidt Conference, abstract 1p.Africa, Algeriacarbonatite, Ouzzal

Abstract: Ihouhaouene area in In Ouzzal terrane (Hoggar, South Algeria) is exceptional by numerous carbonatite complexes systematically associated to syenites. They constitute one of the oldest carbonatite emplaced at 2 Ga. Various types of carbonatites are distinguished by their successive placement and pegmatitic to brecciated appearance. The first-generation of carbonatites are always brecciated with elements of syenite and carbonate cement with calcite, apatite, alkali feldspar, wollastonite, clinopyroxene +/- sphene, allanite, quartz and garnet. Late carbonatite intrusions appear in small pegmatitic veins rich in apatite (3-50 mm). All carbonatites are calciocarbonatites (38-50 wt% CaO) with silica content ranging from 5 to 21 wt% SiO2. The high silica content is interpreted as assimilation of syenite material during emplacement. Carbonatites have high Rare Earth Element (REE) concentrations with high Ligh REE/Heavy REE fractionation (e.g. 1088 ppm La, La/Yb= 144-198) and variable concentrations in Th (26.5-197 ppm). The REE concentrations are mainly controlled by apatite phenocrysts (30-40 vol.%) with 4-9 wt% REE. In late pegmatitic carbonatite, REE-rich apatites are green-yellow phenocrysts with britholite exsolution (up to 40 vol.%, Ca4(REE)6 (SiO4,PO4)6 (OH,F,Cl)2). Britholites are hexagonal and occur as fine lamellar exsolutions (<10 um) in the same crystallographic axis (001) than apatites or as irregularshaped grains (10-200 um). All britholites contain 8-16 wt% La, 21-43 wt% Ce and 7-12 wt% Nd. The apatite-britholite exsolutions correspond to a substitution of the trivalent rareearth elements (REE3+) and Si4+ for Ca2+ and P5+. The REE substitution is accompanied by a change in volatile composition with F-rich apatite and Cl-rich britholite indicating that Si and Cl-rich hydrothermal fluids are present at the late stage of carbonatite evolution leading to REEenrichment and the crystallization of REE minerals.
DS201705-0824
2017
Dobrzhinetskaya,L.F., Mukhin, P., Wang, Q., Sokhonchuk, T.Moissanite ( SiC) with metal-silicide and silicon inclusions from tuff of Israel: Raman spectroscopy and electron microscopy studies.Lithos, Vol. 282, pp. 1-11.Asia, IsraelMoissanite

Abstract: Here, we present studies of natural SiC that occurs in situ in tuff related to the Miocene alkaline basalt formation deposited in northern part of Israel. Raman spectroscopy, SEM and FIB-assisted TEM studies revealed that SiC is primarily hexagonal polytypes 4H-SiC and 6H-SiC, and that the 4H-SiC polytype is the predominant phase. Both SiC polytypes contain crystalline inclusions of silicon (Sio) and inclusions of metal-silicide with varying compositions (e.g. Si58V25Ti12Cr3Fe2, Si41Fe24Ti20Ni7V5Zr3, and Si43Fe40Ni17). The silicides crystal structure parameters match Si2TiV5 (Pm-3 m space group, cubic), FeSi2Ti (Pbam space group, orthorhombic), and FeSi2 (Cmca space group, orthorhombic) respectively. We hypothesize that SiC was formed in a local ultra-reduced environment at respectively shallow depths (60-100 km), through a “desilification” reaction of SiO2 with highly reducing fluids (H2O-CH4-H2-C2H6) arisen from the mantle “hot spot” and passing through alkaline basalt magma reservoir. SiO2 (melt) interacting with the fluids may originate from the walls of the crustal rocks surrounding this magmatic reservoir. The “desilification” process led to the formation of SiC and the reduction of metal-oxides to native metals, alloys, and silicides. The latter were trapped by SiC during its growth. Hence, interplate “hot spot” alkali basalt volcanism can now be included as a geological environment where SiC, silicon, and silicides can be found.
DS201708-1628
2017
Dongre, A.Ultramafic lamprophyre from the Wajrakarur kimberlite field of southern India and its petrogenetic significance.11th. International Kimberlite Conference, PosterIndiadeposit - Wajrakarur
DS201707-1319
2017
Dongre, A., Chalapathi Rao, N.V., Viljpoen, K.S., Lehmann, B.Petrology, genesis and geodynamic implication of the Mesoproterozoic - Late Cretaceous Timmasamudram kimberlite cluster, Wajrakarur field, eastern Dharwar Craton, southern India.Geoscience Frontiers, Vol. 8, pp. 541-553.Indiadeposit - Timmasamudram

Abstract: New mineralogical and bulk-rock geochemical data for the recently recognised Mesoproterozoic (ca. 1100 Ma) and late Cretaceous (ca. 90 Ma) kimberlites in the Timmasamudram cluster (TKC) of the Wajrakarur kimberlite field (WKF), Eastern Dharwar Craton, southern India, are presented. On the basis of groundmass mineral chemistry (phlogopite, spinel, perovskite and clinopyroxene), bulk-rock chemistry (SiO2, K2O, low TiO2, Ba/Nb and La/Sm), and perovskite Nd isotopic compositions, the TK-1 (macrocrystic variety) and TK-4 (Macrocrystic variety) kimberlites in this cluster are here classified as orangeites (i.e. Group II kimberlites), with geochemical characteristics that are very similar to orangeites previously described from the Bastar Craton in central India, as well as the Kaapvaal Craton in South Africa. The remaining kimberlites (e.g., TK-2, TK-3 and the TK-1 microcrystic variant), are more similar to other 1100 Ma, Group I-type kimberlites of the Eastern Dharwar Craton, as well as the typical Group I kimberlites of the Kaapvaal Craton. Through the application of geochemical modelling, based on published carbonated peridotite/melt trace element partition coefficients, we show that the generation of the TKC kimberlites and the orangeites results from low degrees of partial melting of a metasomatised, carbonated peridotite. Depleted mantle (TDM) Nd perovskite model ages of the 1100 Ma Timmasamudram kimberlites show that the metasomatic enrichment of their source regions are broadly similar to that of the Mesoproterozoic kimberlites of the EDC. The younger, late Cretaceous (ca. 90 Ma) TK-1 (macrocrystic variant) and TK-4 kimberlites, as well as the orangeites from the Bastar Craton, share similar Nd model ages of 1100 Ma, consistent with a similarity in the timing of source enrichment during the amalgamation of Rodinia supercontinent. The presence of late Cretaceous diamondiferous orangeite activity, presumably related to the location of the Marion hotspot in southern India at the time, suggests that thick lithosphere was preserved, at least locally, up to the late Cretaceous, and was not entirely destroyed during the breakup of Gondwana, as inferred by some recent geophysical models.
DS201709-1980
2011
Dorjnamjaa, D., Voinkov, D.M., Kondratov, L.S., Selenge, D., Altanshagai, G., Enkhbatar, B.Concerning diamond and gold bearing astropipes of Mongolia.International Journal of Astronomy and Astrophysics, Vol. 1, pp. 98-104.Asia, Mongoliaastropipes, impact craters

Abstract: In this paper we present summation of eighteen year’s investigation of the all gold and diamond-bearing astropipes of Mongolia. Four astropipe structures are exemplified by the Agit Khangay (10 km in diameter, 470 38' N; 960 05' E), Khuree Mandal (D=11 km; 460 28' N; 980 25' E), Bayan Khuree (D=1 km; 440 06' N; 1090 36' E), and Tsenkher (D=7 km; 980 21' N; 430 36' E) astropipes of Mongolia. Detailed geological and gas-geochemical investigation of the astropipe structures show that diamond genesis is an expression of collision of the lithospheric mantle with the explosion process initiated in an impact collapse meteor crater. The term "astropipes" (Dorjnamjaa et al., 2010, 2011) is a neologism and new scientific discovery in Earth science and these structures are unique in certain aspects. The Mongolian astropipes are genuine "meteorite crater" structures but they also contain kimberlite diamonds and gold. Suevite-like rocks from the astropipes contain such minerals, as olivine, coesite, moissanite (0,6 mm), stishovite, coesite, kamacite,tektite, khamaravaevite (mineral of meteorite titanic carbon), graphite-2H, khondrite, picroilmenite, pyrope, phlogopite, khangaite (tektite glass, 1,0-3,0 mm in size), etc. Most panned samples and hand specimens contain fine diamonds with octahedrol habit (0, 2-2,19 mm, 6,4 mg or 0,034-0,1 carat) and gold (0,1-5 g/t). Of special interest is the large amount of the black magnetic balls (0,05-5,0 mm) are characterized by high content of Ti, Fe, Co, Ni, Cu, Mn, Mg, Cd, Ga, Cl, Al, Si, K. Meanwhile, shatter cones (size approx. 1.0 m) which are known from many meteorite craters on the Earth as being typical of impact craters were first described by us Khuree Mandal and Tsenkher astropipe structures. All the described meteorite craters posses reliable topographic, geological, mineralogical, geochemical, and aerospace mapping data, also some geophysical and petrological features (especially shock metamorphism) have been found, all of which indicate that these structures are a proven new type of gold-diamond-bearing impact structure, termed here "astropipes". The essence of the phenomenon is mantle manifestation and plume of a combined nuclear-magma-palingenesis interaction.
DS201702-0211
2016
Dostal, J.Rare metal deposits associated with alkaline/peralkaline igneous rocks.Reviews in Economic Geology, Vol. 18, pp. 33-54.GlobalAlkalic

Abstract: Highly evolved alkaline/peralkaline igneous rocks host deposits of rare earth elements (REE) including Y as well as Zr, Hf, Nb, Ta , U and Th. The host rocks spanning from silica-undersaturated (nepheline syenites) to silica-oversaturated (granites) occur in intraplate tectonic environments, mainly in continental settings and are typically associated with rifting, faulting and/or crustal extension. They range in age from Neoarchean/Paleoproterozoic to Mesozoic, but several significant deposits are of Mesoproterozoic age. The deposits/prospects can be subdivided into three types. The first is hosted by nepheline syenitic rocks of large, layered alkaline intrusions where the mineralization commonly occurs in layers rich in REE-bearing minerals which mostly show cumulate textures (e.g., Thor Lake/Nechalacho, Canada; Ilimaussaq, Greenland; Lovozero, Russia; Kipawa, Canada; Norra Kärr, Sweden; Pilanesberg, South Africa). The second type includes mineralization in peralkaline granitic rocks where REE-bearing minerals are usually disseminated. The mineralization is typically hosted by pegmatites (including the NYF-type), felsic dikes and minor granitic intrusions (e.g., Strange Lake, Canada; Khaldzan-Buregtey, Mongolia; Ghurayyah, Saudi Arabia; Bokan, Alaska, United States). The third type is disseminated and very fine-grained and hosted by peralkaline felsic volcanic/volcaniclastic rocks, mostly of trachytic composition (e.g., Dubbo Zirconia and Brockman/Hastings, Australia). The bulk of the REE is present in ore/accessory minerals which in some mineralized zones, particularly in cumulate rocks from alkaline complexes, can reach >10 vol.%. Mineralization is composed of a variety of REE-bearing minerals which frequently show complex replacement textures. They include fluorocarbonates, phosphates, silicates and oxides. Economically most important are bastnäsite, monazite, xenotime, loparite, eudialyte, synchysite and parasite. Many other minerals are either sparse or it is difficult with present technology to profitably extract REE from them on a commercial scale. Compared to carbonatite-hosted REE deposits, the REE mineralization in alkaline/peralkaline complexes has lower light REE concentrations but has commonly higher contents of heavy REE and Y and shows a relative depletion of Eu. Elevated concentrations of U and Th of the ore assemblages make gamma-ray (radiometric) surveys an important exploration tool. The host peralkaline (granitic, trachytic and nepheline syenitic) magmas undergo extensive fractional crystallization which is protracted in part due to high contents of halogens and alkalis. The REE mineralization in these rocks is related to late stages of magma evolution, and typically records two mineralization periods. The first produces the primary magmatic ore assemblages which are associated with the crystallization of fractionated peralkaline magma rich in rare metals. This assemblage is commonly overprinted during the second period by the late magmatic to hydrothermal fluids which remobilize and enrich the original ore. The parent magmas are derived from a metasomatically enriched mantle-related lithospheric source by very low degrees of partial melting triggered probably by uplift (adiabatic) or mantle plume activity. The rare metal deposits/mineralization related to peralkaline igneous rocks represent one of the most economically important resources of heavy REE including Y. In addition to REE, some of these deposits contain economically valuable concentrations of other rare metals including Zr, Nb, Ta, Hf, Be, U and Th as well as phosphates.
DS201708-1629
2017
Draper, J.C.M.Ilmenite generations in orangeite from Banankoro, Guinea: implications for exploration.11th. International Kimberlite Conference, PosterAfrica, Guineadeposit - Banankoro
DS201707-1320
2017
Duncan, M.S., Dasgupta, R.Rise of Earth's atmospheric oxygen controlled by efficient subduction of organic carbon.Nature Geoscience, Vol. 10, 6, pp. 387-392.Mantlesubduction - carbon

Abstract: The net flux of carbon between the Earth’s interior and exterior, which is critical for redox evolution and planetary habitability, relies heavily on the extent of carbon subduction. While the fate of carbonates during subduction has been studied, little is known about how organic carbon is transferred from the Earth’s surface to the interior, although organic carbon sequestration is related to sources of oxygen in the surface environment. Here we use high pressure–temperature experiments to determine the capacity of rhyolitic melts to carry carbon under graphite-saturated conditions in a subducting slab, and thus to constrain the subduction efficiency of organic carbon, the remnants of life, through time. We use our experimental data and a thermodynamic model of CO2 dissolution in slab melts to quantify organic carbon mobility as a function of slab parameters. We show that the subduction of graphitized organic carbon, and the graphite and diamond formed by reduction of carbonates with depth, remained efficient even in ancient, hotter subduction zones where oxidized carbon subduction probably remained limited. We suggest that immobilization of organic carbon in subduction zones and deep sequestration in the mantle facilitated the rise (~103–5 fold) and maintenance of atmospheric oxygen since the Palaeoproterozoic and is causally linked to the Great Oxidation Event. Our modelling shows that episodic recycling of organic carbon before the Great Oxidation Event may also explain occasional whiffs of atmospheric oxygen observed in the Archaean.
DS201701-0009
2016
Earth ExplorerMagnetic inversion results for Ngami land availabe for download.http://geoscienceportal.geosoft.com/Botswana/search, Dec. 22, 1p. OverviewAfrica, BotswanaGeophysics - Geosoft

Abstract: A regional-scale geophysical inversion of magnetic field data in the Ngamiland region of northwestern Botswana is now available for download from the Botswana Geoscience Portal, a partnership initiative of the Botswana Geoscience Institute (BGI), industry sponsors and Geosoft. The earth modelling results represent Botswana’s latest push to provide geoscience data free of charge to mineral explorers, researchers and other stakeholders from around the world. They were generated by the Geosoft Professional Services Group using VOXI Earth Modelling, the company’s high performance inversion software. "The VOXI inversion results are outstanding, even more so because the area of interest is vast, comprising more than 35 million cells," said Motsamai Tarzan Kwadiba, Principal Geophysicist for the BGI. "The outcome provides a springboard for a variety of research opportunities such as seismotectonic studies for seismic hazard assessment and earthquake risk mitigation, area selection for earth resources exploration and management, and investigations of the anatomy and evolution of the Okavango rift zone." Since its launch in April 2016, over 1000 multi-disciplinary datasets have been downloaded from the Botswana Geoscience Portal. Stakeholders from more than 35 countries have visited the repository to access the 10 gigabytes of pre-competitive geoscience data. The new inversion results add clear 3D images of the shallow crust beneath the Okavango delta region, one of the world’s largest inland deltas. Often referred to as the ‘jewel’ of the Kalahari and Africa's last Eden, the 22000 square-kilometer Okavango delta itself is an alluvial fan contained within a seismically active graben structure at the south-western extremity of the East African Rift system.
DS201702-0212
2017
Eaton-Magana, S., Ardon, T., Zaitsev, A.M.Inclusion and point defect characteristics of Marange graphite bearing diamonds after high temperature annealing.Diamond and Related Materials, Vol. 71, pp. 20-29,Africa, ZimbabweDeposit - Marange

Abstract: This study gives an analysis of the effect of low-pressure, high-temperature annealing on the infrared, Raman, and photoluminescence (PL) features, as well as the inclusion characteristics, of cubo-octahedral diamond plates from the Marange deposits in Zimbabwe. The samples showed strong inclusion-related zoning which consists of micron-sized particles identified as graphite and these grew noticeably larger with annealing at temperatures of 300 °C to 1700 °C. Within the natural diamonds, the graphite inclusions (detected by Raman spectroscopy) had a grain size of approximately 1 ?m, which increased to 3 ?m after 1200 °C and 14 ?m after 1700 °C annealing and their hexagonal morphology was discernible. From the geometry of these grains, we determined that they were oriented within the {111} family of planes. The infrared absorption and PL spatial maps were collected after every temperature step to study the effects of annealing on the defects, and photomicrographs and Raman spectra were collected to study the graphite inclusions. The graphitic inclusions grew much larger as the stressed diamond surrounding them converted to graphite. Many nitrogen-related optical centers, including NV? and H3 are no longer detected after high temperature annealing within the cuboid regions as these may have been transformed to hydrogen-bearing complexes such as NVH and N2VH. The presence of CH4 is detected in the unannealed Marange diamonds, but was no longer observed in Raman spectra after 1200 °C annealing. This CH4 disappearance along with changes in inclusion morphology could provide a method to detect heat treatment if these mixed-habit samples are sourced to create treated black gem diamond.
DS201708-1569
2017
Eaton-Magana, S., Ardon, T., Zaitsev, A.M.LPHT annealing of brown to yellow type 1a diamonds.Diamond and Related Materials, Vol. 77, pp. 159-170.Technologydiamond morphology

Abstract: Low-pressure, high-temperature (LPHT) annealing of yellow-to-brown type Ia natural diamonds was performed to monitor its effects on optical centers within diamond, changes in the observed color, and to assess the process's viability as a commercial gem treatment. With LPHT annealing only, the mostly brown diamonds showed a shift towards yellow coloration; Vis-NIR absorption spectra showed this change was due to a modest increase in H3 intensity. Even at long annealing times (24 h at 1800 °C) or annealing at high temperatures (2000 °C for five minutes), the diamonds did not significantly lose brown coloration. LPHT annealing showed itself as an ineffective means to break apart the vacancy clusters causing the brown color or causing nitrogen disaggregation, which resulted in only a small H3 generation. With LPHT annealing, “amber centers”—a group of several independent bands in the IR between 4200 and 4000 cm? 1 that disappear with HPHT annealing—were seen to anneal out gradually at various temperatures from 1700 to 2000 °C. In contrast, high-pressure, high-temperature (HPHT) annealing effectively removes brown color at similar time/temperature conditions. Without the high stabilizing pressure provided by HPHT annealing techniques, the LPHT annealing showed pronounced damage on inclusions and dramatic surface etching. In subsequent experiments, LPHT annealing was used as a follow-up to laboratory irradiation. The irradiation-related vacancies created greater concentrations of H3 and the vacancy-assisted disaggregation of nitrogen created donors which led to a high concentration of H2 centers. This combination of defects resulted in a pronounced and favorable shift towards saleable yellow colors due to an increase in H3 and a dramatic increase in the H2 center, which led to the suppression of the remaining brownish component. The annealing characteristics for many centers detected by Vis-NIR absorption spectroscopy, FTIR absorption spectroscopy, and photoluminescence spectroscopy were chronicled throughout the study and compared with other LPHT annealing studies and HPHT annealing experiments.
DS201712-2684
2017
Eaton-Magana, S., Shigley, J.E., Breeding, C.M.Observations on HPHT-grown synthetic diamonds: a review.Gems & Gemology, Vol. 53, 3, pp. 262-285.Technologysynthetics

Abstract: his article presents statistical data and distinctive features for several thousand HPHT-grown synthetic diamonds examined by GIA from 2007 through 2016. This study, the first comprehensive summary published on such a large number and wide variety of samples, describes the reliable means of identifying them, with a focus on material currently marketed for jewelry use. The color of HPHT synthetic diamonds analyzed by GIA has shifted noticeably during this time—in the early years, orange-yellow, yellow, and yellow-orange samples comprised the overwhelming majority, while colorless and blue samples are much more prevalent today. HPHT synthetics are making inroads into the large diamond market, with cut stones larger than 10 carats, as well as the colorless melee market, where small HPHT synthetics are being mass-produced in China. HPHT synthetics can be identified by their distinctive fluorescence patterns using the DiamondView luminescence imaging instrument, the lack of “strain” (anomalous birefringence) when viewed through crossed polarizers, and to a lesser extent by the detection of various features in photoluminescence (PL) spectroscopy. This material may also display magnetism and a short-wave fluorescence and phosphorescence reaction that are inconsistent with similarly colored natural diamonds.
DS201703-0400
2017
Edmonds, M., Manning, C.Synthesizing our understanding of Earth's deep carbon. Udachnaya pipe used as an example.EOS Transaction of AGU, https://doi.org/10.1029/2017EO67913RussiaCarbon
DS201704-0623
2017
Edmonds, M., Wallace, P.J.Volatiles and exsolved vapor in volcanic systems.Elements, Vol. 13, 1, pp. 29-34.MantleMagmatism

Abstract: The role of volatiles in magma dynamics and eruption style is fundamental. Magmatic volatiles partition between melt, crystal, and vapor phases and, in so doing, change magma properties. This has consequences for magma buoyancy and phase equilibria. An exsolved vapor phase, which may be distributed unevenly through reservoirs, contains sulfur and metals that are either transported into the atmosphere or into ore deposits. This article reviews the controls on volatile solubility and the methods to reconstruct the volatile budget of magmas, focusing particularly on the exsolved vapor phase to explore the role of volatiles on magma dynamics and on eruption style.
DS201704-0624
1969
Egorov, L.S.Melilitic rocks of the Meimecha Kotui Province, Northern Siberia. ***IN RUSNedra Publishing House, Leningrad., 249p. *** in RUSRussiaMelilites
DS201709-1981
2017
Egorova, E., Afanasev, V.Mineralogical features for determining age of kimberlites from Siberian craton by kimberlitic indicator minerals from placers. Mayat, Muna, Tychan, KenkemeGoldschmidt Conference, abstract 1p.Russia, Siberiageochemistry

Abstract: The history of kimberlite magmatism in the Siberian craton comprised the Middle Paleozoic (Late Devonian), Triassic, and Jurassic-Cretaceouse events. The Middle Paleozoic event produced greatest amounts of diamond-bearing kimberlites; diamond contents in the Triassic rocks are much lower, while the Jurassic-Cretaceous kimberlites are actually barren [1]. Minerals derived from kimberlites of different ages often coexist in placers and dispersion trains, which poses problems to the use of mineralogical methods for diamond exploration. The problem can be solved by knowing the morphological features of kimberlite indicator minerals typical of each magmatic event [2]. Garnets from Middle Paleozoic kimberlites have the following features: a) chemistry corresponding to diverse parageneses, including those of diamond assemblage; b) weak to strong wear; predominant medium and high wear degrees; c)signatures of dissolution in Late Devonian laterite weathering profiles. Garnets from Triassic kimberlites differ in a) lower paragenetic diversity; few or absent garnets of diamond assemblage; b) only low wear degree; strong wear restricted to garnets from Triassic kimberlites hosted by coastal sediments; c) no dissolution signatures. Jurassic-Cretaceous ages of kimberlites can be inferred from a) changes in paragenetic diversity as a result of deep metasomatism and predominance of shallow lherzolite varieties; no diamond assemblage garnets; b) weak wear; c) no dissolution signatures. The approach was used to estimate the ages of kimberlites in some kimberlite provinces. As a result, we inferred the existence of Middle Paleozoic kimberlites in the Kyutyungde graben, in the catchments of the Mayat, Billakh (Anabar area), and Muna rivers, in the MarkhaMorkoka interfluve, and in the Tychan diamond province (Krasnoyarsk region); Triassic kimberlites in the northern slope of the Olenek uplift and within the Bulkur uplift; and Late Jurassic-Early Cretaceous kimberlites in the Kenkeme catchment north of Yakutsk city.
DS201708-1630
2017
Elazar, O.Melting of hydrous carbonated eclogite at 4-6 Gpa and 900-1200 C: implications for the generation of diamond forming fluids.11th. International Kimberlite Conference, OralMantlediamond genesis
DS201709-1982
2017
Elburg, M.A., Andersen, T., Mahlaku, S.M., Cawthorn, R.G., Kramers, J.A potassic magma series in the Pilanesberg alkaline complex.Goldschmidt Conference, abstract 1p.Africa, South Africaalkaline rocks

Abstract: The Pilanesberg Alkaline Complex (South Africa) consists of a partially eroded phonolitic-trachytic package of lavas and tuffs, intruded by consanguinous syenites and nepheline syenites (foyaites). The latter have been divided in several units, based on their colour and mineralogy. Most of the foyaitic units are sodic in composition, but whole rock analyses show that some samples are more potassic, with Na2O/K2O<0.8. This observation, together with old reports of leucite-bearing lavas [1], could suggest the existence of a second, potassic magmatic lineage. To investigate whether the observed potassium-enrichment is a primary feature, or the result of deuteric alteration, the mineralogical distinction between sodic and potassic samples was investigated. The mineralogy of the sodic samples is dominated by nepheline, alkali-feldspar and aegirine, ± titanite, amphibole, biotite, and late agpaitic phases [2]. Within the potassic samples, the main primary ferromagnesian mineral is biotite, which shows conspicuous zoning in thin section; nepheline has been extensively replaced by sodalite and cancrinite, but alkali-feldspar appears relatively unaltered. No agpaitic minerals were observed. U-Pb isotope systematics of titanite are similar for sodic and potassic samples in terms of the age (ca. 1.4 Ga) and composion of common Pb; Ar-Ar dating of biotite also gives ca. 1.4 Ga, showing that biotite is a primary magmatic phase. Compositions of the biotite in sodic and potassic samples are similar, with the sodic samples having slightly higher Fe# (independent of whole rock Fe#), higher Na, but lower (Na+K) and Ba. Zoning in biotite from potassic samples is related to a decrease in Mg, Ti and F in the rim of the crystals. Despite the primary character of the biotite, the question whether the potassic samples reflect a combination of alteration and perhaps minor crustal contamination, or a separate mag
DS201707-1321
2017
Elburg, M.A., Cawthorn, R.G.Source and evolution of the alkaline Pilanesberg complex, South Africa.Chemical Geology, Vol. 455, pp. 148-165.Africa, South Africaalkaline rocks

Abstract: The Pilanesberg Complex (South Africa) is one of the world's largest but least studied alkaline complexes. It consists of trachytes, phonolites, syenites and nepheline syenites (foyaites) and the preservation of the volcanic carapace makes it unique among the larger alkaline complexes. The intrusive history of the Pilanesberg Complex shows similarities to the Greenland Kangerlussuaq Intrusion, and our new whole-rock major and trace element analyses, combined with existing data, show that the complex belongs to the Sr-rich type of evolved alkaline rocks, more similar to the complexes of the Kola Peninsula than Ilímaussaq. Despite the absence of mafic lithologies, comparison with experimental studies shows that the parental magma was most likely an alkali basalt. Significant iron enrichment is caused by an early stage of fractionation involving clinopyroxene and amphibole rather than olivine and plagioclase, reflecting water-rich compositions and intermediate levels of oxygen fugacity. This fractionation trend has led to strong enrichment in Sr and Ba, but only moderate levels of Y and middle to heavy rare earth elements, and minimal Eu-anomaly. Late-stage water-rich fluids caused significant autometasomatism in most units. New U-Pb dating of titanite constrains the age of the Pilanesberg Complex as 1395 + 10/? 11 Ma. Initial 87Sr/86Sr isotope ratios around 0.7028 (?Sr1395 = ? 1) are typical for a moderately depleted mantle source, unlike the local lithospheric mantle. The combination of an enriched trace-element signature and depleted isotopic characteristics is evidence for small degrees of partial melting. Epsilon Sr values are similar to those reported for other alkaline complexes worldwide, emplaced in crust with contrasting geological histories; this likely reflects lithospheric metasomatism shortly before magmatism and minimal crustal contamination.
DS201702-0213
2017
Eppelbaum, L., Kutasov, I., Pilchin, A.Markers of thermal conditions within lithosphere. Lecture Notes in Earth Science Systems, Pt. 6.4, 51p. pdfMantleGeothermometry
DS201702-0214
2017
Eppelbaum, L.V.Quantitative analysis of piezoelectric and seismoelectric anomalies in subsurface geophysics.European Geoscience Union Conference, April, Vienna, Vol. 19, EGU2017-2344. 1p. AbstractMantleGeophysics - seismics

Abstract: The piezoelectric and seismo-electrokinetic phenomena are manifested by electrical and electromagnetic processes that occur in rocks under the influence of elastic oscillations triggered by shots or mechanical impacts.
DS201703-0401
2016
Eppelbaum, L.V., Vaksman, V.L.Makhtesh Ramon Complex deposit ( southern Israel) - a window to the upper mantle.International Journal of Mining Science, Vol. 3, 1, pp. 1-28.Europe, IsraelKimberlite, Lamproite

Abstract: An integrated analysis of several regional geological and geophysical factors allowed to select the Makhtesh Ramon area (northern Negev, Israel) for sesarching diamondiferous associations. The most important regional factor is the Middle Cretaceous maximum in the development of upper mantle hot spots brightly appearing in this area. Analysis of magnetic (paleomagnetic), self-potential and ionselective data inambogously indicate presence of some bodies possibly having kimberlite (lamproite) origin occurring at small depths (8 - 50 m) in the western Makhtesh Ramon. Repeated erosion processes in the area caused removing most part of sedimentary associations that significantly simplified the processes of mineral sampling and rock withdrawn for geochemical and petrological analyses. Comprehensive mineralogical analyses enabled to detect the following minerals-satellites of diamond associations: chrome-diopside, orange garnet, bright-crimson pyrope, picroilmenite, moissanite, corundum, black spinel, olivine, anatase and tourmaline (including black samples). These minerals do not rolled and oxidized that is an additional evidence of the neighboring occurrence of the indigenous rocks. Data of electronic microscopy show that the grains of (1) picroilmenite and (2) pyrope contain, respectively: (1) cobalt, chrome, magnesium and nickel and (2) chrome, magnesium and aluminum. This indicates that both picroilmenite and pyrope have the hyper-abyssal origin that also is an indicator of the possible occurring of diamondiferous pipes. List of secondary-importance satellite minerals includes feldspars, pyroxenes, magnetite, hematite, ilmenite, galenite, pyrite, limonite, mica, chromite, leucoxene, zircon, rutile, etc. These minerals (by their considering with the first group) are also indicators of diamond-bearing of the studied area. Identification of small plates of gold and silver as well as considerable traces of La, Ce, Th, Nb and Ta (Rare Earth Elements) also may be associated with the nearest kimberlite rock occurrence. The total number of recognized microdiamonds consists of more than 300 units; five diamonds (> 1 mm) were identified (sizes of the most largest crystals are 1.2 and 1.35 mm). Thus, on the basis of a set of geological-geophysical factors and identification of the mentioned minerals we can definitely estimate that the Makhtesh Ramon area is perspective for discovering diamondiferous rocks (kimberlite or lamproite pipes) as well as diamond crystals in loose deposits. Discovered silver- and gold-bearing and REE signatures may have independent importance.
DS201710-2225
2017
Ernst, W.G.Earth's thermal evolution, mantle convection, and Hadean onset of plate tectonics.Journal of Asian Earth Sciences, Vol. 145, pt. B, pp. 334-348.Mantleconvection, tectonics

Abstract: During Solar System condensation, the early Earth formed through planetesimal accretion, including collision of a Mars-sized asteroid. These processes rapidly increased the overall thermal budget and partial fusion of the planet. Aided by heat supplied by radioactivity and infall of the Fe-Ni core, devolatilization and chemical-density stratification attended planetary growth. After the thermal maximum at ?4.4 Ga, terrestrial temperatures gradually declined as an early Hadean magma ocean solidified. By ?4.3-4.2 Ga, H2O oceans + a dense CO2-rich atmosphere blanketed the terrestrial surface. Near-surface temperatures had fallen well below the low-P solidi of dry peridotite, basalt, and granite, ?1300, ?1120, and ?950 °C, respectively. At less than half their melting T, rocky materials existed as thin lithospheric platelets in the surficial Hadean Earth. Upper mantle stagnant-lid convection may have operated locally, but was rapidly overwhelmed by heat build-up-induced asthenospheric circulation, rifting and subduction, because massive heat transfer required vigorous mantle overturn in the early, hot planet. Bottom-up mantle overturn, involving abundant plume ascent, brought deep-seated heat to the surface. It decreased over time as cooling, plate enlargement, and top-down plate descent increased. Thickening, lateral extension, and contraction typified the post-Hadean lithosphere. Geologic evolutionary stages included: (a) ?4.5-4.4 Ga, the magma ocean solidified, generating ephemeral, ductile platelets; (b) ?4.4-2.7 Ga, small oceanic and continental plates were produced, then were destroyed by mantle return flow before ?4.0 Ga; eventually, continental material began to accumulate as largely subsea, sialic crust-capped lithospheric collages; (c) ?2.7-1.0 Ga, progressive suturing of old shields and younger orogenic belts led to cratonal plates typified by emerging continental freeboard, intense sedimentary differentiation, and episodic glaciation during transpolar plate drift; temporally limited stagnant-lid mantle convection occurred beneath growing supercontinents; (d) ?1.0 Ga-present, laminar-flowing mantle cells are capped by giant, stately moving plates. Near-restriction of komatiitic lavas to the Archean, and formation of multicycle sediments, ophiolite complexes ± alkaline igneous rocks, and high-pressure/ultrahigh-pressure (HP/UHP) metamorphic belts in youngest Proterozoic and Phanerozoic orogens reflect increasing density of cool oceanic plates, but decreasing subductability of enlarging, more buoyant continental plates. Attending assembly of supercontinents, negative buoyancy of thickening oceanic lithosphere began to control the overturn of suboceanic mantle as cold, top-down convection. The scales and dynamics of hot asthenospheric upwelling versus plate foundering and mantle return flow (bottom-up plume ascent versus top-down plate subduction) evolved gradually, due to planetary cooling. After accretion of the Earth, heat transfer through mantle convection has resulted in the existence of surficial rocky plates or platelets, and vigorous, lithosphere-coupled mantle overturn since ?4.4 Ga. Thus plate-tectonic processes have typified the Earth’s thermal history since Hadean time.
DS201708-1631
2017
Fagan, A.Geochemistry and geothermobarometry of lherzolite and pyroxenite xenoliths from the CH-33, CH-52 & CH-58 Diamondiferous kimberlite pipes at Chidliak ( Baffin Island, Canada).11th. International Kimberlite Conference, PosterCanada, Nunavut, Baffin Islanddeposit - CH-33, CH-52, CH-58
DS201709-1983
2014
Falls, S.Clarity, cut and culture: the many meanings of diamond.University Press, 216p.Technologybook review

Abstract: Images of diamonds appear everywhere in American culture. And everyone who has a diamond has a story to tell about it. Our stories about diamonds not only reveal what we do with these tiny stones, but also suggest how we create value, meaning, and identity through our interactions with material culture in general. Things become meaningful through our interactions with them, but how do people go about making meaning? What can we learn from an ethnography about the production of identity, creation of kinship, and use of diamonds in understanding selves and social relationships? By what means do people positioned within a globalized political-economy and a compelling universe of advertising interact locally with these tiny polished rocks? This book draws on 12 months of fieldwork with diamond consumers in New York City as well as an analysis of the iconic De Beers campaign that promised romance, status, and glamour to anyone who bought a diamond to show that this thematic pool is just one resource among many that diamond owners draw upon to engage with their own stones. The volume highlights the important roles that memory, context, and circumstance also play in shaping how people interpret and then use objects in making personal worlds. It shows that besides operating as subjects in an ad-burdened universe, consumers are highly creative, idiosyncratic, and theatrical agents.
DS201708-1632
2017
Farr, H.Melt evolution of the Finsch orangeite, South Africa.11th. International Kimberlite Conference, OralAfrica, South Africadeposit - Finsch
DS201708-1633
2017
Farr, H.Petrography and geochronology of the Nxau kimberlites, north-west Botswana.11th. International Kimberlite Conference, PosterAfrica, Botswanadeposit - Nxau
DS201711-2510
2017
Farrapo Albuquerque, D., SandFranca Lucas, G., MarceloAssumpcao, P.M., Lucas, M.B., CondoriQuispe, C., Oliveira, M.E.Crustal structure of the Amazonian craton and adjacent provinces in Brazil.Journal of South American Earth Sciences, Vol. 79, pp. 431-442.South America, Brazilcraton

Abstract: The study of the crust using receiver functions can provide valuable geological information, such as average crustal composition, its formation dynamics and the tectonic evolution of a region, as well as serve as an initial reference for the generation of seismic wave velocity models to improve earthquake location. To fill in gaps in information on the crust of the Amazonian Craton and adjacent provinces in Brazil, we used receiver functions and H-k stacking to estimate crustal thicknesses and the VP/VS ratios. The results indicate that the crust of the study region is predominantly felsic, with an average VP/VS around 1.73 and an average thickness of 38.2 km, with a range of 27.4-48.6 km. Minimum curvature interpolation of the crustal thickness values has made it possible to delimitate of the Amazonian Craton, which corresponds to the area with an average thickness equal to or greater than 39 km. In addition, it was possible to identify its potential cratonic blocks, as well as the Paranapanema Block of Paraná Basin. The geometry of the craton, defined by its crustal thickness, is corroborated by the distribution of natural seismicity that accompanies its edges. These are related to suture zones between the Amazonian, São Francisco/Congo and Paranapanema paleocontinents. The sedimentary basins that have undergone rifting processes have a thinner crust, usually less than 37 km thick. Due to the great variability of the results, it was not possible to determine a characteristic value of c
DS201708-1634
2017
Fedortchouk, Y.Three styles of diamond resorption in a single kimberlite: does crustal xenolith play a role?11th. International Kimberlite Conference, OralTechnologyDiamond resorption

Abstract: Kimberlite magmas, the primary source of diamonds, have many features indicative of explosive eruptions and high volatile contents. The main approaches used to establish exsolution of fluid during magma ascent include theoretical modeling and experimental estimates of volatile solubility in kimberlite-like melts. Both approaches are hampered by the poorly constrained composition of kimberlite melts. Resorption features on diamonds are very sensitive to the presence and composition of the kimberlite fluid as well as to temperature and pressure. Here, we use direct evidence from diamond resorption features as a new method for investigating the parameters of fluid exsolution. The method is based on experimental reproduction of diamond resorption in kimberlite melts with and without an exsolved fluid phase. We studied 802 diamonds from two kimberlites (BK1 and AK15) from the Orapa cluster, Botswana. Samples from the BK1 pipe include three lithologies: two coherent kimberlites (CK-A and CK-B) and a pyroclastic kimberlite (massive volcaniclastic kimberlite, MVK). The known depth of diamond samples in each kimberlite lithology allows us to demonstrate an increase in the intensity of kimberlite-induced resorption with depth of diamond recovery in the drill holes. Each kimberlite lithology has a different proportion of diamonds with kimberlite-induced resorption, which is unique in style in each lithology: glossy surfaces in MVK due to reaction with C-O-H fluid, rough corroded surfaces in CK-B due to reaction with volatile-undersaturated melt, and a combination of glossy surfaces with corroded features in CK-A due to an overprint of melt resorption after fluid resorption. Both diamond resorption and kimberlite textures in the BK1 kimberlite show evidence of fluid exsolution only in CK-A and MVK lithologies, but no fluid presence in CK-B. The observed diamond resorption features may be controlled by (1) a temporary separation of the rising magma column into a bubblerich head and bubble-poor volatile-depleted tail and (2) fluid exsolution at depths greater than decompressional degassing. We discuss how the depth of fluid exsolution from kimberlite melt may affect the diamond grade and the resorption of diamond populations in a kimberlite.
DS201708-1635
2017
Fedortchouk, Y.Diamond surface features and metasomatic processes in subcratonic mantle.11th. International Kimberlite Conference, PosterMantlemetasomatism
DS201710-2226
2017
Fedortchouk, Y., Chinn, I.L., Kopylova, M.G.Three styles of diamond resorption in a single kimberlite: effects of volcanic degassing and assimilation.Geology, Vol. 45, 10. pp. 871-874.Africa, Botswanadeposit - Orapa BK1 and AK15

Abstract: Kimberlite magmas, the primary source of diamonds, have many features indicative of explosive eruptions and high volatile contents. The main approaches used to establish exsolution of fluid during magma ascent include theoretical modeling and experimental estimates of volatile solubility in kimberlite-like melts. Both approaches are hampered by the poorly constrained composition of kimberlite melts. Resorption features on diamonds are very sensitive to the presence and composition of the kimberlite fluid as well as to temperature and pressure. Here, we use direct evidence from diamond resorption features as a new method for investigating the parameters of fluid exsolution. The method is based on experimental reproduction of diamond resorption in kimberlite melts with and without an exsolved fluid phase. We studied 802 diamonds from two kimberlites (BK1 and AK15) from the Orapa cluster, Botswana. Samples from the BK1 pipe include three lithologies: two coherent kimberlites (CK-A and CK-B) and a pyroclastic kimberlite (massive volcaniclastic kimberlite, MVK). The known depth of diamond samples in each kimberlite lithology allows us to demonstrate an increase in the intensity of kimberlite-induced resorption with depth of diamond recovery in the drill holes. Each kimberlite lithology has a different proportion of diamonds with kimberlite-induced resorption, which is unique in style in each lithology: glossy surfaces in MVK due to reaction with C-O-H fluid, rough corroded surfaces in CK-B due to reaction with volatile-undersaturated melt, and a combination of glossy surfaces with corroded features in CK-A due to an overprint of melt resorption after fluid resorption. Both diamond resorption and kimberlite textures in the BK1 kimberlite show evidence of fluid exsolution only in CK-A and MVK lithologies, but no fluid presence in CK-B. The observed diamond resorption features may be controlled by (1) a temporary separation of the rising magma column into a bubble-rich head and bubble-poor volatile-depleted tail and (2) fluid exsolution at depths greater than decompressional degassing. We discuss how the depth of fluid exsolution from kimberlite melt may affect the diamond grade and the resorption of diamond populations in a kimberlite.
DS201707-1322
2017
Fei, H., Yamazaki, D., Sakurai, M., Miyajima, N., Ohfuji, H., Katsura, T., Yamamoto, T.A nearly water-saturated mantle transition zone inferred from mineral viscosity. Wadsleyite, ringwooditeScience Advances, Vol. 3, 6, 7p.Mantlewater

Abstract: An open question for solid-earth scientists is the amount of water in Earth’s interior. The uppermost mantle and lower mantle contain little water because their dominant minerals, olivine and bridgmanite, have limited water storage capacity. In contrast, the mantle transition zone (MTZ) at a depth of 410 to 660 km is considered to be a potential water reservoir because its dominant minerals, wadsleyite and ringwoodite, can contain large amounts of water [up to 3 weight % (wt %)]. However, the actual amount of water in the MTZ is unknown. Given that water incorporated into mantle minerals can lower their viscosity, we evaluate the water content of the MTZ by measuring dislocation mobility, a property that is inversely proportional to viscosity, as a function of temperature and water content in ringwoodite and bridgmanite. We find that dislocation mobility in bridgmanite is faster by two orders of magnitude than in anhydrous ringwoodite but 1.5 orders of magnitude slower than in water-saturated ringwoodite. To fit the observed mantle viscosity profiles, ringwoodite in the MTZ should contain 1 to 2 wt % water. The MTZ should thus be nearly water-saturated globally.
DS201708-1636
2017
Fei, Y.Stability of Fe3+ bearing majorite in the Earth's mantle.11th. International Kimberlite Conference, OralMantlemajorite
DS201709-1984
2017
Feneyrol, J., Giuliani, G., Demaiffe, D., Ohenstetter, D., Fallick, A.E., Dubessy, J., Martelet, J-E., Rakotondrazafy, A.F.M., Omito, E., Ichangi, D., Nyamai, C., Wamunyu, W.Age and origin of the tsavorite and tanzanite mineralozing fluids in the Neoproterozoic Mozambique metamorphic belt.The Canadian Mineralogist, Vol. 55, pp. 763-786.Africa, Kenya, Tanzania, Madagascartanzanite

Abstract: The genetic model previously proposed for tsavorite- (and tanzanite-) bearing mineralization hosted in the Neoproterozoic Metamorphic Mozambique Belt (stretching from Kenya through Tanzania to Madagascar) is refined on the basis of new Sm-Nd age determinations and detailed Sr-O-S isotope and fluid-inclusion studies. The deposits are hosted within meta-sedimentary series composed of quartzites, graphitic gneisses, calc-silicate rocks intercalated with meta-evaporites, and marbles. Tsavorite occurs either in nodules (also called “boudins”) oriented parallel to the metamorphic foliation in all of the deposits in the metamorphic belt or in quartz veins and lenses located at the hinges of anticlinal folds (Lelatema fold belt and Ruangwa deposits, Tanzania). Gem tanzanite occurs in pockets and lenses in the Lelatema fold belt of northern Tanzania. The Sm-Nd isotopic data for tsavorites and tanzanites hosted in quartz veins and lenses from Merelani demonstrate that they formed at 600 Ma, during the retrograde metamorphic episode associated with the East African Orogeny. The tsavorites hosted in nodules do not provide reliable ages: their sedimentary protoliths had heterogeneous compositions and their Sm-Nd system was not completely rehomogenized, even at the local scale, by the fluid-absent metamorphic recrystallization. The initial 87Sr/86Sr isotopic ratios of calcite from marble and tanzanites from Merelani fit with the strontium isotopic composition of Neoproterozoic marine carbonates. Seawater sediment deposition in the Mozambique Ocean took place around 720 Ma. The quartz-zoisite O-isotopic thermometer indicates a temperature of formation for zoisite between 385 and 448 °C. The sulfur isotopic composition of pyrite (between –7.8 and –1.3‰ V-CDT) associated with tsavorite in the Lelatema fold belt deposits suggests the contribution of reduced marine sulfate. The sulfur in pyrite in the marbles was likely derived from bacterial sulfate reduction which produced H2S. Fluid inclusion data from tsavorite and tanzanite samples from the Merelani mine indicate the presence of a dominant H2S-S8±(CH4)±(N2)±(H2O)-bearing fluid. In the deposits in Kenya and Madagascar, the replacement of sulfate by tsavorite in the nodules and the boron isotopic composition of tourmaline associated with tsavorite are strong arguments in favor of the participation of evaporites in garnet formation.
DS201703-0402
2016
Ferrero, S., Wunder, B., Ziemann, M.A., Walle, M., O'Brien, P.J.Carbonatitic and granitic melts produced under conditions of primary immiscibility during anatexis in the lower crust. Oberpfalz areaEarth and Planetary Science Letters, Vol. 454, pp. 121-131.Europe, Czech RepublicBohemian Massif

Abstract: Carbonatites are peculiar magmatic rocks with mantle-related genesis, commonly interpreted as the products of melting of CO2-bearing peridotites, or resulting from the chemical evolution of mantle-derived magmas, either through extreme differentiation or secondary immiscibility. Here we report the first finding of anatectic carbonatites of crustal origin, preserved as calcite-rich polycrystalline inclusions in garnet from low-to-medium pressure migmatites of the Oberpfalz area, SW Bohemian Massif (Central Europe). These inclusions originally trapped a melt of calciocarbonatitic composition with a characteristic enrichment in Ba, Sr and LREE. This interpretation is supported by the results of a detailed microstructural and microchemical investigation, as well as re-melting experiments using a piston cylinder apparatus. Carbonatitic inclusions coexist in the same cluster with crystallized silicate melt inclusions (nanogranites) and COH fluid inclusions, suggesting conditions of primary immiscibility between two melts and a fluid during anatexis. The production of both carbonatitic and granitic melts during the same anatectic event requires a suitable heterogeneous protolith. This may be represented by a sedimentary sequence containing marble lenses of limited extension, similar to the one still visible in the adjacent central Moldanubian Zone. The presence of CO2-rich fluid inclusions suggests furthermore that high CO2 activity during anatexis may be required to stabilize a carbonate-rich melt in a silica-dominated system. This natural occurrence displays a remarkable similarity with experiments on carbonate-silicate melt immiscibility, where CO2 saturation is a condition commonly imposed.
DS201711-2511
2017
Ferrerro, S.., Wunder, B., Ziemann, M.A., Walle, M., O'Brien, P.J.Carbonatitic and granitic melts produced under conditions of primary immiscibility during anatexis in the lower crust.Earth and Planetary Science Letters, Vol. 454, pp. 121-131.Mantlecarbonatites

Abstract: Carbonatites are peculiar magmatic rocks with mantle-related genesis, commonly interpreted as the products of melting of CO2-bearing peridotites, or resulting from the chemical evolution of mantle-derived magmas, either through extreme differentiation or secondary immiscibility. Here we report the first finding of anatectic carbonatites of crustal origin, preserved as calcite-rich polycrystalline inclusions in garnet from low-to-medium pressure migmatites of the Oberpfalz area, SW Bohemian Massif (Central Europe). These inclusions originally trapped a melt of calciocarbonatitic composition with a characteristic enrichment in Ba, Sr and LREE. This interpretation is supported by the results of a detailed microstructural and microchemical investigation, as well as re-melting experiments using a piston cylinder apparatus. Carbonatitic inclusions coexist in the same cluster with crystallized silicate melt inclusions (nanogranites) and COH fluid inclusions, suggesting conditions of primary immiscibility between two melts and a fluid during anatexis. The production of both carbonatitic and granitic melts during the same anatectic event requires a suitable heterogeneous protolith. This may be represented by a sedimentary sequence containing marble lenses of limited extension, similar to the one still visible in the adjacent central Moldanubian Zone. The presence of CO2-rich fluid inclusions suggests furthermore that high CO2 activity during anatexis may be required to stabilize a carbonate-rich melt in a silica-dominated system. This natural occurrence displays a remarkable similarity with experiments on carbonate-silicate melt immiscibility, where CO2 saturation is a condition commonly imposed. In conclusion, this study shows how the investigation of partial melting through melt inclusion studies may unveil unexpected processes whose evidence, while preserved in stiff minerals such as garnet, is completely obliterated in the rest of the rock due to metamorphic re-equilibration. Our results thus provide invaluable new insights into the processes which shape the geochemical evolution of our planet, such as the redistribution of carbon and strategic metals during orogenesis.
DS201705-0825
2017
Fershtater, G.B., Yudalevich, Z.A.Mantle metasomatism and magma formation in continental lithosphere: dat a on xenoliths in alkali basalts from the Makhtesh Ramon, Negrev Desert, Israel.Petrology, Vol. 25, 2, pp. 181-205.Asia, IsraelBasanites
DS201708-1637
2017
Fitzpayne, A.New constraints on MARID-PIC rocks based on mineral and bulk-rock geochemical data: implications for mantle metasomatism and alkaline magmatism.11th. International Kimberlite Conference, OralMantlemetasomatism

Abstract: The LILE-enrichments and radiogenic Sr isotope compositions of lamproites and other alkaline magmas have commonly been attributed to the occurrence of phlogopite-rich rocks such as MARID (Mica-AmphiboleRutile-Ilmenite-Diopside) in their mantle sources. To provide new constraints on the relationship between mantle metasomatism and alkaline magmatism, we have investigated the major and trace element compositions of MARID and PIC (Phlogopite-Ilmenite-Clinopyroxene) xenoliths, hosted in kimberlites and orangeites from the Kimberley area, South Africa. As MARID and PIC xenoliths often do not exhibit their complete mineral assemblages, such phlogopite-rich rocks are better classified using geochemical criteria such as mineral major and trace element compositions (e.g. clinopyroxene chondrite-normalised Ce/Yb; MARID = 16- 60 vs PIC = 10-21). New data indicate that major element compositions of phlogopite and clinopyroxene grains from PIC xenoliths are similar to those in peridotite xenoliths from the Kaapvaal craton; furthermore, MARID minerals exhibit broader compositional ranges than previously reported, and also partly overlap those in peridotites. These results necessitate the reconsideration of a genetic link between MARID/PIC rocks and metasomatised peridotites. Importantly, similarities in the trace element compositions of MARID and other on- and off-craton peridotitic clinopyroxene indicate that MARID-like metasomatic fluids may be a ubiquitous feature of the lithospheric mantle. Comparing bulk-rock and average mineral trace element ratios suggests that melting of the silicate components of MARID rocks may contribute to the trace element enrichments in alkaline magmas (specifically magmas in the “lamproite clan”).
DS201708-1638
2017
Fitzpayne, A.Multiple metasomatic events recorded in MARID xenoliths.11th. International Kimberlite Conference, PosterMantlemetasomatism
DS201708-1639
2017
Foley, S.F.The carbon cycle in the continental lithosphere and the generation of alkaline mafic melts in cratonic and rift ridges.11th. International Kimberlite Conference, OralMantlecarbon
DS201701-0010
2016
Ford, H.A., Long, M.D., Wirth, E.A.Mid-lithospheric discontinuities and complex anistropic layering in the mantle lithosphere beneath the Wyoming and Superior provinces.Journal of Geophysical Research, Vol. 121, 9, pp. 6675-6697.United States, CanadaGeophysics

Abstract: The observation of widespread seismic discontinuities within Archean and Proterozoic lithosphere is intriguing, as their presence may shed light on the formation and early evolution of cratons. A clear explanation for the discontinuities, which generally manifest as a sharp decrease in seismic velocity with depth, remains elusive. Recent work has suggested that midlithospheric discontinuities (MLDs) may correspond to a sharp gradient in seismic anisotropy, produced via deformation associated with craton formation. Here we test this hypothesis beneath the Archean Superior and Wyoming Provinces using anisotropic Ps receiver function (RF) analysis to characterize the relationship between MLDs and seismic anisotropy. We computed radial and transverse component RFs for 13 long-running seismic stations. Of these, six stations with particularly clear signals were analyzed using a harmonic regression technique. In agreement with previous studies, we find evidence for multiple MLDs within the cratonic lithosphere of the Wyoming and Superior Provinces. Our harmonic regression results reveal that (1) MLDs can be primarily explained by an isotropic negative velocity gradient, (2) multiple anisotropic boundaries exist within the lithospheric mantle, (3) the isotropic MLD and the anisotropic boundaries do not necessarily occur at the same depths, and (4) the depth and geometry of the anisotropic boundaries vary among stations. We infer that the MLD does not directly correspond to a change in anisotropy within the mantle lithosphere. Furthermore, our results reveal a surprising level of complexity within the cratonic lithospheric mantle, suggesting that the processes responsible for shaping surface geology produce similar structural complexity at depth.
DS201707-1323
2017
Forster, M.W., Orelevic, D., Schmuck, H.R., Buhre, S., Veter, M., Mertz-Kraus, R., Foley, S.F., Jacob, D.E.Melting and dynamic metasomatism of mixed harzburgite + glimmerite mantle source: implications for the genesis of orogenic potassic magmas.Chemical Geology, Vol. 455, pp. 182-191.Mantlemetasomatism

Abstract: Tectonically young, orogenic settings are commonly the sites of post-collisional silica-rich ultrapotassic magmas with extreme K2O-contents of up to 9 wt% and K2O/Na2O > 2. Many experimental studies investigating the generation of these melts have concentrated on melting of homogenous phlogopite bearing peridotites, whereas geochemical signatures indicate the involvement of at least two types of source rocks: ultra-depleted and K and trace elements-enriched ones. We report the results of melting experiments at 1–2 GPa of mixed glimmerite and harzburgite, in which these rock types make up two halves each capsule. Melting begins in the glimmerite, and its metasomatic effects on the harzburgite are apparent at 1100 °C even before melt pools are visible. The first melts are Na-rich, seen in zoning of olivines and as growth of clinopyroxene in the harzburgite, but change at higher degrees of melting to produce a typical lamproite-like melt with K2O > 10 wt%. A major advantage of this study is the preservation of distinct melts in different parts of the capsule, which reflect a process of dynamic metasomatism: within the harzburgite matrix, the infiltrating melt derived from melting of the glimmerite changes consistently with the distance of travel through the harzburgite, enabling quantification of the metasomatic effects as an increase in SiO2 and K2O. This results principally from assimilation of orthopyroxene, which increases the Ol/Opx ratio of the residual harzburgite. The effects of quench olivine growth are recognizable and can be quantified due to a step-change in composition at the glimmerite/harzburgite border: the large total surface area of olivine and small melt fraction mean that the amount of quench olivine is high within the harzburgite, but negligible in the almost completely molten glimmerite. Melts of the glimmerite contain up to 8–10 wt% K2O and 53 wt% SiO2, which increase to 55–56 wt% after interaction with the harzburgite. Mediterranean lamproites resemble melts of glimmerite, whereas melts that have interacted with harzburgite are more similar to less potassic, but more SiO2-rich shoshonites of the Mediterranean region.
DS201712-2685
2017
Fortaleche, D., Lucas, A., Muyal, J., Hsu, T., Padua, P.The Colombian emerald industry: winds of change. Gems & Gemology, Vol. 53, 3, pp. 332-358.South America, Colombiaemerald

Abstract: Colombia is synonymous with fine emerald, and production is believed to date back well over a thousand years. Over the centuries the beautiful verdant gemstone, which emerges from areas that are also a lush green, has been linked to violence and human exploitation. Nevertheless, the desire of the Colombian people to mine for this treasure and strike it rich has endured, with enough dreams coming true to drive their passion. In recent years, industry changes have accelerated, perhaps more profoundly than ever before. While government ownership and regulation, criminal activity, and violence have affected production over the years, the industry’s greatest opportunities may still be ahead. Multinational companies are investing heavily in Colombian emerald mining, which has led to modernization. The government’s position on emerald mining has also improved dramatically in this period. Calls for transparency and traceability have led to branding and a revamping of the industry’s image. The loose system of independent miners (figure 1) is seeing efforts at formalization. These landmark changes are occurring at a time when most of the country’s emerald reserves have yet to be mined. In October 2015, a joint GIA and Colombian team met at the First International Emerald Symposium in Bogotá to interview industry leaders and government officials. Many topics involving industry change were discussed at the symposium. Afterward, the team traveled to Colombia’s major mines and visited dealers and cutters in Bogotá to document the current state of the mine-to-market industry. We were also able to collect rough emerald samples for the GIA laboratory’s country-of-origin reference collection.
DS201711-2512
2017
Foulger, G.R.Origin of the South Atlantic igneous province. ( Lucapa zone)Journal of Volcanology and Geothermal Research, in press available, 19p.Africa, Angola, Democratic Republic of Congocarbonatites

Abstract: The South Atlantic Igneous Province comprises the Paraná Basalts, Rio Grande Rise, Tristan archipelago and surrounding guyot province,Walvis Ridge, Etendeka basalts and, in somemodels, the alkaline igneous lineament in the Lucapa corridor, Angola. Although these volcanics are often considered to have a single generic origin, complexities that suggest otherwise are observed. The Paraná Basalts erupted ~5 Ma before sea-floor spreading started in the neighborhood, and far more voluminous volcanic margins were emplaced later. A continental microcontinent likely forms much of the Rio Grande Rise, and variable styles of volcanism built the Walvis Ridge and the Tristan da Cunha archipelago and guyot province. Such complexities, coupled with the northward-propagating mid-ocean ridge crossing amajor transverse transtensional intracontinental structure, suggest that fragmentation of Pangaea was complex at this latitude and that the volcanism may have occurred in response to distributed extension. The alternative model, a deep mantle plume, is less able to account for many observations and no model variant can account for all the primary features that include eruption of the Paraná Basalts in a subsiding basin, continental breakup by rift propagation that originated far to the south, the absence of a time-progressive volcanic chain between the Paraná Basalts and the Rio Grande Rise, derivation of the lavas from different sources, and the lack of evidence for a plume conduit in seismic-tomography- and magnetotelluric images. The region shares many common features with the North Atlantic Igneous Province which also features persistent, widespread volcanismwhere a propagating mid-ocean ridge crossed a transverse structural discontinuity in the disintegrating supercontinent.
DS201709-1985
2017
France, L., Boulanger, M., Mollex, G., Devidal, J-L. .Oldoinyo Lengai natrocarbonatite derives from calciocarbonatite.Goldschmidt Conference, abstract 1p.Africa, Tanzaniadeposit, Oldoinyo

Abstract: Carbonatites are rare magmas containing almost no silica; the corresponding crystallized rocks represent the main rare earth elements (REE) deposits in production. Oldoinyo Lengai (Tanzania) is the only active carbonatite volcano on Earth, and may be used as a natural laboratory to identify the parameters responsible for the genesis of the >500 reported fossil occurrences of carbonatite magmas. Nevertheless the carbonatites emitted at Oldoinyo Lengai are unique as alkalirich (natrocarbonatites), and their origin may not be representative of the fossil carbonatites (calcio-, ferro-, magnesio-carbonatites). Here we use three-phases melt inclusions trapped in clinopyroxenes and nephelines from cognate cumulates – that sample the active magma chamber of Oldoinyo Lengai – emitted during the 2007-08 sub-plinian explosive eruption to track the carbonatite presence within the plumbing system, and to eventually quantify its composition at depth. We show that although natrocarbonatites are emitted at Oldoinyo Lengai summit, more classical calciocarbonatites are present at magma chamber depth, consistent with rare natrocarbonatites being derived from more classical calciocarbonatites by further magma differentiation. Those unique cognate samples allows us to provide the first direct measurements of partition coefficients for major and trace elements of natural coexisting in equilibrium carbonatite and silicate melts. Partition coefficients suggests that natrocarbonatites derive from calciocarbonatites by fractionating Ca-rich, and Na-poor phases. The Oldoinyo Lengai can therefore be used as a perfect analogue of fossil igneous systems that are now exhumed, commonly lacking any relation with the initial geodynamic setting, and form REE mineral deposits.
DS201711-2513
2017
Freeburn, R., Bouilhol, P., Maunder, B., Magni, V., van Hunen, J.Numerical models of the magmatic processes induced by slab breakoff.Earth and Planetary Science Letters, Vol. 478, pp. 203-213.Mantlesubduction

Abstract: After the onset of continental collision, magmatism often persists for tens of millions of years, albeit with a different composition, in reduced volumes, and with a more episodic nature and more widespread spatial distribution, compared to normal arc magmatism. Kinematic modelling studies have suggested that slab breakoff can account for this post-collisional magmatism through the formation of a slab window and subsequent heating of the overriding plate and decompression melting of upwelling asthenosphere, particularly if breakoff occurs at depths shallower than the overriding plate. To constrain the nature of any melting and the geodynamic conditions required, we numerically model the collision of two continental plates following a period of oceanic subduction. A thermodynamic database is used to determine the (de)hydration reactions and occurrence of melt throughout this process. We investigate melting conditions within a parameter space designed to generate a wide range of breakoff depths, timings and collisional styles. Under most circumstances, slab breakoff occurs deeper than the depth extent of the overriding plate; too deep to generate any decompressional melting of dry upwelling asthenosphere or thermal perturbation within the overriding plate. Even if slab breakoff is very shallow, the hot mantle inflow into the slab window is not sustained long enough to sufficiently heat the hydrated overriding plate to cause significant magmatism. Instead, for relatively fast, shallow breakoff we observe melting of asthenosphere above the detached slab through the release of water from the tip of the heating detached slab. Melting of the subducted continental crust during necking and breakoff is a more common feature and may be a more reliable indicator of the occurrence of breakoff. We suggest that magmatism from slab breakoff alone is unable to explain several of the characteristics of post-collisional magmatism, and that additional geodynamical processes need to be considered when interpreting magmatic observations.
DS201708-1571
2017
Fritsch, E., Rondeau, B., Devouard, B., Pinsault, L., Latouche, C.Why are some crystals gem quality? Crystal growth considerations on the 'GEM FACTOR'.The Canadian Mineralogist, Vol. 55, 4, pp. 521-533.TechnologyDeposit - Renard 2

Abstract: The purpose of this work is to investigate the crystal growth parameters necessary or sufficient to obtain a crystal specifically of gem quality. We assume adequate chemistry is available. First, nucleation must occur with only a limited number of nuclei, otherwise too many crystals will be produced, and they will be too small to be faceted into a gem. Two growth mechanisms are readily documented for gems: Most commonly there is slow growth, driven by a spiral growth mechanism, leading to large single individuals. There are only a few examples of fast growth leading to gem-quality edifices: examples include “gota de aceite” Colombian emerald or the dendritic “pseudo cube” for gem diamonds. We have not documented the intermediate conditions between these two extremes in the Sunagawa diagram, which would correspond to 2D nucleation growth. The presence of inclusions is to be limited to desirable ones. Thus, in general, a good stability of the growth interface is the best guarantee of good clarity in the final gem. As for the interface, in general, growth conditions must be relatively stable over the period necessary to achieve growth. Perhaps surprisingly, it has become well documented that gem-quality near-colorless diamonds may have experienced quite a complex growth history. Therefore, the term stability has to be re-defined for each system producing a given gem. The length of time it takes to achieve crystallization of the gem has rarely been studied or estimated. Scientific evidence from experimental petrology and the growth of synthetic gems indicates that it does not take millions of years to grow a gem, but that this exercise may be achieved in a week to, arguably, a few years at the most. Available free space to grow does not appear always necessary, but it helps. Otherwise deformation, inclusions, and other negative effects may occur. Finally, no dramatic post-growth events, such as fracturing or etching, should affect the gem crystal.
DS201706-1069
2017
Frost, D.A., Rost, S., Garnero, E.J., Li, M.Seismic evidence for Earth's crusty deep mantle.Earth and Planetary Science Letters, Vol. 470, pp. 54-63.Mantlegeophysics - seismic

Abstract: Seismic tomography resolves anomalies interpreted as oceanic lithosphere subducted deep into Earth's lower mantle. However, the fate of the compositionally distinct oceanic crust that is part of the lithosphere is poorly constrained but provides important constraints on mixing processes and the recycling process in the deep Earth. We present high-resolution seismic array analyses of anomalous P-waves sampling the deep mantle, and deterministically locate heterogeneities in the lowermost 300 km of the mantle. Spectral analysis indicates that the dominant scale length of the heterogeneity is 4 to 7 km. The heterogeneity distribution varies laterally and radially and heterogeneities are more abundant near the margins of the lowermost mantle Large Low Velocity Provinces (LLVPs), consistent with mantle convection simulations that show elevated accumulations of deeply advected crustal material near the boundaries of thermo-chemical piles. The size and distribution of the observed heterogeneities is consistent with that expected for subducted oceanic crust. These results thus suggest the deep mantle contains an imprint of continued subduction of oceanic crust, stirred by mantle convection and modulated by long lasting thermo-chemical structures. The preferred location of the heterogeneity in the lowermost mantle is consistent with a thermo-chemical origin of the LLVPs. Our observations relate to the mixing behaviour of small length-scale heterogeneity in the deep Earth and indicate that compositional heterogeneities from the subduction process can survive for extended times in the lowermost mantle.
DS201701-0011
2016
Fschroeder-Frerkes, F., Woodland, A.B., Uenver-Thiele, I., Klimm, K., Knapp, N.Ca-Eskola in corporation in clinopyroxene: limitations and petrological implications for eclogites and related rocks.Contributions to Mineralogy and Petrology, Vol. 171, pp. 101-TechnologyEclogite

Abstract: Clinopyroxene is an essential mineral in eclogitic rocks. It commonly contains minor amounts of the defect-bearing Ca-Eskola (CaEs, Ca0.5?0.5AlSi2O6) component, with higher concentrations generally considered to indicate a high-pressure origin at least within the coesite stability field. Changes in pressure and temperature conditions can lead to exsolution of this component as a free SiO2 phase, which may have a number of petrological implications. This makes it important to understand the factors that maximize CaEs incorporation in clinopyroxene. We have undertaken a series of experiments at high pressures and temperatures (4-10 GPa and 1000-1350 °C) to further investigate the systematics of CaEs incorporation in eclogite-like clinopyroxene and the factors responsible for maximizing CaEs contents. Two simple chemical systems were chosen that allow unambiguous interpretation of the results: (1) CMAS + H2O and (2) two compositions in the NCMAS system. All experimental products contained clinopyroxene and garnet along with either a free SiO2 phase or a silicate melt. Coexisting garnet is grossular-rich, generally with Xgr ? 0.67. Compositional variations are attributable to the presence or absence of melt and changes in modal amounts of garnet at different pressure-temperature conditions. Even small amounts of H2O lower the solidus temperature and the presence of a melt reduces the SiO2 activity, which destabilizes the CaEs component in clinopyroxene. The CaEs and the Ca-Tschermaks (CaTs, CaAl2SiO6) components in clinopyroxene decrease with increasing jadeite mole fraction, which is also a function of pressure and bulk Al content. Modeling X-ray powder diffraction data yields a molar volume for the CaEs endmember of VCaEs = 60.87(63) cm3, which reasonably agrees with a literature value that was estimated from natural samples. In the presence of coexisting coesite, the CaEs and CaTs do not vary independently of each other, being controlled by the internal equilibrium 2CaEs = CaTs + 3SiO2 (coesite). This relation, observed in simple systems (i.e., CMAS ± Na), is also obeyed by clinopyroxene in more complex, natural analog bulk compositions. An assessment of available experimental data reveals a maximum of 15-18 mol% CaEs in eclogitic clinopyroxene at conditions corresponding to 130-180 km depth. CaEs contents are maximized at high temperatures; i.e., at or near the solidus in the presence of coesite. Thus, this study supports the role of CaEs exsolution in contributing to melt generation during upwelling of eclogite bodies in the mantle, albeit with some caveats. Somewhat higher maximum CaEs contents (~20 mol%) are found in Ca and Al-rich bulk compositions, such as grospydite xenoliths. Such bulk compositions also seem to require the coexistence of kyanite. Other Ca and Al-rich rock types, like rodingites, should have the potential of containing CaEs-rich clinopyroxenes, except that they are SiO2-undersaturated. This emphasizes the further role of bulk composition, in addition to high temperatures, in achieving maximum CaEs contents in high-pressure clinopyroxene.
DS201708-1640
2017
Fulop, A.The emplacement of Voorspoed pipe, South Africa: a take of incremental pipe growth, tephra jets, mixing and a shallow crater.11th. International Kimberlite Conference, PosterAfrica, South Africadeposit - Voorspoed
DS201708-1641
2017
Fulop, A.Geology of the Snap Lake kimberlite dykem Northwest territories, Canada and its metasomatic interaction with granite.11th. International Kimberlite Conference, PosterCanada, Northwest Territoriesdeposit - Snap Lake
DS201707-1324
2016
Fulop, A., Kurszlaukis, S.Monogenetic v. polygenetic kimberlite volcanism: in-depth examination of Tango extension super structure, Attwapiskat kimberlite field, Ontario, Canada.Geological Society of London, Special Publication: Monogenetic volcanism, no. 446, pp. 205-224.Canada, Ontario, Attawapiskatdeposit - Tango

Abstract: Extensive drilling of the Tango Extension kimberlite pipe resulted in the construction of an emplacement model that revealed the complex architecture of two amalgamated pipes: an older pipe, the Tango Extension Deep, which is cut along its northern margin by the smaller Tango Extension pipe. The resulting volcano forms a complex pipe-in-pipe structure called the Tango Extension Super Structure. The emplacement of the Tango Extension Super Structure sequence indicates prolonged hiatuses, which, similar to other volcanoes classified as monogenetic, puts the classical monogenetic and polygenetic definitions of maar-diatreme volcanoes to the test. Although the Tango Extension and Tango Extension Deep volcanoes could be characterized individually as monogenetic volcanoes, the Tango Extension Super Structure shows evidence of the occurrence of the significant hiatuses typical of polygenetic volcanoes. We suggest that hiatuses that are long enough to consolidate earlier tephra unambiguously differentiate polygenetic from monogenetic maar-diatreme volcanoes.
DS201705-0826
2017
Funk, M.T.Diamond Heists.lithographie.org, No. 19, pp. 132-137.GlobalBook - theft
DS201708-1642
2017
Gabanakgosi, K.Slope stability challenges and solutions for mining kimberlite resources hosted in structurally complex country rock: dip slope mining at Jwaneng mine, Botswana.11th. International Kimberlite Conference, OralAfrica, Botswanadeposit - Jwaneng
DS201705-0827
2017
Gaillou, E., Rossman, G.R.On the Beauty of Defects.lithographie.org, No. 19, pp. 40-53.TechnologyBook - diamond colour

Abstract: Extensive study has shown that these inclusions contain mantle-derived fluids (e.g. Navon et al., 1988, Izraeli et al., 2001, 2004 Tomlinson et al., 2009; Logvinova et al., 2011; Zedgenizov et al., 2011; Smith et al., 2012, Smith et al., 2015 Howell et al., 2012b Howell et al., , 2013 Weiss et al., 2013 Weiss et al., , 2015 Rakovan et al., 2014; Smit et al., in press), Here we use the term 'milky' to describe diamonds that contain zones of opalescent to brown or grey opaque appearance (Gaillou and Rossman, 2014). The exact cause of this opacity is yet to be defined, and forms the purpose of this paper.
DS201708-1643
2017
Gainer, D.The geology of the Faraday 3 kimberlite, NWT, Canada.11th. International Kimberlite Conference, PosterCanada, Northwest Territoriesdeposit - Faraday 3
DS201710-2227
2017
Ganey, G.Q., Loso, M.G., Burgess, A.B., Dial, R.J.The role of microbes in snowmelt and radiative forcing on an an Alaskan icefield. Red algaeNature Geoscience, Sept. 18, onlineUnited States, Alaskageomorphology

Abstract: A lack of liquid water limits life on glaciers worldwide but specialized microbes still colonize these environments. These microbes reduce surface albedo, which, in turn, could lead to warming and enhanced glacier melt. Here we present results from a replicated, controlled field experiment to quantify the impact of microbes on snowmelt in red-snow communities. Addition of nitrogen-phosphorous-potassium fertilizer increased alga cell counts nearly fourfold, to levels similar to nitrogen-phosphorus-enriched lakes; water alone increased counts by half. The manipulated alga abundance explained a third of the observed variability in snowmelt. Using a normalized-difference spectral index we estimated alga abundance from satellite imagery and calculated microbial contribution to snowmelt on an icefield of 1,900?km2. The red-snow area extended over about 700?km2, and in this area we determined that microbial communities were responsible for 17% of the total snowmelt there. Our results support hypotheses that snow-dwelling microbes increase glacier melt directly in a bio-geophysical feedback by lowering albedo and indirectly by exposing low-albedo glacier ice. Radiative forcing due to perennial populations of microbes may match that of non-living particulates at high latitudes. Their contribution to climate warming is likely to grow with increased melt and nutrient input.
DS201706-1070
2017
Ganne, J., Feng, X.Primary magmas and mantle temperatures through time.Geochemistry, Geophysics, Geosystems: G3, Vol. 18, pp. 872-888.Mantlegeothermometry

Abstract: Chemical composition of mafic magmas is a critical indicator of physicochemical conditions, such as pressure, temperature, and fluid availability, accompanying melt production in the mantle and its evolution in the continental or oceanic lithosphere. Recovering this information has fundamental implications in constraining the thermal state of the mantle and the physics of mantle convection throughout the Earth's history. Here a statistical approach is applied to a geochemical database of about 22,000 samples from the mafic magma record. Potential temperatures (Tps) of the mantle derived from this database, assuming melting by adiabatic decompression and a Ti-dependent (Fe2O3/TiO2?=?0.5) or constant redox condition (Fe2+/?Fe?=?0.9 or 0.8) in the magmatic source, are thought to be representative of different thermal “horizons” (or thermal heterogeneities) in the ambient mantle, ranging in depth from a shallow sublithospheric mantle (Tp minima) to a lower thermal boundary layer (Tp maxima). The difference of temperature (?Tp) observed between Tp maxima and minima did not change significantly with time (?170°C). Conversely, a progressive but limited cooling of ?150°C is proposed since ?2.5 Gyr for the Earth's ambient mantle, which falls in the lower limit proposed by Herzberg et al. [2010] (?150-250°C hotter than today). Cooling of the ambient mantle after 2.5 Ga is preceded by a high-temperature plateau evolution and a transition from dominant plumes to a plate tectonics geodynamic regime, suggesting that subductions stabilized temperatures in the Archaean mantle that was in warming mode at that time.
DS201701-0012
2016
Ganne, J., Feng, X., Rey, P., De Andrade, V.Statistical petrology reveals a link between supercontinents cycle and mantle global climate.American Mineralogist, Vol. 101, pp. 2768-2773.MantleGeostatistics

Abstract: The breakup of supercontinents is accompanied by the emplacement of continental flood basalts and dike swarms, the origin of which is often attributed to mantle plumes. However, convection modeling has showed that the formation of supercontinents result in the warming of the sub-continental asthenospheric mantle (SCAM), which could also explain syn-breakup volcanism. Temperature variations during the formation then breakup of supercontinents are therefore fundamental to understand volcanism related to supercontinent cycles. Magmatic minerals record the thermal state of their magmatic sources. Here we present a data mining analysis on the first global compilation of chemical information on magmatic rocks and minerals formed over the past 600 million years: a time period spanning the aggregation and breakup of Pangea, the last supercontinent. We show that following a period of increasingly hotter Mg-rich magmatism with dominant tholeiitic affinity during the aggregation of Pangea, lower-temperature minerals crystallized within Mg-poorer magma with a dominant calc-alkaline affinity during Pangea disassembly. These trends reflect temporal changes in global mantle climate and global plate tectonics in response to continental masses assembly and dispersal. We also show that the final amalgamation of Pangea at ~300 Myr led to a long period of lithospheric collapse and cooling until the major step of Pangea disassembly started at ~125 Myr. The geological control on the geosphere magma budget has implications on the oxidation state and temperature of the Earth’s outer envelopes in the Phanerozoic and may have exerted indirect influence on the evolution of climate and life on Earth.
DS201703-0403
2017
Gao, J., Niu, J., Qin, S., Wu, X.Ultradeep diamonds originate from deep subducted sedimentary carbonates.Science China Earth Sciences, Vol. 60, 2, pp. 207-217.TechnologySubduction

Abstract: Diamonds are renowned as the record of Earth’s evolution history. Natural diamonds on the Earth can be distinguished in light of genetic types as kimberlitic diamonds (including peridotitic diamonds and eclogitic diamonds), ultrahigh-pressure metamorphic diamonds and ophiolitic diamonds. According to the inclusion mineralogy, most diamonds originated from continental lithospheric mantle at depths of 140-250 km. Several localities, however, yield ultradeep diamonds with inclusion compositions that require a sublithospheric origin (>~250 km). Ultradeep diamonds exhibit distinctions in terms of carbon isotope composition, N-concentration, mineral inclusions and so on. The present study provides a systematic compilation concerning the features of ultradeep diamonds, based on which to expound their genesis affinity with mantle-carbonate melts. The diamond-parental carbonate melts are proposed to be stemmed from the Earth’s crust through subduction of oceanic lithosphere. Ultradeep diamonds are classified into a subgroup attaching to kimberlitic diamonds grounded by formation mechanism, and present connections in respect of carbon origin to eclogitic diamonds, ultrahigh-pressure metamorphic diamonds and ophiolitic diamonds.
DS201707-1325
2016
Gao, J., Niu, J., Qin, S., Wu, X.Ultradeep diamonds originate from deep subducted sedimentary carbonates.Science China Earth Sciences, Vol. 60, 2, 3p.MantleUHP

Abstract: Diamonds are renowned as the record of Earth’s evolution history. Natural diamonds on the Earth can be distinguished in light of genetic types as kimberlitic diamonds (including peridotitic diamonds and eclogitic diamonds), ultrahigh-pressure metamorphic diamonds and ophiolitic diamonds. According to the inclusion mineralogy, most diamonds originated from continental lithospheric mantle at depths of 140–250 km. Several localities, however, yield ultradeep diamonds with inclusion compositions that require a sublithospheric origin (>~250 km). Ultradeep diamonds exhibit distinctions in terms of carbon isotope composition, N-concentration, mineral inclusions and so on. The present study provides a systematic compilation concerning the features of ultradeep diamonds, based on which to expound their genesis affinity with mantle-carbonate melts. The diamond-parental carbonate melts are proposed to be stemmed from the Earth’s crust through subduction of oceanic lithosphere. Ultradeep diamonds are classified into a subgroup attaching to kimberlitic diamonds grounded by formation mechanism, and present connections in respect of carbon origin to eclogitic diamonds, ultrahigh-pressure metamorphic diamonds and ophiolitic diamonds.
DS201706-1071
2016
Gao, J., Niu, J.J., Qin, S., Wu, X.Ultradeep diamonds originate from deep subducted sedimentary carbonates.Science China Earth Sciences, 12p. * engMantlesubduction, carbon cycle

Abstract: Diamonds are renowned as the record of Earth’s evolution history. Natural diamonds on the Earth can be distinguished in light of genetic types as kimberlitic diamonds (including peridotitic diamonds and eclogitic diamonds), ultrahigh-pressure metamorphic diamonds and ophiolitic diamonds. According to the inclusion mineralogy, most diamonds originated from continental lithospheric mantle at depths of 140-250 km. Several localities, however, yield ultradeep diamonds with inclusion compositions that require a sublithospheric origin (>~250 km). Ultradeep diamonds exhibit distinctions in terms of carbon isotope composition, N-concentration, mineral inclusions and so on. The present study provides a systematic compilation concerning the features of ultradeep diamonds, based on which to expound their genesis affinity with mantle-carbonate melts. The diamond-parental carbonate melts are proposed to be stemmed from the Earth’s crust through subduction of oceanic lithosphere. Ultradeep diamonds are classified into a subgroup attaching to kimberlitic diamonds grounded by formation mechanism, and present connections in respect of carbon origin to eclogitic diamonds, ultrahigh-pressure metamorphic diamonds and ophiolitic diamonds.
DS201708-1644
2017
Gao, X-Y.Multiphase solid inclusions in UHP eclogite from the Dabie orogen: constraints on anatectic melts during continental collision.11th. International Kimberlite Conference, PosterChinaUHP
DS201708-1645
2017
Garanin, K.Zarya diamond deposit, Yakutian Province, Russia.11th. International Kimberlite Conference, PosterRussia, Yakutiadeposit - Zarya
DS201708-1646
2017
Garanin, V.The relationship among various morphological types of diamonds within diamond deposits in Russia: genesis, growth, dissolution and real diamond grade.11th. International Kimberlite Conference, PosterRussiadiamond morphology
DS201705-0828
2017
Garanin, V.K., Kriulina, G.Y.Diamonds in Russia. ( discoveries)lithographie.org, No. 19, pp. 94-103.RussiaBook - history
DS201703-0404
2017
Gaudet, M.The principal role of silicic crustal xenolith assimilation in the formation of Kimberley type pyroclastic kimberlites.Vancouver Kimberlite Cluster, Feb. 28, 1p. AbstractCanada, QuebecDeposit - Renard 65
DS201708-1647
2017
Gaudet, M.The principal role of silicic crustal xenolith assimilation in the formation of Kimberley-type pyroclastic kimberlites - a petrographic study of the Renard 65 kimberlite pipe, Quebec, Canada.11th. International Kimberlite Conference, OralCanada, QuebecDeposit - Renard 65

Abstract: The Renard 65 pipe is located in the Otish Mountains, Quebec, Canada. It is one of nine diamondiferous kimberlite pipes in the ~ 640 Ma Renard cluster and is the largest of four pipes in the Renard Mine reserve. Detailed characterizations of the petrographic and compositional features of these pipe-infilling kimberlite rock types supports their classification into three geological units: Kimb65a, Kimb65b, and Kimb65d. These pipe-infilling kimberlites are interpreted to represent the solidified products of two separate magmatic events: Phase A containing Kimb65a, and Phase B containing Kimb65b and Kimb65d. This research demonstrates that the interclast matrix modal mineralogy (diopside + phlogopite + serpentine) in pyroclastic rock types in the Renard 65 kimberlites are inconsistent with origins by hydrothermal alteration involving hydrous meteoric fluids. Detailed investigation of the reactions between granitic and gneissic crustal xenolith lithologies and their host kimberlites, suggests that reactions occur at both magmatic and subsolidus temperatures involving significant volumetric proportions of xenoliths. The assimilation of crustal xenoliths, and contamination of the kimberlite magmas primarily by Si, are demonstrated to result in enhanced degassing of magmatic volatiles during emplacement and stabilization of the hybrid groundmass assemblage diopside + phlogopite + serpentine over the non hybrid groundmass assemblage calcite + phlogopite + serpentine. It is thus interpreted that the spatial distribution of transitional to Kimberley-type pyroclastic kimberlite rock types, which are characterized by diopside-rich and calcite-poor matrix assemblages as observed in the Renard 65 pipe and other similar pipes, is a function of crustal xenolith distribution in the magma during emplacement. This model not only accounts for the features of Kimberley-type pyroclastic kimberlite rock types, but also the spatial distribution of these rock types in numerous pipes which is often not consistent with lateral textural gradations as has been previously proposed. These results further indicate that the different mineralogy and textures of Fort-à-la-Corne-type pyroclastic kimberlites with respect to Kimberley-type pyroclastic kimberlites may be a consequence of not only the structural controls imparted by the host rock lithology with implications for emplacement-related processes, but also the absence of contamination of the magma by silicic crustal xenoliths.
DS201708-1648
2017
Gaudet, M.Subsolidus compositional modification of kimberlitic spinel in the Renard 65 kimberlite pipe, Quebec, Canada - implications for the use of spinel chemistry in the identification of kimberlite phases.11th. International Kimberlite Conference, PosterCanada, Quebecdeposit - Renard 65
DS201709-1986
2017
Gem notesDiamond with concentric inclusionsGems & Gemology, p. 228.Technologydiamond inclusions
DS201712-2700
2017
Gems & GemologyHigh quality diamond from Brazilian kimberlite. Lab notes - LipariGems & Gemology, Vol. 53, 3, p. 360.South America, Brazil, Bahiadeposit - Brauna
DS201705-0829
2017
Gervasoni, F., Klemme, S., Rohrbach, A., Grutzner, T., Berndt, J.Experimental constraints on mantle metasomatism caused by silicate and carbonate melt.Lithos, Vol. 282-283, pp. 173-186.MantleCarbonatite

Abstract: Metasomatic processes are responsible for many of the heterogeneities found in the upper mantle. To better understand the metasomatism in the lithospheric mantle and to illustrate the differences between metasomatism caused by hydrous silicate and carbonate-rich melts, we performed various interaction experiments: (1) Reactions between hydrous eclogite-derived melts and peridotite at 2.2-2.5 GPa and 900-1000 °C reproduce the metasomatism in the mantle wedge above subduction zones. (2) Reactions between carbonate-rich melts and peridotite at 2.5 GPa and 1050-1000 °C, and at 6 GPa and 1200-1250 °C simulate metasomatism of carbonatite and ultramafic silicate-carbonate melts in different regions of cratonic lithosphere. Our experimental results show that partial melting of hydrous eclogite produces hydrous Si- and Al-rich melts that react with peridotite and form bi-mineralic assemblages of Al-rich orthopyroxene and Mg-rich amphibole. We also found that carbonate-rich melts with different compositions react with peridotite and form new metasomatic wehrlitic mineral assemblages. Metasomatic reactions caused by Ca-rich carbonatite melt consume the primary peridotite and produce large amounts of metasomatic clinopyroxene; on the other hand, metasomatism caused by ultramafic silicate-carbonate melts produces less clinopyroxene. Furthermore, our experiments show that ultramafic silicate-carbonate melts react strongly with peridotite and cause crystallization of large amounts of metasomatic Fe-Ti oxides. The reactions of metasomatic melts with peridotite also change the melt composition. For instance, if the carbonatite melt is not entirely consumed during the metasomatic reactions, its melt composition may change dramatically, generating an alkali-rich carbonated silicate melt that is similar in composition to type I kimberlites.
DS201706-1072
2017
Gervasoni, F., Klemme, S., Rohrbach, A., Grutzner, T., Berndt, J.Experimental constraints on the stability of baddeleyite and zircon in carbonate and silicate carbonate melts.American Mineralogist, Vol. 102, pp. 860-866.carbonatite

Abstract: Carbonatites are rare igneous carbonate-rich rocks. Most carbonatites contain a large number of accessory oxide, sulfide, and silicate minerals. Baddeleyite (ZrO2) and zircon (ZrSiO4) are common accessory minerals in carbonatites and because these minerals host high concentrations of U and Th, they are often used to determine the ages of formation of the carbonatite. In an experimental study, we constrain the stability fields of baddeleyite and zircon in Ca-rich carbonate melts with different silica concentrations. Our results show that SiO2-free and low silica carbonate melts crystallize baddeleyite, whereas zircon only crystallizes in melts with higher concentration of SiO2. We also find that the zirconsilicate baghdadite (Ca3ZrSi2O9) crystallizes in intermediate compositions. Our experiments indicate that zircon may not be a primary mineral in a low-silica carbonatite melt and care must be taken when interpreting zircon ages from low-silica carbonatite rocks.
DS201708-1570
2017
Gibson, S.A.On the nature and origin of garnet in highly refractory Archean lithospheric mantle: constraints from garnet exsolved in Kaapvaal craton orthopyroxenes.Mineralogical Magazine, Vol. 81, 4, pp. 781-809.Africa, South Africagarnet

Abstract: The widespread occurrence of pyrope garnet in Archean lithospheric mantle remains one of the ‘holy grails’ of mantle petrology. Most garnets found in peridotitic mantle equilibrated with incompatible-trace-element-enriched melts or fluids and are the products of metasomatism. Less common are macroscopic intergrowths of pyrope garnet formed by exsolution from orthopyroxene. Spectacular examples of these are preserved in both mantle xenoliths and large, isolated crystals (megacrysts) from the Kaapvaal craton of southern Africa, and provide direct evidence that some garnet in the sub-continental lithospheric mantle initially formed by isochemical rather than metasomatic processes. The orthopyroxene hosts are enstatites and fully equilibrated with their exsolved phases (low-Cr pyrope garnet ±± Cr-diopside). Significantly, P-TP-T estimates of the post-exsolution orthopyroxenes plot along an unperturbed conductive Kaapvaal craton geotherm and reveal that they were entrained from a large continuous depth interval (85 to 175 km). They therefore represent snapshots of processes operating throughout almost the entire thickness of the sub-cratonic lithospheric mantle. New rare-earth element (REE) analyses show that the exsolved garnets occupy the full spectrum recorded by garnets in mantle peridotites and also diamond inclusions. A key finding is that a few low-temperature exsolved garnets, derived from depths of ~90 km, are more depleted in light REEs than previously observed in any other mantle sample. Importantly, the REE patterns of these strongly LREE-depleted garnets resemble the hypothetical composition proposed for pre-metasomatic garnets that are thought to pre-date major enrichment events in the sub-continental lithospheric mantle, including those associated with diamond formation. The recalculated compositions of pre-exsolution orthopyroxenes have higher Al22O33 and CaO contents than their post-exsolution counterparts and most likely formed as shallow residues of large amounts of adiabatic decompression melting in the spinel-stability field. It is inferred that exsolution of garnet from Kaapvaal orthopyroxenes may have been widespread, and perhaps accompanied cratonization at ~ 2.9 to 2.75 Ga. Such a process would considerably increase the density and stability of the continental lithosphere.
DS201709-1987
2017
Gibson, S.A.On the nature and origin of garnet in highly refractory Archean lithospheric mantle: constraints from garnet exsolved in Kaapvaal craton orthopyroxenes.Mineralogical Magazine, Vol. 81, 4, pp. 781-809.Africa, South Africagarnet mineralogy

Abstract: The widespread occurrence of pyrope garnet in Archean lithospheric mantle remains one of the ‘holy grails’ of mantle petrology. Most garnets found in peridotitic mantle equilibrated with incompatible-trace-element-enriched melts or fluids and are the products of metasomatism. Less common are macroscopic intergrowths of pyrope garnet formed by exsolution from orthopyroxene. Spectacular examples of these are preserved in both mantle xenoliths and large, isolated crystals (megacrysts) from the Kaapvaal craton of southern Africa, and provide direct evidence that some garnet in the sub-continental lithospheric mantle formed initially by isochemical rather than metasomatic processes. The orthopyroxene hosts are enstatites and fully equilibrated with their exsolved phases (low-Cr pyrope garnet?±?Cr-diopside). Significantly, P-T estimates of the post-exsolution orthopyroxenes plot along an unperturbed conductive Kaapvaal craton geotherm and reveal that they were entrained from a large continuous depth interval (85 to 175?km). They therefore represent snapshots of processes operating throughout almost the entire thickness of the sub-cratonic lithospheric mantle. New rare-earth element (REE) analyses show that the exsolved garnets occupy the full spectrum recorded by garnets in mantle peridotites and also diamond inclusions. A key finding is that a few low-temperature exsolved garnets, derived from depths of ?90?km, are more depleted in light rare-earth elements (LREEs) than previously observed in any other mantle sample. Importantly, the REE patterns of these strongly LREE-depleted garnets resemble the hypothetical composition proposed for pre-metasomatic garnets that are thought to pre-date major enrichment events in the sub-continental lithospheric mantle, including those associated with diamond formation. The recalculated compositions of pre-exsolution orthopyroxenes have higher Al2O3 and CaO contents than their post-exsolution counterparts and most probably formed as shallow residues of large amounts of adiabatic decompression melting in the spinel-stability field. It is inferred that exsolution of garnet from Kaapvaal orthopyroxenes may have been widespread, and perhaps accompanied cratonization at ?2.9 to 2.75 Ga. Such a process would considerably increase the density and stability of the continental lithosphere.
DS201709-1988
2017
Giebel, R.J., et al.Fluid mineral interaction and REE mineralization in the Palabora carbonatite complex.Goldschmidt Conference, abstract 1p.Africa, South Africacarbonatite, Palabora

Abstract: The Palabora Carbonatite Complex (PCC) in South Africa intruded at 2060 Ma into Archean basement. The tripartite pipe-like intrusion is represented by a northern and southern pyroxenite and the central Loolekop pipe. Carbonatites and phoscorites of the Loolekop pipe experienced at least 4 stages of mineralization, recrystallization and redistibution reflected by an (1) orthomagmatic, (2) late-magmatic, (3) sulphide and (4) post-magmatic phase (Giebel et al., 2017). These four stages exhibit considerable variability of REE mineralization and especially stages 2 and 4 show intense fluid-rock interaction textures. We present microtextural and compositional data on apatite and phlogopite along a 2 km depth profile through the Loolekop pipe and investigate how these data reflect fluidmineral interaction with depth during stage (2). A special focus lies on understanding the behaviour, sources and sinks of REE elements. While fluid-apatite interaction causes a dissolution of apatite coupled with a precipitation of monazite at apatite rims, the fluid-phlogopite interaction induces a chloritization of phlogopite and an occasional formation of britholite along strongly dissolved phlogopite rims. We suspect that REE are transported into the system by this late-magmatic fluid rather than being released by the dissolution of orthomagmatic REE-bearing minerals. Combining these observations with fluid inclusion textures and microthermometry, we will investigate the nature and composition of the involved fluids and will try to model REE mineralisation processes during late-magmatic fluidmineral ineraction
DS201707-1326
2017
Giebel, R.J., Gauert, C.D.K., Marks, M.A.W., Costin, G., Markl, G.Multi stage formation of REE minerals in the Palabora carbonatite complex, South Africa.American Mineralogist, Vol. 102, pp. 1218-1233.Africa, South Africacarbonatite - Palabora

Abstract: The 2060 Ma old Palabora Carbonatite Complex (PCC), South Africa, comprises diverse REE mineral assemblages formed during different stages and reflects an outstanding instance to understand the evolution of a carbonatite-related REE mineralization from orthomagmatic to late-magmatic stages and their secondary post-magmatic overprint. The 10 rare earth element minerals monazite, REE-F-carbonates (bastnäsite, parisite, synchysite), ancylite, britholite, cordylite, fergusonite, REE-Ti-betafite, and anzaite are texturally described and related to the evolutionary stages of the PCC. The identification of the latter five REE minerals during this study represents their first described occurrences in the PCC as well as in a carbonatite complex in South Africa. The variable REE mineral assemblages reflect a multi-stage origin: (1) fergusonite and REE-Ti-betafite occur as inclusions in primary magnetite. Bastnäsite is enclosed in primary calcite and dolomite. These three REE minerals are interpreted as orthomagmatic crystallization products. (2) The most common REE minerals are monazite replacing primary apatite, and britholite texturally related to the serpentinization of forsterite or the replacement of forsterite by chondrodite. Textural relationships suggest that these two REE-minerals precipitated from internally derived late-magmatic to hydrothermal fluids. Their presence seems to be locally controlled by favorable chemical conditions (e.g., presence of precursor minerals that contributed the necessary anions and/or cations for their formation). (3) Late-stage (post-magmatic) REE minerals include ancylite and cordylite replacing primary magmatic REE-Sr-carbonates, anzaite associated with the dissolution of ilmenite, and secondary REE-F-carbonates. The formation of these post-magmatic REE minerals depends on the local availability of a fluid, whose composition is at least partly controlled by the dissolution of primary minerals (e.g., REE-fluorocarbonates). This multi-stage REE mineralization reflects the interplay of magmatic differentiation, destabilization of early magmatic minerals during subsequent evolutionary stages of the carbonatitic system, and late-stage fluid-induced remobilization and re-/precipitation of precursor REE minerals. Based on our findings, the Palabora Carbonatite Complex experienced at least two successive stages of intense fluid–rock interaction.
DS201708-1649
2017
Gilika, O.Building a geometallurgical model for Orapa mine, Botswana.11th. International Kimberlite Conference, PosterAfrica, Botswanadeposit - Orapa
DS201705-0830
2017
Giovanardi, T., Girardi, V.A.V., Correia, C.T., Sinigoi, S., Tassinari, C.C.G., Mazzucchelli, M.The growth and contamination mechanism of the Cana Brava layered mafic-ultramafic complex: new field and geochemical evidences.Mineralogy and Petrology, in press available 24p.South America, BrazilGeochemistry

Abstract: The Cana Brava complex is the northernmost of three layered complexes outcropping in the Goiás state (central Brasil). New field and geochemical evidences suggest that Cana Brava underwent hyper- to subsolidus deformation during its growth, acquiring a high-temperature foliation that is generally interpreted as the result of a granulite-facies metamorphic event. The increase along the stratigraphy of the incompatible elements abundances (LREE, Rb, Ba) and of the Sr isotopic composition, coupled with a decrease in ?Nd(790), indicate that the complex was contaminated by the embedded xenoliths from the Palmeirópolis Sequence. The geochemical data suggest that the contamination occurred along the entire magma column during the crystallization of the Upper Mafic Zone, with in situ variations determined by the abundance and composition of the xenoliths. These features of the Cana Brava complex point to an extremely similarity with the Lower Sequence of the most known Niquelândia intrusion (the central of the three complexes). This, together with the evidences that the two complexes have the same age (c.a. 790 Ma) and their thickness and units decrease northwards suggests that Cana Brava and Niquelândia are part of a single giant Brasilia body grown through several melt impulses.
DS201708-1650
2017
Giuliani, A.Olivine zoning and the evolution of kimberlite systems.11th. International Kimberlite Conference, OralGlobalolivine
DS201708-1651
2017
Giuliani, A.Tracing mantle metasomatism using combined stable (S,O) and radiogenic (Sr, Nd, Hf, Pb) isotope geochemistry: case studies from mantle xenoliths of the Kimberley kimberlites.11th. International Kimberlite Conference, PosterAfrica, South Africadeposit - Kimberley Pool
DS201709-1989
2017
Giuliani, A., et al.Southwestern Africa on the burner: Pleistocene carbonatite volcanism linked to mantle upwelling in Angola. CatandaGoldschmidt Conference, abstract 1p.Africa, Angolacarbonatite, Catanda

Abstract: The origin of intraplate carbonatitic to alkaline volcanism in Africa is controversial. A tectonic control, i.e., decompression melting associated with far-field stress, is suggested by correlation with lithospheric sutures, repeated magmatic cycles in the same areas over several million years, synchronicity across the plate, and lack of clear age progression patterns. Conversely, a dominant role for mantle convection is supported by the coincidence of Cenozoic volcanism with regions of lithospheric uplift, positive free-air gravity anomalies, and slow seismic velocities. To improve constraints on the genesis of African volcanism, here we report the first radiometric and isotopic results for the Catanda complex, which hosts the only extrusive carbonatites in Angola. Apatite (U-Th-Sm)/He and phlogopite 40Ar/39Ar ages of Catanda aillikite lavas indicate eruption at ca. 500–800 ka, more than 100 m.y. after emplacement of abundant kimberlites and carbonatites in this region. The lavas share similar high-? (HIMU)–like Sr-Nd-Pb-Hf isotope compositions with other young mantle-derived volcanics from Africa (e.g., Northern Kenya Rift; Cameroon Line). The position of the Catanda complex in the Lucapa corridor, a long-lived extensional structure, suggests a possible tectonic control for the volcanism. The complex is also located on the Bié Dome, a broad region of fast Pleistocene uplift attributed to mantle upwelling. Seismic tomography models indicate convection of deep hot material beneath regions of active volcanism in Africa, including a large area encompassing Angola and northern Namibia. This is strong evidence that intraplate late Cenozoic volcanism, including the Catanda complex, resulted from the interplay between mantle convection and preexisting lithospheric heterogeneities.
DS201707-1327
2017
Giuliani, A., Soltys, A., Phillips, D., Kamenetsky, V.S., Maas, R., Goemann, K., Woodhead, J.D., Drysdale, R.N., Griffin, W.L.The final stages of kimberlite petrogenesis: petrography, mineral chemistry, melt inclusions and Sr-C-O isotope geochemistry of the Bultfontein kimberlite ( Kimberley, South Africa.Chemical Geology, Vol. 455, pp. 342-256.Africa, South Africadeposit - Bultfontein

Abstract: The petrogenesis of kimberlites is commonly obscured by interaction with hydrothermal fluids, including deuteric (late-magmatic) and/or groundwater components. To provide new constraints on the modification of kimberlite rocks during fluid interaction and the fractionation of kimberlite magmas during crystallisation, we have undertaken a detailed petrographic and geochemical study of a hypabyssal sample (BK) from the Bultfontein kimberlite (Kimberley, South Africa). Sample BK consists of abundant macrocrysts (> 1 mm) and (micro-) phenocrysts of olivine and lesser phlogopite, smaller grains of apatite, serpentinised monticellite, spinel, perovskite, phlogopite and ilmenite in a matrix of calcite, serpentine and dolomite. As in kimberlites worldwide, BK olivine grains consist of cores with variable Mg/Fe ratios, overgrown by rims that host inclusions of groundmass phases (spinel, perovskite, phlogopite) and have constant Mg/Fe, but variable Ni, Mn and Ca concentrations. Primary multiphase inclusions in the outer rims of olivine and in Fe-Ti-rich (‘MUM’) spinel are dominated by dolomite, calcite and alkali carbonates with lesser silicate and oxide minerals. Secondary inclusions in olivine host an assemblage of Na-K carbonates and chlorides. The primary inclusions are interpreted as crystallised alkali-Si-bearing Ca-Mg-rich carbonate melts, whereas secondary inclusions host Na-K-rich C-O-H-Cl fluids. In situ Sr-isotope analyses of groundmass calcite and perovskite reveal similar 87Sr/86Sr ratios to perovskite in the Bultfontein and the other Kimberley kimberlites, i.e. magmatic values. The ?18O composition of the BK bulk carbonate fraction is above the mantle range, whereas the ?13C values are similar to those of mantle-derived magmas. The occurrence of different generations of serpentine and occasional groundmass calcite with high 87Sr/86Sr, and elevated bulk carbonate ?18O values indicate that the kimberlite was overprinted by hydrothermal fluids, which probably included a significant groundwater component. Before this alteration the groundmass included calcite, monticellite, apatite and minor dolomite, phlogopite, spinel, perovskite and ilmenite. Inclusions of groundmass minerals in olivine rims and phlogopite phenocrysts show that olivine and phlogopite also belong to the magmatic assemblage. We therefore suggest that the crystallised kimberlite was produced by an alkali-bearing, phosphorus-rich, silica-dolomitic melt. The alkali-Si-bearing Ca-Mg-rich carbonate compositions of primary melt inclusions in the outer rims of olivine and in spinel grains with evolved compositions (MUM spinel) support formation of these melts after fractionation of abundant olivine, and probably other phases (e.g., ilmenite and chromite). Finally, the similarity between secondary inclusions in kimberlite olivine of this and other worldwide kimberlites and secondary inclusions in minerals of carbonatitic, mafic and felsic magmatic rocks, suggests trapping of residual Na-K-rich C-O-H-Cl fluids after groundmass crystallisation. These residual fluids may have persisted in pore spaces within the largely crystalline BK groundmass and subsequently mixed with larger volumes of external fluids, which triggered serpentine formation and localised carbonate recrystallisation.
DS201707-1328
2017
Giuliani, A.M., Tappe, S., Rooney, T.O., McCoy-West, A.J., Yaxley, G.M., Mezger, K.Editorial: the role of intraplate magmas and their inclusions in Earth's mantle evolution.Chemical Geology, Vol. 455, pp. 1-5.Mantlemagmatism

Abstract: Carbon isotope compositions and the distribution of nitrogen and hydrogen in diamonds from 18 eclogites from Nurbinskaya kimberlites were studied in situ in polished plates. Cathodoluminescence images show that most of the diamonds have complex growth structures with distinctive cores, intermediate and rim zones. In some diamonds the cores display dissolution features, and intermediate growth zones are separated from the cores by narrow rounded oscillatory zones. At least three crystals show interrupted multistage diamond growth; variations in ? ¹³C of 2–3‰ occur across the contacts between distinct zones. Generally, ?¹³C within the diamond cores varies only by 1–2‰, in rare cases up to 3.3‰. ?¹³C values are usually lower in the intermediate zones and drop further towards the rims by up to 3‰. High-resolution SIMS profiles show that variations in ?¹³C across the diamond growth zones are sharp with no evidence of diffusive relaxation.
DS201712-2686
2017
Gladkochub, D.P., Donskaya, T.V., Sklyarov, E.V., Kotov, A.B., Vladykin, N.V., Pisarevsky, S.A., Larin, A.M., Salnikova, E.B., Saveleva, V.B., Sharygin, V.V., Starikova, A.E., Tolmacheva, E.V., Velikoslavinsky, S.D., Mazukabzov, A.M., Bazarova, E.P., KovaThe unique Katugin rare metal deposit ( southern Siberia): constraints on age and genesis.Ore Geology Reviews, in press available, 18p.Russia, Siberiadeposit - Katugin

Abstract: We report new geological, mineralogical, geochemical and geochronological data about the Katugin Ta-Nb-Y-Zr (REE) deposit, which is located in the Kalar Ridge of Eastern Siberia (the southern part of the Siberian Craton). All these data support a magmatic origin of the Katugin rare-metal deposit rather than the previously proposed metasomatic fault-related origin. Our research has proved the genetic relation between ores of the Katugin deposit and granites of the Katugin complex. We have studied granites of the eastern segment of the Eastern Katugin massif, including arfvedsonite, aegirine-arfvedsonite and aegirine granites. These granites belong to the peralkaline type. They are characterized by high alkali content (up to 11.8?wt% Na2O?+?K2O), extremely high iron content (FeO?/(FeO??+?MgO)?=?0.96-1.00), very high content of most incompatible elements - Rb, Y, Zr, Hf, Ta, Nb, Th, U, REEs (except for Eu) and F, and low concentrations of CaO, MgO, P2O5, Ba, and Sr. They demonstrate negative and CHUR-close ?Nd(t) values of 0.0…?1.9. We suggest that basaltic magmas of OIB type (possibly with some the crustal contamination) represent a dominant part of the granitic source. Moreover, the fluorine-enriched fluid phases could provide an additional source of the fluorine. We conclude that most of the mineralization of the Katugin ore deposit occurred during the magmatic stage of the alkaline granitic source melt. The results of detailed mineralogical studies suggest three major types of ores in the Katugin deposit: Zr mineralization, Ta-Nb-REE mineralization and aluminum fluoride mineralization. Most of the ore minerals crystallized from the silicate melt during the magmatic stage. The accessory cryolites in granites crystallized from the magmatic silicate melt enriched in fluorine. However, cryolites in large veins and lens-like bodies crystallized in the latest stage from the fluorine enriched melt. The zircons from the ores in the aegirine-arfvedsonite granite have been dated at 2055?±?7?Ma. This age is close to the previously published 2066?±?6?Ma zircon age of the aegirine-arfvedsonite granites, suggesting that the formation of the Katugin rare-metal deposit is genetically related to the formation of peralkaline granites. We conclude that Katugin rare-metal granites are anorogenic. They can be related to a Paleoproterozoic (?2.05?Ga) mantle plume. As there is no evidence of the 2.05?Ga mantle plume in other areas of southern Siberia, we suggest that the Katugin mineralization occurred on the distant allochtonous terrane, which has been accreted to Siberian Craton later.
DS201705-0831
2017
Glas, M.Diamond Studies.lithographie.org, No. 19, pp. 36-39.TechnologyBook - review
DS201709-1990
2017
Glenn, D.R., Fu, R.R., Kehayias, P., Le Sage, D., Lima, E.A., Weiss, B.P., Walsworth, R.L.Micrometer-scale magnetic imaging of geological samples using a quantum diamond microscope. ( remnant magnetism meteorites)Geochemistry, Geophysics, Geosystems: G3, in press availableTechnologygeophsyics - magnetics

Abstract: Remanent magnetization in geological samples may record the past intensity and direction of planetary magnetic fields. Traditionally, this magnetization is analyzed through measurements of the net magnetic moment of bulk millimeter to centimeter sized samples. However, geological samples are often mineralogically and texturally heterogeneous at submillimeter scales, with only a fraction of the ferromagnetic grains carrying the remanent magnetization of interest. Therefore, characterizing this magnetization in such cases requires a technique capable of imaging magnetic fields at fine spatial scales and with high sensitivity. To address this challenge, we developed a new instrument, based on nitrogenvacancy centers in diamond, which enables direct imaging of magnetic fields due to both remanent and induced magnetization, as well as optical imaging, of room-temperature geological samples with spatial resolution approaching the optical diffraction limit. We describe the operating principles of this device, which we call the quantum diamond microscope (QDM), and report its optimized image-area-normalized magnetic field sensitivity (20 µT?µm/Hz½), spatial resolution (5 µm), and field of view (4 mm), as well as trade-offs between these parameters. We also perform an absolute magnetic field calibration for the device in different modes of operation, including three-axis (vector) and single-axis (projective) magnetic field imaging. Finally, we use the QDM to obtain magnetic images of several terrestrial and meteoritic rock samples, demonstrating its ability to resolve spatially distinct populations of ferromagnetic carriers.
DS201707-1329
2017
Goes, S., Agrusta, R., van Hunen, J., Garel, F.Subduction - transition zone interaction: a review.Geosphere, Vol. 13, 3, pp. 644-8.Mantlesubduction

Abstract: As subducting plates reach the base of the upper mantle, some appear to flatten and stagnate, while others seemingly go through unimpeded. This variable resistance to slab sinking has been proposed to affect long-term thermal and chemical mantle circulation. A review of observational constraints and dynamic models highlights that neither the increase in viscosity between upper and lower mantle (likely by a factor 20–50) nor the coincident endothermic phase transition in the main mantle silicates (with a likely Clapeyron slope of –1 to –2 MPa/K) suffice to stagnate slabs. However, together the two provide enough resistance to temporarily stagnate subducting plates, if they subduct accompanied by significant trench retreat. Older, stronger plates are more capable of inducing trench retreat, explaining why backarc spreading and flat slabs tend to be associated with old-plate subduction. Slab viscosities that are ?2 orders of magnitude higher than background mantle (effective yield stresses of 100–300 MPa) lead to similar styles of deformation as those revealed by seismic tomography and slab earthquakes. None of the current transition-zone slabs seem to have stagnated there more than 60 m.y. Since modeled slab destabilization takes more than 100 m.y., lower-mantle entry is apparently usually triggered (e.g., by changes in plate buoyancy). Many of the complex morphologies of lower-mantle slabs can be the result of sinking and subsequent deformation of originally stagnated slabs, which can retain flat morphologies in the top of the lower mantle, fold as they sink deeper, and eventually form bulky shapes in the deep mantle.
DS201704-0625
2016
Gold, D., Doden, A.G., Mbalu-Keswa, C., Tedeski, J.R., Mathur, R.The Rogue kimberlite dikes in Indiana County, Pennsylvania Part 1. unusual intrusive habit of kimberlite dikes in coal seams.Guidebook 81st annual field conference of Pennsylvania Geologists, Oct. 6-8, pp. 121-160.United States, PennsylvaniaDeposit - Rogue
DS201704-0626
2016
Gold, D., Doden, A.G., Mbalu-Keswa, C., Tedeski, J.R., Mathur, R.Supplement to guidebook: Petrography of the Tanoma and Ernest kimberlites.Guidebook 81st annual field conference of Pennsylvania Geologists, Oct. 6-8, pp. 263-268.United States, PennsylvaniaDeposit - Rogue
DS201707-1330
2017
Golovin, A.V., Sharygin, I.S., Korsakov, A.V.Origin of alkaline carbonates in kimberlites of the Siberian craton: evidence from melt inclusions in mantle olivine of the Udachnaya-East pipe.Chemical Geology, Vol. 455, pp. 357-375.Russiadeposit - Udachnaya East

Abstract: Alkaline carbonates hexagonal zemkorite (Na,K)2Ca(CO3)2 and orthorhombic shortite Na2Ca2(CO3)3 were found among groundmass minerals in kimberlites from some localities worldwide, including the unserpentinised units of the Udachnaya-East kimberlite. However, the source of alkalis and the origin of the unusual minerals in these kimberlites remain highly debatable. It is generally considered that they have hydrothermal or metasomatic origin while sodium may come from a crustal source. Orthorhombic nyerereite (Na,K)2Ca(CO3)2 and shortite were identified as daughter phases in secondary melt inclusions (MI) in olivine from the deepest mantle xenoliths (i.e., sheared peridotites) and in olivine xenocrysts derived from disintegrated mantle rocks from the Udachnaya-East pipe by Raman spectroscopy and SEM-EDS. The melt, hosted as the inclusions in olivine, was entrapped at a mantle depth. On the basis of similar mineralogy of MI to groundmass of the unserpentinised kimberlites, we suggest relation of MI to the Udachnaya kimberlite melts. The MI solidus temperature is as high as 500 °?. Generally, MI nyerereite is considered as a magmatic mineral but experiments show it to be stable at relatively low temperatures (LT) T ? 360 °?. Thus, strictly speaking, it is a subsolidus mineral formed from high-temperature (HT) (T < 800 °?) hexagonal (Na,K)2Ca(CO3)2 carbonate. Shortite is also a subsolidus mineral, which may form by several subsolidus reactions in multicomponent systems, such as kimberlites, while breakdown of the HT hexagonal phase (Na,K)2Ca(CO3,SO4)2 into Na2Ca2(CO3)3 (shortite) and K3Na(SO4)2 (aphthitalite) is the basic mechanism. The solidus temperature for the Udachnaya-East kimberlite is about 300 °? indicating that LT orthorhombic nyerereite may crystallise directly from the melt as well. Thus, (Na,K)2Ca(CO3)2 and Na2Ca2(CO3)3 carbonates in the groundmass of the unserpentinised Udachnaya-East kimberlites are of magmatic/subsolidus origin. This scenario for the origin of Na-K-Ca and Na-Ca carbonates in the Udachnaya-East kimberlites may have implications for other kimberlites elsewhere.
DS201712-2687
2016
Gonzales-Platas, J., Alvaro, M., Nestola, F., Angel, R.J. .EosFIT7-GUI: a new graphical user interface for equation of state calculations, analyses and teaching.Journal of Applied Crystallography, Vol. 49, pp. 1377-1382.Technologyanalyses

Abstract: EosFit7-GUI is a full graphical user interface designed to simplify the analysis of thermal expansion and equations of state (EoSs). The software allows users to easily perform least-squares fitting of EoS parameters to diffraction data collected as a function of varying pressure, temperature or both. It has been especially designed to allow rapid graphical evaluation of both parametric data and the EoS fitted to the data, making it useful both for data analysis and for teaching.
DS201710-2228
2017
Gonzalez, C.M., Gorczyk, W.Decarbonation in an intracratonic setting: insight from petrological- thermomechanical modeling.Journal of Geophysical Research: Solid Earth, Vol. 122, 8, pp. 5992-6013.Mantlegeothermometry

Abstract: Cratons form the stable core roots of the continental crust. Despite long-term stability, cratons have failed in the past. Cratonic destruction (e.g., North Atlantic Craton) due to chemical rejuvenation at the base of the lithosphere remains poorly constrained numerically. We use 2-D petrological-thermomechanical models to assess cratonic rifting characteristics and mantle CO2 degassing in the presence of a carbonated subcontinental lithospheric mantle (SCLM). We test two tectonothermal SCLM compositions: Archon (depleted) and Tecton (fertilized) using 2 CO2 wt % in the bulk composition to represent a metasomatized SCLM. We parameterize cratonic breakup via extensional duration (7-12 Ma; full breakup), tectonothermal age, TMoho (300-600°C), and crustal rheology. The two compositions with metasomatized SCLMs share similar rifting features and decarbonation trends during initial extension. However, we show long-term (>67 Ma) stability differences due to lithospheric density contrasts between SCLM compositions. The Tecton model shows convective removal and thinning of the metasomatized SCLM during failed rifting. The Archon composition remained stable, highlighting the primary role for SCLM density even when metasomatized at its base. In the short-term, three failed rifting characteristics emerge: failed rifting without decarbonation, failed rifting with decarbonation, and semifailed rifting with dry asthenospheric melting and decarbonation. Decarbonation trends were greatest in the failed rifts, reaching peak fluxes of 94 × 104 kg m?3. Increased TMoho did not alter the effects of rifting or decarbonation. Lastly, we show mantle regions where decarbonation, mantle melting in the presence of carbonate, and preservation of carbonated mantle occur during rifting.
DS201711-2514
2017
Gonzalez-Jimenez, J.M., Camprubi, A., Colas, V., Griffin, W.L., Proenza, J.A., O'Reilly, S.Y., Centeno-Garcia, El., Garcia-Casco, A., Belousova, E., Talavera, C., Farre-de-Pablo, J., Satsukawa, T.The recycling of chromitites in ophiolites from southwestern North America. ( Baja)Lithos, in press available, 52p.United States, Californiachromitites

Abstract: Podiform chromitites occur in mantle peridotites of the Late Triassic Puerto Nuevo Ophiolite, Baja California Sur State, Mexico. These are high-Cr chromitites [Cr# (Cr/Cr + Al atomic ratio = 0.61-0.69)] that contain a range of minor- and trace-elements and show whole-rock enrichment in IPGE (Os, Ir, Ru). That are similar to those of high-Cr ophiolitic chromitites crystallised from melts similar to high-Mg island-arc tholeiites (IAT) and boninites in supra-subduction-zone mantle wedges. Crystallisation of these chromitites from S-undersaturated melts is consistent with the presence of abundant inclusions of platinum-group minerals (PGM) such as laurite (RuS2)-erlichmanite (OsS2), osmium and irarsite (IrAsS) in chromite, that yield TMA ? TRD model ages peaking at ~ 325 Ma. Thirty-three xenocrystic zircons recovered from mineral concentrates of these chromitites yield ages (2263 ± 44 Ma to 278 ± 4 Ma) and Hf-O compositions [?Hf(t) = ? 18.7 to + 9.1 and 18O values < 12.4‰] that broadly match those of zircons reported in nearby exposed crustal blocks of southwestern North America. We interpret these chromitite zircons as remnants of partly digested continental crust or continent-derived sediments on oceanic crust delivered into the mantle via subduction. They were captured by the parental melts of the chromitites when the latter formed in a supra-subduction zone mantle wedge polluted with crustal material. In addition, the Puerto Nuevo chromites have clinopyroxene lamellae with preferred crystallographic orientation, which we interpret as evidence that chromitites have experienced high-temperature and ultra high-pressure conditions (< 12 GPa and ~ 1600 °C). We propose a tectonic scenario that involves the formation of chromitite in the supra-subduction zone mantle wedge underlying the Vizcaino intra-oceanic arc ca. 250 Ma ago, deep-mantle recycling, and subsequent diapiric exhumation in the intra-oceanic basin (the San Hipólito marginal sea) generated during an extensional stage of the Vizcaino intra-oceanic arc ca. 221 Ma ago. The TRD ages at ~ 325 Ma record a partial melting event in the mantle prior to the construction of the Vizcaino intra-oceanic arc, which is probably related to the Permian continental subduction, dated at ~ 311 Ma.
DS201706-1073
2017
Good, D.J., Cabri, L.J., Ames, D.E.PGM facies variations for Cu-PGE deposits in the Coldwell alkaline complex, Ontario, Canada.Ore Geology Reviews, in press available 36p.Canada, Ontarioalkaline rocks

Abstract: Accurate characterization of the platinum group mineral (PGM) assemblages for Cu-Ni-PGE deposits are typically constrained by sample size and the difficulty of finding statistically significant numbers of grains, which is expected given the low concentrations of platinum group elements (<2 ppm), the great variety of PGM, and the likelihood that a few large grains (>75 µm) can account for large fractions of total mass. Despite these limitations, an accurate survey of PGM from different deposit types would have significant value towards developing deposit models and respective exploration strategies. In this study, we present results for a comprehensive evaluation of PGM at four copper-PGE occurrences hosted within separate but co-genetic gabbro or troctolite intrusions in the Coldwell Alkaline Complex and confirm that accurate surveys are possible with sufficient sample material and efficient PGM concentration methods. The PGM concentration methods used include: (1) hydroseparation of sieved size fractions of pulverized material, and (2) panning of grain separates produced by electric pulse disaggregation of drill core specimens. A favourable comparison of the results has verified the reliability of each method and added confidence that the PGM assemblages identified at three of the four locations are fully characterized. Precious metal mineral (PMM) assemblages are determined for the Main zone and W Horizon at the Marathon deposit, and the main zones at each of the Geordie Lake deposit and Area 41 occurrence. A total of 10,824 PMM grains (PGE and Au-Ag) and 68 mineral species, including 16 unknown minerals, were identified, of which 768 grains and 31 species occur at the Main zone, 523 grains and 41 species at Area 41,9485 grains and 43 species at W horizon, and 56 grains and 12 species at Geordie Lake. The PMM are grouped as follows: Pd-Ge, PGE-S-As, Pt-Fe alloy, Pd-Cu-Pb-Au, Pd-Ni-S, Pd-Pt-Sn, Pt-As, Pd-As, Pd-Pt-Sb-As, Pd-Pt-Bi-Te, and Au-Ag. All of the deposits were found to contain similar proportions of Pd-Pt-Sb-As, Pd-Pt-Bi-Te and Au-Ag minerals. But the W Horizon and Area 41 are distinguished from the Marathon Main zone and Geordie Lake deposits by the presence of minerals in the PGE-S-As, Pt-Fe alloy, Pd ± Cu ± Pb ± Au and Pd-Ge groups. Taken together, the PMM assemblages for deposits in the Coldwell exhibit a strong correlation to PGE enrichment relative to the range for mantle Cu/Pd values (1000-10,000). And there is no relationship between the abundances of Pd-Pt-Bi-Te and Pd-Pt-Sb-As minerals that are commonly associated with hydrous phases, and the intensity of hydrothermal alteration. Thus minerals found only at the W Horizon and Area 41, where significant PGE upgrading has occurred, including Pt-Fe alloys, rustenburgite, marathonite, palladogermanide, unknown Rh-Ni-Fe-sulfide, Au-Pd-Cu alloy, braggite, coldwellite, laurite, zvyagintsevite, laflammeite, and unknown phases Pd5As2, Pd3As, Pd3(As,Pb,Bi) might be considered as index minerals for PGE enriched types of mineralization in the Coldwell.
DS201708-1652
2017
Goodarzi, P.Oxygen fugacity as a control on the distribution of diamond in the sub-cratonic lithospheric mantle.11th. International Kimberlite Conference, PosterMantleBlank
DS201709-1991
2017
Goodarzi, P.Y., Berry, A.J., Pearson, D.G., Yaxley, G.M., Newville, M.Garnet as a recorder of metasomatism in the sub-continental lithospheric mantle. Goldschmidt Conference, abstract 1p.Africa, Namibiadeposit , Louwerensia

Abstract: Metasomatism by fluid or melt is commonly attributed as the cause of chemical and modal heterogeneity observed in peridotite xenoliths from the sub-continental lithospheric mantle. Documented manifestations are (1) perturbation of the oxygen fugacity (fO2), which may affect the stability of carbon-bearing phases, and (2) trace-element enrichment, typified by the shape of REEN patterns. Garnet, which contains Fe2+ and Fe3+ in measurable quantities, and exhibits prominent variation in REEN patterns between samples, may record the metasomatic history of the mantle. Here we report variations of fO2 and trace element concentrations for a suite of 22 garnet-bearing peridotite xenoliths from the Louwrensia kimberlite, south-central Namibia. The xenoliths span an estimated pressure range between 2.7 and 4.5 GPa. Fe3+/?Fe of garnet was determined by Fe K-edge XANES spectroscopy. Concomitant fO2 was calculated using the oxybarometer calibration of Miller et al. [1]. The trace element concentrations of all phases were determined by LA-ICP-MS. A global dataset comprising 454 garnet REEN patterns from 19 kimberlites has been compiled. The REEN pattern of each sample was fit to orthogonal polynomial functions that parameterise the abundance, slope, quadratic curvature, and cubic curvature [2]. Quadratic and cubic curvature correlate with abundance, albeit with considerable scatter. There is, however, an absence of correlation between REEN patterns and fO2, depth, or modal abundance. This is in contrast to correlations and trends observed for basaltic melts that clearly identify petrogenetic trends. The partitioning of REEs between garnet and co-existing phases in these samples highlights pronounced trace-element disequilibrium and hence question the validity of considering garnet REEN in isolation as a means of discerning metasomatic history
DS201709-1992
2017
Goodenough, K.M., Shaw, R., Deady, E.Interaction of alkaline magmatism and carbonatites: a recipe for REE enrichment?Goldschmidt Conference, abstract 1p.Mantlecarbonatites

Abstract: The rare earth elements (REE) are critical metals that have been the subject of considerable recent research. In the published literature, REE deposits are typically divided into classes, which commonly include ‘alkaline igneous rocks’ and ‘carbonatites’ [1]. However, our recent work, carried out as part of the EURARE and HiTech AlkCarb projects, suggests that many deposits of the REE and other critical metals may be formed where late-stage carbonatites and associated fluids interact with alkaline igneous rocks. A key question is whether these carbonatites are formed by liquid immiscibility from the host alkaline magmas, or whether they are introduced from other sources. A classic example of a mineral deposit formed in this way is at Ivigtut in Greenland, where late-stage F and CO2 rich fluids interacted with alkali granitic melts to form a cryolite (Na3AlF6) deposit, with associated metasomatism and REE mobilisation. Isotopic evidence indicates that these late-stage fluids may have been carbonatite-derived [2]. Our more recent work indicates that REE enrichment in many alkaline igneous complexes may be generated by a similar mechanism. In the alkaline igneous province of NW Scotland, late-stage metasomatism by CO2-rich fluids has generated metasomatised veins with TREO up to 2 wt% [3]. Similar features are observed in the Ditra? Alkaline Igneous complex in Romania, where REE mineralisation is represented by monazite- and carbonate-rich veins cutting syenitic host rocks [4]; and at the Kizilcaören REE deposit in Turkey. This talk will provide an overview of the formation of REE mineralisation in this type of magmatic-hydrothermal system and consider future research questions.
DS201709-1993
2017
Goodenough, K.M., Wall, F., Merriman, D.The Rare Earth Elements: demand, global resources and challenges for resourcing future generations.Natural Resources Research, in press available, 16p.Globalrare earths

Abstract: The rare earth elements (REE) have attracted much attention in recent years, being viewed as critical metals because of China’s domination of their supply chain. This is despite the fact that REE enrichments are known to exist in a wide range of settings, and have been the subject of much recent exploration. Although the REE are often referred to as a single group, in practice each individual element has a specific set of end-uses, and so demand varies between them. Future demand growth to 2026 is likely to be mainly linked to the use of NdFeB magnets, particularly in hybrid and electric vehicles and wind turbines, and in erbium-doped glass fiber for communications. Supply of lanthanum and cerium is forecast to exceed demand. There are several different types of natural (primary) REE resources, including those formed by high-temperature geological processes (carbonatites, alkaline rocks, vein and skarn deposits) and those formed by low-temperature processes (placers, laterites, bauxites and ion-adsorption clays). In this paper, we consider the balance of the individual REE in each deposit type and how that matches demand, and look at some of the issues associated with developing these deposits. This assessment and overview indicate that while each type of REE deposit has different advantages and disadvantages, light rare earth-enriched ion adsorption types appear to have the best match to future REE needs. Production of REE as by-products from, for example, bauxite or phosphate, is potentially the most rapid way to produce additional REE. There are still significant technical and economic challenges to be overcome to create substantial REE supply chains outside China.
DS201706-1074
2017
Gorbachev, N.S., Shapovalov, Yu.B., Kostyuk, A.V.Experimental study of the apatite carbonate H2O system at P=0.5 Gpa and T=1200C efficiency of fluid transport in carbonatite.Doklady Earth Sciences, Vol. 473, 1, pp. 350-353.carbonatite

Abstract: This study presents geochemical data on organic-rich rock samples collected from Riphean—Lower Paleozoic strata (potential source rocks) of the southern Siberian Platform and compositional data on hydrocarbon biomarkers (steranes, terpanes, n-alkanes, 12- and 13-methylalkanes, isoprenanes) and diamondoid hyrocarbons from core samples collected from the Kulindinskaya-1 well, which was drilled by RN-Exploration in 2012 within the Katanga saddle.
DS201707-1331
2017
Gorczyk, W., Mole, D.R., Barnes, S.J.Plume lithosphere interaction at craton margins throughout Earth history.Tectonophysics, in press availableMantlecraton - plumes

Abstract: Intraplate continental magmatism represents a fundamental mechanism in Earth's magmatic, thermal, chemical and environmental evolution. It is a process intimately linked with crustal development, large-igneous provinces, metallogeny and major global environmental catastrophes. As a result, understanding the interactions of continental magmas through time is vital in understanding their effect on the planet. The interaction of mantle plumes with the lithosphere has been shown to significantly affect the location and form of continental magmatism, but only at modern mantle conditions. In this study, we perform numerical modelling for Late Archean (1600 °C), Paleoproterozoic (1550 °C), Meso-Neoproteroic (1500 °C) and Phanerozoic (1450 °C) mantle potential temperatures (Tp) to assess the time-space magmatic effects of ambient-mantle- and plume- lithosphere interaction over Earth's thermal history. Within these experiments, we impinge a mantle plume, with a time-appropriate Tp, onto a ‘step-like’ lithosphere, to evaluate the effect of craton margins on continental magmatism through time. The results of this modelling demonstrate that lithospheric architecture controls the volume and location of continental magmatism throughout Earth history, irrespective of ambient mantle or plume Tp. In all plume models, mantle starting plumes (diameter 300 km) impinge on the base of the lithosphere, and spread laterally over > 1600 km, flowing into the shallowest mantle, and producing the highest volume magmas. In ambient-mantle only models, Archean and Paleoproterozoic Tp values yield significant sub-lithospheric melt volumes, resulting in ‘passive’ geodynamic emplacement of basaltic magmatic provinces, whereas no melts are extracted at > 100 km for Meso-Neoproterozoic and Phanerozoic Tp. This indicates a major transition in non-subduction related continental magmatism from plume and ambient mantle to a plume-dominated source around the Mesoproterozoic. While the experiments presented here show the variation in plume-lithosphere interaction through time, the consistency in melt localisation indicates the lithosphere has been a first-order control on continental magmatism since its establishment in the Mesoarchean.
DS201706-1075
2017
Gordadze, G.N., Kerimov, V.Yu., Gaiduk, A.V., Giruts, M.V., Lobusev, M.A., Serov, S.G., Kuznetsov, N.B., Romanyuk, T.V.Hydrocarbon biomarkers and diamondoid hydrocarbons from Late Precambrian and Lower Cambrian rocks of the Katanga Saddle ( Siberian Platform).Geochemistry International, Vol. 55, 4, pp. 360-366.Russia, Siberiadiamondoid

Abstract: A broad suite of geological materials were studied a using a handheld laser-induced breakdown spectroscopy (LIBS) instrument. Because LIBS is simultaneously sensitive to all elements, the full broadband emission spectrum recorded from a single laser shot provides a ‘chemical fingerprint’ of any material - solid, liquid or gas. The distinguishing chemical characteristics of the samples analysed were identified through principal component analysis (PCA), which demonstrates how this technique for statistical analysis can be used to identify spectral differences between similar sample types based on minor and trace constituents. Partial least squares discriminant analysis (PLSDA) was used to distinguish and classify the materials, with excellent discrimination achieved for all sample types. This study illustrates through four selected examples involving carbonate minerals and rocks, the oxide mineral pair columbite-tantalite, the silicate mineral garnet and native gold how portable, handheld LIBS analysers can be used as a tool for real-time chemical analysis under simulated field conditions for element or mineral identification plus such applications as stratigraphic correlation, provenance determination and natural resources exploration.
DS201705-0832
2017
Goussi Ngalamo, J.F., Bisso, D., Abdelsalam, M.G., Atekwana, E.A., Katumwehe, A.B., Ekodeck, G.E.Geophysical imaging of metacratonization in the northern edge of the Congo craton in Cameroon.Journal of African Earth Sciences, Vol. 129, pp. 94-107.Africa, CameroonCraton, Congo

Abstract: We used the World Gravity Map (WGM 2012) data to investigate the Archean Congo craton and the Oubanguides orogenic belt in Cameroon. The Oubanguides orogenic belt constitutes, from northwest to southeast, the Neoproterozoic West Cameroon domain, the Paleoproterozoic-Neoproterozoic Adamawa-Yade domain, and the dominantly Neoproterozoic Yaoundé domain (the crustal expression of the suture zone between the Congo craton and the orogenic terranes). We analyzed the WGM 2012 data to identify different gravity anomalies. We also applied the two-dimensional (2D) radially-averaged power spectral analysis to the WGM 2012 data to estimate the Moho depth. Additionally, we developed a 2D forward gravity model along a Nsbnd S profile to image the lithospheric structure of the Precambrian entities. We found that: (1) the Congo craton, the Yaoundé domain, the southeastern part of the West Cameroon domain, and the northern part of the Adamawa-Yade domain are characterized by low gravity anomaly. (2) the southern part of the Adamawa-Yade domain is marked by a pronounced E-W trending high gravity anomaly. (3) the crust is thicker beneath the Congo craton, the Yaoundé domain and the southern part of the Adamawa-Yade domain. (4) the presence of a denser lower crust material beneath the southern part of the Adamawa-Yade domain. We propose that this denser crustal material is an under-thrusted portion of the Congo craton that has been densified through metacratonization processes that accompanied collision between the craton and the orogenic terranes. This is in good agreement with geological and geochemical observations indicating that the northern edge of the Congo craton and the Adamawa-Yade domain had undergone metacratonization during the Neoproterozoic. Our suggestion is also in good agreement with observations which show that the margins of many cratons worldwide have been decratonized due to subduction processes. Our work highlights the importance of potential field geophysical data in mapping the metacratonized margins of cratons.
DS201708-1653
2017
Greaney, A.Chalcophile elements in the mantle.11th. International Kimberlite Conference, PosterMantlechalcophile
DS201710-2229
2017
Greber, N.Plate tectonics started at least 3.5 billion years ago.Science News, Sept. 21, 1p.Mantletitanium, Plate Tectonics

Abstract: Plate tectonics may have gotten a pretty early start in Earth’s history. Most estimates put the onset of when the large plates that make up the planet’s outer crust began shifting at around 3 billion years ago. But a new study in the Sept. 22 Science that analyzes titanium in continental rocks asserts that plate tectonics began 500 million years earlier. Nicolas Greber, now at the University of Geneva, and colleagues suggest that previous studies got it wrong because researchers relied on chemical analyses of silicon dioxide in shales, sedimentary rocks that bear the detritus of a variety of continental rocks. These rocks’ silicon dioxide composition can give researchers an idea of when continental rocks began to diverge in makeup from oceanic rocks as a result of plate tectonics.But weathering can wreak havoc on the chemical makeup of shales. To get around that problem, Greber’s team turned to a new tool: the ratios of two titanium isotopes, forms of the same element that have different masses. The proportion of titanium isotopes in the rocks is a useful stand-in for the difference in silicon dioxide concentration between continental and oceanic rocks, and isn’t so easily altered by weathering. Those data helped the team estimate that continental rocks — and therefore plate tectonics — were already going strong by 3.5 billion years ago.
DS201704-0627
2017
Greig, J., Besserer, D., Raffle, K.Exploring forgotten diamond-bearing ground in the North Slave Craton. Muskox and JerichoVancouver Kimberlite Cluster, Apr. 5, 1p. AbstractCanada, NunavutDeposit - Jericho
DS201708-1654
2017
Gress, M.Three phases of diamond growth spanning > 2.0 Ga beneath Letlhakane established by Re-Os and Sm-Nd systematics of individual eclogitic sulphide, garnet and clinopyroxene inclusions.11th. International Kimberlite Conference, OralAfrica, Botswanadeposit - Letlhakane

Abstract: The diamondiferous Letlhakane kimberlites are part of the Orapa kimberlite cluster (˜ 93.1 Ma) in north-eastern Botswana, located on the edge of the Zimbabwe Craton, close to the Proterozoic Magondi Mobile Belt. Here we report the first Re-Os ages of six individual eclogitic sulphide inclusions (3.0 to 35.7?g) from Letlhakane diamonds along with their rhenium, osmium, iridium and platinum concentrations, and carbon isotope, nitrogen content and N-aggregation data from the corresponding growth zones of the host diamonds. For the first time, Re-Os data will be compared to Sm-Nd ages of individual eclogitic silicate inclusions recovered from the same diamonds using a Triton Plus equipped with four 1013? amplifiers. The analysed inclusion set currently encompasses pairs of individual sulphides from two diamonds (LK040 sf4 & 5, LK113 sf1 & 2) and two sulphide inclusions from separate diamonds (LK048, LK362). Ongoing work will determine the Sm-Nd ages and element composition of multiple individual eclogitic garnets (LK113/LK362, n=4) and an eclogitic clinopyroxene (LK040) inclusion. TMA ages of the six sulphides range from 1.06 to 2.38 Ga (± 0.1 to 0.54 Ga) with Re and Os contents between 7 and 68 ppb and 0.03 and 0.3 ppb, respectively. The host diamond growth zones have low nitrogen abundances (21 to 43 ppm N) and high N-aggregation (53 to 90% IaB). Carbon isotope data suggests the involvement of crustal carbon (?13C between -19.3 to -22.7 ± 0.2 per mill) during diamond precipitation. Cathodoluminescence imaging of central plates from LK040 and LK113 displays homogenous internal structure with no distinct zonation. The two sulphide inclusions from LK040 define an 'isochron' of 0.92 ± 0.23 Ga (2SD) with initial 187Os/188Os = 1.31 ± 0.24. Sulphides from LK113 have clear imposed diamond morphology and indicate diamond formation at 0.93 ± 0.36 Ga (2SD) with initial 187Os/188Os = 0.69 ± 0.44. The variation in the initial 187Os/188Os does not justify including these inclusions (or any from other diamonds) on the same isochron and implies an extremely heterogeneous diamond crystallisation environment that incorporated recycled Os. C1-normalized osmium, iridium and platinum (PGE) compositions from the analysed sulphide inclusions display enrichment in Ir (3.4 to 33) and Pt (2.3 to 28.1) in comparison to eclogitic xenolith data from Orapa that are depleted relative to chondrite. The Re-Os isochrons determined in this study are within error of previously reported ages from the adjacent (˜40km) Orapa diamond mine (1.0 to 2.9 Ga) based on sulphide inclusions and a multi-point 990 ± 50 Ma (2SD) isochron for composite (n=730) silicate inclusions. Together with additional new Sm-Nd isochron age determinations from individual silicate inclusions from Letlhakane (2.3 ± 0.02 (n = 3); 1.0 ± 0.14 (n = 4) and 0.25 ± 0.04 Ga (n = 3), all 2SE) these data suggest a phase of Mesoproterozoic diamond formation as well as Neoarchean/Paleoproterozoic and Mesozoic diamond growth, in punctuated events spanning >2.0 Ga.
DS201708-1655
2017
Gress, M.Variation in diamond growth events recorded in Botswanan diamonds.11th. International Kimberlite Conference, PosterAfrica, Botswanadiamond morphology
DS201705-0833
2017
Gress, M.U., Pearson, D.G., Timmerman, S., Chinn, I.L., Koornneef, J., Davies, G.R.Diamond growth beneath Letlhakane established by Re-Os and Sm-Nd systematics of individual eclogitic sulphide, garnet and clinopyroxene inclusions.European Geosciences Union General Assembly 2017, Vienna April 23-28, 1p. 5540 AbstractAfrica, BotswanaDeposit - Letlhakane

Abstract: The diamondiferous Letlhakane kimberlites are part of the Orapa kimberlite cluster (˜ 93.1 Ma) in north-eastern Botswana, located on the edge of the Zimbabwe Craton, close to the Proterozoic Magondi Mobile Belt. Here we report the first Re-Os ages of six individual eclogitic sulphide inclusions (3.0 to 35.7?g) from Letlhakane diamonds along with their rhenium, osmium, iridium and platinum concentrations, and carbon isotope, nitrogen content and N-aggregation data from the corresponding growth zones of the host diamonds. For the first time, Re-Os data will be compared to Sm-Nd ages of individual eclogitic silicate inclusions recovered from the same diamonds using a Triton Plus equipped with four 1013? amplifiers. The analysed inclusion set currently encompasses pairs of individual sulphides from two diamonds (LK040 sf4 & 5, LK113 sf1 & 2) and two sulphide inclusions from separate diamonds (LK048, LK362). Ongoing work will determine the Sm-Nd ages and element composition of multiple individual eclogitic garnets (LK113/LK362, n=4) and an eclogitic clinopyroxene (LK040) inclusion. TMA ages of the six sulphides range from 1.06 to 2.38 Ga (± 0.1 to 0.54 Ga) with Re and Os contents between 7 and 68 ppb and 0.03 and 0.3 ppb, respectively. The host diamond growth zones have low nitrogen abundances (21 to 43 ppm N) and high N-aggregation (53 to 90% IaB). Carbon isotope data suggests the involvement of crustal carbon (?13C between -19.3 to -22.7 ± 0.2 per mill) during diamond precipitation. Cathodoluminescence imaging of central plates from LK040 and LK113 displays homogenous internal structure with no distinct zonation. The two sulphide inclusions from LK040 define an 'isochron' of 0.92 ± 0.23 Ga (2SD) with initial 187Os/188Os = 1.31 ± 0.24. Sulphides from LK113 have clear imposed diamond morphology and indicate diamond formation at 0.93 ± 0.36 Ga (2SD) with initial 187Os/188Os = 0.69 ± 0.44. The variation in the initial 187Os/188Os does not justify including these inclusions (or any from other diamonds) on the same isochron and implies an extremely heterogeneous diamond crystallisation environment that incorporated recycled Os. C1-normalized osmium, iridium and platinum (PGE) compositions from the analysed sulphide inclusions display enrichment in Ir (3.4 to 33) and Pt (2.3 to 28.1) in comparison to eclogitic xenolith data from Orapa that are depleted relative to chondrite. The Re-Os isochrons determined in this study are within error of previously reported ages from the adjacent (˜40km) Orapa diamond mine (1.0 to 2.9 Ga) based on sulphide inclusions and a multi-point 990 ± 50 Ma (2SD) isochron for composite (n=730) silicate inclusions. Together with additional new Sm-Nd isochron age determinations from individual silicate inclusions from Letlhakane (2.3 ± 0.02 (n = 3); 1.0 ± 0.14 (n = 4) and 0.25 ± 0.04 Ga (n = 3), all 2SE) these data suggest a phase of Mesoproterozoic diamond formation as well as Neoarchean/Paleoproterozoic and Mesozoic diamond growth, in punctuated events spanning >2.0 Ga.
DS201708-1656
2017
Griffin, W.Super-reducing conditions in ancient and modern volcanic systems: implications for the carbon budget of the deep lithosphere.11th. International Kimberlite Conference, OralLithosphereCarbon
DS201708-1658
2017
Grutter, H.Tracing kimberlitic indicators to their kimberlite source at Chidliak, Nunavut, Canada, re-visited: the unexpected accuracy of a simplified Mahalanobis-distance approach.11th. International Kimberlite Conference, OralCanada, Nunavut, Baffin IslandDeposit - Chidliak
DS201708-1659
2017
Grutter, H.Discrete Al-Ca-Ti metasomatism at 53kbar in chromite+garnet+diamond peridotites from Newlands kimberlite field, South Africa.11th. International Kimberlite Conference, PosterAfrica, South Africadeposit - Newslands
DS201708-1660
2017
Gu, T.1aB diamond and its geological implications.11th. International Kimberlite Conference, PosterAfrica, Botswanadeposit - Karowe
DS201709-1994
2017
Guarino, V., Wu, F-Y., Melluso, L., de Barros Gomes, C., Tassinari, C.C.G., Ruberti, E., Brilli, M.U Pb ages, geochemistry, C-O-Nd-Sr-Hf isotopes and petrogeneis of the Catalao II carbonatitic complex ( Alto Paranaiba igneous province, Brazil): implucations for regional scale heterogeneities in the Brazilian carbonatite associations.International Journal of Earth Sciences, Vol. 106, 6, pp. 1963-1989.South America, Brazilcarbonatite - Catalao II

Abstract: The Catalão II carbonatitic complex is part of the Alto Paranaíba Igneous Province (APIP), central Brazil, close to the Catalão I complex. Drill-hole sampling and detailed mineralogical and geochemical study point out the existence of ultramafic lamprophyres (phlogopite-picrites), calciocarbonatites, ferrocarbonatites, magnetitites, apatitites, phlogopitites and fenites, most of them of cumulitic origin. U–Pb data have constrained the age of Catalão I carbonatitic complex between 78 ± 1 and 81 ± 4 Ma. The initial strontium, neodymium and hafnium isotopic data of Catalão II (87Sr/86Sri= 0.70503–0.70599; ?Ndi= ?6.8 to ?4.7; 176Hf/177Hf = 0.28248–0.28249; ?Hfi= ?10.33 to ?10.8) are similar to the isotopic composition of the Catalão I complex and fall within the field of APIP kimberlites, kamafugites and phlogopite-picrites, indicating the provenance from an old lithospheric mantle source. Carbon isotopic data for Catalão II carbonatites (?13C = ?6.35 to ?5.68 ‰) confirm the mantle origin of the carbon for these rocks. The origin of Catalão II cumulitic rocks is thought to be caused by differential settling of the heavy phases (magnetite, apatite, pyrochlore and sulphides) in a magma chamber repeatedly filled by carbonatitic/ferrocarbonatitic liquids (s.l.). The Sr–Nd isotopic composition of the Catalão II rocks matches those of APIP rocks and is markedly different from the isotopic features of alkaline-carbonatitic complexes in the southernmost Brazil. The differences are also observed in the lithologies and the magmatic affinity of the igneous rocks found in the two areas, thus demonstrating the existence of regional-scale heterogeneity in the mantle sources underneath the Brazilian platform.
DS201707-1332
2016
Guowu, L., Guangming, Y., Fude, L., Ming, X., Xiangkun, G., Baoming, P., Fourestier, J.Fluorcalciopyrochlore, a new mineral species from Bayan Obo, inner Mongolia, P.R. China.The Canadian Mineralogist, Vol. 54, pp. 1285-1291.China, Mongoliacarbonatite - Bayan Obo

Abstract: Fluorcalciopyrochlore, ideally (Ca,Na)2Nb2O6F, cubic, is a new mineral species (IMA2013-055) occurring in the Bayan Obo Fe-Nb-REE deposit, Inner Mongolia, People's Republic of China. The mineral is found in a dolomite-type niobium rare-earth ore deposit. Associated minerals are dolomite, aegirine, riebeckite, diopside, fluorite, baryte, phlogopite, britholite-(Ce), bastnäsite-(Ce), zircon, magnetite, pyrite, fersmite, columbite-(Fe), monazite-(Ce), rutile, and others. Crystals mostly form as octahedra {111}, dodecahedra {110}, and cubes {100}, or combinations thereof, and generally range in size from 0.01 to 0.3 mm. It is brownish-yellow to reddish-orange in color with a light yellow streak. Crystals of fluorcalciopyrochlore are translucent to transparent with an adamantine to greasy luster on fractured surfaces. It has a conchoidal fracture. No parting or cleavage was observed. The Mohs hardness is 5, and the calculated density is 4.34(1) g/cm3. The empirical formula is (Ca1.14Na0.74Ce0.06Sr0.03Th0.01Fe0.01Y0.01La0.01Nd0.01)?2.02(Nb1.68Ti0.29Zr0.02Sn0.01)?2.00O6.00(F0.92O0.08)?1.00 on the basis of 7(O,F) anions pfu. The simplified formula is (Ca,Na)2Nb2O6F. The strongest four reflections in the X-ray powder-diffraction pattern [d in Å (I) hkl] are: 6.040 (9) 1 1 1, 3.017 (100) 2 2 2, 2.613 (17) 0 0 4, 1.843 (29) 0 4 4, and 1.571 (15) 2 2 6. The unit-cell parameters are a 10.4164(9) Å, V 1130.2(2) Å3, Z = 8. The structure was solved and refined in space group FdEmbedded Image m with R = 0.05. The type material is deposited in the Geological Museum of China, Beijing, People's Republic of China, catalogue number M12182.
DS201708-1661
2017
Gurney, J.J.Multiple phases of mantle metasomatism revealed by x-ray CT scanning of southern african Diamondiferous eclogites.11th. International Kimberlite Conference, OralAfrica, Southen Africametasomatism

Abstract: In this study, a private collection of diamondiferous eclogite xenoliths has been made available for non-destructive investigation. All samples have at least one diamond visible. The samples are predominantly sourced from the Excelsior and Newlands mines (South Africa), with additional samples from Roberts Victor mine (South Africa) and Orapa (Botswana). 3D volume models of the samples were created using X-ray tomography. The 3D images reveal abundant secondary veining that is clearly younger than the eclogite. Diamonds are located in fluid pathways and occur in both altered garnet and altered clinopyroxene. Most of the veining is unrelated to the spatial positioning of diamond in the samples. In some instances, early veining has annealed or partially annealed, suggesting a range in timing of at least some of the several metasomatic events that have affected the rock. Importantly, in the most graphic examples, a clear distinction can be seen between diamond-bearing and non-diamond-bearing veins, even where sulphide is present in abundance in the non-diamond-bearing veins. The amount of diamond detected in the xenoliths varies from a single crystal to well over 50 diamonds forming more than 9% of the rock. This extreme value contrasts with the diamond recovery from currently viable diamond mines of less than 2ppm or 0.0002%. The morphology of the diamonds includes step-faced flat-faced octahedra, single crystals and aggregates. This is particularly a feature of diamonds in the Excelsior specimens. In the samples from Newlands and Orapa, in contrast, diamond surfaces reflect resorption processes such as rounding and corrosion of the diamonds. The following conclusions can be drawn from this study: Diamonds in this collection, sourced from within the Kalahari craton, appear to have formed by a metasomatic process during which fluids infiltrated pre-existing mantle-derived eclogite; Several metasomatic events have occurred during the residence of the eclogite in the mantle; Some of these metasomatic events have been diamond-friendly, whilst others have been diamond-neutral or diamond-destructive; Diamond can be present at very high concentrations along particular metasomatic fluid pathways in eclogitic mantle rocks; The absolute timing of diamond formation is still to be determined.
DS201708-1662
2017
Haggerty, S.Relation between micro- and macro-diamonds: myth, myopia or both?11th. International Kimberlite Conference, PosterTechnologymicrodiamonds
DS201701-0013
2016
Haggerty, S.E.Kimberlite discoveries in NW Liberia: tropical exploration & preliminary results.Journal of Geochemical Exploration, Vol. 173, pp. 99-109.Africa, LiberiaKimberlite

Abstract: This report is brief in context and rich in unexpected discovery. With > 2 km of erosion, kimberlite models predict the near-complete removal of pipes with exposures to the pipe-root-zones of dikes. Exploration in NW Liberia has, indeed, uncovered eight kimberlite dikes (~ 10 m wide) but also an en echelon pipe, comparable in size to the Kimberley pipe and De Beers' pipe in South Africa. Discoveries are in a narrow 200-300 m wide valley of extraordinary thick bush, undergrowth, and organic overburden. Ilmenite and co-existing leucoxene were used as diagnostic tracers for detecting hard rock kimberlite in this tropical terrane. Micro-diamonds show that the redox state of ilmenite is a potentially useful proxy as an index for macro-diamond preservation. The tectonic control of kimberlites is complex, with diverse lithologies. Discoveries include a well-defined regional trend for kimberlite dikes along paleo-fracture zones, Precambrian in age (Liberia Trend), coupled with kimberlite dikes on the craton that are traced to Mesozoic oceanic transform faults (the Sierra Leone Trend). Although long predicted, this is the first report of kimberlite dike-trends in Liberia that are similar in orientation to those in Sierra Leone. An explosive blow on a Liberia-Trend dike demonstrates a similarity to the dynamics attendant in rich (50-500 cpht) diamond-bearing dikes in Sierra Leone, and in South Africa of comparable age. The potentially high grade dikes, along with the pipe (~ 500 × 50 m), now more reasonably accounts for the enormous number of alluvial diamonds (blood and non-conflict), recovered over more than seven decades, downstream from the discovery cluster. A neglected region since the classic work by Bardet (1974), and with few contributions on Liberia since then, an update is considered timely, particularly in the context of discoveries of diamond-bearing kimberlite.
DS201709-1995
2017
Haggerty, S.E.Carbonado Diamond: a review of properties and origin.Gems & Gemology, Vol. 53, 2, summer, pp. 180-188.South America, Brazil, Africa, Central African Republiccarbonado

Abstract: Carbonado diamond is found only in Brazil and the Central African Republic. These unusual diamond aggregates are strongly bonded and porous, with melt-like glassy patinas unlike any conventional diamond from kimberlites-lamproites, crustal collisional settings, or meteorite impact. Nearly two centuries after carbonado's discovery, a primary host rock compatible with the origin of conventional diamond at high temperatures and pressures has yet to be identified. Models for its genesis are far-reaching and range from terrestrial subduction to cosmic sources. Copyright of Gems & Gemology is the property of Gemological Institute of America and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.
DS201711-2515
2017
Haggerty, S.E.Majorite-indicative ultradeep (>300km) xenoliths with spinel associations from the Jagersfontein kimberlite, South Africa.South African Journal of Geology, Vol. 120, 1, pp. 1-20.Africa, South Africadeposit - Jagersfontein

Abstract: Our earlier studies continued in a diligent search for rare ultradeep xenoliths in the kimberlite diatreme at Jagersfontein. The search has met with moderate success insofar as 20 majorite-bearing (decomposed to *gt + lamellar px) xenoliths are identified. Discrete gts (1 to 2 cm), gt-rich layers (2 to 3 cm) in lherzolites, and rare megacrystic gts (>3 cm) from xenoliths characterize the ultradeep suite. Pyroxene lamellae are crystallographically controlled along {111} gt planes, but px may also be prismatic, lensoidal, coarsely graphic, or annular to gt; jigsaw, rather than 120° dihedral textures, are typical. Gt ranges from Pyr68-74 mole% and CaO - Cr2O3 relations, with two exceptions, are distinctly lherzolitic. Cpx37-46 = Wo mole%, Jd 3-19 mole%, with 0.4 to 2.4 wt% Cr2O3; opx = 92 to 95 mole% en, and ol averages 92.5 mole% with maximum wt% 0.1 CaO, 0.4 NiO, and 0.1 Cr2 O3. A new class of 10 ultradeep xenoliths has lamellar spinel (Cr/Cr + Al = 0.74; Mg/Mg + Fe = 0.58) in addition to cpx with gt >3wt% Cr2O3 (c.f. 0.5 to 1.5 for sp-free types). Five samples are texturally linked but are compositional outliers to the central body of data: two are sp hosts (Cr# 0.69, Mg# 0.76) and (Cr# 0.74, Mg# 0.57) to gt (Pyr72) + cpx (Jd14); one is a gt megacryst (Pyr80) with sp (Cr# 57, Mg# 69); and the remaining two are unusually rich in chromium with gt = 7.3 to 8.2 wt% Cr2O3, rimmed by cpx (2.3 to 3.3 wt% Cr2O3). In addition, there are 17 xenoliths with compositional affinities to the ultradeep suite but lacking the texturally diagnostic lamellar intergrowths of cpx in gt are possibly completely equilibrated to gt + irregular cpx. Results from the new collection substantiate our earlier conclusions that the mantle was sampled by the Jagersfontein kimberlite from the lower lithosphere (250 to 350 km) and the transition zone (435 km) with diagnostic high P-T majorite in lherzolite that decomposed to gt + px at one or more interruptive stations (e.g. lithosphere-asthenosphere boundary), and at one or another time, en route to the surface. Homogeneous majorite occurs as diamond inclusions at Jagersfontein but these are eclogitic, leading to the proposition that the source region in the asthenosphere was an unassimilated mixture of lherzolite and eclogite in the Mid-Cretaceous at the time of kimberlite sampling. Important questions arise: Is majorite primordial; did majorite form exclusively from the transition of pyroxene; or did subsequent dissolution into coexisting garnet take place? Why has majorite not been identified in eclogite, nor diamonds of lherzolitic affinity? Does the formation of majorite and the crystallization of encapsulating diamond imply distinct high P-T events?
DS201703-0405
2017
Haissen, F., Cambeses, A., Montero, P., Bea, F., Dilek, Y., Mouttaqi, A.The Archean kaisilite nepheline syenites of the Awsard intrusive massif ( Reguibat Shield, West African craton, Morocco) and its relationship to alkaline magmatism of Africa.Journal of African Earth Sciences, Vol. 127, pp. 16-50.Africa, MoroccoCraton - magmatism
DS201704-0628
2017
Hannington, M., Petersen, S., Kratschell, A.Subsea mining moves closer to shore.Nature Geoscience, Vol. 10, 3, pp. 158-159.TechnologyMining - seabed

Abstract: Mining the deep seabed is fraught with challenges. Untapped mineral potential under the shallow, more accessible continental shelf could add a new dimension to offshore mining and help meet future mineral demand.
DS201708-1663
2017
Hardman, M.Robust new statistical approaches to the discrimination of mantle- and crust-derived low -Cr garnets using major and trace element data.11th. International Kimberlite Conference, OralMantlegarnets
DS201706-1076
2017
Harmon, R.S., Hark, R.R., Throckmorton, C.S., Rankey, E.C., Wise, M.A., Somers, A.M., Collins, L.M.Geochemical fingerprinting by handheld laser-induced breakdown spectroscopy. (LIBS)Geostandards and Geoanalytical Research, in press availableTechnologyspectroscopy

Abstract: A broad suite of geological materials were studied a using a handheld laser-induced breakdown spectroscopy (LIBS) instrument. Because LIBS is simultaneously sensitive to all elements, the full broadband emission spectrum recorded from a single laser shot provides a ‘chemical fingerprint’ of any material - solid, liquid or gas. The distinguishing chemical characteristics of the samples analysed were identified through principal component analysis (PCA), which demonstrates how this technique for statistical analysis can be used to identify spectral differences between similar sample types based on minor and trace constituents. Partial least squares discriminant analysis (PLSDA) was used to distinguish and classify the materials, with excellent discrimination achieved for all sample types. This study illustrates through four selected examples involving carbonate minerals and rocks, the oxide mineral pair columbite-tantalite, the silicate mineral garnet and native gold how portable, handheld LIBS analysers can be used as a tool for real-time chemical analysis under simulated field conditions for element or mineral identification plus such applications as stratigraphic correlation, provenance determination and natural resources exploration.
DS201708-1664
2017
Harris, G.Mantle composition, age and geotherm beneath the Darby kimberlite field, west central Rae craton.11th. International Kimberlite Conference, PosterCanada, Yukondeposit - Darby

Abstract: The Rae craton in Canada’s North contains several kimberlite fields and has been the subject of episodic diamond exploration, with proven diamond-bearing deposits. However, relatively little is known about the deep mantle lithosphere that underpins the architecturally complex crust of this craton. The Darby Kimberlite field, located ~120 km southwest of the community of Kugaaruk, Nunavut, provides an opportunity to study the mantle beneath the western portion of the central Rae craton via mantle xenoliths. The Darby kimberlite field contains eight kimberlite bodies erupted at circa 540 Ma. Five of the kimberlites have proven to be diamond-bearing including the 12 hectare ‘Iceberg’ kimberlite. Mantle xenoliths were collected from kimberlite float above proven kimberlite targets across the property. Most of the surface kimberlite is highly altered and hence the peridotite xenoliths they contain are generally serpentinized or deeply-weathered. Eclogites/pyroxenites were recovered from each locality visited. A total of 33 mantle xenoliths exceeding one cm in maximum dimension (14 peridotites and 19 “eclogites”) were selected for mineral chemistry and bulk analysis. Four peridotite xenoliths contain fresh garnet. Clinopyroxenes from kimberlite heavy mineral concentrate provide a preliminary geotherm for the West Central Rae lithosphere and indicate a lithospheric depth of ~200 km. Using Ni-in-garnet temperatures, four garnet peridotites and 49 peridotitic garnets from concentrate yield two distinct mantle sampling depths. Whole rock Re-depletion ages for Darby peridotites range from Mesoarchean to Paleoproterozoic. Archean whole rock TMA ages for the eclogites/pyroxenites are consistent with a Mesoarchean age for the western Central Rae lithosphere, older than the lithosphere beneath the Repulse Bay block to the East. The anomalously high abundance of eclogite/pyroxenite xenoliths and garnet concentrate found in the Darby field (58 % of xenoliths and 82 % of concentrate) is at odds with the abundance of eclogite thought to be present in cratonic lithospheric mantle from xenocryst studies (~one to five %). The high abundance may be related to the proximity of the field to the proposed suture between the Committee Block and the Queen Maud Block to the far West of the Rae craton
DS201712-2688
2017
Harris, G.A., Pearson, D.G., Liu, J., Hardman, M.F., Kelsch, D.Mantle composition, age and geotherm beneath the Darby kimberlite field, west central Rae craton.45th. Annual Yellowknife Geoscience Forum, p. 33 abstractCanada, Northwest Territoriesdeposit - Darby

Abstract: New geological and geophysical research on Canada’s Rae craton are providing an increasingly good baseline for diamond exploration. This study uses mantle xenoliths and xenocrysts from the Darby property, located ~200 km southwest of the community of Kugaaruk, Nunavut, to provide new information on the lithospheric mantle and diamond potential of the western portion of the central Rae. Peridotite xenoliths containing enough fresh olivine have a median Mg# value of 92.5, indistinguishable from the median value of 92.6 typical of cratonic peridotites world-wide. Only of the 14 peridotitic xenoliths contain fresh garnet. Of these, garnet in one sample is classified as harzburgitic (G10), giving a minimum pressure of 4.7 GPa using the P38 geobarometer (38 mW/m2 model geothermal gradient), while garnets from three peridotites are classified as lherzolitic (G9). 52 garnets picked from concentrate have lherzolitic affinities. Lherzolitic diopsides from kimberlite heavy mineral concentrate yield a lithospheric thickness of ~ 200 km. The four garnet peridotite xenoliths and 49 peridotitic garnets from concentrate yield two distinct modes in mantle sampling depths using Ni thermometry, when projected to the Cpx geotherm. A cluster of samples from the higher Ca/Cr lherzolitic garnets equilibrated at 765 to 920 °C with a group of peridotitic garnets (50 % of xenoliths and 28 % of concentrate) from the lower Ca/Cr lherzolitic garnets with anomalously high Ti concentrations yielding super-adiabatic TNi values The aluminum-in-olivine thermometer applied to olivines filtered to be “garnet facies yielded a mantle sampling portion of the mantle cargo from the diamond stability field. A suite of pyroxenitic xenoliths are a feature of each Darby kimberlite target. New screening techniques indicate that these rocks likely originate close to the crust mantle boundary. Osmium isotope analyses of the Darby peridotites reveal whole-rock Re-depletion ages ranging from Mesoarchean to Paleoproterozoic. The pyroxenite xenoliths have very radiogenic Os isotope compositions and provide the first age information from pyroxenites/“eclogites” beneath the Rae craton. Their resulting Archean whole rock TMA ages are consistent with a Mesoarchean age of the western Central Rae lithosphere older than the lithosphere beneath the Repulse Bay block in the East section of the Rae craton (Liu et al., 2016. Precambrian Research 272). The highly depleted olivine compositions, thick cold lithosphere, and Archean ages of the Darby peridotite xenoliths clearly indicate the presence of 200 km thick cold cratonic lithospheric mantle beneath the western segment of the central Rae craton circa 540 Ma. The Archean model ages of most of the pyroxenites support this, notwithstanding the fact that some of these rocks could be sampling either crust or mantle lithologies very close to the crust-mantle boundary. Mantle sampling took place well into the diamond stability field at Darby.
DS201706-1077
2017
Harrison, J.C., St. Onge, M.R., Paul, D., Brodaric, B.A new geological map and map database for Canada north of 60.GAC annual meeting, 1p. AbstractCanadamap
DS201708-1665
2017
Harte, B.Tracing lithsophere melt compositions using polymict peridotites11th. International Kimberlite Conference, PosterMantlemelting
DS201708-1666
2017
Harte, B.The petrology of the Kaapvaal craton mantle lithosphere - a synposis based on xenolith field counts.11th. International Kimberlite Conference, PosterAfrica, South Africa, mantleXenoliths
DS201707-1333
2016
Hassan, R., Muller, R.D., Gurnis, M., Williams, S.E., Flament, N.A rapid burst in hotspot motion through the interaction of tectonics and deep mantle flow.Nature Geoscience, Vol. 533, 7603, pp. 239-242.Mantleplumes

Abstract: Volcanic hotspot tracks featuring linear progressions in the age of volcanism are typical surface expressions of plate tectonic movement on top of narrow plumes of hot material within Earth’s mantle1. Seismic imaging reveals that these plumes can be of deep origin2—probably rooted on thermochemical structures in the lower mantle3, 4, 5, 6. Although palaeomagnetic and radiometric age data suggest that mantle flow can advect plume conduits laterally7, 8, the flow dynamics underlying the formation of the sharp bend occurring only in the Hawaiian–Emperor hotspot track in the Pacific Ocean remains enigmatic. Here we present palaeogeographically constrained numerical models of thermochemical convection and demonstrate that flow in the deep lower mantle under the north Pacific was anomalously vigorous between 100 million years ago and 50 million years ago as a consequence of long-lasting subduction systems, unlike those in the south Pacific. These models show a sharp bend in the Hawaiian–Emperor hotspot track arising from the interplay of plume tilt and the lateral advection of plume sources. The different trajectories of the Hawaiian and Louisville hotspot tracks arise from asymmetric deformation of thermochemical structures under the Pacific between 100 million years ago and 50 million years ago. This asymmetric deformation waned just before the Hawaiian–Emperor bend developed, owing to flow in the deepest lower mantle associated with slab descent in the north and south Pacific.
DS201707-1334
2017
Hatton, C., Robey, J.The eminent eight. IKC and history of conference and the prominent delegates ( ones who initiated the idea and followed through attending all 10 conferences to date).Geobulletin, Vol. 60, 1, March pp. 19-23.GlobalIKC history
DS201711-2516
2017
Havig, J.R., Hamilton, T.L., Bachan, A., Kump, L.R.Sulfur and carbon isotopic evidence for metabolic pathway evolution and a four stepped Earth system progression across the Archean and Paleoproterozoic.Earth-Science Reviews, Vol. 174, pp. 1-21.Mantlegeochronology

Abstract: The Earth's mantle has provided a ready redox gradient of sulfur compounds (SO2, H2S) since the stabilization of the crust and formation of the ocean over 4 billion years ago, and life has evolved a multitude of metabolic pathways to take advantage of this gradient. These transitions are recorded in the sulfur and carbon isotope signals preserved in the rock record, in the genomic records of extant microorganisms, and in the changing mantle and crust structure, composition and cycling. Here, we have assembled approximately 20,000 sulfur (?34S, ?33S, ?36S) and carbon (?13C) isotope data points from scientific publications spanning over five decades of geochemical analyses on rocks deposited from 4.0 to 1.5 Ga. We place these data in the context of molecular clock and tectonic and surface redox indicators to identify overarching trends and integrate them into a holistic narrative on the transition of the Earth's surface towards more oxidizing conditions. The greatest extreme in ?34S values of sulfide minerals (? 45.5 to 54.9‰) and sulfate minerals (? 13.6 to 46.6‰) as well as ?13C values in carbonate minerals (? 16.8 to 29.6‰) occurred in the period following the Great Oxidation Event (GOE), while the greatest extremes in organic carbon ?13C values (? 60.9 to 2.4‰) and sulfide and sulfate mineral ?33S and ?36S values (? 4.0 to 14.3‰ and ? 12.3 to 3.2‰, respectively) occurred prior to the GOE. From our observations, we divide transitions in Earth's history into four periods: Period 1 (4.00 to 2.80 Ga) during which geochemical cycles were initialized, Period 2 (2.80 to 2.45 Ga) during which S and C isotope systems exhibit changes as conditions build up to the GOE, Period 3 (2.45 to 2.00 Ga) encompassing the GOE, and Period 4 (after 2.00 Ga) after which S and C isotopic systems remained relatively constant marking a time of Earth system geochemical quiescence. Using these periods, we link changes in S and C isotopes to molecular clock work to aid in interpreting emerging metabolic functions throughout Earth's history while underscoring the need for better proxies for robust evolutionary analyses. Specifically, results indicate: 1) an early development of sulfide oxidation and dissimilatory sulfite reduction followed by disproportionation and then sulfate reduction to sulfite resulting in a fully biologically mediated sulfur cycle by ~ 3.25 Ga; 2) support for the acetyl coenzyme-A pathway as the most likely earliest form of biologically mediated carbon fixation following methanogenesis; 3) an increasingly redox-stratified ocean in the Neoarchean with largely oxic surface water and euxinic bottom water during the first half of the Paleoproterozoic; and 4) that secular changes in Earth system crustal cycling dynamics and continent formation likely played a key role in driving the timing of the GOE. Finally, based on geochemical data, we suggest that the Paleoproterozoic be divided into a new Era of the Eoproterozoic (from 2.45 to 2.00 Ga) and the Paleoproterozoic (from 2.00 to 1.60 Ga).
DS201709-1996
2017
Hawkesworth, C., Cawood, P., Dhuime, B., Kemp, T.I.S.Earth's continental lithosphere through time.Annual Review of Earth and Planetary Sciences, Vol. 45, pp. 169-198.Mantletectonics

Abstract: The record of the continental lithosphere is patchy and incomplete; no known rock is older than 4.02 Ga, and less than 5% of the rocks preserved are older than 3 Ga. In addition, there is no recognizable mantle lithosphere from before 3 Ga. We infer that there was lithosphere before 3 Ga and that ?3 Ga marks the stabilization of blocks of continental lithosphere that have since survived. This was linked to plate tectonics emerging as the dominant tectonic regime in response to thermal cooling, the development of a more rigid lithosphere, and the recycling of water, which may in turn have facilitated plate tectonics. A number of models, using different approaches, suggest that at 3 Ga the volume of continental crust was ?70% of its present day volume and that this may be a minimum value. The continental crust before 3 Ga was on average more mafic than that generated subsequently, and this pre-3 Ga mafic new crust had fractionated Lu/Hf and Sm/Nd ratios as inferred for the sources of tonalite-trondhjemite-granodiorite and later granites. The more intermediate composition of new crust generated since 3 Ga is indicated by its higher Rb/Sr ratios. This change in composition was associated with an increase in crustal thickness, which resulted in more emergent crust available for weathering and erosion. This in turn led to an increase in the Sr isotope ratios of seawater and in the drawdown of CO2. Since 3 Ga, the preserved record of the continental crust is marked by global cycles of peaks and troughs of U-Pb crystallization ages, with the peaks of ages appearing to match periods of supercontinent assembly. There is increasing evidence that the peaks of ages represent enhanced preservation of magmatic rocks in periods leading up to and including continental collision in the assembly of supercontinents. These are times of increased crustal growth because more of the crust that is generated is retained within the crust. The rates of generation of continental crust and mantle lithosphere may have remained relatively constant at least since 3 Ga, yet the rates of destruction of continental crust have changed with time. Only relatively small volumes of rock are preserved from before 3 Ga, and so it remains difficult to establish which of these are representative of global processes and the extent to which the rock record before 3 Ga is distorted by particular biases.
DS201709-1997
2017
Hawkesworth, C., Kendall, M., Daly, M., Cawood, P., Dhuime, B.Within plate and subduction related settings in the Archean.Goldschmidt Conference, abstract 1p.Mantlesubduction

Abstract: There is much discussion of the timing of the onset of plate tectonics, yet there is increasing evidence that magma types similar to those from recent within plate and subduction related settings were generated in different areas at broadly similar times in the early Archaean. It may therefore be helpful to consider when plate tectonics became the dominant mechanism associated with the generation of continental crust, rather than just when it started. To do this we discuss the geochemical and mechanical characteristics of the lithosphere in the search to discern differences between Early Archaean and younger tectonic environments. Seismic tomography allows increasingly detailed mapping of the lithosphere, and it provides some evidence that the degree of anisotropy is different in different Archaean terrains. Structural styles also appear to vary from basin and swell, or vertical tectonics, as in the Australia Pilbara and southern Africa, to those with more strongly developed regional fabrics and greater seismic anisotropy, as in North America. These terrains tend to be characterized by inferred within-plate and subduction-related magmatism respectively, and we consider possible links between the degree of crustal and mantle anisotropy and the nature of the magmatic record. At least in some areas, terrains with stronger regional fabrics may be younger than those in which such fabrics are less well developed. A model is developed for the generation and stabilization of continental lithosphere in the Archaean. It seeks to reconcile evidence for hot shallow melting with melt fractions up to 40% to generate residual peridotites now preserved as mantle xenoliths, and the lower degrees of melting required to generate the mafic sources of TTGs (fractionated Lu/Hf and Sm/Nd, and perhaps not Rb/Sr).
DS201710-2230
2017
Hawkesworth, C.J., Cawood, P.A., Dhuime, B., Kemp, T.I.S.Earth's continental lithosphere through time.Annual Review of Earth and Planetary Sciences, Vol. 45, pp. 169-198.MantleGeochronology

Abstract: The record of the continental lithosphere is patchy and incomplete; no known rock is older than 4.02 Ga, and less than 5% of the rocks preserved are older than 3 Ga. In addition, there is no recognizable mantle lithosphere from before 3 Ga. We infer that there was lithosphere before 3 Ga and that ?3 Ga marks the stabilization of blocks of continental lithosphere that have since survived. This was linked to plate tectonics emerging as the dominant tectonic regime in response to thermal cooling, the development of a more rigid lithosphere, and the recycling of water, which may in turn have facilitated plate tectonics. A number of models, using different approaches, suggest that at 3 Ga the volume of continental crust was ?70% of its present-day volume and that this may be a minimum value. The continental crust before 3 Ga was on average more mafic than that generated subsequently, and this pre-3 Ga mafic new crust had fractionated Lu/Hf and Sm/Nd ratios as inferred for the sources of tonalite-trondhjemite-granodiorite and later granites. The more intermediate composition of new crust generated since 3 Ga is indicated by its higher Rb/Sr ratios. This change in composition was associated with an increase in crustal thickness, which resulted in more emergent crust available for weathering and erosion. This in turn led to an increase in the Sr isotope ratios of seawater and in the drawdown of CO2. Since 3 Ga, the preserved record of the continental crust is marked by global cycles of peaks and troughs of U-Pb crystallization ages, with the peaks of ages appearing to match periods of supercontinent assembly. There is increasing evidence that the peaks of ages represent enhanced preservation of magmatic rocks in periods leading up to and including continental collision in the assembly of supercontinents. These are times of increased crustal growth because more of the crust that is generated is retained within the crust. The rates of generation of continental crust and mantle lithosphere may have remained relatively constant at least since 3 Ga, yet the rates of destruction of continental crust have changed with time. Only relatively small volumes of rock are preserved from before 3 Ga, and so it remains difficult to establish which of these are representative of global processes and the extent to which the rock record before 3 Ga is distorted by particular biases.
DS201703-0406
2017
He, D., Liu, Y., Gao, C., Chen, C., Hu, Z., Gao, S.SiC dominated ultra-reduced mineral assemblage in carbonatitic xenoliths from the Dalihu basalt, Inner Mongolia, China.American Mineralogist, Vol. 102, pp. 312-320.China, MongoliaCarbonatite

Abstract: SiC and associated ultra-reduced minerals were reported in various geological settings, however, their genesis and preservation mechanism are poorly understood. Here, we reported a SiC-dominated ultra-reduced mineral assemblage, including SiC, TiC, native metals (Si, Fe, and Ni) and iron silicide, from carbonatitic xenoliths in Dalihu, Inner Mongolia. All minerals were identified in situ in polished/thin sections. SiC is 20-50 ?m in size, blue to colorless in color, and usually identified in the micro-cavities within the carbonatitic xenolith. Four types of SiC polytypes were identified, which are dominated by ?-SiC (3C polytype) and 4H polytype followed by 15R and 6H. These SiC are featured by 13C-depleted isotopic compositions (?13C = ?13.2 to ?22.8‰, average = ?17.7‰) with obvious spatial variation. We provided a numerical modeling method to prove that the C isotopic composition of the Dalihu SiC can be well-yielded by degassing. Our modeling results showed that degassing reaction between graphite and silicate can readily produce the low ?13C value of SiC, and the spatial variations in C isotopic composition could have been formed in the progressive growth process of SiC. The detailed in situ occurring information is beneficial for our understanding of the preservation mechanism of the Dalihu ultra-reduced phase. The predominant occurrence of SiC in micro-cavities implies that exsolution and filling of CO2 and/or CO in the micro-cavities during the diapir rising process of carbonatitic melt could have buffered the reducing environment and separated SiC from the surrounding oxidizing phases. The fast cooling of host rock, which would leave insufficient time for the complete elimination of SiC, could have also contributed to the preservation of SiC.
DS201708-1667
2017
Heaman, L.Ages and sources of mantle eclogites: ID-TIMS-U-Pb-Sr isotope systematics of clinopyroxene.11th. International Kimberlite Conference, PosterMantleeclogite
DS201708-1668
2017
Helmstaedt, H.The life cycle of Diamondiferous cratons - a leitmotif with infinite variations.11th. International Kimberlite Conference, OralMantlediamond genesis
DS201709-1998
2017
Henry, H., Afonso, J.C., Satsukawa, T., Griffin, W.L., O'Reilly, S.Y., Kaczmarek, M-A., Tilhac, R., Gregoire, M., Ceuleneer, G.The unexplored potential impact of pyroxenite layering on upper mantle seismic properties.Goldschmidt Conference, abstract 1p.Europe, Spain, United States, Californiageophysics - seismics

Abstract: It is now accepted that significant volumes of pyroxenites are generated in the subduction factory and remain trapped in the mantle. In ophiolites and orogenic massifs the geometry of pyroxenite layers and their relationships with the host peridotite can be observed directly. Since a large part of what is known about the upper mantle structure is derived from the analysis of seismic waves, it is crucial to integrate pyroxenites in the interpretations. We modeled the seismic properties of a peridotitic mantle rich in pyroxenite layers in order to determine the impact of layering on the seimsic properties. To do so, EBSD data on deformed and undeformed pyroxenites from the Cabo Ortegal complex (Spain) and the Trinity ophiolite (California, USA) respectively are combined with either A or B-type olivine fabrics in order to model a realistic pyroxenite-rich upper mantle. Consideration of pyroxeniterich domains within the host mantle wall rock is incorporated in the calculations using the Schoenberg and Muir group theory [1]. This quantification reveals the complex dependence of the seismic signal on the deformational state and relative abundance of each mineral phase. The incorporation of pyroxenites properties into geophysical interpretations in understanding the lithospheric structure of subduction zones will lead to more geologically realistic models.
DS201701-0014
2016
Heron, P.J., Pysklywec, R.N., Stephenson, R.Identifying mantle lithosphere inheritance in controlling intraplate orogenesis.Journal of Geophysical Research, Vol. 121, 9, pp. 6966-6987.MantleGeodynamics

Abstract: Crustal inheritance is often considered important in the tectonic evolution of the Wilson Cycle. However, the role of the mantle lithosphere is usually overlooked due to its difficulty to image and uncertainty in rheological makeup. Recently, increased resolution in lithosphere imaging has shown potential scarring in continental mantle lithosphere to be ubiquitous. In our study, we analyze intraplate deformation driven by mantle lithosphere heterogeneities from ancient Wilson Cycle processes and compare this to crustal inheritance deformation. We present 2-D numerical experiments of continental convergence to generate intraplate deformation, exploring the limits of continental rheology to understand the dominant lithosphere layer across a broad range of geological settings. By implementing a "jelly sandwich" rheology, common in stable continental lithosphere, we find that during compression the strength of the mantle lithosphere is integral in generating deformation from a structural anomaly. We posit that if the continental mantle is the strongest layer within the lithosphere, then such inheritance may have important implications for the Wilson Cycle. Furthermore, our models show that deformation driven by mantle lithosphere scarring can produce tectonic patterns related to intraplate orogenesis originating from crustal sources, highlighting the need for a more formal discussion of the role of the mantle lithosphere in plate tectonics.
DS201706-1078
2017
Hess, T.L., Carter, M., Sundell, K.The search for diamonds in the Laramie Mountains of the Wyoming Archean province, USA.GSA Annual Meeting, 1p. AbstractUnited States, Wyoming, Colorado Plateaudeposit - Iron Mountain

Abstract: Casper College undergraduate students investigated the feasibility of finding hidden kimberlite pipes by means of geological mapping, geophysics, and stream sediment sampling. The Precambrian Laramie Mountains of southeastern Wyoming, locally known as the Iron Mountain Kimberlite district, was chosen based on previous work conducted by the Wyoming State Geological Survey (WSGS), geology of the region, and known kimberlite pipes. Data was collected using micro gravimeter - Scintrex CG-5, magnetometer - G-858 MagMapper, and electrical resistivity - SuperSting R8/IP/SP. Target one was chosen while pre-mapping the area and a topographic bowl like depression was identified. Micro gravimeter data was collected on a 56m transect at 8m intervals. Magnetometer data was collected in an area of 122m by 92m running in a 8m parallel array. Electrical resistivity was collected along a 56m transect at 8m intervals. Target two was chosen because the WSGS identified a regional magnetic anomaly and follow-up research was needed. Microgravimeter data was collected on a 56m transect at 8m intervals. Magnetometer data was collected from an area of 122m by 92m running in an 8m parallel array. Electrical resistivity was collected along a 56m transect at 8m intervals. Two drill site locations were selected based on the geophysical results to prove kimberlite is present at depth. Sediment samples were taken along Middle Sybille Creek and yielded a variety of pink to very deep red and purple colored garnets which have been sent in for EPMA (electron probe micro analyses) testing to determine the garnet-spinel compositions. Once complete the geochemical analyses will help determine if either target has a greater potential to be a diamondiferous kimberlite pipe.
DS201708-1669
2017
Hetman, C.Letseng diamond mine, Lesotho: a variant of kimberley-type pyroclastic kimberlite emplacement.11th. International Kimberlite Conference, OralAfrica, LesothoDeposit - Letseng

Abstract: The Letšeng Diamond Mine comprises two adjacent kimberlites, the Main and Satellite pipes. Very low grade and low frequency of high value stones preclude use of standard evaluation methods, increasing the need for high confidence geology models. New results of drillcore investigations, including core logging, country rock dilution measurements, indicator mineral abundances and petrography are integrated with open pit mapping and macrodiamond production data to present updated 3D geological models of the Main and Satellite pipes. Letšeng was emplaced ~90 Ma and forms part of a Cretaceous kimberlite province extending across southern Africa. The Letšeng bodies are steep-sided volcanic pipes that are infilled with multiple asymmetric phases of kimberlite separated by near-vertical, sharp, cross-cutting internal contacts. There are associated marginal carbonate-cemented country-rock breccias and sub-vertical kimberlite dykes that can occur within a zone of well-developed carbonate veining adjacent to the pipes. The pipe infills are dominated by kimberlite closely resembling Kimberley-type pyroclastic kimberlite (KPK; formerly tuffisitic kimberlite; Scott Smith et al. 2013) that contains common large megaxenoliths of massive and brecciated country rock basalt. Other textural varieties include hypabyssal kimberlite (HK), transitional HK-KPK and resedimented volcaniclastic kimberlite (RVK). Each phase of kimberlite represents a separate magmatic system. In each KPK there is a continuum of crystallization from the magmaclast selvages to the intermagmaclast matrix. As documented elsewhere, the HK-KPK transition involves an increasing (i) degree of deuteric replacement of olivine, (ii) amount of incorporated country rock xenoliths and (iii) textural modification of the magma prior to solidification subsurface within the diatreme. These conclusions negate some other proposed modes of emplacement.
DS201710-2231
2017
Hetman, C.Highland Gems: Letseng, Kao, Mothae, Monastery11th International Kimberlite Field Trip Guide, Sept. 59p. PdfAfrica, Lesothodeposit - Letseng, Kao, Mothae, Monastery
DS201706-1079
2017
Hier-Majumder, S., Tauzin, B.Pervasive upper mantle melting beneath the western USA.Earth and Planetary Science Letters, Vol. 463, pp. 25-35.United Statesmelting

Abstract: We report from converted seismic waves, a pervasive seismically anomalous layer above the transition zone beneath the western US. The layer, characterized by an average shear wave speed reduction of 1.6%, spans over an area of ?1.8×106 km2?1.8×106 km2 with thicknesses varying between 25 and 70 km. The location of the layer correlates with the present location of a segment of the Farallon plate. This spatial correlation and the sharp seismic signal atop of the layer indicate that the layer is caused by compositional heterogeneity. Analysis of the seismic signature reveals that the compositional heterogeneity can be ascribed to a small volume of partial melt (0.5 ± 0.2 vol% on average). This article presents the first high resolution map of the melt present within the layer. Despite spatial variations in temperature, the calculated melt volume fraction correlates strongly with the amplitude of P-S conversion throughout the region. Comparing the values of temperature calculated from the seismic signal with available petrological constraints, we infer that melting in the layer is caused by release of volatiles from the subducted Farallon slab. This partially molten zone beneath the western US can sequester at least 1.2×1017 kg1.2×1017 kg of volatiles, and can act as a large regional reservoir of volatile species such as H or C.
DS201705-0834
2017
Hilgner, A., Greiff, S., Quast, D.Gemstones in the first millennium AD. Mines, trade, workshops and symbolism. Romisch-Germanisches Zentralmuseum Leibniz-Forschungsinstitut fur Archaologie Mainz International Conference Oct. 20-22, 2015, pp. 155-217.GlobalBook - gemstones
DS201712-2689
2017
Hiyate, A.Shore finds potential partner in Rio Tinto. Rio signs option to earn majority stake in Saskatchewan project.Diamonds In Canada Magazine, Northern Miner, Nov. pp. 6-8.Canada, Saskatchewandeposit - Star-Orion
DS201712-2690
2017
Hiyate, A.Stornoway crafts breakage plan for Renard plant $ 22 M waste-sorting circuit to be commissioned in early 2018.Diamonds In Canada Magazine, Northern Miner, Nov. pp. 9-11.Canada, Quebecdeposit - Renard
DS201712-2691
2017
Hiyate, A.Gahcho Kue makes the grade. Partners raise 2017 production guidance for new NWT mine.Diamonds In Canada Magazine, Northern Miner, Nov. pp. 12-14.Canada, Northwest Territoriesdeposit - Gahcho Kue
DS201712-2692
2017
Hiyate, A., Hefferman, V.Dominion's latest transformation .. Next chapter Washington Companies takeover is just the latest twist in the company's history.Diamonds In Canada Magazine, Northern Miner, Nov. pp. 4-5.Canada, Northwest Territoriesdeposit - Ekati
DS201708-1670
2017
Hiyoveni, R.The Nxaunxau kimberlites of northern Botswana.11th. International Kimberlite Conference, PosterAfrica, Botswanadeposit - Nxaunxau
DS201711-2517
2017
Hodder, T.J.Kimberlite indicator mineral results derived from glacial sediments ( till) in the Southern Indian Lake area of north central Manitoba ( parts of NTS 64B15, 64G1,2,7,8).Manitoba Geological Survey, Open File OF2017-2, 13p. PdfCanada, Manitobageochemistry
DS201706-1080
2017
Hodder, T.J., Kelley, S.E., Trommelen, M.S., Ross, M., Rinne, M.L.The Kaskattama highland: till composition and indications of a new Precambrian In lier in the Hudson Bay Lowland?GAC annual meeting, 1p. AbstractCanada, Manitobageochemistry
DS201708-1671
2017
Hoefer, H.E.Redox state of Archean kyanite/corundum eclogites and garnet pyroxenites from Bellsbank, South Africa.11th. International Kimberlite Conference, PosterAfrica, South Africadeposit - Bellsbank

Abstract: An oceanic crustal origin is the commonly accepted paradigm for mantle-derived eclogites. However, the significance of the aluminous members of the eclogite suite, containing kyanite and corundum, has long been underrated and their role neglected in genetic models of cratonic evolution. Here, we present a geochemical and petrological study of a suite of kyanite- and corundum-bearing eclogites from the Bellsbank kimberlite, S. Africa, which originate from depths between 150 and 200 km. Although clearly of high-pressure provenance, these rocks had a low-pressure cumulative origin with plagioclase and olivine as major cumulate phases. This is shown by the very pronounced positive Eu anomalies, low REE abundances, and ?18O values lower than the Earth’s mantle. Many chemical features are identical to modern-day troctolitic cumulates including a light REE depletion akin to MORB, but there are also distinguishing features in that the eclogites are richer in Na, Fe, and Ni. Two of the eclogites have a minimum age of ~3.2 Ga, defined by the extremely unradiogenic 87Sr/86Sr (0.7007) in clinopyroxene. Phase equilibria indicate that the parent melts were formed by partial melting below an Archean volcanic center that generated (alkali-)picritic to high-alumina tholeiitic melts from a mantle whose oxygen fugacity was lower than today. Fractional crystallization produced troctolites with immiscible sulfide melt droplets within the mafic crust. Instability of the mafic crust led to deep subduction and re-equilibration at 4–6 GPa. Phase relationships plus the presence of a sample with appreciable modal corundum but no Eu anomaly suggest that kyanite- and corundum-bearing eclogites may also originate as plagioclase-free, higher pressure cumulates of highly aluminous clinopyroxene, spinel, and olivine. This is consistent with the crystallizing phase assemblage from an olivine tholeiitic to picritic magma deeper in the Archean oceanic crust or uppermost mantle. We postulate that the magmatic and subduction processes driving modern plate tectonics already existed in the Meso- to Early Archean.
DS201710-2232
2017
Hoffmann, J.E.Oxygenation by a changing crust.Nature Geoscience, Vol. 10, 10, pp. 713-714.Mantlemetasomatism

Abstract: Serpentine minerals in Earth's early upper continental crust suppressed atmospheric oxygen levels until the upper crust became granitic.
DS201707-1335
2016
Hogarth, D.D.Chemical trends in the Meech Lake Quebec, carbonatites and fenites.The Canadian Mineralogist, Vol 54, pp. 1105-1128.Canada, Quebeccarbonatite - Meech Lake

Abstract: Near Meech Lake, Québec, the edges of Mesoproterozoic carbonatite dikes are composed of calcite, dolomite, fluorapatite, phlogopite, amphibole, and pyrochlore. The carbonatite is separated from amphibole-fenite by a narrow, fine-grained reaction selvage of phlogopite pierced with long prisms of amphibole. The amphibole is mainly richterite, but it extends to magnesio-arfvedsonite (overgrowth, crystal rim). Uranium-rich pyrochlore is metamict and ranges from calciopyrochlore to kenopyrochlore with Ta-U enrichment in crystal rims. Chemical characteristics of the suite are: (1) F and Nb highest in the selvage, and (2) decline of Sr and Ce outwards from the carbonatite. A similar pattern (this research) is found at Fen, Norway. Rare earths are enriched in LREE with smooth downward-sloping patterns, in chondrite-normalized curves, to HREE. Two major surges of mineralization are suggested: (1) early, metasomatic-alkalic, creating fenites with enrichment in Mg, Na, and K; and (2) later igneous depositing carbonatites and introducing first F, P, and Nb, then Ca, Sr, and Ce. Thermochemical and geochronological data place carbonate equilibration at 700 °C and the emplacement at 1026 Ma b.p. Calciocarbonatites, in monzonitic orthogneiss, are enriched in Ba and Ce. They are composed of baryte, calcite, phlogopite, fluorapatite, magnesio-riebeckite, and non-metamict allanite-(Ce). A mica selvage is present, but amphibole fenite is almost completely lacking. Magnesiocarbonatite has a well-developed selvage against granite but lacks significant amphibole fenite. In breccia cement at nearby Fortune Lake, pyrochlore is associated with abundant fluorapatite but lacks carbonates. The Cambro-Proterozoic calciocarbonatite near Fen, Norway is particularly Nb-rich in breccia zones, and pyroxene fenite takes the place of amphibole fenite at Meech Lake. In contrast to a relatively anorogenic regime during carbonatite petrogenesis at Fen, metamorphism has obscured pyrochlore zonation and enhanced amphibole growth at Meech Lake
DS201706-1081
2017
Hogg, S., Munro, S.The geophysical history of discoveries in the James Bay Lowlands from the Victor kimberlite to the Ring of Fire copper and nickel deposits.exploration17.com, 1p. AbstractCanada, Ontariogeophysics

Abstract: The James Bay Lowlands is a large remote area of Northern Ontario with very limited access. The Archean basement rocks lie beneath a layer of Paleozoic limestone, up to 300 m thick, that is topped by glacial till and bog. This setting, without outcrop or hard geological knowledge, presented a blank slate well suited to airborne geophysical exploration. This paper presents the aeromagnetic survey methodology and analysis techniques that evolved from the initial kimberlite aeromagnetic program carried out by Selco in 1979 through the 1989 DeBeers discovery of the Victor kimberlite and the 1993 Spider/KWG discovery of the older sub-Paleozoic Kyle series kimberlites and eventually the Ring of Fire. Without property constraints the exploration methodology was a cycle of survey-interpret-drill then move on and repeat as discoveries and finances permitted. After 3 cycles of kimberlite discovery a Spider/KWG/DeBeers partnership encountered VMS copper mineralization in 2001. An airborne EM survey in 2003 identified a number of excellent prospects and the most technically promising became the Noront Eagles Nest MMS nickel deposit that began the Ring of Fire saga. These greenfield discoveries, in a blind geological environment beneath limestone cover, illustrate the potential effectiveness of geophysically directed exploration.
DS201710-2233
2017
Hoover, D.B., Karfunkel, J., Ribeiro, L.C.B., Michelfelder, G.., Moraes, R.A.V., Krambrock, K., Quintao, D., Walde, D.Diamonds of the Alto Paranaiba, Brazil: Nixon's prediction verified?The Australian Gemmologist, Vol. 26, 5&6, pp. 88-99.South America, Brazil, Minas Geraisdeposit - Alto Paranaiba

Abstract: The authors, in a paper in this journal in 2009, note a puzzle, that in spite of extensive exploration for diamonds by major producers in the Alto Paranaiba region of West Minas Gerais State, Brazil, no primary source, such as kimberlites, for the many diamonds produced since their discovery over 250 years has been found. To answer this puzzle we propose that the diamonds are present within a large extrusive volcanic unit probably derived from the Serra Negra alkaline-carbonatitic complex which comprises a super volcano. This origin fits with the 1995 prediction of Nixon on the future direction of diamona-exploration that extrusive units may contain very large volumes of ore, and that carbonatitic emplacement sources need to be considered. The authors argue, based on available evidence from geology and geophysics, that such an origin is compatible with the known data, but that much additional information is needed to substantiate these ideas. Diamonds of the Alto Paraniaba, Brazil: Nixon's prediction verified?
DS201702-0215
2016
Hopper, E., Fischer, K.M., Rondenay, S., Hawman, R.B., Wagner, L.S.Imaging crustal structure beneath the southern Appalachians with wavefield migration.Geophysical Research Letters, Vol. 43, 23, pp. 12,054-62.United StatesGeophysics - seismics

Abstract: To constrain crustal structures in the southern Appalachians and the suture zone with the Gondwanan-affinity Suwannee terrane, we applied the 2-D generalized Radon transform wavefield migration method to the scattered incident P wavefield recorded by the EarthScope Southeastern Suture of the Appalachian Margin Experiment and adjacent Transportable Array stations. We resolve the root of thickened crust beneath the high topography of the Blue Ridge Mountains and estimate its density contrast with the mantle to be only 104?±?20?kg/m3. A weak velocity contrast across the crustal root Moho is observed and may be related to an ongoing crustal delamination event, possibly contributing to local tectonic rejuvenation. Beneath the Suwannee terrane, we confirm prior observations of a gently south-southeastward dipping crustal suture, indicating the terminal collision of Laurentia and Gondwana involved several hundred kilometers of overthrusting.
DS201705-0835
2017
Howard, J.M.Crater of Diamonds - The Natural State's Gem of a Park.lithographie.org, No. 19, pp. 86-93.United States, ArkansasBook - Crater of Diamonds
DS201708-1672
2017
Howarth, G.Origin of mantle derived carbonate nodules from the Bultfontein kimberlite.11th. International Kimberlite Conference, OralAfrica, South Africadeposit - Bultfontein
DS201710-2234
2017
Howarth, G.H., Harris, C.Discriminating between pyroxenite and peridotite sources for continental flood basalts ( CFB) in southern Africa using olivine chemistry.Earth and Planetary Science Letters, Vol. 475, pp. 143-151.Africaperidotites

Abstract: Continental Flood Basalts (CFB) result from voluminous outpourings of magma that often precede continental break-up. Notwithstanding the petrogenetic importance of CFBs, the nature of the mantle source for such magmas is contentious, particularly with regard to picrites with Ni-rich olivine phenocrysts. Previous studies have suggested that Ni-rich olivines associated with plume volcanism in regions of thickened (>90 km) lithosphere are related to either source mineralogy differences (peridotite versus pyroxenite) or change in olivine-melt partitioning due to pressure increase. In order to evaluate these two hypotheses, we present trace element data for olivines from the Karoo CFB Tuli and Mwenezi picrites and the Etendeka CFB Horingbaai/LTZ-L type picrites, all of which erupted in regions of thickened (>90 km) lithosphere in southern Africa. Karoo picrite olivines are Ni-rich, Ca- and Mn-poor, and have low (<1.4) 100*Mn/Fe. These compositions are consistent with a pyroxenitic source. Etendeka Horingbaai/LTZ-L picrite olivines do not show Ni-enrichment, but are characterized by high Al and Cr, and high (>1.4) 100*Mn/Fe, which is more consistent with high temperature melting of a dominantly peridotitic source. We also show that the Karoo and Etendeka olivines are characterized by distinct Mn/Zn ratios of <13 and >15, respectively.In addition, bulk rock geochemical data compilations and previously reported olivine for Karoo and Etendeka CFBs are discussed in order to further constrain source components based on previously described pyroxenite melt geochemical indices such as MgO-CaO systematics, FeO/MnO, Zn/Fe, and FC3MS (FeO/CaO-3*MgO/SiO2). These geochemical indices suggest a pyroxenite-dominated source for Karoo CFBs as well as for Etendeka ferropicrites whereas a peridotite-dominated source is indicated for Etendeka Horingbaai/LTZ-L type picrites analyzed in this study. Based on our data, Ni-enrichment of olivine in plume-related magmas in regions of thickened lithosphere in southern Africa is not ubiquitous. We therefore suggest that mineralogical variation of the source is a more likely major control of olivine chemistry and parent melt variations for Karoo and Etendeka CFBs. We also show that olivine Mn-Zn correlations are a useful discriminator for source variation and recommend the use of olivine for a pyroxenite-dominated source relative to olivine for a peridotite-dominated source.
DS201708-1673
2017
Howell, D.DiaMap: new applications for processing IR spectra of fluid rich diamonds and mapping diamonds containing isolated nitrogen ( type Ib) and boron ( type II b)11th. International Kimberlite Conference, PosterTechnologyspectroscopy
DS201706-1082
2017
Hrncir, J., Karlestrom, K., Dahl, P.Wyoming on the run - toward final Paleoproterozoic assembly of Laurentia. Geology Forum Comment, April 1p.United Statescraton

Abstract: Paleoproterozoic suture zones mark the formation of supercontinent Nuna and provide a record of North America's assembly. Conspicuously young ages (ca. 1.715 Ga) associated with deformation in southeast Wyoming craton argue for a more protracted consolidation of Laurentia, long after peak metamorphism in the Trans-Hudson orogen. Using paleomagnetic data from the newly dated 1899 ± 5 Ma Sourdough mafic dike swarm (Wyoming craton), we compare the relative positions of Wyoming, Superior, and Slave cratons before, during, and after peak metamorphism in the Trans-Hudson orogen. With these constraints, we refine a collisional model for Laurentia that incorporates Wyoming craton after Superior and Slave cratons united, redefining the Paleoproterozoic sutures that bind southern Laurentia.
DS201709-1999
2017
Huang, J-X., Xiong, Q., Griffin, W.L., Martin, L., Toledo, V., O'Reilly, S.Y.Moissanite in volcanic systems: super reduced conditions in the mantle.Goldschmidt Conference, abstract 1p.Mantlemoissanite

Abstract: Moissanite (SiC) occurs in mantle and mantle-generated rocks from different tectonic settings. SiC is stable only at low oxygen fugacity (ƒO2) ?IW. Israeli SiC is assiociated with corundum, Fe globules, native V and other phases in Cretaceous pyroclastic rocks from Mt Carmel and associated alluvial deposits[1]. The SiC grains contain inclusions of Si metal, FeSi2, FeTiSi2, FeAlSi2 and CaSi2+xSi2-x, which were liquids before being trapped during SiC crystallization. SiC has been found included in corundum, associated with Fe-Ti silicides, connecting the formation of SiC, reduced melts in corundum and conrundum itself. All grains are of the 6H polytype. ?13C ranges from - 32.1 to -24.5‰ and ?30Si from -0.68 to +1.42‰. These SiC grains are one product of the interaction of basaltic magma and mantle methane in a volcanic plumbing system. SiC crystallized from metallic melts that became immiscible during the reduction of the magma. Its low ?13C may reflect Rayleigh fractionation under reduced conditions; the variation in Si isotopes may reflect fractionation between SiC and immiscible metallic melts. SiC samples from the Udachnaya and Mir kimberlite pipes contain inclusions of Si metal, FeSi2, FeSi, FeTiSi2, Si(N,O). The SiC has ?13C ranging from -28.5 to -24.8‰, and ?30Si from -1.72 to +1.42‰. SiC from harzburgites, chromitites and pyroxenites of the Tibetan Zedang ophiolites have inclusions of Si metal and unmixed Fe-Ni-Ti-Si alloy. Their ?13C ranges from -30.6 to -24.7‰ and ?30Si from -0.85 to +1.26‰. SiC samples from these different settings show very similar characteristics, implying that they may be formed in similar mantle conditions, where the flux of mantle methane gradually reduces magmas and interacts with them to produce different reduced phases at different stages.
DS201708-1572
2017
Hueck, M., Oriolo, S., Dunkl, I., Wemmer, K., Oyhantcabal, P., Schanofski, M., Stipp Basei, M.A., Siegesmund, S.Phanerozoic low temperature evolution of the Uruguayan shield along the South American passive margin.Journal of the Geological Society, Vol. 174, pp. 609-626.South America, Uruguaymagmatism

Abstract: The crystalline basement of Uruguay was assembled during the Brasiliano Orogeny in the Neoproterozoic Era and was later affected by discrete tectonic activity. A new multi-method low-temperature dataset including (U–Th)/He ages from both zircon and apatite, T–t modelling and K–Ar dating of fine sericite fractions and fault gouge reveal a detailed post-orogenic geological history spanning the Phanerozoic Eon. The juxtaposition of the terranes that compose the area was achieved in the Ediacaran Period, and post-collision was marked by intense exhumation, in which the crystalline basement reached near-surface conditions by the early to mid-Palaeozoic. Regional subsidence promoted sedimentation in the Paraná Basin until the Permian, covering and reheating much of the basement that is at present exposed. Afterwards, deposition and volcanism were mostly confined to its current limits. Regional exhumation of the shield during the Permo-Triassic exposed much of the northern portion of the basement, and the south was further affected by the opening of the South Atlantic Ocean during the Mesozoic. Little exhumation affected the Uruguayan Shield during the Cenozoic, as reflected in its modest topography. The reactivation of inherited Neoproterozoic structures influenced the development of Mesozoic basins and the present-day landscape.
DS201701-0015
2016
Hulett, S.R.W., Simonetti, A., Rasbury, E.T., Hemming, G.Recycling of subducted crustal components into carbonatite melts revealed by boron isotopes.Nature Geoscience, Vol. 9, pp. 904-908.MantleMagmatism

Abstract: The global boron geochemical cycle is closely linked to recycling of geologic material via subduction processes that have occurred over billions of years of Earth’s history. The origin of carbonatites, unique melts derived from carbon-rich and carbonate-rich regions of the upper mantle, has been linked to a variety of mantle-related processes, including subduction and plume-lithosphere interaction. Here we present boron isotope (?11B) compositions for carbonatites from locations worldwide that span a wide range of emplacement ages (between ~40 and ~2,600?Ma). Hence, they provide insight into the temporal evolution of their mantle sources for ~2.6 billion years of Earth’s history. Boron isotope values are highly variable and range between ?8.6‰ and +5.5‰, with all of the young (<300?Ma) carbonatites characterized by more positive ?11B values (>?4.0‰), whereas most of the older carbonatite samples record lower B isotope values. Given the ?11B value for asthenospheric mantle of ?7 ± 1‰, the B isotope compositions for young carbonatites require the involvement of an enriched (crustal) component. Recycled crustal components may be sampled by carbonatite melts associated with mantle plume activity coincident with major tectonic events, and linked to past episodes of significant subduction associated with supercontinent formation.
DS201708-1674
2017
Hutchison, M.The mantle of Scotland viewed through the Glen Gollaidh allikite.11th. International Kimberlite Conference, PosterEurope, Scotlandallikite
DS201708-1675
2017
Hutchison, M.Diamond exploration and prospectivity of western Australia.11th. International Kimberlite Conference, PosterAustraliaexploration
DS201702-0216
2017
ICMMICMM's water stewardship position statement.ICMM, Jan. 10, 6p.TechnologyWater management

Abstract: This position statement sets out ICMM members’ approach to water stewardship. Water stewardship is the use of water in ways that are socially equitable, environmentally sustainable, and economically beneficial.1 Effective stewardship requires collaboration and concerted action from all parties, including government, civil society, business and local communities through inclusive stakeholder engagement.
DS201703-0407
2017
Iizuka, T., Yamaguchi, T., Itano, K., Hibiya, Y., Suzuki, K.What Hf isotopes in zircon tell us about crust mantle evolution.Lithos, Vol. 274-275, pp. 304-327.MantleGeochronology

Abstract: The 176Lu-176Hf radioactive decay system has been widely used to study planetary crust-mantle differentiation. Of considerable utility in this regard is zircon, a resistant mineral that can be precisely dated by the U-Pb chronometer and record its initial Hf isotope composition due to having low Lu/Hf. Here we review zircon U-Pb age and Hf isotopic data mainly obtained over the last two decades and discuss their contributions to our current understanding of crust-mantle evolution, with emphasis on the Lu-Hf isotope composition of the bulk silicate Earth (BSE), early differentiation of the silicate Earth, and the evolution of the continental crust over geologic history. Meteorite zircon encapsulates the most primitive Hf isotope composition of our solar system, which was used to identify chondritic meteorites best representative of the BSE (176Hf/177Hf = 0.282793 ± 0.000011; 176Lu/177Hf = 0.0338 ± 0.0001). Hadean-Eoarchean detrital zircons yield highly unradiogenic Hf isotope compositions relative to the BSE, providing evidence for the development of a geochemically enriched silicate reservoir as early as 4.5 Ga. By combining the Hf and O isotope systematics, we propose that the early enriched silicate reservoir has resided at depth within the Earth rather than near the surface and may represent a fractionated residuum of a magma ocean underlying the proto-crust, like urKREEP beneath the anorthositic crust on the Moon. Detrital zircons from world major rivers potentially provide the most robust Hf isotope record of the preserved granitoid crust on a continental scale, whereas mafic rocks with various emplacement ages offer an opportunity to trace the Hf isotope evolution of juvenile continental crust (from ?Hf[4.5 Ga] = 0 to ?Hf[present] = + 13). The river zircon data as compared to the juvenile crust composition highlight that the supercontinent cycle has controlled the evolution of the continental crust by regulating the rates of crustal generation and intra-crustal reworking processes and the preservation potential of granitoid crust. We use the data to explore the timing of generation of the preserved continental crust. Taking into account the crustal residence times of continental crust recycled back into the mantle, we further propose a model of net continental growth that stable continental crust was firstly established in the Paleo- and Mesoarchean and significantly grew in the Paleoproterozoic.
DS201703-0408
2017
Ikenne, M., Souhassou, M., Arai, S., Soulaimani, A.A historical overview of Moroccan magmatic events along the northwest edge of the West African craton.Journal of African Earth Sciences, Vol. 127, pp. 3-15.Africa, MoroccoCraton - magmatism

Abstract: Located along the northwestern edge of the West African Craton, Morocco exhibits a wide variety of magmatic events from Archean to Quaternary. The oldest magmatic rocks belong to the Archean Reguibat Shield outcrops in the Moroccan Sahara. Paleoproterozoic magmatism, known as the Anti-Atlas granitoids, is related to the Eburnean orogeny and initial cratonization of the WAC. Mesoproterozoic magmatism is represented by a small number of mafic dykes known henceforth as the Taghdout mafic volcanism. Massive Neoproterozoic magmatic activity, related to the Pan-African cycle, consists of rift-related Tonian magmatism associated with the Rodinia breakup, an Early Cryogenian convergent margin event (760-700 Ma), syn-collisional Bou-Azzer magmatism (680-640 Ma), followed by widespread Ediacaran magmatism (620-555 Ma). Each magmatic episode corresponded to a different geodynamic environment and produced different types of magma. Phanerozoic magmatism began with Early Cambrian basaltic (rift?) volcanism, which persisted during the Middle Cambrian, and into the Early Ordovician. This was succeeded by massive Late Devonian and Carboniferous, pre-Variscan tholeiitic and calc-alkaline (Central Morocco) volcanic flows in basins of the Moroccan Meseta. North of the Atlas Paleozoic Transform Zone, the Late Carboniferous Variscan event was accompanied by the emplacement of 330-300 Ma calc-alkaline granitoids in upper crustal shear zones. Post-Variscan alkaline magmatism was associated with the opening of the Permian basins. Mesozoic magmatism began with the huge volumes of magma emplaced around 200 Ma in the Central Atlantic Magmatic Province (CAMP) which was associated with the fragmentation of Pangea and the subsequent rifting of Central Atlantic. CAMP volcanism occurs in all structural domains of Morocco, from the Anti-Atlas to the External Rif domain with a peak activity around 199 Ma. A second Mesozoic magmatic event is represented by mafic lava flows and gabbroic intrusions in the Internal Maghrebian flysch nappes as well as in the external Mesorif. This event consists of Middle-Upper Jurassic MORB tholeiites emplaced during opening of the Alpine Tethys ocean. The Central High Atlas also records Early Cretaceous alpine Tethys magmatism associated with the aborted Atlas rift, or perhaps linked to plume activity on the edge of the WAC. Cenozoic magmatism is associated with Tertiary and Quaternary circum-Mediterranean alkaline provinces, and is characterized by an intermittent activity over 50 Ma from the Anti-Atlas to the Rif Mountain along a SW-NE volcanic lineament which underlines a thinned continental lithosphere.
DS201709-2000
2017
Ilyina, O.V., Pokhilenko, L.N., Agashev, A.M.Characteristics of platinum group elements ( PGE) distribution in mantle xenoliths from kimberlite Udachnaya pipe ( Yakutia).Goldschmidt Conference, abstract 1p.Russia, Yakutiadeposit - Udachnaya

Abstract: We report PGE data in xenoliths of the deformed and granular peridotites. The deformed peridotites are the most deep-seated rocks and represent a narrow range of depth (180-220 km) while granular peridotites are located throughout the section of the lithospheric mantle. PGE distribution in the deformed peridotites [1] generally corresponds to that in our granular peridotites and xenoliths from Lesotho [2]. But in contrast with broad range of PGE concentrations in granular peridotites, the deformed peridotites show nearly flat pattern from Os to Pt, except of Pd (Fig.1). Granular peridotites show good positive correlation between PGE and Fe2O3. We suppose that they enriched in PGE by iron phase during its evolution. As for deformed peridotites we propose that they were depleted in Ir and Os followed by the increase of Ga and Cpx on the first stage of mantle metasomatism. On the last stage the enrichment of Pt, Pd and Re was probably a result of submicron sulphide phase’s presipitation in the interstices of mantle rocks.
DS201712-2693
2017
Ionov, D.A., Doucet, L.S., Pogge von Strandmann, A.E., Golovin, A.V., Korsakov, A.V.Links between deformation, chemical enrichment and Li isotope compositions in the lithospheric mantle of the central Siberian craton.Chemical Geology, Vol. 475, pp. 105-121.Russia, Siberiacraton, geochronology

Abstract: We report the concentrations ([Li]) and isotopic compositions of Li in mineral separates and bulk rocks obtained by MC-ICPMS for 14 previously studied garnet and spinel peridotite xenoliths from the Udachnaya kimberlite in the central Siberian craton as well as major and trace element compositions for a new suite of 13 deformed garnet peridotites. The deformed Udachnaya peridotites occur at > 5 GPa; they are metasomatized residues of melt extraction, which as a group experienced greater modal and chemical enrichments than coarse peridotites. We identify two sub-groups of the deformed peridotites: (a) mainly cryptically metasomatized (similar to coarse peridotites) with relatively low modal cpx (< 6%) and garnet (< 7%), low Ca and high Mg#, sinusoidal REE patterns in garnet, and chemically unequilibrated garnet and cpx; (b) modally metasomatized with more cpx and garnet, higher Ca, Fe and Ti, and equilibrated garnet and cpx. The chemical enrichments are not proportional to deformation degrees. The deformation in the lower lithosphere is caused by a combination of localized stress, heating and fluid ingress from the pathways of ascending proto-kimberlite melts, with metasomatic media evolving due to reactions with wall rocks. Mg-rich olivine in spinel and coarse garnet Udachnaya peridotites has 1.2-1.9 ppm Li and ?7Li of 1.2-5.0‰, i.e. close to olivine in equilibrated fertile to depleted off-craton mantle peridotites from literature data, whereas olivine from the deformed peridotites has higher [Li] (2.4-7.5 ppm) and a broader range of ?7Li (1.8-11.6‰), which we attribute to pre-eruption metasomatism. [Li] in opx is higher than in coexisting olivine while ?7LiOl-Opx (?7LiOl ? ?7LiOpx) ranges from ? 6.6 to 7.8‰, indicating disequilibrium inter-mineral [Li] and Li-isotope partitioning. We relate these Li systematics to interaction of lithospheric peridotites with fluids or melts that are either precursors of kimberlite magmatism or products of their fractionation and/or reaction with host mantle. The melts rich in Na and carbonates infiltrated, heated and weakened wall-rock peridotites to facilitate their deformation as well as produce high [Li] and variable, but mainly high, ?7Li in olivine. The carbonate-rich melts preferentially reacted with the opx without achieving inter-mineral equilibrium because opx is consumed by such melts, and because of small volumes and uneven distribution of the metasomatic media, as well as short time spans between the melt infiltration and the capture of the wall-rock fragments by incoming portions of ascending kimberlite magma as xenoliths. Trapped interstitial liquid solidified as cryptic components responsible for high [Li] and the lack of ?7Li balance between olivine and opx, and bulk rocks. Unaltered ?26Mg values (0.20-0.26‰) measured in several olivine separates show no effects of the metasomatism on Mg-isotopes, apparently due to high Mg in the peridotites.
DS201712-2694
2007
Ivanic, T.The chromite-garnet peridotite assemblages and their role in the evolution of the mantle lithosphere.Thesis, Phd. University of Edinburgh, 257p. Pdf from authorAfrica, South Africadeposit - Newlands, Bobbejaan
DS201709-2001
2017
Ivanov, O.A., Logvinova, A.M., Pokhilenko, N.P.Characteristics of nitrogen impurity in octahedral diamonds from Snap Lake ( Slave craton, Canada).Goldschmidt Conference, abstract 1p.Canada, Northwest Territoriesdeposit - Snap Lake

Abstract: The nitrogen concentration and aggregation form reflect the conditions of diamond formation and diamond evolution in primary source [1]. FTIR measurements were made on 40 colorless or slightly greenish octahedral diamonds from Snap Lake kimberlite dyke system. Studied diamonds differ in nitrogen content, distribution and aggregation degree. The total nitrogen content in different diamond zones is up to 1600 ppm. Diamonds have been classified into two groups on the basis of nitrogen aggregation degree in them. Group 1 includes poorly-aggregated-nitrogen diamonds. We suggest that such diamonds belong to the same generation such as cubic diamonds from Snap Lake [2]. The low degree of nitrogen aggregation in diamonds is indicative of short mantle residence and suggests that they crystallized shortly before kimberlite eruption. Diamonds of Group 2 are characterized by high nitrogen aggregation degree (up to 98.6%). Group 2 includes diamonds either with uniform nitrogen distribution throughout the crystal volume or with a predominance of Bdefect in the center. Inhomogeneity in nitrogen distribution from the center to the edge of the octahedral crystals indicates, at least, about the two, or even more growth stages of a part of the studied diamonds. High nitrogen aggregation degree according to “annealing” model is evidence of diamond staying in the high temperature region or of their residence in the mantle conditions. Results obtained support that significant part of octahedral diamonds from Snap Lake may have formed at the base of a thick lithospheric mantle at depth below 300 km [3].
DS201707-1336
2017
Ivanova, O.A., Logvinova, A.M., Pokhilenko, N.P.Inclusions in diamonds from Snap Lake kimberlites ( Slave craton, Canada): geochemical features of crystallization.Doklady Earth Sciences, Vol. 474, 1, pp. 490-493.Canada, Northwest Territoriesdeposit - Snap Lake

Abstract: The results of integrated studies of inclusion-containing diamonds from kimberlites of the Snap Lake dike complex (Canada) are presented. Features of the morphology, defect–impurity composition, and internal structure of the diamonds were determined by optic and scanning microscopy. The chemical composition of crystalline inclusions (olivine, garnet, and pyroxene) in diamonds was studied using a microanalyzer with an electronic probe. The inclusions of ultramafic paragenesis in the diamond (87%) are predominant. Carbonates, sulfide and hydrated silicate phases were found only in multiphase microinclusions. The large phlogopite inclusion studied was similar in composition to earlier studied nanosize inclusions of high-silica mica in diamonds from Snap Lake kimberlites. Revealed features of studied diamonds and presence of high-silica mica suggest that diamonds from Snap Lake have formed as the result of interaction between enriched in volatile and titanium high-potassium carbonate–silicate melts and peridotitic substrate at the base of thick lithospheric mantle.
DS201708-1676
2017
Jackson, C.New insights into volatile-rich mantle metasomatism at the Bultfontein diamond mine, Kimberley, South Africa.11th. International Kimberlite Conference, PosterAfrica, South Africadeposit - Bultfontein
DS201709-2002
2017
Jackson, C., Gibson, S.New insights into sulfur-rich mantle metasomatism at Bultfontein, Kimberley.Goldschmidt Conference, abstract 1p.Africa, South Africadeposit - Bultfontein

Abstract: Metasomatised regions of Earth’s sub-continental lithospheric mantle potentially represent a large volatile reservoir. Nevertheless, the mechanisms involved in the storage and upward transport of volatiles such as C and S, from the convecting mantle and/or subducting slabs, are poorly understood. We have carried out a systematic microanalytical study of a suite of sulfide-rich mantle peridotites from the Bultfontein diamond mine, Kimberley. EDS mapping of large (>2mm), interstitial base metal sulfides in the Bultfontein xenoliths has identified distinct Ni-rich regions (pentlandite). The Ni-rich sulfides are adjacent to olivine with Ni poor rims (<0.2 wt% NiO). Diffusion profiles between the protolith olivines and adjacent sulfides are used to estimate the timing of the S-rich metasomatic event. The presence of large unequilibrated olivine indicates that Nisulfides were introduced immediately prior to kimberlite emplacement. The calculated composition of melt in equilibrium with metasomatic clinopyroxenes in the Bultfontein sulphide-bearing peridotites shows a strong correlation to high-density carbonatitic fluids trapped in diamonds. This association is extended by the wealth of metasomatic sulfides in the Bultfontein xenoliths. Moreover, Ni-rich sulfides (~25 wt%) are the most common mineral inclusion in peridotitic diamonds, implying that diamonds crystallise from a S-saturated fluid. Many studies attribute the metasomatism at Bultfontein to silicate melts associated with the kimberlite, but we explore the possibility of metasomatism by reactive percolation of a volatile-rich agent with carbonatitic affinity. The S-rich nature of the metasomatism and the correlation with diamond high-density fluids has great implications for the transport of volatiles from the deep mantle to shallow regions of the craton.
DS201703-0409
2017
Jackson, M.G., Konter, J.G., Becker, T.W.Primordial helium entrained by the hottest mantle plumes.Nature Geoscience, Jan. 7, 1p. PreviewEurope, IcelandHot spots

Abstract: Helium isotopes provide an important tool for tracing early-Earth, primordial reservoirs that have survived in the planet’s interior1, 2, 3. Volcanic hotspot lavas, like those erupted at Hawaii and Iceland, can host rare, high 3He/4He isotopic ratios (up to 50 times4 the present atmospheric ratio, Ra) compared to the lower 3He/4He ratios identified in mid-ocean-ridge basalts that form by melting the upper mantle (about 8Ra; ref. 5). A long-standing hypothesis maintains that the high-3He/4He domain resides in the deep mantle6, 7, 8, beneath the upper mantle sampled by mid-ocean-ridge basalts, and that buoyantly upwelling plumes from the deep mantle transport high-3He/4He material to the shallow mantle beneath plume-fed hotspots. One problem with this hypothesis is that, while some hotspots have 3He/4He values ranging from low to high, other hotspots exhibit only low 3He/4He ratios. Here we show that, among hotspots suggested to overlie mantle plumes9, 10, those with the highest maximum 3He/4He ratios have high hotspot buoyancy fluxes and overlie regions with seismic low-velocity anomalies in the upper mantle11, unlike plume-fed hotspots with only low maximum 3He/4He ratios. We interpret the relationships between 3He/4He values, hotspot buoyancy flux, and upper-mantle shear wave velocity to mean that hot plumes—which exhibit seismic low-velocity anomalies at depths of 200 kilometres—are more buoyant and entrain both high-3He/4He and low-3He/4He material. In contrast, cooler, less buoyant plumes do not entrain this high-3He/4He material. This can be explained if the high-3He/4He domain is denser than low-3He/4He mantle components hosted in plumes, and if high-3He/4He material is entrained from the deep mantle only by the hottest, most buoyant plumes12. Such a dense, deep-mantle high-3He/4He domain could remain isolated from the convecting mantle13, 14, which may help to explain the preservation of early Hadean (>4.5 billion years ago) geochemical anomalies in lavas sampling this reservoir1, 2, 3.
DS201709-2003
2017
Jacob, D.E., Stern, R.A., Chapman, J., Piazoli, S.Insights into diamond formation from polycrystalline diamond aggregates. DiamonditesGoldschmidt Conference, abstract 1p.Africa, South Africadeposit - Venetia

Abstract: Polycrystalline diamond aggregates (diamondites) are produced by rapid crystal nucleation caused by extreme carbon supersaturation in mantle fluids. They may form episodically and under variable chemical conditions, providing snapshots of diamond formation in the Earth’s mantle. Diamondites, thus, represent an extreme end member of diamond formation mechanisms, while forming via the same processes and ingredients as the gem-sized diamonds. We present results on a large suite of diamondites from the Venetia mine (South Africa), comprising a complete characterisation of the diamonds and their silicate inclusions and intergrowths. The highlighted characteristic of this sample suite is its heterogeneity in all aspects, from affiliated silicate to diamond composition and texture of the diamond aggregates. The diamond grains in the samples are intergrown with silicates (garnets, clinopyroxenes, phlogopites) comprising a websteritic-eclogitic and a peridotiticpyroxenitic suite of minerals. Diamonds, regardless of their affiliation based on their silicate phases, overlap in carbon and nitrogen composition and have ?13C values between -28 and -8 ‰, ?15N values of 0.8 to 16.3 ‰ and nitrogen contents of 4 to 2329 ppm. The entire range of carbon and nitrogen variability of the suite is also reflected in some individual samples. Cathodoluminescence imaging visualizes different zones in the samples that can be interpreted as different growth events with differing nitrogen contents and ?15N decoupled from ?13C values, in line with the variability off nitrogen aggregation states. Electron backscatter diffraction analyses identify an original texture of randomly intergrown diamond grains that is partly changed by deformation and newly grown smaller diamond grains. The large overall variability suggesting episodic formation of diamondite with nitrogen from crustal sources.
DS201702-0217
2017
Jacob, J.Overview of the Namibian diamond megaplacer: past, present and future potential.PDAC 2017, March 6, 1p. AbstractAfrica, NamibiaAlluvials
DS201709-2004
2016
Jacob, J., Prins, C.Construction of an expert opinion based virtual orebody for a Diamondiferous linear beach deposit. South African Institute of Mining and Metallurgy, Vol. 116, 7, pp. 629-336.Africa, Namibiatechnology, alluvials
DS201709-2005
2016
Jacob, J., Prins, C.Using the proportion of barren samples as a proxy for minimum grade in a Diamondiferous linear beach deposit - an application of the Nachman model.South African Institute of Mining and Metallurgy, Vol. 116, 8, pp. 731-737.Africa, Namibiadeposit - Orange River

Abstract: Over the past 80 years, the Namibian diamondiferous marine placer has been studied extensively to develop solutions for mining and sampling challenges. The types of studies include the statistical modelling of the distributions of the stone counts per sample; investigating the relationship between geology and the grade distribution; assessing the quality potential of the entrapment of the available diamond pulse; using predetermined acceptability of barren samples (zero proportion (Zp) samples) to model distributions; optimal sample sizes; and more. During early-stage project evaluation it is more important to find out if a particular area is likely to be above a specific cut-off grade than to focus on sampling for the purpose of accurate resource estimation. Previous work using mixed Poisson and Sichel distributions to model the abundant onshore diamond data has been very successful in modelling the long-tailed nature of these linear beach deposits. The means of these distributions are, however, sensitive to extreme values. Technical and cost constraints prevent a similar scale of sample collection in an adjacent, geologically equivalent, submerged beach environment. A method not sensitive to extreme values is thus required to make early-stage assessments of the likelihood that the grade of a particular target is above a minimum cut-off grade. The Nachman model describes the functional relationship between the mean population density and proportion of barren patches ( Zp) in a patchy environment. A prerequisite for using the Nachman model is that the underlying data must be modelled using a negative binomial distribution (NBD). The case study data is from an analogous area adjacent to the exploration target and meets the NBD requirement. It is thus appropriate to apply the Nachman model. The Nachman model provides an opportunity to use the observed Zpto predict the mean grade for an area at the very early stage of an exploration project. In future, early-stage exploration data from a homogenous geological zone exhibiting characteristics of the Nachman model assumptions can thus be used to rank and target those areas that show potential to be above the minimum required grade cut-off for follow-up sampling and inclusion in the mine planning cycle.
DS201712-2695
2005
Jacob, R.J.The erosional and Cainozoic deposition history of the Lower Orange River southwestern Africa.Thesis, Phd. University of Glasgow, 178p. PdfAfrica, South Africadeposit - Lower Orange River

Abstract: A series of terraces flanking the Lower Orange River in the study area were deposited after ca. 90% of the incision had occurred, thus only the late stage incision/depositional history of this margin is able to be addressed here. Two principal suites of river terraces are distinguished by their palaeo-courses, bedrock strath levels, overall geometry and clast assemblages: an older, higher lying Proto suite and a younger Meso suite. The Proto suite represents a long, post-Eocene, through the Oligocene into the Early Miocene, phase of incision, followed by a prolonged period of aggradation where up to 90 m of fluvial, diamondiferous deposits accumulated during the Early-Middle Miocene. The Meso suite of deposits represents shorter phrases of incision and aggradation in the Pilo-Pleistocene. The Proto and Meso deposits were built in response to both base level rise and increased supply of material from tributaries draining the Great Escarpment locally, with clast assemblage and downstream fining data indicating the latter to be the more important variable. River incision into bedrock is a topic of great interest to fluvial geomorphologists, although most data are derived from active tectonic settings. The incision of a large river into a plateau surface is relatively rare, the best known example being the Colorado River in the young (6 Ma) Grand Canyon. The Orange River in the study area represents a long-lived example of this setting, with the present day dissected topography having evolved from more confined canyon-like walls following the early incision of the Orange River in the Early Tertiary. Although a long-lived incision, the modern channel is not graded in the study area, and is actively incising. The world-wide dataset of incision rates in modern rivers indicates that the Orange River could have completed its entire incision within less than a million years. The continued downcutting of this river so long after the initial incision event is indicative of the roles of intermittent, ongoing epeirogenesis and/or eustatic influences (both of which cannot be proven at this stage), tributary input from the plateau rim (Great Escarpment) or merely the long tag time involved in landscape adjustment following incision into a plateau surface.
DS201708-1677
2017
Jacques, L.Insights into the petrogenesis of the West Kimberley lamproites from trace elements in olivine.11th. International Kimberlite Conference, OralAustralialamproites
DS201708-1678
2017
Jakubec, J.Mining for diamonds - history and present.11th. International Kimberlite Conference, OralGlobalBlank
DS201708-1679
2017
Jakubec, J.Underground diamond mining at Ekati and Diavik mines.11th. International Kimberlite Conference, PosterCanada, Northwest Territoriesdeposit - Ekati, Diavik
DS201708-1680
2017
Janney, P.Hidden reservoirs in the continental lithosphere? Evidence from Hf-Sr-Nd-Pb isotopes in southern African kimberlite megacrysts.11th. International Kimberlite Conference, OralAfrica, Southern Africageochronology
DS201708-1681
2017
Janney, P.Geochemistry of the Namaqualand, Busmanland and Warmbad melillitite and kimberlite provinces of South Africa and Namibia: the southern extension of the African kimberlitic megalineament.11th. International Kimberlite Conference, PosterAfrica, South Africa, Namibiageochemistry, lineament
DS201705-0836
2017
Janse, B.Geology of Diamond.lithographie.org, No. 19, pp. 10-23.TechnologyBook - geology
DS201705-0837
2017
Jaszczak, J.A., Dunnell, K.The Magnificent Mineralogy of Diamond.lithographie.org, No. 19, pp. 24-35.TechnologyBook - mineralogy
DS201711-2518
2017
Jebrak, M., Montel, J-M.Educating the resource geologist of the future: between observation and imagination.Elements, Vol. 13, pp. 331-336.Globalresources

Abstract: Training geologists for a career in the mining industry has changed over the years. It has become at the same time more specialized and with a broader approach. The modern resource geologist needs to understand new styles of ore deposits, the impact of energy transition on the types of deposits and to implement mining processes, the increasing number of mining regulations, and the shift toward educating populations in countries that are new to mining. Based on observation and imagination, rooted in fundamental science, the education of a resource geologist has been transformed by the digital revolution and the integration of the principles of sustainable development. Training future resource geologists means changing the role of teachers to better develop the imaginations of their students and to increasing what students know about the social impact of mining.
DS201708-1682
2017
Jeffcoate. A.3-D geological model of the BK16 kimberlite pipe located within the Orapa kimberlite field (OKF) in Botswana.11th. International Kimberlite Conference, PosterAfrica, Botswanadeposit - BK-16
DS201704-0629
2017
Jennings, E.S., Holland, T.J.B., Maclennan, J., Gibson, S.A.The composition of melts from a heterogeneous mantle and the origin of ferropicrite: application of a thermodynamic model.Journal of Petrology, Vol. 57, 11-12, pp. 2289-2310.MantleGeochemistry
DS201702-0218
2016
Jennings, E.S., Holland, T.J.B., Shorttle, O., Gibson, S.The composition of melts from a heterogeneous mantle and origin of ferropicrite: application of a thermodynamic model.Journal of Petrology, In press available 22p.MantleEclogite, melting

Abstract: Evidence for chemical and lithological heterogeneity in the Earth’s convecting mantle is widely acknowledged, yet the major element signature imparted on mantle melts by this heterogeneity is still poorly resolved. In this study, a recent thermodynamic melting model is tested on a range of compositions that correspond to potential mantle lithologies (harzburgitic to pyroxenitic), to demonstrate its applicability over this compositional range, in particular for pyroxenite melting. Our results show that, despite the model’s calibration in peridotitic systems, it effectively reproduces experimental partial melt compositions for both Si-deficient and Si-excess pyroxenites. Importantly, the model accurately predicts the presence of a free silica phase at high pressures in Si-excess pyroxenites, indicating the activation of the pyroxene-garnet thermal divide. This thermal divide has a dominant control on solidus temperature, melt productivity and partial melt composition. The model is used to make new inferences on the link between mantle composition and melting behaviour. In silica-deficient and low-pressure (olivine-bearing) lithologies, melt composition is not very sensitive to source composition. Linearly varying the source composition between peridotite and basaltic pyroxenite, we find that the concentration of oxides in the melt tends to be buffered by the increased stability of more fusible phases, causing partial melts of even highly fertile lithologies to be similar to those of peridotite. An exception to this behaviour is FeO, which is elevated in partial melts of silica-deficient pyroxenite even if the bulk composition does not have a high FeO content relative to peridotite. Melt Al2O3 and MgO vary predominantly as a function of melting depth rather than bulk composition. We have applied the thermodynamic model to test the hypothesis that Fe-rich mantle melts such as ferropicrites are derived by partial melting of Si-deficient pyroxenite at elevated mantle potential temperatures. We show that the conspicuously high FeO in ferropicrites at a given MgO content does not require a high-Fe mantle source and is indeed best matched by model results involving around 0-20% melting of silica-deficient pyroxenite. A pyroxenite source lithology also accounts for the low CaO content of ferropicrites, whereas their characteristic low Al2O3 is a function of their high pressure of formation. Phanerozoic ferropicrites are exclusively located in continental flood basalt (CFB) provinces and this model of formation confirms that lithological heterogeneity (perhaps recycled oceanic crust) is present in CFB mantle sources.
DS201703-0410
2017
Jia, X., Wang, X., Yang, W.Petrogenesis and geodynamic implications of the Early Paleozoic potassic and ultrapotassic rocks in the south Chin a block.Journal of Asian Earth Sciences, Vol. 135, pp. 80-94.ChinaAlkaline rocks

Abstract: In this paper, some potassic and ultrapotassic rocks in the South China Block (SCB) have been recognized, according to a set of new geochronological, geochemical and Sr-Nd isotopic data. Zircon U-Pb dating from six plutons yield consistent crystallization ages of 445-424 Ma. These potassic and ultrapotassic rocks can be geochemically subdivided into three groups. Group 1, represented by the Longchuan gabbro, longmu diabase, Tangshang and Danqian diorite (445-433 Ma), have low silica contents (SiO2 = 47.38-54.16 wt.%), and high MgO (4.21-9.51 wt.%) and total alkalis (Na2O + K2O = 3.08-5.57 wt.%), with K2O/Na2O ratios of 0.62-1.82. They are enriched in LREE and depleted in Ba, Sr and Ta-Nb-Ti, and exhibit relatively high initial 87Sr/86Sr ratios (0.70561-0.71128), low ?Nd(430 Ma) values (?8.4 to ?3.2), suggesting that they were most plausibly generated by the partial metling of enriched mantle source (EMI). Group 2, from the Huwei diorite (424 Ma), have 45.68-52.87 wt.% of SiO2, 5.79-9.25 wt.% of MgO and 52-65 of mg-number. They have significantly higher Th (9.92 ppm), Ce (88.0-115 ppm) concentration and Ce/Yb (27.6-46.8), Th/Yb ratios (2.58-7.99), and relatively low initial 87Sr/86Sr ratios (0.70501-0.70599), and high ?Nd(430 Ma) values (?2.1 to ?1.5). We propose that they originated from the partial melting of the depleted mantle source with subsequent contamination by crustal materials. Group 3, represented by the Daning lamprophyre (?445 Ma), has SiO2 contents ranging from 41.73 wt.% to 45.22 wt.%, MgO from 13.74 wt.% to 15.16 wt.%, and mg-muber from 73 to 77, with high K2O/Na2O ratios (>2.0). They have 87Sr/86Sr ratios of 0.62912-0.70384 and ?Nd(t = 430 Ma) values of ?6.4 to ?6.3, indicating that the source components are close to the EMI source, with significant sediments involved. These Silurian potassic and ultrapotassic rocks in the SCB can be responsible for post-orogenic delamination and intra-plate extension. And the delamination had a small size and a long duration, and a negligible impact.
DS201711-2519
2017
Johnson, B.W., Goldblatt, C.A secular increase in continental crust nitrogen during the Precambrian. Glacial tillsGeochemical Perspectives Letters, Vol. 4, pp. 24-28.Mantlegeomorphology

Abstract: Recent work indicates the presence of substantial geologic nitrogen reservoirs in the mantle and continental crust. Importantly, this geologic nitrogen has exchanged between the atmosphere and the solid Earth over time. Changes in atmospheric nitrogen (i.e. atmospheric mass) have direct effects on climate and biological productivity. It is difficult to constrain, however, the evolution of the major nitrogen reservoirs through time. Here we show a secular increase in continental crust nitrogen through Earth history recorded in glacial tills (2.9 Ga to modern), which act as a proxy for average upper continental crust composition. Archean and earliest Palaeoproterozoic tills contain 66 ± 100 ppm nitrogen, whereas Neoproterozoic and Phanerozoic tills contain 290 ± 165 ppm nitrogen, whilst the isotopic composition has remained constant at ~4‰. Nitrogen has accumulated in the continental crust through time, likely sequestered from the atmosphere via biological fixation. Our findings support dynamic, non-steady state behaviour of nitrogen through time, and are consistent with net transfer of atmospheric N to geologic reservoirs over time.
DS201704-0630
2017
Johnson, T.E., Brown, M., Gardiner, N.J., Kirkland, C.L., Smithies, R.H.Earth's first stable continents did not form by subduction.Nature, Vol. 543, pp. 239-242.MantleGeodynamics

Abstract: The geodynamic environment in which Earth’s first continents formed and were stabilized remains controversial1. Most exposed continental crust that can be dated back to the Archaean eon (4 billion to 2.5 billion years ago) comprises tonalite-trondhjemite-granodiorite rocks (TTGs) that were formed through partial melting of hydrated low-magnesium basaltic rocks2; notably, these TTGs have ‘arc-like’ signatures of trace elements and thus resemble the continental crust produced in modern subduction settings3. In the East Pilbara Terrane, Western Australia, low-magnesium basalts of the Coucal Formation at the base of the Pilbara Supergroup have trace-element compositions that are consistent with these being source rocks for TTGs. These basalts may be the remnants of a thick (more than 35?kilometres thick), ancient (more than 3.5 billion years old) basaltic crust4, 5 that is predicted to have existed if Archaean mantle temperatures were much hotter than today’s6, 7, 8. Here, using phase equilibria modelling of the Coucal basalts, we confirm their suitability as TTG ‘parents’, and suggest that TTGs were produced by around 20 per cent to 30 per cent melting of the Coucal basalts along high geothermal gradients (of more than 700 degrees Celsius per gigapascal). We also analyse the trace-element composition of the Coucal basalts, and propose that these rocks were themselves derived from an earlier generation of high-magnesium basaltic rocks, suggesting that the arc-like signature in Archaean TTGs was inherited from an ancestral source lineage. This protracted, multistage process for the production and stabilization of the first continents—coupled with the high geothermal gradients—is incompatible with modern-style plate tectonics, and favours instead the formation of TTGs near the base of thick, plateau-like basaltic crust9. Thus subduction was not required to produce TTGs in the early Archaean eon.
DS201712-2696
2018
Jollands, M.C., Hanger, B.J., Yaxley, G.M., Hermann, J., Kilburn, M.R.Timescales between mantle metasomatism and kimberlite ascent indicated by diffusion profiles in garnet crystals from periodotite xenoliths.Earth and Planetary Science Letters, Vol. 481, pp. 143-153.Africa, South Africadeposit - Wesselton

Abstract: Rare garnet crystals from a peridotite xenolith from the Wesselton kimberlite, South Africa, have distinct zones related to two separate episodes of mantle metasomatism. The garnet cores were firstly depleted through melt extraction, then equilibrated during metasomatism by a potentially diamond-forming carbonate-bearing or proto-kimberlitic fluid at 1100-1300?°C and 4.5-5.5 GPa. The garnet rim chemistry, in contrast, is consistent with later overgrowth in equilibrium with a kimberlite at around and . This suggests that the rock was physically moved upwards by up to tens of kilometres between the two metasomatic episodes. Preserved high Ca, Al and Cr contents in orthopyroxenes suggest this uplift was tectonic, rather than magmatic. Diffusion profiles were measured over the transitions between garnet cores and rims using electron microprobe (Mg, Ca, Fe for modelling, plus Cr, Mn, Ti, Na, Al) and nano Secondary Ion Mass Spectrometry (NanoSIMS; 89Y, along with 23Na, Ca, Cr, Fe, Mn and Ti) analyses. The short profile lengths (generally <10 ?m) and low Y concentrations (0.2-60 ppm) make the NanoSIMS approach preferable. Diffusion profiles at the interface between the zones yield constraints on the timescale between the second metasomatic event and eruption of the kimberlite magma that brought the xenolith to the surface. The time taken to form the diffusion profiles is on the order of 25 days to 400 yr, primarily based on modelling of Y diffusion along with Ca, Fe and Mg (multicomponent diffusion) profiles. These timescales are too long to be produced by the interaction of the mantle xenolith with the host kimberlite magma during a single-stage ascent to the crust (hours to days). The samples offer a rare opportunity to study metasomatic processes associated with failed eruption attempts in the cratonic lithosphere.
DS201705-0838
2017
Jones, A., Alvaro, M., McMillan, P., Price, D., Milledge, J.Lonsdaleite signatures and shock remnants in mantle diamond?European Geosciences Union General Assembly 2017, Vienna April 23-28, 1p. 16597 AbstractChinaDeposit - Liaoning
DS201709-2006
2017
Jones, A., Wood, B., Mikhail, S.Oldest diamond crystallisation on Earth: a metal driven Hadean growth model related to core formation.Goldschmidt Conference, abstract 1p.Mantlediamond genesis

Abstract: When hot liquid metal drained towards the core during and shortly after Earth accretion, exceptional conditions may have led to the first global crystallisation of diamond. Newly reported metallic iron trapped in large mantle diamond invites comparison between commercial Fe-Ni-Co “HPHT” diamond growth and natural environments. We evaluate possible conditions for Hadean diamond crystallisation from liquid ironrich metal where thermal and compositional gradients influence diamond crystallization. The solubility of up to 6% carbon has little effect on the phase transitions of the metallic iron phase diagram and carbon generally decreases with increasing pressure in solid iron based on calculated enthalpies. Models for core differentiation provide two scenarios (i) from an accumulated metal “pond” (ii) from massive downward mobile metal diapirs. A refinement arises from a parameterization of self-propagating downward fractures filled by turbulent liquid iron as proposed by Stephenson to send a transponder to the core; negatively buoyant diamond crystals would float. Experiments show that diamond growth under these conditions is fast (~1 carat per hour) and micro-textures of natural diamond with metallic inclusions retain substantial isotopic heterogeneities. We speculate that if the oldest diamond trapped metallic iron on its way to form the core, such “stranded core” might be recognized by trace element compositions, and could retain anomalous isotopic signatures of W and Hf.
DS201712-2697
2017
Jones, A.G., Alfonso, J.C., Fullea, J.Geochemical and geophysical constrains on the dynamic topography of the southern African plateau.Geochemistry, Geophysics, Geosystems, Vol. 18, 10, pp. 3556-3575.Africa, South Africageodynamics

Abstract: The deep mantle African Superswell is considered to contribute to the topographic uplift of the Southern African Plateau, but dynamic support estimates vary wildly depending on the approach and data used. One reason for these large disparities is that the role of lithospheric structure, key in modulating deep dynamic contributions to elevation, is commonly ignored or oversimplified in convection studies. We use multiple high-quality geophysical data coupled with xenolith-based geochemical constraints to compute the isostatic lithospheric contribution to the elevation of the Plateau, facilitating isolation of the current dynamic component from the total observed elevation. We employ a multiobservable stochastic algorithm to invert geoid anomaly, surface-wave dispersion data, magnetotelluric data, and surface heat flow to predict elevation in a fully thermodynamically and internally-consistent manner. We find that a compositionally layered 230?±?7 km thick lithosphere is required to simultaneously fit all four data types, in agreement with abundant independent xenolith evidence. Our stochastic modeling indicates a lithospheric contribution to elevation of the order of 670 m, which implies dynamic support arising from the convecting sublithospheric mantle of ?650 m. Our results have important implications for the understanding of lithospheric-deep mantle feedback mechanisms and for calibrating dynamic topography estimates from global convection studies.
DS201701-0016
2016
Jones, A.P., McMillan P.F., Salzmann, C.G., Alvaro, M., Nestola, F., Prencipe, M., Dobson, D., Hazael, R., Moore, M.Structual characterization of natural diamond shocked to 60 Gpa; implications for Earth and Planetary Systems.Lithos, In press availableTechnologyDiamond morphology

Abstract: The possible presence of the high-density carbon polymorph with hexagonal symmetry known as “lonsdaleite” provides an important marker for shock impact events. It is typically considered to form as a metastable phase produced from graphite or other carbonaceous precursors. However, its existence has recently been called into question. Here we collected high-resolution synchrotron X-ray diffraction data for laboratory-shocked and natural impact diamonds that both show evidence for deviations from cubic symmetry, that would be consistent with the appearance of hexagonal stacking sequences. These results show that hexagonality can be achieved by shocking diamond as well as from graphite precursors. The diffraction results are analyzed in terms of a general model that describes intermediate stacking sequences between pure diamond (fully cubic) and “lonsdaleite” (fully hexagonal) phases, with provision made for ordered vs disordered stacking arrangements. This approach provides a “hexagonality index” that can be used to characterize and distinguish among samples that have experienced different degrees of shock or static high pressure-high temperature treatments. We have also examined the relative energetics of diamond and “lonsdaleite” structures using density functional theoretical (DFT) methods. The results set limits on the conditions under which a transformation between diamond and “lonsdaleite” structures can be achieved. Calculated Raman spectra provide an indicator for the presence of extended hexagonal stacking sequences within natural and laboratory-prepared samples. Our results show that comparable crystallographic structures may be developed by impact-generated shockwaves starting from ambient conditions using either of the two different allotropes of carbon (diamond, graphite). This broadens the scope for its occurrence in terrestrial and planetary systems.
DS201708-1683
2017
Jones, T.Experimental milling of olivine: implications for ascent and eruption of kimberlite.11th. International Kimberlite Conference, OralMantleMineralogy - olivine
DS201708-1684
2017
Jones, T.Kimberlitic olivine attrition: fingerprinting environments and timescales.11th. International Kimberlite Conference, PosterMantleolivine
DS201709-2007
2016
Judeel, G., Swanepoel, T., Holder, A., Swarts, B., van Strijp, T., Cloete, A.Extension of the Culli nan diamond mine No. 1 shaft underneath the existing operating shaft, with emphasis on rock engineering considerations.South African Institute of Mining and Metallurgy, Vol. 116, 8, pp. 745-752.Africa, South Africadeposit - Cullinan

Abstract: In 2012, Cullinan Diamond Mine began an expansion programme with the shaft deepening and development of access to the C-Cut 1 block at approximately 839 m below surface. The expansion programme is funded by a combination of bank loans and retained operating profit generated by the mine. Continuous production during deepening of the No. 1 Shaft, which is the rock hoisting shaft, was therefore critical for sustainability and efficiency as well as overall funding of the project. The deepening method, support design and verification, as well as learning outcomes pertaining to the extension of the No. 1 Shaft underneath the existing operating shaft are summarized, with emphasis on the importance of gaining some understanding of the shaft's host rock mass.
DS201709-2008
2017
Kalasnikova, T.V., Solovea, L.V., Kostrovitsky, S.I.Metasomatic features in the mantle xenoliths from Obnajennaya kimberlite pipe - the mineral composition evidence.Goldschmidt Conference, abstract 1p.Russiadeposit - Obnajennaya

Abstract: The modal metasomatic alteration for lithosphere mantle may be investigated using mantle xenoliths from kimberlite pipes. The mantle xenoliths from upper-Jurassic Obnajennaya kimberlite pipe (Kuoika field, Yakutia) were studied. Three main xenoliths groups in Obnajennaya pipe were distinguished based on the petrographic and geochemical features: 1. Sp, Sp-Grt, Grt harzburgites - lherzolites, Sp, Sp-Grt, Grt olivine websterites and Sp, Sp-Grt, Grt websterite (so-called magnesium group - about 80 % from xenoliths). The high magnesium mineral composition, high estimated temperature (1250 - 1500°?) for exsolution pyroxene megacrystals, presence of sulphide globules and distribution curves for rare earth elements in garnets (La-Yb increasing) are to assume the crystallisation from melt. The 10% magnesium mantle xenoliths are observed the secondary metasomatic phlogopite and amphibole (pargasite). The clinopyroxene distribution curves demonstrate the wide range of values and altered samples show higher content HFSE group elements that primary clinopyroxene. The increasing of HFSE and rare earth element concentrations can also be traced by the amphibole chemical composition. The 40Ar/39Ar dating of phlogopite from was result 1639 ± 5 Ma nearly corresponding to the time of Siberian craton accretion Thus during Siberian craton accretion (about 1.7 Ga) the melts-fluids enriching Nb + Ta and REE impacted on lithosphere mantle under Kuoika field. 2. Eclogites and Grt clinopyroxenites with similar mineral composition (about 10-15% xenoliths). The high ?O18 for garnet and clinopyroxene (5.7–5.8‰) allows to assume subduction genesis. 3. Phl-Ilm rocks characterizing ferrous mineral composition (~ 10 % xenoliths). This group are charactetrized are ferrous mineral composition. The 40Ar/39Ar phlogopite dating resulted to 800-500 Ma, signed the potassium and titanium metasomatic fluide – melt influenced
DS201709-2009
2017
Kaldos, R., Guzmics, T., Vaczi, T., Berkesi, M., Dankhazi, Z., Szabo, C.3D Raman mapping of melt inclusions in Kerimasi alkaline and carbonatite rocks.Goldschmidt Conference, abstract 1p.Africa, Tanzaniadeposit - Kerimasi

Abstract: The use of confocal HR-Raman mapping opens new perspectives in studying melt inclusions. Our major goal is to show advantages of this powerful technique through case studies carried out on alkaline and carbonatite rocks of Kerimasi volcano (East African Rift). Raman spectrometry is one of the few methods that enable qualitative nondestructive analysis of both solid and fluid phases, therefore it is widely used for the identification of minerals and volatiles within melt and fluid inclusions. For better understanding of petrogenetic processes in carbonatite systems it is essential to find all mineral phases in the melt inclusions trapped in intrusive or volcanic rocks. Previous Raman spectroscopic point measurements in melt inclusions revealed the presence of daughter phases (e.g. alkali carbonates, hydrocarbonates) [1] but utilizing Raman mapping on them even provides information on their size, shape and distribution. Raman 3D mapping were applied on unheated multiphase melt inclusions of intrusive and volcanic rocks with high spatial resolution (XY plane < 1 micron) with a depth scan (Z step) as low as 0.5 micron at every XY point, parallel to the surface of the host minerals. Analysis below the surface of the host mineral is especially useful because we can avoid the loss of sensitive (e.g. water soluble) phases and contamination of the melt inclusions, moreover unexposed melt inclusions are suitable for further analytical measurements (e.g. EPMA, microthermometry). By scanning multiple layers 2D or 3D Raman images can be gained, thus we can get an insight into post entrapment crystallization processes that contribute to a more precise description of the evolution of alkaline and carbonatite rocks.
DS201709-2010
2017
Kamber, B.S.Why Archean cratons differ from younger continental lithosphere.Goldschmidt Conference, abstract 1p.Mantlecraton

Abstract: The most outstanding features of Archaean cratons are their extraordinary thickness and enduring longevity. Seismically, Archaean cratonic fragments are sharplybounded deep roots of buoyant cold lithospheric mantle, clearly distinguishable from non-cratonic lithosphere. The age of diamond inclusions and the Os-isotope composition of deep cratonic xenoliths support a model of coeval formation of the crustal and residual mantle portions. Archaean and post-Archaean crust also differ, not in bulk composition, but in crustal architecture. Key drivers of crustal rearrangment were the radioactive heat-producers U, Th and K. In the early Earth, high radioactive heat production led to self-organisation into evolved, potassic upper and refractory lower crust. The lag time between crust formation and reorganisation was much shorter than today. An additional factor contributing to cratonic restructuring was the emplacement of dense supracrustal rocks in ensialic greenstone belts, leading to gravitational inversion. The dome and keel architecture of Archaean cratons was thus driven by crustal radioactive heat and high temperature mantle melting, yielding dense, low viscosity lavas piling up at surface. A pleasing complementary observation from cratonic mantle roots is that refractory mantle nodules also suggest very high degrees of melting and extraction. Thus, the most logical conclusion seems that the komatiite mantle source was up to 500ºC hotter than modern asthenosphere. With higher degree and depth of melting, a thicker and severely depleted bouyant cratonic residue was formed, perfectly equipped to preserve the Archaean crustal record. However, there are significant inconsistencies in this otherwise convincing line of reasoning. They include: Archaean crust is not especially thick, the dunites expected after very high degree melting are rare, many cratonic harzburgites are much richer in orthopyroxene than predicted [1], and cratonic harzburgites often contain garnet. Finding a solution to these issues has important ramifications for secular evolution of the continents and thermal evolution of the mantle. In this presentation, I will contrast the various proposed solutions, including purging of surprisingly carbonated ancient mantle [e.g. 2], onset of plate tectonics, a Neoarchaean superplume event and collapse of Hadean cumulate barriers.
DS201707-1337
2017
Kamenetsky, V.S., Maas, R., Kamenetsky, M.B., Yaxley, G.M., Ehrig, K., Zellmer, G.F., Bindeman, I.N., Sobolev, A.V., Kuzmin, D.V., Ivanov, A.V., Woodhead, J., Schilling, J-G.Multiple mantle sources of continental magmatism: insights from high Ti picrites of Karoo and other large igneous provinces.Chemical Geology, Vol. 455, pp. 22-31.Africa, South Africamagmatism

Abstract: Magmas forming large igneous provinces (LIP) on continents are generated by extensive melting in the deep crust and underlying mantle and associated with break-up of ancient supercontinents, followed by formation of a new basaltic crust in the mid-oceanic rifts. A lack of the unifying model in understanding the sources of LIP magmatism is justified by lithological and geochemical complexity of erupted magmas on local (e.g. a cross-section) and regional (a single and different LIP) scales. Moreover, the majority of LIP rocks do not fit general criteria for recognizing primary/primitive melts (i.e. < 8 wt% MgO and absence of high-Fo olivine phenocrysts). This study presents the mineralogical (olivine, Cr-spinel, orthopyroxene), geochemical (trace elements and Sr-Nd-Hf-Pb isotopes) and olivine-hosted melt inclusion compositional characteristics of a single primitive (16 wt% MgO), high-Ti (2.5 wt% TiO2) picrite with high-Mg olivine (up to 91 mol% Fo) from the Letaba Formation in the ~ 180 Ma Karoo LIP (south Africa). The olivine compositions (unusually high ?18O (6.17‰), high NiO (0.36–0.56 wt%) and low MnO and CaO (0.12–0.20 and 0.12–0.22 wt%, respectively)) are used to argue for a non-peridotitic mantle source. This is supported by the enrichment of the rock and melts in most incompatible trace elements and depletion in heavy rare earth elements (e.g. high Gd/Yb) that reflects residual garnet in the source of melting. The radiogenic isotopes resemble those of the model enriched mantle (EM-1) and further argue for a long-term enrichment of the source in incompatible trace elements. The enriched high-Ti compositions, strongly fractionated incompatible trace elements, presence of primitive olivine and high-Cr spinel in the Letaba picrites are closely matched by olivine-phyric rocks from the ~ 260 Ma Emeishan (Yongsheng area, SW China) and ~ 250 Ma Siberian (Maimecha-Kotuy region, N Siberia) LIPs. However, many other compositional parameters (e.g. trace element and ?18O compositions of olivine phenocrysts, Fe2 +/Fe3 + in Cr-spinel, Sr-Nd-Hf isotope ratios) only partially overlap or even diverge. We thus imply that parental melts of enriched picritic rocks with forsteritic olivine from three major continental igneous provinces – Karoo, Emeishan and Siberia cannot be assigned to a common mantle source and similar melting conditions. The Karoo picrites also exhibit some mineralogical and geochemical similarities with rocks and glasses in the south Atlantic Ridge and adjacent fracture zones. The geodynamic reconstructions of the continental plate motions since break-up of the Gondwanaland in the Jurassic support the current position of the source of the Karoo magmatism in the southernmost Atlantic. Co-occurrence of modern and recent anomalous rocks with normal mid-ocean ridge basalts in this region can be related to blocks/rafts of the ancient lithosphere, stranded in the ambient upper mantle and occasionally sampled by rifting-related decompressional melting.
DS201703-0411
2017
Kaminski, V., Viezzoli, A.Modeling induced polarization effects in helicopter time domain electromagnetic data: Field case studies ( Drybones Bay, NWT)Geophysics, Vol. 82, 2, pp. B49-B61.Canada, Northwest TerritoriesGeophysics, deposit - Drybones

Abstract: Induced polarization (IP) effects are becoming more evident in time-domain helicopter airborne electromagnetic (AEM) data thanks to advances in instrumentation, mainly due to improvements in the signal-to-noise ratio and hence better data quality. Although the IP effects are often manifested as negative receiver voltage values, which are easy to detect, in some cases, IP effects can distort recovered transients in other ways so they may be less obvious and require careful data analysis and processing. These effects represent a challenge for modeling and inversion of the AEM data. For proper modeling of electromagnetic transients, the chargeability of the subsurface and other parameters describing the dispersion also need to be taken into consideration. We use the Cole-Cole model to characterize the dispersion and for modeling of the IP effects in field AEM data, collected by different airborne systems over different geologies and exploration targets, including examples from diamond, gold, and base metal exploration.
DS201704-0631
2017
Kaminsky, F., Wirth, R.Nitride, carbonitride and nitrocarbide inclusions in the lower mantle diamonds: a key to the balance of nitrogen in the Earth.Geophysical Research Abstracts, Vol. 19, EGRU2017-1751, April 1p.MantleDiamond, inclusions, nitrogen

Abstract: A few years ago a series of iron carbides Fe3C, Fe2C, Fe7C3 and Fe23C6 (haxonite) containing up to 7.3-9.1 at.% N (N/(N+C) = 0.19-0.27) was identi?ed as inclusions in diamonds from the Juina area, Brazil in association with native iron and graphite (Kaminsky and Wirth, 2011). Subsequently nitrocarbides and carbonitrides Fe3(C,N) and Fe9(C,N)4 (nitroyarlongite) containing 12.8-18.42 at.% N (N/(N+C) = 0.37-0.60) were identi?ed in a lower-mantle microxenolith in association with ferropericlase and two post-spinel oxides Mg-Cr-Fe-O (CT phase; Mg-xieite) and Ca-Cr-O (new mineral) with an orthorhombic structure (Kaminsky et al., 2015). Recently pure nitrides Fe3N with a trigonal structure P312 and Fe2N with an orthorhombic structure Pbcn were identi?ed among mineral inclusions from diamonds in the same area. They have admixtures of Cr (0.68-1.8 at.%), Ni (0.35-0.93 at.%) and Mn (0-1.22 at.%). Fe2N contains also an admixture of 5.1-7.6 at.% Si. The nitrides associate with nitroyarlongite Fe9(N0.8C0.2)4 and iron carbide Fe7C3, which contain nanocrystals of moissanite, hexagonal 6H polytype of SiC. Fe7C3 crystallizes, in the Fe-C system, the ?rst in association with diamond at pressures starting from 130 GPa, i.e. within the lowermost mantle, the D[U+02BA] layer. Native iron and a series of nitride-carbonitride-nitrocarbide-carbides associated with Fe7C3 form as a result of in?ltration of the Fe-Ni melt from the outer core into the lowermost mantle. This melt contains up to 10 % light elements, such as C, N, O and Si, which may be the source of nitrides-carbides. The existence of nitrides in the lower mantle helps to solve the problem of ‘missing nitrogen’ in the Earth’s nitrogen balance and consider the Earth’s core as the major reservoir of nitrogen. According to calculations, the total amount of nitrogen in the Earth’s core is 9,705 ×1021 grams, and in the mantle ?500 ×1021 grams (95 % and 4.5 % of the total amount of nitrogen respectively). In such a case the average concentration of nitrogen in the Earth is ?1,710 ppm, which is similar to the concentration of nitrogen in chondrites.
DS201705-0839
2017
Kaminsky, F., Wirth, R.Nitride, carbonitride and nitrocarbide inclusions in lower-mantle diamonds: a key to the balance of nitrogen in the Earth.European Geosciences Union General Assembly 2017, Vienna April 23-28, 1p. 1751 AbstractMantleDiamond inclusions

Abstract: A few years ago a series of iron carbides Fe3C, Fe2C, Fe7C3 and Fe23C6 (haxonite) containing up to 7.3-9.1 at.% N (N/(N+C) = 0.19-0.27) was identified as inclusions in diamonds from the Juina area, Brazil in association with native iron and graphite (Kaminsky and Wirth, 2011). Subsequently nitrocarbides and carbonitrides Fe3(C,N) and Fe9(C,N)4 (nitroyarlongite) containing 12.8-18.42 at.% N (N/(N+C) = 0.37-0.60) were identified in a lower-mantle microxenolith in association with ferropericlase and two post-spinel oxides Mg-Cr-Fe-O (CT phase; Mg-xieite) and Ca-Cr-O (new mineral) with an orthorhombic structure (Kaminsky et al., 2015). Recently pure nitrides Fe3N with a trigonal structure P312 and Fe2N with an orthorhombic structure Pbcn were identified among mineral inclusions from diamonds in the same area. They have admixtures of Cr (0.68-1.8 at.%), Ni (0.35-0.93 at.%) and Mn (0-1.22 at.%). Fe2N contains also an admixture of 5.1-7.6 at.% Si. The nitrides associate with nitroyarlongite Fe9(N0.8C0.2)4 and iron carbide Fe7C3, which contain nanocrystals of moissanite, hexagonal 6H polytype of SiC. Fe7C3 crystallizes, in the Fe-C system, the first in association with diamond at pressures starting from 130 GPa, i.e., within the lowermost mantle, the D? layer. Native iron and a series of nitride-carbonitride-nitrocarbide-carbides associated with Fe7C3 form as a result of infiltration of the Fe-Ni melt from the outer core into the lowermost mantle. This melt contains up to 10 % light elements, such as C, N, O and Si, which may be the source of nitrides-carbides. The existence of nitrides in the lower mantle helps to solve the problem of 'missing nitrogen' in the Earth's nitrogen balance and consider the Earth's core as the major reservoir of nitrogen. According to calculations, the total amount of nitrogen in the Earth's core is 9,705 × 1021 grams, and in the mantle 500 × 1021 grams (95 % and 4.5 % of the total amount of nitrogen respectively). In such a case the average concentration of nitrogen in the Earth is 1,710 ppm, which is similar to the concentration of nitrogen in chondrites. References 1. Kaminsky, F. V., Wirth, R. (2011) Iron carbide inclusions in lower-mantle diamond from Juina, Brazil. Canadian Mineralogist 49(2), 555-572. 2. Kaminsky, F. V., Wirth, R., Schreiber, A. (2015) A microinclusion of lower-mantle rock and some other lower-mantle inclusions in diamond.
DS201709-2011
2017
Kaminsky, F., Wirth, R.Nitrides and carbonnitrides from the lowermost mantle and their importance in the search for Earth's "lost" nitrogen.American Mineralogist, Vol. 102, pp. 1667-1676.Mantlenitrogen

Abstract: The first finds of iron nitrides and carbonitride as inclusions in lower-mantle diamond from Rio Soriso, Brazil, are herein reported. These grains were identified and studied with the use of transmission electron microscopy (TEM), electron diffraction analysis (EDX), and electron energy loss spectra (EELS). Among nitrides, trigonal Fe3N and orthorhombic Fe2N are present. Carbonitride is trigonal Fe9(N0.8C0.2)4. These mineral phases associate with iron carbide, Fe7C3, silicon carbide, SiC, Cr-Mn-Fe and Mn-Fe oxides; the latter may be termed Mn-rich xieite. Our identified finds demonstrate a wide field of natural compositions from pure carbide to pure nitride, with multiple stoichiometries from M5(C,N)3 to M23(C,N)6 and with M/(C,N) from 1.65 to 3.98. We conclude that the studied iron nitrides and carbonitrides were formed in the lowermost mantle as the result of the infiltration of liquid metal, containing light elements from the outer core into the D? layer, with the formation of the association: native Fe0 + iron nitrides, carbides, and transitional compounds + silicon carbide. They indicated that major reservoirs of nitrogen should be expected in the core and in the lowermost mantle, providing some solution to the problem of nitrogen balance in the Earth
DS201703-0412
2017
Kaminsky, F.V.The Earth's lower mantle.Springer.com/ us/book/ 9783319556833, ebook $ 119.00MantleBook - lower mantle

Abstract: Presents the first comprehensive overview of the composition and structure of the Earth’s lower mantleSummarizes geological, mineralogical, experimental and geophysical data on the Deep Earth. Broadens readers’ understanding and presents a compositional model of the lowermost mantle and geodynamic processes at the core/mantle boundary.
DS201703-0413
2017
Kaminsky, F.V.General physical and chemical models of the Earth's lower mantle.Springer.com/us/ book/ 9783319556833, Chapter 2MantleGeophysics - seismic, geothermometry
DS201703-0414
2017
Kaminsky, F.V.Lower mantle mineral associations.Springer.com/us/ book/ 9783319556833, Chapter 3Mantle, Africa, South Africa, Guinea, Australia, South America, BrazilMineralogy - carbonatite
DS201703-0415
2017
Kaminsky, F.V.Ultramafic lower mantle mineral association - Bridgmanite, periclase, peroviskite, silica, jeffbenite, majorite garnet, ilmenite, moissaniteSpringer.com/us/ book/ 9783319556833, Chapter 4TechnologyMineralogy
DS201703-0416
2017
Kaminsky, F.V.Mafic lower mantle mineral association - major minerals, anhydrous aluminous, hydrous aluminous , dense hydrous magnesian silicatesSpringer.com/us/ book /9783319556833, Chapter 5TechnologyMineralogy
DS201703-0417
2017
Kaminsky, F.V.Carbonatitic lower mantle mineral association.Springer.com/us /book/ 9783319556833, Chapter 6Mantle, South America, BrazilMineralogy - carbonatite
DS201703-0418
2017
Kaminsky, F.V.Diamond in the lower mantle. Morphology, luminescence, EPR, IR, istopic C, Ni, structure, originSpringer.com/us/ book/ 9783319556833, Chapter 7Mantle, South America, BrazilMineralogy - diamond
DS201703-0419
2017
Kaminsky, F.V.Role of iron spin crossover and other physicochemical transformations in the lower mantle.Springer.com/us /book/ 9783319556833, Chapter 8MantleMineralogy
DS201703-0420
2017
Kaminsky, F.V.D" transitional layer between lower mantle and outer core.Springer.com/us /book/ 9783319556833, Chapter 9MantleMantle - core mantle boundary
DS201703-0421
2017
Kaminsky, F.V.Seismic heterogeneities and their nature in the lower mantle.Springer.com/ us/book/ 9783319556833, Chapter 10MantleGeophysics - seismic
DS201705-0840
2017
Kaminsky, F.V., Lin, J-F.Iron partioning in natural lower-mantle minerals: toward a chemically homogeneous lower mantle.American Mineralogist, Vol. 102, pp. 824-832.MantleBridgmanite
DS201711-2520
2017
Kaminsky, F.V., Wirth, R.Nitrides and carbonitrides from the lower mantle and their importance in the search for Earth's 'lost' nitrogen.Proceedings of XXXIV held Aug. 4-9. Perchuk International School of Earth Sciences, At Miass, Russia, 2p. AbstractMantlenitrogen

Abstract: The first finds of iron nitrides and carbonitride as inclusions in lower-mantle diamond from Rio Soriso, Brazil, are herein reported. These grains were identified and studied with the use of transmission electron microscopy (TEM), electron diffraction analysis (EDX), and electron energy loss spectra (EELS). Among nitrides, trigonal Fe3N and orthorhombic Fe2N are present. Carbonitride is trigonal Fe9(N0.8C0.2)4. These mineral phases associate with iron carbide, Fe7C3, silicon carbide, SiC, Cr-Mn-Fe and Mn-Fe oxides; the latter may be termed Mn-rich xieite. Our identified finds demonstrate a wide field of natural compositions from pure carbide to pure nitride, with multiple stoichiometries from M5(C,N)3 to M23(C,N)6 and with M/(C,N) from 1.65 to 3.98. We conclude that the studied iron nitrides and carbonitrides were formed in the lowermost mantle as the result of the infiltration of liquid metal, containing light elements from the outer core into the D? layer, with the formation of the association: native Fe? + iron nitrides, carbides, and transitional compounds + silicon carbide. They indicated that major reservoirs of nitrogen should be expected in the core and in the lowermost mantle, providing some solution to the problem of nitrogen balance in the Earth.
DS201711-2521
2017
Kang, J-T, Ionov, D.A., Liu, F., Zhang, C-L., Golovin, A.V., Qin, L-P., Zhang, Z-F., Huang, F.Calcium isotopic fractionation in mantle peridotites by melting and metasomatism and Ca isotope composition of the Bulk Silicate Earth.Earth and Planetary Science Letters, Vol. 474, pp. 128-137.Mantleperidotites

Abstract: To better constrain the Ca isotopic composition of the Bulk Silicate Earth (BSE) and explore the Ca isotope fractionation in the mantle, we determined the Ca isotopic composition of 28 peridotite xenoliths from Mongolia, southern Siberia and the Siberian craton. The samples are divided in three chemical groups: (1) fertile, unmetasomatized lherzolites (3.7-4.7 wt.% Al2O3); (2) moderately melt-depleted peridotites (1.3-3.0 wt.% Al2O3) with no or very limited metasomatism (LREE-depleted cpx); (3) strongly metasomatized peridotites (LREE-enriched cpx and bulk rock) further divided in subgroups 3a (harzburgites, 0.1-1.0% Al2O3) and 3b (fertile lherzolites, 3.9-4.3% Al2O3). In Group 1, ?44/40Ca of fertile spinel and garnet peridotites, which experienced little or no melting and metasomatism, show a limited variation from 0.90 to 0.99‰ (relative to SRM 915a) and an average of 0.94 ± 0.05‰ (2SD, ), which defines the Ca isotopic composition of the BSE. In Group 2, the ?44/40Ca is the highest for three rocks with the lowest Al2O3, i.e. the greatest melt extraction degrees (average ‰, i.e. ?0.1‰ heavier than the BSE estimate). Simple modeling of modal melting shows that partial melting of the BSE with ranging from 0.10 to 0.25 can explain the Group 2 data. By contrast, ?44/40Ca in eight out of nine metasomatized Group 3 peridotites are lower than the BSE estimate. The Group 3a harzburgites show the greatest ?44/40Ca variation range (0.25-0.96‰), with ?44/40Ca positively correlated with CaO and negatively correlated with Ce/Eu. Chemical evidence suggests that the residual, melt-depleted, low-Ca protoliths of the Group 3a harzburgites were metasomatized, likely by carbonate-rich melts/fluids. We argue that such fluids may have low (?0.25‰) ?44/40Ca either because they contain recycled crustal components or because Ca isotopes, similar to trace elements and their ratios, may be fractionated by kinetic and/or chromatographic effects of melt percolation in the mantle. The ?44/40Ca in Group 3b lherzolites (0.83-0.89‰) are lower than in the BSE as well, but the effects of metasomatism on ?44/40Ca are smaller, possibly because of the high Ca contents in their protoliths and/or smaller ?44/40Ca differences between the protoliths and metasomatic agents. The BSE estimates based on fertile peridotites in this study fall in the ?44/40Ca ranges for oceanic and continental basalts, various meteorites (achondrites; carbonaceous, ordinary and enstatite chondrites), Mars, and the Moon. These results provide benchmarks for the application of Ca isotopes to planet formation, mantle evolution, and crustal recycling.
DS201708-1573
2017
Karakas, O., Degruyter, W., Bachmann, O., Dufek, J.life time and size of shallow magma bodies controlled by crustal-scale magmatism.Nature Geoscience, Vol. 10, 6, p. 446.Mantlemagmatism

Abstract: Magmatic processes on Earth govern the mass, energy and chemical transfer between the mantle, crust and atmosphere. To understand magma storage conditions in the crust that ultimately control volcanic activity and growth of continents, an evaluation of the mass and heat budget of the entire crustal column during magmatic episodes is essential. Here we use a numerical model to constrain the physical conditions under which both lower and upper crustal magma bodies form. We find that over long durations of intrusions (greater than 105 to 106?yr), extensive lower crustal mush zones develop, which modify the thermal budget of the upper crust and reduce the flux of magma required to sustain upper crustal magma reservoirs. Our results reconcile physical models of magma reservoir construction and field-based estimates of intrusion rates in numerous volcanic and plutonic localities. Young igneous provinces (less than a few hundred thousand years old) are unlikely to support large upper crustal reservoirs, whereas longer-lived systems (active for longer than 1 million years) can accumulate magma and build reservoirs capable of producing super-eruptions, even with intrusion rates smaller than 10?3 to 10?2?km3?yr?1. Hence, total duration of magmatism should be combined with the magma intrusion rates to assess the capability of volcanic systems to form the largest explosive eruptions on Earth.
DS201701-0017
2016
Karato, S-I.Physical basis of trace element partitioning: a review.American Mineralogist, Vol. 101, pp. 2577-2593.TechnologyReview article

Abstract: Experimental observations on the dissolution of elements in minerals and melts and the partitioning between the two materials show that the concentration (or the partition coefficient) of trace elements depends on the properties of elements as well as those of relevant materials (minerals and melts) and the thermochemical conditions. Previous models of element solubility in minerals contain a vague treatment of the role of the stiffness of the element and have a difficulty in explaining some observations including the solubility of the noble gases. A modified theory of element solubility in minerals is presented where the role of elasticity of both matrix mineral and the element is included using the continuum theory of point defects by Eshelby (1951, 1954, 1956). This theory provides a framework to explain the majority of observations and shows a better fit to the published results on the effective elastic constants relevant to element partitioning. However, the concept of “elasticity of the trace element” needs major modification when the site occupied by a trace element has large excess charge. The experimental data of the solubility coefficients of noble gases in melts show strong dependence on the atomic size that invalidates the “zero-charge” model for noble gas partitioning. A simple model of element solubility in melts is proposed based on the hard sphere model of complex liquids that provides a plausible explanation for the difference in the dissolution behavior between noble gases and other charged elements. Several applications of these models are discussed including the nature of noble gas behavior in the deep/early Earth and the water distribution in the lithosphere/asthenosphere system.
DS201701-0018
2016
Kargin, A.V., Nosova, A.A., Postnikov, A.V., Chugaev, A.V., Postnikova, O.V., Popova, L.P., Poshibaev, V.V., Sazonova, L.V., Dokuchaev, A.Ya., Smirnova, M.D.Devonian ultramafic lamprophyre in the Irkineeva Chadobets trough in the southwest of the Siberian platform: age, composition, and implications for diamond potential prediction.Geology of Ore Deposits, Vol. 58, 5, pp. 383-403.RussiaLamprophyre - aillikite

Abstract: The results of geochronological, mineralogical, petrographical, and geochemical study of the Ilbokich ultramafic lamprophyre are reported. The specific features in the mineral and chemical compositions of the studied ultramafic lamprophyre indicate that it can be regarded as a variety similar to aillikite, while other differences dominated by K-feldspar can be referred to damtjernite. According to Rb-Sr analysis, ultramafic lamprophyre dikes intruded at the turn of the Early and Middle Devonian, about 392 Ma ago. This directly proves the existence of Early Paleozoic alkali-ultramafic magmatism in the northern part of the southwest Siberian Platform. A finding of Devonian alkali-ultramafic lamprophyre is of dual predictive importance. On the one hand, it is indicative of the low probability of finding large diamond-bearing deposits in close association with aillikite. On the other hand, it can be indicative of a possible large Devonian diamond province in the studied territory, where diamondiferous kimberlite is structurally separated from aillikite.
DS201709-2012
2017
Kargin, A.V., Sazonova, L.V., Nosova, A.A., Lebedeva, N.M.The mantle metasomatism associated with kimberlite magmatism, the Grib kimberlite pipe, Arkhangelsk diamond province, Russia.Goldschmidt Conference, abstract 1p.Russia, Archangeldeposit - Grib

Abstract: Here we present major (EMPA) and trace element (SIMS, LA-ICP-MS) data for garnet and clinopyroxene from mantlederived xenoliths of coarse and sheared garnet peridotite [1, 2] and clinopyroxene-phlogopite metasomatic rocks from the Grib kimberlite, the Arkhangelsk diamond province, Russia, and provide new insights into the metasomatic processes that occur within the subcontinental lithospheric mantle (SCLM) during the kimberlite melts generation and ascent. The obtained data allowed us to reconstruct the following sequence of metasomatic events associated with the generation of the Grib kimberlite: 1. Ascent of high-temperature asthenospheric or mantle plume material resulted in a partial melting of a carbonated peridotite and led to the generation of high-temperature REEenriched proto-kimberlite melts containing significant amounts of carbonate, Fe-Ti and K-H2O. These protokimberlite melts started to interact with the surrounding mantle rocks during its evolution and ascent, and caused metasomatic modification of both coarse and sheared peridotites at the base of SCLM (T and P estimates are 1220°C and 70 kbar). 2. Further evolution of proto-kimberlite melts during the ascent and the interaction with the surrounding mantle (e.g. mantle-rock assimilation and/or percolative fractional crystallization) led to changes in the kimberlite composition from REE-enriched carbonate-dominated to carbonate-rich ultramafic silicate magmas with lower REE contents. 3. During the ascent, carbonate-rich ultramafic silicate kimberlite melts progressively metasomatised sorrounding SCLM from garnet-phlogopite peridotite through garnetphlogopite peridotite to clinopyroxene-phlogopite rocks under T and P estimated as 830°C and 40 kbar. At this stage, the fractionated of Fe-Ti-bearing megacrysts occurred.
DS201711-2522
2017
Kargin, A.V., Sazonova, L.V., Nosova, A.A., Lebedeva, N.M., Tretyachenko, V.V., Abersteiner, A.Cr-rich clinopyroxene megacrysts from the Grib kimberlite, Arkangelsk province, Russia: relation to clinopyroxene-phlogopite xenoliths and evidence for mantle metasomatism by kimberlite melts.Lithos, in press available, 52p.Russia, Archangeldeposit - Grib

Abstract: To provide new insights into the origin of megacrysts and metasomatism of the subcontinental lithospheric mantle (SCLM), we present a detailed petrographic and geochemical investigation of clinopyroxene-phlogopite xenoliths and clinopyroxene megacrysts from the Grib kimberlite (Arkhangelsk diamond province, Russia). Clinopyroxene megacrysts and clinopyroxene from clinopyroxene-phlogopite xenoliths have similar petrography, major and trace element compositions, and are therefore classified as Cr-rich megacrysts. Geothermobarometry suggests that Cr-rich clinopyroxenes originate from within the SCLM (3.6-4.7 GPa and 764-922 °C). Phlogopite from clinopyroxene-phlogopite xenoliths have low-Ti and -Cr compositions that overlaps with phlogopite megacrysts from the Grib kimberlite. The clinopyroxene-phlogopite rocks within the SCLM are the main source for Cr-rich clinopyroxene and low-Ti phlogopite megacrysts in the Grib kimberlite matrix. Trace element compositions of studied Cr-rich clinopyroxenes have similar geochemical features to clinopyroxenes megacrysts occurrences worldwide and overlap with clinopyroxenes from phlogopite-garnet peridotite xenoliths from the Grib kimberlite. The strong depletion in Ti, Nb, Ta and to a lesser extent in Zr and Hf in clinopyroxene reflects equilibrium with Ti-oxides, such as ilmenite. The clinopyroxene-phlogopite xenoliths could be the final product of metasomatism of garnet peridotites within the SCLM beneath the Grib kimberlite. The calculated equilibrium of clinopyroxene melt compositions suggests that the metasomatic agents were derived from silicate-bearing kimberlite melts. The presence of veinlets infilled with kimberlitic mineral assemblages in clinopyroxene grains suggests that the clinopyroxene-phlogopite rocks experienced intense interactions with kimberlite melt after their formation, but before their entrainment into the host kimberlite magma. This interaction resulted in the formation of high-Ti and -Cr phlogopite and high-Ti clinopyroxene rims, zones and grains with spongy textures. Finally, we propose the sequence of metasomatic events that occurred in the SCLM and the subsequent formation of the Grib kimberlite.
DS201709-2013
2017
Karlstrom, L., Paterson, S.R., Jellinek, A.M.A reverse energy cascade for crustal magma transport.Nature Geoscience, Vol. 10, pp. 604-608.Mantlemagmatism

Abstract: Direct constraints on the ascent, storage and eruption of mantle melts come primarily from exhumed, long-frozen intrusions. These structures, relics of a dynamic magma transport network, encode how Earth’s crust grows and differentiates over time. Furthermore, they connect mantle melting to an evolving distribution of surface volcanism. Disentangling magma transport processes from the plutonic record is consequently a seminal but unsolved problem. Here we use field data analyses, scaling theory and numerical simulations to show that the size distribution of intrusions preserved as plutonic complexes in the North American Cordillera suggests a transition in the mechanical response of crustal rocks to protracted episodes of magmatism. Intrusion sizes larger than about 100?m follow a power-law scaling expected if energy delivered from the mantle to open very thin dykes and sills is transferred to intrusions of increasing size. Merging, assimilation and mixing of small intrusions into larger ones occurs until irreversible deformation and solidification dissipate available energy. Mantle magma supply over tens to hundreds of thousands of years will trigger this regime, a type of reverse energy cascade, depending on the influx rate and efficiency of crustal heating by intrusions. Identifying regimes of magma transport provides a framework for inferring subsurface magmatic processes from surface patterns of volcanism, information preservation in the plutonic record, and related effects including climate.
DS201708-1685
2017
Kaur, G.Mineralogy of the biotite bearing Gundrapalli lamproite, Nalgonda district, Telangana, India.11th. International Kimberlite Conference, PosterIndialamproites
DS201706-1083
2017
Kelley, S.E., Ross, M., Elliott, B., Normandeau, P.X.Glacial dispersal patterns in three dimensions from a pair of buried kimberlites, Lac de Gras region.GAC annual meeting, 1p. AbstractCanada, Northwest Territoriesgeochemisty

Abstract: Drift prospecting has been a successful mineral exploration tool in previously glaciated terrains. Based on the concepts of glacial dynamics, and related sediment production, transport and deposition, drift prospecting surveys assess compositional variability within glacial sediments and trace indicators of mineralization back to a buried bedrock source. The time-transgressive nature of shifting ice flow direction and related till production is an important factor, controlling the shape and extent of dispersal patterns in till. The effect of changing ice flow on the composition of till has been well-studied in both map view, as well as longitudinally in cross section (i.e., dispersal curves). Fewer studies have looked at dispersal patterns holistically in three-dimensions. Here, we use 94 reverse circulation (RC) boreholes, yielding 254 till samples, to reconstruct the subsurface geometry of a dispersal train from a pair of buried kimberlite pipes (DO-27 and DO-18) in the Northwest Territories. Discrete smooth interpolation modeling in SKUA-GOCAD based on downhole data allows for visualization of geochemical anomalies within the till column, as well as the subsurface density of kimberlite indicator mineral grains. Through the combination of borehole data, field work, and modeling, we are able to compare three-dimensional dispersal patterns in the subsurface with local ice flow records, measured from erosional ice flow indicators in the field. This dataset allows us to evaluate the role that changing ice flow, as well as local bedrock surface topography, play in controlling dispersal and deposition of clastic sediment by past ice sheets. Our modeling documents buried palimpsest terrains along older ice flow trajectories, demonstrating lateral and vertical variability within a single, relatively thin and discontinuous till sheet. Furthermore, we observe relationships between local indicator mineral concentrations and bedrock topography, with indicator mineral dispersal concentrated along a bedrock-controlled topographic low aligned with the most recent ice flow. This work demonstrates the benefit of detailed mapping and visualization of a dispersal plume, even in areas of relatively thin and discontinuous till cover, highlighting the role basal topography and shifting ice flow plays on shaping the surface expression of a dispersal train.
DS201712-2698
2017
Kelley, S.E., Ross, M., Stirling, R.A., Normandeau, P.X., Elliott, B.The application of 3D indicator minerals datasets to regional scale modeling of glacial sediments in the Lac de Gras area.45th. Annual Yellowknife Geoscience Forum, p. 101 abstract posterCanada, Northwest Territoriesgeomorphology
DS201708-1686
2017
Kemppinen, L.First evidence of molybdenite in diamond hosted sulphide inclusions and possible implications for the Re-Os dating of diamonds.11th. International Kimberlite Conference, PosterTechnologydiamond inclusions
DS201708-1687
2017
Kemppinen, L.Sulphide inclusions in sub-lithospheric diamonds: major and trace element and sulphur isotope composition.11th. International Kimberlite Conference, PosterTechnologydiamond inclusions
DS201704-0632
2017
Kendrick, M.A., Hemond, C., Kamenetsky, V.S., Danyushevsky, L., Devey, C.W.Seawater cycled throughout Earth's mantle in partially serpentinized lithosphere.Nature Geoscience, Vol. 10, 3, pp. 222-228.MantleGeochemistry - water

Abstract: The extent to which water and halogens in Earth’s mantle have primordial origins, or are dominated by seawater-derived components introduced by subduction is debated. About 90% of non-radiogenic xenon in the Earth’s mantle has a subducted atmospheric origin, but the degree to which atmospheric gases and other seawater components are coupled during subduction is unclear. Here we present the concentrations of water and halogens in samples of magmatic glasses collected from mid-ocean ridges and ocean islands globally. We show that water and halogen enrichment is unexpectedly associated with trace element signatures characteristic of dehydrated oceanic crust, and that the most incompatible halogens have relatively uniform abundance ratios that are different from primitive mantle values. Taken together, these results imply that Earth’s mantle is highly processed and that most of its water and halogens were introduced by the subduction of serpentinized lithospheric mantle associated with dehydrated oceanic crust.
DS201702-0219
2017
Keppler, H.Fluids and trace element transport in subduction zones. ( Review paper).American Mineralogist, Vol. 102, pp. 5-20.MantleSubduction
DS201702-0220
2016
Khachatryan, G.K.Nitrogen and hydrogen in world diamonds as indicators of their genesis and tool for prospecting of primary diamond deposits. *** in RussianDSc Thesis *** in Russian, 254p. Abstract in Russian as well.GlobalDiamond genesis
DS201712-2699
2017
Khanna, T.C., Subba Rao, D.V., Bizimis, M., Satyanarayanan, M., Krishna, A.K., SeshaSai, V.V.~2.1 Ga intraoceanic magmatism in the central India tectonic zone: constraints from the petrogenesis of ferropicrites in the Mahakoshal suprarcustal belt.Precambrian Research, Vol. 302, pp. 1-17.Indiapicrites
DS201706-1084
2017
Khlebopros, R.G., Zakhvataev, V.E., Gabuda, S.P., Kozlova, S.G., Slepkov, V.A.Possible mantle phase transitions by the formation of Si02 peroxides: implications for mantle convection.Doklady Earth Sciences, Vol. 473, 2, pp. 416-418.Mantleconvection

Abstract: On the basis of quantum-chemical calculations of the linear to isomeric bent transition of the SiO2 molecule, it is suggested that the bent to linear transition of SiO2 forms can occur in melted mantle minerals of the lower mantle. This may be important for the formation of the peculiarities of mantle convection and origination of plumes.
DS201708-1688
2017
Khoza, D.Kimberlite exploration under thick Kalahari cover using the powerful SPECTREM-PLUS AEM system.11th. International Kimberlite Conference, OralAfrica, Botswanageophysics
DS201708-1689
2017
Khoza, D.New and revised crustal and upper mantle terrain boundaries in southern Africa: implications for kimberlite exploration and emplacement.11th. International Kimberlite Conference, PosterAfrica, South Africatectonics
DS201706-1085
2016
Kilian, T.M., Chamberlain, K.R., Evans, D.A.D., Bleeker, W., Cousens, B.L.Wyoming on the run - toward final Paleoproterozoic assembly of Laurentia. Geology, Vol. 44, pp. 863-866.United Statescraton

Abstract: Paleoproterozoic suture zones mark the formation of supercontinent Nuna and provide a record of North America’s assembly. Conspicuously young ages (ca. 1.715 Ga) associated with deformation in southeast Wyoming craton argue for a more protracted consolidation of Laurentia, long after peak metamorphism in the Trans-Hudson orogen. Using paleomagnetic data from the newly dated 1899 ± 5 Ma Sourdough mafic dike swarm (Wyoming craton), we compare the relative positions of Wyoming, Superior, and Slave cratons before, during, and after peak metamorphism in the Trans-Hudson orogen. With these constraints, we refine a collisional model for Laurentia that incorporates Wyoming craton after Superior and Slave cratons united, redefining the Paleoproterozoic sutures that bind southern Laurentia.
DS201707-1338
2017
Kiseeva, E.S., Kamenetsky, V.S., Yaxley, G.M., Shee, S.R.Mantle melting versus mantle metasomatism - the chicken or the egg dilemma.Chemical Geology, Vol. 455, pp. 120-130.Mantlemetasomatism

Abstract: Most eclogitic mantle xenoliths brought to the surface exhibit a certain degree of enrichment with incompatible elements, usually attributed to the effect of mantle metasomatism by a putative metasomatic fluid. The metasomatic overprint is represented mainly by enrichments in Na, K, Ba, Ti and LREE and the original source of this fluid remains unknown. In this paper, we present a detailed petrological study of a typical eclogitic mantle xenolith from the Roberts Victor kimberlite mine in South Africa. We find that its textural and mineralogical features present strong evidence for incipient melting. The melting assemblage we observe did not necessarily require introduction of additional components, that is: in-situ melting alone could produce highly incompatible element enriched melt without involvement of a hypothetical and speculative “metasomatic event”. Due to the higher abundance in incompatible elements and lower solidus temperature than peridotites, mantle eclogites, some of which represent previously subducted oceanic crust, are much more plausible sources of mantle metasomatism, but on the other hand, they can be considered as highly metasomatised themselves. This brings us to the “chicken or egg” dilemma – was the secondary mineral assemblage in mantle lithologies a result or a source of mantle metasomatism?
DS201709-2014
2017
Kiseeva, E.S., Vasiukov, D.M., Wood, B.J., McCammon, C., Stachel, T., Chumakov, A., Dubrovinsky, L.Oxidation state of majoritic garnet inclusions in diamond.Goldschmidt Conference, abstract 1p.Africa, South Africadeposit, Jagersfontein

Abstract: Diamond inclusions are the only samples from the mantle transition zone (410-660 km) and the lower mantle. Majoritic garnet is a rare inclusion, limited to pressures of ~8-20 Gpa with Si content being indicative of depth of re-equilibration. These garnet inclusions can therefore provide information on properties of the transition zone such as oxidation state. In this study, we used Synchrotron Mössbauer Source (SMS) to determine the ferric-ferrous ratios of 13 small (30 to 100 micrometers diameter) majoritic inclusions in diamonds from Jagersfontein. The studied inclusions have pyroxenitic affinities [1], with compositions intermediate between typical peridotite and eclogite. They contain 4.62-11.2 wt% CaO, 0.03-0.34 wt% Cr2O3 and Mg# of 0.65-0.81. Minimum pressures for their equilibration using Beyer and Frost [2] barometer are between 8 and 18 GPa with at least 4 of these inclusions being formed in the transition zone. The Fe3+/Fetotal ratios in the garnets increase from 0.08±0.01 to 0.30±0.03 with increasing pressure. These values define a clear extension of the trend apparent in the data from peridotite xenoliths crystallised at lower pressures. Thermodynamic calculations suggest that these high ferric contents correspond to oxygen fugacities above the FeFeO (IW) buffer, which means that the high Fe3+ contents were not generated by disproportionation of Fe2+ to Fe3+ and Fe0 . It is more likely that carbonate was the oxidising agent responsible for generating the high Fe3+ of these garnets.
DS201708-1690
2017
Kiseeva, K.Oxidation state of majoritic inclusions in diamond.11th. International Kimberlite Conference, OralTechnologydiamond inclusions
DS201708-1691
2017
Kitayama, Y.Co-magmatic sulfides and sulfates in the Udachnaya-East pipe ( Siberia): sulfur speciation and isotopic composition in kimberlites and their mantle sources.11th. International Kimberlite Conference, PosterRussia, Siberiadeposit - Udachnaya-East

Abstract: Kimberlites of the Udachnaya-East pipe (Siberia) include a uniquely dry and serpentine-free rock type with anomalously high contents of chlorine (Cl ? 6.1 wt%), alkalies (Na2O + K2O ? 10 wt%) and sulfur (S ? 0.50 wt%), referred to as a “salty” kimberlite. The straightforward interpretation is that the Na-, K-, Cl- and S-rich components originate directly from a carbonate-chloride kimberlitic magma that is anhydrous and alkali-rich. However, because brines and evaporites are present on the Siberian craton, previous studies proposed that the kimberlitic magma was contaminated by the assimilation of salt-rich crustal rocks. To clarify the origin of high Cl, alkalies and S in this unusual kimberlite, here we determine its sulfur speciation and isotopic composition and compare it to that of non-salty kimberlites and kimberlitic breccia from the same pipe, as well as potential contamination sources (hydrothermal sulfides and sulfates, country-rock sediment and brine collected in the area). The average ?34S of sulfides is ? 1.4 ± 2.2‰ in the salty kimberlite, 2.1 ± 2.7‰ in the non-salty kimberlites and 14.2 ± 5.8‰ in the breccia. The average ?34S of sulfates in the salty kimberlites is 11.1 ± 1.8‰ and 27.3 ± 1.6‰ in the breccia. In contrast, the ?34S of potential contaminants range from 20 to 42‰ for hydrothermal sulfides, from 16 to 34‰ for hydrothermal sulfates, 34‰ for a country-rock sediment (Chukuck suite) and the regional brine aquifer. Our isotope analyses show that (1) in the salty kimberlites, neither sulfates nor sulfides can be simply explained by brine infiltration, hydrothermal alteration or the assimilation of known salt-rich country rocks and instead, we propose that they are late magmatic phases; (2) in the non-salty kimberlite and breccia, brine infiltration lead to sulfate reduction and the formation of secondary sulfides – this explains the removal of salts, alkali-carbonates and sulfates, as well as the minor olivine serpentinization; (3) hydrothermal sulfur was added to the kimberlitic breccia, but not to the massive kimberlites. In situ measurements of sulfides confirm this scenario, clearly showing the addition of two sulfide populations in the breccia (pyrite-pyrrhotites with average ?34S of 7.9 ± 3.4‰ and chalcopyrites with average ?34S of 38.0 ± 0.4‰) whereas the salty and non-salty kimberlites preserve a unique population of djerfisherites (Cl- and K-rich sulfides) with ?34S values within the mantle range. This study provides the first direct evidence of alkaline igneous rocks in which magmatic sulfate is more abundant than sulfide. Although sulfates have been rarely reported in mantle materials, sulfate-rich melts may be more common in the mantle than previously thought and could balance the sulfur isotope budget of Earth's mantle.
DS201709-2015
2017
Kitayama, Y., et al.Origin of salt nodules in the Udachnaya- East kimberlites? Insights from Sr-Nd and S isotopes.Goldschmidt Conference, abstract 1p.Russiadeposit, Udachnaya

Abstract: Salty fluids are stable in the lithospheric mantle [1] and thus we may expect to find them in extrusive volcanic rocks as well. In Siberia, the Udachnaya-East kimberlite hosts extremely well preserved ‘nodules’ of molten salts that do not present any relicts sedimentary textures [2]. It is still debated, however, whether these nodules are genetically linked to the kimberlitic magma. Here we used a combination of radiogenic (Rb-Sr, SmNd) and stable (S) isotopes analyses to investigate the origin of these nodules Salt-rich nodules, including chloride (95% chloride; n=2) and chloride-carbonate nodules (70% chloride + 30% alkali-carbonate; n=2) were studied, as well as host kimberlites (n=4), country-rock sediment and regional brine for comparison. On an evolution diagram, water and acetic acid leachates of chloride nodules define a linear array that, if interpreted as an isochron, yields an apparent age of 355 Ma, within error of the emplacement age of the kimberlite and an initial 87Sr/86Srt=355Ma of 0.710 ± 0.003. Bulk and carbonate fractions of chloride-carbonate nodules define an initial 87Sr/86Srt=355Ma (0.706 ±0.002) and 143Nd/144Ndt=355Ma (0.5123 ±0.0002) that overlap with those of the kimberlite (initial 87Sr/86Srt=355Ma =0.705 ±0.001 and 143Nd/144Ndt=355Ma =0.5124 ±0.0001). 87Sr/86Srt=355Ma of the brine and host sediment (0.7088) cannot explain the Sr isotopic composition of the chloride nodules. A dual origin for the nodules is thus possible, depending on their carbonate contents. In terms of sulfur isotopes, sulfates of the chloridecarbonate nodules and the salty kimberlite are undistinguishable (?34S=11‰). Sulfates of a chloride nodule have distinctly heavier isotopic compositions (?34S=18‰) but their Sr isotopes imply they cannot be explained by the assimilation of known sedimentary components or post magmatic fluid circulation (?34S=34‰ for host sediment and brine). In this contribution, we will discuss the robustness of both approches and propose some explanation(s) for the occurence of these salt nodules.
DS201707-1339
2017
Kitayama, Y., Thomassot, E., Galy, A., Golovin, A., Korsakov, A., d'Eyrames, E., Assayag, N., Bouden, N., Ionov, D.Co-magmatic sulfides and sulfates in the Udachnaya-East pipe ( Siberia): a record of the redox state and isotopic composition of sulfur in kimberlites and their mantle sources.Chemical Geology, Vol. 455, pp. 315-330.Russiadeposit - Udachnaya East

Abstract: Kimberlites of the Udachnaya-East pipe (Siberia) include a uniquely dry and serpentine-free rock type with anomalously high contents of chlorine (Cl ? 6.1 wt%), alkalies (Na2O + K2O ? 10 wt%) and sulfur (S ? 0.50 wt%), referred to as a “salty” kimberlite. The straightforward interpretation is that the Na-, K-, Cl- and S-rich components originate directly from a carbonate-chloride kimberlitic magma that is anhydrous and alkali-rich. However, because brines and evaporites are present on the Siberian craton, previous studies proposed that the kimberlitic magma was contaminated by the assimilation of salt-rich crustal rocks. To clarify the origin of high Cl, alkalies and S in this unusual kimberlite, here we determine its sulfur speciation and isotopic composition and compare it to that of non-salty kimberlites and kimberlitic breccia from the same pipe, as well as potential contamination sources (hydrothermal sulfides and sulfates, country-rock sediment and brine collected in the area). The average ?34S of sulfides is ? 1.4 ± 2.2‰ in the salty kimberlite, 2.1 ± 2.7‰ in the non-salty kimberlites and 14.2 ± 5.8‰ in the breccia. The average ?34S of sulfates in the salty kimberlites is 11.1 ± 1.8‰ and 27.3 ± 1.6‰ in the breccia. In contrast, the ?34S of potential contaminants range from 20 to 42‰ for hydrothermal sulfides, from 16 to 34‰ for hydrothermal sulfates, 34‰ for a country-rock sediment (Chukuck suite) and the regional brine aquifer. Our isotope analyses show that (1) in the salty kimberlites, neither sulfates nor sulfides can be simply explained by brine infiltration, hydrothermal alteration or the assimilation of known salt-rich country rocks and instead, we propose that they are late magmatic phases; (2) in the non-salty kimberlite and breccia, brine infiltration lead to sulfate reduction and the formation of secondary sulfides – this explains the removal of salts, alkali-carbonates and sulfates, as well as the minor olivine serpentinization; (3) hydrothermal sulfur was added to the kimberlitic breccia, but not to the massive kimberlites. In situ measurements of sulfides confirm this scenario, clearly showing the addition of two sulfide populations in the breccia (pyrite-pyrrhotites with average ?34S of 7.9 ± 3.4‰ and chalcopyrites with average ?34S of 38.0 ± 0.4‰) whereas the salty and non-salty kimberlites preserve a unique population of djerfisherites (Cl- and K-rich sulfides) with ?34S values within the mantle range. This study provides the first direct evidence of alkaline igneous rocks in which magmatic sulfate is more abundant than sulfide. Although sulfates have been rarely reported in mantle materials, sulfate-rich melts may be more common in the mantle than previously thought and could balance the sulfur isotope budget of Earth's mantle.
DS201708-1692
2017
Kjarsgaard, B.Discrimination of Whiskey kimberlite eruptive phases utilizing portable XRF spectrometry data.11th. International Kimberlite Conference, PosterCanada, Northwest Territoriesdeposit - Whiskey
DS201709-2016
2017
Kjarsgaard, B.A., Heaman, L.M., Sarkar, C., Pearson, D.G.The North American mid-Cretaceous kimberlite corridor: wet, edge-driven decompression melting of an OIB-type deep mantle source.Geochemistry, Geophysics, Geosystems: G3, Vol. 18, 7, pp. 2727-2747.Canada, Somerset Island, Saskatchewan, United States, Kansasmagmatism, convection, diamond genesis

Abstract: Thirty new high-precision U-Pb perovskite and zircon ages from kimberlites in central North America delineate a corridor of mid-Cretaceous (115–92 Ma) magmatism that extends ?4000 km from Somerset Island in Arctic Canada through central Saskatchewan to Kansas, USA. The least contaminated whole rock Sr, Nd, and Hf isotopic data, coupled with Sr isotopic data from groundmass perovskite indicates an exceptionally limited range in Sr-Nd-Hf isotopic compositions, clustering at the low ?Nd end of the OIB array. These isotopic compositions are distinct from other studied North American kimberlites and point to a sublithospheric source region. This mid-Cretaceous kimberlite magmatism cannot be related to mantle plumes associated with the African or Pacific large low-shear wave velocity province (LLSVP). All three kimberlite fields are adjacent to strongly attenuated lithosphere at the edge of the North American craton. This facilitated edge-driven convection, a top-down driven processes that caused decompression melting of the transition zone or overlying asthenosphere. The inversion of ringwoodite and/or wadsleyite and release of H2O, with subsequent metasomatism and synchronous wet partial melting generates a hot CO2 and H2O-rich protokimberlite melt. Emplacement in the crust is controlled by local lithospheric factors; all three kimberlite fields have mid-Cretaceous age, reactivated major deep-seated structures that facilitated kimberlite melt transit through the lithosphere.
DS201709-2017
2017
Klein, B.Z., Jagoutz, O., Behn, M.D.Archean crustal compositions promote full mantle convection.Earth and Planetary Science Letters, Vol. 474, pp. 516-526.Mantlesubduction

Abstract: Higher mantle potential temperatures characterized the early Earth, resulting in thicker, more mafic oceanic crust entering subduction systems. This change in the composition of subducted slabs, combined with the enhanced temperature contrast between the slab and ambient mantle, would have altered the buoyancy forces driving subduction in the early Earth. Here we investigate this “compositional effect” through a combination of petrologic and thermal modeling. Specifically, we construct density profiles for sinking slabs under modern and early Earth conditions based on a range of mafic crust and mantle compositions. Slab and mantle densities are then determined from mineral assemblages calculated using the thermodynamic modeling program Perple_X along slab geotherms estimated from an analytic thermal model. Consistent with previous studies, we find that modern MORB compositions are typically less dense than the ambient mantle in the basalt barrier zone, located immediately beneath the mantle transition zone. By contrast, possible early Earth oceanic crust compositions are denser than ambient mantle at all depths down to 1000 km. This compositional effect results in slabs that would have more readily penetrated the transition zone, promoting single-layered convection and effective mantle mixing in the early Earth.
DS201707-1340
2017
Klonowska, I., Janak, M., Majka, J., Petrik, I., Froitzheim, N., Gee, D.Microdiamond on Areskutan confirms UHP metamorphism in the Seve Nappe Complex of the Scandinavian Caledonides.Journal of Metamorphic Geology, Vol. 35, 5, pp. 541-564.Europe, SwedenUHP

Abstract: Metamorphic diamond in crustal rocks provides important information on the deep subduction of continental crust. Here we present a new occurrence of diamond within the Seve Nappe Complex of the Scandinavian Caledonides, on Åreskutan in Jämtland County, Sweden. Microdiamond is found in-situ as single and composite (diamond + carbonate) inclusions within garnet, in kyanite-bearing paragneisses. The rocks preserve the primary peak pressure assemblage of Ca,Mg-rich garnet + phengite + kyanite + rutile, with polycrystalline quartz surrounded by radial cracks indicating breakdown of coesite. Calculated P-T conditions for this stage are 830-840 ºC and 4.1-4.2 GPa, in the diamond stability field. The ultrahigh-pressure (UHP) assemblage has been variably overprinted under granulite facies conditions of 850-860 ºC and 1.0-1.1 GPa, leading to formation of Ca,Mg-poor garnet + biotite + plagioclase + K-feldspar + sillimanite + ilmenite + quartz. This overprint was the result of nearly isothermal decompression, which is corroborated by Ti-in-quartz thermometry. Chemical Th-U-Pb dating of monazite yields ages between 445 and 435 Ma, which are interpreted to record post-UHP exhumation of the diamond-bearing rocks. The new discovery of microdiamond on Åreskutan, together with other evidence of ultrahigh-pressure metamorphism (UHPM) within gneisses, eclogites and peridotites elsewhere in the Seve Nappe Complex, provide compelling arguments for regional (at least 200 km along the unit) UHPM of substantial parts of this far-travelled allochthon. The occurrence of UHPM in both rheologically weak (gneisses) and strong lithologies (eclogites, peridotites) speaks against the presence of large tectonic overpressure during metamorphism.
DS201702-0221
2017
Klonowska, I., Janak, M., Majka, J., Petrik, I., Froitzheim, N., Gee, D.G., sasinkova, V.Microdiamond on Areskutan confirms regional UHP metamorphism in the Seve Nappe complex of the Scandinavian Caledonides.Journal of Metamorphic Geology, in press availableEurope, Sweden, NorwayUHP

Abstract: Metamorphic diamond in crustal rocks provides important information on the deep subduction of continental crust. Here we present a new occurrence of diamond within the Seve Nappe Complex of the Scandinavian Caledonides, on Åreskutan in Jämtland County, Sweden. Microdiamond is found in-situ as single and composite (diamond + carbonate) inclusions within garnet, in kyanite-bearing paragneisses. The rocks preserve the primary peak pressure assemblage of Ca,Mg-rich garnet + phengite + kyanite + rutile, with polycrystalline quartz surrounded by radial cracks indicating breakdown of coesite. Calculated P-T conditions for this stage are 830-840 °C and 4.1-4.2 GPa, in the diamond stability field. The ultrahigh-pressure (UHP) assemblage has been variably overprinted under granulite facies conditions of 850-860 °C and 1.0-1.1 GPa, leading to formation of Ca,Mg-poor garnet+biotite+ plagioclase+K-feldspar+sillimanite+ilmenite+quartz. This overprint was the result of nearly isothermal decompression, which is corroborated by Ti-in-quartz thermometry. Chemical Th-U-Pb dating of monazite yields ages between 445 and 435 Ma, which are interpreted to record post-UHP exhumation of the diamond-bearing rocks. The new discovery of microdiamond on Åreskutan, together with other evidence of ultrahigh-pressure metamorphism (UHPM) within gneisses, eclogites and peridotites elsewhere in the Seve Nappe Complex, provide compelling arguments for regional (at least 200 km along strike of the unit). UHPM of substantial parts of this far-travelled allochthon. The occurrence of UHPM in both rheologically weak (gneisses) and strong lithologies (eclogites, peridotites) speaks against the presence of large tectonic overpressure during metamorphism.
DS201703-0422
2017
Klonowska, I., Janak, M., Majka, J., Petrik, I., Froitzheim, N., Gee, D.G., Sasinkova, V.Microdiamond on Areskutan confirms regional UHP metamorphism in the Seve Nappe Complex of the Scandinavian Caledonides.Journal of Metamorphic Geology, in press availableEurope, SwedenMicrodiamond

Abstract: Metamorphic diamond in crustal rocks provides important information on the deep subduction of continental crust. Here, we present a new occurrence of diamond within the Seve Nappe Complex (SNC) of the Scandinavian Caledonides, on Åreskutan in Jämtland County, Sweden. Microdiamond is found in situ as single and composite (diamond+carbonate) inclusions within garnet, in kyanite-bearing paragneisses. The rocks preserve the primary peak pressure assemblage of Ca,Mg-rich garnet+phengite+kyanite+rutile, with polycrystalline quartz surrounded by radial cracks indicating breakdown of coesite. Calculated P-T conditions for this stage are 830-840 °C and 4.1-4.2 GPa, in the diamond stability field. The ultrahigh-pressure (UHP) assemblage has been variably overprinted under granulite facies conditions of 850-860 °C and 1.0-1.1 GPa, leading to formation of Ca,Mg-poor garnet+biotite+plagioclase+K-feldspar+sillimanite+ilmenite+quartz. This overprint was the result of nearly isothermal decompression, which is corroborated by Ti-in-quartz thermometry. Chemical Th-U-Pb dating of monazite yields ages between 445 and 435 Ma, which are interpreted to record post-UHP exhumation of the diamond-bearing rocks. The new discovery of microdiamond on Åreskutan, together with other evidence of ultrahigh-pressure metamorphism (UHPM) within gneisses, eclogites and peridotites elsewhere in the SNC, provide compelling arguments for regional (at least 200 km along strike of the unit) UHPM of substantial parts of this far-travelled allochthon. The occurrence of UHPM in both rheologically weak (gneisses) and strong lithologies (eclogites, peridotites) speaks against the presence of large tectonic overpressure during metamorphism.
DS201709-2018
2017
Klonowska, I., Janek, M., Majka, J., Petrik, I., Froitzheim, N., Gee, D.G., Sasinkova, V.Microdiamond on Areskutan confirms regional UHP metamorphism in the Seve Nappe Complex of the Scandinavian Caledonides.Journal of Metamorphic Geology, Vol. 35, 5, pp. 541-564.Europe, Scandinaviamicrodiamond

Abstract: Metamorphic diamond in crustal rocks provides important information on the deep subduction of continental crust. Here, we present a new occurrence of diamond within the Seve Nappe Complex (SNC) of the Scandinavian Caledonides, on Åreskutan in Jämtland County, Sweden. Microdiamond is found in situ as single and composite (diamond+carbonate) inclusions within garnet, in kyanite-bearing paragneisses. The rocks preserve the primary peak pressure assemblage of Ca,Mg-rich garnet+phengite+kyanite+rutile, with polycrystalline quartz surrounded by radial cracks indicating breakdown of coesite. Calculated P–T conditions for this stage are 830–840 °C and 4.1–4.2 GPa, in the diamond stability field. The ultrahigh-pressure (UHP) assemblage has been variably overprinted under granulite facies conditions of 850–860 °C and 1.0–1.1 GPa, leading to formation of Ca,Mg-poor garnet+biotite+plagioclase+K-feldspar+sillimanite+ilmenite+quartz. This overprint was the result of nearly isothermal decompression, which is corroborated by Ti-in-quartz thermometry. Chemical Th–U–Pb dating of monazite yields ages between 445 and 435 Ma, which are interpreted to record post-UHP exhumation of the diamond-bearing rocks. The new discovery of microdiamond on Åreskutan, together with other evidence of ultrahigh-pressure metamorphism (UHPM) within gneisses, eclogites and peridotites elsewhere in the SNC, provide compelling arguments for regional (at least 200 km along strike of the unit) UHPM of substantial parts of this far-travelled allochthon. The occurrence of UHPM in both rheologically weak (gneisses) and strong lithologies (eclogites, peridotites) speaks against the presence of large tectonic overpressure during metamorphism.
DS201708-1693
2017
Kobussen, A.Application of machine learning tecniques to exploration: an example using self-organizing maps for garnet data.11th. International Kimberlite Conference, OralTechnologyindicator minerals
DS201705-0841
2017
Kohn, S., Speich, L., Smith, C., Bulanova, G.Developments in FTIR spectroscopy of diamonds and better constraints on diamond thermal histories.European Geosciences Union General Assembly 2017, Vienna April 23-28, 1p. 16438 AbstractAfrica, Zimbabwe, Australia, South America, BrazilDeposit - Murowa, Argyle, Machado River

Abstract: Fourier Transform Infrared (FTIR) spectroscopy is a commonly-used technique for investigating diamonds. It gives the most useful information if spatially-resolved measurements are used [1]. In this contribution we discuss the best way to acquire and present FTIR data from diamonds, using examples from Murowa (Zimbabwe), Argyle (Australia) and Machado River (Brazil). Examples of FTIR core-to-rim line scans, maps with high spatial resolution and maps with high spectral resolution that are fitted to extract the spatial variation of different nitrogen and hydrogen defects are presented. Model mantle residence temperatures are calculated from the concentration of A and B nitrogen-containing defects in the diamonds using known times of annealing in the mantle. A new, two-stage thermal annealing model is presented that better constrains the thermal history of the diamond and that of the mantle lithosphere in which the diamond resided. The effect of heterogeneity within the analysed FTIR volume is quantitatively assessed and errors in model temperatures that can be introduced by studying whole diamonds instead of thin plates are discussed. The kinetics of platelet growth and degradation will be discussed and the potential for two separate, kinetically-controlled defect reactions to be used to constrain a full thermal history of the diamond will be assessed. [1] Kohn, S.C., Speich, L., Smith, C.B. and Bulanova, G.P., 2016. FTIR thermochronometry of natural diamonds: A closer look.
DS201709-2019
2017
Kohonen, F.J., Johnson, S.P., Wingate, M.T.D., Kirkland, C.L., Fletcher, I.R., Dunkley, D.J., Roberts, M.P., Sheppard, S., Muhling, J.R., Rasmussen, B.Radiogenic heating and craton margin plate stresses as drivers for intraplate orogeny.Journal of Metamorphic Geology, Vol. 35, 6, pp. 631-661.Mantlegeothermometry

Abstract: The Proterozoic belts that occur along the margins of the West Australian Craton, as well as those in intraplate settings, generally share similar geological histories that suggest a common plate-margin driver for orogeny. However, the thermal drivers for intraplate orogenesis are more poorly understood. The Mutherbukin Tectonic Event records a protracted period of Mesoproterozoic reworking of the Capricorn Orogen and offers significant insight into both the tectonic drivers and heat sources of long-lived intraplate orogens. Mineral assemblages and tectonic fabrics related to this event occur within a 50 km-wide fault-bound corridor in the central part of the Gascoyne Province in Western Australia. This zone preserves a crustal profile, with greenschist facies rocks in the north grading to upper amphibolite facies rocks in the south. The P–T–t evolution of 13 samples from 10 localities across the Mutherbukin Zone is investigated using phase equilibria modelling integrated with in situ U–Pb monazite and zircon geochronology. Garnet chemistry from selected samples is used to further refine the P–T history and shows that the dominant events recorded in this zone are prolonged D1 transpression between c. 1,320 and 1,270 Ma, followed by D2 transtension from c. 1,210 to 1,170 Ma. Peak metamorphic conditions in the mid-crust reached >650°C and 4.4–7 kbar at c. 1,210–1,200 Ma. Most samples record a single clockwise P–T evolution during this event, although some samples might have experienced multiple perturbations. The heat source for metamorphism was primarily conductive heating of radiogenic mid- and upper crust, derived from earlier crustal differentiation events. This crust was thickened during D1 transpression, although the thermal effects persisted longer than the deformation event. Peak metamorphism was terminated by D2 transtension at c. 1,210 Ma, with subsequent cooling driven by thinning of the radiogenic crust. The coincidence of a sedimentary basin acting as a thermal lid and a highly radiogenic mid-crustal batholith restricted to the Mutherbukin Zone accounts for reworking being confined to a discrete crustal corridor. Our results show that radiogenic regions in the shallow to mid crust can elevate the thermal gradient and localize deformation, causing the crust to be more responsive to far-field stresses. The Mutherbukin Tectonic Event in the Capricorn Orogen was synchronous with numerous Mesoproterozoic events around the West Australian Craton, suggesting that thick cratonic roots play an important role in propagating stresses generated at distant plate boundaries.
DS201705-0842
2017
Koivula, J.I., Skalwold, E.A.Diamond: Intimate Portraits.lithographie.org, No. 19, pp. 54-61.TechnologyBook - diamond inclusions
DS201702-0222
2017
Kolesnichenko, M.V., Zedgenizov, D.A., Litasov, K.D., Safonova, I.Y., Ragozin, A.L.Heterogenesous distribution of water in the mantle beneath the central Siberian Craton: implications for Udachnaya kimberlite pipe.Gondwana Research, in press available 18p.RussiaDeposit - Udachnaya

Abstract: The paper presents new petrographic, major element and Fourier transform infrared (FTIR) spectroscopy data and PT-estimates of whole-rock samples and minerals of a collection of 19 relatively fresh peridotite xenoliths from the Udachnaya kimberlite pipe, which were recovered from its deeper levels. The xenoliths are non-deformed (granular), medium-deformed and highly deformed (porphyroclastic, mosaic-porphyroclastic, mylonitic) lherzolites, harzburgite and dunite. The lherzolites yielded equilibration temperatures (T) and pressures (P) ranging from 913 to 1324 °C and from 4.6 to 6.3 GPa, respectively. The non-deformed and medium-deformed peridotites match the 35 mW/m2 conductive continental geotherm, whereas the highly deformed varieties match the 45 mW/m2 geotherm. The content of water spans 2 ± 1-95 ± 52 ppm in olivine, 1 ± 0.5-61 ± 9 ppm in orthopyroxene, and 7 ± 2-71 ± 30 ppm in clinopyroxene. The amount of water in garnets is negligible. Based on the modal proportions of mineral phases in the xenoliths, the water contents in peridotites were estimated to vary over a wide range from < 1 to 64 ppm. The amount of water in the mantle xenoliths is well correlated with the deformation degree: highly deformed peridotites show highest water contents (64 ppm) and those medium-deformed and non-deformed contain ca. 1 ppm of H2O. The high water contents in the deformed peridotites could be linked to metasomatism of relatively dry diamondiferous cratonic roots by hydrous and carbonatitic agents (fluids/melts), which may cause hydration and carbonation of peridotite and oxidation and dissolution of diamonds. The heterogeneous distribution of water in the cratonic mantle beneath the Udachnaya pipe is consistent with the models of mantle plume or veined mantle structures proposed based on a trace element study of similar xenolithic suits. Mantle metasomatism beneath the Siberian Craton and its triggered kimberlite magmatism could be induced by mantle enrichment in volatiles (H2O, CO2) supplied by numerous subduction zones which surrounded the Siberian continent in Neoproterozoic-Cambrian time.
DS201706-1086
2017
Kolesnichenko, M.V., Zedgenizov, D.A., Litasov, K.D., Safonova, I.Y., Ragozin, A.L.Heterogeneous distribution of water in the mantle beneath the central Siberian craton: implications from the Udachachnaya kimberlite pipe.Gondwana Research, Vol. 47, pp. 249-266.Russiadeposit - Udachnaya

Abstract: The paper presents new petrographic, major element and Fourier transform infrared (FTIR) spectroscopy data and PT-estimates of whole-rock samples and minerals of a collection of 19 relatively fresh peridotite xenoliths from the Udachnaya kimberlite pipe, which were recovered from its deeper levels. The xenoliths are non-deformed (granular), medium-deformed and highly deformed (porphyroclastic, mosaic-porphyroclastic, mylonitic) lherzolites, harzburgite and dunite. The lherzolites yielded equilibration temperatures (T) and pressures (P) ranging from 913 to 1324 °C and from 4.6 to 6.3 GPa, respectively. The non-deformed and medium-deformed peridotites match the 35 mW/m2 conductive continental geotherm, whereas the highly deformed varieties match the 45 mW/m2 geotherm. The content of water spans 2 ± 1-95 ± 52 ppm in olivine, 1 ± 0.5-61 ± 9 ppm in orthopyroxene, and 7 ± 2-71 ± 30 ppm in clinopyroxene. The amount of water in garnets is negligible. Based on the modal proportions of mineral phases in the xenoliths, the water contents in peridotites were estimated to vary over a wide range from < 1 to 64 ppm. The amount of water in the mantle xenoliths is well correlated with the deformation degree: highly deformed peridotites show highest water contents (64 ppm) and those medium-deformed and non-deformed contain ca. 1 ppm of H2O. The high water contents in the deformed peridotites could be linked to metasomatism of relatively dry diamondiferous cratonic roots by hydrous and carbonatitic agents (fluids/melts), which may cause hydration and carbonation of peridotite and oxidation and dissolution of diamonds. The heterogeneous distribution of water in the cratonic mantle beneath the Udachnaya pipe is consistent with the models of mantle plume or veined mantle structures proposed based on a trace element study of similar xenolithic suits. Mantle metasomatism beneath the Siberian Craton and its triggered kimberlite magmatism could be induced by mantle enrichment in volatiles (H2O, CO2) supplied by numerous subduction zones which surrounded the Siberian continent in Neoproterozoic-Cambrian time.
DS201704-0633
2017
Kooijman, E., Smit, M.A., Ratschbacher, L., Kylander-Clark, A.R.C.A view into crustal evolution at mantle depths.Earth and Planetary Science Letters, Vol. 465, pp. 59-69.MantleGeothermometry

Abstract: Crustal foundering is an important mechanism in the differentiation and recycling of continental crust. Nevertheless, little is known about the dynamics of the lower crust, the temporal scale of foundering and its role in the dynamics of active margins and orogens. This particularly applies to active settings where the lower crust is typically still buried and direct access is not possible. Crustal xenoliths derived from mantle depth in the Pamir provide a unique exception to this. The rocks are well-preserved and comprise a diverse set of lithologies, many of which re-equilibrated at high-pressure conditions before being erupted in their ultrapotassic host lavas. In this study, we explore the petrological and chronological record of eclogite and felsic granulite xenoliths. We utilized accessory minerals - zircon, monazite and rutile - for coupled in-situ trace-element analysis and U-(Th-)Pb chronology by laser-ablation (split-stream) inductively coupled plasma mass spectrometry. Each integrated analysis was done on single mineral zones and was performed in-situ in thin section to maintain textural context and the ability to interpret the data in this framework. Rutile thermo-chronology exclusively reflects eruption (View the MathML source11.17±0.06Ma), which demonstrates the reliability of the U-Pb rutile thermo-chronometer and its ability to date magmatic processes. Conversely, zircon and monazite reveal a series of discrete age clusters between 55-11 Ma, with the youngest being identical to the age of eruption. Matching age populations between samples, despite a lack of overlapping ages for different chronometers within samples, exhibit the effectiveness of our multi-mineral approach. The REE systematics and age data for zircon and monazite, and Ti-in-zircon data together track the history of the rocks at a million-year resolution. The data reveal that the rocks resided at 30-40 km depth along a stable continental geotherm at 720-750?°C until 24-20 Ma, and were subsequently melted, densified, and buried to 80-90 km depth - 20 km deeper than the present-day Moho - at View the MathML source930±35°C. The material descended rapidly, accelerating from 0.9-1.7 mm?yr?1 to 4.7-5.8 mm?yr?1 within 10-12 Myr, and continued descending after reaching mantle depth at 14-13 Ma. The data reflect the foundering of differentiated deep-crustal fragments (2.9-3.5 g?cm?3) into a metasomatized and less dense mantle wedge. Through our new approach in constraining the burial history of rocks, we provided the first time-resolved record of this crustal-recycling process. Foundering introduced vestiges of old evolved crust into the mantle wedge over a relatively short period (c. 10 Myr). The recycling process could explain the variability in the degree of crustal contamination of mantle-derived magmatic rocks in the Pamir and neighboring Tibet during the Cenozoic without requiring a change in plate dynamics or source region.
DS201710-2235
2017
Koornneef, J.M., Gress, M.U., Chinn, I.L., Jelsma, H.A., Harris, J.W., Davies, G.R.Archaean and Proterozoic diamond growth from contrasting styles of large scale magmatism.Nature Communications, Vol. 8, 10.1038/s41467-017-00564-xAfrica, South Africadiamond inclusions

Abstract: Precise dating of diamond growth is required to understand the interior workings of the early Earth and the deep carbon cycle. Here we report Sm-Nd isotope data from 26 individual garnet inclusions from 26 harzburgitic diamonds from Venetia, South Africa. Garnet inclusions and host diamonds comprise two compositional suites formed under markedly different conditions and define two isochrons, one Archaean (2.95?Ga) and one Proterozoic (1.15?Ga). The Archaean diamond suite formed from relatively cool fluid-dominated metasomatism during rifting of the southern shelf of the Zimbabwe Craton. The 1.8 billion years younger Proterozoic diamond suite formed by melt-dominated metasomatism related to the 1.1?Ga Umkondo Large Igneous Province. The results demonstrate that resolving the time of diamond growth events requires dating of individual inclusions, and that there was a major change in the magmatic processes responsible for harzburgitic diamond formation beneath Venetia from the Archaean to the Proterozoic.
DS201708-1694
2017
Kopylova, M.Peridotite xenoliths of the Chidliak kimberlite province (NE Canada): The North Atlantic cratonic mantle with recent thermal and Ti-Na metasomatic disturbance.11th. International Kimberlite Conference, OralCanada, Nunavut, Baffin IslandDeposit - Chidliak
DS201708-1695
2017
Kopylova, M.Hydration of the lithospheric mantle in the northern Slave craton ( Canada): constraints from combined FTIR and ESRD measurements on peridotite xenoliths.11th. International Kimberlite Conference, PosterCanada, Northwest Territorieshydration
DS201704-0634
2017
Korhonen, F.J., Johnson, S.P., Wingate, M.T.D., Fletcher, I.R., Dunkley, D.J., Roberts, M.P., Sheppard, S., Muhling, J.R., Rasmussen, B.Radiogenic heating and craton-margin plate stresses as drivers for intraplate orogeny.Journal of Metamorphic Geology, in press availableMantleCraton

Abstract: The Proterozoic belts that occur along the margins of the West Australian Craton, as well as those in intraplate settings, generally share similar geological histories that suggest a common plate-margin driver for orogeny. However, the thermal drivers for intraplate orogenesis are generally more poorly understood. The Mutherbukin Tectonic Event records a protracted period of Mesoproterozoic reworking of the Capricorn Orogen and offers significant insight into both the tectonic drivers and heat sources of long-lived intraplate orogens. Mineral assemblages and tectonic fabrics related to this event occur within a 50 km-wide fault-bound corridor in the central part of the Gascoyne Province in Western Australia. This zone preserves a crustal profile, with greenschist facies rocks in the north grading to upper amphibolite facies rocks in the south. The P- T-t evolution of 13 samples from 10 localities across the Mutherbukin Zone is investigated using phase equilibria modelling integrated with in situ U-Pb monazite and zircon geochronology. Garnet chemistry from selected samples is used to further refine the P-T history and shows that the dominant events recorded in this zone are prolonged D1 transpression between c. 1320 and 1270 Ma, followed by D2 transtension from c. 1210 to 1170 Ma. Peak metamorphic conditions in the mid-crust reached >650 °C and 4.4-7 kbar at c. 1210-1200 Ma. Most samples record a single clockwise P-T evolution during this event, although some samples might have experienced multiple perturbations. The heat source for metamorphism was primarily conductive heating of radiogenic mid- and upper crust, derived from earlier crustal differentiation events. This crust was thickened during D1 transpression, although the thermal effects persisted longer than the deformation event. Peak metamorphism was terminated by D2 transtension at c. 1210 Ma, with subsequent cooling driven by thinning of the radiogenic crust. The coincidence of a sedimentary basin acting as a thermal lid and a highly radiogenic mid-crustal batholith restricted to the Mutherbukin Zone accounts for reworking being confined to a discrete crustal corridor. Our results show that radiogenic regions in the shallow to mid crust can elevate the thermal gradient and localize deformation, causing the crust to be more responsive to far-field stresses. The Mutherbukin Tectonic Event in the Capricorn Orogen was synchronous with numerous Mesoproterozoic events around the West Australian Craton, suggesting that thick cratonic roots play an important role in propagating stresses generated at distant plate boundaries.
DS201707-1341
2017
Kornprobst, J.The forgotten fit of the circum-Atlantic continents.Comptes Rendus Geoscience, Vol. 349, pp. 42-48.Technologyplate tectonics

Abstract: Boris Choubert was a strong supporter of Wegener's continental drift theory. In 1935, he published a very accurate fit of the circum-Atlantic continents, which was based on continental edges instead of coastlines; in the same paper, he interpreted the Palaeozoic belts as the result of horizontal movements of the Precambrian blocks; so, he greatly expanded the role of continental drift through time. This original and very prophetic work was almost completely ignored by his contemporaries. Thirty years later (1965), Bullard, Everett and Smith published in turn a similar but more sophisticated fit; they did not acknowledge Choubert's initial work. Bullard's fit was met with immediate and tremendous success. The present paper analyses the reasons why Boris Choubert was frustrated of his pioneering role. This lack of recognition is related to: (1) a great evolution in the geological concepts between 1935 and 1965, and (2) a poor choice of Choubert, regarding the title of his 1935 article.
DS201708-1696
2017
Korolev, N.The origin of type II diamonds: insights from contrasting mineral inclusions in Culli nan type I and type II stones.11th. International Kimberlite Conference, OralAfrica, South Africadeposit - Cullinan
DS201708-1697
2017
Korolev, N.Origin of upper mantle eclogites from the Catoca pipe, (N-E Angola).11th. International Kimberlite Conference, PosterAfrica, Angoladeposit - Catoca
DS201709-2020
2017
Kotova, J., Fedortchouk, Y., Wirth, R., Whitehouse, M., JakubovaUHP-UHT melting and diamond formation. MicrodiamondsGoldschmidt Conference, abstract 1p.MantleUHP

Abstract: Exhumed ultrahigh-pressure (UHP) terranes, involving slices of deeply subducted crustal rocks, provide unique material for studying material transfer in subduction zones. Diamond-bearing UHP rocks with sedimentary protoliths allow for tracing melting processes at both UHP and UHT including carbon cycling in the Earth. We studied microdiamonds and associated phases in two contrasting lithologies, (1) acid, quartzofeldpathic UHP gneiss composed of garnet, kyanite, feldspar, quartz and biotite, with a high ASI characteristic of sedimentary rocks, and (2) intermediate garnet-clinopyroxene rock containing quartz, feldspar, minor kyanite and biotite, which is metaluminous. Whereas rock (1) contains exclusively single octahedral diamonds with perfect crystal shape in garnet, kyanite (more common) and zircon, the microdiamonds in the rock (2) occur mostly as clusters of cuboid shape in garnet and zircon. Micro-Raman and FIB TEM data document presence of graphite, quartz and rutile at diamond/host interface or in separate multiple solid inclusions (MSI) whereas carbonates are practically absent. The morphology and lack of inclusions reflect relatively slow growth of the octahedral diamonds (rock 1) at lower fluid supersaturation. Individual deep and symmetrical negative trigons (AFM) on the (111) plane suggest dissolution by a residual silicate-carbonate melt. In contrast, polycrystallline character of diamond cuboids (rock 2) along with their common dissolution and formation of numerous tetragonal etch pits reflect relatively rapid growth of these grains from highly supersaturated fluid/melt. Peak P-T conditions for the UHP rocks of ? 1100ºC at 4.5 GPa are located above the phengite dehydration melting curve, where silicate melts are produced and may coexist with carbonate melts. In view of the light carbon isotope composition and lack of carbonates, we suggest that the diamonds crystallized from the graphitized primordial organic matter under reducing conditions at presence of silicate melt.
DS201703-0423
2016
Kowpaczuy, P.AUVs for subsea exploration.Society of Exploration Geophysics, Dallas annual meeting, Ocean Floor Geophysics Inc. 27ppt.TechnologyGeophysics
DS201705-0843
2017
Kramm, U., Korner, T., Kittel, M., Baier, H., Sindern, S.Triassic emplacement age of the Kalkfeld complex, NW Namibia: implications for carbonatite magmatism and its relationship to the Tristan Plume.International Journal of Earth Sciences, in press available 17p.Africa, NamibiaAlkaline rocks

Abstract: Rb-Sr whole-rock and mineral isotope data from nepheline syenite, tinguaite, and carbonatite samples of the Kalkfeld Complex within the Damaraland Alkaline Province, NW Namibia, indicate a date of 242?±?6.5 Ma. This is interpreted as the age of final magmatic crystallization in the complex. The geological position of the complex and the spatially close relationship to the Lower Cretaceous Etaneno Alkaline Complex document a repeated channeling of small-scale alkaline to carbonatite melt fractions along crustal fractures that served as pathways for the mantle-derived melts. This is in line with Triassic extensional tectonic activity described for the nearby Omaruru Lineament-Waterberg Fault system. The emplacement of the Kalkfeld Complex more than 100 Ma prior to the Paraná-Etendeka event and the emplacement of the Early Cretaceous Damaraland intrusive complexes excludes a genetic relationship to the Tristan Plume. The initial ?Sr-?Nd pairs of the Kalkfeld rocks are typical of younger African carbonatites and suggest a melt source, in which EM I and HIMU represent dominant components.
DS201711-2523
2017
Kramm, U., Korner, T., Kittel, M., Baier, H., Sindern, S.Triassic emplacement age of the Kalkfeld complex, NW Namibia: implications for carbonatite magmatism and its relationship to the Tristan Plume.International Journal of Earth Sciences, Vol. 106, pp. 2797-2813.Africa, Namibiacarbonatites

Abstract: Rb-Sr whole-rock and mineral isotope data from nepheline syenite, tinguaite, and carbonatite samples of the Kalkfeld Complex within the Damaraland Alkaline Province, NW Namibia, indicate a date of 242?±?6.5 Ma. This is interpreted as the age of final magmatic crystallization in the complex. The geological position of the complex and the spatially close relationship to the Lower Cretaceous Etaneno Alkaline Complex document a repeated channeling of small-scale alkaline to carbonatite melt fractions along crustal fractures that served as pathways for the mantle-derived melts. This is in line with Triassic extensional tectonic activity described for the nearby Omaruru Lineament-Waterberg Fault system. The emplacement of the Kalkfeld Complex more than 100 Ma prior to the Paraná-Etendeka event and the emplacement of the Early Cretaceous Damaraland intrusive complexes excludes a genetic relationship to the Tristan Plume. The initial ?Sr-?Nd pairs of the Kalkfeld rocks are typical of younger African carbonatites and suggest a melt source, in which EM I and HIMU represent dominant components.
DS201708-1698
2017
Kriulina, G.Micro inclusions in diamonds from deposits of different genetic kimberlite types.11th. International Kimberlite Conference, PosterRussiadiamond inclusions
DS201708-1699
2017
Kriulina, G.Forecast diamond quality in the deposit.11th. International Kimberlite Conference, PosterRussiadiamond resource
DS201710-2236
2017
Kruger, K., Maphane, K.Desert Gems: Bostwana's major mines. Orapa, Letlhakane and Damtshaa mines.11th International Kimberlite Field Trip Guide, Sept. 23p. PdfAfrica, Botswanadeposit - Orapa, Letlhakane, Damtshaa
DS201707-1342
2017
Kueter, N., Soesilo, J., Fedortchouk, Y., Nestola, F., Belluco, L., Troch, J., Walle, M., Guillong, M., Von Quadt, A., Driesner, T.Tracing the depositional history of Kalimantan diamonds by zircon proveneance and diamond morphology studies. Appendix 1 and 2Academia.edu, Supplementary material app. 1 and 2, both 10p.Asia, Kalimantandeposit - Kalimantan

Abstract: Diamonds in alluvial deposits in Southeast Asia are not accompanied by indicator minerals suggesting primary kimberlite or lamproite sources. The Meratus Mountains in Southeast Borneo (Province Kalimantan Selatan, Indonesia) provide the largest known deposit of these so-called “headless” diamond deposits. Proposals for the origin of Kalimantan diamonds include the adjacent Meratus ophiolite complex, ultra-high pressure (UHP) metamorphic terranes, obducted subcontinental lithospheric mantle and undiscovered kimberlite-type sources. Here we report results from detailed sediment provenance analysis of diamond-bearing Quaternary river channel material and from representative outcrops of the oldest known formations within the Alino Group, including the diamond-bearing Campanian–Maastrichtian Manunggul Formation. Optical examination of surfaces of diamonds collected from artisanal miners in the Meratus area (247 stones) and in West Borneo (Sanggau Area, Province Kalimantan Barat; 85 stones) points toward a classical kimberlite-type source for the majority of these diamonds. Some of the diamonds host mineral inclusions suitable for deep single-crystal X-ray diffraction investigation. We determined the depth of formation of two olivines, one coesite and one peridotitic garnet inclusion. Pressure of formation estimates for the peridotitic garnet at independently derived temperatures of 930–1250 °C are between 4.8 and 6.0 GPa. Sediment provenance analysis includes petrography coupled to analyses of detrital garnet and glaucophane. The compositions of these key minerals do not indicate kimberlite-derived material. By analyzing almost 1400 zircons for trace element concentrations with laser ablation ICP-MS (LA-ICP-MS) we tested the mineral's potential as an alternative kimberlite indicator. The screening ultimately resulted in a small subset of ten zircons with a kimberlitic affinity. Subsequent U–Pb dating resulting in Cretaceous ages plus a detailed chemical reflection make a kimberlitic origin unfavorable with respect to the regional geological history. Rather, trace elemental analyses (U, Th and Eu) suggest an eclogitic source for these zircons. The age distribution of detrital zircons allows in general a better understanding of collisional events that formed the Meratus orogen and identifies various North Australian Orogens as potential Pre-Mesozoic sediment sources. Our data support a model whereby the majority of Kalimantan diamonds were emplaced within the North Australian Craton by volcanic processes. Partly re-deposited into paleo-collectors or residing in their primary host, these diamond-deposits spread passively throughout Southeast Asia by terrane migration during the Gondwana breakup. Terrane amalgamation events largely metamorphosed these diamond-bearing lithologies while destroying the indicative mineral content. Orogenic uplift finally liberated their diamond-content into new, autochthonous placer deposits.
DS201710-2237
2017
Kulrenya, M.V., Chernyshov, G.S., Serdyukov, A.S., Duchkov, A.A.Procedure and results of seismic investigations into causes of landslides in permafrost rocks.Journal of Mining Science, Vol. 52, 5, pp. 835-841.Russiadeposit - Yubilieny

Abstract: The article focuses on seismic monitoring of causes of landslides. Such studies are of great importance in open pit mining in permafrost rocks. Extensive mining-induced impact in combination with natural thawing of permafrost as a consequence of the planet warming may end in catastrophe. The authors describe a procedure for plotting velocity profiles of seismic waves along slopes in the presence of extremely contrast discontinuities conditioned by permafrost rocks. The presented approach enables studying slip surfaces of landslides and detecting potential failure zones where wave velocities are lower due to extensive jointing. The processed field data obtained in the area near Chagan-Uzun settlement in Kosh-Agach district of the Republic of Altai are reported.
DS201706-1087
2017
Kumar, R., Bansal, A.R., Anand, P., Rao, V.K., Singh, U.Mapping of magnetic basement in the central India from aeromagnetic dat a for scaling geology.Geophysical Prospecting, in press availableIndiageophysics - aermagnetics

Abstract: The Central Indian region is having complex geology covering the Godavari Graben, the Bastar Craton (including the Chhattisgarh Basin), the Eastern Ghat Mobile Belt, the Mahanadi Graban and some part of the Deccan Trap, the Northern Singhbhum Orogen and the Eastern Dharwar Craton. The region is well covered by reconnaissance scale aeromagnetic data, analyzed for the estimation of basement and shallow anomalous magnetic sources depth using scaling spectral method. The shallow magnetic anomalies are found to vary from 1 to 3 km whereas magnetic basement depth values are found to vary from 2 to 7 km. The shallowest basement depth of 2 km corresponds to the Kanker granites, a part of the Bastar Craton, whereas deepest basement depth of 7 km is for the Godavari Basin and the southeastern part of the Eastern Ghat Mobile Belts near the Parvatipuram Bobbili fault. The estimated basement depth values correlate well with the values found from earlier geophysical studies. The earlier geophysical studies are limited to few tectonic units whereas our estimation provides detailed magnetic basement mapping in the region. The magnetic basement and shallow depth values in the region indicate complex tectonic, heterogeneity and intrusive bodies at different depth which can be attributed to different thermo-tectonic processes since Precambrian.
DS201701-0019
2016
Kumari, S., Paul, D., Stracke, A.Open system models of isotopic implications for crustal growth and mantle heterogeneity.Geochimica et Cosmochimica Acta, Vol. 195, pp. 142-157.MantleConvection
DS201706-1088
2017
Kupers, S.A., Schmidt, M., Campbell, I.A petrographic and geochemical analysis of the KRVY kimberlite, Lake Timiskaming kimberlite field, Ontario Canada.GSA Annual Meeting, 1p. AbstractCanada, Ontariodeposit - Krvy

Abstract: The Lake Tamiskaming Kimberlite Field, in Ontario, Canada is host to multiple kimberlite pipes, such as the KRVY Kimberlite Pipe, south of Latchford, Ontario. Drill core of this kimberlite pipe, collected by Temex Resources Corporation, confirmed the diamondiferous nature, with microdiamonds being retrieved. Thin sections of the drill core samples suggest the pipe is highly altered through serpentinization. Euhedral to subhedral grains of mica, such as phlogopite and biotite, compose the phenocryst and matrix components of the samples. Electron microprobe analysis will be used to determine the composition of the micas, in order to constrain the origin conditions of these grains, determining if the grains originate from crustal or magmatic components. Micro X-ray Diffraction will determine the mineralogy in the samples. Other likely xenocrystic minerals include quartz, etc. Textural and compositional attributes of the KRVY Kimberlite will be compared to data collected from the approximately twelve known kimberlite pipes within 25 kilometres (15.5 miles) of the specified kimberlite in order to find similarities or patterns. Geochemical analysis will better constrain the formation conditions of this pipe and allow comparison with other surrounding pipes in the Lake Tamiskaming Kimberlite Field.
DS201707-1343
2016
Kurszlaukis, S., Lorenz, V.Differences and similarities between emplacement models of kimberlite and basaltic maar-diatreme volcanoes.Geological Society of London, Special Publication: Monogenetic volcanism, no. 446, pp. 101-122.Technologydiatremes

Abstract: Most kimberlite maar-diatreme volcanoes erupted during the Tertiary or earlier and therefore their tephra rings and, less often, their near-surface diatreme-filling deposits have usually been eliminated by erosion. Poorly eroded Quaternary non-kimberlite maar-diatreme volcanoes, especially those of mafic and ultramafic magma types, have the same diatreme size range (diameter and depth) as kimberlite pipes and show similar internal volcaniclastic diatreme lithofacies. In addition, these young volcanoes often have a more or less preserved tephra ring consisting of hundreds to perhaps a few thousand thin tephra beds. Volcanological analyses of the xenolith-rich primary volcaniclastic deposits both within these diatremes and in the tephra ring beds reflect phases of explosive pipe growth and are of convincingly phreatomagmatic origin. The similarities between non-kimberlite pipes and kimberlite pipes suggest to some researchers that phreatomagmatic processes were also responsible for pipe excavation processes in kimberlite maar-diatreme volcanoes. In contrast, other researchers have suggested that kimberlite maar-diatreme volcanoes were emplaced largely by magmatic processes as a consequence of exsolution and the explosive expansion of juvenile volatiles. We therefore analysed and compared some key geological features of kimberlite and ultrabasic to basic ‘basaltic’ maar-diatreme volcanoes to determine similarities and differences with respect to their emplacement behaviour.
DS201705-0844
2016
Kwan, K., Legault, J.Tli Kwi Cho shootout. III GeophysicsSEG Annual Meeting Dallas, 14 ppt.Canada, Northwest TerritoriesDeposit - Tli Kwi Cho
DS201703-0424
2017
LaFlamme, C., McFarlane, C.R.M., Fisher, C.M., Kirkland, C.L.Multi-mineral geochronology: insights into crustal behaviour during exhumation of an orogenic root.Contributions to Mineralogy and Petrology, in press available, 18p.CanadaCraton, Rae, Hearne
DS201708-1700
2017
Lamb, K.Kimberlite intrusions, Kimberlitic as dispersal, diamond transport and diamond deposition: the potential role of Earth Systems Modelling in diamond exploration.11th. International Kimberlite Conference, PosterTechnologyEarth Systems Modelling
DS201708-1574
2017
Lamb, S., Moore, J.D., Smith, E., Stern, T.Episodic kinematics in continental rifts modulated by changes in mantle melt fraction.Nature, Vol. 547, 7661, pp. 84-88.Mantlemelting

Abstract: Oceanic crust is created by the extraction of molten rock from underlying mantle at the seafloor ‘spreading centres’ found between diverging tectonic plates. Modelling studies have suggested that mantle melting can occur through decompression as the mantle flows upwards beneath spreading centres, but direct observation of this process is difficult beneath the oceans. Continental rifts, however—which are also associated with mantle melt production—are amenable to detailed measurements of their short-term kinematics using geodetic techniques. Here we show that such data can provide evidence for an upwelling mantle flow, as well as information on the dimensions and timescale of mantle melting. For North Island, New Zealand, around ten years of campaign and continuous GPS measurements in the continental rift system known as the Taupo volcanic zone reveal that it is extending at a rate of 6-15?millimetres per year. However, a roughly 70-kilometre-long segment of the rift axis is associated with strong horizontal contraction and rapid subsidence, and is flanked by regions of extension and uplift. These features fit a simple model that involves flexure of an elastic upper crust, which is pulled downwards or pushed upwards along the rift axis by a driving force located at a depth greater than 15?kilometres. We propose that flexure is caused by melt-induced episodic changes in the vertical flow forces that are generated by upwelling mantle beneath the rift axis, triggering a transient lower-crustal flow. A drop in the melt fraction owing to melt extraction raises the mantle flow viscosity and drives subsidence, whereas melt accumulation reduces viscosity and allows uplift—processes that are also likely to occur in oceanic spreading centres.
DS201707-1344
2016
Larionova, Y.O., Sazonova, L.V., Lebedeva, N.M., Nosova, A., Tretyachenko, V.V., Travin, A.V., Kargin, A.V., Yudin, D.S.Kimberlite age in the Arkhangelsk province, Russia: isotopic geochronologic Rb-Sr and 40Ar/39Ar and mineralogical dat a on phlogopite.Petrology, Vol. 24, 6, pp. 562-593.Russiageochronology

Abstract: The paper reports detailed data on phlogopite from kimberlite of three facies types in the Arkhangelsk Diamondiferous Province (ADP): (i) massive magmatic kimberlite (Ermakovskaya-7 Pipe), (ii) transitional type between massive volcaniclastic and magmatic kimberlite (Grib Pipe), and (iii) volcanic kimberlite (Karpinskii-1 and Karpinskii-2 pipes). Kimberlite from the Ermakovskaya-7 Pipe contains only groundmass phlogopite. Kimberlite from the Grib Pipe contains a number of phlogopite populations: megacrysts, macrocrysts, matrix phlogopite, and this mineral in xenoliths. Phlogopite macrocrysts and matrix phlogopite define a single compositional trend reflecting the evolution of the kimberlite melt. The composition points of phlogopite from the xenoliths lie on a single crystallization trend, i.e., the mineral also crystallized from kimberlite melt, which likely actively metasomatized the host rocks from which the xenoliths were captured. Phlogopite from volcaniclastic kimberlite from the Karpinskii-1 and Karpinskii-2 pipes does not show either any clearly distinct petrographic setting or compositional differentiation. The kimberlite was dated by the Rb–Sr technique on phlogopite and additionally by the 40Ar/39Ar method. Because it is highly probable that phlogopite from all pipes crystallized from kimberlite melt, the crystallization age of the kimberlite can be defined as 376 ± 3 Ma for the Grib Pipe, 380 ± 2 Ma for the Karpinskii-1 pipe, 375 ± 2 Ma for the Karpinskii-2 Pipe, and 377 ± 0.4 Ma for the Ermakovskaya-7 Pipe. The age of the pipes coincides within the error and suggests that the melts of the pipes were emplaced almost simultaneously. Our geochronologic data on kimberlite emplacement in ADP lie within the range of 380 ± 2 to 375 ± Ma and coincide with most age values for Devonian alkaline–ultramafic complexes in the Kola Province: 379 ± 5 Ma; Arzamastsev and Wu, 2014). These data indicate that the kimberlite was formed during the early evolution of the Kola Province, when alkaline–ultramafic complexes (including those with carbonatite) were emplaced.
DS201708-1701
2017
Laroulandie, C.Barium and titanium enrichment of zoned phlogopite xenocrysts and phenocrysts in the Adamantin kimberlites, Quebec, Canada.11th. International Kimberlite Conference, PosterCanada, Quebecdeposit - Adamantin
DS201707-1345
2017
Laurs, B.M.Recent alluvial diamond mining in South Africa. Fieldtrip leader M. De Wit 35th. IGC CongressJournal of Gemmology, Vol. 35, 6, pp. 484-485.Africa, South Africadeposit - Tirisano
DS201706-1089
2017
Lavecchia, A., Thieulot, C., Beekman, F., Cloetingh, S., Clark, S.Lithosphere erosion and continental breakup: interaction of extension, plume upwelling and melting.Earth and Planetary Science Letters, Vol. 467, pp. 89-98.Mantlemelting

Abstract: We present the results of thermo-mechanical modelling of extension and breakup of a heterogeneous continental lithosphere, subjected to plume impingement in presence of intraplate stress field. We incorporate partial melting of the extending lithosphere, underlying upper mantle and plume, caused by pressure-temperature variations during the thermo-mechanical evolution of the conjugate passive margin system. Effects of melting included in the model account for thermal effects, causing viscosity reduction due to host rock heating, and mechanical effects, due to cohesion loss. Our study provides better understanding on how presence of melts can influence the evolution of rifting. Here we focus particularly on the role of melting for the temporal and spatial evolution of passive margin geometry and rift migration. Depending on the lithospheric structure, melt presence may have a significant impact on the characteristics of areas affected by lithospheric extension. Pre-existing lithosphere heterogeneities determine the location of initial breakup, but in presence of plumes the subsequent evolution is more difficult to predict. For small distances between plume and area of initial rifting, the development of symmetric passive margins is favored, whereas increasing the distance promotes asymmetry. For a plume-rifting distance large enough to prevent interaction, the effect of plumes on the overlying lithosphere is negligible and the rift persists at the location of the initial lithospheric weakness. When the melt effect is included, the development of asymmetric passive continental margins is fostered. In this case, melt-induced lithospheric weakening may be strong enough to cause rift jumps toward the plume location.
DS201708-1702
2017
Lawless, P.J.Relationships between the Diamond Trading Company ( DTC) round aperture diamond sieve ( DS) plates.11th. International Kimberlite Conference, PosterTechnologyDTC
DS201702-0223
2017
Le Voyer, M.Deep mantle chemistry surprise: carbon content not uniform.Nature Communications, Jan. 13, 1p.MantleDiamond inclusions
DS201705-0845
2017
Lebedeva, N., Kargin, A., Sazonova, L., Nosova, A.Geochemistry of clinopyroxene megacrysts from the Grib kimberlite pipe, Arkhangelsk province, Russia: metasomatic origin and genetic relationship with clinopyroxene phlogopite metasomatic xenoliths.European Geosciences Union General Assembly 2017, Vienna April 23-28, 1p. 220 AbstractRussia, Archangel, Kola PeninsulaDeposit - Grib

Abstract: Kimberlite is a composite rock that contains juvenile magmatic material and xenoliths of crustal and mantle rocks, including metasomatically reworked rocks and megacrysts. In spite of nearly 40-50 years of continuous study of kimberlites and SCLM, some aspects of their origin remain controversial. In particular, it is unclear yet whether the megacrysts are magmatic or metasomatic in origin and how they are related to kimberlite magmas. In this contribution, we compare the major (EMPA) and trace element (SIMS, LA-ICP-MS) compositions of clinopyroxene megacrysts from the Grib kimberlite (Arkhangelsk province, Russia) with clinopyroxenes from metasomatic clinopyroxene-phlogopite xenoliths and garnet peridotite xenoliths. The Grib kimberlite (376±3 Ma, Larionova et al., 2016) is located in the central part of the Arkhangelsk province (the northern part of the East European craton) in the Chernoozero kimberlite field. The geochemical composition of the kimberlites is similar to widespread South Africa group I kimberlites . The Grib kimberlite is well known for hosting a variety of mantle xenoliths, e.g., garnet peridotite, sheared peridotite, eclogite, metasomatised mantle material, as well as megacrysts of clinopyroxene, garnet, olivine, phlogopite, and ilmenite. The clinopyroxene megacrysts occur as rounded or angular grains up to 2 cm in size. They are usually surrounded by ultrafine kimberlite rim. The xenoliths of the metasomatic clinopyroxene-phlogopite rocks reach up to 6 cm in size and have a granoblastic texture. They consist of clinopyroxene (55 vol. %), phlogopite (45 vol. %) and minor calcite, barite, perovskite. Some clinopyroxene grains contain inclusion of relict olivine that is similar in composition to olivine from mantle-derived peridotite xenoliths within the Grib kimberlite (Sazonova et al., 2015). This suggests that these xenoliths could be formed by metasomatic reworking of SCLM peridotites. The megacryst clinopyroxene is compositionally similar to the clinopyroxene found in metasomatic xenoliths and corresponds to diopside. As compared to the typical clinopyroxene megacrysts worldwide, it has higher Mg# (>0.92), Cr# (0.21-0.62) and Ca# values (0.47-0.49) and lower Ti (659-1966 ppm) composition. The clinopyroxenes have (La/Sm)CI values from 0.58 to 1.57, and trace element patterns with deep negative Ti and shallow negative Zr-Hf anomalies. The major and trace-element compositions of these clinopyroxenes are very close to those of clinopyroxenes from garnet peridotite xenoliths in the Grib pipe (Kargin et al., 2016) that could be formed during the ascent and interaction of kimberlite mamas with a surrounding lithospheric mantle after crystallization of garnet and ilmenite megacrysts. Calculations showed that metasomatic agents in equilibrium with clinopyroxene megacrysts are similar in composition to kimberlite, which is consistent with proposed model. To sum up, we suggest that the formation of clinopyroxenes of megacrysts and mantle-derived clinopyroxene-phlogopite metasomatic xenoliths from the Grib kimberlite was related to the late-stage metasomatic reworking of SCLM by kimberlite magmas.
DS201705-0846
2017
LeBreton, R.Dat a gathering and integration in geotechnical applications- the Diavik experience.Canadian Institute of Mining and Metallurgy, abstract, 1/4p.Canada, Northwest TerritoriesDeposit - Diavik
DS201702-0224
2017
Lenardic, A.Plate tectonics: a supercontinental boost.Nature Geoscience, Vol. 10, pp. 4-5.PangeaTectonics

Abstract: 180 million years ago Earth's continents were amalgamated into one supercontinent called Pangaea. Analysis of oceanic crust formed since that time suggests that the cooling rate of Earth was enhanced in the wake of Pangaea's dispersal.
DS201708-1703
2017
Lepine, I.Geochemistry and geology of the Renard 2 coherent kimberlitic phases, Quebec, Canada - spatial distribution and diamond content.11th. International Kimberlite Conference, PosterCanada, Quebecdeposit - Renard 2
DS201708-1704
2017
Lepine, I.3D geological modeling of the Renard 2 pipe, Quebec, Canada: from exploration to extraction.11th. International Kimberlite Conference, PosterCanada, Quebecdeposit - Renard
DS201707-1346
2017
Lepore, G.O., Bindi, L., Pedrazzi, G., Conticelli, S., Bonazzi, P.Structural and chemical variations in phlogopite from lamproitic rocks of the central Mediterranean region.Lithos, in press available, 69p.Europe, Italylamproite

Abstract: Micas from mafic ultrapotassic rocks with lamproitic affinity from several localities of the Central Mediterranean region were studied through single-crystal X-ray diffraction (SC-XRD), electron microprobe analysis (EMPA) and Secondary Ion Mass Spectrometry (SIMS); Mössbauer Spectroscopy (MöS), when feasible, was also applied to minimise the number of unknown variables and uncertainties. Lamproitic samples analysed cover the most important Central Mediterranean type localities, from Plan d'Albard (Western Alps) to Sisco (Corsica), Montecatini Val di Cecina and Orciatico (Tuscany, Italy) and Torre Alfina (Northern Latium, Italy). The studied crystals show distinctive chemical and structural features; all of them belong to the phlogopite-annite join and crystallise in the 1 M polytype, except for micas from Torre Alfina, where both 1 M and 2 M1 polytypes were found. Studied micas have variable but generally high F and Ti contents, with Mg/(Mg + Fe) ranging from ~ 0.5 to ~ 0.9; 2M1 crystals from Torre Alfina radically differ in chemical composition, showing high contents of Ti and Fe as well as of Al in both tetrahedra and octahedra, leading to distinctive structural distortions, especially in tetrahedral sites. SIMS data indicate that studied micas are generally dehydrogenated with OH contents ranging from ~ 0.2 apfu (atoms per formula unit) for Orciatico and Torre Alfina to ~ 1.4 for Plan d'Albard crystals; this feature is also testified by the length of the c parameter, which decreases with the loss of hydrogen and/or the increase of the F ? OH substitution. Chemical and structural data suggest that the entry of high charge octahedral cations is mainly balanced by an oxy mechanism and, to a lesser extent, by a M3 +,4 +-Tschermak substitution. Our data confirm that Ti preferentially partitions into the M2 site and that different Ti and F contents, as well as different K/Al values, are both dependant upon fH2O and the composition of magma rather than controlled by P and T crystallisation conditions. The obtained data help to discriminate among lamproite-like rocks formed within a complex geodynamic framework but still related to a destructive tectonic margin and evidence different trends for micas from the youngest Torre Alfina (Northern Latium) lamproites, referred to the Apennine orogeny and those of the older lamproites from Orciatico, Montecatini Val di Cecina (Tuscany), Western Alps, and Corsica, the latter referred to the Alpine orogeny. Phlogopite crystals from the older lamproites fall within the compositional and structural field of worldwide phlogopites from both within-plate and subduction-related settings. Phlogopite from the Plio-Pleistocene lamproite-like occurrence in Tuscany and Northern Latium, despite crystals with low Mg# of the Torre Alfina rock plot well within the general field of the other crystals in less evolved samples, follows a different evolution trend similar to that of shoshonites from Tuscany and Northern Latium. On this basis, we argue that the observed differences are inherited by slight differences in the magma compositions that are related with different genetic and evolution pathways.
DS201706-1090
2017
Levin, V., Servali, A., VanTongeren, J., Menke, W., Darbyshire, F.Crust-mantle boundary in eastern North America, from the (oldest) craton to the (youngest) rift.Geological Society of America, SPE 526 pp. 107-132.United Statescraton

Abstract: The North American continent consists of a set of Archean cratons, Proterozoic orogenic belts, and a sequence of Phanerozoic accreted terranes. We present an ~1250-km-long seismological profile that crosses the Superior craton, Grenville Province, and Appalachian domains, with the goal of documenting the thickness, internal properties, and the nature of the lower boundary of the North American crust using uniform procedures for data selection, preparation, and analysis to ensure compatibility of the constraints we derive. Crustal properties show systematic differences between the three major tectonic domains. The Archean Superior Province is characterized by thin crust, sharp Moho, and low values of Vp/Vs ratio. The Proterozoic Grenville Province has some crustal thickness variation, near-uniform values of Vp/Vs, and consistently small values of Moho thickness. Of the three tectonic domains in the region, the Grenville Province has the thickest crust. Vp/Vs ratios are systematically higher than in the Superior Province. Within the Paleozoic Appalachian orogen, all parameters (crustal thickness, Moho thickness, Vp/Vs ratio) vary broadly over distances of 100 km or less, both across the strike and along it. Internal tectonic boundaries of the Appalachians do not appear to have clear signatures in crustal properties. Of the three major tectonic boundaries crossed by our transect, two have clear manifestations in the crustal structure. The Grenville front is associated with a change in crustal thickness and crustal composition (as reflected in Vp/Vs ratios). The Norumbega fault zone is at the apex of the regional thinning of the Appalachian crust. The Appalachian front is not associated with a major change in crustal properties; rather, it coincides with a zone of complex structure resulting from prior tectonic episodes, and thus presents a clear example of tectonic inheritance over successive Wilson cycles.
DS201708-1575
2017
Levin, V., Servali, A., VanTongeren, J., Menke, W., Darbyshire, F.Crust mantle boundary in eastern North America, from the (oldest) craton to the (youngest) rift.Geological Society of London, Chapter 6, pp. 107-132.United States, Canadatectonics

Abstract: The North American continent consists of a set of Archean cratons, Proterozoic orogenic belts, and a Sequence of Phanerozoic accreted terranes. We present an ~1250-km-long seismological profile that crosses the Superior craton, Grenville Province, and Appalachian domains, with the goal of documenting the thickness, internal properties, and the nature of the lower boundary of the North American crust using uniform procedures for data selection, preparation, and analysis to ensure compatibility of the constraints we derive. Crustal properties show systematic differences between the three major tectonic domains. The Archean Superior Province is characterized by thin crust, sharp Moho, and low values of Vp/Vs ratio. The Proterozoic Grenville Province has some crustal thickness variation, near-uniform values of Vp/Vs, and consistently small values of Moho thickness. Of the three tectonic domains in the region, the Grenville Province has the thickest crust. Vp/Vs ratios are systematically higher than in the Superior Province. Within the Paleozoic Appalachian orogen, all parameters (crustal thickness, Moho thickness, Vp/Vs ratio) vary broadly over distances of 100 km or less, both across the strike and along it. Internal tectonic boundaries of the Appalachians do not appear to have clear signatures in crustal properties. Of the three major tectonic boundaries crossed by our transect, two have clear manifestations in the crustal structure. The Grenville front is associated with a change in crustal thickness and crustal composition (as reflected in Vp/Vs ratios). The Norumbega fault zone is at the apex of the regional thinning of the Appalachian crust. The Appalachian front is not associated with a major change in crustal properties; rather, it coincides with a zone of complex structure resulting from prior tectonic episodes, and thus presents a clear example of tectonic inheritance over successive Wilson cycles.
DS201709-2021
2017
Li, J., Xhu, F., Dong, J., Liu, J., LaI, X., Chen, B., Meng, Y.Experimental investigations into the fate of subducted carbonates and origin of super deep diamonds.Goldschmidt Conference, abstract 1p.Mantlepetrology

Abstract: Carbonates are common rock-forming minerals in the Earth’s crust and act as sinks of atmospheric carbon dioxide. Subduction of hydrothermally altered oceanic lithosphere returns carbon to the interior, where more than three quarters of Earth’s carbon is stored. The contribution of subducted carbonates to the Earth's long-term deep carbon cycle is uncertain and has recently emerged as a topic of intense debate [1]. Moreover, mantle-slab interaction has been proposed as a mechanism to produce super-deep diamonds, thus questioning the use of certain mineral inclusions to infer lower-mantle origin [2]. Here we report new data on the chemical stability and reaction kinetics of carbonates in the mantle from multianvil and diamond-anvil-cell experiments. Our results suggest that carbon can be sequestered into deep Earth through reaction freezing and that the index minerals for super-deep diamonds are not reliable indicators for their formation depths.
DS201710-2238
2017
Li, M., Zhong, S.The source location of mantle plumes from 3D spherical models of mantle convection.Earth and Planetary Science Letters, Vol. 478, pp. 47-58.Mantleplumes

Abstract: Mantle plumes are thought to originate from thermal boundary layers such as Earth's core-mantle boundary (CMB), and may cause intraplate volcanism such as large igneous provinces (LIPs) on the Earth's surface. Previous studies showed that the original eruption sites of deep-sourced LIPs for the last 200 Myrs occur mostly above the margins of the seismically-observed large low shear velocity provinces (LLSVPs) in the lowermost mantle. However, the mechanism that leads to the distribution of the LIPs is not clear. The location of the LIPs is largely determined by the source location of mantle plumes, but the question is under what conditions mantle plumes form outside, at the edges, or above the middle of LLSVPs. Here, we perform 3D geodynamic calculations and theoretical analyses to study the plume source location in the lowermost mantle. We find that a factor of five decrease of thermal expansivity and a factor of two increase of thermal diffusivity from the surface to the CMB, which are consistent with mineral physics studies, significantly reduce the number of mantle plumes forming far outside of thermochemical piles (i.e., LLSVPs). An increase of mantle viscosity in the lowermost mantle also reduces number of plumes far outside of piles. In addition, we find that strong plumes preferentially form at/near the edges of piles and are generally hotter than that forming on top of piles, which may explain the observations that most LIPs occur above LLSVP margins. However, some plumes originated at pile edges can later appear above the middle of piles due to lateral movement of the plumes and piles and morphologic changes of the piles. ?65-70% strong plumes are found within 10 degrees from pile edges in our models. Although plate motion exerts significant controls over the large-scale mantle convection in the lower mantle, mantle plume formation at the CMB remains largely controlled by thermal boundary layer instability which makes it difficult to predict geographic locations of most mantle plumes. However, all our models show consistently strong plumes originating from the lowermost mantle beneath Iceland, supporting a deep mantle plume origin of the Iceland volcanism.
DS201710-2239
2017
Li, W-Y., Huang, F., Yu, H-M., Xu, J., Halama, R., Teng, F-Z.Barium isotopic composition of the mantle constrained by carbonatites.Goldschmidt Conference, 1p. AbstractAfrica, Tanzania, east Africa, Canada, Europe, Germany, Greenlandcarbonatite

Abstract: Deep mantle origin and ultra-reducing conditions in podiform chromitite: diamonds, moissanite, and other unusual minerals in podiform chromitites from the Pozanti-Karsanti ophiolite, southern Turkey
DS201710-2240
2017
Lian, D., Yang, J., Dilek, Y., Wu, W., Zhang, Z., Xiong, F., Liu, F., Zhou, W.Deep mantle origin and ultra-reducing conditions in podiform chromitite: diamonds, moissanite, and other unusual minerals in podiform chromitites from the Pozanti-Karsanti ophiolite, southern Turkey.Americam Mineralogist, Vol. 103, 5p.Europe, Turkeymoissanites

Abstract: The Pozanti-Karsanti ophiolite situated in the eastern Tauride belt, southern Turkey, is a well-preserved oceanic lithosphere remnant comprising, in ascending order, mantle peridotite, ultramafic and mafic cumulates, isotropic gabbros, sheeted dikes, and basaltic pillow lavas. Two types of chromitites are observed in the Pozanti-Karsanti ophiolite. One type of chromitites occurs in the cumulate dunites around the Moho, and the other type of chromitites is hosted by the mantle harzburgites below the Moho. The second type of chromitites has massive, nodular, and disseminated textures. We have conducted the mineral separation work on the podiform chromitites hosted by harzburgites. So far, more than 100 grains of microdiamond and moissanite (SiC) have been recovered from the podiform chromitite. The diamonds and moissanite are accompanied by large amounts of rutile. Besides zircon, monazite and sulfide are also very common phases within the separated minerals. The discovery of diamond, moissanite, and the other unusual minerals from podiform chromitite of the Pozanti-Karsanti ophiolite provides new evidences for the common occurrences of these unusual minerals in ophiolitic peridotites and chromitites. This discovery also suggests that deep mantle processes and materials have been involved in the formation of podiform chromitite.
DS201711-2524
2017
Liddell, M.V., Bastow, I., Darbyshire, F., Gilligan, A., Pugh, S.The formation of Laurentia: evidence from shear wave splitting.Earth and Planetary Science Letters, Vol. 479, pp. 170-178.Canada, Nunavut, Baffin Islandgeophysics - seismics

Abstract: The northern Hudson Bay region in Canada comprises several Archean cratonic nuclei, assembled by a number of Paleoproterozoic orogenies including the Trans-Hudson Orogen (THO) and the Rinkian-Nagssugtoqidian Orogen. Recent debate has focused on the extent to which these orogens have modern analogues such as the Himalayan-Karakoram-Tibet Orogen. Further, the structure of the lithospheric mantle beneath the Hudson Strait and southern Baffin Island is potentially indicative of Paleoproterozoic underthrusting of the Superior plate beneath the Churchill collage. Also in question is whether the Laurentian cratonic root is stratified, with a fast, depleted, Archean core underlain by a slower, younger, thermally-accreted layer. Plate-scale process that create structures such as these are expected to manifest as measurable fossil seismic anisotropic fabrics. We investigate these problems via shear wave splitting, and present the most comprehensive study to date of mantle seismic anisotropy in northern Laurentia. Strong evidence is presented for multiple layers of anisotropy beneath Archean zones, consistent with the episodic development model of stratified cratonic keels. We also show that southern Baffin Island is underlain by dipping anisotropic fabric, where underthrusting of the Superior plate beneath the Churchill has previously been interpreted. This provides direct evidence of subduction-related deformation at 1.8 Ga, implying that the THO developed with modern plate-tectonic style interactions.
DS201710-2241
2017
Lineweaver, C.Scientist produce best estimate of Earth's composition.Physics.org, Sept. 18, 2p.Mantlechemical composition

Abstract: Scientists at ANU have produced the best estimate of Earth's elemental composition which will help them understand how the Earth formed 4.6 billion years ago. The Solar System began as a dense blob in a molecular cloud of hydrogen gas and dust that collapsed under its own gravity, forming the early Sun, Earth and other planets. Co-researcher Associate Professor Charley Lineweaver said the Earth's chemical composition was set at that early stage of formation. "The four most abundant elements - iron, oxygen, silicon and magnesium - make up more than 90 per cent of the Earth's mass, but working out exactly what the Earth is made of is tricky," said Dr Lineweaver from the Research School of Earth Sciences and the Research School of Astronomy and Astrophysics at ANU. "Seismological studies of earthquakes inform us about the Earth's core, mantle and crust, but it's hard to convert this information into an elemental composition. "Our deepest drilling has only scratched the surface down to 10 kilometres of our 6,400 kilometre radius planet. Rocks at the surface only come from as deep as the upper mantle." The research is published in the international journal Icarus and is available here. Lead author ANU PhD scholar Haiyang Wang said the team made the most comprehensive estimates of the Earth's composition based on a meta-analysis of previous estimates of the mantle and core, and a new estimate of the core's mass. "Our work focused on getting realistic uncertainties so that our reference model can be used in future comparisons of the Earth with the Sun, or with Mars or with any other body in the Solar System," said Mr Wang from the ANU Research School of Astronomy and Astrophysics. Co-researcher Professor Trevor Ireland from the ANU Research School of Earth Sciences said planetary scientists would find many uses for this new composition record. "This will have far-reaching importance, not only for planetary bodies in our Solar System but also other star systems in the universe," he said.
DS201705-0847
2017
Lithographie Ltd.Diamond: The ultimate gemstone. Chapters listed seperatelylithographie.org, Mineral Monograph no. 19, 160p.GlobalBook - diamond
DS201705-0848
2017
Lithographie Ltd.Literature and Cited works.lithographie.org, No. 19, pp. 138-152.GlobalBook - references
DS201705-0849
2017
Litvin, Y., Kuzyura, A.Fractional ultrabasic basic evolution of upper mantle magmatism: evidence from xenoliths in kimberlites, inclusions in diamonds and experiments.European Geosciences Union General Assembly 2017, Vienna April 23-28, 1p. 4773 AbstractMantleMelting

Abstract: Ultrabasic peridotites and pyroxenites together with basic eclogites are the upper-mantle in situ rocks among xenoliths in kimberlites. Occasionally their diamond-bearing varieties have revealed within the xenoliths. Therewith the compositions of rock-forming minerals demonstrate features characteristic for primary diamond-included minerals of peridotite and eclogite parageneses (the elevated contents of Cr-component in peridotitic garnets and Na-jadeitic component in eclogitic clinopyroxenes). High-pressure experimental study of melting equilibria on the multicomponent peridotie-pyroxenite system olivine Ol - orthopyroxene Opx - clinopyroxene Cpx - garnet Grt showed that Opx disappeared in the peritectic reaction Opx+L?Cpx (Litvin, 1991). As a result, the invariant peritectic equilibrium Ol+Opx+Cpx+Grt+L of the ultrabasic system was found to transform into the univariant cotectic assemblage Ol+Cpx+Grt+L. Further experimental investigation showed that olivine reacts with jadeitic component (Jd) with formation of garnet at higher 4.5 GPa (Gasparik, Litvin, 1997). Study of melting relations in the multicomponent system Ol - Cpx - Jd permits to discover the peritectic point Ol+Omph+Grt+L (where Omph - omphacitic clinopyroxene) at concentration 3-4 wt.% Jd-component in the system. The reactionary loss of Opx and Ol makes it possible to transform the 4-phase garnet lherzolite ultrabasic association into the bimineral eclogite assemblage. The regime of fractional Ol, Cpx and Grt crystallization must be accompanied by increasing content of jadeitic component in residual melts that causes the complete "garnetization of olivine". In the subsequent evolution, the melts would have to fractionate for basic SiO2-saturated compositions responsible for petrogenesis of eclogite varieties marked with accessory corundum Crn, kyanite Ky and coesite Coe. Both the peritectic mechanisms occur in regime of fractional crystallization. The sequence of the upper-mantle fractional ultrabasic-basic magmatic evolution and petrogenesis may be controlled by the following melting relations: from Ol, Opx, L field to cotectic curve Ol, Opx, Cpx, L, peritectic point Ol, Opx, Cpx, Grt, L (loss of Opx), cotectic curve Ol, (Cpx+Jd), Grt, L, peritectic point Ol, (Cpx?Omph), Grt, L (loss of Ol), divariant field Omph,Grt,L, cotectic curve Ky, Omph, Grt, L, eutectic point Ky,Coe,Omph, Grt,L, subsolidus assemblage Ky,Coe,Omph, Grt. The fractional ultrabasic-basic evolution of the upper-mantle silicate-carbonate-carbon melts-solutions, which are responsible for genesis of diamond-and-inclusions associations and diamond-bearing peridotites and eclogites, follows the similar physico-chemical mechanisms (Litvin et al., 2016). This is illustrated by fractional syngenesis diagram for diamonds and associated minerals which construction is based on evidence from high pressure experiments. References Gasparik T., Litvin Yu.A (1997). Stability of Na2Mg2Si2O7 and melting relations on the forsterite - jadeite join at pressures up to 22 GPa.
DS201705-0850
2017
Litvin, Y., Spivak, A.Ultrabasic basic change over primary inclusions in lower mantle diamonds: mineralogical and experimental evidence for crucial role of stishovite paradox.European Geosciences Union General Assembly 2017, Vienna April 23-28, 1p. 4785 AbstractMantleMelting

Abstract: Melting relations of the lower-mantle magmatic system MgO - FeO - CaO - SiO2 are characterized by peritectic reaction of bridgmanite (Mg,Fe)SiO3 and melt with formation of Fe-rich phases of periclase-wustite solid solutions (MgO•FeO)ss and stishovite SiO2. The reaction proceeds also in melts-solutions of lower-mantle diamond-parental system MgO - FeO - CaO - SiO2 - (Mg-Fe-Ca-Na-carbonate) - C. Xenoliths of lower mantle rocks were never found among the deep mantle derived materials. Estimation of lower-mantle mineralogy as ferropericlase+ bridgmanite+ Ca-perovskite association is inferred from high-pressure subsolidus experiments with ultrabasic pyrolite composition (Akaogi, 2007). The paradoxical in situ paragenesis of stishovite and ferropericlase as primary inclusions in lower-mantle diamonds (Kaminsky, 2012) takes its explanation from the bridgmanite peritectic reaction (effect of "stishovite paradox") (Litvin et al., 2014). Based on the data for inclusions, physico-chemical study on syngenesis of diamonds and primary inclusions has experimentally revealed the ferropericlase-bridgmanite-Ca-perovskite-stishovite-magnesiowustite-(Mg-Fe-Ca-Na-carbonate)-carbon compositions of the lower-mantle diamond-forming system .(Litvin et al., 2016). The generalized diagram of diamong-forming media characterizes the variable compositions of growths melts for diamonds and paragenetic phases and their genetic relationships with lower mantle matter, and it is the reason for genetic classifying primary inclusions. Fractional ultrabasic-basic evolution and continuous paragenetic transition from ultrabasic bridgmanite-ferropericlase to basic stishovite-magnesiowustite assemblages in the of lower-mantle diamond-parental melts-solutions are providing by the physico-chemical mechanism of stishovite paradox. References Akaogi M. (2007). Phase transformations of minerals in the transition zone and upper part of the lower mantle.
DS201706-1091
2017
Litvin, Y.A., Spivak, A.V., Simonova, D.A., Dubrovinsky, L.S.The stishovite paradox in the evolution of lower mantle magmas and diamond forming melts ( experiment at 24 and 26 Gpa)Doklady Earth Sciences, Vol. 473, pp. 444-448.Technologydiamond - ultradeep

Abstract: Experimental studies of phase relations in the oxide-silicate system MgO-FeO-SiO2 at 24 GPa show that the peritectic reaction of bridgmanite controls the formation of stishovite as a primary in situ mineral of the lower mantle and as an effect of the stishovite paradox. The stishovite paradox is registered in the diamond-forming system MgO-FeO-SiO2-(Mg-Fe-Ca-Na carbonate)-carbon in experiments at 26 GPa as well. The physicochemical mechanisms of the ultrabasic-basic evolution of deep magmas and diamondforming media, as well as their role in the origin of the lower mantle minerals and genesis of ultradeep diamonds, are studied.
DS201706-1092
2017
Litvin, Yu.A., Bovkun, A.V., Androsova, N.A., Garanin, V.K.The system ilmenite-carbonatite-carbon in the origin of diamond: correlation between the titanium content and the diamond potential of kimberlite.Doklady Earth Sciences, Vol. 473, 1, pp. 286-290.Mantlecarbonatite

Abstract: Experimental studies of melting relations in the system ilmenite-K-Na-Mg-Fe-Ca carbonatite-carbon at 8 GPa and 1600°C provide evidence for the effect of liquid immiscibility between ilmenite and carbonatite melts. It is shown that the solubility of ilmenite in carbonatitic melts is negligible and does not depend on its concentration in experimental samples within 25-75 wt %. However, carbonatite-carbon melts are characterized by a high diamond-forming efficiency. This means that the correlation between the concentration of TiO2 and diamond content is problematic for mantle chambers and requires further, more complex, experimental studies.
DS201708-1705
2017
Liu, F.Ocean-continent transition to supersubduction zone origin of the western Yarlung Zangbo ophiolites in southwest Tibet, China: constraints from the petrology, mineralogy and geochemistry of the peridotites.11th. International Kimberlite Conference, PosterChina, Tibetsubduction

Abstract: The ophiolites that crop out discontinuously along the ?2000 km Yarlung Zangbo Suture zone (YZSZ) between the Nanga Parbat and Namche Barwa syntaxes in southern Tibet represent the remnants of Neotethyan oceanic lithosphere (Fig. 1a). We have investigated the internal structure and the geochemical makeup of mafic-ultramafic rock assemblages that are exposed in the westernmost segment of the YZSZ where the suture zone architecture displays two distinct sub-belts of ophiolitic and mélange units separated by a continental Zhongba terrane (Fig. 1b). These two sub-belts include the Daba – Xiugugabu in the south (Southern sub-belt, SSB) and the Dajiweng – Saga in the north (Northern sub-belt, NSB). We present new structural, geochemical, geochronological data from upper mantle peridotites and mafic dike intrusions occurring in these two sub-belts and discuss their tectonomagmatic origin. In-situ analysis of zircon grains obtained from mafic dikes within the Baer, Cuobuzha and Jianabeng massifs in the NSB, and within the Dongbo, Purang, Xiugugabu, Zhaga and Zhongba in the SSB have yielded crystallization ages ranging between130 and 122 Ma. Dike rocks in both sub-belts show N-MORB REE patterns and negative Nb, Ta and Ti anomalies, reminiscent of those documented from SSZ ophiolites. Harzburgitic host rocks of the mafic dike intrusions mainly display geochemical compositions of abyssal peridotites (Fig. 2), with the exception of the Dajiweng harzburgites, which show the geochemical signatures of forearc peridotites (Lian et al., 2016). Extrusive rocks that are spatially associated with these peridotite massifs in both sub-belts also have varying compositional and geochemical features. Tithonian to Valanginian (150 – 135 Ma) basaltic rocks in the Dongbo massif have OIB-like geochemistry and 138 Ma basaltic lavas in the Purang massif have EMORB-like geochemistry (Liu et al., 2015). Tuffaceous rocks in the Dajiweng massif are 140 Ma in age and show OIB-like geochemistry. We interpret these age and geochemical data to reflect a rifted continental margin origin of the extrusive rock units in both sub-belts. These data and structural observations show that the western Yarluang Zangbo ophiolites represent fragments of an Ocean-Continent Transition (OCT) peridotites altered by fluids in an initial supersubduction setting. We infer that mafic-ultramafic rock assemblages exposed in the SSB and NSB initially formed in an ocean – continent transition zone (OCTZ) during the late Jurassic, and that they were subsequently emplaced in the forearc setting of an intraoceanic subduction zone within a Neotethyan seaway during 130 to 122 Ma. The NSB and SSB are hence part of a single, S-directed nappe sheet derived from a Neotethyan seaway located north of the Zhongba terrane.
DS201708-1706
2017
Liu, J.Age and evolution of the lithospheric mantle beneath southern Baffin Island, Nunavut, Canada.11th. International Kimberlite Conference, PosterCanada, Nunavut, Baffin Islandgeochronology
DS201704-0635
2017
Liu, P., Massonne, H-J., Zhang, J., Wu, Y., Jin, Z.Intergranular coesite inclusions in dolomite from the Dabie Shan: constraints on the preservation of coesite in UHP rocks.Terra Nova, in press availableChinaCoesite

Abstract: Intergranular coesite is extremely rare in, and bears crucial information on the formation and preservation of, ultrahigh-pressure (UHP) rocks. Here, we report the first occurrence of intergranular coesite in a metasedimentary rock, which occurs in the Ganjialing area in the Dabie Shan, east-central China, and contains abundant coesite inclusions in both garnet and dolomite. We investigated the content of structural water in these minerals with Fourier transform infrared spectroscopy. Our new results undermine the ubiquity of the “pressure-vessel” model and highlight the role of reaction kinetics in preserving coesite due to the availability of water in UHP rocks.
DS201702-0225
2017
Liu, Y., Hou, Z.A synthesis of mineralization styles with an integrated genetic model of carbonatite syenite hosted REE deposits in the Cenozoic Mianning Dechang REE Metalogenetic belt, the eastern Tibetan Plateau, southwestern China.Journal of Asian Earth Sciences, in press available, 134p.China, TibetCarbonatite

Abstract: The Cenozoic Mianning-Dechang (MD) rare earth element (REE) belt in eastern Tibet is an important source of light REE in southwest China. The belt is 270 km long and 15 km wide. The total REE resources are >3 Mt of light rare earth oxides (REO), including 3.17 Mt of REO at Maoniuping (average grade = 2.95 wt.%), 81,556 t at Dalucao (average grade = 5.21 wt.%), 0.1 Mt at Muluozhai (average grade = 3.97 wt.%), and 5764 t of REO at Lizhuang (average grade = 2.38 wt.%). Recent results from detailed geological surveys, and studies of petrographic features, ore-forming ages, ore forming conditions, and wallrock alteration are synthesized in this paper. REE mineralization within this belt is associated with carbonatite-syenite complexes, with syenites occurring as stocks intruded by carbonatitic sills or dikes. The mineralization is present as complex vein systems that contain veinlet, stringer, stockwork, and brecciated pipe type mineralization. Carbonatites in these carbonatite-related REE deposits (CARDs) are extremely rich in light REEs, Sr (>5000 ppm), and Ba (>1000 ppm), and have low Sr/Ba and high Ba/Th ratios, and radiogenic Sr-Nd isotopic compositions. These fertile magmas, which may lead to the formation of REE deposits, were generated by the partial melting of sub-continental lithospheric mantle (SCLM) that was metasomatized by REE- and CO2-rich fluids derived from subducted marine sediments. We suggest that this refertilization occurred along cratonic margins and, in particular, at a convergent margin where small-volume carbonatitic melts ascended along trans-lithospheric faults and transported REEs into the overlying crust, leading to the formation of the CARDs. The formation of fertile carbonatites requires a thick lithosphere and/or high pressures (>25 kbar), a metasomatized and enriched mantle source, and favorable pathways for magma to ascend into the overlying crust where REE-rich fluids exsolve from cooling magma. The optimal combination of these three factors only occurs along the margins of a craton with a continental root, rather than in modern subduction zones where the lithosphere is relatively thin. U-Pb zircon dating indicates that the Maoniuping, Lizhuang, and Muluozhai alkali igneous complexes in the northern part of the belt formed at 27-22 Ma, whereas the Dalucao complex in the southern part of the belt formed at 12-11 Ma. Biotite and arfvedsonite in Lizhuang and Maoniuping REE deposit have 40Ar/39Ar ages of 30.8 ± 0.4 Ma (MSWD = 0.98) and 27.6 ± 2.0 Ma (MSWD = 0.06), respectively. Biotitaion alteration in syenite and fenitization caused by the relatively amount of carbonatite on syenite and host rocks is the main alteration along the whole belt. Initial Sr (0.7059-0.7079), 143Nd/144Nd (0.5123-0.5127), and 207Pb/204Pb (15.601-15.628) and 208Pb/204Pb (38.422-38.604) isotopic compositions of fluorite, barite, celestite, and calcite in the MD belt are similar to those of the associated syenite and carbonatite. Given the relatively high contents of Cl, F, SO42-, and CO2 in the rocks of the complexes, it is likely that the REEs were transported by these ligands within hydrothermal fluids, and the presence of bastnäsite indicates that the REEs were precipitated as fluorocarbonates. Petrographic, fluid inclusion, and field studies of the ores indicate that bastnäsite and other REE minerals formed during the final stages (<300°C) of the evolution of magmatic-hydrothermal systems in the belt. The mineralization formed from magmatic and meteoric fluids containing CO2 derived from the decarbonation of carbonatite, as indicated by C-O isotopic values of hydrothermal calcite and bastnäsite (?13C= -4.8 to -8.7 and ?18O = 5.8 to 12.5 ‰) and O-H isotopic values of quartz (330°C) and arfvedsonite (260°C), which correspond to fluid isotope compositions of ?18O = 0.3 to 9.8‰ and ?D = -70.0 to -152.8‰ in the belt. This study indicates that formation the largest REE deposits are related to voluminous carbonatite-syenite complexes, compositionally similar ore-forming fluids, extensive alteration, multiple stages of REE mineralization, and tectonic setting.
DS201704-0636
2017
Liu, Y., Hou, Z.A synthesis of minerlization styles with an integrated genetic model of carbonatite syenite hosted REE deposits in the Cenozoic Mianning Dechang REE metallogenic belt, the eastern Tibetan Plateau, southwestern China.Journal of Asian Earth Sciences, Vol. 137, pp. 35-79.China, TibetCarbonatite

Abstract: he Cenozoic Mianning-Dechang (MD) rare earth element (REE) belt in eastern Tibet is an important source of light REE in southwest China. The belt is 270 km long and 15 km wide. The total REE resources are >3 Mt of light rare earth oxides (REO), including 3.17 Mt of REO at Maoniuping (average grade = 2.95 wt.%), 81,556 t at Dalucao (average grade = 5.21 wt.%), 0.1 Mt at Muluozhai (average grade = 3.97 wt.%), and 5764 t of REO at Lizhuang (average grade = 2.38 wt.%). Recent results from detailed geological surveys, and studies of petrographic features, ore-forming ages, ore forming conditions, and wallrock alteration are synthesized in this paper. REE mineralization within this belt is associated with carbonatite-syenite complexes, with syenites occurring as stocks intruded by carbonatitic sills or dikes. The mineralization is present as complex vein systems that contain veinlet, stringer, stockwork, and brecciated pipe type mineralization. Carbonatites in these carbonatite-related REE deposits (CARDs) are extremely rich in light REEs, Sr (>5000 ppm), and Ba (>1000 ppm), and have low Sr/Ba and high Ba/Th ratios, and radiogenic Sr-Nd isotopic compositions. These fertile magmas, which may lead to the formation of REE deposits, were generated by the partial melting of sub-continental lithospheric mantle (SCLM) that was metasomatized by REE- and CO2-rich fluids derived from subducted marine sediments. We suggest that this refertilization occurred along cratonic margins and, in particular, at a convergent margin where small-volume carbonatitic melts ascended along trans-lithospheric faults and transported REEs into the overlying crust, leading to the formation of the CARDs. The formation of fertile carbonatites requires a thick lithosphere and/or high pressures (>25 kbar), a metasomatized and enriched mantle source, and favorable pathways for magma to ascend into the overlying crust where REE-rich fluids exsolve from cooling magma. The optimal combination of these three factors only occurs along the margins of a craton with a continental root, rather than in modern subduction zones where the lithosphere is relatively thin.
DS201712-2701
2017
Liu, Y-L., Ling, M-X., Williams, I.S., Yang, X-Y., Yan Wang, C., Sun, W.The formation of the giant Bayan Obo REE-Nb-Fe deposit, north China, Mesoproterozoic carbonatite and overprinted Palaeozoic dolomitization.Ore Geology Reviews, in press available, 47p.Chinadeposit - Bayan Obo

Abstract: The Bayan Obo ore deposit in Inner Mongolia, North China, the largest-known rare earth element (REE) deposit in the world, is closely associated with carbonatite dykes. Scarce zircon grains, with a wide range of ages and diverse origins, have been extracted from the Wu dyke, a REE-enriched calcitic carbonatite dyke 2?km from the East Ore Body of the Bayan Obo deposit. Three zircon populations were identified based on ages and trace element compositions: 1) Captured zircons with Paleoproterozoic and Archean ages. These zircons have REE patterns and moderate Th/U ratios similar to zircon with silicate inclusions from basement igneous rocks, which have been recognized as contaminants from wall rocks. 2) Carbonatite magmatic zircons with Mesoproterozoic ages. These zircons have high to extremely high Th/U ratios (13-1600), a characteristic signature of the Bayan Obo deposit. Two zircon grains yielded concordant 206Pb/238U ages (1.27?±?0.11?Ga???1.42?±?0.18?Ga) and 208Pb/232Th age (1.26?±?0.20?Ga) with calcite inclusions, indicating that the Wu dyke was emplaced at ca. 1.34?Ga, which coincides with a worldwide generation of Mesoproterozoic kimberlites, lamprophyres, carbonatites, and anorogenic magmatism. 3) Hydrothermal zircons with Caledonian and Triassic ages. The Caledonian zircon has 206Pb/238U age of 381?±?4?Ma and 208Pb/232Th age of 367?±?14?Ma with dolomite inclusion. These evidences are consistent with multiple stages of mineralization, Mesoproterozoic calcite carbonatite magmatism interacted by protracted fluxing of subduction-released Caledonian fluids during the closure of the Palaeo-Asian Ocean, coupled with interaction with the mantle wedge and metasomatism of overlying sedimentary carbonate.
DS201701-0020
2016
Liu, Z., Du, W., Shinmei, T., Greaux, S., Zhou, C., Arimoto, T., Kunimoto, T., Irifune, T.Garnets in the majorite pyrope system: symmetry, lattice microstain, and order-disorder of cations.Physics and Chemistry of Minerals, in press available 9p.TechnologyGarnet morphology

Abstract: We present a systematic experimental study on the phase transition, lattice microstrain, and order-disorder of cations for garnets in the majorite-pyrope system. Polycrystalline gem-quality garnets were synthesized at high pressure and high temperature using a Kawai-type multi-anvil apparatus. A phase transition from a cubic to tetragonal structure is clearly observed for garnets with the majorite content of more than 74 mol % through X-ray diffraction (XRD) and Raman scattering studies. Microstrain of garnets, evaluated with the Williamson-Hall plot on XRD profiles, shows a nonlinear dependence of the garnet compositions. The variation of the XRD peak broadening suggests the lattice microstrain of these garnets may be associated with the local structural heterogeneities due to the substitution of different cations via the coupled substitution (Mg2+ + Si4+ = 2Al3+) in the garnet structure. The width variation of Raman scattering peaks indicates that cation disorder occurs in the garnet structure for intermediate compositions. It is found that intermediate garnets and end-members have a minimum of microstrain, while those between end-members and intermediate compositions possess a larger microstrain.
DS201708-1707
2017
Lobatiamang, S.Geology of the KX36 kimberlite, central Botswana.11th. International Kimberlite Conference, PosterAfrica, Botswanadeposit - KX36
DS201709-2022
2017
Logvinova, A.M., Wirth, R., Sobolev, N.V.Hydrous silicates within black cloudy zone in diamonds.Goldschmidt Conference, abstract 1p.Canada, Northwest Territoriesdeposit - Diavik

Abstract: Is there the existence of a water-rich zone in the mantle, currently one of the most discussed problem in mantle petrology? There are recent studies of low-water content in nominally anhydrous minerals in diamonds [1] and the chemistry of exceptionally rare phlogopite inclusions coexisting with peridotitic and eclogitic minerals in kimberlite-hosted diamonds [2]. Previous studies have shown that some rapidly formed diamonds reflect the composition of the environment in which they formed [3]. The minerals trapped during nucleation stage remain shielded from any changing conditions during further diamond growth or later mantle metasomatism. Thus, the analysis of diamond microinclusions is a major tool for the direct study of mantle high-density fluids (HDFs) from which the diamonds have precipitated [4]. Using transmission electron microscopy (TEM) techniques, we have investigated hydrous silicates inside nanometerscale, polyphased unclusions, especially in dark cloudy alluvial and kimberlite diamonds. Clinohumite, phlogopite, and phengite were detected. Hydrous silicate phases are accompanied by Ba-Sr-Ca -Fe-Mg carbonates, in addition to sulfides, oxides (magnetite, rutile, ilmenite), F-apatite, KCl, graphite, and fluid bubbles. A contrast occurs between clinohumite associated with phlogopite, F-apatite and highMg carbonates, but phengite, accompanied by a Al, Kbearing, unidentified silicate. These inclusions reflect the composition of fluid from which the host diamond crystallized. The mica composition, in most cases, has excess Si, similar to the high-silica mica identified within diamond microinclusions from Diavik [5]. The fluid-bearing carbonatitic-silicic diamonds grew in water-rich environments with extremely high K-activity, compared to most diamonds, which grew only within limited zones in the Earth’s mantle.
DS201707-1347
2016
Lorenz, V., Suhr, P., Suhr, S.Phreatomagmatic maar-diatreme volcanoes and their incremental growth: a model.Geological Society of London, Special Publication: Monogenetic volcanism, No. 446, pp. 29-59.Technologydiatremes

Abstract: We report here a growth model for phreatomagmatic maar-diatreme volcanoes with respect to the number of eruptions documented in the tephra beds of maar tephra rings and the upper bedded diatreme facies. We show that the number of tephra beds in large diatremes is larger than that in maar tephra rings. Base surges that lack sufficient momentum to scale high maar crater walls deposit their tephra only inside the crater. Thus the total number of eruptions at large maar-diatreme volcanoes will be larger than the number recorded in maar tephra rings. As many maar-diatreme volcanoes erupt dominantly accidental clasts, an incremental mathematical model was applied to study the growth of diatremes. The model is based only on the ejection of distinct amounts of accidental clasts per unit eruption and the chosen number of eruptions is assumed to be identical. The incremental growth of cone-shaped diatremes follows cube-root functions with respect to diameter and depth and slows down with ongoing eruptions. In nature, small and large maar-diatreme volcanoes are formed and filled syn-eruptively, mostly by tephra, depending on the duration and quantity of magma involved in phreatomagmatic eruptions. In our opinion, this mathematical model is the only current method able to model the growth of diatremes.
DS201709-2023
2017
Loudin, L.C.Photoluminescence mapping of optical defects in HPHT synthetic diamond.Gems & Gemology, Vol. 53, 2, summer, pp. 168-179.Technologyluminesence

Abstract: Photoluminescence (PL) mapping provides a means to identify the distribution of optical centers in diamond. To demonstrate the impact of this method on the field of gemology and the study of diamonds, photoluminescence maps were acquired from a laboratory-irradiated brownish orange HPHT synthetic diamond of mixed diamond type. Acquisition time for each PL map was less than four minutes. Analysis of the maps confirmed that optical centers are incorporated in diamond growth sectors, such as {111} octahedral, {100} cubic, {110} dodecahedral, and {113} trapezohedral. The remarkable correlation between optical defects and growth sectors in the sample demonstrates that high-speed photoluminescence mapping is ideal for rapidly determining the distribution of optical defects resulting from both diamond growth and treatments. We anticipate that this technique will allow gemological labs to continue to identify increasingly sophisticated synthetic diamonds and color treatments, helping to ensure consumer confidence in the diamond industry.
DS201706-1093
2017
Louro, V., Cawood, P., Mantovani, M., Biondo Ribeiro, V.Tectonic insights of the southwest Amazon craton from geophysical, geochemical and mineralogical dat a of Figueira Branca mafic-ultramafic suite, Brazil.Tectonophysics, Vol. 708, pp. 96-107.South America, Brazilcraton - Amazon

Abstract: The Figueira Branca Suite is a layered mafic-ultramafic complex in the Jauru Terrane, southwest Amazon Craton. New lithological, geochemical, gamma-ray and potential field data, integrated with geological, isotope and paleomagnetic data are used to characterize this pulse of Mesoproterozoic extension-related magmatism. The Figueira Branca Suite formed through juvenile magma emplacement into the crust at 1425 Ma, coeval with the later stages of the Santa Helena Orogen. Gabbros and peridotite-gabbros display increasing enrichment of LREE, interpreted as evidence of progressive fractionation of the magma. Magnetic and gamma-ray data delimit the extent of magmatism within the suite to four bodies to the north of Indiavaí city. Modelling gravity and magnetic field data indicate that the anomalous sources are close to the surface or outcropping. These intrusions trend northwest over 8 km, with significant remanent magnetization that is consistent with published direction obtained through paleomagnetic data. The emplacement, mineralogy and geochemical signature point towards a back-arc extension tectonic framework in the later stages of the Santa Helena Orogen.
DS201706-1094
2017
Lu, J-G, Xiong, Q., Griffin, W.L., Zheng, J-P., Huang, J-X., O'Reilly, S.Y., Satsuskawa, T., Pearson, N.J.Uplift of the southeastern Australian lithosphere: thermal tectonic evolution of garnet pyroxenite xenoliths from western Victoria.Geological Society of America, SPE 526 pp. 27-48.Australiageothermometry

Abstract: Detailed petrography, microstructure, and geochemistry of garnet pyroxenite xenoliths in Holocene basanite tuffs from maars at Lakes Bullenmerri and Gnotuk (western Victoria, southeastern Australia) have been used to track their igneous and metamorphic history, enabling the reconstruction of the thermal-tectonic evolution of the lithospheric mantle. The exsolution of orthopyroxene and garnet and rare spinel, plagioclase, and ilmenite from complex clinopyroxene megacrysts suggests that the xenoliths originally were clinopyroxene-dominant cumulates associated with minor garnet, orthopyroxene, or spinel. The compositions of exsolved phases and their host clinopyroxene were reintegrated using measured modal proportions to show that the primary clinopyroxene was enriched in Al2O3 (5.53-13.63 wt%) and crystallized at ~1300-1500 °C and 16-30 kbar. These cumulates then underwent extensive exsolution, recrystallization, and reaction during cooling, and finally equilibrated at ~950-1100 °C and 12-18 kbar before entrainment in the basanites. Rare earth element (REE) thermobarometry of garnets and coexisting clinopyroxenes preserves evidence of an intermediate stage (1032 °C and 21 kbar). These results imply that the protoliths of the garnet pyroxenite formed at a range of depths from ~50 to 100 km, and then during or shortly after cooling, they were tectonically emplaced to higher levels (~40-60 km; i.e., uplifted by at least 10-20 km) along the prevailing geotherm. This uplift may have been connected with lithosphere-scale faulting during the Paleozoic orogeny, or during Mesozoic-Cenozoic rifting of eastern Australia.
DS201708-1576
2017
Lu, J-G., Xiong, Q., Griffin, W.L., Zheng, J-P., Huang, J-X., O'Reilly, S.Y., Satsukawa, T., Pearson, N.J.Uplift of southeastern Australian lithosphere: thermal tectonic evolution of garnet pyroxenite xenoliths from western Victoria.Geological Society of London, Chapter 2, pp. 27-48.Australia, Victoriaxenoliths

Abstract: Detailed petrography, microstructure, and geochemistry of garnet pyroxenite xenoliths in Holocene basanite tuffs from maars at Lakes Bullenmerri and Gnotuk (western Victoria, southeastern Australia) have been used to track their igneous and metamorphic history, enabling the reconstruction of the thermal-tectonic evolution of the lithospheric mantle. The exsolution of orthopyroxene and garnet and rare spinel, plagioclase, and ilmenite from complex clinopyroxene megacrysts suggests that the xenoliths originally were clinopyroxene-dominant cumulates associated with minor garnet, orthopyroxene, or spinel. The compositions of exsolved phases and their host clinopyroxene were reintegrated using measured modal proportions to show that the primary clinopyroxene was enriched in Al2O3 (5.53–13.63 wt%) and crystallized at ~1300–1500 °C and 16–30 kbar. These cumulates then underwent extensive exsolution, recrystallization, and reaction during cooling, and finally equilibrated at ~950–1100 °C and 12–18 kba
DS201704-0637
2017
Lucas, A., Bhatt, N., Singhania, M., Sachdeva, K., Hsu, T., Padua, P.Jaipur India: the global gem and jewelery power of the pink city. Emerald, Tanzanite Gems & Gemology, Vol. 52, 4, pp. 332-367.IndiaGemstones - emerald, tanzanite

Abstract: In 2015, a field team from GIA visited the Indian city of Jaipur to capture the full scope of its gem and jewelry industry: colored stone cutting, wholesale trading, jewelry design, manufacturing, and retail. The authors documented the current state of the industry from a manufacturing as well as a business perspective. The results substantiated many of the team's prior assessments but also brought to light recent developments with far-reaching effects. The impact of vertical integration, consolidation, globalization, and jewelry television retail far exceeded expectations. Once known as a colored stone manufacturing center, Jaipur has rapidly climbed the value chain into jewelry manufacturing and retail by successfully incorporating experience and tradition with technology and innovation.
DS201705-0851
2017
Macdonald, R., Baginski, B., Zozulya, D.Differing responses of zircon, chevkinite - (Ce), monazite-(Ce) and fergusonite-(Y) to hydrothermal alteration: Evidence from the Keivy alkaline province, Kola Peninsula.Mineralogy and Petrology, in press available 22p.Russia, Kola PeninsulaAlkaline rocks

Abstract: A quartzolite from the Rova occurrence, Keivy alkali granite province, Kola Peninsula, Russia, is used to examine the differing responses of certain rare-metal minerals during interaction with hydrothermal fluids. The minerals are two silicates [chevkinite-(Ce) and zircon], a phosphate [monazite-(Ce)] and an oxide [fergusonite-(Y)]. Textural evidence is taken to show that the dominant alteration mechanism was interface-coupled dissolution-reprecipitation. Zircon was the most pervasively altered, possibly by broadening of cleavage planes or fractures; the other minerals were altered mainly on their rims and along cracks. The importance of cracks in promoting fluid access is stressed. The compositional effects of the alteration of each phase are documented. The hydrothermal fluids carried few ligands capable of transporting significant amounts of rare-earth elements (REE), high field strength elements (HFSE) and actinides; alteration is inferred to have been promoted by mildly alkaline, Ca-bearing fluids. Expansion cracks emanating from fergusonite-(Y) are filled with unidentified material containing up to 35 wt% UO2 and 25 wt% REE2O3, indicating late-stage, short-distance mobility of these elements. Electron microprobe chemical dating of monazite yielded an age of 1665 ± 22 Ma, much younger than the formation age of the Keivy province (2.65-2.67 Ga) but comparable to that of the Svecofennian metamorphic event which affected the area (1.9-1.7 Ga) or during fluid-thermal activation of the region during rapakivi granite magmatism (1.66-1.56 Ga). Dates for altered monazite range from 2592 ± 244 Ma to 773 ± 88 Ma and reflect disturbance of the U-Th-Pb system during alteration.
DS201710-2242
2017
MacDougall, J.G., Jadamec, M.A., Fischer, K.M.The zone of influence of the subducting slab in the asthenospheric mantle.Journal of Geophysical Research: Solid Earth, Vol. 122, 8, pp. 6599-6624.Mantlesubduction

Abstract: Due to the multidisciplinary nature of combined geodynamics and shear wave splitting studies, there is still much to be understood in terms of isolating the contributions from mantle dynamics to the shear wave splitting signal, even in a two-dimensional (2-D) mantle flow framework. This paper investigates the viscous flow, lattice preferred orientation (LPO) development, and predicted shear wave splitting for a suite of buoyancy-driven subduction models using a non-linear rheology to shed light on the nature of the slab-driven asthenospheric flow and plate-mantle coupling. The slab-driven zone of influence in the mantle, LPO fabric, and resulting synthetic splitting are sensitive to slab strength and slab initial slab dip. The non-linear viscosity formulations leads to dynamic reductions in asthenospheric viscosity extending over 600 km into the mantle wedge and over 300 km behind the trench, with peak flow velocities occurring in models with a weaker slab and moderate slab dip. The olivine LPO fabric in the asthenosphere generally increases in alignment strength with increased proximity to the slab but can be transient and spatially variable on small length scales. The results suggest that LPO formed during initial subduction may persist into the steady state subduction regime. Vertical flow fields in the asthenosphere can produce shear wave splitting variations with back azimuth that deviate from the predictions of uniform trench-normal anisotropy, a result that bears on the interpretation of complexity in shear wave splitting observed in real subduction zones. Furthermore, the models demonstrate the corner flow paradigm should not be equated with a 2-D subduction framework.
DS201712-2702
2017
Mackintosh, V., Kohn, B., Gleadow, A., Tian, Y.Phanerozoic morphotectonic evolution of the Zimbabwean craton: unexpected outcomes from a multiple low temperature thermochronology study.Tectonics, Vol. 36, 10, in press availableAfrica, Zimbabwecraton, geothermometry

Abstract: The fragmentary Phanerozoic geological record of the anomalously elevated Zimbabwe Craton makes reconstructing its history difficult using conventional field methods. Here we constrain the cryptic Phanerozoic evolution of the Zimbabwe Craton using a spatially extensive apatite (U-Th-Sm)/He (AHe), apatite fission track (AFT), and zircon (U-Th)/He (ZHe) data set. Joint thermal history modeling reveals that the region experienced two cooling episodes inferred to be the denudational response to surface uplift. The first and most significant protracted denudation period was triggered by stress transmission from the adjacent ~750-500 Ma Pan-African orogenesis during the amalgamation of Gondwana. The spatial extent of this rejuvenation signature, encompassing the current broad topographic high, could indicate the possible longevity of an ancient topographic feature. The ZHe data reveal a second, minor denudation phase which began in the Paleogene and removed a kilometer-scale Karoo cover from the craton. Within our data set, the majority of ZHe ages are younger than their corresponding AHe and AFT ages, even at relatively low eU. This unexpectedly recurrent age “inversion” suggests that in certain environments, moderately, as well as extremely, damaged zircons have the potential to act as ultra-low-temperature thermochronometers. Thermal history modeling results reveal that the zircon radiation damage accumulation and annealing model (ZRDAAM) frequently overpredicts the ZHe age. However, the opposite is true for extremely damaged zircons where the ZHe and AHe data are also seemingly incompatible. This suggests that modification of the ZRDAAM may be required for moderate to extreme damage levels.
DS201703-0425
2016
Macnae, J.Airborne unmanned excluding photography. RPA geophysics .Society of Exploration Geophysics, Dallas annual meeting, RMIT University 27ppt.TechnologyGeophysics
DS201705-0852
2016
Macnae, J.DO-27 and DO-18 (formerly Tli Kwi Cho complex when they were believed to be part of the same kimberlite complex).SEG Annual Meeting Dallas, 24 ppt.Canada, Northwest TerritoriesDeposit - Tli Kwi Cho
DS201709-2024
2016
Madowe, A.Design and implentation of steeper slope angles on a kimberlite open pit diamond operation - a practical approach.South African Institute of Mining and Metallurgy, Vol. 116, 8, pp. 723-731.Africa, Lesothodeposit - Letseng

Abstract: The steepening of slope angles on an open pit mining operation has a material impact on improving the economics of mining. Steepening of slope angles can also increase the risk of slope failure. Slope failures are inherently costly events, because they can be catastrophic, resulting in multiple fatalities, equipment damage, and temporary or permanent closure of a mine. The steepening of the basalt slope angles at Letseng Diamond Mine followed operational improvements that were introduced through improved blasting practices and geotechnical controls. The steeper slope design resulted in a 6 Mt/a reduction in the peak waste mining compared with the previous mine plan coupled with an increase in the net present value and life of mine. This paper is an outline of the steps that were taken at Letseng to increase slope angles in waste and the resulting improvements to the mine plan.
DS201704-0638
2017
Maeda, F., Ohtani, E., Kamada, S., Sakamaki, T., Hirao, N., Ohishi, Y.Diamond formation in the deep lower mantle: a high pressure reaction of MgCO3 and SiO2.Nature Scientific reports, Jan. 13, 7p. PdfMantleDiamond, genesis

Abstract: Diamond is an evidence for carbon existing in the deep Earth. Some diamonds are considered to have originated at various depth ranges from the mantle transition zone to the lower mantle. These diamonds are expected to carry significant information about the deep Earth. Here, we determined the phase relations in the MgCO3-SiO2 system up to 152?GPa and 3,100?K using a double sided laser-heated diamond anvil cell combined with in situ synchrotron X-ray diffraction. MgCO3 transforms from magnesite to the high-pressure polymorph of MgCO3, phase II, above 80?GPa. A reaction between MgCO3 phase II and SiO2 (CaCl2-type SiO2 or seifertite) to form diamond and MgSiO3 (bridgmanite or post-perovsktite) was identified in the deep lower mantle conditions. These observations suggested that the reaction of the MgCO3 phase II with SiO2 causes formation of super-deep diamond in cold slabs descending into the deep lower mantle.
DS201709-2025
2017
Magalhaes, N., Magna, T., Rapprich, V., Kratky, O., Farquhar, J.Sulfur isotope systematics in carbonatites from Sevattur and Samalpatti, S India.Goldschmidt Conference, abstract 1p.Indiacarbonatites, Sevattur, Samalpatti

Abstract: We report preliminary data for sulfur isotopes from two spatially related Neoproterozoic carbonatite complexes in Tamil Nadu, S India, with the aim of getting further insights into their magmatic and/or post-emplacement histories [1]. The major sulfide phase in these rocks is pyrite, with minor chalcopyrite, whereas sulfate occurs as barite. A bimodal distribution of G34Ssulfide is found for Samalpatti (13.5 to 14.0‰), and Sevattur (?2.1 to 1.4‰) carbonatites. A significantly larger range of G34Ssulfide values is found for the associated Samalpatti silicate rocks (?5.2 to 7.4‰) relative to Sevattur pyroxenites and gabbros (?1.1 to 2.1‰). High G34Ssulfide values for Samalpatti carbonatites are unsual [2,3] but could reflect hydrothermal post-emplacement modification [1] of S isotopes. The low G34Ssulfide values for Sevattur may represent a mantle source signature. The G34Ssulfate is uniformly positive for both complexes, with most data falling in a narrow range (5.7 to 7.8‰) and one datum for a pyroxenite yielding more positive G34Ssulfate = 13.3‰. Data for '33S varies outside of analytical uncertainty (?0.07 to 0.04‰), indicating contribution from a source with a surface-derrived component. The small range of '33S values does not allow us to determine whether these sources contain S fractionated by biogeochemical (mass-dependent) or photochemical (mass-independent, pre GOE) processes. Data for '36S is positive, and varies within uncertainty (0.28 ± 0.15‰). Variations of this magnitude have been observed in other localities, and are not diagnostic of any unique source or process. The sulfur isotope data imply addition of crustal sulfur to Samalpatti. In contrast, sulfur from Sevattur has a mantle-like G34S but '33S with anomalous character. These observations support the idea of a different evolutionary story for these complexes, possibly more complex than previously thought.
DS201709-2026
2017
Magna, T., Wittke, A., Gussone, N., Rapprich, V., Upadhyay, D.Calcium isotope composition of carbonatites - a case study of Sevattur and Samalpatti, S. India.Goldschmidt Conference, abstract 1p.Indiacarbonatites

Abstract: Calcium isotope compositions are presented for two suites of carbonatites and associated alkaline silicate rocks from Neoproterozoic Sevattur and Samalpatti complexes in Tamil Nadu, South India. Despite their geographic proximity, the mean G44/40Ca values are different for Sevattur (G44/40Ca = 0.69 r 0.10‰, n = 7) and Samalpatti (0.81 r 0.16‰, n = 5). The former suite is derived from an enriched mantle source without significant post-emplacement modifications [1] and its Ca isotope composition falls to the lower end of Ca isotope range reported for mantle-derived rocks [2]. Some carbonatites from Samalpatti show a 44Ca-enriched signature which could reflect large-scale low-temperature modification, recognized also by their 13C–18O-enriched isotope systematics and sizeable loss of REE, when compared to pristine carbonatites from the area [1]. This is also consistent with albite–epidote metasomatic sample and shistose pyroxenite from Samalpatti, both showing a 44Ca-depleted signature. Leaching experiments confirm a systematic G44/40Ca offset with isotopically light carbonate relative to bulk sample [also 3]. Pyroxenites from Samalpatti are isotopically heavier than accompanying unmodified carbonatites and their G44/40Ca values fall into the mantle range. In contrast, pyroxenite and phosphate from Sevattur have a G44/40Ca value identical with associated carbonatites, indicating a homogeneous mantle source for the latter complex. For K-rich syenites and monzonites, 40K-decay corrections need to be considered for the intrinsic mass-dependent isotope fractionations considering the Neoproterozoic age and high K/Ca character of some samples.
DS201710-2243
2017
Magni, V.Plate tectonics: crustal recycling evolution.Nature Geoscience, Vol. 10, 9, pp. 623-624.Mantleslab break-off

Abstract: The processes that form and recycle continental crust have changed through time. Numerical models reveal an evolution from extensive recycling on early Earth as the lower crust peeled away, to limited recycling via slab break-off today.
DS201709-2027
2017
Magni, V., Allen, M.B., van Hunen, J., Bouihol, P.Continental underplating after slab break-off.Earth and Planetary Science Letters, Vol. 474, pp. 59-67.Mantle, India-Eurasiasubduction

Abstract: We present three-dimensional numerical models to investigate the dynamics of continental collision, and in particular what happens to the subducted continental lithosphere after oceanic slab break-off. We find that in some scenarios the subducting continental lithosphere underthrusts the overriding plate not immediately after it enters the trench, but after oceanic slab break-off. In this case, the continental plate first subducts with a steep angle and then, after the slab breaks off at depth, it rises back towards the surface and flattens below the overriding plate, forming a thick horizontal layer of continental crust that extends for about 200 km beyond the suture. This type of behaviour depends on the width of the oceanic plate marginal to the collision zone: wide oceanic margins promote continental underplating and marginal back-arc basins; narrow margins do not show such underplating unless a far field force is applied. Our models show that, as the subducted continental lithosphere rises, the mantle wedge progressively migrates away from the suture and the continental crust heats up, reaching temperatures >900?°C. This heating might lead to crustal melting, and resultant magmatism. We observe a sharp peak in the overriding plate rock uplift right after the occurrence of slab break-off. Afterwards, during underplating, the maximum rock uplift is smaller, but the affected area is much wider (up to 350 km). These results can be used to explain the dynamics that led to the present-day crustal configuration of the India–Eurasia collision zone and its consequences for the regional tectonic and magmatic evolution.
DS201709-2028
2016
Mahlangau, T., Moemise, N., Ramakokovhu, M.M., Olubambi, P.A., Shongwe, M.B.Separation of kimberlite from waste rocks using sensor based sorting at Culli nan diamond mine.South African Institute of Mining and Metallurgy, Vol. 116, 4, pp. 343-350.Africa, South Africadeposit - Cullinan

Abstract: Near-infrared (NIR) spectroscopy sorting technology is incorporated in an automated optical mineral sorter that can discriminate between materials using the differences in characteristics when exposed to near-infrared radiation. During September 2014 to April 2015, a pilot plant that utilized NIR technology to discriminate between kimberlite and waste materials was commissioned to determine the viability of including this technology in the diamond winning process flow sheet at Cullinan Diamond Mine. The plant was used to minimize the waste content in the size fraction -70+35 mm that reports to the crushing section and then to the dense media separation process. This paper describes the initial test work, conducted at Mintek, that led to the decision to conduct a pilot-scale study. The mineralogical characterization of the feed and product streams to establish the sorting criteria and the operational data obtained during the pilot plant campaign are described. The results indicated a good possibility of discriminating between the kimberlite and waste material using NIR technology. However, the consistency of discrimination was not good enough to avoid the risk of potential diamond loss. Furthermore, a lower than expected availability of the machine reduced the throughput capabilities.
DS201709-2029
2017
Maier, W.D., O'Brien, H., Peltonen, P., Barnes, S-J.Platinum group element contents of Karelian kimberlites: implications for the PGE budget of the sub-continental lithospheric mantle.Geochimica et Cosmochimica Acta, in press available, 14p.Europe, Finlanddeposit - Kaavi

Abstract: We present high-precision isotope dilution data for Os, Ir, Ru, Pt, Pd and Re in Group I and Group II kimberlites from the Karelian craton, as well as 2 samples of the Premier Group I kimberlite pipe from the Kaapvaal craton. The samples have, on average, 1.38 ppb Pt and 1.33 ppb Pd, with Pt/Pd around unity. These PGE levels are markedly lower, by as much as 80%, than those reported previously for kimberlites from South Africa, Brazil and India, but overlap with PGE results reported recently from Canadian kimberlites. Primitive-mantle-normalised chalcophile element patterns are relatively flat from Os to Pt, but Cu, Ni and, somewhat less so, Au are enriched relative to the PGE (e.g., Cu/Pd > 25.000). Pd/Ir ratios are 3,6 on average, lower than in most other mantle melts. The PGE systematics can be largely explained by two components, (i) harzburgite/lherzolite detritus of the SCLM with relatively high IPGE (Os-Ir-Ru)/PPGE (Rh-Pt-Pd) ratios, and (ii) a melt component that has high PPGE/IPGE ratios. By using the concentrations of iridium in the kimberlites as a proxy for the proportion of mantle detritus in the magma, we estimate that the analysed kimberlites contain 3–27% entrained and partially dissolved detritus from the sub-continental lithospheric mantle, consistent with previous estimates of kimberlites elsewhere (Tappe S. et al., 2016, Chem. Geol. http://dx.doi.org/10.1016/j.chemgeo.2016.08.019). The other major component in the samples is melt, modelled to contain an average of 0.85 ppb Pt and 1.09 ppb Pd. Assuming that Group II kimberlites are derived from relatively metasomatised SCLM, our data suggest that the metasomatised Karelian SCLM is relatively poor in Pt and Pd. If our data are representative of other Group II kimberlites elsewhere, this result could imply that the PGE enrichment in certain continental large igneous provinces, including Bushveld, is not derived from melting of metasomatised SCLM.
DS201710-2244
2017
Maier, W.D., O'Brien, H., Peltonen, P., Barnes, S-J.Platinum group element contents of Karelian kimberlites: implications for the PGE budget of the sub-continental lithospheric mantle.Geochimica et Cosmochimica Acta, Vol. 216, pp. 358-371.Europe, Finlanddeposit - Karelian

Abstract: We present high-precision isotope dilution data for Os, Ir, Ru, Pt, Pd and Re in Group I and Group II kimberlites from the Karelian craton, as well as 2 samples of the Premier Group I kimberlite pipe from the Kaapvaal craton. The samples have, on average, 1.38 ppb Pt and 1.33 ppb Pd, with Pt/Pd around unity. These PGE levels are markedly lower, by as much as 80%, than those reported previously for kimberlites from South Africa, Brazil and India, but overlap with PGE results reported recently from Canadian kimberlites. Primitive-mantle-normalised chalcophile element patterns are relatively flat from Os to Pt, but Cu, Ni and, somewhat less so, Au are enriched relative to the PGE (e.g., Cu/Pd > 25.000). Pd/Ir ratios are 3,6 on average, lower than in most other mantle melts. The PGE systematics can be largely explained by two components, (i) harzburgite/lherzolite detritus of the SCLM with relatively high IPGE (Os-Ir-Ru)/PPGE (Rh-Pt-Pd) ratios, and (ii) a melt component that has high PPGE/IPGE ratios. By using the concentrations of iridium in the kimberlites as a proxy for the proportion of mantle detritus in the magma, we estimate that the analysed kimberlites contain 3-27% entrained and partially dissolved detritus from the sub-continental lithospheric mantle, consistent with previous estimates of kimberlites elsewhere (Tappe S. et al., 2016, Chem. Geol. http://dx.doi.org/10.1016/j.chemgeo.2016.08.019). The other major component in the samples is melt, modelled to contain an average of 0.85 ppb Pt and 1.09 ppb Pd. Assuming that Group II kimberlites are derived from relatively metasomatised SCLM, our data suggest that the metasomatised Karelian SCLM is relatively poor in Pt and Pd. If our data are representative of other Group II kimberlites elsewhere, this result could imply that the PGE enrichment in certain continental large igneous provinces, including Bushveld, is not derived from melting of metasomatised SCLM.
DS201710-2245
2017
Mallard, C., Jacquet, B., Coltice, N.ADOPT: a tool for automatic detection of tectonic plates at the surface of convection model.Geochemistry, Geophysics, Geosystems, Vol. 18, 8, pp. 3197-3208.Mantletectonics

Abstract: Mantle convection models with plate-like behavior produce surface structures comparable to Earth's plate boundaries. However, analyzing those structures is a difficult task, since convection models produce, as on Earth, diffuse deformation and elusive plate boundaries. Therefore we present here and share a quantitative tool to identify plate boundaries and produce plate polygon layouts from results of numerical models of convection: Automatic Detection Of Plate Tectonics (ADOPT). This digital tool operates within the free open-source visualization software Paraview. It is based on image segmentation techniques to detect objects. The fundamental algorithm used in ADOPT is the watershed transform. We transform the output of convection models into a topographic map, the crest lines being the regions of deformation (plate boundaries) and the catchment basins being the plate interiors. We propose two generic protocols (the field and the distance methods) that we test against an independent visual detection of plate polygons. We show that ADOPT is effective to identify the smaller plates and to close plate polygons in areas where boundaries are diffuse or elusive. ADOPT allows the export of plate polygons in the standard OGR-GMT format for visualization, modification, and analysis under generic softwares like GMT or GPlates.
DS201712-2703
2017
Mancinelli, N.J., Fischer, K.M., Dalton, C.A.How sharp is the cratonic lithosphere; asthenosphere transition?Geophysical Research Letters, Vol. 44, 20, pp. 10,189-10,197.Mantlecraton

Abstract: Earth's cratonic mantle lithosphere is distinguished by high seismic wave velocities that extend to depths greater than 200 km, but recent studies disagree on the magnitude and depth extent of the velocity gradient at their lower boundary. Here we analyze and model the frequency dependence of Sp waves to constrain the lithosphere-asthenosphere velocity gradient at long-lived stations on cratons in North America, Africa, Australia, and Eurasia. Beneath 33 of 44 stations, negative velocity gradients at depths greater than 150 km are less than a 2-3% velocity drop distributed over more than 80 km. In these regions the base of the typical cratonic lithosphere is gradual enough to be explained by a thermal transition. Vertically sharper lithosphere-asthenosphere transitions are permitted beneath 11 stations, but these zones are spatially intermittent. These results demonstrate that lithosphere-asthenosphere viscosity contrasts and coupling fundamentally differ between cratons and younger continents.
DS201708-1708
2017
Maphane, K.Evolution of the Orapa A/K1 geology model - insights from analysis of multi-disciplinary datasets.11th. International Kimberlite Conference, OralAfrica, BotswanaDeposit - Orapa A/K1
DS201706-1095
2017
Marshak, S., Domrois, S., Abert, C., Larson, T., Pavlis, G., Hamburger, M., Yang, X., Gilbert, H., Chen, C.The basement revealed: tectonic insight from a digital elevation model of the Great Unconformity, USA cratonic platform.Geology, Vol. 45, 5, pp. 391-394.United Statestectonics - Mid continent

Abstract: Across much of North America, the contact between Precambrian basement and Paleozoic strata is the Great Unconformity, a surface that represents a >0.4 b.y.-long hiatus. A digital elevation model (DEM) of this surface visually highlights regional-scale variability in the character of basement topography across the United States cratonic platform. Specifically, it delineates Phanerozoic tectonic domains, each characterized by a distinct structural wavelength (horizontal distance between adjacent highs) and/or structural amplitude (vertical distance between adjacent lows and highs). The largest domain, the Midcontinent domain, includes long-wavelength epeirogenic basins and domes, as well as fault-controlled steps. The pronounced change in land-surface elevation at the Rocky Mountain Front coincides with the western edge of the Midcontinent domain on the basement DEM. In the Rocky Mountain and Colorado Plateau domains, west of the Rocky Mountain Front, structural wavelength is significantly shorter and structural amplitude significantly higher than in the Midcontinent domain. The Bordering Basins domain outlines the southern and eastern edges of the Midcontinent domain. As emphasized by the basement DEM, several kilometers of structural relief occur across the boundary between these two domains, even though this boundary does not stand out on ground-surface topography. A plot of epicenters on the basement DEM supports models associating intraplate seismicity with the Midcontinent domain edge. Notably, certain changes in crustal thickness also coincide with distinct changes in basement depth.
DS201707-1348
2017
Marshall, E.W., Lassiter, J.C., Barnes, J.D., Luguet, A., Lissner, M.Mantle melt production during the 1.4 Ga Laurentian magmatic event: isotopic constraints from Colorado Plateau mantle xenoliths.Geology, Vol. 45, 6, pp. 519-522.United States, Colorado Plateaumelting - Navajo Volcanics

Abstract: Plutons associated with a 1.4 Ga magmatic event intrude across southwestern Laurentia. The tectonic setting of this major magmatic province is poorly understood. Proposed melting models include anorogenic heating from the mantle, continental arc or transpressive orogeny, and anatexis from radiogenic heat buildup in thickened crust. Re-Os analyses of refractory mantle xenoliths from the Navajo volcanic field (NVF; central Colorado Plateau) yield Re depletion ages of 2.1–1.7 Ga, consistent with the age of the overlying Yavapai and Mazatzal crust. However, new Sm-Nd isotope data from clinopyroxene in peridotite xenoliths from NVF diatremes show a subset of xenoliths that plot on a ca. 1.4 Ga isochron, which likely reflects mantle melt production and isotopic resetting at 1.4 Ga. This suggests that Paleoproterozoic subcontinental lithospheric mantle was involved in the 1.4 Ga magmatic event. Our constraints support a subduction model for the generation of the 1.4 Ga granites but are inconsistent with rifting and anorogenic anatexis models, both of which would require removal of ancient lithosphere.
DS201702-0226
2016
Martin, R.F., Alarie, E., Minarik, W.G., Waczek, Z., McCammon, C.A.Titanium rich magneso-hastingite macrocrysts in a camptonite dike, Lafarge quarry, Montreal Island, Quebec: early crystallization in a pseudo-unary system.The Canadian Mineralogist, Vol. 54, pp. 65-78.Canada, QuebecCamptonite

Abstract: A prominent dike of camptonite cuts the Middle Ordovician Tétreauville Formation of the Trenton Group in the Montréal-Est quarry operated by Lafarge Canada Inc. The “Lafarge” dike is strikingly porphyritic, with largely anhedral macrocrysts of unzoned calcic amphibole up to 13 cm across. The macrocrysts are rimmed with ferri-kaersutite resembling the amphibole in the fine-grained matrix of the camptonite. The magnesio-hastingstite macrocrysts have virtually the same composition as the matrix; they thus grew without much of a boundary layer. The magma crystallized in a disequilibrium way as a pseudo-unary system. The macrocrysts are unusually enriched in Fe3+ (approximately 44% of the total iron), yet locally enclose globules of immiscible sulfide melt. The magma became oxygenated owing to preferential loss of hydrogen upon the dissociation of aqueous gas bubbles. The amygdaloidal macrocrysts have a relatively high ?D value because of this loss of H2; the values of ?18O are typical of an upper mantle source. Camptonite dikes are very common on Mont Royal. Like the Lafarge dike, they likely arose by the disequilibrium crystallization of batches of the parental melt of asthenospheric origin.
DS201708-1577
2017
Matzen, A.K., Wood, B.J., Baker, M.B., Stolper, E.M.The roles of pyroxenite and peridotite in the mantle sources onf oceanic basalt.Nature Geoscience, Vol. 10, pp. 530-535/Mantleperidotites

Abstract: Subduction of oceanic crust generates chemical and lithological heterogeneities in the mantle. An outstanding question is the extent to which these heterogeneities contribute to subsequent magmas generated by mantle melting, but the answer differs depending on the geochemical behaviour of the elements under investigation: analyses of incompatible elements (those that preferentially concentrate into silicate melts) suggest that recycled oceanic crust is an important contributor, whereas analyses of compatible elements (those that concentrate in crystalline residues) generally suggest it is not. Recently, however, the concentrations of Mn and Ni—two elements of varying compatibility—in early-crystallizing olivines, have been used to infer that erupted magmas are mixtures of partial melts of olivine-rich mantle rocks (that is, peridotite) and of metasomatic pyroxene-rich mantle rocks (that is, pyroxenite) formed by interaction between partial melts of recycled oceanic crust and peridotite. Here, we test whether melting of peridotite alone can explain the observed trend in olivine compositions by combining new experimental data on the partitioning of Mn between olivine and silicate melt under conditions relevant to basalt petrogenesis with earlier results on Ni partitioning. We show that the observed olivine compositions are consistent with melts of fertile peridotite at various pressures—importantly, melts from metasomatic pyroxenites are not required. Thus, although recycled materials may well be present in the mantle source regions of some basalts, the Mn and Ni data can be explained without such a contribution. Furthermore, the success of modelling the Mn–Ni contents of olivine phenocrysts as low-pressure crystallization products of partial melts of peridotite over a range of pressures implies a simple new approach for constraining depths of mantle melting.
DS201708-1709
2017
McCandless, T.Geology of the K6-252 kimberlite complex, Alberta.11th. International Kimberlite Conference, PosterCanada, Albertadeposit - K6-252
DS201712-2704
2017
McCandless, T., desGagnes, B., Shimell, M., Read, G.Geology of the K6-252 kimberlite complex, Alberta.45th. Annual Yellowknife Geoscience Forum, p. 102 abstract posterCanada, Albertadeposit - K6-252
DS201707-1349
2017
McDonald, I., Hughes, H.S.R., Butler, I.B., Harris, J.W., Muir, D.Homogenization of sulphide inclusions within diamonds: a new approach to diamond inclusion geochemistry.Geochimica et Cosmochimica Acta, available in press 23p.Africa, Botswanadeposit - Orapa

Abstract: Base metal sulphide (BMS) inclusions in diamonds provide a unique insight into the chalcophile and highly siderophile element composition of the mantle. Entombed within their diamond hosts, these provide a more robust (closed system) sample, from which to determine the trace element, Re-Os and S-isotopic compositions of the mantle than mantle xenoliths or orogenic peridotites, as they are shielded from alteration during ascent to the Earth’s crust and subsequent surface weathering. However, at temperatures below 1100 °C some BMS inclusions undergo subsolidus re-equilibration from an original monosulphide solid solution (Mss) and this causes fractionation of the major and trace elements within the inclusions. Thus to study the subjects noted above, current techniques require the entire BMS inclusion to be extracted for analyses. Unfortunately, ‘flaking’ of inclusions during break-out is a frequent occurrence and hence the risk of accidentally under-sampling a portion of the BMS inclusion is inherent in current practices. This loss may have significant implications for Re-Os isotope analyses where incomplete sampling of a Re-rich phase, such as chalcopyrite that typically occurs at the outer margins of BMS inclusions, may induce significant bias in the Re-Os and 187Os/188Os measurements and resulting model and isochron ages. We have developed a method for the homogenisation of BMS inclusions in diamond prior to their break-out from the host stone. Diamonds are heated to 1100 °C and then quenched to chemically homogenise any sulphide inclusions for both major and trace elements. Using X-ray Computed Microtomography (µCT) we determine the shape and spatial setting of multiple inclusions within a host stone and crucially show that the volume of a BMS inclusion is the same both before and after homogenisation. We show that the homogenisation process significantly reduces the inherent variability of in situ analysis when compared with unhomogenised BMS, thereby widening the scope for multiple methods for quantitative analysis, even on ‘flakes’ of single BMS inclusions. Finally we show that the trace elements present in peridotite (P-type) and eclogitic (E-type) BMS are distinct, with P-type diamonds having systematically higher total platinum-group element (particularly Os, Ir, Ru) and Te and As concentrations. These distinctions suggest that the PGE and semi-metal budgets of mantle-derived partial melts will be significantly dependent upon the type(s) and proportions of sulphides present in the mantle source.
DS201709-2030
2017
McDonald, I., Hughes, H.S.R., Butler, I.B., Harris, J.W., Muir, D.Homogenisation of sulphide inclusions within diamonds: a new approach to diamond inclusion geochemistry.Geochimica et Cosmochimica Acta, in press available, 23p.Technologydiamond inclusions

Abstract: Base metal sulphide (BMS) inclusions in diamonds provide a unique insight into the chalcophile and highly siderophile element composition of the mantle. Entombed within their diamond hosts, these provide a more robust (closed system) sample, from which to determine the trace element, Re-Os and S-isotopic compositions of the mantle than mantle xenoliths or orogenic peridotites, as they are shielded from alteration during ascent to the Earth’s crust and subsequent surface weathering. However, at temperatures below 1100 °C some BMS inclusions undergo subsolidus re-equilibration from an original monosulphide solid solution (Mss) and this causes fractionation of the major and trace elements within the inclusions. Thus to study the subjects noted above, current techniques require the entire BMS inclusion to be extracted for analyses. Unfortunately, ‘flaking’ of inclusions during break-out is a frequent occurrence and hence the risk of accidentally under-sampling a portion of the BMS inclusion is inherent in current practices. This loss may have significant implications for Re-Os isotope analyses where incomplete sampling of a Re-rich phase, such as chalcopyrite that typically occurs at the outer margins of BMS inclusions, may induce significant bias in the Re-Os and 187Os/188Os measurements and resulting model and isochron ages. We have developed a method for the homogenisation of BMS inclusions in diamond prior to their break-out from the host stone. Diamonds are heated to 1100 °C and then quenched to chemically homogenise any sulphide inclusions for both major and trace elements. Using X-ray Computed Microtomography (µCT) we determine the shape and spatial setting of multiple inclusions within a host stone and crucially show that the volume of a BMS inclusion is the same both before and after homogenisation. We show that the homogenisation process significantly reduces the inherent variability of in situ analysis when compared with unhomogenised BMS, thereby widening the scope for multiple methods for quantitative analysis, even on ‘flakes’ of single BMS inclusions. Finally we show that the trace elements present in peridotite (P-type) and eclogitic (E-type) BMS are distinct, with P-type diamonds having systematically higher total platinum-group element (particularly Os, Ir, Ru) and Te and As concentrations. These distinctions suggest that the PGE and semi-metal budgets of mantle-derived partial melts will be significantly dependent upon the type(s) and proportions of sulphides present in the mantle source.
DS201710-2246
2017
McDonald, I., Hughes, H.S.R., Butler, I.B., Harris, J.W., Muir, D.Homogenization of sulphide inclusions within diamonds: a new approach to diamond inclusion geochemistry.Geochimica et Cosmochimica Acta, Vol. 216, pp. 335-357.Technologydiamond inclusions - microtomography

Abstract: Base metal sulphide (BMS) inclusions in diamonds provide a unique insight into the chalcophile and highly siderophile element composition of the mantle. Entombed within their diamond hosts, these provide a more robust (closed system) sample, from which to determine the trace element, Re-Os and S-isotopic compositions of the mantle than mantle xenoliths or orogenic peridotites, as they are shielded from alteration during ascent to the Earth’s crust and subsequent surface weathering. However, at temperatures below 1100 °C some BMS inclusions undergo subsolidus re-equilibration from an original monosulphide solid solution (Mss) and this causes fractionation of the major and trace elements within the inclusions. Thus to study the subjects noted above, current techniques require the entire BMS inclusion to be extracted for analyses. Unfortunately, ‘flaking’ of inclusions during break-out is a frequent occurrence and hence the risk of accidentally under-sampling a portion of the BMS inclusion is inherent in current practices. This loss may have significant implications for Re-Os isotope analyses where incomplete sampling of a Re-rich phase, such as chalcopyrite that typically occurs at the outer margins of BMS inclusions, may induce significant bias in the Re-Os and 187Os/188Os measurements and resulting model and isochron ages. We have developed a method for the homogenisation of BMS inclusions in diamond prior to their break-out from the host stone. Diamonds are heated to 1100 °C and then quenched to chemically homogenise any sulphide inclusions for both major and trace elements. Using X-ray Computed Microtomography (µCT) we determine the shape and spatial setting of multiple inclusions within a host stone and crucially show that the volume of a BMS inclusion is the same both before and after homogenisation. We show that the homogenisation process significantly reduces the inherent variability of in situ analysis when compared with unhomogenised BMS, thereby widening the scope for multiple methods for quantitative analysis, even on ‘flakes’ of single BMS inclusions. Finally we show that the trace elements present in peridotite (P-type) and eclogitic (E-type) BMS are distinct, with P-type diamonds having systematically higher total platinum-group element (particularly Os, Ir, Ru) and Te and As concentrations. These distinctions suggest that the PGE and semi-metal budgets of mantle-derived partial melts will be significantly dependent upon the type(s) and proportions of sulphides present in the mantle source.
DS201708-1578
2017
McIntyre, S.R.N., Lineweaver, C.H., Groves, C.P., Chopra, A.Global biogeography since Pangea.Proceedings of the Royal Society B: Biological sciences, Vol. 284. no 1856, pp.Mantlepangea

Abstract: The break-up of the supercontinent Pangaea around 180 Ma has left its imprint on the global distribution of species and resulted in vicariance-driven speciation. Here, we test the idea that the molecular clock dates, for the divergences of species whose geographical ranges were divided, should agree with the palaeomagnetic dates for the continental separations. Our analysis of recently available phylogenetic divergence dates of 42 pairs of vertebrate taxa, selected for their reduced ability to disperse, demonstrates that the divergence dates in phylogenetic trees of continent-bound terrestrial and freshwater vertebrates are consistent with the palaeomagnetic dates of continental separation.
DS201708-1710
2017
McKinley, T.Deep delineation evaluation drilling methods, Jwaneng mine, Botswana.11th. International Kimberlite Conference, PosterAfrica, Botswanadeposit - Jwaneng
DS201712-2705
2017
McPeak, S., Mallozzi, S., Samson, C., Elliott, B., Junter, J.Estimating overburden depth in a permafrost rich environment using passive seismics: results from the 2017 preliminary survey at Kennady Camp.45th. Annual Yellowknife Geoscience Forum, p. 103 abstract posterCanada, Northwest Territoriesdeposit - Kennady
DS201710-2247
2017
Meert, J.G., Pandit, M.K., Pivarunas, A., Katusin, K., Sinha, A.K.India and Antarctica in the Precambrian: a brief analysis.Geological Society of London Special Publication, Vol. 457, pp. 339-351.IndiaTectonics

Abstract: In this short paper, we outline the potential links between India and the East Antarctica region from Enderby Land to Princess Elizabeth Land using the Mesozoic East Gondwana configuration as a starting point. Palaeomagnetic data indicate that East Gondwana did not exist prior to the Ediacaran-Cambrian. Early Neoproterozoic (1050-950 Ma) deformation in East Antarctica and along the Eastern Ghats Province in India marks the initial contact between the two regions. Volcanism in the Kerguelen hotspot led to final break-up of India and East Antarctica in the Cretaceous. Although connections between the Archaean and Proterozoic provinces of India and East Antarctica have been proposed, the current record of large igneous provinces (or dyke swarms), palaeomagnetic data and geochronology do not show a consistently good match between the two regions.
DS201709-2031
2017
Meert, J.G., Santosh, M.The Columbia supercontinent revisited.Gondwana Research, Vol. 50, pp. 67-83.Globalsupercontinent

Abstract: Just over 15 years ago, a proposal forwarded by Rogers and Santosh (2002) posited the existence of a pre-Rodinia supercontinent which they called Columbia. The conjecture invigorated research into the Paleo-Mesoproterozoic interval that was; in our opinion, inappropriately dubbed ‘the boring billion’. Given the wealth of new information about the supercontinent, this review paper takes a careful look at the paleomagnetic evidence that is used to reconstruct Columbia. Our contribution represents a status report and indicates that; despite the exponential increase in available data, knowledge of the assembly, duration and breakup history of the supercontinent are contentious. The commonality of ~ 1.7–2.1 Ga orogenic systems around the globe are indicative of major changes in paleogeography and growth of larger landmasses. There is continued discussion about the interconnectedness of those orogenic systems in a global picture. Arguments for Columbia posit a ~ 1500–1400 Ma age for maximum packing. Paleomagnetic data from many of the constituent cratons during the 1500–1400 Ma interval can be interpreted to support a large landmass, but the consistency of the proposal cannot be reliably demonstrated for earlier or later times. One of the more intriguing advances are the apparent long-lived connections between Laurentia, Siberia and Baltica that may have formed the core of both Columbia and Rodinia.
DS201708-1711
2017
Melgarejo Draper, J.C.Styles of alteration of Ti oxides of the kimberlite groundmass: implications on the petrogenesis and classification of kimberlites and similar rocks.11th. International Kimberlite Conference, PosterTechnologykimberlite classification
DS201705-0853
2017
Melluso, L., Guarino, V., Lustrino, M., Morra, V., de'Gennaro, R.The REE- and HFSE-bearing phases in the Itatiaia alkaline complex ( Brazil) and geochemical evolution of feldspar-rich felsic melts.Mineralogical Magazine, Vol. 81, 2, pp. 217-250.South America, BrazilAlkaline rocks

Abstract: The Late Cretaceous Itatiaia complex is made up of nepheline syenite grading to peralkaline varieties, quartz syenite and granite, emplaced in the metamorphic rocks of the Serra do Mar, SE Brazil. The nepheline syenites are characterized by assemblages with alkali feldspar, nepheline, Fe-Ti oxides, clinopyroxene, amphibole, apatite and titanite, while the peralkaline nepheline syenites have F-disilicates (rinkite, wöhlerite, hiortdahlite, låvenite), britholite and pyrophanite as the accessory phases. The silica-oversaturated rocks have alkali feldspar, plagioclase, quartz, amphibole, clinopyroxene and Fe-Ti oxides; the chevkinite-group minerals are the featured accessory phases and are found with allanite, fluorapatite, fluorite, zircon, thorite, yttrialite, zirconolite, pyrochlore and yttrocolumbite. The major- and trace-element composition of the Itatiaia rocks have variations linked to the amount of accessory phases, have smooth, enriched chondrite-normalized rare-earth element (REE) distribution patterns in the least-evolved nepheline syenites and convex patterns in the most-evolved nepheline syenites. The REE distribution patterns of the quartz syenites and granites show a typical pattern caused by fractional crystallization of feldspar and amphibole, in an environment characterized by relatively high oxygen fugacity (>NiNiO buffer) and high concentrations of H2O and F, supporting the crystallization of hydrous phases, fluorite and F-disilicates. The removal of small amounts of titanite in the transition from the least-evolved to the most-evolved nepheline syenites stems from petrogenetic models involving REE, and is shown to be a common feature of the magmatic evolution of many other syenitic/ trachytic/ phonolitic complexes of the Serra do Mar and elsewhere.
DS201710-2248
2017
Mercier-Langevin, P.Mineral deposits of Canada: a compilation (1905-2016)Society of Economic Geologists, CD of 1,460 papers. $ 150.00Canadamineral deposits
DS201705-0854
2017
Merdith, A.S., Collins, A.S., Williams, S.E., Pisarevsky, S., Foden, J.F., Archibald, D., Blades, M.L., Alessio, B.L., Armistead, S., Plavsa, D., Clark, C., Muller, R.D.A full plate global reconstruction of the Neoproterozoic.Gondwana Research, in press available 155p.Gondwana, RodiniaGeodynamics

Abstract: Neoproterozoic tectonic geography was dominated by the formation of the supercontinent Rodinia, its break-up and the subsequent amalgamation of Gondwana. The Neoproterozoic was a tumultuous time of Earth history, with large climatic variations, the emergence of complex life and a series of continent-building orogenies of a scale not repeated until the Cenozoic. Here we synthesise available geological and palaeomagnetic data and build the first full-plate, topological model of the Neoproterozoic that maps the evolution of the tectonic plate configurations during this time. Topological models trace evolving plate boundaries and facilitate the evaluation of “plate tectonic rules” such as subduction zone migration through time when building plate models. There is a rich history of subduction zone proxies preserved in the Neoproterozoic geological record, providing good evidence for the existence of continent-margin and intra-oceanic subduction zones through time. These are preserved either as volcanic arc protoliths accreted in continent-continent, or continent-arc collisions, or as the detritus of these volcanic arcs preserved in successor basins. Despite this, we find that the model presented here still predicts less subduction (ca. 90%) than on the modern earth, suggesting that we have produced a conservative model and are likely underestimating the amount of subduction, either due to a simplification of tectonically complex areas, or because of the absence of preservation in the geological record (e.g. ocean-ocean convergence). Furthermore, the reconstruction of plate boundary geometries provides constraints for global-scale earth system parameters, such as the role of volcanism or ridge production on the planet's icehouse climatic excursion during the Cryogenian. Besides modelling plate boundaries, our model presents some notable departures from previous Rodinia models. We omit India and South China from Rodinia completely, due to long-lived subduction preserved on margins of India and conflicting palaeomagnetic data for the Cryogenian, such that these two cratons act as ‘lonely wanderers’ for much of the Neoproterozoic. We also introduce a Tonian-Cryogenian aged rotation of the Congo-São Francisco Craton relative to Rodinia to better fit palaeomagnetic data and account for thick passive margin sediments along its southern margin during the Tonian. The GPlates files of the model are released to the public and it is our expectation that this model can act as a foundation for future model refinements, the testing of alternative models, as well as providing constraints for both geodynamic and palaeoclimate models.
DS201709-2032
2017
Meredith, A.S., Collins, A.S., Williams, S.E., Pisarevsky, S., Foden, J.D., Archibald, D.B., Blades, M.L., Alessio, B.L., Armistead, S., Plavsa, D., Clark, C., Muller, R.D.A full plate global reconstruction of the Neoproterozoic.Gondwana Research, Vol. 50, pp. 84-134.Globalneoproterozoic

Abstract: Neoproterozoic tectonic geography was dominated by the formation of the supercontinent Rodinia, its break-up and the subsequent amalgamation of Gondwana. The Neoproterozoic was a tumultuous time of Earth history, with large climatic variations, the emergence of complex life and a series of continent-building orogenies of a scale not repeated until the Cenozoic. Here we synthesise available geological and palaeomagnetic data and build the first full-plate, topological model of the Neoproterozoic that maps the evolution of the tectonic plate configurations during this time. Topological models trace evolving plate boundaries and facilitate the evaluation of “plate tectonic rules” such as subduction zone migration through time when building plate models. There is a rich history of subduction zone proxies preserved in the Neoproterozoic geological record, providing good evidence for the existence of continent-margin and intra-oceanic subduction zones through time. These are preserved either as volcanic arc protoliths accreted in continent-continent, or continent-arc collisions, or as the detritus of these volcanic arcs preserved in successor basins. Despite this, we find that the model presented here still predicts less subduction (ca. 90%) than on the modern earth, suggesting that we have produced a conservative model and are likely underestimating the amount of subduction, either due to a simplification of tectonically complex areas, or because of the absence of preservation in the geological record (e.g. ocean-ocean convergence). Furthermore, the reconstruction of plate boundary geometries provides constraints for global-scale earth system parameters, such as the role of volcanism or ridge production on the planet's icehouse climatic excursion during the Cryogenian. Besides modelling plate boundaries, our model presents some notable departures from previous Rodinia models. We omit India and South China from Rodinia completely, due to long-lived subduction preserved on margins of India and conflicting palaeomagnetic data for the Cryogenian, such that these two cratons act as ‘lonely wanderers’ for much of the Neoproterozoic. We also introduce a Tonian-Cryogenian aged rotation of the Congo-São Francisco Craton relative to Rodinia to better fit palaeomagnetic data and account for thick passive margin sediments along its southern margin during the Tonian. The GPlates files of the model are released to the public and it is our expectation that this model can act as a foundation for future model refinements, the testing of alternative models, as well as providing constraints for both geodynamic and palaeoclimate models.
DS201708-1712
2017
Mervine, E.Potential for offsetting diamond mine carbon emissions through mineral carbonation of processed kimberlite.11th. International Kimberlite Conference, PosterAfrica, South Africacarbon
DS201708-1713
2017
Meyer, N.A new look at diamonds from the Koffiefontein mine.11th. International Kimberlite Conference, PosterAfrica, South Africadeposit - Koffiefontein

Abstract: The Koffiefontein kimberlite is one of the classic locales on the Kaapvaal Craton and best known for being the first locality where very deep diamonds were recovered. Koffiefontein diamonds were last studied in 1980s and, based on major advances in micro-analytical techniques, here we revisit the mine to provide improved inclusion-based geothermobarometry. Currently, ~70 peridotitic diamonds have been studied with ~150 olivine, Cr-rich pyrope garnet, enstatite, and diopside inclusions liberated. So far, the inclusions were analysed (EPMA) for their major element compositions. The peridotitic inclusion suite is dominated by a highly-depleted harzburgitic association: olivine Mg-number ranges between 93 and 95, harzburgitic garnets contain < 3.00 wt % CaO, and 14 % of garnet inclusions are lherzolitic in paragenesis. Conventional mineral exchange geothermobarometry on non-touching inclusion pairs reveals that diamonds with harzburgitic inclusions derive from close to the base of the lithosphere (1143-1283 °C and 55-65 kbar; 12 diamonds) whilst much rarer lherzolitic inclusions last equilibrated in the upper portion of diamond stable lithosphere (983-1158 °C and 47-52 kbar; 5 diamonds). Both associations fall along a 39 mW/m2 reference geotherm (Hasterok and Chapman, 2011), implying a total lithosphere thickness of ~200 km at 90 Ma. To expand our geothermobarometry data beyond rare garnet-opx associations we conducted high-precision trace element analysis of Al and Ca in olivine inclusions via EPMA. Using long count times (300 sec on peak and each background) and a 200 nA beam current, detection limits of 8 ppm for Al and 6 ppm for Ca were achieved. This technique allowed for trace element analysis of olivine inclusions as small as 20 ?m in diameter. Based on these high-precision Al analyses, the updated Al-inolivine thermometer of Bussweiler et al (2017) extrapolated to a 39 mW/m2 geotherm yielded temperatures of 1124-1278 °C (30 diamonds).
DS201708-1714
2017
Mibe, K.Sound velocity of carbonate melts under high pressure and temperature conditions and the origin of mid-lithospheric discontinuity.11th. International Kimberlite Conference, PosterMantlemelting
DS201706-1096
2017
Mikhail, S., Barry, P.H., Sverjensky, D.A.The relationship between mantle pH and the deep nitrogen cycle.Geochimica et Cosmochimica Acta, in press available 25p.Mantlenitrogen cycle

Abstract: Nitrogen is distributed throughout all terrestrial geological reservoirs (i.e., the crust, mantle, and core), which are in a constant state of disequilibrium due to metabolic factors at Earth’s surface, chemical weathering, diffusion, and deep N fluxes imposed by plate tectonics. However, the behavior of nitrogen during subduction is the subject of ongoing debate. There is a general consensus that during the crystallization of minerals from melts, monatomic nitrogen behaves like argon (highly incompatible) and ammonium behaves like potassium and rubidium (which are relatively less incompatible). Therefore, the behavior of nitrogen is fundamentally underpinned by its chemical speciation. In aqueous fluids, the controlling factor which determines if nitrogen is molecular (N2) or ammonic (inclusive of both NH4+ and NH30) is oxygen fugacity, whereas pH designates if ammonic nitrogen is NH4+ or NH30. Therefore, to address the speciation of nitrogen at high pressures and temperatures, one must also consider pH at the respective pressure-temperature conditions. To accomplish this goal we have used the Deep Earth Water Model (DEW) to calculate the activities of aqueous nitrogen from 1-5 GPa and 600-1000 °C in equilibrium with a model eclogite-facies mineral assemblage of jadeite + kyanite + quartz/coesite (metasediment), jadeite + pyrope + talc + quartz/coesite (metamorphosed mafic rocks), and carbonaceous eclogite (metamorphosed mafic rocks + elemental carbon). We then compare these data with previously published data for the speciation of aqueous nitrogen across these respective P-T conditions in equilibrium with a model peridotite mineral assemblage (Mikhail and Sverjensky, 2014). In addition, we have carried out full aqueous speciation and solubility calculations for the more complex fluids in equilibrium with jadeite + pyrope + kyanite + diamond, and for fluids in equilibrium with forsterite + enstatite + pyrope + diamond. Our results show that the pH of the fluid is controlled by mineralogy for a given pressure and temperature, and that pH can vary by several units in the pressure-temperature range of 1-5 GPa and 600-1000 °C. Our data show that increasing temperature stabilizes molecular nitrogen and increasing pressure stabilizes ammonic nitrogen. Our model also predicts a stark difference for the dominance of ammonic vs. molecular and ammonium vs. ammonia for aqueous nitrogen in equilibrium with eclogite-facies and peridotite mineralogies, and as a function of the total dissolved nitrogen in the aqueous fluid where lower N concentrations favor aqueous ammonic nitrogen stabilization and higher N concentrations favor aqueous N2. Overall, we present thermodynamic evidence for nitrogen to be reconsidered as an extremely dynamic (chameleon) element whose speciation and therefore behavior is determined by a combination of temperature, pressure, oxygen fugacity, chemical activity, and pH. We show that altering the mineralogy in equilibrium with the fluid can lead to a pH shift of up to 4 units at 5 GPa and 1000 °C. Therefore, we conclude that pH imparts a strong control on nitrogen speciation, and thus N flux, and should be considered a significant factor in high temperature geochemical modeling in the future. Finally, our modelling demonstrates that pH plays an important role in controlling speciation, and thus mass transport, of Eh-pH sensitive elements at temperatures up to at least 1000 °C.
DS201707-1350
2017
Mikhail, S., Barry, P.H., Sverjensky, D.A.The relationship between mantle pH and the deep nitrogen cycle.Geochimica et Cosmochimica Acta, Vol. 209, pp. 149-160.Mantlenitrogen

Abstract: Nitrogen is distributed throughout all terrestrial geological reservoirs (i.e., the crust, mantle, and core), which are in a constant state of disequilibrium due to metabolic factors at Earth’s surface, chemical weathering, diffusion, and deep N fluxes imposed by plate tectonics. However, the behavior of nitrogen during subduction is the subject of ongoing debate. There is a general consensus that during the crystallization of minerals from melts, monatomic nitrogen behaves like argon (highly incompatible) and ammonium behaves like potassium and rubidium (which are relatively less incompatible). Therefore, the behavior of nitrogen is fundamentally underpinned by its chemical speciation. In aqueous fluids, the controlling factor which determines if nitrogen is molecular (N2) or ammonic (inclusive of both NH4+ and NH30) is oxygen fugacity, whereas pH designates if ammonic nitrogen is NH4+ or NH30. Therefore, to address the speciation of nitrogen at high pressures and temperatures, one must also consider pH at the respective pressure–temperature conditions. To accomplish this goal we have used the Deep Earth Water Model (DEW) to calculate the activities of aqueous nitrogen from 1–5 GPa and 600–1000 °C in equilibrium with a model eclogite-facies mineral assemblage of jadeite + kyanite + quartz/coesite (metasediment), jadeite + pyrope + talc + quartz/coesite (metamorphosed mafic rocks), and carbonaceous eclogite (metamorphosed mafic rocks + elemental carbon). We then compare these data with previously published data for the speciation of aqueous nitrogen across these respective P-T conditions in equilibrium with a model peridotite mineral assemblage (Mikhail and Sverjensky, 2014). In addition, we have carried out full aqueous speciation and solubility calculations for the more complex fluids in equilibrium with jadeite + pyrope + kyanite + diamond, and for fluids in equilibrium with forsterite + enstatite + pyrope + diamond. Our results show that the pH of the fluid is controlled by mineralogy for a given pressure and temperature, and that pH can vary by several units in the pressure-temperature range of 1–5 GPa and 600–1000 °C. Our data show that increasing temperature stabilizes molecular nitrogen and increasing pressure stabilizes ammonic nitrogen. Our model also predicts a stark difference for the dominance of ammonic vs. molecular and ammonium vs. ammonia for aqueous nitrogen in equilibrium with eclogite-facies and peridotite mineralogies, and as a function of the total dissolved nitrogen in the aqueous fluid where lower N concentrations favor aqueous ammonic nitrogen stabilization and higher N concentrations favor aqueous N2. Overall, we present thermodynamic evidence for nitrogen to be reconsidered as an extremely dynamic (chameleon) element whose speciation and therefore behavior is determined by a combination of temperature, pressure, oxygen fugacity, chemical activity, and pH. We show that altering the mineralogy in equilibrium with the fluid can lead to a pH shift of up to 4 units at 5 GPa and 1000 °C. Therefore, we conclude that pH imparts a strong control on nitrogen speciation, and thus N flux, and should be considered a significant factor in high temperature geochemical modeling in the future. Finally, our modelling demonstrates that pH plays an important role in controlling speciation, and thus mass transport, of Eh-pH sensitive elements at temperatures up to at least 1000 °C.
DS201712-2706
2017
Mikhno, A.O., Musiyachenko, K.A., Shcheptova, O.V., Koraskov, A.V., Rashchenko, S.V.CO2 bearing fluid inclusions associated with diamonds in zircon from the UHP Kokchetav gneisses.Journal of Raman Spectroscopy, Vol. 48, 11, pp. 1566-1573.RussiaUHP - Kokchetav

Abstract: CO2-bearing fluid inclusions coexisting with diamonds were identified in zircons from diamondiferous gneiss in the Kokchetav Massif. This discovery provides evidence for the presence of CO2 in UHP fluids and diamond formation in moderately oxidized conditions in the Kokchetav gneiss. Fluid and multiphase solid inclusions coexisting in zircons represent immiscible melt and fluid captured close to the peak metamorphic conditions for the Kokchetav UHP gneiss. Most of CO2-bearing inclusions are CO2+H2O mixtures except for some cases when they also contain daughter phases (e.g. muscovite, calcite and quartz) tracing the presence of aqueous and solute-rich fluids at different phases of UHP metamorphism. Decrease of pressure and temperature may have been responsible for the reduction of solutes in the CO2-bearing fluid. The lack of CO2-bearing inclusions in garnet porphyroblasts from diamond-bearing gneiss, as well as the common coexistence of aqueous CO2-bearing inclusions with calcite, testify that most likely all CO2 in fluid was consumed by the calcite-forming reaction and hydrous melt was the only remaining growth medium during retrograde metamorphism of the Kokchetav UHPM gneisses. Neither K-cymrite nor kokchetavite was identified among daughter phases in the hydrous melt inclusions in garnet, which indicates that they hardly could originate in a metapelitic system.
DS201702-0227
2017
Milani, L., Bolhar, R., Cawthorn, R.G., Frei, D.In Situ LA-ICP-MS and EPMA trace element characterization of Fe-Ti oxides from the phoscorite carbonatite association at Phalaborwa, South Africa.Mineralium Deposita, in press available, 22p.Africa, South AfricaDeposit - Phalaborwa

Abstract: In situ laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and electron probe microanalysis (EPMA) are used to characterize magnetite and ilmenite of the phoscorite-carbonatite association at Phalaborwa. We trace the behavior of the compatible elements for two different generations of magnetite related to (1) a magmatic stage, with variable Ti-V content, which pre-dates the copper mineralization, and (2) a late hydrothermal, low-Ti, low-temperature event, mostly post-dating sulfide formation. Magnetite is shown to be a robust petrogenetic indicator; no influence on its chemical composition is detected from the intergrowth with the accompanying phases, including the interaction with coexisting sulfides. High spatial resolution EPMA characterize the tiny late-stage hydrothermal magnetite veins, as well as the ilmenite granular and lamellar exsolutions mostly developed in the magnetite from the phoscorite. By combining geochemical data with geothermo-oxybarometry calculations for magnetite-ilmenite pairs, we infer that the most primitive magnetite probably formed at oxygen fugacity above the nickel nickel oxide (NNO) buffer, revealing an evolutionary trend of decreasing temperature and oxygen fugacity. Geochemical similarity exists between magnetite from phoscorite and carbonatite, thus supporting a common mantle source for the phoscorite-carbonatite association.
DS201702-0228
2017
Milani, L., Bolhar, R., Frei, D., Harlov, D.E., Samuel, V.O.Light rare earth element systematics as a tool for investigating the petrogenesis of phoscorite-carbonatite associations, as exemplified by the Phalaborwa Complex, South Africa.Mineralium Deposita, in press available, 21p.Africa, South AfricaDeposit - Phalaborwa

Abstract: In-situ trace element analyses of fluorapatite, calcite, dolomite, olivine, and phlogopite have been undertaken on representative phoscorite and carbonatite rocks of the Palaeoproterozoic Phalaborwa Complex. Textural and compositional characterization reveals uniformity of fluorapatite and calcite among most of the intrusions, and seems to favor a common genetic origin for the phoscorite-carbonatite association. Representing major repositories for rare earth elements (REE), fluorapatite and calcite exhibit tightly correlated light REE (LREE) abundances, suggesting that partitioning of LREE into these rock forming minerals was principally controlled by simple igneous differentiation. However, light rare earth element distribution in apatite and calcite cannot be adequately explained by equilibrium and fractional crystallization and instead favors a complex crystallization history involving mixing of compositionally distinct magma batches, in agreement with previously reported mineral isotope variability that requires open-system behaviour.
DS201701-0021
2016
Milani. L., Bolhar, R., Cawthorn, R.G., Frei, D.In situ LA-ICP-MS and EPMA trace element characterization of Fe-Ti oxides from the phsocorite carbonatite association at Phalaborwa, South Africa.Mineralium Deposita, in press available 22p.Africa, South AfricaCarbonatite

Abstract: In situ laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and electron probe microanalysis (EPMA) are used to characterize magnetite and ilmenite of the phoscorite-carbonatite association at Phalaborwa. We trace the behavior of the compatible elements for two different generations of magnetite related to (1) a magmatic stage, with variable Ti-V content, which pre-dates the copper mineralization, and (2) a late hydrothermal, low-Ti, low-temperature event, mostly post-dating sulfide formation. Magnetite is shown to be a robust petrogenetic indicator; no influence on its chemical composition is detected from the intergrowth with the accompanying phases, including the interaction with coexisting sulfides. High spatial resolution EPMA characterize the tiny late-stage hydrothermal magnetite veins, as well as the ilmenite granular and lamellar exsolutions mostly developed in the magnetite from the phoscorite. By combining geochemical data with geothermo-oxybarometry calculations for magnetite-ilmenite pairs, we infer that the most primitive magnetite probably formed at oxygen fugacity above the nickel nickel oxide (NNO) buffer, revealing an evolutionary trend of decreasing temperature and oxygen fugacity. Geochemical similarity exists between magnetite from phoscorite and carbonatite, thus supporting a common mantle source for the phoscorite-carbonatite association.
DS201708-1715
2017
Milligan, R.Features of apatite in kimberlites from Ekati diamond mine and Snap Lake, Northwest Territories: modelling of kimberlite composition.11th. International Kimberlite Conference, PosterCanada, Northwest Territoriesdeposit - Ekati, Snap Lake

Abstract: Kimberlites are volcanic ultramafic rocks originate from the upper mantle, and some are diamond bearing. Due to assimilation of mantle and crustal material, loss of volatiles, significant alteration and variable compositions of kimberlite seen at the surface, the primary composition and proportion of melt fluids (H2O, CO2) are unknown. Kimberlitic fluid and melt composition have significant effects on the preservation and quality of diamonds carried to the surface. In an attempt to gain predictive knowledge of the economic viability of a kimberlite, it is important to understand the primary and evolving compositions of kimberlite magmas, as well as the behaviour of volatiles during kimberlite eruption. Apatite is a common groundmass mineral in kimberlite, and has a composition sensitive to volatiles and trace elements [Ca5(PO4)3(F,Cl,OH)]. This study will examine the variation of apatite occurrence, composition, texture and trace element distribution in relation to varied kimberlite geologies and explore the potential of apatite as an indicator of fluid history and melt composition. Seven kimberlites have been selected for a study of groundmass apatite. The six Ekati property kimberlites (Koala, Misery, Panda, Beartooth, Leslie and Grizzly) have been chosen for their varying facies and styles of eruption. Panda and Beartooth are resedimented volcaniclastic kimberlites. Misery and Koala are massive volcaniclastic kimberlites. Leslie and Grizzly are pipe-fill coherent kimberlites. The seventh kimberlite, Snap Lake, is a coherent kimberlite dyke. All kimberlites are located in the Northwest Territories, Canada. Selecting kimberlites with diverse eruption styles allows us to test the apatite indicator model for a variety of potential volatile histories. Back scatter electron imaging has been used to identify and discriminate significant differences in apatite abundance and textural characteristics from Ekati kimberlites and Snap Lake. Wavelength dispersive spectroscopic analysis for major and some trace elements (LREE’s, Sr, Ba) reveals primary substitution mechanisms for rare earth element (REE) incorporation into apatite structure. Previous studies show that distribution of trace elements into apatite greatly depends on the growth media. Partitioning of the LREE’s relative to Sr is significantly different between silicate melt, carbonate melt, and aqueous fluid. Experimental partition coefficients between apatite and various growth media are used to test existing hypotheses of kimberlite melt composition. The future aim of this project is to establish apatite as an effective indicator of magmatic fluid and outline the applicability of groundmass apatite as an indicator of diamond preservation potential in kimberlites.
DS201709-2033
2017
Mingming, L., et al.Compositionally distinct ultra-low velocity zones on Earth's core-mantle boundary.Nature Communications, Aug. 2, 4p.Mantlegeophysics - seismics

Abstract: The Earth’s lowermost mantle large low velocity provinces are accompanied by small-scale ultralow velocity zones in localized regions on the core-mantle boundary. Large low velocity provinces are hypothesized to be caused by large-scale compositional heterogeneity (i.e., thermochemical piles). The origin of ultralow velocity zones, however, remains elusive. Here we perform three-dimensional geodynamical calculations to show that the current locations and shapes of ultralow velocity zones are related to their cause. We find that the hottest lowermost mantle regions are commonly located well within the interiors of thermochemical piles. In contrast, accumulations of ultradense compositionally distinct material occur as discontinuous patches along the margins of thermochemical piles and have asymmetrical cross-sectional shape. Furthermore, the lateral morphology of these patches provides insight into mantle flow directions and long-term stability. The global distribution and large variations of morphology of ultralow velocity zones validate a compositionally distinct origin for most ultralow velocity zones.
DS201705-0855
2017
Mining MagazineDat a equals diamonds: De Beers exploration efforts. Overview of SQUIDsMining Magazine, April pp. 24-27.TechnologyGeophysics, SQUID
DS201704-0639
2016
MiningNorth25 Years of Diamondsminingnorth.com, videoCanada, Northwest TerritoriesHistory
DS201704-0640
2017
MiningNorthDiamond Gala - Explorationutube, videoCanadaHistory
DS201701-0022
2016
Mitchell, A.L., Grove, T.L.Experiments on melt-rock reaction in the shallow mantle wedge.Contributions to Mineralogy and Petrology, Vol. 171, pp. 107-MantleSubduction

Abstract: This experimental study simulates the interaction of hotter, deeper hydrous mantle melts with shallower, cooler depleted mantle, a process that is expected to occur in the upper part of the mantle wedge. Hydrous reaction experiments (~6 wt% H2O in the melt) were conducted on three different ratios of a 1.6 GPa mantle melt and an overlying 1.2 GPa harzburgite from 1060 to 1260 °C. Reaction coefficients were calculated for each experiment to determine the effect of temperature and starting bulk composition on final melt compositions and crystallizing assemblages. The experiments used to construct the melt-wall rock model closely approached equilibrium and experienced <5% Fe loss or gain. Experiments that experienced higher extents of Fe loss were used to critically evaluate the practice of “correcting” for Fe loss by adding iron. At low ratios of melt/mantle (20:80 and 5:95), the crystallizing assemblages are dunites, harzburgites, and lherzolites (as a function of temperature). When the ratio of deeper melt to overlying mantle is 70:30, the crystallizing assemblage is a wehrlite. This shows that wehrlites, which are observed in ophiolites and mantle xenoliths, can be formed by large amounts of deeper melt fluxing though the mantle wedge during ascent. In all cases, orthopyroxene dissolves in the melt, and olivine crystallizes along with pyroxenes and spinel. The amount of reaction between deeper melts and overlying mantle, simulated here by the three starting compositions, imposes a strong influence on final melt compositions, particularly in terms of depletion. At the lowest melt/mantle ratios, the resulting melt is an extremely depleted Al-poor, high-Si andesite. As the fraction of melt to mantle increases, final melts resemble primitive basaltic andesites found in arcs globally. An important element ratio in mantle lherzolite composition, the Ca/Al ratio, can be significantly elevated through shallow mantle melt-wall rock reaction. Wall rock temperature is a key variable; over a span of <80 °C, reaction with deeper melt creates the entire range of mantle lithologies from a depleted dunite to a harzburgite to a refertilized lherzolite. Together, the experimental phase equilibria, melt compositions, and reaction coefficients provide a framework for understanding how melt-wall rock reaction occurs in the natural system during melt ascent in the mantle wedge.
DS201703-0426
2017
Mitchell, G.Which type of surveying would be best for my project: PhotoSat, Lidar, Drone, or GPS.photosat.ca, 10p.TechnologyMethods - surveys
DS201708-1716
2017
Mitchell, R.Mineralogy of Kimberley-type pyroclastic kimberlite and the transition to Hypabyssal kimberlite.11th. International Kimberlite Conference, OralBlankkimberlite classification
DS201707-1351
2017
Mitchell, R., Chudy, T., McFarlane, C.R.M., Wu, F-Y.Trace element and isotopic composition of apatite in carbonatites from the Blue River area ( British Columbia, Canada) and mineralogy of associated silicate rocks. Verity, Fir, Gum, Howard Creek, FelixLithos, in press available, 64p.Canada, British Columbiacarbonatite - Blue River

Abstract: Apatites from the Verity, Fir, Gum, Howard Creek and Felix carbonatites of the Blue River (British Columbia, Canada) area have been investigated with respect to their paragenesis, cathodoluminescence, trace element and Sr–Nd isotopic composition. Although all of the Blue River carbonatites were emplaced as sills prior to amphibolite grade metamorphism and have undergone deformation, in many instances magmatic textures and mineralogy are retained. Attempts to constrain the U–Pb age of the carbonatites by SIMS, TIMS and LA–ICP-MS studies of zircon and titanite were inconclusive as all samples investigated have experienced significant Pb loss during metamorphism. The carbonatites are associated with undersaturated calcite–titanite amphibole nepheline syenite only at Howard Creek although most contain clasts of disaggregated phoscorite-like rocks. Apatite from each intrusion is characterized by distinct, but wide ranges, in trace element composition. The Sr and Nd isotopic compositions define an array on a 87Sr/86Sr vs²Nd diagram at 350 Ma indicating derivation from depleted sub-lithospheric mantle. This array could reflect mixing of Sr and Nd derived from HIMU and EM1 mantle sources, and implies that depleted mantle underlies the Canadian Cordillera. Although individual occurrences of carbonatites in the Blue River region are mineralogically and geochemically similar they are not identical and thus cannot be considered as rocks formed from a single batch of parental magma at the same stage of magmatic evolution. However, a common origin is highly probable. The variations in the trace element content and isotopic composition of apatite from each occurrence suggest that each carbonatite represents a combination of derivation of the parental magma(s) from mineralogically and isotopically heterogeneous depleted mantle sources coupled with different stages of limited differentiation and mixing of these magmas. We do not consider these carbonatites as primary direct partial melts of the sub-lithospheric mantle which have ascended from the asthenosphere without modification of their composition.
DS201706-1097
2017
Mitchell, R.H., Smith, D.L.Geology and mineralogy of the Ashram zone carbonatite, Eldor complex, Quebec.Ore Geology Reviews, in press availableCanada, Quebeccarbonatite

Abstract: The Ashram Zone, which is host to the Ashram Rare Earth Element (REE) Deposit, occurs within the Eldor Carbonatite Complex, Québec, Canada. The complex is located within the Paleoproterozoic New Québec Orogen (Labrador Trough), and has been subjected to greenschist metamorphism and folding during the Hudsonian Orogeny at 1.75 Ga. To date, consanguineous undersaturated alkaline rocks have not been recognized within or adjacent to the complex. It is evident that the bulk compositions of the rocks, essentially magnesiocarbonatites and ferrocarbonatites, do not represent those of liquid compositions, as many are complex breccias which have been subjected to later hydrothermal activity. The Ashram Zone is dominated by diverse textural varieties of carbonatite which include: fluorite-rich schlieren carbonatites; coarse-to-medium grained granular carbonatites; fine grained, commonly mosaic-textured, quartz-bearing carbonatites; and colloform carbonatites. Compositional and textural data are provided for the minerals present in the carbonatites. The major rock-forming minerals are diverse Ca-Mg-Fe carbonates, fluorite, and quartz. The carbonates range in their compositional evolution from rare dolomite through ferrodolomite and magnesian siderite to siderite. The principal REE-bearing minerals of the Ashram Deposit are monazite-(Ce) and monazite-(Nd), with lesser amounts of bastnaesite-(Ce) and bastnaesite-(Nd). The minor and accessory mineral suite is characterized by the presence of apatite, phlogopite, xenotime, diverse Sc- and sn-bearing Nb-Ti-minerals (niobian rutile, nioboaeschynite, samarskite), barite, sphalerite, several uncommon, but here relatively abundant, Ba- and Ba-Be minerals (bafertisite, magbasite, barylite, betrandite, sanbornite, cebaite), yangzhumingite, cassiterite, galena, pyrite, and rare magnetite and potassium feldspar. Pyrochlore is absent and the Nb-Ti oxide assemblage is similar to that found in NYF-pegmatites associated with F-rich, A-type granitoids. The mineralogy of the Ashram Deposit, compared to that of other carbonatites associated with undersaturated silicate rocks is unique, especially with respect to the abundance of fluorite and monazite (commonly with Nd-enrichment), Ba-Be-enrichment, the NYF-type Nb-Ti oxide assemblage (especially xenotime, Y-Nb-aeschynite, samarskite), phlogopite-potassium feldspar quartz-rich residua with granitoid characteristics, paucity of magnetite, pyrochlore, and Sr-bearing carbonates. The Ashram Deposit is considered to be a late-magmatic-to-hydrothermal F-REE magnesio-to-ferrocarbonatite derived from as yet unknown consanguineous antecedents.
DS201705-0856
2017
Mitchell, R.H., Welch, M.D., Chakhmouradian, A.R.Nomenclature of the perovskite supergroup: a heirarchical system of classification based on crystal structure and composition.Mineralogical Magazine, Vol. 81, 3, pp. 411-461.TechnologyPerovskite

Abstract: On the basis of extensive studies of synthetic perovskite-structured compounds it is possible to derive a hierarchy of hettotype structures which are derivatives of the arisotypic cubic perovskite structure (ABX3), exemplified by SrTiO3 (tausonite) or KMgF3 (parascandolaite) by: (1) tilting and distortion of the BX6 octahedra; (2) ordering of A- and B-site cations; (3) formation of A-, B- or X-site vacancies. This hierarchical scheme can be applied to some naturally-occurring oxides, fluorides, hydroxides, chlorides, arsenides, intermetallic compounds and silicates which adopt such derivative crystal structures. Application of this hierarchical scheme to naturally-occurring minerals results in the recognition of a perovskite supergroup which is divided into stoichiometric and non-stoichiometric perovskite groups, with both groups further divided into single ABX3 or double A2BB?X6 perovskites. Subgroups, and potential subgroups, of stoichiometric perovskites include: (1) silicate single perovskites of the bridgmanite subgroup; (2) oxide single perovskites of the perovskite subgroup (tausonite, perovskite, loparite, lueshite, isolueshite, lakargiite, megawite); (3) oxide single perovskites of the macedonite subgroup which exhibit second order Jahn-Teller distortions (macedonite, barioperovskite); (4) fluoride single perovskites of the neighborite subgroup (neighborite, parascandolaite); (5) chloride single perovskites of the chlorocalcite subgroup; (6) B-site cation ordered double fluoride perovskites of the cryolite subgroup (cryolite, elpasolite, simmonsite); (7) B-site cation ordered oxide double perovskites of the vapnikite subgroup [vapnikite, (?) latrappite]. Non-stoichiometric perovskites include: (1) A-site vacant double hydroxides, or hydroxide perovskites, belonging to the söhngeite, schoenfliesite and stottite subgroups; (2) Anion-deficient perovskites of the brownmillerite subgroup (srebrodolskite, shulamitite); (3) A-site vacant quadruple perovskites (skutterudite subgroup); (4) B-site vacant single perovskites of the oskarssonite subgroup [oskarssonite]; (5) B-site vacant inverse single perovskites of the cohenite and auricupride subgroups; (6) B-site vacant double perovskites of the diaboleite subgroup; (7) anion-deficient partly-inverse B-site quadruple perovskites of the hematophanite subgroup.
DS201708-1579
2017
Mitchell, R.H., Welch, M.D., Chakhmouradian, A.R.Nomenclature of the perovskite supergroup: a hierachial system of classification based on crystal structure composition.Mineralogical Magazine, Vol. 81, 3, pp. 411-416.Technologyperovskite

Abstract: On the basis of extensive studies of synthetic perovskite-structured compounds it is possible to derive a hierarchy of hettotype structures which are derivatives of the arisotypic cubic perovskite structure (ABX3), exemplified by SrTiO3 (tausonite) or KMgF3 (parascandolaite) by: (1) tilting and distortion of the BX6 octahedra; (2) ordering of A- and B-site cations; (3) formation of A-, B- or X-site vacancies. This hierarchical scheme can be applied to some naturally-occurring oxides, fluorides, hydroxides, chlorides, arsenides, intermetallic compounds and silicates which adopt such derivative crystal structures. Application of this hierarchical scheme to naturally-occurring minerals results in the recognition of a perovskite supergroup which is divided into stoichiometric and non-stoichiometric perovskite groups, with both groups further divided into single ABX3 or double A2BB?X6 perovskites. Subgroups, and potential subgroups, of stoichiometric perovskites include: (1) silicate single perovskites of the bridgmanite subgroup; (2) oxide single perovskites of the perovskite subgroup (tausonite, perovskite, loparite, lueshite, isolueshite, lakargiite, megawite); (3) oxide single perovskites of the macedonite subgroup which exhibit second order Jahn-Teller distortions (macedonite, barioperovskite); (4) fluoride single perovskites of the neighborite subgroup (neighborite, parascandolaite); (5) chloride single perovskites of the chlorocalcite subgroup; (6) B-site cation ordered double fluoride perovskites of the cryolite subgroup (cryolite, elpasolite, simmonsite); (7) B-site cation ordered oxide double perovskites of the vapnikite subgroup [vapnikite, (?) latrappite]. Non-stoichiometric perovskites include: (1) A-site vacant double hydroxides, or hydroxide perovskites, belonging to the söhngeite, schoenfliesite and stottite subgroups; (2) Anion-deficient perovskites of the brownmillerite subgroup (srebrodolskite, shulamitite); (3) A-site vacant quadruple perovskites (skutterudite subgroup); (4) B-site vacant single perovskites of the oskarssonite subgroup [oskarssonite]; (5) B-site vacant inverse single perovskites of the cohenite and auricupride subgroups; (6) B-site vacant double perovskites of the diaboleite subgroup; (7) anion-deficient partly-inverse B-site quadruple perovskites of the hematophanite subgroup.
DS201705-0857
2017
Mitton, S.Carbon from crust to core: a history of deep carbon science. Preparation for book in 2019 Cambridge PressEuropean Geosciences Union General Assembly 2017, Vienna April 23-28, 1p. 10193 AbstractTechnologyBook - carbon

Abstract: As an academic historian of science, I am writing a history of the discovery of the interior workings of our dynamic planet. I am preparing a book, titled Carbon from Crust to Core: A Chronicle of Deep Carbon Science, in which I will present the first history of deep carbon science. I will identify and document key discoveries, the impact of new knowledge, and the roles of deep carbon scientists and their institutions from the 1400s to the present. This innovative book will set down the engaging human story of many remarkable scientists from whom we have learned about Earth's interior, and particularly the fascinating story of carbon in Earth. I will describe a great journey of discovery that has led to a better understanding of the physical, chemical, and biological behaviour of carbon in the vast majority of Earth's interior. My poster has a list of remarkable Deep Carbon Explorers, from Georgius Agricola (1494-1555) to Claude ZoBell (1904-1989). Come along to my poster and add to my compilation: choose pioneers from history, or nominate your colleagues, or even add a selfie! As a biographer, I am keen to add researchers who may have been overlooked in the standard histories of geology and geophysics. And I am always on the lookout for standout stories and personal recollections. I am equipped to do oral history interviews. What's your story? Cambridge University Press will publish the book in 2019.
DS201710-2249
2017
Mjumder, S., Hirschmann, M.M.The origin of volatiles in the Earth's mantle.Geochemistry, Geophysics, Geosystems, Vol. 18, 8, pp. 3078-3092.Mantlevolatiles

Abstract: The Earth's deep interior contains significant reservoirs of volatiles such as H, C, and N. Due to the incompatible nature of these volatile species, it has been difficult to reconcile their storage in the residual mantle immediately following crystallization of the terrestrial magma ocean (MO). As the magma ocean freezes, it is commonly assumed that very small amounts of melt are retained in the residual mantle, limiting the trapped volatile concentration in the primordial mantle. In this article, we show that inefficient melt drainage out of the freezing front can retain large amounts of volatiles hosted in the trapped melt in the residual mantle while creating a thick early atmosphere. Using a two-phase flow model, we demonstrate that compaction within the moving freezing front is inefficient over time scales characteristic of magma ocean solidification. We employ a scaling relation between the trapped melt fraction, the rate of compaction, and the rate of freezing in our magma ocean evolution model. For cosmochemically plausible fractions of volatiles delivered during the later stages of accretion, our calculations suggest that up to 77% of total H2O and 12% of CO2 could have been trapped in the mantle during magma ocean crystallization. The assumption of a constant trapped melt fraction underestimates the mass of volatiles in the residual mantle by more than an order of magnitude.
DS201708-1717
2017
Mkonto, S.Applied geological techniques for the evaluation of kimberlitic tailings mineral resources: the case of Orapa and Letlhakane mines, Botswana11th. International Kimberlite Conference, PosterAfrica, Botswanadeposit - Orapa, Letlhakane
DS201710-2250
2017
Mmualefe, M.K.Desert Gems: Botswana's major mines. Jwaneng diamond mine, Botswana: history, geology and mining.11th International Kimberlite Field Trip Guide, Sept. 31p.Africa, Botswanadeposit - Jwaneng
DS201705-0858
2017
Moe, K., Yang, J-S., Johnson, P., Wang, W.Spectroscopic analysis of microdiamonds in ophiolitic chromitite and peridotite.Lithosphere, 9p.Asia, Tibet, Russia, UralsMicrodiamonds

Abstract: Microdiamonds ?200 ?m in size, occurring in ophiolitic chromitites and peridotites, have been reported in recent years. Owing to their unusual geological formation, there are several debates about their origin. We studied 30 microdiamonds from 3 sources: (1) chromitite ore in Luobusa, Tibet; (2) peridotite in Luobusa, Tibet; and (3) chromitite ore in Ray-Iz, polar Ural Mountains, Russia. They are translucent, yellow to greenish-yellow diamonds with a cubo-octahedral polycrystalline or single crystal with partial cubo-octahedral form. Infrared (IR) spectra revealed that these diamonds are type Ib (i.e., diamonds containing neutrally charged single substitutional nitrogen atoms, Ns0, known as the C center) with unknown broad bands observed in the one-phonon region. They contain fluid inclusions, such as water, carbonates, silicates, hydrocarbons, and solid CO2. We also identified additional microinclusions, such as chromite, magnetite, feldspar (albite), moissanite, hematite, and magnesiochromite, using a Raman microscope. Photoluminescence (PL) spectra measured at liquid nitrogen temperature suggest that these diamonds contain nitrogen-vacancy, nickel, and H2 center defects. We compare them with high-pressure-high-temperature (HPHT) synthetic industrial diamond grits. Although there are similarities between microdiamonds and HPHT synthetic diamonds, major differences in the IR, Raman, and PL spectra confirm that these microdiamonds are of natural origin. Spectral characteristics suggest that their geological formation is different but unique compared to that of natural gem-quality diamonds. Although these microdiamonds are not commercially important, they are geologically important in that they provide an understanding of a new diamond genesis.
DS201708-1718
2017
Mohapi. M.Letseng diamond mine, Lesotho: recent advances in open pit geology and the Main kimberlite pipe.11th. International Kimberlite Conference, PosterAfrica, Lesothodeposit - Letseng
DS201709-2034
2017
Mollex, G., France, L., Furi, E., Bonnet, R., Botcharnikov, R.E., Zimmermann, L., Wilke, S., Deloule, E., Chazot, G., Kazimoto. E.O., Marty, B., Burnard, P.The Oldoinyo Lengai volcano plumbing system architecture, and composition from source to surface.Goldschmidt Conference, abstract 1p.Africa, Tanzaniadeposit, Oldoinyo

Abstract: Cognate xenoliths that have been emitted during the last sub-plinian eruption in 2007-08 at Oldoinyo Lengai (OL) represent a unique opportunity to document the igneous processes occuring within the active magma chamber. Detailed petrographic descriptions coupled to a thermobarometric approach, and to the determination of volatile solubility models, allow us to identify the melt evolution at magma chamber conditions, and the storage parameters (P, T). Results indicate that a fresh phonolite melt (~1060°C) was injected into a crustal magma chamber at 11.5 ±3.5 km depth, in agreement with geophysical surveys performed during the eruption. The phonolite contains high volatile contents: 3.2 wt.% H2O and 1.4 wt.% CO2. The liquid line of descent highlights an evolution to nephelinite compositions by cooling down to 880°C. Our results support previous results related to this eruption, and are similar to the historical products emitted during the whole volcano history, allowing us to suggest that no major modification in the plumbing system has occured during the OL evolution. New noble gas results show that: i. fumaroles display constant He isotopic signature since 1988; ii. Cognate xenoliths documenting the active magma chamber and fumaroles display similar He isotopic values (6.58±0.46RA, and 7.31±0.40RA, respectively); iii. OL He isotopic composition is similar to that of other silicate volcanoes of the Arusha region, and comparable to the typical subcontinental lithospheric mantle (SCLM) range (5.2 to 7.0 RA); iv. Ne isotopic ratio of OL is following the MORB signature. Those results are interpreted as showing that 1/ no major modification in the hydrothermal system architecture has occured since 1988 despite major modification of the summit crater morphology, 2/ no contamination by either the atmospheric gases, or crustal material assimilation has occured between the magma chamber and the surface, and 3/ the source of OL and of the other silicate volcanoes in the Arusha region is a SCLM metasomatized by asthenospheric fluids.
DS201706-1098
2017
Moore, A.E.Quantitative modelling of the apparent decoupling of Mg# and Ni in kimberlitic olivine margins: comment on Cordier et al. Journal of Petrology, 56, pp. 1775-1796.Journal of Petrology, Vol. 58, pp. 1-6.GlobalOlivine
DS201712-2707
2017
Moore, R., Hrkac, C., Nelson, L.Kennady North project 2017 field season update.45th. Annual Yellowknife Geoscience Forum, p. 52 abstractCanada, Northwest Territoriesdeposit - Kennady North
DS201702-0229
2016
Moore, T.P.Moore's Compendium of mineral discoveries, 1960-2015.Mineralogical Record, 2 Volumes 809;813pp., approx $400.00 USTechnologyBook - mineral discoveries

Abstract: It is no exaggeration to say that Moore’s Compendium of Mineral Discoveries 1960-2015 is the most important publication for mineral collectors since Dana’s System of Mineralogy. Think of it as a "What’s New in Minerals" covering the last 55 years, which has truly been a Golden Age of mineral collecting. Detailed information on mineral specimen discoveries made worldwide since 1960 has been gleaned from every major mineral collector magazine in English, German, French, Spanish and Italian, as well as books, mineral dealer catalogs and unpublished manuscripts - all meticulously referenced. The vast majority of the publications have never been indexed and are not available online, so this information has been inaccessible to all collectors lacking a personal library of such journals and the ability to read five languages. The description of each occurrence covers as many aspects as possible, beginning with the general appearance and style of specimens; the sizes, morphologies and habits of major crystals; associated species; geological settings; the histories of the localities; the circumstances of the discoveries, including the names of collectors; interesting or amusing collecting stories; marketing information (i.e. where, when and how specimens have been offered for sale); and whatever else may seem in some way noteworthy.
DS201709-2035
2017
Morrison, S.M., Liu, C., Prabhu, E.A., Li, C., Downs, R.J., Golden, J.J., Fox, P., Hummer, D.R., Meyer, M.B., Hazen, R.M.Network analysis of mineralogical systems.American Mineralogist, in press availableTechnologydata sets

Abstract: A fundamental goal of mineralogy and petrology is the deep understanding of mineral phase relationships and the consequent spatial and temporal patterns of mineral coexistence in rocks, ore bodies, sediments, meteorites, and other natural polycrystalline materials. The multi-dimensional chemical complexity of such mineral assemblages has traditionally led to experimental and theoretical consideration of 2-, 3-, or n-component systems that represent simplified approximations of natural systems. Network analysis provides a dynamic, quantitative, and predictive visualization framework for employing “big data” to explore complex and otherwise hidden higher-dimensional patterns of diversity and distribution in such mineral systems. We introduce and explore applications of mineral network analysis, in which mineral species are represented by nodes, while coexistence of minerals is indicated by lines between nodes. This approach provides a dynamic visualization platform for higher-dimensional analysis of phase relationships, because topologies of equilibrium phase assemblages and pathways of mineral reaction series are embedded within the networks. Mineral networks also facilitate quantitative comparison of lithologies from different planets and moons, the analysis of coexistence patterns simultaneously among hundreds of mineral species and their localities, the exploration of varied paragenetic modes of mineral groups, and investigation of changing patterns of mineral occurrence through deep time. Mineral network analysis, furthermore, represents an effective visual approach to teaching and learning in mineralogy and petrology.
DS201708-1719
2017
Moss, S.Kimberlite emplacement and mantle sampling through time at A154N kimberlite volcano, Diavik diamond mine.11th. International Kimberlite Conference, OralCanada, Northwest TerritoriesDeposit - A154N
DS201708-1720
2017
Motsamai, T.Mineral inclusions in diamonds from Karowe mine, Botswana: examining the mantle sources of a diamond population containing exceptionally large crystals.11th. International Kimberlite Conference, OralAfrica, Botswanadeposit - Karowe
DS201709-2036
2017
Moyen, J-F., Paquette, J-L., Ionov, D.A., Korsakova, A.V., Golovina, A.V., Moine, B.N.Archean lithosphere: evidence from U-Pb zircon dating in crustal xenoliths at Udachanay, Siberian craton.Goldschmidt Conference, abstract 1p.Russiadeposit, Udachnaya

Abstract: Cratons represent the oldest preserved lithospheric domains. Their lithosphere (lithospheric mantle welded to overlying Precambrian crystalline basement) is considered to be particularly robust and long living due to the protecting presence of buoyant and rigid “keels” made up of residual harzburgites. In this study, we report new U—Pb zircon ages on crustal xenoliths from the Udachnaya kimberlite in the Siberian craton; this dataset includes samples from both the upper and lower portions of the crust. The zircon ages agree well with model melt-extraction Re-Os ages on refractory peridotite xenoliths from the same pipe; taken together they allow an integrated view of lithosphere formation. Our data reveal that the present day upper crust is Archaean, whereas both the lower crust and the lithospheric mantle yield Palaeoproterozoic ages. Consequently, the deep lithosphere beneath the Siberian craton was not formed in a single time, but grew in two distinct events, one in the late Archean and the other in the Palaeoproterozoic. We propose a two-stage scenario for the formation of the Siberian craton involving delamination and rejuvenation of the Archean lower lithosphere (lower crust and lithospheric mantle) in the Palaeoproterozoic. This demonstrates that craton formation can be a protracted, multi-stage process, and that the present day crust and mantle do not represent complementary reservoirs formed through the same episode.
DS201709-2037
2017
Moyen, J-F., Paquette, J-L., Ionov, D.A., Korsakova, A.V., Golovina, A.V., Moine, B.N.Paleoproterozoic rejuvenation of an Archean lithosphere: evidence from U-Pb zircon dating in crustal xenoliths at Udachanaya, Siberian craton.Goldschmidt Conference, abstract 1p.Russia, Siberiadeposit, Udachnaya

Abstract: Cratons represent the oldest preserved lithospheric domains. Their lithosphere (lithospheric mantle welded to overlying Precambrian crystalline basement) is considered to be particularly robust and long-lived due to the protecting presence of buoyant and rigid “keels” made up of residual harzburgites. Although the cratons are mostly assumed to form in the Archaean, the timing of their formation remains poorly constrained. In particular, there are very few datasets describing concurrently the age of both the crustal and mantle portions of the lithosphere. In this study, we report new U–Pb ages and Hf isotope compositions for zircons in crustal xenoliths from the Udachnaya kimberlite in the central Siberian craton; this dataset includes samples from both the upper and lower portions of the crust. The zircon ages agree well with model melt-extraction Re–Os ages on refractory peridotite xenoliths from the same pipe; taken together they allow an integrated view of lithosphere formation. Our data reveal that the present day upper crust is Archaean, whereas both the lower crust and the lithospheric mantle yield Paleoproterozoic ages. We infer that the deep lithosphere beneath the Siberian craton was not formed in a single Archaean event, but grew in at least two distinct events, one in the late Archaean and the other in the Paleoproterozoic. Importantly, a complete or large-scale delamination and rejuvenation of the Archaean lower lithosphere (lower crust and lithospheric mantle) took place in the Paleoproterozoic. This further demonstrates that craton formation can be a protracted, multi-stage process, and that the present day crust and mantle may not represent complementary reservoirs formed through the same tectono-magmatic event. Further, deep cratonic lithosphere may be less robust and long living than often assumed, with rejuvenation and replacement events throughout its history.
DS201710-2251
2015
Muniswamy, M.Tectonic setting and structural controls on kimberlite magmatism in Brazil.Thesis, Phd. Universidade Estadual de Campinas ** in PORT, 179p. PdfSouth America, Brazil, Minas Gerais, Rondonia, Mato GrossoMagmatism
DS201703-0427
2017
Myhill, R., Frost, D.J., Novella, D.Hydrous melting and partitioning in and above the mantle transition zone: insights from water-rich MgO SiO2 H2O experiments.Geochimica et Cosmochimica Acta, Vol. 200, pp. 408-421.MantleMelting

Abstract: Hydrous melting at high pressures affects the physical properties, dynamics and chemical differentiation of the Earth. However, probing the compositions of hydrous melts at the conditions of the deeper mantle such as the transition zone has traditionally been challenging. In this study, we conducted high pressure multianvil experiments at 13 GPa between 1200 and 1900 °C to investigate the liquidus in the system MgO-SiO2-H2O. Water-rich starting compositions were created using platinic acid (H2Pt(OH)6) as a novel water source. As MgO:SiO2 ratios decrease, the T-XH2OT-XH2O liquidus curve develops an increasingly pronounced concave-up topology. The melting point reduction of enstatite and stishovite at low water contents exceeds that predicted by simple ideal models of hydrogen speciation. We discuss the implications of these results with respect to the behaviour of melts in the deep upper mantle and transition zone, and present new models describing the partitioning of water between the olivine polymorphs and associated hydrous melts.
DS201704-0641
2017
Nakagawa, T., Spiegelman, M.W.Global scale water circulation in the Earth's mantle: implications for the mantle water budget in the early Earth.Earth and Planetary Science Letters, Vol. 464, pp. 189-199.MantleWater

Abstract: We investigate the influence of the mantle water content in the early Earth on that in the present mantle using numerical convection simulations that include three processes for redistribution of water: dehydration, partitioning of water into partially molten mantle, and regassing assuming an infinite water reservoir at the surface. These models suggest that the water content of the present mantle is insensitive to that of the early Earth. The initial water stored during planetary formation is regulated up to 1.2 OMs (OM = Ocean Mass; 1.4×1021 kg1.4×1021 kg), which is reasonable for early Earth. However, the mantle water content is sensitive to the rheological dependence on the water content and can range from 1.2 to 3 OMs at the present day. To explain the evolution of mantle water content, we computed water fluxes due to subducting plates (regassing), degassing and dehydration. For weakly water dependent viscosity, the net water flux is almost balanced with those three fluxes but, for strongly water dependent viscosity, the regassing dominates the water cycle system because the surface plate activity is more vigorous. The increased convection is due to enhanced lubrication of the plates caused by a weak hydrous crust for strongly water dependent viscosity. The degassing history is insensitive to the initial water content of the early Earth as well as rheological strength. The degassing flux from Earth's surface is calculated to be approximately O(1013) kg/yrO(1013) kg/yr, consistent with a coupled model of climate evolution and mantle thermal evolution.
DS201701-0023
2016
NanodiamondsHow these microscopic diamonds are going to shape the future.Google GIZMODO and nanodiamonds, 10p. OverviewTechnologyNanodiamonds
DS201712-2708
2017
Nascimento, D.B., Schmitt, R.S., Ribeiro, A., Trouw, R.A.J., Paschier, C.W., Basei, M.A.S.Depositional ages and provenance of the Neoproterozoic Damara Supergroup ( Northwest Namibia): implications for the Angola-Congo and Kalahari cratons connection.Gondwana Research, Vol. 52, pp. 153-171.Africa, Namibiacraton

Abstract: The Damara Orogen is composed of the Damara, Kaoko and Gariep belts developed during the Neoproterozoic Pan-African Orogeny. The Damara Belt contains Neoproterozoic siliciclastic and carbonate successions of the Damara Supergroup that record rift to proto-ocean depositional phases during the Rodinia supercontinent break up. There are two conflicting interpretations of the geotectonic framework of the Damara Supergroup basin: i) as one major basin, composed of the Outjo and Khomas basins, related to rifting in the Angola-Congo-Kalahari paleocontinent or, ii) as two independent passive margin basins, one related to the Angola-Congo and the other to the Kalahari proto-cratons. Detrital zircon provenance studies linked to field geology were used to solve this controversy. U-Pb zircon age data were analyzed in order to characterize depositional ages and provenance of the sediments and evolution of the succession in the northern part of the Outjo Basin. The basal Nabis Formation (Nosib Group) and the base of the Chuos Formation were deposited between ca. 870 Ma and 760 Ma. The upper Chuos, Berg Aukas, Gauss, Auros and lower Brak River formations formed between ca. 760 Ma and 635 Ma. It also includes the time span recorded by the unconformity between the Auros and lower Brak River formations. The Ghaub, upper Brak River, Karibib and Kuiseb formations were deposited between 663 Ma and 590 Ma. The geochronological data indicate that the main source areas are related to: i) the Angola-Congo Craton, ii) rift-related intrabasinal igneous rocks of the Naauwpoort Formation, iii) an intrabasinal basement structural high (Abbabis High), and iv) the Coastal Terrane of the Kaoko Belt. The Kalahari Craton units apparently did not constitute a main source area for the studied succession. This is possibly due to the position of the succession in the northern part of the Outjo Basin, at the southern margin of the Congo Craton. Comparison of the obtained geochronological data with those from the literature shows that the Abbabis High forms part of the Kalahari proto-craton and that Angola-Congo and Kalahari cratons were part of the same paleocontinent in Rodinia times.
DS201709-2038
2017
Nasdala, L., Broska, I., Harlov, D.E., Macdonald, R.Recent progress in the study of accessory minerals. Outline of special volume.Mineralogy and Petrology, Vol. 111, 4, pp. 431-433.Technologymineralogy

Abstract: Accessory minerals are a common species in igneous and metamorphic rocks that are not considered characteristic of the host rock and hence do not affect its root name. Accessories tend to be complex in terms of their chemical and isotopic composition and their structural state. In spite of not being major rock constituents, they are, however, of enormous petrologic interest as they contain a record of the formation and post-formation history of their host rock. The study of accessory minerals hence has increased continuously during the past years, and still increases (Fig. 1). Recent progress is driven by new analytical opportunities of (in situ) micro-techniques. More and more the internal textures, that is, elemental, isotopic, and/or structural distribution patterns within individual grains, have come into the focus of researchers; a few examples are compiled in Fig. 2.
DS201705-0859
2017
Nature GeoscienceTo probe a core. Psyche spacecraft could bring a close-up view.Nature Geoscience, Vol. 10, p. 241.MantleGeodynamics
DS201708-1721
2017
Navon, O.Solid molecular nitrogen (N2) inclusions in Juin a diamonds: exsolution at the base of the transition zone.11th. International Kimberlite Conference, OralSouth America, Brazildeposit - Juina

Abstract: Diamonds originating from the transition zone or lower mantle were previously identified based on the chemistry of their silicate or oxide mineral inclusions. Here we present data for such a super-deep origin based on the internal pressure of nitrogen in sub-micrometer inclusions in diamonds from Juina, Brazil. Infrared spectroscopy of four diamonds, rich in such inclusions revealed high concentrations of fully aggregated nitrogen (average of 900 ppm, all in B centers) and almost no platelets. Raman spectroscopy indicated the presence of solid, cubic ?-N2 at 10.9±0.2 GPa (corresponding to a density of 1900 kg/m3). Transmission electron microscopy of two diamonds found two generations of octahedral inclusions: microinclusions (average size: 150 nm, average concentration: 100 ppm) and nanoinclusions (20–30 nm, 350 ppm). EELS detected nitrogen and a diffraction pattern of one nanoinclusion yielded a tetragonal phase, which resembles ?-N2 with a density of 1400 kg/m3 (internal pressure = 2.7 GPa). We also observed up-warping of small areas (?150 nm in size) on the polished surface of one diamond. The ?2 nm rise can be explained by a shallow subsurface microinclusion, pressurized internally to more than 10 GPa. Using available equations of state for nitrogen and diamond, we calculated the pressures and temperatures of mechanical equilibrium of the inclusions and their diamond host at the mantle geotherm. The inclusions originated at the deepest part of the transition zone at pressures of ?22 GPa (630 km) and temperatures of ?1640?°C. We suggest that both generations are the result of exsolution of nitrogen from B centers and that growth took a few million years in a subducting mantle current. The microinclusions nucleated first, followed by the nanoinclusions. Shortly after the exsolution events, the diamonds were trapped in a plume or an ascending melt and were transported to the base of the lithosphere and later to the surface.
DS201708-1722
2017
Navon, O.The chemical and isotopic composition of Diavik fibrous diamonds and their microinclusions.11th. International Kimberlite Conference, PosterCanada, Northwest Territoriesdeposit - Diavik
DS201704-0642
2017
Navon, O., Wirth, R., Schmidt, C., Matat Jabion, B., Schreiber, A., Emmanuel, S.Solid molecular nitrogen ( delta -N2) inclusions in Juin a diamonds: exsolution at the base of the transition zone.Earth and Planetary Science Letters, Vol. 464, pp. 237-247.South America, BrazilDeposit - Juina
DS201707-1352
2017
Nayak, B., Meyer, F.M.Manganilmenite in the magnetite ore body from Pokphur area of Nagaland, north east India and the possibility of microdiamonds in the ophiolites of Indo-Myanmar rangens.Current Science, Vol. 112, 1, pp. 155-160.Indiamineralogy

Abstract: Manganilmenite is found to be associated with the magnetite ore body of Pokphur area in the Nagaland ophiolites, North East India. There is perhaps no earlier description of the mineral from the Indian subcontinent. It occurs as an accessory mineral with magnetite and Fe-chlorite (chamosite). Electron probe micro-analytical data reveal that the mineral contains 5.6–8.5 wt% MnO and traces of MgO, ZnO and Cr2O3, while the TiO2 content remains within narrow limits of 50–53 wt%. The calculated pyrophanite end-member varies from 13% to 18%. Although the magnetite body of Pokphur has been reasonably proved to be a hydrothermally altered product of basic and ultrabasic igneous rocks, and most of the minerals in the magnetite body are supergene in nature, different end-member compositions of mangan–ilmenite indicate that it has originally crystallized with the basic suite of rocks and has survived the alteration process with only marginal effects. Since manganilmenite has been considered as a diamond indicator mineral and ophiolites are a newly documented host of microdiamonds elsewhere in the world, the presence of manganilmenite in the Pokphur magnetite hints towards occurrence of microdiamonds in the ophiolite suite of rocks of the Indo-Myanmar ranges.
DS201705-0860
2017
Nedelec, A., Monnereau, M., Toplis, M.J.The Hadean-Archean transition at 4Ga: from magma trapping in the mantle to volcanic resurfacing of the Earth.Terra Nova, in press availableMantleMagmatism

Abstract: The Hadean-Archaean transition is poorly known because of the dearth of Hadean rocks. A new conceptual model is presented based on variations in mantle potential temperature (Tp) with time. The critical issue is the depth of melting with respect to a negatively buoyant magma sink between 410 and 330 km (14-11 GPa). Hadean plume magmatism begins below the magma sink, leading to generation of a refractory upper mantle reservoir and the minor production of boninite-like magmas near the surface. With cooling, the onset of melting migrates above the magma sink, a situation likely occurring since 3.9 Ga and corresponding to Tps of ~1870°C or less. Therefore, a burst of mafic to ultramafic volcanism was produced at 3.9-3.8 Ga. This extensive volcanism may have triggered gravitational instabilities and favoured the recycling of the Hadean crust into the mantle. Results of this model are discussed in the light of existing isotopic data.
DS201708-1723
2017
Nelson, L.The geology of the Faraday 1 kimberlite, NWT, Canada.11th. International Kimberlite Conference, PosterCanada, Northwest Territoriesdeposit - Faraday 1
DS201708-1724
2017
Nelson, L.The geology of the Faraday 2 kimberlite, NWT, Canada.11th. International Kimberlite Conference, PosterCanada, Northwest Territoriesdeposit - Faraday 2
DS201712-2709
2017
Nelson, L., Hetman, C.M., Diering, M.The geology of the Faraday 2 kimberlite pipe, Northwest Territories.45th. Annual Yellowknife Geoscience Forum, p. 106 abstract posterCanada, Northwest Territoriesdeposit - Faraday 2
DS201712-2710
2017
Nesbitt, H.W., Cormack, A.N., Henderson, G.S.Defect contributions to the heat capacities and stabilities of some chain, ring, and sheet silicates, with implications for mantle minerals.American Mineralogist, Vol. 102, pp. 2220-2229.Mantlemineralogy

Abstract: At temperatures less than ~1500 K, previously published CP data demonstrate that the heat capacities of orthoenstatite, proto-enstatite, diopside, and pseudowollastonite include primarily Debye type vibrational and anharmonic contributions, whereas the alkali chain, sheet, and ring silicates, Na2SiO3, Li2SiO3, K2SiO3, and Na2Si2O5 include a third contribution. The third contribution to CP arises from defect formation due to the mobility Na, K, Li, and O2-. The contribution becomes apparent at temperatures above 700-800 K for Na and K silicates, and above 900-1000 K for Li metasilicate. With strong thermal agitation, alkali-non-bridging oxygen (NBO) bonds are ruptured with the cations exiting their structural sites to occupy interstitial sites, thereby producing intrinsic Frenkel defects, which contribute to the CP of the alkali silicates. The magnitudes of the CP defect contributions correlate inversely with cation-oxygen bond strengths, as measured by bond dissociation energies. K-O and Na-O bond strengths are weak (239 and 257 kJ/mol) and defect contributions are large for these alkali chain, ring, and sheet silicates. The greater bond strength of Li-O (341 kJ/mol) correlates with a weaker defect contribution to the CP of Li2SiO3. Mg-O and Ca-O bonds are stronger still (394 and 464 kJ/mol) and no CP defect contributions are observed for the pyroxenes and pseudowollastonite up to ~1500 K. Above ~800 K a polymerization reaction occurs in Na2SiO3, which produces some Q3 species and free oxygen (O2- or oxide ion). The polymerization reaction annihilates an oxygen structural site so that the O2- produced must reside on non-structural sites thus producing intrinsic anionic defects. The same reactions likely occur in Na2Si2O5 and K2SiO3. Raman spectra of Na2SiO3 indicate >10% of Na+ and ~1.7% of O2- on interstitial sites at 1348 K. Ca- and Mg-bearing mantle minerals subjected to temperature greater than ~1500 K experience the destabilizing effects of disordering (Frenkel defect formation). The minerals may respond either by changing their composition or by changing phase. An abundance of Ca and Na defects in pyroxenes, for example, likely promotes production of new components (e.g., CaAl2SiO6, NaAlSi2O6) in pyroxenes. By their production, Ca and Na defect concentrations are reduced thereby stabilizing the phases. Mg-O bond dissociation and production of intrinsic Mg2+ and O2- point defects within olivine likely destabilize it and promote the phase transition to wadsleyite at the base of the upper mantle.
DS201712-2711
2016
Nestola, F., Burnham, A.D., Peruzzo, L., Tauro, L., Alvaro, M., Walter, M.J., Gunter, M., Anzolini, C., Kohn, S.C.Tetragonal almandine-pyrope phase, TAPP: finally a name for it, the new name jeffbenite.Mineralogical Magazine, Vol. 80, pp. 1219-1232.Technologypyrope

Abstract: Jeffbenite, ideally Mg3Al2Si3O8, previously known as tetragonal-almandine-pyrope-phase (‘TAPP’), has been characterized as a new mineral from an inclusion in an alluvial diamond from São Luiz river, Juina district of Mato Grosso, Brazil. Its density is 3.576 g/cm3 and its microhardness is ?7. Jeffbenite is uniaxial (-) with refractive indexes ??=?1.733(5) and ??=?1.721(5). The crystals are in general transparent emerald green. Its approximate chemical formula is (Mg2.62Fe2+0.27)(Al1.86Cr0.16)(Si2.82Al0.18)O12 with very minor amounts of Mn, Na and Ca. Laser ablation ICP-MS showed that jeffbenite has a very low concentration of trace elements. Jeffbenite is tetragonal with space group I4¯2d, cell edges being a?=?6.5231(1) and c?=?18.1756(3) Å. The main diffraction lines of the powder diagram are [d (in Å), intensity, hkl]: 2.647, 100, 2 0 4; 1.625, 44, 3 2 5; 2.881, 24, 2 1 1; 2.220, 19, 2 0 6; 1.390, 13, 4 2 4; 3.069, 11, 2 0 2; 2.056, 11, 2 2 4; 1.372, 11, 2 0 12. The structural formula of jeffbenite can be written as (M1)(M2)2(M3)2(T1)(T2)2O12 with M1 dominated by Mg, M2 dominated by Al, M3 dominated again by Mg and both T1 and T2 almost fully occupied by Si. The two tetrahedra do not share any oxygen with each other (i.e. jeffbenite is classified as an orthosilicate). Jeffbenite was approved as a new mineral by the IMA Commission on New Minerals and Mineral Names with the code IMA 2014-097. Its name is after Jeffrey W. Harris and Ben Harte, two world-leading scientists in diamond research. The petrological importance of jeffbenite is related to its very deep origin, which may allow its use as a pressure marker for detecting super-deep diamonds. Previous experimental work carried out on a Ti-rich jeffbenite establishes that it can be formed at 13 GPa and 1700 K as maximum P-T conditions.
DS201705-0861
2017
Nestola, F., Cerantola, V., Milani, S., Anzolini, C., McCammon, C., Novella, D., Kupenko, I., Chumakov, A., Rueffer, R., Harris, J.W.Synchroton Mossabauer source technique for in situ measurement of iron bearing inclusions in natural diamonds.European Geosciences Union General Assembly 2017, Vienna April 23-28, 1p. 16340 AbstractSouth America, BrazilDeposit - Juina

Abstract: We describe a new methodology to collect energy domain Mössbauer spectra of inclusions in natural diamonds using a Synchrotron Mössbauer Source (SMS). Measurements were carried out at the Nuclear Resonance beamline ID18 at the European Synchrotron Radiation Facility (Grenoble, France). We applied this non-destructive approach to collect SMS spectra of a ferropericlase inclusion still contained within its diamond host from Juina (Brazil). The high spatial resolution of the measurement (~ 15 ?m) enabled multiple regions of the 190 × 105 ?m2 inclusion to be sampled and showed that while Fe3 +/Fetot values in ferropericlase were below the detection limit (0.02) overall, there was a magnetic component whose abundance varied systematically across the inclusion. Hyperfine parameters of the magnetic component are consistent with magnesioferrite, and the absence of superparamagnetism allows the minimum particle size to be estimated as ~ 30 nm. Bulk Fe3 +/Fetot values are similar to those reported for other ferropericlase inclusions from Juina, and their variation across the inclusion can provide constraints on its history.
DS201712-2712
2017
Nestola, F., Haemyeong, J.H., Taylor, L.A.Mineral inclusions in diamonds may be synchronous but not syngenetic.Nature Communications, Vol. 8, # 14168Technologydiamond inclusions

Abstract: It is widely assumed that mineral inclusions and their host diamonds are ‘syngenetic’ in origin, which means that they formed simultaneously and from the same chemical processes. Mineral inclusions that, instead, were formed earlier with respect to diamonds are termed protogenetic. However, minerals can have the same age as the diamonds in that they become enclosed in and isolated from any further isotopic exchange. But this is termed ‘synchronous’ not ‘syngenetic’. Here we demonstrate conclusively the protogenesis of inclusions in diamonds, based upon data from an exceptional fragment of a diamond-bearing peridotite, its clinopyroxene and a gem-quality diamond. Clinopyroxenes in the xenolith had the same chemistry and crystallographic orientation as those for inclusions in the diamond. With our results with garnets, olivines and sulfides, we can state that a major portion of the mineral inclusions in non-coated, monocrystalline-lithospheric diamonds are protogenetic. Our discovery here presented has implications for all genetic aspects of diamond growth, including their ages.
DS201712-2713
2017
Nicoli, G., Thomassot, E., Schannor, M., Vezinet, A., Jovovic, I.Constraining a Precambrian Wilson Cycle lifespan: an example from the ca. 1.8Ga Nagssugtoqidian Orogen, southeastern Greenland.Lithos, in press available 68p.Europe, GreenlandWilson cycle

Abstract: In the Phanerozoic, plate tectonic processes involve the fragmentation of the continental mass, extension and spreading of oceanic domains, subduction of the oceanic lithosphere and lateral shortening that culminate with continental collision (i.e. Wilson cycle). Unlike modern orogenic settings and despite the collection of evidence in the geological record, we lack information to identify such a sequence of events in the Precambrian. This is why it is particularly difficult to track plate tectonics back to 2.0 Ga and beyond. In this study, we aim to show that a multidisciplinary approach on a selected set of samples from a given orogeny can be used to place constraints on crustal evolution within a P-T-t-d-X space. We combine field geology, petrological observations, thermodynamic modelling (Theriak-Domino) and radiogenic (U-Pb, Lu-Hf) and stable isotopes (?18O) to quantify the duration of the different steps of a Wilson cycle. For the purpose of this study, we focus on the Proterozoic Nagssugtoqidian Orogenic Belt (NOB), in the Tasiilaq area, South-East Greenland. Our study reveals that the Nagssugtoqidian Orogen was the result of a complete three stages juvenile crust production (Xjuv) - recycling/reworking sequence: (I) During the 2.60-2.95 Ga period, the Neoarchean Skjoldungen Orogen remobilised basement lithologies formed at TDM 2.91 Ga with progressive increase of the discharge of reworked material (Xjuv from 75% to 50%; ?18O: 4-8.5‰). (II) After a period of crustal stabilization (2.35-2.60 Ga), discrete juvenile material inputs (?18O: 5-6‰) at TDM 2.35 Ga argue for the formation of an oceanic lithosphere and seafloor spreading over a period of ~ 0.2 Ga (Xjuv from < 25% to 70%). Lateral shortening is set to have started at ca. 2.05 Ga with the accretion of volcanic/magmatic arcs (i.e. Ammassalik Intrusive Complex) and by subduction of small oceanic domains (M1: 520 ± 60 °C at 6.6 ± 1.4 kbar). (III) Continental collision between the North Atlantic Craton and the Rae Craton occurred at 1.84-1.89 Ga. Crustal thickening of ~ 25 km was accompanied by regional metamorphism M2 (690 ± 20 °C at 6.25 ± 0.25 kbar) and remobilization of pre-existing supracrustal lithologies (Xjuv ~ 40%; ?18O: 5-10.5‰). Rates and durations obtained for seafloor spreading (175 ± 25 Ma), subduction (125 ± 75 Ma) and continental collision (ca. 60 Ma) are similar to those observed in Phanerozoic Wilson Cycle but differ from what was estimated for Archean terrains. Therefore, timespans of the different steps of a Wilson cycle might have progressively changed over time as a response to the progressive cratonization of the lithosphere.
DS201708-1725
2017
Nkere, B.Geochemistry of peridotitic clinopyroxene from the Diamondiferous Mbuji-Mayi and Tshibwe kimberlites ( DRC): insight into the compositional and thermal state of the SCLM beneath the eastern Kasai craton.11th. International Kimberlite Conference, PosterAfrica, Democratic Republic of Congodeposit - Mbuji-Mayi
DS201708-1726
2017
Nkotsi, T.Letseng diamond mine, Lesotho: recent advances in open pit geology and the satellite kimberlite pipe.11th. International Kimberlite Conference, PosterAfrica, Lesothodeposit - Letseng
DS201712-2714
2017
Nomura, R., Zhou, Y., Irifune, T.Melting phase relations in the MgSiO3-CaSiO3 system at 24 Gpa.Progress in Earth and Planetary Science, Vol. 4, pp. 34-MantleBridgmanite, perovskite

Abstract: The Earth’s lower mantle is composed of bridgmanite, ferropericlase, and CaSiO3-rich perovskite. The melting phase relations between each component are key to understanding the melting of the Earth’s lower mantle and the crystallization of the deep magma ocean. In this study, melting phase relations in the MgSiO3-CaSiO3 system were investigated at 24 GPa using a multi-anvil apparatus. The eutectic composition is (Mg,Ca)SiO3 with 81-86 mol% MgSiO3. The solidus temperature is 2600-2620 K. The solubility of CaSiO3 component into bridgmanite increases with temperature, reaching a maximum of 3-6 mol% at the solidus, and then decreases with temperature. The same trend was observed for the solubility of MgSiO3 component into CaSiO3-rich perovskite, with a maximum of 14-16 mol% at the solidus. The asymmetric regular solutions between bridgmanite and CaSiO3-rich perovskite and between MgSiO3 and CaSiO3 liquid components well reproduce the melting phase relations constrained experimentally.
DS201705-0862
2017
Norman, N.Diamonds in Africa - a tribute to Tom Clifford.lithographie.org, No. 19, pp. 70-85.AfricaBook - Clifford's Rule
DS201707-1353
2017
Nosova, A., Tretyachenko, V.V., Sazonova, L.V., Kargin, A.V., Lebedeva, N.M., Khovostikov, V.A., Burmii, Zh.P., Kondrorashov, I.A., Tretyachenko, V.V.Geochemistry and oxygen isotopic composition of olivine in kimberlites from the Arkhangelsk province: contribution of mantle metasomatism.Petrology, Vol. 25, 2, pp. 150-180.Russia, Archangel, Kola Peninsuladeposit - Grib, Pionerskaya

Abstract: The paper presents data on the composition of olivine macrocrysts from two Devonian kimberlite pipes in the Arkhangelsk diamond province: the Grib pipe (whose kimberlite belongs to type I) and Pionerskaya pipe (whose kimberlite is of type II, i.e., orangeite). The dominant olivine macrocrysts in kimberlites from the two pipes significantly differ in geochemical and isotopic parameters. Olivine macrocrysts in kimberlite from the Grib pipe are dominated by magnesian (Mg# = 0.92–0.93), Ti-poor (Ti < 70 ppm) olivine possessing low Ti/Na (0.05–0.23), Zr/Nb (0.28–0.80), and Zn/Cu (3–20) ratios and low Li concentrations (1.2–2.0 ppm), and the oxygen isotopic composition of this olivine ?18O = 5.64‰ is higher than that of olivine in mantle peridotites (?18O = 5.18 ± 0.28‰). Olivine macrocrysts in kimberlite from the Pionerskaya pipe are dominated by varieties with broadly varying Mg# = 0.90–0.93, high Ti concentrations (100–300 ppm), high ratios Ti/Na (0.90–2.39), Zr/Nb (0.31–1.96), and Zn/Cu (12–56), elevated Li concentrations (1.9–3.4 ppm), and oxygen isotopic composition ?18O = 5.34‰ corresponding to that of olivine in mantle peridotites. The geochemical and isotopic traits of low-Ti olivine macrocrysts from the Grib pipe are interpreted as evidence that the olivine interacted with carbonate-rich melts/fluids. This conclusion is consistent with the geochemical parameters of model melt in equilibrium with the low-Ti olivine that are similar to those of deep carbonatite melts. Our calculations indicate that the variations in the ?18O of the olivine relative the “mantle range” (toward both higher and lower values) can be fairly significant: from 4 to 7‰ depending on the composition of the carbonate fluid. These variations were formed at interaction with carbonate fluid, whose ?18O values do not extend outside the range typical of mantle carbonates. The geochemical parameters of high-Ti olivine macrocrysts from the Grib pipe suggest that their origin was controlled by the silicate (water–silicate) component. This olivine is characterized by a zoned Ti distribution, with the configuration of this distribution between the cores of the crystals and their outer zones showing that the zoning of the cores and outer zones is independent and was produced during two episodes of reaction interaction between the olivine and melt/fluid. The younger episode (when the outer zone was formed) likely involved interaction with kimberlite melt. The transformation of the composition of the cores during the older episode may have been of metasomatic nature, as follows from the fact that the composition varies from grain to grain. The metasomatic episode most likely occurred shortly before the kimberlite melt was emplaced and was related to the partial melting of pyroxenite source material.
DS201705-0863
2017
Nosova, A.A., Dubinina, E.O., Sazonova, L.V., Vargin, A.V., lebedeva, N.M., Khvostikov, V.A., Burmii, Zh.P., Kondrashov, I.A., Tretyachenko, V.V.Geochemistry and oxygen isotopic composition of olivine in kimberlites from the Arkhangelsk Province: contribution of mantle metasomatism.Petrology, Vol. 25, 2, pp. 150-180.Russia, Archangel, Kola PeninsulaDeposit - Grib, Pionerskaya

Abstract: The paper presents data on the composition of olivine macrocrysts from two Devonian kimberlite pipes in the Arkhangelsk diamond province: the Grib pipe (whose kimberlite belongs to type I) and Pionerskaya pipe (whose kimberlite is of type II, i.e., orangeite). The dominant olivine macrocrysts in kimberlites from the two pipes significantly differ in geochemical and isotopic parameters. Olivine macrocrysts in kimberlite from the Grib pipe are dominated by magnesian (Mg# = 0.92-0.93), Ti-poor (Ti < 70 ppm) olivine possessing low Ti/Na (0.05-0.23), Zr/Nb (0.28-0.80), and Zn/Cu (3-20) ratios and low Li concentrations (1.2-2.0 ppm), and the oxygen isotopic composition of this olivine ?18O = 5.64‰ is higher than that of olivine in mantle peridotites (?18O = 5.18 ± 0.28‰). Olivine macrocrysts in kimberlite from the Pionerskaya pipe are dominated by varieties with broadly varying Mg# = 0.90-0.93, high Ti concentrations (100-300 ppm), high ratios Ti/Na (0.90-2.39), Zr/Nb (0.31-1.96), and Zn/Cu (12-56), elevated Li concentrations (1.9-3.4 ppm), and oxygen isotopic composition ?18O = 5.34‰ corresponding to that of olivine in mantle peridotites. The geochemical and isotopic traits of low-Ti olivine macrocrysts from the Grib pipe are interpreted as evidence that the olivine interacted with carbonate-rich melts/fluids. This conclusion is consistent with the geochemical parameters of model melt in equilibrium with the low-Ti olivine that are similar to those of deep carbonatite melts. Our calculations indicate that the variations in the ?18O of the olivine relative the “mantle range” (toward both higher and lower values) can be fairly significant: from 4 to 7‰ depending on the composition of the carbonate fluid. These variations were formed at interaction with carbonate fluid, whose ?18O values do not extend outside the range typical of mantle carbonates. The geochemical parameters of high-Ti olivine macrocrysts from the Grib pipe suggest that their origin was controlled by the silicate (water-silicate) component. This olivine is characterized by a zoned Ti distribution, with the configuration of this distribution between the cores of the crystals and their outer zones showing that the zoning of the cores and outer zones is independent and was produced during two episodes of reaction interaction between the olivine and melt/fluid. The younger episode (when the outer zone was formed) likely involved interaction with kimberlite melt. The transformation of the composition of the cores during the older episode may have been of metasomatic nature, as follows from the fact that the composition varies from grain to grain. The metasomatic episode most likely occurred shortly before the kimberlite melt was emplaced and was related to the partial melting of pyroxenite source material.
DS201705-0864
2017
Novella, D., Dolejs, D., Myhill, R., Pamato, M.G., Manthilake, G., Frost, D.J.Melting phase relations in the systems Mg2SiO4-H2O and MgSiO3-H2O and the formation of hydrous melts.Geochimica et Cosmochimica Acta, Vol. 204, pp. 68-82.MantleMelting

Abstract: High-pressure and high-temperature melting experiments were conducted in the systems Mg2SiO4-H2O and MgSiO3-H2O at 6 and 13 GPa and between 1150 and 1900 °C in order to investigate the effect of H2O on melting relations of forsterite and enstatite. The liquidus curves in both binary systems were constrained and the experimental results were interpreted using a thermodynamic model based on the homogeneous melt speciation equilibrium, H2O + O2? = 2OH?, where water in the melt is present as both molecular H2O and OH? groups bonded to silicate polyhedra. The liquidus depression as a function of melt H2O concentration is predicted using a cryoscopic equation with the experimental data being reproduced by adjusting the water speciation equilibrium constant. Application of this model reveals that in hydrous MgSiO3 melts at 6 and 13 GPa and in hydrous Mg2SiO4 melts at 6 GPa, water mainly dissociates into OH? groups in the melt structure. A temperature dependent equilibrium constant is necessary to reproduce the data, however, implying that molecular H2O becomes more important in the melt with decreasing temperature. The data for hydrous forsterite melting at 13 GPa are inconclusive due to uncertainties in the anhydrous melting temperature at these conditions. When applied to results on natural peridotite melt systems at similar conditions, the same model infers the presence mainly of molecular H2O, implying a significant difference in physicochemical behaviour between simple and complex hydrous melt systems. As pressures increase along a typical adiabat towards the base of the upper mantle, both simple and complex melting results imply that a hydrous melt fraction would decrease, given a fixed mantle H2O content. Consequently, the effect of pressure on the depression of melting due to H2O could not cause an increase in the proportion, and hence seismic visibility, of melts towards the base of the upper mantle.
DS201708-1727
2017
Nowicki, T.Estimation of commercial diamond grades based on microdiamonds: a case study of the Koidu mine, Sierra Leone. 11th. International Kimberlite Conference, OralAfrica, Sierra Leonedeposit - Koidu
DS201705-0865
2017
NWT & Nunavut Chamber of Mines3D kimberlite mineral chemistry dat a from promising Slave Geological Province.Northwest Territories Geoscience Office, Open File report 2017-011Canada, Northwest TerritoriesGeochemistry
DS201705-0866
2017
Obale, O.From conflict to illicit.pacweb.org, 36 pdf.Africa, Cameroon, Central African RepublicDiamond industry
DS201705-0867
2017
Ogden, J.M.Rethinking laboratory reports for the geographical origin of gems.Journal of Gemmology, Vol. 35, 5, pp. 416-423.TechnologyReports - gem reports, tests, grades

Abstract: The proliferation of gemmological laboratory reports and the need for transparency to best protect against litigation suggest that some gem-testing laboratories should consider changes in the wording and content of their geographical origin reports. Based on the author's recent broader study of the legal aspects of the opinions provided by experts in the field of art and antiques, the main proposals presented here are that statements of opinion rather than fact should be clearly expressed as such where they are presented on a report, rather than relegating all mention of 'opinion' to the 'terms and conditions', and that the basic nature of the observational or analytical evidence on which any opinions are based should be noted. In addition, a laboratory might usefully provide some indication of the level of confidence in its opinion.
DS201709-2039
2017
Ogungbuyi, P.I., Janney, P.E., Harris, C.The geochemistry and genesis of Marinkas Quellen carbonatite complex, southwestern Namibia.Goldschmidt Conference, abstract 1p.Africa, Namibiacarbonatite

Abstract: The 525 Ma Marinkas Quellen (MQ) Complex of southern Namibia, part of the Kuboos-Bremen Line (KBL) of alkaline igneous centers [1] consists of granites, nepheline syenites and carbonatites and is the only carbonatite locality in the KBL [1]. MQ carbonatite variteties include calciocarbonatites, magnesiocarbonatites and ferrocarbonatites. The enrichments in Ba, Nb and the REE vary widely in the carbonatites, with La ranging from 45 to 11154 ppm. All the carbonatites are characterised by large Zr, Hf, Ti depletions. Zr/Hf ratios ranges from 40 to 500, all greater than the chondritic value of 36. Such large Zr/Hf fractionations are often associated with carbonatite metasomatism. The values of carbon and oxygen isotope ratios of bulk carbonate in Marinkas Quellen carbonatites vary significantly (e.g., ?13C = -3.95 to -6.02‰; ?18 O = 8.84 to 22.22‰). The carbon isotope compositions are in the mantle range, while the oxygen isotope values extend to higher than typical mantle values, presumably due to interaction with hydrous fluids. All but two of the carbonatite samples have initial 87Sr/86Sr ratios falling in the range of 0.70236 to 0.70408. Of the remaining samples, one, a ferrocarbonatite, has a higher value of 0.70503 that is likely due to contamination by the surrounding rock or assimilation in the lower crust or Sr exchange with groundwater. The other, a magnesiocarbonatite, appears to have experienced an increase in its Rb/Sr ratio due to alteration, resulting in an over-corrected initial 87Sr/86Sr value. The relatively low Sr isotope ratios of most samples, plus their HNd(t) values (+3.9 to +4.8) values suggest that the carbonatite magma was generated from a long-lived low Rb/Sr, high Sm/Nd, relatively depleted mantle source. The radiogenic Pb isotope composition of the carbonatites (206Pb/204Pbi ratios from 18.06 to 22.38), suggests a high U/Pb source, akin to the HIMU mantle end member. This points to a sub-lithospheric (asthenospheric) source with only a relatively minor contribution from enriched lithospheric mantle
DS201704-0643
2017
Ohta, K., Yagi, T., Hirose, K., Ohishi, Y.Thermal conductivity of ferropericlase in the Earths's lower mantle.Earth and Planetary Science Letters, Vol. 465, pp. 29-37.MantleGeothermometry

Abstract: (Mg,?Fe)O ferropericlase (Fp) is one of the important minerals comprising Earth's lower mantle, and its thermal conductivity could be strongly influenced by the iron content and its spin state. We examined the lattice thermal conductivity of (Mg,?Fe)O Fp containing 19 mol% iron up to 111 GPa and 300 K by means of the pulsed light heating thermoreflectance technique in a diamond anvil cell. We confirmed a strong reduction in the lattice thermal conductivity of Fp due to iron substitution as reported in previous studies. Our results also show that iron spin crossover in Fp reduces its lattice thermal conductivity as well as its radiative conduction. We also measured the electrical conductivity of an identical Fp sample up to 140 GPa and 2730 K, and found that Fp remained an insulator throughout the experimental conditions, indicating the electronic thermal conduction in Fp is negligible. Because of the effects of strong iron impurity scattering and spin crossover, the total thermal conductivity of Fp at the core-mantle boundary conditions is much smaller than that of bridgmanite (Bdg). Our findings indicate that Bdg (and post-perovskite) is the best heat conductor in the Earth's lower mantle, and distribution of iron and its valence state among the lower mantle minerals are key factors to control the lower mantle thermal conductivity.
DS201705-0868
2016
Oldenburg, D., Kang, S., fournier, D.Airborne IP at Tli Kwi Cho.SEG Annual Meeting Dallas, 19 ppt.Canada, Northwest TerritoriesDeposit - Tli Kwi Cho
DS201710-2252
2017
O'Neill, C., Marchi, S., Zhang, S., Bottke, W.Impact driven subduction on the Hadean Earth.Nature Geoscience, Vol. 10, 10, pp. 793-797.Mantlesubduction

Abstract: Impact cratering was a dominant geologic process in the early Solar System that probably played an active role in the crustal evolution of the young terrestrial planets. The Earth’s interior during the Hadean, 4.56 to 4 billion years ago, may have been too hot to sustain plate tectonics. However, whether large impacts could have triggered tectonism on the early Earth remains unclear. Here we conduct global-scale tectonic simulations of the evolution of the Earth through the Hadean eon under variable impact fluxes. Our simulations show that the thermal anomalies produced by large impacts induce mantle upwellings that are capable of driving transient subduction events. Furthermore, we find that moderate-sized impacts can act as subduction triggers by causing localized lithospheric thinning and mantle upwelling, and modulate tectonic activity. In contrast to contemporary subduction, the simulated localized subduction events are relatively short-lived (less than 10?Myr) with relatively thin, weak plates. We suggest that resurgence in subduction activity induced by an increased impact flux between 4.1 and 4.0 billion years ago may explain the coincident increase in palaeointensity of the magnetic field. We further suggest that transient impact-driven subduction reconciles evidence from Hadean zircons for tectonic activity with other lines of evidence consistent with an Earth that was largely tectonically stagnant from the Hadean into the Archaean.
DS201707-1354
2017
Ootes, L., Jackson, V.A., Davis, W.J., Bennett, V., Smar, L., Cousens, B.L.Parentage of Archean basement within a Paleoproterozoic orogen and implications for on-craton diamond preservation: Slave craton and Wopmay orogen, northwest Canada.Canadian Journal of Earth Sciences, Vol. 54, pp. 203-232.Canada, Northwest Territorieskimberlite

Abstract: The Wopmay orogen is a Paleoproterozoic accretionary belt preserved to the west of the Archean Slave craton, northwest Canada. Reworked Archean crystalline basement occurs in the orogen, and new bedrock mapping, U–Pb geochronology, and Sm–Nd isotopic data further substantiate a Slave craton parentage for this basement. Detrital zircon results from unconformably overlying Paleoproterozoic supracrustal rocks also support a Slave craton provenance. Rifting of the Slave margin began at ca. 2.02 Ga with a second rift phase constrained between ca. 1.92 and 1.89 Ga, resulting in thermal weakening of the Archean basement and allowing subsequent penetrative deformation during the Calderian orogeny (ca. 1.88–1.85 Ga). The boundary between the western Slave craton and the reworked Archean basement in the southern Wopmay orogen is interpreted as the rifted cratonic margin, which later acted as a rigid backstop during compressional deformation. Age-isotopic characteristics of plutonic phases track the extent and evolution of these processes that left penetratively deformed Archean basement, Paleoproterozoic cover, and plutons in the west, and “rigid” Archean Slave craton to the east. Diamond-bearing kimberlite occurs across the central and eastern parts of the Slave craton, but kimberlite (diamond bearing or not) has not been documented west of ?114°W. It is proposed that while the crust of the western Slave craton escaped thermal weakening, the mantle did not and was moved out of the diamond stability field. The Paleoproterozoic extension–convergence cycle preserved in the Wopmay orogen provides a reasonable explanation as to why the western Slave craton appears to be diamond sterile.
DS201708-1728
2017
O'Reilly, S.Geodynamic amd geophsyical consequences of stealth(y) mantle metasomatism: craton evolution and metallogeny.11th. International Kimberlite Conference, OralMantlecraton, metasomatism

Abstract: Mantle metasomatism is a relatively recent concept introduced in the early 1970s when detailed studies of lithospheric mantle rock fragments (xenoliths), brought to the surface of in basaltic to kimberlitic magmas, became widespread. Two main types of metasomatism were defined: modal (or patent) metasomatism describes the introduction of new minerals; cryptic metasomatism describes changes in composition of pre-existing minerals without formation of new phases. A new type of metasomatism is introduced here, stealth metasomatism; this process involves the addition of new phases (e.g. garnet and/or clinopyroxene), but is a “deceptive” metasomatic process that adds phases indistinguishable mineralogically from common mantle peridotite phases. The recognition of stealth metasomatism reflects the increasing awareness of the importance of refertilisation by metasomatic fluid fronts in determining the composition of mantle domains. Tectonically exposed peridotite massifs provide an opportunity to study spatial relationships of metasomatic processes on a metre to kilometre scale. The nature of mantle fluids can be determined from the nature of fluid inclusions in mantle minerals and indirectly from changes in the chemical (especially trace-element) compositions of mantle minerals. Metasomatic fluids in off-craton regions cover a vast spectrum from silicate to carbonate magmas containing varying types and abundances of dissolved fluids and solutes including brines, C-O-H species and sulfur-bearing components. Fluid inclusions in diamond and deep xenoliths reveal the presence of high-density fluids with carbonatitic and hydro-silicic and/or saline-brine end-members. The deep cratonic xenolith data also reinforce the importance of highly mobile melts spanning the kimberlite-carbonatite spectrum and that may become immiscible with changing conditions. A critical conceptual advance in understanding Earth’s geodynamic behaviour is emerging from understanding the linkage between mantle metasomatism and the physical properties of mantle domains recorded by geophysical data. For example, metasomatic refertilisation of cratonic lithospheric mantle increases its density, lowers its seismic velocity and strongly affects its rheology. Introduction of heat-producing elements (U, Th, K) increases heat production, and the key to understanding electromagnetic signals from mantle domains may be closely related to fluid distribution and type (e.g. carbonatitic) and its residence in or between grains. The lithospheric mantle is a palimpsest recording the multiple fluid events that have affected each domain since it formed. These events, involving different fluids and compositions, have repeatedly overprinted variably depleted original mantle wall-rocks. This produces a complex, essentially ubiquitously metasomatised lithospheric mantle, heterogeneous on scales of microns to terranes and perhaps leaving little or no “primary” mantle wall-rock. Decoding this complex record by identifying significant episodes and processes is a key to reconstructing lithosphere evolution and the nature and origin of the volatile flux from the deep Earth through time.
DS201707-1355
2017
Oriolo, S., Oyhantcabal, P., Wemmer, K., Siegesmund, S.Contemporaneous assembly of Western Gondwana and final Rodinia break-up: implications for the supercontinent cycle.Geoscience Frontiers, in press available 15p.Gondwana, Rodiniageodynamics

Abstract: Geological, geochronological and isotopic data are integrated in order to present a revised model for the Neoproterozoic evolution of Western Gondwana. Although the classical geodynamic scenario assumed for the period 800–700 Ma is related to Rodinia break-up and the consequent opening of major oceanic basins, a significantly different tectonic evolution can be inferred for most Western Gondwana cratons. These cratons occupied a marginal position in the southern hemisphere with respect to Rodinia and recorded subduction with back-arc extension, island arc development and limited formation of oceanic crust in internal oceans. This period was thus characterized by increased crustal growth in Western Gondwana, resulting from addition of juvenile continental crust along convergent margins. In contrast, crustal reworking and metacratonization were dominant during the subsequent assembly of Gondwana. The Río de la Plata, Congo-São Francisco, West African and Amazonian cratons collided at ca. 630–600 Ma along the West Gondwana Orogen. These events overlap in time with the onset of the opening of the Iapetus Ocean at ca. 610–600 Ma, which gave rise to the separation of Baltica, Laurentia and Amazonia and resulted from the final Rodinia break-up. The East African/Antarctic Orogen recorded the subsequent amalgamation of Western and Eastern Gondwana after ca. 580 Ma, contemporaneously with the beginning of subduction in the Terra Australis Orogen along the southern Gondwana margin. However, the Kalahari Craton was lately incorporated during the Late Ediacaran–Early Cambrian. The proposed Gondwana evolution rules out the existence of Pannotia, as the final Gondwana amalgamation postdates latest connections between Laurentia and Amazonia. Additionally, a combination of introversion and extroversion is proposed for the assembly of Gondwana. The contemporaneous record of final Rodinia break-up and Gondwana assembly has major implications for the supercontinent cycle, as supercontinent amalgamation and break-up do not necessarily represent alternating episodic processes but overlap in time.
DS201706-1099
2017
O'Sullivan, D., Bailey, D.G.Major and trace element compositions of garnets from New York state kimberlites: a window in the lower crust and upper mantle.GSA Annual Meeting, 1p. AbstractUnited States, New Yorkdeposit - Taughannock Creek, Ithica, Dewitt Reservoir

Abstract: Kimberlites are unusual igneous rocks that are not only the singular source of gem quality diamonds, but also a source of upper mantle and lower crustal material for scientific study. As kimberlite magmas rise, they disaggregate xenoliths from the surrounding country rocks. One mineral that is commonly picked up and transported to the surface is garnet, and their compositions have been correlated with different mantle conditions and source materials. The goal of our study is to use garnet compositions to characterize the diversity of lithologies sampled by Mesozoic kimberlitic intrusions in New York State. Approximately 90 kimberlitic dikes cut through the Paleozoic sedimentary rocks of central New York State, most clustered around the cities of Ithaca and Syracuse. Samples of garnet-bearing kimberlites were collected from both of these localities (Taughannock Creek, Ithaca and Dewitt Reservoir, Syracuse), in order to compare the garnet populations present to see if the two dikes sampled similar mantle and crustal materials. Garnets were extracted from both dikes, and their bulk compositions were obtained using energy-dispersive, x-ray spectrometry (SEM-EDS). We were able to identify four major compositional groups of garnets: 1) low to moderate Cr pyrope, 2) high Cr pyrope, 3) almandine, and 4) grossular. Samples of each of these were then analyzed for trace element composition by laser ablation, inductively coupled plasma, mass spectrometry (LA-ICP-MS). Both dikes contain macrocrysts of almandine and Cr-bearing pyrope (up to ~ 5 wt. % Cr2O3); garnets with a high grossular component were only found in the Dewitt kimberlite. Based on the classification of Gurney et al. (1984), none of the garnets indicate a high diamond potential for either kimberlite. While the pyrope and almandine macrocrysts in both dikes are broadly similar in composition, sub-populations of garnets can be recognized based on trace element profiles. Preliminary analysis of the data suggests that the kimberlite intrusions in central New York sampled garnets from a heterogeneous mantle source and, in addition, sampled garnets from a Grenvillian lower crust.
DS201705-0869
2017
Palke, A.C., Renfro, N.D., Berg, R.B.Melt inclusions in alluvial sapphires from Montana, USA: formation of sapphires as a restitic component of lower crustal melting?Lithos, Vol. 278-281, pp. 43-53.United States, MontanaSapphires

Abstract: We report here compositions of glassy melt inclusions hosted in sapphires (gem quality corundum) from three alluvial deposits in Montana, USA including the Rock Creek, Dry Cottonwood Creek, and Missouri River deposits. While it is likely that sapphires in these deposits were transported to the surface by Eocene age volcanic events, their ultimate origin is still controversial with many models suggesting the sapphires are xenocrysts with a metamorphic or metasomatic genesis. Melt inclusions are trachytic, dacitic, and rhyolitic in composition. Microscopic observations allow separation between primary and secondary melt inclusions. The primary melt inclusions represent the silicate liquid that was present at the time of sapphire formation and are enriched in volatile components (8-14 wt.%). Secondary melt inclusions analyzed here for Dry Cottonwood Creek and Rock Creek sapphires are relatively volatile depleted and represent the magma that carried the sapphires to the surface. We propose that alluvial Montana sapphires from these deposits formed through a peritectic melting reaction during partial melting of a hydrated plagioclase-rich protolith (e.g. an anorthosite). The heat needed to drive this reaction was likely derived from the intrusion of mantle-derived mafic magmas near the base of the continental lithosphere during rollback of the Farallon slab around 50 Ma. These mafic magmas may have ended up as the ultimate carrier of the sapphires to the surface as evidenced by the French Bar trachybasalt near the Missouri River deposit. Alternatively, the trachytic, rhyolitic, and dacitic secondary melt inclusions at Rock Creek and Dry Cottonwood Creek suggests that the same magmas produced during the partial melting event that generated the sapphires may have also transported them to the surface. Determining the genesis of these deposits will further our understanding of sapphire deposits around the world and may help guide future sapphire prospecting techniques. This work is also important to help reveal the history of mantle-derived mafic magmas as they pass through the continental crust.
DS201710-2253
2017
Palmer, M.R.Boron in subduction zones.Elements, Vol. 13, pp. 237-242.Mantlesubduction
DS201710-2254
2017
Pandey, A., Chalapathi Rao, N.V., Chakrabarti, R., Shaoo, S.Petrogenesis of a Mesoproterozoic shoshonitic lamprophyre dyke from the Wajrakarur kimberlite field, eastern Dharwar craton, southern India: geochemical and Sr-Nd isotopic evidence for a modified sub-continental lithospheric mantle.Lithos, in press availableIndiadeposit - Wajrakarur

Abstract: Mineralogy and geochemistry of the Udirpikonda lamprophyre, located within the Mesoproterozoic diamondiferous Wajrakarur kimberlite field (WKF), towards the western margin of the Paleo-Mesoproterozoic Cuddapah basin are presented. The lamprophyre is characterised by a panidiomorphic-porphyritic texture imparted by clinopyroxene, olivine and biotite set in a groundmass of feldspar and spinel. Olivine occurs as the microphenocrysts with a composition range of Fo87-78. Clinopyroxenes display reverse as well as oscillatory optical zoning and are diopsidic in nature with a variation in the composition from core (Wo47 En28 Fs20Ac5) to rim (Wo46En41Fs11Ac3). Biotite (Mg# < 0.6) is the only mica present and spinels are titano-magnetites showing ulvospinel- magnetite solid solution. Plagioclase is the dominant feldspar with a variable compositional range of An41-8Ab82-56Or33-3. Based on the mineralogy, the lamprophyre can be classified to be of calc-alkaline variety but its geochemistry display mixed signals of both alkaline and calc-alkaline lamprophyres. K2O/Na2O ranges from 1.49 to 2.79, making it distinctly potassic and highlights its shoshonitic character. Moderate Mg# (60-65), Ni (110-200 ppm) and Cr (110-260 ppm) contents in the bulk-rock indicate substantial fractional crystallization of olivine and clinopyroxene. Fractionated chondrite normalized REE patterns (average (La/Yb)N = 37.56) indicates involvement of an enriched mantle source from within the garnet stability field whereas slightly negative Ta-Nb-Ti and Hf anomalies displayed on the primitive mantle normalized multi-element spider gram highlight involvement of a subducted component in the mantle source. Given the spatial disposition of the studied lamprophyre, the age of the emplacement is considered to be coeval with WKF kimberlites (~ 1.1 Ga) and the initial 143Nd/144Nd (0.510065-0.510192) and 87Sr/86Sr (0.705333-0.706223) are strikingly similar to those observed for the Smoky Butte lamproites, Montana, USA. Fluid-related subduction enrichment of the mantle source is apparent from the enriched ratios of La/Nb, Ba/Nb and (Hf/Sm)N, (Ta/La)N < 1. Petrogenetic modelling reveals melt generation from 1 to 2% partial melting of an enriched mantle source that subsequently underwent fractional crystallization. Our study provides geochemical and isotopic evidence for a sub-continental lithospheric mantle (SCLM) modified by subduction and asthenospheric upwelling in the Eastern Dharwar Craton. The partial melting of a resulting heterogeneous Eastern Dharwar Craton SCLM to generate Udiripikonda lamprophyre and Wajrakarur kimberlites has been attributed to the Mesoproterozoic regional lithospheric extension event.
DS201702-0230
2017
Pandey, A., Pandey, R., Pandit, D., Pankaj, P., Chalapathi Rao, N.V.A note on the origin of clinopyroxene megacrysts from the Udiripikonda lamprophyre, eastern Dharwar craton, southern India.Journal of India Geophysical Union, Vol. 21, 2, pp. 124-131.IndiaLamprophyre
DS201712-2715
2017
Panina, L.I., Rokosova, E.Yu., Isakova, A.T., Tolstov, A.V.Mineral composition of alkaline lamprophyres of the Tomto massif as reflection of their genesis.Russian Geology and Geophysics, Vol. 58, pp. 887-902.Russiamonchiquites
DS201710-2255
2017
Pant, N.C., Dasgupta, S.An introduction to the crustal evolution of India and Antarctica: the supercontinent connectionGeological Society of London Special Publication, Vol. 457, pp. 1-6.Indiatectonics
DS201709-2040
2017
Parat, F., Baudoin, C., Michel, T., Tiberi, D., Gautier, S.CO2 rich nephelinite differentiation and carbonate silicate immiscibility ( North Tanzanian divergence.)Goldschmidt Conference, abstract 1p.Africa, Tanzaniacarbonatites

Abstract: North Tanzanian Divergence is the first stage of continental break-up of East African Rift and one of the most concentrated areas of carbonatite magmatism with Natron basin in the North (2 Ma-present - Lengai) and Manyara basin in the southern part (0.4-0.9 Ma). The Manyara basin has volcanic activities with mafic magmas as melilitites (Labait), Mg-nephelinites and carbonatite (Kwaraha), and more differentiated magmas as Mg-poor nephelinites (Hanang) recording deep magmatic environment and differentiation in the crust of CO2-rich alkaline magmas. Melilitite and Mg-nephelinite with olivine-cpx-phlogopite record mantle environment at 1.5 GPa-1300°C with water content in melt of 0.1- 0.4 wt% H2O (1-4 ppm in olivine, FTIR). Although fractional crystallization can be considered as an important process during ascent, leading to Mg-poor nephelinite with cpx-melanite-nepheline, complex zonation of cpx (e.g. abrupt change of Mg#, Nb/Ta, and H2O) recorded open system with multiple carbonate-rich silicate immiscibility and melilititic melt replenishment. The low water content of cpx (25 ppm H2O; FTIR) indicates that 0.3 wt% H2O was present during carbonate-rich nephelinite crystallization at crustal level (600 MPa - 1050°C). The interstitial melt entrapped as melt inclusions (MI) in nepheline evolved to CO2-rich and H2O-poor phonolitic composition with 6 wt% CO2 and 1 wt% S at logfO2=FMQ+1 to 1.5 (Fe3+/?Fe=0.3 - S6+/?S=0.55, XANES). At 200 MPa, phonolitic melt in MI reaches carbonate saturation and immiscibility process leads to trachytic melt with high CO2, S and halogen content (0.43 wt% CO2, SIMS; 2 wt% S, 0.84 wt% Cl; 2.54 wt% F) and very low H2O content (<0.1wt%, Raman) and an anhydrous Ca-Na±S,K carbonate liquid. The Ca-Na carbonatitic liquid in Mg-poor nephelinite represents an early stage of the evolution path towards carbonatitic magmatism as observed in Kwaraha and Lengai. Manyara volcanism has similarities with the Natron volcanism with multistage evolution and silicate-carbonatite magmatism but differ by their volatile components (up to 10 H2O wt% in Lengai nephelinite). This can be interpreted in term of depth of partial melting with H2O-CO2 lithospheric mantle source (Natron) and deep anhydrous CO2-rich asthenospheric mantle source in the southern part of rift initiation (Manyara) and percolation of deep CO2-rich silicate liquid leading to lithospheric mantle metasomatism.
DS201708-1729
2017
Parks, B.Deciphering the composition and structure of Wyoming craton mantle lithosphere: insights from peridotite xenoliths.11th. International Kimberlite Conference, OralUnited States, Wyomingperidotite
DS201709-2041
2017
Parra-Avila, L.A.The Paleoproterozoic Baoule-Mossi domain, West African craton: plate tectonics at 2.3-2.0Ga?Goldschmidt Conference, abstract 1p.Africageochronology

Abstract: Despite advances in understanding the evolution of the West African Craton (WAC), much debate still hinges over its geodynamic evolution. In the case of the Paleoproterozoic Baoulé-Mossi domain, part of the problem is that most studies are localized and fail to present large-scale correlations. To address this, we present the integrated results of zircon U-Pb geochronology, O and Hf isotopes, and whole-rock geochemistry datasets obtained from felsic intrusions across Ghana, Burkina Faso, Mali and Guinea. Combining the new and existing U-Pb age data reveals that magmatism was continuous for approximately 150 Myrs, and involved migration of a magmatic front from east to west. Mafic and felsic magmatism was coeval, and a small amount of inherited zircons as old as 3.5 Ga were identified. The Hf- isotope data reveal the existence of two different crustal domains, with subtlely different Hf isotope signatures. These data also hint at a crustal source component potentially as old as 2.8 Ga in some rocks. The two isotopic domains are separated by a less radiogenic sliver of crust across the Banfora Belt. O isotope compositions (zircon d18O from 6.5 to 11 ‰), corroborate evidence for a crustal source. Geochemical data from felsic intrusions indicates that the studied rocks are not TTG equivalents as previously described but are more akin to modern granitic intrusions. The intrusions are either two mica (muscovite/biotite) or one mica (biotite), and some are amphibole rich. These intrusions are mainly calc-alkaline and magnesian and range from metaluminous (SiO2<65%) to peraluminous (SiO2>65%). They predominantly show arc-type trace element signatures. The combination of the different spatially extensive data sets favors a plate tectonic regime for the period between 2.3 and 2.0 Ga. Under this scenario, two, predominately juvenile, crustal blocks developed in an arc-type setting. This evolved into a continental arc-type setting and later, upon the indentation of the Archean Kenema-Man domain at 2.1-2.0 Ga, into a continent-continent collisional setting.
DS201701-0024
2016
Partnership Africa CanadaFrom conflict to illicit mapping the diamond trade from Central African Republic to Cameroon.Partnership Africa Canada, 36p. PdfAfrica, Central African Republic, CameroonHistory

Abstract: The Central African Republic (CAR) is the only source of traditionally defined conflict diamonds in the world today. Since May 2013, exports of its diamonds have been under international embargo by both the United Nations and the Kimberley Process (KP), the initiative that regulates the production and trade of rough diamonds. CAR was suspended from the KP after a March 2013 coup d’état that sparked widespread civil unrest in the country. The coup was the inevitable outcome of years of political instability forged by a coalition of rebel groups, known as Séléka, who attacked the government and incrementally seized territory, including the strategic diamond-mining town of Bria.2 On March 24, 2013 Séléka captured the capital city of Bangui and overthrew the government, initiating a bitter internal conflict that continues to fester to this day. The civil war and regime change forced the United Nations and the international community to impose economic sanctions on CAR. Not only were all diamond exports prohibited, the KP urged diamond-trading countries to exercise enhanced vigilance and ensure that diamonds produced in CAR were seized and not allowed to circulate in legitimate trade.3 While the ban on CAR’s exports was partially lifted in 2016 from regions deemed to be KP compliant, that has not stopped the flow of CAR’s conflict diamonds to international markets—while it was under full embargo or regions still prevented from trading today. This report examines the smuggling of diamonds from the Central African Republic into Cameroon. Further, it focuses on the impact this illicit trade has on Cameroon’s internal controls as well as the broader integrity of the diamond supply chain. The report describes the methods used and the key actors involved in this illicit trade. It concludes that the KP and frontline countries like Cameroon need to do more to interrupt the illicit trade of conflict diamonds from CAR and support each other in taking action.
DS201709-2042
2017
PDAC NewsletterDe Beers hosts (for the 3rd year) Canadian top geoscience students at Diamond Day as part of the Sudbury Student Conference. Nicole Januszczak and Stephan Kurszlaukis providing guidance.PDAC Newsletter, July 25, 1/2p.Technologyexploratio, students

Abstract: Nicole Januszczak, part of De Beers’ Canadian exploration team, and Stephan Kurszlaukis, a kimberlite petrologist working at De Beers Canada’s Calgary Operational Support Centre, volunteered their time to participate in the Student-Industry Mineral Exploration Workshop organized by the Prospectors and Developers Association of Canada in Sudbury, ON. Twenty-six senior geoscience students from across Canada were hand-picked from post-secondary institutions across the country to take part in the event designed to provide a unique opportunity to experience many facets of the mineral exploration industry. Two of the students who took part in the event are working as summer employees for De Beers Exploration in Canada.
DS201702-0231
2017
Pearson, G.The complex history of the mantle roots beneath the Slave Craton and surrounding regions.Vancouver Kimberlite Cluster, Jan. 26, 1/4p. AbstractCanada, Northwest Territories, NunavutGeochronology
DS201708-1730
2017
Pearson, G.Trace elements in gem quality diamonds from the De Beers Victor mine, Ontario, Canada.11th. International Kimberlite Conference, PosterCanada, Ontario, Attawapiskatdeposit - Victor
DS201705-0870
2017
Pearson, G., Krebs, M., Stachel. T., Woodland, S., Chinn, I., Kong, J.Trace elements in gem-quality diamonds: origin and evolution of diamond-forming fluid inclusions.European Geosciences Union General Assembly 2017, Vienna April 23-28, 1p. 19281 AbstractTechnologyDiamond inclusions
DS201708-1731
2017
Pell, J.Conodont geothermometry in pyroclastic kimberlite: constraints on emplacement temperature and cooling histories.11th. International Kimberlite Conference, PosterCanada, Nunavut, Baffin IslandGeothermometry

Abstract: Kimberlites are mantle-derived ultramafic rocks preserved in volcanic and sub-volcanic edifices and are the main primary source of diamonds. The temperatures of formation, transport, eruption and deposition remain poorly constrained despite their importance for understanding the petrological and thermodynamic properties of kimberlite magmas and styles of volcanic eruption. Here, we present measured values of Colour Alteration Indices (CAI) for conodonts recovered from 76 Paleozoic carbonate xenoliths found within 11 pipes from the Chidliak kimberlite field on Baffin Island, Nunavut, Canada. The dataset comprises the largest range of CAI values (1.5 to 8) and the highest CAI values reported to date for kimberlite-hosted xenoliths. Thermal models for cooling of the Chidliak kimberlite pipes and synchronous heating of conodont-bearing xenoliths indicate time windows of 10–20 000 h and, for these short time windows, the measured CAI values indicate heating of the xenoliths to temperatures of 225 to >925 ?C. We equate these temperatures with the minimum temperatures of the conduit-filling kimberlite deposit (i.e. emplacement temperature, TE). The majority of the xenoliths record CAI values of between 5 and 6.5 suggesting heating of xenoliths to temperatures of 460 ?C–735 ?C. The highest CAI values are consistent with being heated to 700 ?C–925 ?C and establish the minimum conditions for welding or formation of clastogenic kimberlite deposits. Lastly, we use TE variations within and between individual pipes, in conjunction with the geology of the conduit-filling deposits, to constrain the styles of explosive volcanic eruption.
DS201708-1732
2017
Pell, J.A tale of two pipes: using whole rock geochemistry to see through alteration and contamination at the CH-6 & CH-7 kimberlites, Chidliak kimberlite province, Baffin Island, Nunavut.11th. International Kimberlite Conference, PosterCanada, Nunavut, Baffin IslandDeposit - Chidliak
DS201708-1733
2017
Pendock, N.Mapping heat flow from a time series of satellite temperature images as a regional exploration tool for kimberlites.11th. International Kimberlite Conference, OralTechnologyGeothermometry
DS201703-0428
2015
Peng, P.Precambrian mafic dyke swarms in the North Chin a craton and their geological implications.Science China Earth Sciences, Vol. 58, 5, pp. 649-675.ChinaCraton, North China

Abstract: A map of major Precambrian mafic dyke swarms and related units in the North China Craton is compiled, and the features and geological implications of these swarms are demonstrated. The Archean dyke swarms are available to portray the early crustal growth and cratonization. The middle Paleoproterozoic (2200-1850 Ma) swarms and related magmatic series could constrain the tectonic evolution: They approve that the craton was amalgamated by two sub-cratons. The late Paleoproterozoic (1800-1600 Ma), Mesoproterozoic (1400-1200 Ma) and Neoproterozoic (1000-800 Ma) series swarms are important in paleogeographic reconstruction: they indicate that North China might have connected with some of the North European and North American cratons during Proterozoic. Dyke swarms are not only geological timescales and tectonic markers but also evolution indicators of lithospheric mantle: they imply a rejuvenation of the sub-continental lithospheric mantle of North China at 1780-1730 Ma. These swarms occurred with several rifts, including the Hengling (2200-1970 Ma), Xuwujia (1970-1880 Ma), Xiong’er (1800-1600 Ma), Yan-Liao (1730-1200 Ma), and Xu-Huai (1000-800 Ma). Among them, the Xuwujia rift was possibly continental arc associated; whereas the others were intra-continental. In addition, the Xiong’er and Xu-Huai rifts were possibly triple junctions along the present southern and southeastern margins of the Craton, respectively. Different tectonic settings of these rifts and dyke swarms would result in diversified series of ore deposits.
DS201707-1356
2016
Perchuk, A.L., Safonov, O.G., Smit, C.A., van Reenen, D.D., Zkharov, V.S., Gerya, T.V.Precambrian ultra hot orogenic factory: making and reworking of continental crust.Tectonophysics, in press availableMantleUHP

Abstract: Mechanisms of Precambrian orogeny and their contribution to the origin of ultrahigh temperature granulites, granite-greenstone terranes and net crustal growth remain debatable. Here, we use 2D numerical models with 150 °C higher mantle temperatures compared to present day conditions to investigate physical and petrological controls of Precambrian orogeny during forced continental plates convergence. Numerical experiments show that convergence between two relatively thin blocks of continental lithosphere with fertile mantle creates a short-lived cold collisional belt that later becomes absorbed by a long-lived thick and flat ultra-hot accretionary orogen with Moho temperatures of 700–1100 °C. The orogen underlain by hot partially molten depleted asthenospheric mantle spreads with plate tectonic rates towards the incoming lithospheric block. The accretionary orogeny is driven by delamination of incoming lithospheric mantle with attached mafic lower crust and invasion of the hot partially molten asthenospheric wedge under the accreted crust. A very fast convective cell forms atop the subducting slab, in which hot asthenospheric mantle rises against the motion of the slab and transports heat towards the moving orogenic front. Juvenile crustal growth during the orogeny is accompanied by net crustal loss due to the lower crust subduction. Stability of an ultra-hot orogeny is critically dependent on the presence of relatively thin and warm continental lithosphere with thin crust and dense fertile mantle roots subjected to plate convergence. Increased thickness of the continental crust and subcontinental lithospheric mantle, pronounced buoyancy of the lithospheric roots, and decreased mantle and continental Moho temperature favor colder and more collision-like orogenic styles with thick crust, reduced magmatic activity, lowered metamorphic temperatures, and decreased degree of crustal modification. Our numerical modeling results thus indicate that different types of orogens (cold, mixed-hot and ultra-hot) could be created at the same time in the Early Earth, depending on compositional and thermal structures of interacting continental blocks.
DS201712-2716
2017
Pereira, R.S., Fuck, R.A., Soares Franca, O., Leite, A.A.Evidence of young, proximal and primary (YPP) diamond source occurring in alluviums in the Santa Antonio do Bonito, Santo Inacio and Douradhinho rivers in Coromandel region, Minas Gerais.Brazilian Journal of Geology, Vol. 47, 3, pp. 383-401.South America, Brazildeposit - Alta Paranaiba

Abstract: Magmatism associated with the Alto Paranaíba structural high comprises kimberlites, kamafugites, and alkaline complexes, forming an approximately 400 x 150 km NW-SE belt in the southern São Francisco Craton. Dating of some intrusions reveals ages between 120 and 75 Ma. Chemical analyses of garnet recovered in alluvium from traditional diamond digging areas indicate peridotitic garnet windows in Três Ranchos and Coromandel. Six hundred and eighty (680) diamonds acquired or recovered during mineral exploration in the digging areas of Romaria, Estrela do Sul, Três Ranchos and Coromandel show unique characteristics, certain populations indicating young, proximal and primary sources (YPP). Analyses of 201 stones from Santo Antônio do Bonito, Santo Inácio and Douradinho rivers alluvium, Coromandel, present no evidence of transport, characterizing a proximal source. Within these river basins, exposures of the Late Cretaceous Capacete Formation basal conglomerate contain mainly small rounded and/or angular quartzite pebbles and of basic and ultrabasic rocks, as well as kimberlite minerals (garnet, ilmenite, spinel, sometimes diamond). A magnetotelluric profile between the Paraná and Sanfranciscana basins shows that the thick underlying lithosphere in the Coromandel region coincides with the peridotitic garnet window and with a diamond population displaying proximal source characteristics. Diamond-bearing kimberlite intrusions occur in different areas of Alto Paranaíba.
DS201712-2717
2017
Persikov, E.S., Bukhtiyarov, P.G., Sokol, A.G.Viscosity of hydrous kimberlite and basaltic melts at high pressures.Russian Geology and Geophysics, Vol. 58, pp. 1093-1100.Mantlekimberlite

Abstract: New experimental data on the temperature and pressure dependences of the viscosity of synthetic hydrous kimberlite melts (82 wt.% silicate + 18 wt.% carbonate; degree of depolymerization: 100NBO/T = 313 for anhydrous melts and 100NBO/T = 247 for melts with 3 wt.% H2O) were obtained at a water pressure of 100 MPa and at lithostatic pressures of 5.5 and 7.5 GPa in the temperature range 1300-1950 °C. The temperature dependence of the viscosity of these melts follows the exponential Arrhenius-Frenkel-Eyring equation in the investigated range of temperatures and pressures. The activation energies of viscous flow for hydrous kimberlite melts were first shown to increase linearly with increasing pressure. Under isothermal conditions (T = 1800 °C), the viscosity of hydrous kimberlite melts increases exponentially by about an order of magnitude as the pressure increases from 100 MPa to 7.5 GPa. The new experimental data on the viscosity of hydrous kimberlite melts (error ± 30 rel.%) are compared with forecast viscosity data for anhydrous kimberlite and basaltic melts (100NBO/T = 51.5) and for hydrous basaltic melts (100NBO/T = 80). It is shown that at comparable temperatures, the viscosity of hydrous kimberlite melts at a moderate pressure (100 MPa) is about an order of magnitude lower than the viscosity of hydrous basaltic melts, whereas at a high pressure (7.5 GPa) it is more than twice higher. It is first established that water dissolution in kimberlite melts does not affect seriously their viscosity (within the measurement error) at both moderate (100 MPa) and high (7.5 GPa) pressures, whereas the viscosity of basaltic melts considerably decreases with water dissolution at moderate pressures (100 MPa) and remains unchanged at high pressures (P > 3.5 GPa).
DS201708-1734
2017
Pervov, V.Catoca kimberlite pipe diatreme/crater transition and dynamics of the crater sedimentation.11th. International Kimberlite Conference, PosterAfrica, Angoladeposit - Catoca
DS201712-2718
2017
Phani, P.R.C.Petrology and geochemistry of kimberlites from Lattavaram and Anumpalli clusters Anantapur district Anfhra Pradesh India.Thesis, Phd. Osmania University 258p., http://shodhganga.inflibnet.ac.in/handle/10603/178609.India, Andhra Pradeshdeposit - Lattavaram, Anumpalli

Abstract: The thesis is organized into six chapters. The first chapter enunciates general concepts of kimberlite geology covering literature, previous work, definitions, classification, mode of occurrence, regional geological history, global and Indian occurrences of kimberlites. The second chapter elucidates the common principles and practices applied and adopted in diamond exploration applicable to the Indian context, to some extent exemplifying the kimberlite clusters of the study area. A six-stage exploration strategy, applicable to Indian geological scenario, has been proposed. The third chapter portrays the general geological setting of the study area comprising Lattavaram and Anumpalli kimberlite clusters along with spatial morphologies of the pipes and various field geological characteristics illustrated through field photographs. The fourth chapter describes various mineralogical and petrographic characteristics observed in the pipes and their associated calcretes as well of the study area emphasising their genetic significance. The fifth chapter characteristically articulates the whole rock geochemistry with the aid of major, trace and rare earth element analyses to depict the classification of the pipes under study. This chapter also demonstrates calcrete geochemistry of calcretes associated with the kimberlite pipes of the study area in detail, perhaps for the first time. The sixth chapter describes the petrogenetic inferences including source region, partial melting, temperature, density and viscosity etc., derived from geochemical analyses and thereby demonstrates the diamond prospectivity of Lattavaram and Anumpalli kimberlite pipes. In a nutshell, this research work aims to present a detailed account of petrography, geochemistry, petrogenesis and diamond prospectivity of kimberlites from Lattavaram and Anumpalli clusters in light of recently discovered pipes. For the first time, petrographic and geochemical analyses of kimberlitic calcretes are presented and interpreted.
DS201712-2719
2017
Phani, P.R.C., Srinivas, M.Quantitative study of indicator minerals on kimberlite pipe-5 at Muligiripalli, Wajrakarur field, southern India. Preliminary results of loam sampling.Russian Mineralogical Society 200th. Anniversary meeting Oct. 10-13., 4p. Abstract pdfIndiadeposit - Pipe-5, Wajrakakarur

Abstract: In an attempt to study the kimberlite indicator minerals (KIMs), loam sampling in the close vicinity of the pipes has been carried out on some kimberlites of the WKF. In this paper, preliminary results of KIMs derived out of loam sampling on one of the WKF pipes at Muligiripalli (pipe-5) are presented. Surface loam sampling has been carried out in the topographically low-lying areas in the close proximity of the pipe outcrop. Four composite samples, at a spacing of ~100 meters, weighing 25 kg each have been collected and sieved through 1 mm mesh. Approximately 5 kg of ‘-1’ fraction has been obtained after sieving which is further subjected to coning and quartering. The material has been subjected to heavy mineral (HM) separation using a manual jig. The HM further screened through Frantz’s isodynamic separator to separate magnetic mineral grains. The HM assemblage includes ilmenite, chromite, Cr-diopside, olivine and sphene. ). To ascertain the kimberlitic nature of the HM grains and thereby to check diamondiferous nature of this pipe, additonal loam sampling to obtain more number of mineral grains to carry out Electron Microprobe Analysis (EPMA) is planned.
DS201711-2525
2017
Phani, R.Kimberlite indicator minerals in Nutimadugu catchment, Anantapur district, Andhra Pradesh, India.Proceedings of XXXIV held Aug. 4-9. Perchuk International School of Earth Sciences, At Miass, Russia, 1p. AbstractIndiamineral chemistry

Abstract: The present study examines an unexplored catchment (60 Sq. Km.) at Nutimadugu village, in Anantapur district, on the right bank of Penna River (Fig.1), to attest the occurrence of kimberlite indicator minerals (KIMs). The left bank is famous for diamondiferous kimberlites known as Timmasamudram Kimberlite Cluster. About eight stream sediment samples (~15kg in weight), were collected from the catchment with an approximate sample sapcing of one kilometer. The -1mm fraction of the stream sediments was reduced to heavy mineral concentrate (HMC) using traditional techniques. The selected mineral grains were probed for major elements using electron probe microanalysis (EPMA). Majority (75%) are chromite grains. Uvaravite and grossularite garnets and few grains of ilmenite are also present. The chromite grains plot in the world wide kimberlitic chromite field, with few in the diamond inclusion field (Fig.2 & 3). The garnet grains plot in the G12 field and found to be wehrlitic in character (Fig.4 & 5). On the contrary, the ilmenite grains plot in the non-kimberlitic field (Fig. 6), which might have been derived from the supracrustal rocks occurring to the east of the catchment. Thus this study highlights that the catchment stands as a priority target for further field investigations.
DS201708-1735
2017
Phillips, D.Provenance history of detrital diamond deposits, West Coast of Namqualand, South Africa.11th. International Kimberlite Conference, OralAfrica, South Africadeposit - Namaqualand
DS201708-1736
2017
Phillips, D.A comparison of geochronology methods applied to kimberlites and related rocks from the Karelian craton, Finland.11th. International Kimberlite Conference, PosterEurope, Finlandgeochronology
DS201701-0025
2016
Piazolo, S., Kaminsky, F.V., Trimby, P., Evans, L., Luzin, V.Carbonado revisited: insights from neutron diffraction, high resolution orientation mapping and numerical simulations.Lithos, in press available 13p.TechnologyCarbonado

Abstract: One of the most controversial diamond types is carbonado, as its origin and geological history are still under debate. Here, we investigate selected carbonado samples using neutron diffraction and high resolution orientation mapping in combination with numerical simulations. Neutron diffraction analyses show that fine grained carbonado samples exhibit a distinct lack of crystallographic preferred orientation. Quantitative crystallographic orientation analyses performed on transmission electron microscope (TEM) sections reveal that the 2-10 ?m grains exhibit locally significant internal deformation. Such features are consistent with crystal plastic deformation of a grain aggregate that initially formed by rapid nucleation, characterized by a high number of nucleation sites and no crystallographic preferred orientation. Crystal plastic deformation resulted in high stress heterogeneities close to grain boundaries, even at low bulk strains, inducing a high degree of lattice distortion without significant grain size reduction and the development of a crystallographic preferred orientation. Observed differences in the character of the grain boundary network and internal deformation structures can be explained by significant post-deformation annealing occurring to variable degrees in the carbonado samples. Differences in intensity of crystal bending and subgrain boundary sharpness can be explained by dislocation annihilation and rearrangement, respectively. During annealing grain energy is reduced resulting in distinct changes to the grain boundary geometry. Grain scale numerical modelling shows that anisotropic grain growth, where grain boundary energy is determined by the orientation of a boundary segment relative to the crystallographic orientation of adjacent grains results in straight boundary segments with abrupt changes in orientation even if the boundary is occurring between two triple junctions forming a “zigzag” pattern. In addition, in diamond anisotropic grain growth results in triple junctions that rarely show 120° angles. Our results support the interpretation that carbonados may have undergone at least 2 or 3 stages of development with rapid nucleation, crystal plastic deformation to low strains and variable degrees of post-deformation annealing. Such a history is commonly observed in Earth's crustal or mantle rocks. Hence, for carbonados it is not necessary to invoke an extraordinary and/or extraterrestrial origin and history. The combination of methods utilized here, promises to help advance our understanding of diamond and diamond aggregates in the future.
DS201701-0026
2016
Piet, H., Badro, J., Nabiel, F., Dennenwaldt, T., Shim, S-H., Cantoni, M., Hebert, C., Gillet, P.Spin and valence dependence on iron partitioning in Earth's deep mantle.Proceedings of National Academy of Science USA, Vol. 113, no. 40, pp. 11127-11130.MantleUHP

Abstract: We performed laser-heated diamond anvil cell experiments combined with state-of-the-art electron microanalysis (focused ion beam and aberration-corrected transmission electron microscopy) to study the distribution and valence of iron in Earth's lower mantle as a function of depth and composition. Our data reconcile the apparently discrepant existing dataset, by clarifying the effects of spin (high/low) and valence (ferrous/ferric) states on iron partitioning in the deep mantle. In aluminum-bearing compositions relevant to Earth's mantle, iron concentration in silicates drops above 70 GPa before increasing up to 110 GPa with a minimum at 85 GPa; it then dramatically drops in the postperovskite stability field above 116 GPa. This compositional variation should strengthen the lowermost mantle between 1,800 km depth and 2,000 km depth, and weaken it between 2,000 km depth and the D" layer. The succession of layers could dynamically decouple the mantle above 2,000 km from the lowermost mantle, and provide a rheological basis for the stabilization and nonentrainment of large low-shear-velocity provinces below that depth.
DS201705-0871
2017
Pilchin, A., Eppelbaum, L.V.Concentration of PGE during the Early Earth evolution: a review.Natural Resources Forum, Vol. 8, pp. 172-233.MantleMineralogy

Abstract: Numerous unique geological processes [1] took place during the early Earth evolution; several of them, especially those occurring in the Hadean—Early Archean and later, are reflected in the modern geological (geophysical, geochemical, etc.) pattern. One such significant enigmatic feature is the preservation of extremely dense and heavy platinum group elements (PGEs): Pt, Pd, Rh, Ru, Ir, Os. Concentration of PGEs during this period could have taken place in two ways: 1) presence of particular matter capable of preserving PGEs near the earth's surface, 2) transportation of PGEs by magma flows from deep lithospheric (asthenospheric) layers (slabs) to the subsurface. Clearly, much of the dense and heavy PGEs did not sink through to the Earth’s mantle (core) at the time of the magma-ocean, and occur near Earth’s surface in abundances for formation of ore deposits with PGE concentrations found to be 2 - 3 orders of magnitude greater than those in their host media. Their enrichments are associated in numerous cases with such enigmatic phenomena as formation of anorthosites and anorthosite-bearing layered magmatic intrusions. PGE deposits and mineralization zones are also found in associations with chromitites, dunites and serpentinites. In this review, problems related to the initial concentration and preservation of PGEs, their association with anorthosites, and formation of layered intrusions are discussed in detail. The main aim of this article is analysis of the requirements—initial concentration and preservation of PGE and PGM (Platinum Group Minerals) during the early Earth evolution, as well as examination of the distribution behavior of some PGEs in different ore deposits and meteorites. It is supposed that meteoritic bombardment of Earth has played a significant role in formation of PGEs deposits. Some conclusions made in this article may be useful for developing and enhancing strategies of prospecting for PGEs deposits.
DS201701-0027
2016
Pilet, S., Abe, N., Rochat, L., Kaczmarek, M-A., Hirano. N., Machida, S., Buchs, D.M., Baumgartner, P.O., Muntener, O.Pre-subduction metasomatic enrichment of the oceanic lithosphere induced by plate flexure.Nature Geoscience, Vol. 9, pp. 898-903.MantleSubduction

Abstract: Oceanic lithospheric mantle is generally interpreted as depleted mantle residue after mid-ocean ridge basalt extraction. Several models have suggested that metasomatic processes can refertilize portions of the lithospheric mantle before subduction. Here, we report mantle xenocrysts and xenoliths in petit-spot lavas that provide direct evidence that the lower oceanic lithosphere is affected by metasomatic processes. We find a chemical similarity between clinopyroxene observed in petit-spot mantle xenoliths and clinopyroxene from melt-metasomatized garnet or spinel peridotites, which are sampled by kimberlites and intracontinental basalts respectively. We suggest that extensional stresses in oceanic lithosphere, such as plate bending in front of subduction zones, allow low-degree melts from the seismic low-velocity zone to percolate, interact and weaken the oceanic lithospheric mantle. Thus, metasomatism is not limited to mantle upwelling zones such as mid-ocean ridges or mantle plumes, but could be initiated by tectonic processes. Since plate flexure is a global mechanism in subduction zones, a significant portion of oceanic lithospheric mantle is likely to be metasomatized. Recycling of metasomatic domains into the convecting mantle is fundamental to understanding the generation of small-scale mantle isotopic and volatile heterogeneities sampled by oceanic island and mid-ocean ridge basalts.
DS201709-2043
2017
Pimenta Martins, L.G., Matos, M.J.S., Paschoal, A.R., Freire, P.T.C., Andrade, N.F., Aguiar, A.L., Kong, J., Neves, B.R.A., de Oliveira, A.B., Mazzoni, M.S.C., Souza Filhio, A.G., Cancad, L.G.Raman evidence for pressure induced formation of diamondene.Nature Communications, Vol. 8, 9p.Technologydiamondene

Abstract: Despite the advanced stage of diamond thin-film technology, with applications ranging from superconductivity to biosensing, the realization of a stable and atomically thick two-dimensional diamond material, named here as diamondene, is still forthcoming. Adding to the outstanding properties of its bulk and thin-film counterparts, diamondene is predicted to be a ferromagnetic semiconductor with spin polarized bands. Here, we provide spectroscopic evidence for the formation of diamondene by performing Raman spectroscopy of double-layer graphene under high pressure. The results are explained in terms of a breakdown in the Kohn anomaly associated with the finite size of the remaining graphene sites surrounded by the diamondene matrix. Ab initio calculations and molecular dynamics simulations are employed to clarify the mechanism of diamondene formation, which requires two or more layers of graphene subjected to high pressures in the presence of specific chemical groups such as hydroxyl groups or hydrogens.
DS201702-0232
2016
Plethean, J.J.J., Kalnins, L.M., van Hunen, J., Biffi, P.G., Davies, R.J., McCaffrey, K.J.W.Madagascar's escape from Africa: a resolution plate reconstruction for the Western Somali Basin and for supercontinent dispersal.Geochemistry, Geophysics, Geosystems: G3, Vol. 17, 2, pp. 5036-5055.Africa, MadagascarTectonics

Abstract: Accurate reconstructions of the dispersal of supercontinent blocks are essential for testing continental breakup models. Here, we provide a new plate tectonic reconstruction of the opening of the Western Somali Basin during the breakup of East and West Gondwana. The model is constrained by a new comprehensive set of spreading lineaments, detected in this heavily sedimented basin using a novel technique based on directional derivatives of free-air gravity anomalies. Vertical gravity gradient and free-air gravity anomaly maps also enable the detection of extinct mid-ocean ridge segments, which can be directly compared to several previous ocean magnetic anomaly interpretations of the Western Somali Basin. The best matching interpretations have basin symmetry around the M0 anomaly; these are then used to temporally constrain our plate tectonic reconstruction. The reconstruction supports a tight fit for Gondwana fragments prior to breakup, and predicts that the continent-ocean transform margin lies along the Rovuma Basin, not along the Davie Fracture Zone (DFZ) as commonly thought. According to our reconstruction, the DFZ represents a major ocean-ocean fracture zone formed by the coalescence of several smaller fracture zones during evolving plate motions as Madagascar drifted southwards, and offshore Tanzania is an obliquely rifted, rather than transform, margin. New seismic reflection evidence for oceanic crust inboard of the DFZ strongly supports these conclusions. Our results provide important new constraints on the still enigmatic driving mechanism of continental rifting, the nature of the lithosphere in the Western Somali Basin, and its resource potential.
DS201710-2256
2017
Pogge von Strandmann, P.A.E., Desrochers, A., Murphy, M.J., Finlay, A.J., Selby, D., Lenton, T.M.Global climate stabilisation by chemical weathering during the Hirnantian glaciation.Geochemical Perspectives Letters, Vol. 3, pp. 230-237.Canada, Quebec, Anticosti Islandcarbon cycle

Abstract: Chemical weathering of silicate rocks is a primary drawdown mechanism of atmospheric carbon dioxide. The processes that affect weathering are therefore central in controlling global climate. A temperature-controlled “weathering thermostat” has long been proposed in stabilising long-term climate, but without definitive evidence from the geologic record. Here we use lithium isotopes (?7Li) to assess the impact of silicate weathering across a significant climate-cooling period, the end-Ordovician Hirnantian glaciation (~445 Ma). We find a positive ?7Li excursion, suggestive of a silicate weathering decline. Using a coupled lithium-carbon model, we show that initiation of the glaciation was likely caused by declining CO2 degassing, which triggered abrupt global cooling, and much lower weathering rates. This lower CO2 drawdown during the glaciation allowed climatic recovery and deglaciation. Combined, the data and model provide support from the geological record for the operation of the weathering thermostat.
DS201708-1737
2017
Poitras, S.Evidence for a >200 km thick diamond -bearing root beneath the Central Mackenzie Valley, Northwest Territories, Canada: diamond indicator mineral geochemistry from the Horn Plateau and Trout Lakes regions.11th. International Kimberlite Conference, OralCanada, Northwest Territoriesindicator minerals
DS201709-2044
2017
Pokhilenko, L.N.Exotic olivine glimmerites of Yakutia - the related polymict breccias.Goldschmidt Conference, abstract 1p.Russiaglimmerite

Abstract: The rocks, which are totally comprised of olivine and mica, have been found among the xenoliths of the Udachnaya-East pipe (Yakutia). The essential amount (first percents) of ilmenite of different morphology has been found in two rocks. These exotic olivine glimmerites appeared to be similar to the polymict breccia in the wide variations of olivine (LUV709/11 and LUV659/11 - Mg#(%): 86-93 and 83-91, respectively), phlogopite ((wt.%), LUV659/11: SiO2 38.5-40.6, TiO2 2.5-6, Al2O3 11.3-14, Cr2O3 0.4-1, MgO 19.8-23.1, FeO 6.1-7.9, Na2O 0.5-1.3, K2O 8.6-9.9), ilmenite (LUV709/11: Mg#(%) 23.6-47.8; Cr2O3 (wt.%): 0.63-1.01) compositions and also in the abundance of accessory minerals (chromite, rutile, sulphides, calcite, dolomite, siderite, barite). The compositions of rock-forming minerals of the glimmerites do not fall within the compositional fields of similar minerals from the peridotites of kimberlite xenoliths but strongly overlap with that from the polymict breccias. Moreover, the compositions of phlogopite from the glimmerites have demonstrated similar in Al, Fe and Ti composition kimberlite trend typical of phlogopites from the polymict breccia of the South Africa. Unusual olivine glimmerites LUV659/11 and LUV709/11 were probably formed from the ancient protokimberlite melts like polymict breccias. Initially they have been strongly depleted and hence olivine is the main rock-forming mineral. Therefore, two main stages of metasomatic retreatment before the capture by kimberlite can be recognized. One is related with Ti and Fe introduction (ilmenite formation), another, more strong, with abundant introduction of Al and alkalis (mainly K) with a consequent formation of abundant phlogopite. These stages probably had several phases as evidenced by the compositional variations of the formed minerals.
DS201703-0429
2017
Popova, E., Lushnikov, S.G., Yakovenchuk, V.N.The crystal structure of loparite: a new acentric variety.Mineralogy and Petrology, in press availablePerovskite, REE

Abstract: The crystal structure of the cubic modification of the natural mineral loparite has been studied for the first time by the methods of the X-ray diffraction analysis (?MoK ? radiation, 105 independent reflections with I > 3?(I), R = 0.041 in the anisotropic approximation). The structure belongs to the perovskite type (ABO 3) with the double period of the cubic unit cell, a = 7.767(1) Å (sp. gr. Pn3m; Z = 2 for the composition (Ca,Na,Ce)(Na,Ce)3(Ti,Nb)2Ti2O12. Period doubling is explained by ordering of cations both in the A and the B positions.
DS201708-1738
2017
Potter, N.Inclusions in perovskite magnetite silicate rocks from Afrikanda, Russia: clues to the early history of carbonatites.11th. International Kimberlite Conference, PosterRussiacarbonatites
DS201707-1357
2017
Potter, N.J., Kamenetsky, V.S., Simonetti, A., Goemann, K.Different types of liquid immiscibility in carbonatite magmas: a case stufy of the Oldoinyo Lengai 1993 lava and melt inclusions.Chemical Geology, Vol. 455, pp. 376-384.Africa, Tanzaniadeposit - Oldoinyo Lengai

Abstract: Oldoinyo Lengai is situated within the Gregory Rift Valley (northern Tanzania) and is the only active volcano erupting natrocarbonatite lava. This study investigates the texture and mineralogy of the June 1993 lava at Oldoinyo Lengai, and presents petrographic evidence of liquid immiscibility between silicate, carbonate, chloride, and fluoride melt phases. The 1993 lava is a porphyritic natrocarbonatite consisting of abundant phenocrysts of alkali carbonates, nyerereite and gregoryite, set in a quenched groundmass, composed of sodium carbonate, khanneshite, Na-sylvite and K-halite, and a calcium fluoride phase. Dispersed in the lava are silicate spheroids (< 2 mm) with a cryptocrystalline silicate mineral assemblage wrapped around a core mineral. We have identified several textural features preserved in the silicate spheroids, melt inclusions, and carbonatite groundmass that exhibit evidence of silicate-carbonate, carbonate-carbonate and carbonate-halide immiscibility. Rapid quenching of the lava facilitated the preservation of the end products of these liquid immiscibility processes within the groundmass. Textural evidence (at both macro- and micro-scales) indicates that the silicate, carbonate, chloride and fluoride phases of the lava unmixed at different stages of evolution in the magmatic system.
DS201707-1358
2017
Prasad, R.Cr-diopsides from Lattavaram and Kalyanadurgam kimberlites, Anantapur district, southern India: inferences from loam sampling.Role of Geophysics in Earth and Environmental Studies , March 1p. AbstractIndiamineralogy

Abstract: A comparison of major element content in Cr-diopside mineral grains, from loam samples, of two kimberlite pipes each from Lattavaram (P-3 and P-4) and Kalyanadurgam (KL-1 and KL-2) clusters of Wajrakarur Kimberlite Field (WKF) has been presented here. The two selected Lattavaram pipes are well exposed whereas the Kalyanadurgam pipes are concealed under 1.5 to 2 meter thick alluvium and calcrete, which is endowed with easily identifiable kimberlitic indicator minerals (KIMs). The indicator minerals are mantle derived xenocrystic types like pyrope garnet, Cr-diopside, ilmenite, chromite and olivine which provide inferences on their petrogenesis. It is observed that Cr-diopside is a prominent mineral constituent in both these locations and plays a vital role in reconnaissance diamond exploration. Surface in-situ loam sampling was carried out and ~15 kg of sample has been collected, to segregate heavy minerals which were concentrated by panning and jigging. In total, 66 Cr-diopside grains in total; 26 from Lattavaram and 40 from Kalyanadurgam were picked under the microscope and studied for their major element geochemistry by EPMA. In Lattavaram area, 25 grains were identified to be of C5 class and one grain belongs to C3. In Kalyandurgam, it is observed that 39 grains belong to CP5 category and one grain to C2 class. The range of Cr2O3 weight% for Lattavaram samples is 0.94- 2.8 and that for Kalyanadurgam samples is 0.54- 6.34. It is envisaged that the entries of Fe, Al, Na, Ca, and Cr into the clinopyroxene structure are strongly affected by the P-T-X conditions during mineral crystallization. It is observed that the mantle derived kimberlitic Cr-diopside is low in Fe-content relative to that of crustal rocks. This study revealed that Cr-diopsides of investigated pipes are of kimberlitic nature and plot in the diamond inclusion field thereby signifying the prospectivity of the pipes.
DS201712-2720
2017
Presser Baez, J.L.Presser states this is a series of short essays, a task that during this time helped to understand and improve the definition of the craton (Lito-Archon) Rio de la plata. It is intended to be published at the 7th. Brazilian Symposium of Diamond Geology injaimeleonardobp@ gmail.com, Nov. 16, 25p. Lito-archon-Jaime.pdfSouth America, Brazil, Paraguay, globalcraton - Rio de la plata
DS201702-0233
2016
Presser, J.L.B.Diamantes en Paraguay, Cincuenta an Os de occurrencia. ** PortBoletin del Museo Nacional de Historia Narural del Paraguay, Vol. 20, 2, pp. 154-187. pdf available in * PortSouth America, ParaguayLamproite

Abstract: Diamonds in Eastern-Paraguay began to be recognized in the 60s of last century near the town of Capiibary Dept. San Pedro; but it was only formalized the occurrence in 2008. In Capiibary and around, over 100 macro (1 ~ 3 mm) diamond (colorless, shades of brown and rare shades of pink, blue and green) were recovered from alluvial deposits. Micro-diamonds and small macro-diamonds were separated from sediment (conglomeratic/breccia´s/others; rich in indicators mineral: eclogitic garnets, rounded ilmenite, chromite, frosting-tourmaline, zircon, etc.) interpreted as reworked primary source. In the same locality 20 diamonds in its external morphology, internal structure, its mineral inclusions and the nitrogen content and state of aggregation were studied. The late 90s of last century diamonds were recovered from re-worked volcanic facies a probable pipe of Mesozoic picrític calc-alkaline lamprophyre, in the vicinity of the town of La Colmena in the Dept. Paraguari. Few later years (2003), some ten kilometers to the east, a mining company announced that it had found macro-diamond in a lamproite dyke (also Mesozoic) of 4 meters wide, along the Cordillera del Ybytyruzú, Dept. of Guaira. The same mining company notice that have found macro (~ 1 mm) diamonds in other departments of East Paraguay. It was also in late 2003 that were found in stream sediments, alluvium, soil and primary weathered rock /primary reworked -macro (millimeter) diamonds (colorless, yellow, pink, green, brown) accompanied by high concentration of indicator minerals (eclogitic garnets, rounded ilmenite, chromite, rutile, frosting-tourmaline, Fe-Ti-staurolite, zircon, etc.) around the town of Puentesiño (and adjacent areas), Dept. of Concepcion. More recently regional research work allowed locate macro (> 0.5 to 2 mm) diamonds in alluvial deposits and fine/coarse sediments (probable primary re-worked rock -also accompanied by high concentration of indicator minerals: rounded ilmenite, chromite, rutile, frosting-tourmaline, zircons, etc.) between the Department Concepción-Amambay -in the vicinity of Mesozoic carbonatitic alkaline complex. Officially between the 90s of last century to date have collected (Paraguay-East) around 5000 (for diamonds/indicator minerals) samples of stream sediment, soil, termite nest, weathered rock. Some samples (Puentesiño-around and Capiibary and vicinity) produced indicator minerals were analyzed in their chemical composition: eclogitic garnets (G-3 and G-4); picro-chromites (some with Zn and Mn); chromite-spinel; Mn-ilmenite, Ti-K-tourmaline (frosting-tourmaline); rutile and Fe-Ti-estaurolites. Eclogitic-garnets, picro-chromites and frosting-tourmaline reproduces compatible parameters with its association with diamonds (in the mantle and/or primary rocks). The composition of chromite-spinel, K-Ti-tourmaline, Mn-ilmenite and Zircons supported by the types of eclogitic-garnets and some forms of diamonds-corrosion suggest that the primary source for the diamonds try to lamproites. The tectonic environment, deduced from seismic tomography (Model TX2011 -dVs%) -supported by calculations of P in eclogitic garnets and in picro-chromites, correspond to a block Archon (Apa) of Rio de La Plata Craton. Archon- block that it would be deep (about 250-280 km deep) and thus ideal for the occurrence of primary productive sources of diamond.
DS201702-0234
2016
Presser, J.L.B., Farina-Dolsa, S., Larroza-Cristaldo, F.A., Rocca, M., Alonso, R.N., Acededo, R.D., Cabral-Antunez, N.D., Baller, L., Zarza-Lima, P.R., Sekatcheff, J.M.Modeled mega impact structures in Paraguay: II the eastern region. **PortBoletin del Museo Nacional de Historia Narural del Paraguay, Vol. 20, 2, pp. 205-213. pdf available in * PortSouth America, ParaguayImpact Crater

Abstract: We report here the discovery and study of several new modeled large impact craters in Eastern Paraguay, South America. They were studied by geophysical information (gravimetry, magnetism), field geology and also by microscopic petrography. Clear evidences of shock metamorphic effects were found (e.g., diaplectic glasses, PF, PDF in quartz and feldspar) at 4 of the modeled craters: 1) Negla: diameter:~80-81 km., 2) Yasuka Renda D:~96 km., 3) Tapyta, D: ~80 km. and 4) San Miguel, D: 130-136 km. 5) Curuguaty, D: ~110 km. was detected and studied only by geophysical information. Target-rocks range goes from the crystalline Archaic basement to Permian sediments. The modeled craters were in some cases cut by tholeiitic/alkaline rocks of Mesozoic age and partially covered by lavas of the basaltic Mesozoic flows (Negla, Yasuka Renda, Tapyta and Curuguaty). One of them was covered in part by sediments of Grupo Caacupé (age: Silurian/Devonian). Some of these modeled craters show gold, diamonds, uranium and REE mineral deposits associated. All new modeled large impact craters are partially to markedly eroded.
DS201710-2257
2017
Presser, J.L.B., Tondo, M.J., Dolsa, S.F., Rocca, M.C.L., Alonso, R.N., Benetiz, P., Larroza, F.A., Duarte, B.J.R., Cabral-Antunez, N.D.Brief comments on the impact metamorphism in Cerro Leon quartzites, western Paraguay. English abstract ** in PORTPyroclastic Flow, Vol. 7, 1,pp. 16-24.South America, Paraguayimpact diamonds

Abstract: The petrographic study of two samples (quartzite and impactite) of Cerro León, a mountain range located in the middle of very probable impact basins (Cerro Leon-1, 2, 3 and 4-department of Alto Paraguay, Western-Paraguay) indicated evidences of impact metamorphism: PDFs (Not decorated and decorated) and diaplectic glass. Associated with diaplectic glass, impact diamonds or diamond/lonsdaleite crystals (micro and small macros) were observed with a range of morphologies including isolated and mostly agglutinated crystal varieties. Impact diamonds estimated to have formed by carbonate impact metamorphism present in the sedimentary target-rock of the Silurian/Devonian age. The identification of elements that reveal the impact metamorphism, in the analyzed samples of the Cerro León, evidences that the area of occurrence that would have been indicated as Very Probable Impact Basin, would be more of an Impact Basin.
DS201707-1359
2017
Presser, J.L.B., Vladykin, N.V., Bitschene, P.R., Tondo, M.J., Acevedo, R.D., Alonso, R., Benitez, P.Olivine-lamproite from Ybtyruzu lamproite field, eastern Paraguay. *** In SpaPyroclastic Flow *** Spa, Vol. 7, 1, pp. 1-15.South America, Paraguaylamproite

Abstract: Numerous Mesozoic bodies of lamproite-like intrusions are located NE and E of the city of Villarrica, Guairá Department, in eastern Paraguay. This magmatic field, known as Ybytyruzú Field, lies immediately on the margin of the SW part of Paranapanemá cratonic-block, just of the Asunción rift backs-horst and so related to deep crustal/lithospheric fracture zones.Mostly of observed rocks are weathered, however fresh samples were collected in dykes from Acaty (=Yzu-2), Tacuarita (=Yzu-7); lava/breccias from Mbocayaty (=Yzu-3); and sill from Salto Boni (=Yzu-6). They intrude, both, the sediments (Independencia Group and Misiones Formation) and the tholeiitic basalts of the Paraná Basin. In the present study we have performed petrographic and mineral chemistry data to show that all of the study rocks, from the Ybytyruzú Field, are lamproites (leucite lamproite from Yzu-2/Yzu-3/Yzu-7 and sanidine lamproite from Yzu-6).With respect to Yzu-2, Yzu-3 and Yzu-6, the following analyzes show the lamproite character: -phenocrysts/microphenocrysts of: olivine (mg# (Mg/(Mg+Fe)) 0.80-0.85), Al-poor diopside (Al2O3 0.53-2.09% and TiO2 0.65-1.61%), phlogopite/Al-poor-Ti phlogopite (mg# 0.76-0.85, TiO2 5.8-10.2% and Al2O3 12.7-13.9%), Mg-Ti magnetites and leucite (pseudomorphs). -and matrix phases of: Al-poor diopside (Al2O3 0.39-2.46% and TiO2 0.43-1.55%), Al-poor-Ti phlogopite/biotite (mg# 0.57-0.80, TiO2 5.6-10.2% and Al2O3 8.9-12.8%), Mg-Ti magnetites/Ti-magnetites; sanidine (0-4.0% Fe2O3, 0-2.6% BaO and 0-2.5% Na2O). And as accessory phases, ilmenite (0.2-5.7% MgO and 0.3-6.6% MnO), K and Ti-rich Feeckermanite/richterite (1.32-3.6% K2O and 4.7-9.0% TiO2), K-rich Fe-Mg-Mn amphiboles, apatite and quartz (Yzu-6). And so, Ybytyruzú lamproite-like intrusions authenticates the true lamproitic province in Paraguay. III; INTERNATIONAL, 2000 BRAZIL 2000; 3 1ST INTERNATIONAL GEOLOGICAL CONGRESS; ABSTRACTS VOLUME
DS201701-0028
2016
Prokopyev, I.R., Borisenko, A.S., Borovikov, A.A., Pavlova, G.G.Origin of REE rich ferrocarbonatites in southern Siberia ( Russia): implications based on melt and fluid inclusions.Mineralogy and Petrology, Vol. 110, pp. 845-859.Russia, SiberiaCarbonatite

Abstract: Fe-rich carbonatites with a mineral assemblage of ankerite-calcite or siderite are widespread in southern Siberia, Russia. The siderite carbonatites are associated with F-Ba-Sr-REE mineralization and have a 40Ar/39Ar age of 117.2 ± 1.3 Ma. Melt and fluid inclusions suggest that the carbonatites formed from volatile-rich alkali- and chloride-bearing carbonate melts. Ankerite-calcite carbonatites formed from carbonatite melt at a temperature of more than 790 °C. The ferrocarbonatites (the second phase of carbonatite intrusion) formed from a sulfate-carbonate-chloride fluid phase (brine-melt) at >650 °C and ?360 MPa. The brine-melt fluid phase had high concentrations of Fe and LREEs. A subsequent hydrothermal overprint contributed to the formation of economically important barite-Sr-fluorite-REE mineralization in polymict siderite breccia.
DS201710-2258
2017
Prokopyev, I.R., Doroshkevich, A.G., Redina, A.A.Magnetite apatite dolomitic rocks of Ust-Chulman ( Aldan Shield, Russia): Seligdar type carbonatites?Mineralogy and Petrology, in press available 10p.Russiacarbonatite

Abstract: The Ust-Chulman apatite ore body is situated within the Nimnyrskaya apatite zone at the Aldan shield in Russia. The latest data confirm the carbonatitic origin of the Seligdar apatite deposit (Prokopyev et al. in Ore Geol Rev 81:296-308, 2017). The results of our investigations demonstrate that the magnetite-apatite-dolomitic rocks of the Ust-Chulman are highly similar to Seligdar-type dolomitic carbonatites in terms of the mineralogy and the fluid regime of formation. The ilmenite and spinel mineral phases occur as solid solutions with magnetite, and support the magmatic origin of the Ust-Chulman ores. The chemical composition of REE- and SO3-bearing apatite crystals and, specifically, monazite-(Ce) mineralisation and the formation of Nb-rutile, late hydrothermal sulphate minerals (barite, anhydrite) and haematite are typical for carbonatite complexes. The fluid inclusions study revealed similarities to the evolutionary trend of the Seligdar carbonatites that included changes of the hydrothermal solutions from highly concentrated chloride to medium-low concentrated chloride-sulphate and oxidized carbonate-ferrous.
DS201703-0430
2016
Prouty, M.Miniature magnetometrers for small UAVS.Society of Exploration Geophysics, Dallas annual meeting, Geometrics, 22ppt.TechnologyGeophysics
DS201706-1100
2017
Pufahl, P.K., Groat, L.A.Sedimentary and igneous phosphate deposits: formation and exploration: an invited paper. ( carbonatite)Economic Geology, Vol. 112, pp. 483-516.Russia, Kola Peninsula, Europe, Finland, Canada, British Columbiadeposit - Khibina, Fir, Siilinjarvi

Abstract: Phosphorus is the central ingredient in fertilizer that allows modern agriculture to feed the world’s population. This element, also critical in a host of industrial applications, is a nonrenewable resource that is sourced primarily from the phosphatic mineral apatite, hosted in sedimentary and igneous ores. World phosphate resources are estimated by the U.S. Geological Survey at ca. 300,000 Mt, of which 95% are sedimentary and 5% are igneous. Current known USGS reserve estimates are sufficient for a maximum of 200 to 300 years; the exploration and discovery of new resources, enhanced mining technologies, and new technologies aimed at the recovery and recycling of P from sewage and agricultural runoff will all contribute to extending P production. Igneous ores are generally associated with Phanerozoic carbonatites and silica-deficient alkalic intrusions that typically average 5 to 15 wt % P2O5, which can be beneficiated to high-grade concentrates of at least 30 wt % P2O5 with few contaminants. Carbonatites are typically the smallest and youngest parts of a carbonatite-alkaline rock complex that formed during fractional crystallization of a calcic parental alkaline silicate melt, or from liquid immiscibility of a carbonate-rich nephelinite that underwent magmatic fractionation and differentiation during ascent from the mantle source. Fluorapatite generally crystallizes early, near the liquidus, and over a small temperature interval below the apatite saturation temperature that varies strongly with temperature, SiO2 and CaO concentrations, and the aluminosity of the melt. Carbonatite-alkaline rock complexes commonly possess a concentric, zonal structure thought to reflect caldera volcanism. Pathfinder elements in soils, sediments, tills, and vegetation include Nb, rare earth elements (REEs), P, Ba, Sr, F, U, and Th, and in water, F, Th, and U are indicators. Remote sensing techniques with the ability to identify minerals rich in CO3, REEs, and Fe2+ that are characteristic of carbonatites are also important exploration tools that may provide vectors to ore. Sedimentary phosphorite is a marine bioelemental sedimentary rock that contains >18 wt % P2O5. While small peritidal phosphorites formed in Precambrian coastal environments, economically significant upwelling-related phosphorite did not accumulate until the late Neoproterozoic and continued through the Phanerozoic. Coastal upwelling delivered deep, P-rich waters to continental shelves and in epeiric seas to drive phosphogenesis and form the largest phosphorites on Earth. High-grade deposits formed as a result of hydraulic concentration of phosphate grains to form granular beds with minimal gangue. The amalgamation of these beds into decameter-thick, stratiform ore zones is generally focused along the maximum flooding surface, which is a primary exploration target in upwelling-related phosphorite. In addition to P, other elements concentrated in igneous and sedimentary phosphorites are Se, Mo, Zn, Cu, and Cr, which are important agricultural micronutrients. Other saleable by-products include U and REEs. The U concentration in sedimentary phosphorite is generally between 50 and 200 ppm, but can be as high as 3,000 ppm, making it an increasingly important source of U for the nuclear industry. The concentration of REEs in some sedimentary phosphorites is comparable to the world’s richest igneous and Chinese clay-type REE deposits. The source of the dissolved P in upwelling ocean water is ultimately derived from the chemical weathering of continental rocks, the process that links igneous and sedimentary phosphorites through time and space. The covarying temporal relationship of igneous and sedimentary deposits suggests that plate tectonics and the concentration of apatite in a progressively more felsic crust underpins the feedback processes regulating the biogeochemical cycling of P. Critical to the generation of greenfield exploration targets is the recognition that large P deposits emerged in the late Neoproterozoic. The geological environments conducive for exploration can be constrained from an understanding of ore-forming processes by the use of complementary petrological techniques, including fieldwork, petrography, sedimentology, sequence stratigraphy, and geochemistry.
DS201704-0644
2017
Putirka, K.D.Down the crater: where magmas are stored and why they erupt. Elements, Vol. 13, 1, pp. 11-16.MantleMagmatism

Abstract: Magmas are erupted from a wide range of depths. Olivine compositions, for example, indicate magma storage in the lower crust and upper mantle, while clinopyroxene and amphibole record middle to upper crust storage. Pre-eruptive magmas also often cool by 100-300?°C, frequently at middle-upper crust depths, indicating clogged, ephemeral volcanic pathways. These coolings imply that mafic recharge is not a sufficient cause for eruption and that crystallization-induced vapor saturation is a more proximal eruption trigger. But an improved understanding of eruption mechanisms require precise identifications of what are herein termed "ultimate", "proximal," and "immediate" causes of eruption.
DS201708-1739
2017
Pypus, G.New surprises at old discoveries: exploration and sampling of the AK11 kimberlite, Orapa kimberlite field, Botswana.11th. International Kimberlite Conference, PosterAfrica, Botswanadeposit - AK11
DS201708-1740
2017
Pypus, G.Exploration and sampling of the BK02 kimberlite, Orapa field, Botswana.11th. International Kimberlite Conference, PosterAfrica, Botswanadeposit - BK02
DS201709-2045
2017
Radhakrishna, T., Soumya, G.S., Satyanarayana, K.V.V.Paleomagnetism of the Cretaceous lamproites from Gondwana basin of the Damodar Valley in India and migration of the Kerguelen plume in the southeast Indian Ocean.Journal of Geodynamics, Vol. 109, pp. 1-9.Indialamproites

Abstract: The paper presents new palaeomagnetic results and reassesses complete set of published palaeomagnetic results on the lamproite intrusions in the Gondwana formations of the Eastern India. Altogether eleven sites register reliable characteristic magnetisations corresponding to the c. 110 Ma emplacement age of the lamproites. A mean ChRM is estimated with D = 331.3°; I = ?62.4° (?95 = 6.2°, k = 55; N = 11). The palaeomagnetic pole of ? = 14.9°: ? = 287.6° (A95 = 8.4°) is established for the lamproites and it averaged the secular variation and confirms to the Geocentric Axial Dipole (GAD). The pole compares remarkably well with the grand mean pole reported for the Rajmahal traps that are attributed to represent location of the Kerguelen mantle plume head. The palaeolatitudes transferred to Rajmahal coordinates (25.05°: 87.84°) are situated ?6° north of the present location of the Kerguelen hotspot location. The interpretations are consistent with earlier suggestions of southward migration of the plume based on palaeomagnetic results of Site 1138 of the ODP Leg 183 and with the predictions of numerical models of global mantle circulation.
DS201709-2046
2017
Radu, I.B., Harris, C., Moine, B., Costin, G., Cottin, J-Y.Subduction relics in the cratonic root - evidence from delta O18O variations in eclogite xenoliths.Goldschmidt Conference, abstract 1p.Africa, South Africadeposit, Roberts Victor, Jagersfontein
DS201710-2259
2017
Radu, I-B., Moine, B., Ionov, D., Korsakov, A., Golovin, A., Mikhailenko, D., Cottin, J-Y.Kyanite-bearing eclogite xenoliths from the Udachnaya kimberlite, Siberian craton, Russia.Bulletin de la Societe Geologique de France *eng, Vol. 188, 1-2, 14p.Russia, Siberiadeposit - Udachnaya

Abstract: Xenoliths brought up by kimberlite magmas are rare samples of otherwise inaccessible lithospheric mantle. Eclogite xenoliths are found in most cratons and commonly show a range of mineral and chemical compositions that can be used to better understand craton formation. This study focuses on five new kyanite-bearing eclogites from the Udachnaya kimberlite pipe (367±5 Ma). They are fine-to coarse-grained and consist mainly of “cloudy” clinopyroxene (cpx) and garnet (grt). The clinopyroxene is Al,Na-rich omphacite while the garnet is Ca-rich, by contrast to typical bi-mineral (cpx+grt) eclogites that contain Fe- and Mg-rich garnets. The Udachnaya kyanite eclogites are similar in modal and major element composition to those from other cratons (Dharwar, Kaapvaal, Slave, West African). The kyanite eclogites have lower REE concentrations than bi-mineral eclogites and typically contain omphacites with positive Eu and Sr anomalies, i.e. a “ghost plagioclase signature”. Because such a signature can only be preserved in non-metasomatised samples, we infer that they were present in the protoliths of the eclogites. It follows that subducted oceanic crust is present at the base of the Siberian craton. Similar compositions and textures are also seen in kyanite eclogites from other cratons, which we view as evidence for an Archean, subduction-like formation mechanism related to craton accretion. Thus, contrary to previous work that classifies all kyanite eclogites as type I (IK), metasomatized by carbonatite/kimberlitic fluids, we argue that some of them, both from this work and those from other cratons, belong to the non-metasomatized type II (IIB). The pristine type IIB is the nearest in composition to protoliths of mantle eclogites because it contains no metasomatic enrichments.
DS201702-0235
2016
Rakin, V.I., Kovalchuk, O.Y., Pomazansky, B.S.Dissymmetrization of artificial and natural diamonds,Doklady Earth Sciences, Vol. 471, 2, pp. 1303-1306.TechnologyDiamond crystallography

Abstract: The occurrence rates of combinatorial types of simple polyhedra {111} are analyzed for natural and artificial diamonds. The empirical occurrence rates of 14 possible polyhedra in an isotropic environment are obtained based on numeral simulation of growth forms of octahedral crystals by the Monte-Carlo method. The phenomenon of dissymmetrization by Curie’s principle related to the crystallization conditions is established for artificial and natural diamonds.
DS201708-1741
2017
Ranger, I.Punctuated long lived emplacement history of kimberlites from the Renard cluster, Superior Province, Canada indicated by new high precision U-Pb groundmass perovskite dating.11th. International Kimberlite Conference, OralCanada, Quebecdeposit - Renard
DS201708-1742
2017
Rapopo, M.The Liqhobong kimberlite cluster: a perspective on the distinct geology, emplacement, dilution and diamond grades for each intrusion.11th. International Kimberlite Conference, PosterAfrica, Lesothodeposit - Liqhobong
DS201708-1743
2017
Rapopo, M.The geology of the Liqhobong main pipe kimberlite.11th. International Kimberlite Conference, PosterAfrica, Lesothodeposit - Liqhobong
DS201708-1744
2017
Rapp, R.P.Metasomatism of cratonic lithosphere by hydrous, silica-rich, fluids derived from recycled sediment: experimental insights at 5-7GPa.11th. International Kimberlite Conference, OralTechnologymetasomatism
DS201709-2047
2017
Rapprich, V., Pecskay, Z., Magna, T., Mikova, J.Age disparity for spatially related Sevattur and Samalpatti carbonatite complexes.Goldschmidt Conference, abstract 1p.Indiacarbonatites

Abstract: The Neoproterozoic Sevattur and Samalpatti alkaline– carbonatite complexes in S India were supposedly emplaced into regional metagranite at ~800 Ma [1]. Both complexes are close to each other (~4 km apart), with a similar NE–SW elongated oval shape arranged along NE–SW trending lineament formed by the Koratti–Attur tectonic zone [2]. Both complexes share a similar setting with central syenite intrusion mantled with a discontinuous ring and/or crescentshaped suites of carbonatites, pyroxenites, gabbros, and dunites. In contrast to identical tectonic position and similar structure, the two complexes differ significantly in geochemistry and Sr–Nd–Pb–O–C isotope compositions. The Sevattur suite is derived from an enriched mantle source without significant post-emplacement modification whilst extensive hydrothermal overprint by crustal fluids must have occurred to result in the observed 13C–18O-enriched systematics reported for the Samalpatti carbonatites [3]. Some Samalpatti pyroxenites, though, show a clear mantle signature [3]. We report preliminary K–Ar age-data, that indicate a prolonged period of the magmatic activity in this area. Sevattur gabbro and pyroxenite (both Bt-fraction) as well as one Samalpatti Cr-rich silicocarbonatite (Amp-fraction) yielded the range of ages at 700–800 Ma, consistent with previous reports [see 3 for details]. The new K–Ar data from syenites display significantly younger ages of 560–576 Ma for Samalpatti and 510–540 Ma for Sevattur, regardless of the mineral fraction used (Bt or Kfs). The K–Ar results are being supplemented by systematic U–Pb analyses of zircons. If proven true, the age disparity would have profound consequences on our understanding of carbonatite evolution.
DS201702-0236
2016
Rastsvetaeva, R.K., Chukanov, N.V., Aksenov, S.M.The crystal chemistry of lamprophyllite related minerals: a review. European Journal of Mineralogy, Vol. 28, pp. 915-930.TechnologyMineral chemistry

Abstract: The crystal structures of the lamprophyllite-related minerals are based upon HOH modules consisting of a central octahedral O sheet sandwiched between two heteropolyhedral H sheets. The general crystal-chemical formula for these minerals can be written as [10-11]A2 [[6]M1[6]M22[6]2M3X2] [[5]L2(Si2O7)2O2], where the contents of the O and H sheets are given in square brackets in this order and A = Ba, Sr, K, Na,; M1 = Na, Mn2+; M2 = Na, Mn2+, Fe2+, Ca; M3 = Ti, Mn2+, Mg, Fe3+, Fe2+; L = Ti, Fe3+; X = OH, O, F. According to the unit-cell parameters and symmetry, lamprophyllite-related minerals can be subdivided into five structure types: I (monoclinic polytypes, C2/m); II (orthorhombic polytypes, Pnmn), III (nabalamprophyllite, BaNa[Na3Ti (OH)2][Ti2(Si2O7)2O2], monoclinic, P2/m, with an ordered arrangement of the interlayer Ba2+ and Na+ cations), IV (triclinic, P1) and V (triclinic, Embedded Image ). The triclinic members (types IV and V) include schüllerite and its analogues, which differ from the lamprophyllite-group minerals sensu stricto in their symmetry and topology of the HOH modules. The end-member formulae of lamprophyllite-related minerals and the position of schüllerite in the ranks of heterophyllosilicates are discussed.
DS201702-0237
2017
Ravenscroft, P.Diamond Resource Evaluation - evolution of techniques from African roots.PDAC 2017, March 6, 1p. AbstractTechnologyEconomics - evaluation
DS201708-1745
2017
Rayner, M.New insights into volcanic processes and diamond grades from deep mining at Argyle.11th. International Kimberlite Conference, OralAustraliaDeposit - Argyle
DS201710-2260
2017
Rebetsky, Yu.L., Sim, L.A., Kozyrev, A.A.Possible mechanism of horizontal overpressure generation of the Khibiny, Lovozero, and Kovdor ore clusters on the Kola Peninsula.Geology of Ore Deposits, Vol. 59, 4, pp. 265-280.Russia, Kola Peninsuladeposit - Khibiny, Lovozero, Kovdor

Abstract: The paper discusses questions related to the generation of increasing crustal horizontal compressive stresses compared to the idea of the standard gravitational state at the elastic stage or even from the prevalence of horizontal compression over vertical stress equal to the lithostatic pressure. We consider a variant of superfluous horizontal compression related to internal lithospheric processes occurrin in the crust of orogens, shields, and plates. The vertical ascending movements caused by these motions at the sole of the crust or the lithosphere pertain to these and the concomitant exogenic processes giving rise to denudation and, in particular, to erosion of the surfaces of forming rises. The residual stresses of the gravitational stressed state at the upper crust of the Kola Peninsula have been estimated for the first time. These calculations are based on the volume of sediments that have been deposited in Arctic seas beginning from the Mesozoic. The data speak to the possible level of residual horizontal compressive stresses up to 90 MPa in near-surface crustal units. This estimate is consistent with the results of in situ measurements that have been carried out at the Mining Institute of the Kola Science Center, Russian Academy of Sciences (RAS), for over 40 years. It is possible to forecast the horizontal stress gradient based on depth using our concept on the genesis of horizontal overpressure, and this forecasting is important for studying the formation of endogenic deposits.
DS201712-2721
2017
Reddy, K.V.S.Precambrian lithostratigraphy of Dharwar craton and adjoining fold and mobile belts.Journal of the Geological Society of India, Vol. 90, 4, pp. 507-Indiacraton
DS201709-2048
2017
Reimink, J.R., Carlson, R.W., Shirey, S.B., Pearson, D.G.Crustal evolution of the Archean Slave craton, NWT.Goldschmidt Conference, abstract 1p.Canada, Northwest Territoriesgeochronology

Abstract: The Slave craton, located in the northwestern portion of the Canadian Shield, contains the oldest known remnant of evolved crust on Earth [1?3] and more extensive suites of granitoid basement gneisses with crystallization ages that nearly span the breadth of the Archean. Portions of these basement gneisses form the Central Slave Basement Complex (CSBC), a belt of exposures recording magmatic events that occurred approximately every 100?150 million years from 3.5?2.7 Ga [4]. When considered with the 4.02 Ga Acasta Gneiss Complex, the good exposure and wide age range of basement gneisses of the Slave craton provide a unique record of the geological processes involved in continent formation. A suite of 3.5?2.7 gyr old Slave craton granitoids collected from a 200 km-long traverse of the CSBC has intermediate to felsic compositions, textures that range from migmatitic gneisses to preservation of primary magmatic features. Preliminary Sm-Nd isotope systematics, as well as zircon U-Pb and Hf isotope data suggest that the granitoids reflect both the products of reworking of Hadean crust, as indicated by the presence of 142Nd deficits in some of the units, but also new additions from the mantle as indicated both in the chemical composition and initial isotopic composition of other rock units. For those samples that derive from remelting of older crustal materials, the initial Hf isotopic composition of zircons are most consistent with a source component that includes Hadean mafic crust. The multiple U-Pb age peaks documented by accessory minerals show a close correspondence with age spectra from the welldocumented mantle lithosphere beneath this region [5] illustrating the coupled evolution of crust and mantle.
DS201707-1360
2017
Reis, N.J., Nadeau, S., Fraga, L.M., Menezes Betiollo, L., Telma Lins Faraco, M., Reece, J., Lachhman, D., Ault, R.Stratigraphy of the Roraima Supergroup along the Brazil Guyana border in the Guiana shield, northern Amazonian craton - results of the Brazil Guyana geology and geodiversity mapping project.Brazil Journal of Geology, Vol. 47, 1, pp. 43-57.South America, Brazil, Guyanacraton

Abstract: The Geological and Geodiversity Mapping binational program along the Brazil?Guyana border zone allowed reviewing and in? tegrating the stratigraphy and nomenclature of the Roraima Supergroup along the Pakaraima Sedimentary Block present in northeastern Brazil and western Guyana. The area mapped corresponds to a buffer zone of approximately 25 km in width on both sides of the border, of a region extending along the Maú?Ireng River between Mount Roraima (the tri? ple?border region) and Mutum Village in Brazil and Monkey Mountain in Guyana. The south border of the Roraima basin is overlain exclusively by effusive and volcaniclastic rocks of the Surumu Group of Brazil and its correlated equivalent the Burro?Burro Group of Guyana.
DS201703-0431
2017
Reutsky, V.N.Carbon isotope fractionation in models of diamond forming media under lithoscopic pressure temperature conditions. ***In RUSInstitute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Dsc. 252p. *** in RUS available pdfMantleDiamond - genesis
DS201712-2722
2017
Reyes, A.V., Wolfe, A.P., Tierney, J.E., Silver, P.A., Royer, D.L., Greenwood, D.R., Buryak, S., Davies, J.H.F.L.Paleoenvironmental research on early Cenozoic sediment fills in Lac de Gras kimberlite pipes: progress and prospects.45th. Annual Yellowknife Geoscience Forum, p. 65 abstractCanada, Northwest Territoriesdeposit - Giraffe

Abstract: Several Lac de Gras kimberlite pipes host thick accumulations of stratified post-eruptive lacustrine sediment and peat. Given the range of Lac de Gras kimberlite emplacement ages, these fills - though rare - provide a unique sedimentary archive of paleoenvironments during the sustained Early Cenozoic “greenhouse” interval, in a high-latitude region otherwise devoid of Phanerozoic sediment cover. Extensive exploration drilling has provided a valuable window into this unique sedimentary record, which would have otherwise remained covered by Quaternary glacial deposits. Our focus to date has been multidisciplinary study of the Giraffe pipe sediment fill: an ~80 m-thick sequence of post-eruptive lacustrine silt overlain by peat, which paints a remarkable picture of a humid-temperate Middle Eocene forest ecosystem on the Canadian Shield. Post-eruptive chronology is provided by interbedded distal tephra horizons, likely sourced from Alaska, that have been dated by glass fission-track and zircon U-Pb techniques. Paleoclimate proxies derived from pollen, wood cellulose oxygen isotopes, and biomarkers converge on reconstructed mean annual temperatures >17 °C warmer than present, with mean winter temperatures above freezing, and mean annual precipitation ~4x present. Two independent reconstructions of CO2 from well preserved conifer foliage suggest that this warming occurred under relatively modest atmospheric CO2 concentrations of 430-630 ppm. These findings provide direct field-based evidence for dramatic past arctic warming at CO2 concentrations that were well within the range of projections under “business-as-usual” emissions scenarios, underscoring the capacity for exceptional polar amplification of climate change under modest CO2 concentrations once both fast and slow feedbacks processes become expressed. Our studies at Giraffe pipe also highlight the scientific value of archived exploration drill core in the Lac de Gras kimberlite field, particularly with respect to pipes that are unremarkable for the purpose of diamond exploration.
DS201708-1746
2017
Richardson, S.Old unradiogenic Os in deep mantle metallic liquid from large gem II a diamonds.11th. International Kimberlite Conference, OralMantlediamond morphology
DS201711-2526
2017
Richet, P.The creation of the world and the birth of chronology. HISTORYComptes Rendus Geoscience, Vol. 349, pp. 226-232.Technologyhistory

Abstract: The eternity of the world and, correlatively, the cyclical nature of time were agreed upon by all Greek philosophical schools except the Platonists. As for matter, all of them posited that it was eternal so that the idea that something could be made from nothing was considered as pure absurdity. With the advent of Christianity, however, a matter coeternal with God raised fundamental theological difficulties. Toward the end of the second century, apologists such as Tatian the Assyrian, Theophilus of Antioch, Irenaeus of Lyons or Tertullian thus emphasized God's absolute freedom and power by claiming that Creation had been made from nothing. Along with the Passion of Christ and the Last Judgment, the initial moment defined by the Creation then conferred to time an irreversible, linear orientation and to history both a new sense and an obsessing concern for chronology. Unambiguously, the Creation became the reference point for the world's history. From Scripture analyses, one determined that it took place about 5500 years earlier within a framework where the History of man and that of the earth were not distinct. Having designed a consistent, universal time scale from chronological data recorded for all ancient peoples, Eusebius of Caesarea could thus attribute to the Great Flood the fossils found on the top of Mount Lebanon. The short Mosaic chronologies were eventually rejected during the 18th century, but Eusebius’ chronological procedure was unknowingly transposed when a relative geological timescale was then set up from the fossil record. The close association of Creation with Christian dogma in turn induced some circles to reject the second law of thermodynamics at the end of the 19th century and, a few decades later, the thesis of an expanding universe. In both cases, the reason was that continuously increasing entropy would imply some low-entropy initial state akin to a Creation.
DS201702-0238
2017
Righter, K., Nickodem, K., Pando, K., Danielson, L., Boujibar, A., Righter, M., Lapen, T.J.Distribution of Sb, As, Ge and in between metal and silicate during acccretion and core formation in the Earth.Geochimica et Cosmochimica Acta, Vol. 198, pp. 1-16.MantleCore chemistry

Abstract: A large number of siderophile (iron-loving) elements are also volatile, thus offering constraints on the origin of volatile elements in differentiated bodies such as Earth, Moon, Mars and Vesta. Metal-silicate partitioning data for many of these elements is lacking, making their overall mantle concentrations in these bodies difficult to model and origin difficult to distinguish between core formation and volatile depletion. To address this gap in understanding, we have undertaken systematic studies of four volatile siderophile elements - Sb, As, Ge and In - at variable temperature and variable Si content of metal. Several series were carried out at 1 GPa, and between 1500 and 1900 °C, for both C saturated and C-free conditions. The results show that temperature causes a decrease in the metal/silicate partition coefficient for all four elements. In addition, activity coefficients for each element have been determined and show a very strong dependence on Si content of Fe alloy. Si dissolved in metal significantly decreases the metal/silicate partition coefficients, at both 1600 and 1800 °C. The combination of temperature and Si content of the metal causes reduction of the metal-silicate partition coefficient to values that are close to those required for an origin of mantle As, Sb, Ge, and In concentrations by metal-silicate equilibrium processes. Combining these new results with previous studies on As, Sb, Ge, and In, allowed derivation of predictive expressions for metal/silicate partition coefficients for these elements which can then be applied to Earth. The expressions are applied to two scenarios for continuous accretion of Earth; specifically for constant and increasing fO2 during accretion. The results indicate that mantle concentrations of As, Sb, Ge, and In can be explained by metal-silicate equilibrium during an accretion scenario. The modeling is not especially sensitive to either scenario, although all element concentrations are explained better by a model with variable fO2. The specific effect of Si is important and calculations that include only S and C (and no Si) cannot reproduce the mantle As, Sb, Ge, and In concentrations. The final core composition in the variable fO2 model is 10.2% Si, 2% S, and 1.1% C (or XSi = 0.18, XS = 0.03, and XC = 0.04. These results suggest that core formation (involving a Si, S, and C-bearing metallic liquid) and accretion were the most important processes establishing many of Earth’s mantle volatile elements (indigenous), while post-core formation addition or re-equilibration (exogenous) was of secondary or minor importance.
DS201706-1101
2017
Roberge, M., Bureau, H., Bolfan-Casanova, N., Raepsaet, C., Surble, S., Khodja, H., Auzende, A-L., Cordier, P., Fiquet, G.Chlorine in wadsleyite and ringwoodite: an experimental study.Earth and Planetary Science Letters, Vol. 467, pp. 99-107.Mantlechlorine

Abstract: We report concentrations of Chlorine (Cl) in synthetic wadsleyite (Wd) and ringwoodite (Rw) in the system NaCl-(Mg,?Fe)2SiO4 under hydrous and anhydrous conditions. Multi-anvil press experiments were performed under pressures (14-22 GPa) and temperatures (1100-1400?°C) relevant to the transition zone (TZ: 410-670 km depth). Cl and H contents were measured using Particle Induced X-ray Emission (PIXE) and Elastic Recoil Detection Analysis (ERDA) respectively. Results show that Cl content in Rw and Wd is significantly higher than in other nominally anhydrous minerals from the upper mantle (olivine, pyroxene, garnet), with up to 490 ppm Cl in anhydrous Rw, and from 174 to 200 ppm Cl in hydrous Wd and up to 113 ppm Cl in hydrous Rw. These results put constrains on the Cl budget of the deep Earth. Based on these results, we propose that the TZ may be a major repository for major halogen elements in the mantle, where Cl may be concentrated together with H2OH2O and F (see Roberge et al., 2015). Assuming a continuous supply by subduction and a water-rich TZ, we use the concentrations measured in Wd (174 ppm Cl) and in Rw (106 ppm Cl) and we obtain a maximum value for the Cl budget for the bulk silicate Earth (BSE) of 15.1 × 1022 g Cl, equivalent to 37 ppm Cl. This value is larger than the 17 ppm Cl proposed previously by McDonough and Sun (1995) and evidences that the Cl content of the mantle may be higher than previously thought. Comparison of the present results with the budget calculated for F (Roberge et al., 2015) shows that while both elements abundances are probably underestimated for the bulk silicate Earth, their relative abundances are preserved. The BSE is too rich in F with respect to heavy halogen elements to be compatible with a primordial origin from chondrites CI-like (carbonaceous chondrites CC) material only. We thus propose a combination of two processes to explain these relative abundances: a primordial contribution of different chondritic-like materials, including EC-like (enstatite chondrites), possibly followed by a distinct fractionation of F during the Earth differentiation due to its lithophile behavior compared to Cl, Br and I.
DS201708-1747
2017
Roberts, M.Varied emplacement mechanisms with adjacent kimberlite vents, Jwaneng mine, Botswana11th. International Kimberlite Conference, OralAfrica, BotswanaDeposit - Jwaneng
DS201710-2261
2017
Robey, J.First Gems: Kimberley and surrounds, South Africa. Big Hole, Finsch, Koffiefontein, Kareevlei11th International Kimberlite Field Trip Guide, Sept. 62p. PdfAfrica, South Africadeposit - Kimberley, Finsch, Koffiefontein, Kareevlei
DS201710-2262
2017
Robinson, P.T., Yang, J., Tian, Y., Zhu, H.Diamonds, super reduced and crustal minerals in chromitites of the Hegenshan and Sartohay ophiolites, central Asian orogenic belt, China.Acta Geologica Sinica, Vol. 91, s1, p. 32 abstractChinadiamond inclusions

Abstract: The Central Asian Orogenic Belt (CAOB) is a huge tectonic mélange that lies between the North China Craton and the Siberian Block. It is composed of multiple orogenic belts, continental fragments, magmatic and metamorphic rocks, suture zones and discontinuous ophiolite belts. Although the Hegenshan and Sartohay ophiolites are separated by nearly 3000 km and lie in completely different parts of the CAOB, they are remarkably similar in many respects. Both are composed mainly of serpentinized peridotite and dunite, with minor gabbro and sparse basalt. They both host significant podiform chromitites that consist of high-Al, refractory magnesiochromite with Cr#s [100Cr/(Cr+Al)] averaging >60. The Sartohay ophiolite has a zircon U-Pb age of ca. 300 Ma and has been intruded by granitic plutons of similar age, resulting in intense hydrothermal activity and the formation of gold-bearing listwanites. The age of the Hegenshan is not firmly established but is thought to have formed in the Carboniferous. Like many other ophiolites that we have investigated in other orogenic belts, the chromitites in these two bodies have abundant diamonds, as well as numerous super-reduced and crustal minerals. The diamonds are mostly, colorless to pale yellow, 200-300 ?m across and have euhedral to anhedral shapes. They all have low carbon isotopes (?14C = ?18 to ?29) and some have visible inclusions. These are accompanied by numerous super-reduced minerals such as moissanite, native elements (Fe, Cr, Si, Al, Mn), and alloys (e.g., Ni-Mn-Fe, Ni-Fe-Al, Ni-Mn-Co, Cr-Ni-Fe, Cr-Fe, Cr-Fe-Mn), as well as a wide range of oxides, sulfides and silicates. Grains of zircon are abundant in the chromitites of both ophiolites and range in age from Precambrian to Cretaceous, reflecting both incorporation of old zircons and modification of grains by hydrothermal alteration. Our investigation confirms that high-Al, refractory chromitites in these two ophiolites have the same range of exotic minerals as high-Cr metallurgical chromitites such as those in the Luobusa ophiolite of Tibet. These collections of exotic minerals in ophiolitic chromitites indicate complex, multi-stage recycling of oceanic and continental crustal material at least to the mantle transition zone, followed by uprise and emplacement of the peridotites into relatively shallow ophiolites.
DS201710-2263
2012
Robles-Cruz, S.E., Melgarejo, J.C., Gali, S., Escayola, M.Major and trace element compositions of indicator minerals that occur as macro and megacrysts, and of xenoliths, from kimberlites in northeastern Angola.Minerals NOTE Date, Vol. 2, pp. 318-337.Africa, Angoladeposits - Tchiuzo, Anomaly 116, Catoca, Alt Cuilo-4, Cuilo-63, Cucumbi-79.

Abstract: In this study, we compare the major- and trace-element compositions of olivine, garnet, and clinopyroxene that occur as single crystals (142 grains), with those derived from xenoliths (51 samples) from six kimberlites in the Lucapa area, northeastern Angola: Tchiuzo, Anomaly 116, Catoca, Alto Cuilo-4, Alto Cuilo-63 and Cucumbi-79. The samples were analyzed using electron probe microanalysis (EPMA) and laser-ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS). The results suggest different paragenetic associations for these kimberlites in the Lucapa area. Compositional overlap in some of the macrocryst and mantle xenolith samples indicates a xenocrystic origin for some of those macrocrysts. The presence of mantle xenocrysts suggests the possibility of finding diamond. Geothermobarometric calculations were carried out using EPMA data from xenoliths by applying the program PTEXL.XLT. Additional well calibrated single-clinopyroxene thermobarometric calculations were also applied. Results indicate the underlying mantle experienced different equilibration conditions. Subsequent metasomatic enrichment events also support a hypothesis of different sources for the kimberlites. These findings contribute to a better understanding of the petrogenetic evolution of the kimberlites in northeastern Angola and have important implications for diamond exploration.
DS201708-1580
2017
Rocco, I., Zanetti, A., Melluso, L., Morra, V.Ancient depleted and enriched mantle lithosphere domains in northern Madagascar: geochemical and isotopic evidence from spinel-to-plagioclase-bearing ultramafic xenoliths. Massif d'Ambre and BobaombyChemical Geology, in press available, 16p.Africa, Madagascarmelting

Abstract: Mantle xenoliths hosted in Cenozoic alkaline rocks of northern Madagascar (Massif d'Ambre and Bobaomby volcanic fields) are spinel lherzolites, harzburgites and rare websterites. Petrography, electron microprobe, LA-ICP-MS and thermal ionization mass spectrometry techniques allowed to recognize domains characterized by variable degree of partial melting and extent of re-enrichment processes: 1) refractory spinel-to-spinel + plagioclase-lherzolites, with clinopyroxenes having marked LREE (Light Rare Earth Elements) depletion ((La/Yb)N ~ 0.2) and very high 143Nd/144Nd (0.513594), which represent a limited and shallow portion of old mantle that suffered low degree partial melting (2–3%) and was later accreted to the lithosphere. These lherzolites acted as a low-porosity region, being, in places, percolated by small volumes of melts shortly before eruption; 2) lherzolites and harzburgites that suffered variable degrees of partial melt extraction (up to 15%), assisted and/or followed by pervasive, porous flow infiltration of alkaline melts in a relatively large porosity region, leading to the creation of a wide area rich in secondary mineral phases (i.e. olivine, clinopyroxene and pargasitic amphibole), enriched in incompatible elements (e.g., LaN/YbN in clinopyroxene up to 15) and having radiogenic Sr and unradiogenic Nd; 3) websterites and wehrlite-bearing samples that record differentiation processes of alkaline melts highly enriched in Th, U and LREE, not yet documented in the erupted volcanics of northern Madagascar. The mantle xenoliths of northern Madagascar show a regional decrease of the equilibration temperature from to SW (up to 1180 °C, Nosy Be Archipelago) to the NE (up to 900 °C, Bobaomby district). A significant lithologic and geochemical variation of the shallow lithospheric mantle beneath northern Madagascar is noted, in contrast with the relatively uniform geochemical and isotopic composition of the host alkali basalt and basanite lavas.
DS201709-2049
2017
Rodionov, N.V. , Lepekhina, E.N., Antonov, A.V., Petrov, O.V., Belyatsky, B.V., Shevchenko, S.S., Sergeev, S.A.Pyrochlore and baddeleyite from carbonatites of the Paleozoic polyphase Kovdor Massif ( N. Karelia).Goldschmidt Conference, abstract 1p.Russia, Kareliacarbonatite. Kovdor

Abstract: Pyrochlore is the main host of rare-metal elements of carbonatite rocks, including phoscorites, typical for prolonged history of alkaline magma crystallization at the mafic-ultramafic polyphase Kovdor massif. Pyrochlore associated with baddeleyite, zircon, zirkelite, zirkonolite and forms octahedral and cube-octahedral poikilitic crystals up to 2-5 cm, and represented by U, Ba-Sr and REE species of pyrochlore subgroup. The studied Kovdor pyrochlores are characterized by increased up to 6.5% U and an extremely high Th – up to 40%, with Th/U up to 500. Pyrochlore U-Pb SHRIMP ages of 290-364 Ma correlate with variations in U of different samples, whereas the Th and common Pb have a minor effect on this value. Obtained ages are significantly underestimated and may reflect the influence of the matrix effect or later low-temperature closing of the U-Pb pyrochlore system, as well as the actual transformations of pyrochlore crystal matrix due to the interaction with the late carbonate fluids. Thus the early pyrochlores and U-pyrochlores crystallized at 364 Ma within phoscorites and early calcite carbonatites, whereas Sr-Ba pyrochlores of late calcitedolomite carbonatite formed at 340 Ma, and Th-pyrochlore rims occured at the later stages of the interaction with metasomatizing fluids 290 m.y. ago. Kovdor baddeleyite is also charecterized by high composition heterogeneity determined by the difference in its origin from olivinites to ore-bearing foscorites and postmagmatic syenites. But baddeleyite from calcitemagnetite mineral association have uniform U: 184 ±40, Th: 6.4 ±1.7, ¦REE: 34 ±6, Hf: 7629 ± 599, Nb: 3595 ±840, Ti: 56 ±14, Y: 22 ±4 ppm, and HHf: +6.5 ±1.7 at the age of 379 ±6 Ma. The U-Pb SHRIMP age data demonstrate the concordance of all studied baddeleyite samples and the absence of a significant age difference between baddeleyites of the carbonatite phase: 379 ±3 and foscorites: 379 ±4 Ma. The weighted average age for all the studied baddeleyite samples (n = 8) is 379 ±2.4 Ma at MSWD of 0.6. This can also indicate a relatively short time-interval of magmatism in the formation of Kovdor polyphase massif which did not exceed 5 m.y. and could be related to the Devonian mantleplume activity.
DS201705-0872
2017
Rollinson, H., Adetunji, J., Lenaz, D., Szilas, K.Archean chromitites show constant Fe3+/Efe in Earth's asthenospheric mantle since 3.8 Ga.Journal of Petrology, in press available 42p.Europe, Greenland, Africa, ZimbabweMelting, Fiskenaesset Compex, Ujaragssuit, Limpopo belt
DS201712-2723
2017
Romanowicz, B.The bouyancy of Earth's deep mantle.Nature, Vol. 551, 7680, p. 321.Mantlegeophysics

Abstract: The physical nature of two regions called large low-shear-velocity provinces at the base of Earth's mantle is uncertain. A measurement of their density has implications for our understanding of mantle dynamics.
DS201702-0239
2017
Rooney, T.O., Nelson, W.R., Ayalew, D., Hanan, B., Yirgu, G., Kappelman, J.Melting the lithosphere: metasomes as a source for mantle derived magmas.Earth and Planetary Science Letters, Vol. 461, pp. 105-118.MantleMetasomatism

Abstract: Peridotite constitutes most of the Earth's upper mantle, and it is therefore unsurprising that most mantle-derived magmas exhibit evidence of past equilibrium with an olivine-dominated source. Although there is mounting evidence for the role of pyroxenite in magma generation within upwelling mantle plumes, a less documented non-peridotite source of melts are metasomatic veins (metasomes) within the lithospheric mantle. Here we present major and trace element analyses of 66 lavas erupted from a small Miocene shield volcano located within the Ethiopian flood basalt province. Erupted lavas are intercalated with lahars and pyroclastic horizons that are overlain by a later stage of activity manifested in small cinder cones and flows. The lavas form two distinctive petrographic and geochemical groups: (A) an olivine-phyric, low Ti group (1.7-2.7 wt.% TiO2; 4.0-13.6 wt.% MgO), which geochemically resembles most of the basalts in the region. These low Ti lavas are the only geochemical units identified in the later cinder cones and associated lava flows; (B) a clinopyroxene-phyric high Ti group (3.1-6.5 wt.% TiO2; 2.8-9.2 wt.% MgO), which resembles the Oligocene HT-2 flood basalts. This unit is found intercalated with low Ti lavas within the Miocene shield. In comparison to the low Ti group, the high Ti lavas exhibit a profound depletion in Ni, Cr, Al, and Si, and significant enrichment in Ca, Fe, V, and the most incompatible trace elements. A characteristic negative K anomaly in primitive-mantle normalized diagrams, and Na2O > K2O, suggests a source rich in amphibole, devoid of olivine, and perhaps containing some carbonate and magnetite. While melt generation during rift development in Ethiopia is strongly correlated with the thermo-chemical anomalies associated with the African Superplume, thermobaric destabilization and melting of mantle metasomes may also contribute to lithospheric thinning. In regions impacted by mantle plumes, such melts may be critical to weakening of the continental lithosphere and the development of rifts.
DS201712-2724
2017
Ross, M., Kelley, S.E., Janzen, R.J.D., Stirling, R.A., Normandeau, P.X., Elliott, B.Tracing the breadcrumbs back tp their source: exploring geological factors controlling production of atypical glacial dispersal patterns of indicator minerals45th. Annual Yellowknife Geoscience Forum, p. 67 abstractCanada, Northwest Territoriesgeochemistry - indicator minerals

Abstract: Tracing surficial dispersal patterns of indicator minerals within glacial sediments in the main up-ice direction has greatly contributed to numerous mineral discoveries of economic value in the Northwest Territories. However, many cases have also reported perplexing scenarios of dispersal trains seemingly lacking a source, or known sources without a spatially associated dispersal train at the surface. These ‘special’ cases often hinder exploration efforts, and tend to remain poorly understood; yet these cases are becoming increasingly important to decipher as exploration moves into more complex terrains. We present an overview of our research done in the Lac de Gras area over the past few years in collaboration with the Northwest Territories Geological Survey and their partners investigating the effect of multiple ice flows, variable bedrock topography and drift thickness, and the complexities of glacial sedimentary environments on 2D and 3D mechanical (detrital) dispersion. Our research draws from surface and subsurface datasets from various sources at both the regional and local scales. We show that despite the occurrence of relatively long, continuous, surficial patterns extending in the direction of the latest-strongest ice flow event in the region, a subtle record of the time-transgressive glacial history is also frequently preserved. These records yield information about the net effect on sediment dispersion of multiple ice flow phases, bedrock geology, basal topography, and glacial depositional processes. Our findings suggest these geological factors played a key role in producing some of the most irregular and enigmatic dispersal patterns in the region. They also offer insights into how to best characterize and explain the signal (or lack thereof) from elusive buried sources of potential economic interest.
DS201703-0432
2017
Ross, P-S., Carrasco Nunez, G., Hayman, P.Felsic maar-diatreme volcanoes: a review.Bulletin of Volcanology, Vol. 79, 2 in press availableSouth America, MexicoDiatremes

Abstract: Felsic maar-diatreme volcanoes host major ore deposits but have been largely ignored in the volcanology literature, especially for the diatreme portion of the system. Here, we use two Mexican tuff rings as analogs for the maar ejecta ring, new observations from one diatreme, and the economic geology literature on four other mineralized felsic maar-diatremes to produce an integrated picture of this type of volcano. The ejecta rings are up to 50 m+ thick and extend laterally up to ?1.5 km from the crater edge. In two Mexican examples, the lower part of the ejecta ring is dominated by pyroclastic surge deposits with abundant lithic clasts (up to 80% at Hoya de Estrada). These deposits display low-angle cross-bedding, dune bedforms, undulating beds, channels, bomb sags, and accretionary lapilli and are interpreted as phreatomagmatic. Rhyolitic juvenile clasts at Tepexitl have only 0-25% vesicles in this portion of the ring. The upper parts of the ejecta ring sequences in the Mexican examples have a different character: lithic clasts can be less abundant, the grain size is typically coarser, and the juvenile clasts can be different in character (with some more vesicular fragments). Fragmentation was probably shallower at this stage. The post-eruptive maar crater infill is known at Wau and consists of reworked pyroclastic deposits as well as lacustrine and other sediments. Underneath are bedded upper diatreme deposits, interpreted as pyroclastic surge and fall deposits. The upper diatreme and post-eruptive crater deposits have dips larger than 30° at Wau, with approximately centroclinal attitudes. At still lower structural levels, the diatreme pyroclastic infill is largely unbedded; Montana Tunnels and Kelian are good examples of this. At Cerro de Pasco, the pyroclastic infill seems bedded despite about 500 m of post-eruptive erosion relative to the pre-eruptive surface. The contact between the country rocks and the diatreme is sometimes characterized by country rock breccias (Kelian, Mt. Rawdon). Pyroclastic rocks in the diatreme are typically poorly sorted, and ash-rich. They contain a heterolithic mix of juvenile clasts and lithic clasts from various stratigraphic levels. Megablocks derived from the ejecta ring or the country rocks are often found in the diatremes. Evidence for multiple explosions is in the form of steep crosscutting pyroclastic bodies within some diatremes and fragments of pyroclastic rocks within other pyroclastic facies. Pyroclastic rocks are cut by coherent felsic dikes and plugs which may have been feeders to lava domes at the surface. Allowing for the difference in magma composition, felsic maar-diatreme volcanoes have many similarities with their ultramafic to mafic equivalents. Differences include a common association with felsic domes, inside the crater or just outside (Wau), although the domes within the crater may be destroyed during the eruption (Hoya de Estrada, Tepexitl); the dikes and plugs feeding and invading felsic diatremes seem larger; the processes of phreatomagmatic explosions involving felsic magmas may be different.
DS201712-2725
2017
Rossoni, M.B., Bastos Neto, A.C., Souza, V.S., Marquea, J.C., Dantas, E., Botelho, N.F., Giovannini, A.L., Pereira, V.P.U-Pb zircon geochronological investigation on the Morro dos Seis Lagos carbonatite complex and associated Nb deposit ( Amazonas, Brazil).Journal of South American Earth Sciences, Vol. 80, pp. 1-17.South America, Brazilcarbonatite

Abstract: We present results of U-Pb dating (by MC-ICP-MS) of zircons from samples that cover all of the known lithotypes in the Seis Lagos Carbonatite Complex and associated lateritic mineralization (the Morro dos Seis Lagos Nb deposit). The host rock (gneiss) yielded an age of 1828 ± 09 Ma interpreted as the crystallization time of this unit. The altered feldspar vein in the same gneiss yielded an age of 1839 ± 29 Ma. Carbonatite samples provided 3 groups of ages. The first group comprises inherited zircons with ages compatible with the gneissic host rock: 1819 ± 10 Ma (superior intercept), 1826 ± 5 Ma (concordant age), and 1812 ± 27 Ma (superior intercept), all from the Orosirian. The second and the third group of ages are from the same carbonatite sample: the superior intercept age of 1525 ± 21 Ma (MSWD ¼ 0.77) and the superior intercept age of 1328 ± 58 Ma (MSWD ¼ 1.4). The mineralogical study indicates that the ~1.3 Ga zircons have affinity with carbonatite. It is, however, a tendence rather than a well-defined result. The data allow state that the age of 1328 ± 58 Ma represents the maximum age of the carbonatite. Without the same certainty, we consider that the data suggest that this age may be the carbonatite age, whose emplacement would have been related to the evolution of the K'Mudku belt. The best age obtained in laterite samples (a superior intercept age of 1828 ± 12 Ma) is considered the age of the main source for the inherited zircons related to the gneissic host rock.
DS201706-1102
2017
Rozel, A.B., Golabek, G.J., Jain, C., Tackley, P.J., Gerya, T.Continental crust formation on early Earth controlled by intrusive magmatism.Nature, online availableMantlegeodynamics

Abstract: The global geodynamic regime of early Earth, which operated before the onset of plate tectonics, remains contentious. As geological and geochemical data suggest hotter Archean mantle temperature1, 2 and more intense juvenile magmatism than in the present-day Earth3, 4, two crust-mantle interaction modes differing in melt eruption efficiency have been proposed: the Io-like heat-pipe tectonics regime dominated by volcanism5, 6 and the “Plutonic squishy lid” tectonics regime governed by intrusive magmatism, which is thought to apply to the dynamics of Venus7, 8, 9. Both tectonics regimes are capable of producing primordial tonalite-trondhjemite-granodiorite (TTG) continental crust5, 10 but lithospheric geotherms and crust production rates as well as proportions of various TTG compositions differ greatly9, 10, which implies that the heat-pipe and Plutonic squishy lid hypotheses can be tested using natural data11. Here we investigate the creation of primordial TTG-like continental crust using self-consistent numerical models of global thermochemical convection associated with magmatic processes. We show that the volcanism-dominated heat-pipe tectonics model results in cold crustal geotherms and is not able to produce Earth-like primordial continental crust. In contrast, the Plutonic squishy lid tectonics regime dominated by intrusive magmatism results in hotter crustal geotherms and is capable of reproducing the observed proportions of various TTG rocks. Using a systematic parameter study, we show that the typical modern eruption efficiency of less than 40 per cent12 leads to the production of the expected amounts of the three main primordial crustal compositions previously reported from field data4, 11 (low-, medium- and high-pressure TTG). Our study thus suggests that the pre-plate-tectonics Archean Earth operated globally in the Plutonic squishy lid regime rather than in an Io-like heat-pipe regime.
DS201708-1748
2017
Russell, K.Transport and eruption of mantle xenoliths: a lagging problem.11th. International Kimberlite Conference, OralMantleXenoliths
DS201712-2726
2017
Sacco, D.A., McKillop, R.J., Ward, B.C.Why your kim-bearing till samples may not be leading you to kimberlite.45th. Annual Yellowknife Geoscience Forum, p. 70 abstractCanada, Northwest Territoriesgeochemistry - indicator minerals

Abstract: Kimberlite indicator mineral (KIM) concentrations in till are commonly used in glaciated areas such as Northwest Territories to identify glacial dispersal from a kimberlitic source. However, sampling of till that has been modified by post-depositional processes, or material that is not till, can obscure the original glacial dispersion and mislead exploration efforts. The recognition of subtle changes in material type or the occurrence of till modification is obstructed by periglacial processes that homogenize the landscape. Due to restrictions of scale, it is nearly impossible to identify and represent these subtle landscape variations in regional-scale surficial mapping. The uniform till cover depicted in the regional mapping does not reflect reality, and therefore does not provide the necessary surficial context to inform till sampling programs and evaluation efforts. The Northwest Territories Geological Survey and several private exploration companies have recognized the importance of identifying differences in material type and processes that can remobilize and alter the composition of till. Recent improvements in the availability of high-resolution imagery and digital elevation data have provided the means to perform more detailed surficial studies at a scale that is more applicable to diamond exploration. As a result, multiple high-resolution surficial mapping and associated sediment sample data evaluations have been initiated in and around the Lac de Gras region. These studies have reinforced that there is significant spatial variation in the suitability for till sampling, and found that subglacial meltwater corridors and glacial lakes were common. Furthermore, a many of the previously collected till samples were affected by these processes, which can have a significant influence on KIM concentrations and the shape of their dispersal patterns. Meltwater can truncate dispersals and concentrate heavy minerals. Glacial lakes can either dilute or concentrate heavy minerals depending on whether the environment was proximal or distal. Specific landform assemblages and characteristics have been documented that can be used to identify these dispersal-modifying processes, and used to produce a surficial context that is more suitable to exploration. This improved surficial context facilitates the collection of in situ till samples and the interpretation of existing surface sediment data resulting in lower-risk exploration targets.
DS201707-1361
2017
Saha, A., Ganguly, S., Ray, J., Koeberl, C., Thoni, M., Sarbajna, C., Sawant, S.S.Petrogenetic evolution of Cretaceous Samchampi Samteran alkaline complex, Mikir Hills, northeast India: implications on multiple melting events of heterogeneous plume and metasomatized sub continental lithospheric mantle.Gondwana Research, Vol. 48, pp. 237-256.Indiacarbonatite

Abstract: The Samchampi (26° 13?N: 93° 18?E)-Samteran (26° 11?N: 93° 25?E) alkaline complex (SSAC) occurs as an intrusion within Precambrian basement gneisses in the Karbi-Anglong district of Assam, Northeastern India. This intrusive complex comprises a wide spectrum of lithologies including syenite, ijolite-melteigite, alkali pyroxenite, alkali gabbro, nepheline syenite and carbonatite (nepheline syenites and carbonatites are later intrusives). In this paper, we present new major, trace, REE and Sr-Nd isotope data for different lithologies of SSAC and discuss integrated petrological and whole rock geochemical observations with Sr-Nd isotope systematics to understand the petrogenetic evolution of the complex. Pronounced LILE and LREE enrichment of the alkaline-carbonatite rocks together with steep LREE/HREE profile and flat HREE-chondrite normalized patterns provide evidence for parent magma generation from low degree partial melting of a metasomatized garnet peridotite mantle source. LILE, HFSE and LREE enrichments of the alkaline-silicate rocks and carbonatites are in agreement with the involvement of a mantle plume in their genesis. Nb-Th-La systematics with incompatible trace element abundance patterns marked by positive Nb-Ta anomalies and negative K, Th and Sr anomalies suggest contribution from plume-derived OIB-type mantle with recycled subduction component and a rift-controlled, intraplate tectonic setting for alkaline-carbonatite magmatism giving rise to the SSAC. This observation is corroborated by enriched 87Sr/86Srinitial (0.705562 to 0.709416) and 143Nd/144Ndinitial (0.512187 to 0.512449) ratios for the alkaline-carbonatite rocks that attest to a plume-related enriched mantle (~ EM II) source in relation to the origin of Samchampi-Samteran alkaline complex. Trace element chemistry and variations in isotopic data invoke periodic melting of an isotopically heterogeneous, metasomatized mantle and generation of isotopically distinct melt batches that were parental to the different rocks of SSAC. Various extents of plume-lithosphere interaction also accounts for the trace element and isotopic variations of SSAC. The Srinitial and Ndinitial (105 Ma) isotopic compositions (corresponding to ?Nd values of ? 6.37 to ? 1.27) of SSAC are consistent with those of Sung Valley, Jasra, Rajmahal tholeiites (Group II), Sylhet Traps and Kerguelen plateau basalts.
DS201709-2050
2017
Salnikova, E.B., Chakhmouradian, A.R., Stifeeva, M.V., Reguir, E.P., Nikiforov, A.V.Calcic garnets as a promising U-Pb geochronometers. Kola PeninsulaGoldschmidt Conference, abstract 1p.Russiacarbonatite, Belyaya Zima

Abstract: Calcic garnets are an important – although somewhat neglected – member of the garnet group. Typically, these mineral are members of complex solid solutions involving largely substitutions in the Fe3+/Al and Si sites and at least eight different end-members. The absolute majority of garnets in this family are Ti-Mg-Fe2+(± Al ± Zr)-bearing andradite transitional to morimotoite and schorlomite. Importantly, these garnets occur as common accessory minerals in a wide range of igneous and rocks, including nepheline syenites, alkali feldspar syenites, melteigite-urtites, nephelinites, melilitolites, melilitites, calcite carbonatites, ultramafic lamprophyres, orangeites, contaminated kimberlites, skarns and rodingites. Calcic garnets have a great capacity for atomic substitutions involving high-field-strength elements and, even more importantly, rare earths (up to 4000 ppm, including Y), Th and U (both up to 100 ppm) at low levels of common Pb. Their (La/Yb)cn ratio varies over two orders of magnitude (from < 0.01 to ~1), making these minerals a sensitive indicator of crystal fractionation, degassing and other magma-evolution processes. Given these unique compositional characteristics and surprising lack of interest in these minerals in the previous literature, we explored the possibility of using calcic garnets as a U-Pb geochronometer. For this purpose, we selected samples of well-crystallized igneous garnet from four very different rock types of different age, including: carbonatite (Afrikanda) from the Devonian Kola Alkaline Province, carbonatite from the Neoproterozoic Belaya Zima complex (Central-Asian mobile belt), ijolite from the Chick Ordovician igneous complex (Central-Asian mobile belt), granitic pegmatite from the Eden Lake complex in the Paleoproterozoic Trans-Hudson orogen, and feldspathoid syenite from the Cinder Lake alkaline complex in the Archean Knee Lake greenstone belt. U-Pb TIMS ages of the studied garnets are mostly concordant and reveal perfect correspondence with reported U-Pb zircon or perovskite ages as well as Sm-Nd isochrone age for these complexes. Therefore we can advertise calcic garnets as a promising tool for U-Pb geochronological studies.
DS201706-1103
2017
Sampaio, E.E.S., Barbosa, J.S.F., Corrrea-Gomes, L.C.New insight on the paleoproterozoic evolution of the Sao Francisco craton: reinterpretation of the geology, the suture zones and the thicknesses of the crustal blocks using geophysical and geological data.Journal of South American Earth Science, Vol. 76, pp. 290-305.South America, Brazilcraton - Sao Francisco

Abstract: The Archean-Paleoproterozoic Jequié (JB) and Itabuna-Salvador-Curaçá (ISCB) blocks and their tectonic transition zone in the Valença region, Bahia, Brazil are potentially important for ore deposits, but the geological knowledge of the area is still meager. The paucity of geological information restricts the knowledge of the position and of the field characteristics of the tectonic suture zone between these two crustal segments JB and ISCB. Therefore, interpretation of geophysical data is necessary to supplement the regional structural and petrological knowledge of the area as well as to assist mining exploration programs. The analysis of the airborne radiometric and magnetic data of the region has established, respectively, five radiometric domains and five magnetic zones. Modeling of a gravity profile has defined the major density contrasts of the deep structures. The integrated interpretation of the geophysical data fitted to the known geological information substantially improved the suture zone (lower plate JB versus upper plate ISCB) delimitation, the geological map of the area and allowed to estimate the thicknesses of these two blocks, and raised key questions about the São Francisco Craton tectonic evolution.
DS201712-2727
2018
Santosh, M., Hari, K.R., He, X-F., Han, Y-S., Manu Prasanth, M.P.Oldest lamproites from Peninsular India track the onset of Paleoproterozoic plume induced rifting and the birth of Large Igneous Province.Gondwana Research, Vol. 55, pp. 1-20.Indialamproites - Nuapada

Abstract: Potassic and ultrapotassic magmatism from deep lithospheric sources in intra-cratonic settings can be the signal of subsequent voluminous mafic magmatism and the formation of Large Igneous Provinces (LIPs) triggered by mantle plumes. Here we report for the first time, precise zircon U-Pb age data from a suite of lamproites in the Bastar Craton of central India that mark the onset of Paleoproterozoic rifting and culminating in the formation of extensive mafic dyke swarms as the bar codes of one of the major LIP events during the Precambrian evolution of the Indian shield. The lamproites from the Nuapada field occur as dismembered dykes and are composed of phenocrysts and microphenocrysts of altered olivine together with microphenocrysts of phlogopite and magnetite within a groundmass of chlorite and calcite with accessory rutile, apatite and zircon. The rocks compositionally correspond to olivine phlogopite lamproite and phlogopite lamproite. Geochemical features of the lamproites correlate with their counterparts in Peninsular India and other similar suites elsewhere in the world related to rift settings, and also indicate OIB-like magma source. The associated syenite shows subduction-related features, possibly generated in a post-collisional setting. Magmatic zircon grains with high Th/U ratios in the syenite from the Nuapada lamproite form a coherent group with an upper intercept age of 2473 ± 8 Ma representing the timing of emplacement of the magma. Zircon grains in three lamproite samples yield four distinct age groups at ca. 2.4 Ga, 2.2 Ga, 2.0 Ga and 0.8 Ga. The 2.4 Ga group corresponds to xenocrysts entrained from the syenite whereas the 2.2 Ga group is considered to represent the timing of emplacement of the lamproites. The ca. 2.0 Ga zircon grains correlate with the major thermal imprint associated with mafic magmatism and dyke emplacement in southern Bastar and the adjacent Dharwar Cratons. A few young zircon grains in the syenite and lamproites show a range of early to middle Neoproterozoic ages from 879 to 651 Ma corresponding to younger thermal event(s) as also represented by granitic veins cutting across these rocks and extensive silicification. Zircon Lu-Hf isotope data suggest magma derivation from a refertilized Paleo-Mesoarchean sub-continental lithospheric mantle, or OIB-type sources. The differences in Hf-isotope composition among the zircon grains from different age groups indicate that the mantle sources of the lamproite are heterogeneous at the regional scale. A combination of the features from geochemical and zircon Hf isotope data is consistent with asthenosphere-lithosphere interaction during the lamproite magma evolution. The timing of lamproite emplacement in central India correlates with the global 2.2 Ga record of LIPs. We link the origin of the related mantle plume to the recycling of subducted slabs associated with the prolonged subduction-accretion history prior to the Neoarchean cratonization, as well as the thermal blanket effect of the Earth’s oldest supercontinent. Pulsating plumes and continued rifting generated voluminous dyke swarms across the Bastar and Dharwar Cratons, forming part of a major global rifting and LIP event.
DS201704-0645
2017
Sarafian, E., Gaetani, G.A., Hauri, E.H., Sarafian, A.R.Experimental constraints on the damp peridotite solidus and oceanic mantle potential temperature.Science, Vol. 355, 6328, pp. 942-945.MantleGeothermometry

Abstract: Decompression of hot mantle rock upwelling beneath oceanic spreading centers causes it to exceed the melting point (solidus), producing magmas that ascend to form basaltic crust ~6 to 7 kilometers thick. The oceanic upper mantle contains ~50 to 200 micrograms per gram of water (H2O) dissolved in nominally anhydrous minerals, which -relative to its low concentration-has a disproportionate effect on the solidus that has not been quantified experimentally. Here, we present results from an experimental determination of the peridotite solidus containing known amounts of dissolved hydrogen. Our data reveal that the H2O-undersaturated peridotite solidus is hotter than previously thought. Reconciling geophysical observations of the melting regime beneath the East Pacific Rise with our experimental results requires that existing estimates for the oceanic upper mantle potential temperature be adjusted upward by about 60°C.
DS201708-1749
2017
Sarkar, C.Geochronology and mantle source characteristics of kimberlites and related rocks from the Rae Craton, Melville Peninsula, Nunavut, Canada.11th. International Kimberlite Conference, PosterCanada, Nunavut, Melville Peninsulageochronology
DS201711-2527
2017
Saveliev, D.E., Puchkov, V.N., Sergeev, S.N., Misabirov, I.I.Deformation induced decomposition of enstatite in mantle peridotite and its role in partial melting and chromite ore formation.Doklady Earth Sciences, Vol. 476, 1, pp. 1058-1061.Mantleperidotite

Abstract: Deformed orthopyroxene grains are studied in detail in mantle peridotite. It is shown that deformation of enstatite is accompanied by its decomposition with the formation of low-temperature phases (pargasite, Fe-rich olivine) and restite represented by depleted enstatite, forsterite, and small newly formed chrome spinellide grains. The role of plastic deformation in initiation of partial melting of peridotite and in the formation new chrome spinellide grains is discussed.
DS201701-0029
2016
Savelieva, V.B., Danilova, Yu.V., Bazarova, E.P., Ivanov, A.V., Kamenetsky, V.S.Carbonatite magmatism of the southern Siberian Craton 1 Ga ago: evidence for the beginning of breakup of Laurasia in the early Neoproterozoic.Doklady Earth Sciences, Vol. 471, 1, pp. 1140-1143.RussiaCarbonatite

Abstract: Apatite and biotite from dolomite?ankerite and calcite?dolomite carbonatite dikes emplaced into the Paleoproterozoic metamorphic rock complex in the southern part of the Siberian Craton are dated by the U-Pb (LA-ICP-MS) and 40Ar-39Ar methods, respectively. Proceeding from the lower intercept of discordia with concordia, the age of apatite from calcite?dolomite carbonatite is estimated to be 972 ± 21 Ma and that for apatite from dolomite?ankerite carbonatite, as 929 ± 37 Ma. Values derived from their upper intercept have no geological sense. The ages obtained for biotite by the 40Ar-39Ar method are 965 ± 9 and 975 ± 14 Ma. It means that the formation of carbonatites reflects the earliest phases of the Neoproterozoic stage in extension of the continental lithosphere.
DS201704-0646
2017
Schmetzer, K., Gilg, H.A., Vaupel, E.Synthetic emeralds grown by Richard Nacken in the mid-1920's: properties, growth technique, and historical account.Gems & Gemology, Vol. 52, 4, pp. 368-392.Europe, GermanySynthetic - emeralds

Abstract: Chemical and microscopic examination of the first gem-quality synthetic emeralds of facetable size proves that Prof. Richard Nacken grew two main types of emerald by flux methods in the mid-1920s. One of these two types, grown with colorless beryl seeds in molybdenum-bearing and vanadium-free fluxes, has not previously been mentioned in the literature and would appear to be unknown to gemologists. The other main type, which has already been described in gemological publications, was grown from molybdenum- and vanadium-bearing fluxes. In drawing these conclusions, rough and faceted synthetic emeralds produced by Nacken were available for study from two principal sources: the Deutsches Museum in Munich, to which Nacken had donated samples in 1961, and family members who had inherited such crystals. Chemical, morphological, and microscopic properties are given, and circumstances concerning the developmental history of the Nacken production, including the possibility of collaboration with IG Farben (a subject of past speculation), are discussed as well. The latter has recently been elucidated by the discovery of original documents from the IG Farben gemstone plant, preserved in the Archives of the German Federal State of Saxony-Anhalt.
DS201707-1362
2017
Schulte-Pelkum, V., Mahan, K., Shen, W., Stachnik, J.The distribution and composition of high velocity lower crust across the continental US: comparison of seismic and xenolith dat a and implications for lithospheric dynamics and history.Tectonics, in press availableUnited Statesgeophysics

Abstract: The magnetotelluric component of the EarthScope USArray program has covered over 35% of the continental United States. Resistivity tomography models derived from these data image lithospheric structure and provide constraints on the distribution of fluids and melt within the lithosphere. We present a three-dimensional resistivity model of the northwestern United States which provides new insight into the tectonic assembly of western North America from the Archean to present. Comparison with seismic tomography models reveals regions of correlated and anti-correlated resistivity and velocity that help identify thermal and compositional variations within the lithosphere. Recent (Neogene) tectonic features reflected in the model include the subducting Juan de Fuca–Gorda plate which can be traced beneath the forearc to more than 100 km depth, high lithospheric conductivity along the Snake River Plain, and pronounced lower-crustal and upper-mantle conductivity beneath the Basin and Range. The latter is abruptly terminated to the northwest by the Klamath–Blue Mountains Lineament, which we interpret as an important structure during and since the Mesozoic assembly of the region. This boundary is interpreted to separate hot extended lithosphere from colder, less extended lithosphere. The western edge of Proterozoic North America, as indicated by the Cretaceous initial 87Sr/86Sr = 0.706 contour, is clearly reflected in the resistivity model. We further image an Archean crustal block (“Pend Oreille block”) straddling the Washington/Idaho border, which we speculate separated from the Archean Medicine Hat block in the Proterozoic. Finally, in the modern Cascades forearc, the geometry and internal structure of the Eocene Siletz terrane is reflected in the resistivity model. The apparent eastern edge of the Siletz terrane under the Cascades arc suggests that pre-Tertiary rocks fill the Washington and Oregon back-arc.
DS201708-1750
2017
Schulze, D.Mg-metasomatized Fe-rich dunites from the Thaba Putsoa kimberlite, Lesotho: headstones in a kimberlite graveyard.11th. International Kimberlite Conference, PosterAfrica, Lesothodeposit - Thaba Putsoa
DS201708-1751
2017
Schwank, S.Innovative kimberlite dike mining technologies.11th. International Kimberlite Conference, PosterAfrica, South Africadike, mining
DS201709-2051
2017
Schweitzer, K.M., Luguet, A., Nowell, G.M., Burton, K.W.Highly siderophile element ( HSE) and Hf-Os isotope signatures of carbonatites.Goldschmidt Conference, abstract 1p.Globalcarbonatites

Abstract: Carbonatites are carbonate-rich and SiO2-poor magmas with a low viscosity and low melting temperature (see [1]) making them amongst the most mobile and unusual melts produced on Earth. They occur worldwide in a range of tectonic settings, including continental rift (e.g. Tanzania, Kaiserstuhl), oceanic intraplate (e.g. Cape Verde), convergent margins (e.g. Italy) and cratons (e.g. Canada), with eruption ages spanning from 3 Ga (3007 Ma Tupertalik, Greenland, [2]) to present day (Oldoinyo Lengai, Tanzania). Nevertheless, their genesis and source remain poorly understood and the subject of much debate. They are considered to be either products of direct low-degree partial melting of a carbonated mantle source, products of immiscible separation from a carbonated silicate melt or formed by fractional crystallisation from a carbonated alkalirich silicate melt (see [1] and references therein). In order to gain further insight into the genesis and mantle source of these unusual magmas, we will present the first combined HSE and Os-Hf isotope systematics on a suite of carbonatites representative of their large age span and compositional range (Ca, Mg, Fe and Na-rich).
DS201701-0030
2016
Science NewsEarth's rarest diamonds formed in pockets of liquid metal. Type 11Science News, Dec. 15, 1p.TechnologyDiamond morphology
DS201708-1752
2017
Scott Smith, B.Kimberlites - from mantle to mine.11th. International Kimberlite Conference, OralGlobalclassification
DS201708-1753
2017
Seifert, T.A mantle metasomatic injection event linked to Permo-Carboniferous lamprophyre magmatism and associated rare metal ore deposition ( Sn-W-Mo-Sc-In-Li-Ag(Au) in-base metal) in the eastern European Variscides.11th. International Kimberlite Conference, PosterEuropemagmatism

Abstract: Located at the northwestern border of the Bohemian Massif in the eastern part of the European Variscides, the Erzgebirge-Krušné hory is one of the most important metallogenic provinces in Europe with a 800-year history of mining. The following rare metal resources are associated with late-Variscan (315 - 280 Ma), postmagmatic mineralization pulses in the Erzgebirge-Krušné hory and surrounded areas: 900 kt Sn, 230 kt W, 10 kt Mo, 1 kt Ta, 300 kt Li, 200 kt Rb, 2 kt Cs, 1.5 kt In, 230 t Ge, 320 t Sc, 14 kt Sb, 10 kt Bi, and 3 kt Ag. At the end of the Variscan Orogeny the regional tectonic regime in Central Europe changed, indicating the beginning of the break-up of the supercontinent. The Late Carboniferous-Early Permian in Europe was a period of widespread basin formation that was associated in many areas with mantle-derived magmatic activity. 300 Ma-old dike swarms in NE England and the Scottish Midland Valley, the Oslo Graben and Scania, radiate from a triple junction in the northernmost part of Jutland. This triple junction marked the axis of a deep-mantle plume centered in this area. In this context it is important to note that the mantle plume center is surrounded by significant lamprophyre intrusions which show in some districts spatial-time relationships to Sn-W-polymetallic, Ag-base metal, and U mineralization. During the Late Carboniferous and Early Permian an extensive magmatic province developed within the present northern and central Europe, intimately with extensional tectonics, in an area stretching from southern Scandinavia, through the North Sea, into Northern Germany. Peak magmatic activity was concentrated in a narrow time-span from 300 to 280 Ma. Simultaneously in Stephanian-Early Permian an intensive bimodal magmatism associated with intra-continental extensional setting occurs in the European Variscides. Permo-Carboniferous volcanism in the Spanish Central System, Iberian Ranges, Cantabrian Chain, Pyrenees and the French Massif Central includes a range of mafic calc-alkaline and shoshonitic rock types, and lamprophyres (spessartites and camptonites) with age data between 300-270 Ma. The Mid-European Variscides show a large number of Permo-Carboniferous magmatic complexes with similar ages (Halle Volcanic Complex, Saar-Nahe Basin, Thuringian Forest, Harz Mts., Northwest-Saxonian Volcanic Complexes, bimodal volcanic rocks of the Sub-Erzgebirge basin and the Rhyolite Complex of Tharandt as well as Li-F-Sn small intrusion granites and lamprophyric intrusions in the Erzgebirge. It is important to note that the late-Variscan W-Mo, Sn-W-Mo, Ag-bearing Sn-In-base metal, Ag-Sb-base metal, and U mineralizations in the Erzgebirge-Krušné hory are spatially and temporal associated with intrusion centers of Permo-Carboniferous post-collisional mafic and rhyolitic (sub)volcanic bimodal magmatism (315-290 Ma) along deep-rooted NW-SE fault zones, especially at the intersections with NE-SW, E-W, and N-S major regional structural zones. The bimodal lamprophyre-rhyolite assemblage in the Erzgebirge / Sub-Erzgebirge basin area was formed during intracontinental rifting in a 'Fast Extension' setting by melting of a metasomatic enriched mantle source. The emplacement of fluid-enriched lamprophyres and F-rich rhyolitic intrusions at the same time is probably associated with decompression melting of updoming asthenosphere which is possibly associated with the above mentioned mantle plume.
DS201708-1754
2017
Seifert, T.Cal-alkaline mica-lamprophyres and F-Sn rhyolite intrusions associated F-Sn explosive breccia pipes and their relationship to Sn- polymetallic mineralization.11th. International Kimberlite Conference, PosterEuropealkaline rocks
DS201702-0240
2016
Sengupta, D., Van Gosen, B.S.Placer type rare earth element deposits.Reviews in Economic Geology, Vol. 18, pp. 81-100.GlobalREE placers
DS201712-2728
2017
Seryotkin, Yu.V., Skvortsova, V.L., Logvinova, A.M., Sobolev, N.V.Results of study of crystallographic orientation of olivine and diamond from Udachnaya kimberlite pipe, Yakutia.Doklady Earth Sciences, Vol. 476, 2, pp. 1155-1158.Russia, Yakutiadeposit - Udachnaya

Abstract: The crystallographic orientation of three diamonds and 19 olivine inclusions from Udachnaya kimberlite pipe was studied using monocrystal X-ray diffractometry. No epitaxial olivine inclusions were found.
DS201708-1755
2017
Shaikh, A.The P3 kimberlite, Wajrakarur field, India: mineralogy, and major and trace element compositions of olivines as records of their magmatic versus xenocrystic origin.11th. International Kimberlite Conference, OralIndiadeposit - P3

Abstract: A mineralogical study of the hypabyssal facies, late Cretaceous macrocrystic pulse of TK1 intrusion and the Mesoproterozoic aphanitic pulse of TK4 intrusion in the Wajrakarur Kimberlite Field of southern India shows that the rocks contain macrocrysts of forsteritic olivine, phenocrysts and microphenocrysts of Al–Na-poor diopside and phlogopite set in a groundmass mainly of Al–Na-poor diopside and phlogopite. Other groundmass minerals are spinel, perovskite and fluorapatite in TK1, and spinel, titanite, chlorite, calcite and gittinsite in TK4. Krichterite and perovskite occur only as inclusions in phlogopite and titanite, respectively in TK4. Late-stage deuteric phases include pyrite and barite in TK1, and strontianite, chalcopyrite, galena and pentlandite in TK4. Diopside microphenocrysts in TK4 exhibit oscillatory zoning with characteristics of diffusion controlled magmatic growth. TK1 spinels show magmatic trend 2 that evolves from magnesiochromite and culminates in titaniferous magnetite, whereas TK4 spinels are less evolved with magnesiochromite composition only. TK1 phlogopites show a simple compositional trend that is typical of lamproite micas, while four distinct growth zones are observed in TK4 phlogopites with the following compositional characteristics: zone I: high Cr2O3 and TiO2 and low BaO; zone II: low Cr2O3; zone III: low TiO2 and high BaO; zone IV: low BaO. Forsterite contents and trace element concentrations reveal two xenocrystic core populations and one magmatic rim population for TK1 olivines. Mineralogically, both TK1 and TK4 are classified as diopside–phlogopite lamproites rather than archetypal kimberlites. The two lamproites are considered to have formed from the same parent magma but crystallised under distinct oxygen fugacity conditions. With elevated content of Fe3+ in phlogopite, spinel and perovskite, TK1 appears to have crystallised in a relatively high oxygen fugacity environment. Multiple growth generations of phlogopite, spinel and fluorapatite in TK4 indicate a complex evolutionary history of the magma. Close spatial and temporal associations of Mesoproterozoic kimberlites and lamproites in southern India can possibly be explained by a unifying model which accounts for the generation of diverse magmas from a range of geochemical resevoirs in a continental rift setting.
DS201707-1363
2017
Shaikh, A.M., Patel, S.C., Ravi, S., Behera, D., Pruseth, K.L.Mineralogy of the TK1 and TK4 'kimberlites' in the Timmasamudram cluster, Wajrakur kimberlite field, India: implications for lamproite magmatism in a field of kimberlites and ultramafic lamprophyres.Chemical Geology, Vol. 455, pp. 208-230.Indiadeposit - Wajrakur

Abstract: A mineralogical study of the hypabyssal facies, late Cretaceous macrocrystic pulse of TK1 intrusion and the Mesoproterozoic aphanitic pulse of TK4 intrusion in the Wajrakarur Kimberlite Field of southern India shows that the rocks contain macrocrysts of forsteritic olivine, phenocrysts and microphenocrysts of Al–Na-poor diopside and phlogopite set in a groundmass mainly of Al–Na-poor diopside and phlogopite. Other groundmass minerals are spinel, perovskite and fluorapatite in TK1, and spinel, titanite, chlorite, calcite and gittinsite in TK4. K-richterite and perovskite occur only as inclusions in phlogopite and titanite, respectively in TK4. Late-stage deuteric phases include pyrite and barite in TK1, and strontianite, chalcopyrite, galena and pentlandite in TK4. Diopside microphenocrysts in TK4 exhibit oscillatory zoning with characteristics of diffusion controlled magmatic growth. TK1 spinels show magmatic trend 2 that evolves from magnesiochromite and culminates in titaniferous magnetite, whereas TK4 spinels are less evolved with magnesiochromite composition only. TK1 phlogopites show a simple compositional trend that is typical of lamproite micas, while four distinct growth zones are observed in TK4 phlogopites with the following compositional characteristics: zone I: high Cr2O3 and TiO2 and low BaO; zone II: low Cr2O3; zone III: low TiO2 and high BaO; zone IV: low BaO. Forsterite contents and trace element concentrations reveal two xenocrystic core populations and one magmatic rim population for TK1 olivines. Mineralogically, both TK1 and TK4 are classified as diopside–phlogopite lamproites rather than archetypal kimberlites. The two lamproites are considered to have formed from the same parent magma but crystallised under distinct oxygen fugacity conditions. With elevated content of Fe3 + in phlogopite, spinel and perovskite, TK1 appears to have crystallised in a relatively high oxygen fugacity environment. Multiple growth generations of phlogopite, spinel and fluorapatite in TK4 indicate a complex evolutionary history of the magma. Close spatial and temporal associations of Mesoproterozoic kimberlites and lamproites in southern India can possibly be explained by a unifying model which accounts for the generation of diverse magmas from a range of geochemical resevoirs in a continental rift setting.
DS201710-2264
2017
Sharpe, D.R., Kjarsgaard, B.A., Knight, R.D., Russell, H.A.J., Kerr, D.E.Glacial dispersal and flow history, East Arm area of Great Slave Lake, NWT, Canada.Quaternary Science Reviews, Vol. 165, pp. 49-72.Canada, Northwest Territoriesgeomorphology

Abstract: Little work has been completed on paleo-ice-sheet flow indicators of the Laurentide Ice Sheet, west of the Keewatin Ice Divide. Field mapping, sampling and analysis of glaciogenic sediment (?500 sample sites) in a ?33,000 km2 region near the East Arm of Great Slave Lake in northwestern Canada, provided a rare opportunity to improve understanding of sediment erosion and transport patterns. Glacially-eroded bedrock and sedimentary landforms record east to west flow with NW and SW divergence, mapped within a portion of the Great Slave Lake flow tract. Transported till reflects a similar divergent flow pattern based on dispersal geometries for multiple indicators (e.g., heavy minerals and lithic fragments), which are aligned with the dominant and latest ice flow direction. Glaciofluvial erosion (e.g., s-forms and till removal), transport, and deposition (mainly as esker sediment) are set within 0.3-3 km wide meltwater erosional corridors, spaced regularly at 10-15 km intervals. Transport paths and distances are comparable in till and esker sediment, however, distances appear to be greater (?5-25 km) in some esker constituents and indicator minerals are typically more concentrated in esker sediment than in till. Corridors form a divergent array identical to the pattern of ice-flow features. The congruence of ice and meltwater flow features is interpreted to be a response to a similar ice sheet gradient, and close timing of events (late dominant glacial ice flow and meltwater flow). The similarity in glacial and glaciofluvial flow patterns has important ramifications for event reconstruction and for exploration geologists utilizing mineral and geochemical tracing methods in this region, and possibly other parts of northern Canada. The correspondence between East Arm dispersal patterns, landforms and flow indicators supports interpretation of a simple and predictable single flow divergence model. This is in contrast to previous, multi-flow models, in which fan-shaped geometries are often reported to result from multiple transport events, compared to single-flow divergence. The observed widespread effects of glaciofluvial processes (e.g., erosional corridors) indicate a need to update existing terrain process models.
DS201708-1756
2017
Sharygin, I.Carbonate inclusions in Cr-pyropes derived from the mantle beneath central Aldan superterranes of Siberian craton.11th. International Kimberlite Conference, PosterRussiaPyropes

Abstract: Mantle-derived lherzolitic and harzburgitic Cr-pyropes from lamprophyres of the Chompolo field (Central Aldan superterrane, North Asian Craton) were studied using micro-Raman spectroscopy and electron microprobe microanalysis. These garnets enclose graphite coexisting with forsterite, diopside, Ba-Cl-phlogopite, tschermakite, rutile, magnesiochromite, Mg-ilmenite, apatite, chalcopyrite, dolomite, magnesite and lindsleyite inclusions. The PT conditions of residence of graphite-bearing assemblage in the mantle were estimated, using a combination of mineral thermometers and barometers, to be as high as 2.87–3.55 GPa and 710–770 °C. Generally, graphite within inclusions is well ordered; D1 and D2 disordered bands in its spectra are restricted to inclusion edges. The residual pressure up to 2.1 GPa was inferred for graphite assuming pressure dependence of the G-band upshift (1580 cm?1 at ambient conditions vs 1588.6 cm?1 at 2.1 GPa). Disordered graphite most likely appears due to the stress-induced distortion of the fully ordered graphite crystal structure. The distortion results from difference in the thermoelastic properties of graphite inclusions and their garnet hosts exposed to decompression during ascent to the surface with lamprophyre magma. The mineralogy of inclusions in the studied garnets strongly suggests an episode(s) of metasomatism by carbon-rich agent(s) (COH-fluid or carbonatitic melt) in the lithospheric mantle of the Central Aldan superterrane, which was coeval with the formation of graphite inclusions and the host pyropes. Copyright © 2017 John Wiley & Sons, Ltd.
DS201708-1757
2017
Sharygin, I.Interstitial mineral assemblages in sheared garnet peridotites from Udachnaya-East kimberlite pipe, Siberian craton.11th. International Kimberlite Conference, PosterRussiadeposit - Udachnaya-East

Abstract: Djerfisherite, a Cl-bearing potassium sulfide (K6Na(Fe,Ni,Cu)24S26Cl), is a widespread accessory mineral in kimberlite-hosted mantle xenoliths. Nevertheless, the origin of this sulfide in nodules remains disputable. It is usually attributed to the replacement of primary Fe–Ni–Cu sulfides when xenoliths interact with a K-and Cl-enriched hypothetical melt/fluid. The paper is devoted to a detailed study of the composition and morphology of djerfisherite from a representative collection (22 samples) of the deepest mantle xenoliths—sheared garnet peridotite, taken from the Udachnaya-East kimberlite pipe (Yakutia). Four types of djerfisherite were distinguished in the mantle rocks on the basis of morphology, spatial distribution, and relationships with the rock-forming and accessory minerals in the nodules. Type 1 was found in the rims of polysulfide inclusions in the rock-forming minerals of the xenoliths; there, it was younger than the primary sulfide assemblage pyrrhotite + pentlandite ± chalcopyrite. Type 2 formed rims around large polysulfide segregations (pyrrhotite+ pentlandite) in the xenolith interstices. Type 3 formed individual grains in the xenolith interstices together with other sulfides, silicates, oxides, phosphates, and carbonates. Type 4 was present as a daughter phase in the secondary melt inclusions which occurred in healed cracks in the rock-forming minerals of the xenoliths. Along with djerfisherite, the inclusions contained silicates, oxides, phosphates, carbonates, alkaline sulfates, chlorides, and sulfides. The results indicate that djerfisherite from the xenoliths is consanguine with kimberlite. Djerfisherite both in the sheared-peridotite xenoliths from the Udachnaya-East pipe and in different xenoliths from other kimberlite pipes worldwide formed owing to the interaction between the nodules and kimberlitic melts. Djerfisherite forming individual grains in the melt inclusions and xenolith interstices crystallized directly from the infiltrating kimberlitic melt. Djerfisherite bounding the primary Fe–Ni ± Cu sulfides formed by their replacement as a result of a reaction with the kimberlitic melt.
DS201707-1364
2017
Sharygin, I.S., Litasov, K.D., Shatskiy, A., Safonov, O.G., Golovin, A.V., Ohtani, E., Pokhilenko, N.P.Experimental constraints on orthopyroxene dissolution in alkali-carbonate melts in the lithospheric mantle: implications for kimberlite melt composition and magma ascent.Chemical Geology, Vol. 455, pp. 44-56.Mantlekimberlite, carbonatite

Abstract: Although kimberlite magma carries large amounts of mantle-derived xenocrysts and xenoliths (with sizes up to meters), this magma ascends from the Earth's mantle (> 150–250 km) to the surface in a matter of hours or days, which enables diamonds to survive. The recently proposed assimilation-fuelled buoyancy model for kimberlite magma ascent emphasizes the importance of fluid CO2 that is produced via the reactive dissolution of mantle-derived orthopyroxene xenocrysts into kimberlite melt, which initially has carbonatitic composition. Here, we use a series of high-pressure experiments to test this model by studying the interaction of orthopyroxene (Opx) with an alkali-dolomitic melt (simplified to 0.7Na2CO3 + 0.3K2CO3 + 2CaMg(CO3)2), which is close to the melt that is produced by the partial melting of a kimberlite source, at P = 3.1–6.5 GPa and T = 1200–1600 °C, i.e., up to pressures that correspond to depths (~ 200 km) from where the ascent of kimberlite magma would start. During the first set of experiments, we study the reaction between powdered Opx and model carbonate melt in a homogeneous mixture. During the second set of experiments, we investigate the mechanism and kinetics of the dissolution of Opx crystals in alkali-dolomitic melt. Depending on the P-T conditions, Opx dissolves in the alkali-dolomitic melt (CL) either congruently or incongruently via the following reactions: Mg2Si2O6 (Opx) + CaMg(CO3)2 (CL) = CaMgSi2O6 (clinopyroxene) + 2MgCO3 (CL) and Mg2Si2O6 (Opx) = Mg2SiO4 (olivine) + SiO2 (CL). The experiments confirm that the dissolution of Opx causes gradual SiO2 enrichment in the initial carbonate melt, as previously suggested. However, the assimilation of Opx by carbonate melt does not produce fluid CO2 in the experiments because the CO2 is totally dissolved in the evolved melt. Thus, our results clearly demonstrate the absence of exsolved CO2 fluid at 3.1–6.5 GPa in ascending kimberlite magma and disprove the assimilation-fuelled buoyancy model for kimberlite magma ascent in the lithospheric mantle. We alternatively suggest that the extreme buoyancy of kimberlite magma at depths of 100–250 km is an exclusive consequence of the unique physical properties (i.e., low density, ultra-low viscosity and, thus, high mobility) of the kimberlite melt, which are dictated by its carbonatitic composition.
DS201704-0647
2017
Shatskiy, A., Litasov, K.D., Sharygin, I.S., Ohtani, E.Comparison of primary kimberlite melt in a garnet lherzolite mantle source: constraints from melting phase relations in anhydrous Udachnaya-East kimberlite with variable CO2 content at 6.5GPa.Earth and Planetary Science Letters, Vol. 465, pp. 208-227.RussiaDeposit - Udachnaya-East

Abstract: The critical issue in the study of kimberlites, known as principal host rocks of diamonds, is the reconstruction of their primary melt composition, which is poorly constrained due to contamination by xenogenic materials, significant loss of volatiles during eruption, and post-magmatic alteration. It is generally accepted that the last equilibration of primary kimberlite melt with surrounding mantle (garnet lherzolite) occurred beneath cratons at 5-7 GPa (150-230 km depths). However, the subliquidus mineral assemblages obtained in kimberlite melting experiments at mantle pressures differ from lherzolite, probably owing to unaccounted loss of CO2. Here we present experiments at 6.5 GPa and 1200-1600 °C on unaltered kimberlite with an addition of 2-22 mol% CO2 over its natural abundance in the rock (13 mol%), but keeping proportions of other components identical to those in an exceptionally fresh anhydrous kimberlite from Udachnaya-East pipe in Siberia. We found that the partial melt achieves equilibrium with garnet lherzolite at 1500 °C and 19-23 mol% CO2 in the system. Under these conditions this melt contains (mol%): SiO2 = 9, FeO = 6-7, MgO = 23-26, CaO = 16, Na2O = 4, K2O = 1, and CO2 = 30-35. We propose, therefore, the alkali-rich carbonatitic composition of primary kimberlite melt and loss of 34-45 mol% (34-46 wt%) CO2 during ascent of the kimberlite magma to the surface.
DS201712-2729
2018
Shavers, E.J., Ghulam, A., Encarnacion, J.Surface alteration of a melelitite-clan carbonatite and the potential for remote carbonatite detection. AvonOre Geology Reviews, Vol. 92, pp. 19-28.United States, Missouricarbonatite
DS201708-1758
2017
Shchukin, V.Diamond bearing in the north of European Russia and the new diamond deposits discovery.11th. International Kimberlite Conference, PosterRussiadeposit -
DS201708-1759
2017
Shchukina, E.Origin of coarse granular and equigranular eclogites from V.Grib kimberlite pipe, Arkangelsk regiona, NW Russia.11th. International Kimberlite Conference, OralRussia, Archangeldeposit - Grib
DS201705-0873
2017
Shigley, J.Diamonds as Gemstones.lithographie.org, No. 19, pp. 62-69.TechnologyBook - polished
DS201708-1760
2017
Shilmi, E.Contrasting thermal structure, melt depletion and metasomatism of mantle lithosphere beneath two Proterozoic terranes west of the Kaapvaal craton, southern Africa.11th. International Kimberlite Conference, OralAfrica, Southern Africageothermometry
DS201708-1761
2017
Shirey, S.Diamond ages: what they mean and how they can be interpreted.11th. International Kimberlite Conference, PosterMantlegeochronology
DS201702-0241
2017
Shor, R.Letseng: the challenges of a low yielding diamond resource ( Lesotho).PDAC 2017, March 6, 1p. AbstractAfrica, LesothoDeposit - Letseng

Abstract: Uneconomical two decades ago, the Letseng diamond mine in Lesotho is today a major source of 50-carat-plus Type IIa diamonds. It is also the lowest-yielding diamond mine in the world, averaging about 1.5 carats of diamonds per hundred tons of ore against an industry average of one carat per ton. First opened in 1975, the previous operators of the mine (Rio Tinto and De Beers) struggled to maintain its operation because very large diamonds were mixed in with its very low production. The mine closed in 1982 after seven years of loss-making operation. In the 2000’s, three changes profoundly affected the diamond industry: 1. The price of large diamonds appreciated very strongly compared to more commercial sizes and qualities, 2. Improvements in ore processing technology that reduces potential damage or outright destruction of large crystals, and 3. Improvements in X-Ray technology that enhances the ability to identify low fluorescence, Type IIa and fancy color diamonds. This technology also allows for identification of very large diamonds in kimberlite before primary crushing. Letseng reopened in 2006 and has been operating at a profit despite its very low yield and relatively low volume, of about 100,000 carats yearly. The company continues to upgrade its technology which resulted in the recovery of 90 diamonds larger than 50 carats last year. Letseng also serves as a model for other small “boutique” mines such as Kerowe, the Botswana operation which yielded the 1109 ct Lesedi la Rona diamond in 2015 and the Lulo concession in Angola which have come on line recently.
DS201707-1365
2017
Shortlle, O.Hot mantle rising.Nature Geoscience, Vol. 10, 6, p. 400.Mantleplumes
DS201709-2052
2017
Shorttle, O.Geodynamics: hot mantle rising.Nature Geoscience, Vol. 10, 6, p. 400.Mantlegeothermometry

Abstract: The long-term cooling of Earth's mantle is recorded in the declining temperature and volume of its volcanic outpourings over time. However, analyses of 89-million-year-old lavas from Costa Rica suggest that extremely hot mantle still lurks below.
DS201708-1762
2017
Shu, Q.50 myr kimberlite magmatism in the Fort a la Corne field, Sask craton, recorded by zircon megacrysts.11th. International Kimberlite Conference, OralCanada, Saskatchewandeposit - Fort a la Corne
DS201708-1763
2017
Shu, Q.Eclogites and garnet pyroxenites from Kimberley, W. Kaapvaal craton, South Africa: severe metasomatism of basaltic cumulates.11th. International Kimberlite Conference, PosterAfrica, South Africametasomatism
DS201707-1366
2017
Shuzovatov, S.Y., Zedgenizov, D.A., Rakevich, A.L.Spectroscopic constraints on growth of Siberian mixed habit diamonds.Contributions to Mineralogy and Petrology, Vol. 172, pp. 46-64.Russiadeposit -Mir, Internationalnaya, Udachnaya, Nyurbinskaya

Abstract: Notable within-crystal variability of mineralogical and geochemical properties of single natural diamonds are commonly attributed to changing chemistry of parental fluids, sources of carbon and redox conditions of diamond precipitation. A distinct type of compositional heterogeneity (mixed-habit structure) is well-known to occur in diamonds as well as in many other minerals due to purely “structural” reasons that are unequal crystal chemistry of crystallographically different faces and selective absorption and fractionation of impurities between adjacent growth pyramids. Based on the combined cathodoluminescence, Fourier-transformed infrared spectroscopy and photoluminescence spectroscopy, study of nine diamond crystals with different growth histories and external morphology, but all showing mixed-habit patterns at different growth stages, we show that mixed-diamonds may grow in closed system conditions or with a slowly decreasing growth rate from a media with a much lower impurity content than previously thought. Intracrystal nitrogen distribution seems to be a function of growth rate even in the cases of unusual impurity partitioning between growth sectors. Generally poor with IR-active hydrogen at moderate nitrogen aggregation parameters, studied diamonds likely resemble the low hydrogen content from the growth medium that, for cubic diamonds, was typically suggested hydrogen-rich and a crucial factor for growth of cubic and mixed-habit diamonds. We also show that mixed-habit diamond growth may occur not only in peridotitic suite but also in an extended field of geochemical affinities from high-Ni to low-Ni or maybe even Ni-free environments, such as pyroxenitic or eclogitic.
DS201711-2528
2017
Siegel, C., Bryan, S.E., Allen, C.M.Use and abuse of zircon based thermometers: a critical review and a recommended approach to identify antecrystic zircons.Earth-Science Reviews, Vol. 176, pp. 87-116.Technologygeothermometry

Abstract: Zircon- and bulk-rock Zr-based thermometric parameters have become fundamental to petrogenetic models of magmatism, from which broader geochronological and tectonic implications are being made. In particular, petrogenetic models have become increasingly reliant on Ti concentration in zircon geothermometry (TZircTi) and zircon saturation temperature (TZircsat). A feature of many of these studies is an implicit assumption that all zircons present in the host igneous rock are autocrystic, that is, crystallised from the surrounding melt. However, it has long been recognised that zircons present in an igneous rock can be inherited either from the surrounding country rock or source region (xenocrysts), or from earlier phases of magmatism or the magmatic plumbing system (antecrysts). Distinguishing these different origins for zircon crystals or domains within crystals is not straightforward. Here, we first review the utility and reliability of zircon-based thermometers for petrogenetic studies and show that TZircsat is a theoretical temperature and cannot be used to constrain magmatic or partial melting temperatures. It is a dynamic variable that changes during magma crystallisation, and essentially increases as fractional crystallisation proceeds, whereas true magmatic temperatures (TMagma) decrease. Generally, in Temperature-SiO2 space, the cross-over point of these two temperatures is magmatic system dependent, and also affected by the type of calibration used for the TZircsat calculations. Consequently, each magmatic system needs to be evaluated independently to assess the validity and usefulness of TZircsat. A fundamental conclusion of TZircsat and TMagma relationships assessed here is that new zircon generally only crystallises in silicic (granitic/rhyolitic) melt compositions, and thus autocrystic zircons should not be assumed to be present in igneous rocks with bulk compositions < 64 wt% SiO2, although inherited and minor zircons crystallising from late-stage differentiated melt pockets can be present. This highlights the importance of discriminating autocrystic from inherited zircons in igneous rocks. We then review techniques available to discriminate autocrystic from inherited zircons, and propose a new methodology to assist in the identification of autocrystic zircons for emplacement age determination and separate evaluation of inherited zircon components. The approach uses two strands of data: 1) zircon data such as zircon morphologies, textures, compositions and U-Pb ages, and 2) whole-rock data, in particular SiO2 and coupled geothermometry (TZircsat and TMagma) to estimate whether the magma was zircon-saturated or undersaturated. To test this new protocol, we use as examples, several Phanerozoic granitic rocks intersected by drilling in Queensland where contextual information is limited, and show how antecrystic and xenocrystic zircons and monazites can be distinguished. In contrast, where zircons are metamict (for example, high U and Th-rich zircons), much of the ability to discriminate is impacted because such zircons have suffered Pb loss and have modified compositions (e.g., higher TZircTi). We recommend an integrated approach incorporating whole-rock chemistry, independent geothermometric constraints, zircon composition, textures and ages obtained by routine cathodoluminescence and LA-ICP-MS or ion microprobe analysis to provide increased confidence for the discrimination of inherited zircons from autocrystic zircons and determination of the emplacement age.
DS201712-2730
2017
Siegel, C., Bryan, S.E., Allen, C.M., Gust, D.A.Use and abuse of zircon based thermometers: a critical review and recommended approach to identify antecrystic zircons.Earth Science Reviews, Vol. 176, 10.1016Technologygeothermometry

Abstract: Zircon- and bulk-rock Zr-based thermometric parameters have become fundamental to petrogenetic models of magmatism, from which broader geochronological and tectonic implications are being made. In particular, petrogenetic models have become increasingly reliant on Ti concentration in zircon geothermometry (TZircTi) and zircon saturation temperature (TZircsat). A feature of many of these studies is an implicit assumption that all zircons present in the host igneous rock are autocrystic, that is, crystallised from the surrounding melt. However, it has long been recognised that zircons present in an igneous rock can be inherited either from the surrounding country rock or source region (xenocrysts), or from earlier phases of magmatism or the magmatic plumbing system (antecrysts). Distinguishing these different origins for zircon crystals or domains within crystals is not straightforward. Here, we first review the utility and reliability of zircon-based thermometers for petrogenetic studies and show that TZircsat is a theoretical temperature and cannot be used to constrain magmatic or partial melting temperatures. It is a dynamic variable that changes during magma crystallisation, and essentially increases as fractional crystallisation proceeds, whereas true magmatic temperatures (TMagma) decrease. Generally, in Temperature-SiO2 space, the cross-over point of these two temperatures is magmatic system dependent, and also affected by the type of calibration used for the TZircsat calculations. Consequently, each magmatic system needs to be evaluated independently to assess the validity and usefulness of TZircsat. A fundamental conclusion of TZircsat and TMagma relationships assessed here is that new zircon generally only crystallises in silicic (granitic/rhyolitic) melt compositions, and thus autocrystic zircons should not be assumed to be present in igneous rocks with bulk compositions < 64 wt% SiO2, although inherited and minor zircons crystallising from late-stage differentiated melt pockets can be present. This highlights the importance of discriminating autocrystic from inherited zircons in igneous rocks. We then review techniques available to discriminate autocrystic from inherited zircons, and propose a new methodology to assist in the identification of autocrystic zircons for emplacement age determination and separate evaluation of inherited zircon components. The approach uses two strands of data: 1) zircon data such as zircon morphologies, textures, compositions and U-Pb ages, and 2) whole-rock data, in particular SiO2 and coupled geothermometry (TZircsat and TMagma) to estimate whether the magma was zircon-saturated or undersaturated. To test this new protocol, we use as examples, several Phanerozoic granitic rocks intersected by drilling in Queensland where contextual information is limited, and show how antecrystic and xenocrystic zircons and monazites can be distinguished. In contrast, where zircons are metamict (for example, high U and Th-rich zircons), much of the ability to discriminate is impacted because such zircons have suffered Pb loss and have modified compositions (e.g., higher TZircTi). We recommend an integrated approach incorporating whole-rock chemistry, independent geothermometric constraints, zircon composition, textures and ages obtained by routine cathodoluminescence and LA-ICP-MS or ion microprobe analysis to provide increased confidence for the discrimination of inherited zircons from autocrystic zircons and determination of the emplacement age.
DS201703-0433
2016
Singh, V.K., Slabunov, A.Two types of Archean supracrustal belts in the Bundelk hand craton, India: geology, geochemistry, age and implication for craton crustal evolution.Journal of Geological Society of India, Vol. 88, 5, pp. 539-548.IndiaCraton, Bundelkhand

Abstract: Two Archaean supracrustal complexes are documented in the Bundelkhand craton viz. 1) the Central Bundelkhand greenstone complex (formed the Babina and Mauranipur belts), and 2) the Southern Bundelkhand metasedimentary (paragneisses, schists) complex (formed the Girar belt). The Central Bundelkhand greenstone complex consists of (i) an early assemblage composed of basic-ultrabasic, felsic volcanics, banded iron formation (BIF), and (ii) a late assemblage which contains felsic volcanics. The U-Pb zircon ages of felsic volcanics from the early assemblage, formed in an arc-type subduction setting, are 2813 Ma (Mesoarchaean). The U-Pb zircon ages of felsic volcanics from the late assemblage, which also occur in subduction settings as an active continental marginal type, are 2542 Ma (Neoarchaean). The Girar belt, located in the southern part of the craton, consists generally of metasedimentary rocks namely quartzites and BIFs. Quartzites are represented by fuchsite- and hematite- bearing quartz arenite and lesser quartz pebble conglomerates that have been subjected to low-grade metamorphism. BIF is represented by thinly-bedded quartz-hematite (±magnetite) rocks. Some lenses of marble and chlorite schist are present at the contact between the two formations. BIF is fairly rich in Cr and Ni, poor in Zr, Hf, Ba, Th, Sr, Yb and Lu, and displays a distinct positive Euanomaly (Eu/Eu* = 1.14-2.46). Zircons from quartzites give two U-Pb ages: 3432±9.7 Ma and 3252±6.4 Ma. The Sm-Nd isotope study of quartzite from the Girar belt shows that the TDM is 3.29 Ga. This TDM correlates well with the U-Pb ages of zircon and indicates that the continental crust in the Girar area began to form in the Paleoarchaean (3.4-3.2 Ga). The Central Bundelkhand greenstone complex was thus formed in a subduction-accretion setting in Mesoarchaean (ca 2.8 Ga) and Neoarchaean (2.54 Ga) time, and the Southern Bundelkhand metasedimentary complex originated in a sedimentary basin on the old continental crust apparently at ca ~ 2.7 Ga.
DS201707-1367
2017
Sinmyo, R., McCammon, C., Dubrovinsky, L.The spin state of Fe3+ in lower mantle bridgmanite.American Mineralogist, Vol. 102, pp. 1263-1269.Mantlebridgmanite

Abstract: Iron- and aluminum-bearing MgSiO3 bridgmanite is the most abundant mineral in the Earth’s interior; hence its crystal chemistry is fundamental to expanding our knowledge of the deep Earth and its evolution. In this study, the valence and spin state of iron in well-characterized Al-free Fe3+-rich bridgmanite were investigated by means of Mössbauer spectroscopy to understand the effect of ferric iron on the spin state. We found that a minor amount of Fe3+ is in the low-spin state above 36 GPa and that its proportion does not increase substantially with pressure up to 83 GPa. This observation is consistent with recent experimental studies that used Mössbauer and X-ray emission spectroscopy. In the Earth’s deep lower mantle, Fe3+ spin crossover may take place at depths below 900 and 1200 km in pyrolite and MORB, respectively. However, the effect of spin crossover on physical properties may be small due to the limited amount of Fe3+ in the low-spin state.
DS201709-2053
2017
Sirotina, E.A., Bobrov, A.V.Minerals of chromium in the Earth's mantle. ***RUSSGeos Moscow, 159.p pdf availableMantlechromium
DS201707-1368
2017
Skipton, D.R., Schneider, D.A., Kellett, D.A., Joyce, N.L.Deciphering the Paleoproterozoic cooling history of the northeastern Trans-Hudson Orogen, Baffin Island ( Canada), using 40Ar/39Ar step heating and UV laser thermochrobology.Lithos, Vol. 284-285. pp. 69-90.Canada, Nunavut, Baffin Islandgeothermometry

Abstract: The previously unstudied cooling and exhumation history of mid-crustal rocks exposed on southeastern Baffin Island (Canada) provides new insights into the post-orogenic evolution of the Paleoproterozoic Trans-Hudson Orogen (THO). New 40Ar/39Ar step-heat analyses of biotite, muscovite and phlogopite and core-to-rim intra-grain 40Ar/39Ar analyses of muscovite have a range of apparent ages compatible with slow regional cooling following peak metamorphism. Twenty-nine amphibolite- to granulite-facies rocks were dated using the 40Ar/39Ar step-heating laser (CO2) method. 40Ar/39Ar spot analyses were performed across muscovite grains from three samples using an ultraviolet (UV) laser to investigate intra-grain 40Ar/39Ar age variations. Step-heating apparent ages range from ca. 1788–1622 Ma for biotite, 1720–1630 Ma for phlogopite and 1729–1657 Ma for muscovite. UV spot 40Ar/39Ar analyses in the three muscovite grains range from ca. 1661–1640 Ma, 1675–1645 Ma and 1680–1652 Ma, with core-to-rim apparent age gradients of 20–30 Myr. Previous studies resolved peak metamorphism in this region to between ca. 1860 and 1820 Ma and identified late- to post-THO zircon and monazite populations at ca. 1800–1750 Ma. Numerical diffusion models for Ar in muscovite were conducted to test different Proterozoic cooling and exhumation scenarios. Comparisons with our 40Ar/39Ar ages attest to cooling rates of ~ 1–2 °C/Myr following peak metamorphism and ~ 1.5–2.5 °C/Myr after ca. 1740 Ma. Anomalously old apparent 40Ar/39Ar ages, in cases equivalent to U–Pb zircon rim and monazite ages, likely result from incorporation of excess Ar. The results suggest that mid-crustal rocks on southeastern Baffin Island remained hotter than ~ 420–450 °C for ~ 150–200 Myr after peak metamorphism, with subsequent slow cooling and denudation rates that are typical of Proterozoic orogens. The apparent absence of orogenic collapse implies that, despite high temperatures and estimated maximum crustal thicknesses comparable to those of large, hot orogens, the THO remained gravitationally stable during its terminal phase.
DS201709-2054
2017
Smart, K., Tappe, S., Simonetti, A., Simonetti, S., Woodland, A., Harris, C.The redox state of mantle eclogites.Goldschmidt Conference, abstract 1p.Mantleeclogites

Abstract: Mantle-derived eclogite xenoliths are key for studying the evolution of the cratonic lithosphere, because geochemical evidence suggests that they typically represent fragments of Archean and Proterozoic oceanic lithosphere [1]. Recently, it has been suggested that eclogite xenoliths can serve as redox sensors of the Precambrian upper mantle using V/Sc as a redox proxy [2]. However, metasomatism can change the original oxidation state of the cratonic mantle [3], thereby limiting its use for monitoring mantle redox evolution. Circa 1.8–2.2 Ga eclogite xenoliths erupted with Jurassic kimberlites of the northern Slave craton have geochemical features that indicate oceanic crust protoliths [4, 5]. Such Paleoproterozoic ages are common for Slave craton mantle eclogites [6], linking eclogite formation with 1.9 Ga subduction-collision events at the western craton margin. The eclogites studied here have highly variable Fe3+/?Fe (0.019 – 0.076 ±0.01), with logfO2 (?FMQ-4 to +2 ±0.5) that are both relatively oxidized and reduced compared to Slave mantle peridotite xenoliths [3]. Also, eclogite fO2 positively correlates with some indicies of metasomatism, such as elevated TiO2 in garnet. In addition to considering the time gap between eclogite formation and kimberlite eruption, the highly variable fO2–depth systematics of the eclogites studied here illustrate the drawbacks of using averaged eclogite fO2 to define the redox evolution of the upper mantle. Despite this, the ca. 2 Ga northern Slave craton eclogites have an average depth-corrected logfO2 of ?FMQ-0.5±1.3 (1?) that overlaps with modern MORB, and complies with the upper mantle redox evolution trend predicted using V/Sc ratios of mantlederived melts [2]. However, given the debate around the secuarity of mantle redox [7], further research into the suitability of mantle eclogites as redox sensors is warranted.
DS201705-0874
2017
Smart, K.A., Cartigny, P., Tappe, S., O'Brien, H., Klemme, S.Lithospheric diamond formation as a consequence of methane rich volatile flooding: an example from Diamondiferous eclogite xenoliths of the Karelian craton ( Finland).Geochimica et Cosmochimica Acta, Vol. 206, pp. 312-342.Europe, FinlandDeposit - Lahtojoki

Abstract: A collection of 61 xenocrystic and 12 eclogite xenolith-derived diamonds from the 600 Ma Lahtojoki kimberlite in central Finland has been investigated. Calculated pressure and temperature conditions for the diamondiferous eclogites are in excess of 5.5 GPa and 1300 °C, suggesting residence depths greater than 180 km, near the base of the Karelian cratonic mantle lithosphere. Geochemically, the eclogite xenoliths have gabbroic compositions showing positive Eu and Sr anomalies, relatively low ?REE and elevated Al2O3 contents, yet garnets have ambiguous ?18O values of 5.7‰ and 5.9‰. Gabbroic eclogite formation could therefore be linked to either subduction processes during the 1.9 Ga Svecofennian orogeny or to cumulate processes during 2.1 Ga rift-induced magmatism. Determination of the oxygen fugacity of Lahtojoki eclogite xenoliths from both this work and previous studies suggests that diamond-bearing eclogites may be more reduced (?FMQ-3.5) compared to barren eclogites (?FMQ-1.7). While recycled oceanic crust protoliths for the eclogites remain a possibility, the carbon isotopic compositions and nitrogen abundances of the Lahtojoki diamonds indicate mantle-derived volatile sources. All diamonds (i.e., loose and eclogite xenolith-derived) display a restricted range of ?13C values from ?7.8‰ to ?3.7‰ that overlaps with the carbon isotopic composition of Earth’s mantle. The Lahtojoki diamond ?13C values form a negatively skewed distribution, indicating diamond growth from reduced mantle-derived carbon sources such as methane- (CH4) bearing fluids. Nitrogen contents of the Lahtojoki diamonds range from 40 to 1830 atomic ppm with a mean of ?670 atomic ppm; these elevated nitrogen contents combined with the close association to eclogites suggest an eclogitic or crustal volatile source. However, the Karelian craton was periodically intruded by ultramafic alkaline magmas since at least 1.8 Ga, noting in particular the occurrence of phlogopite-rich kimberlites and olivine lamproites between 1200 and 700 Ma. We argue that this punctuated volatile-rich magmatism simultaneously metasomatised the cratonic mantle lithosphere, forming nitrogen enriched phlogopite-bearing metasomes. We propose that reduced, carbon-bearing and nitrogen-rich fluids were remobilized to form the Lahtojoki diamonds. The diamond-forming event(s) most probably occurred during or shortly prior to the entraining kimberlite magmatism as indicated by the diamond nitrogen aggregation systematics. Involvement of reduced diamond-forming fluids is supported by both the negative skewness of Lahtojoki diamond ?13C values and the more reduced nature of the diamondiferous Lahtojoki eclogites compared with their more oxidized barren counterparts. Our results from the diamondiferous eclogites derived from the deepest parts of the Karelian cratonic mantle root are in support of methane being the stable carbon volatile species at the base of thick continental lithosphere.
DS201707-1369
2017
Smart, K.A., Tappe, S., Simonetti, A., Simonetti, S.S., Woodland, A.B., Harris, C.Tectonic significance and redox state of Paleoproterozoic eclogite and pyroxenite components in the Slave cratonic mantle lithosphere, Voyager kimberlite, Arctic Canada.Chemical Geology, Vol. 455, pp. 98-119.Canadadeposit - Voyager

Abstract: Mantle-derived eclogite and pyroxenite xenoliths from the Jurassic Voyageur kimberlite on the northern Slave craton in Arctic Canada were studied for garnet and clinopyroxene major and trace element compositions, clinopyroxene Pb and garnet O isotopic compositions, and garnet Fe3 +/?Fe contents. The Voyageur xenoliths record a wide range of pressures, but are cooler compared to mantle xenoliths derived from the nearby, coeval Jericho kimberlite. The CaO, TiO2 and Zr contents of Voyageur eclogites increase with depth, which is also observed in northern Slave peridotite xenoliths, demonstrating ‘bottom-up’ metasomatic processes within cratonic mantle lithosphere. The Voyageur eclogites have positive Eu anomalies, flat HREEN patterns, and major element compositions that are consistent with ultimate origins from basaltic and gabbroic protoliths within oceanic lithosphere. Clinopyroxene Pb isotope ratios intercept the Stacey-Kramers two-stage terrestrial Pb evolution curve at ca. 2.1 Ga, and form an array towards the host kimberlite, indicating isotopic mixing. The 2.1 Ga eclogite formation age broadly overlaps with known Paleoproterozoic subduction and collision events that occurred along the western margin of the Slave craton. Unlike the eclogites, the Voyageur pyroxenites contain garnet with distinctive fractionated HREEN, sinusoidal REE patterns of calculated bulk rocks, and clinopyroxene with 206Pb/204Pb ratios that intercept the Stacey-Kramers curve at 1.8 Ga. This suggests a distinct origin as Paleoproterozoic high-pressure mantle cumulates. However, the pyroxenite Pb isotope ratios fall within the eclogite array and could also be explained by protoliths formation at ca. 2.1 Ga followed by minor isotopic mixing during mantle metasomatism. Thus, an alternative scenario involves pyroxenite formation within the mantle section of Paleoproterozoic oceanic lithosphere followed by variable metasomatism after incorporation into cratonic mantle lithosphere. This model allows for a linked petrogenesis of the Voyageur eclogites (crust) and pyroxenites (mantle) as part of the same subducting oceanic slab. Oxygen fugacity determinations for one pyroxenite and ten eclogite xenoliths show a range of 3 log units, from ? 4.6 to ? 1.6 ?FMQ, similar to the range observed for nearby Jericho and Muskox eclogites (?FMQ ? 4.2 to ? 1.5). Importantly, the northern Slave eclogite and pyroxenite mantle components are highly heterogeneous in terms of redox state provided that they range from reduced to oxidized relative to Slave peridotite xenoliths. Moreover, the Voyageur eclogites do not exhibit any trend between oxidation state and equilibration depth, which contrasts with the downward decrease in fO2 shown by Slave and worldwide cratonic peridotite xenoliths. Our investigation of mantle eclogite and pyroxenite fO2 reinforces the important influence of recycled mafic components in upper mantle processes, because their high and variable redox buffering capacity strongly controls volatile speciation and melting relations under upper mantle conditions.
DS201708-1764
2017
Smit, K.Zimni diamond formation through infiltration of recycled methane into sulphide-bearing eclogites.11th. International Kimberlite Conference, OralAfrica, South Africadeposit - Zimni
DS201709-2055
2017
Smit, K.V., Shor, R.Geology and development of the Lomonosov deposit, northwestern Russia.Gems & Gemology, Vol. 53, 2, summer, pp. 144-167.Russiadeposit - Lomonovsov

Abstract: The Siberian craton in Russia hosts many of the country's famous diamond mines. The Lomonosov mine, however, occurs within the boundaries of a different craton-the Baltic shield, most of which lies in Europe. Unlike many diamond mines in South Africa, Canada, and Siberia, the Lomonosov deposit is not in a stable Archean geologic setting. Similar to the Argyle diamond mine in Australia, Lomonosov is in a younger Proterozoic orogenic (or mountain-building) region. Fancy pink diamonds at both these localities likely relate to these Proterozoic tectonic processes. Along with other diamond mines in Proterozoic geologic regions, the Lomonosov deposit (and its fancy-color diamond inventory) demonstrates that the diamond potential of these regions should not be overlooked.
DS201705-0875
2017
Smit, K.V., Stachel, T., Stern, R.A., Shirey, S.B., Steele, A.Diamond formation through isochemical cooling of CHO fluids vs redox buffering: examples from Marange peridotitic and Zimmi eclogitic diamonds.European Geosciences Union General Assembly 2017, Vienna April 23-28, 1p. 9187 AbstractAfrica, Zimbabwe, Sierra LeoneDeposit - Marange, Zimmi

Abstract: Traditional models for diamond formation within the lithospheric mantle invoke either carbonate reduction or methane oxidation. Both these mechanisms require some oxygen exchange with the surrounding wall-rock at the site of diamond precipitation. However, peridotite does not have sufficient buffering capacity to allow for diamond formation via these traditional models and instead peridotitic diamonds may form through isochemical cooling of H 2 O-rich CHO fluids [1]. Marange mixed-habit diamonds from eastern Zimbabwe provide the first natural confirmation of this new diamond growth model [2]. Although Marange diamonds do not contain any silicate or sulphide inclusions, they contain Ni-N-vacancy complexes detected through photoluminescence (PL) spectroscopy that suggest the source fluids equilibrated in the Ni-rich depleted peridotitic lithosphere. Cuboid sectors also contain abundant micro-inclusions of CH 4 , the first direct observation of reduced CH 4-rich fluids that are thought to percolate through the lithospheric mantle [2]. In fluid inclusion-free diamonds, core-to-rim trends in ? 13 C and N content are used to infer the speciation of the diamond-forming fluid. Core to rim trends of increasing ? 13 C with decreasing N content are interpreted as diamond growth from oxidized CO 2-or carbonate-bearing fluids. Diamond growth from reduced species should show the opposite trends-decreasing ? 13 C from core to rim with decreasing N content. Within the CH 4-bearing growth sectors of Marange diamonds, however, such a 'reduced' trend is not observed. Rather, ? 13 C increases from core to rim within a homogeneously grown zone [2]. These contradictory observations can be explained through either mixing between CH 4-and CO 2-rich end-members of hydrous fluids [2] or through closed system precipitation from an already mixed CH 4-CO 2 H 2 O-maximum fluid with XCO 2 (CO 2 /[CO 2 +CH 4 ]) between 0.3 and 0.7 [3]. These results demonstrate that Marange diamonds precipitated from cooling CH 4-CO 2-bearing hydrous fluids rather than through redox buffering. As this growth mechanism applies to both the fluid-rich cuboid and gem-like octahedral sectors of Marange diamonds, a non-redox model for diamond formation from mixed CH 4-CO 2 fluids is indicated for a wider range of gem-quality peridotitic diamonds. Indeed, at the redox conditions of global diamond-bearing lithospheric mantle (FMQ-2 to-4; [4]), CHO fluids are strongly water-dominated and contain both CH 4 and CO 2 as dominant carbon species [5]. By contrast diamond formation in eclogitic assemblages, through either redox buffering or cooling of carbon-bearing fluids, is not as well constrained. Zimmi diamonds from the West African craton have eclogitic sulphide inclusions (with low Ni and high Re/Os) and formed at 650 Ma, overlapping with the timing of subduction [6]. In one Zimmi diamond, a core to rim trend of decreasing ? 13 C (-23.4 to-24.5 %¸) and N content is indicative of formation from reduced C 2 H 6 /CH 4-rich fluids, likely derived from oceanic crust recycled during Neoproterozoic subduction. Unlike mixed CH 4-CO 2 fluids near the water maximum, isochemical cooling or ascent of such reduced CHO fluids is not effficient at diamond precipitation. Furthermore, measurable carbon isotopic variations in diamond are not predicted in this model and therefore cannot be reconciled with the ?1 internal variation seen. Consequently, this Zimmi eclogitic diamond likely formed through redox buffering of reduced subduction-related fluids, infiltrating into sulphide-bearing eclogite.
DS201710-2265
2017
Smit, M.A., Mezger, K.Earth's early 02 cycle suppressed by primitive continents.Nature Geoscience, Vol. 10, pp. 788-792.Mantleoxygen

Abstract: Free oxygen began to accumulate in Earth’s surface environments between 3.0 and 2.4 billion years ago. Links between oxygenation and changes in the composition of continental crust during this time are suspected, but have been difficult to demonstrate. Here we constrain the average composition of the exposed continental crust since 3.7 billion years ago by compiling records of the Cr/U ratio of terrigenous sediments. The resulting record is consistent with a predominantly mafic crust prior to 3.0 billion years ago, followed by a 500- to 700-million-year transition to a crust of modern andesitic composition. Olivine and other Mg-rich minerals in the mafic Archaean crust formed serpentine minerals upon hydration, continuously releasing O2-scavenging agents such as dihydrogen, hydrogen sulfide and methane to the environment. Temporally, the decline in mafic crust capable of such process coincides with the first accumulation of O2 in the oceans, and subsequently the atmosphere. We therefore suggest that Earth’s early O2 cycle was ultimately limited by the composition of the exposed upper crust, and remained underdeveloped until modern andesitic continents emerged.
DS201708-1765
2017
Smith, C.A tale of three lamproites, their diamonds and settings - Bunder, Majhgawan and Arygle.11th. International Kimberlite Conference, PosterIndia, Australiadeposit - Bunder, Majhgawan, Argyle
DS201708-1766
2017
Smith, E.Type II b diamonds originate in the sublithospheric mantle.11th. International Kimberlite Conference, OralMantlediamond - type Iib
DS201701-0031
2016
Smith, E.M., Shirey, S.B., Nestola, F., Bullock, E.S., Wang, J., Richardson, S.H., Wang, W.Large gem diamonds from metallic liquid in Earth's deep mantle.Science, Vol. 354, 6318, pp. 1403-1405.MantleDiamond genesis

Abstract: The redox state of Earth’s convecting mantle, masked by the lithospheric plates and basaltic magmatism of plate tectonics, is a key unknown in the evolutionary history of our planet. Here we report that large, exceptional gem diamonds like the Cullinan, Constellation, and Koh-i-Noor carry direct evidence of crystallization from a redox-sensitive metallic liquid phase in the deep mantle. These sublithospheric diamonds contain inclusions of solidified iron-nickel-carbon-sulfur melt, accompanied by a thin fluid layer of methane ± hydrogen, and sometimes majoritic garnet or former calcium silicate perovskite. The metal-dominated mineral assemblages and reduced volatiles in large gem diamonds indicate formation under metal-saturated conditions. We verify previous predictions that Earth has highly reducing deep mantle regions capable of precipitating a metallic iron phase that contains dissolved carbon and hydrogen.
DS201702-0242
2017
Smithson, K.The diamond potential of the Man Craton in West Africa.PDAC 2017, March 6, 1p. AbstractAfrica, Sierra Leone, Guinea, LiberiaDiamond production
DS201703-0446
2017
Smithson, K.The diamond potential of the Man Craton in West Africa.PDAC 2017, March 6, 1p. AbstractAfrica, Sierra Leone, Guinea, LiberiaDiamond production

Abstract: The Man Craton region of West Africa has a rich history of diamonds since they were first discovered in the 1930’s.They are primarily alluvial in source with currently only one kimberlite mine in operation at Koidu in Sierra Leone. The total diamond production from Guinea, Liberia and Sierra Leone over the past 10 years is recorded by the Kimberley Process at around 12.2 million carats with a value of $1.9 billion. The two main producing countries during this period are Guinea, which has yielded 6.7 million carats at an average of $52 per carat, and Sierra Leone where production has reached 5 million carats at a higher value of $277 per carat. Liberia is the smallest producer with 0.4 million carats but these have a high average value of $383 per carat. There are two known age provenances of kimberlites in the Man Craton. The larger, Jurassic age provenance comprises six main clusters of small (generally 10 ha) kimberlite pipes and dykes ranging from the older Bounoudou kimberlites in Guinea, at 153 Ma, through to the younger Tongo kimberlites in Sierra Leone dated at 140 Ma. A single, neo-Proterozoic cluster is known in the Weasua area in Liberia and is dated at 800 Ma. The Jurassic age kimberlites are classified as phlogopite-rich kimberlites with abundant groundmass opaque minerals. The older Weasua kimberlites typically contain less phlogopite and groundmass opaque minerals. Although remnants of diatreme facies are present in some pipes, notably the Banankoro, Koidu and Weasua kimberlites, hypabyssal and transitional facies tend to predominate which would indicate that these kimberlites have been eroded down to the interface between the root and diatreme zones. This suggests potential erosion of up to 2 km over the Man Craton; however geomorphological evidence suggests a lesser amount of erosion has taken place (Skinner et al., 2004). Alluvial diamonds are prevalent throughout the Man Craton and are not restricted to the known kimberlite clusters. This would argue for a wide dispersion of diamonds in the alluvial system as a result of significant landmass uplift and weathering since the time of intrusion. It could also indicate that there are diamondiferous kimberlites yet to be discovered, which is supported by the limited exploration data. It is therefore concluded that there are certain areas of the Man Craton which remain highly prospective for diamondiferous kimberlites.
DS201706-1104
2017
Smye, A.J., Jackson, C.R.M., Konrad-Schnolke, M., Hesse, M.A., Parman, S.W., Shuster, D.L., Ballentine, C.J.Noble gases recycled into the mantle through cold subduction zones.Earth and Planetary Science Letters, Vol. 471, pp. 65-73.Mantlegeochemistry, water cycle

Abstract: Subduction of hydrous and carbonated oceanic lithosphere replenishes the mantle volatile inventory. Substantial uncertainties exist on the magnitudes of the recycled volatile fluxes and it is unclear whether Earth surface reservoirs are undergoing net-loss or net-gain of H2O and CO2. Here, we use noble gases as tracers for deep volatile cycling. Specifically, we construct and apply a kinetic model to estimate the effect of subduction zone metamorphism on the elemental composition of noble gases in amphibole - a common constituent of altered oceanic crust. We show that progressive dehydration of the slab leads to the extraction of noble gases, linking noble gas recycling to H2O. Noble gases are strongly fractionated within hot subduction zones, whereas minimal fractionation occurs along colder subduction geotherms. In the context of our modelling, this implies that the mantle heavy noble gas inventory is dominated by the injection of noble gases through cold subduction zones. For cold subduction zones, we estimate a present-day bulk recycling efficiency, past the depth of amphibole breakdown, of 5-35% and 60-80% for 36Ar and H2O bound within oceanic crust, respectively. Given that hotter subduction dominates over geologic history, this result highlights the importance of cooler subduction zones in regassing the mantle and in affecting the modern volatile budget of Earth's interior.
DS201701-0032
2016
Snow, J.E.Petit spots go big. Mantle enrichment processes.Nature Geoscience, Vol. 9, pp. 862-3.MantlePlume, hotspots

Abstract: Mantle enrichment processes were thought to be limited to parts of oceanic plates influenced by plumes and to continental interiors. Analyses of mantle fragments of the Pacific Plate suggest that such enrichment processes may operate everywhere.
DS201708-1767
2017
Snyder, D.Construction and destruction of some North American cratons.11th. International Kimberlite Conference, OralUnited States, Canadacratons

Abstract: Construction histories of Archean cratons remain poorly understood; their destruction is even less clear because of its rarity, but metasomatic weakening is an essential precursor. By assembling geophysical and geochemical data in 3-D lithosphere models, a clearer understanding of the geometry of major structures within the Rae, Slave and Wyoming cratons of central North America is now possible. Little evidence exists of subducted slab-like geometries similar to modern oceanic lithosphere in these construction histories. Underthrusting and wedging of proto-continental lithosphere is inferred from multiple dipping discontinuities, emphasizing the role of lateral accretion. Archean continental building blocks may resemble the modern lithosphere of oceanic plateau, but they better match the sort of refractory crust expected to have formed at Archean ocean spreading centres. Radiometric dating of mantle xenoliths provides estimates of rock types and ages at depth beneath sparse kimberlite occurrences, and these ages can be correlated to surface rocks. The 3.6–2.6 Ga Rae, Slave and Wyoming cratons stabilized during a granitic bloom at 2.61–2.55 Ga. This stabilization probably represents the final differentiation of early crust into a relatively homogeneous, uniformly thin (35–42 km), tonalite-trondhjemite-granodiorite crust with pyroxenite layers near the Moho atop depleted lithospheric mantle. Peak thermo-tectonic events at 1.86–1.7 Ga broadly metasomatized, mineralized and recrystallized mantle and lower crustal rocks, apparently making mantle peridotite more ‘fertile’ and more conductive by introducing or concentrating sulfides or graphite at 80–120 km depths. This metasomatism may have also weakened the lithosphere or made it more susceptible to tectonic or chemical erosion. Late Cretaceous flattening of Farallon lithosphere that included the Shatsky Rise conjugate appears to have weakened, eroded and displaced the base of the Wyoming craton below 140–160 km. This process replaced the old re-fertilized continental mantle with relatively young depleted oceanic mantle.
DS201701-0033
2017
Snyder, D.B., Humphreys, E., Pearson, D.G.Construction and destruction of some North American cratons. Rae, Slave, WyomingTectonophysics, Vol. 694, pp. 464-486.United States, CanadaMetasomatism

Abstract: Construction histories of Archean cratons remain poorly understood; their destruction is even less clear because of its rarity, but metasomatic weakening is an essential precursor. By assembling geophysical and geochemical data in 3-D lithosphere models, a clearer understanding of the geometry of major structures within the Rae, Slave and Wyoming cratons of central North America is now possible. Little evidence exists of subducted slab-like geometries similar to modern oceanic lithosphere in these construction histories. Underthrusting and wedging of proto-continental lithosphere is inferred from multiple dipping discontinuities, emphasizing the role of lateral accretion. Archean continental building blocks may resemble the modern lithosphere of oceanic plateau, but they better match the sort of refractory crust expected to have formed at Archean ocean spreading centres. Radiometric dating of mantle xenoliths provides estimates of rock types and ages at depth beneath sparse kimberlite occurrences, and these ages can be correlated to surface rocks. The 3.6-2.6 Ga Rae, Slave and Wyoming cratons stabilized during a granitic bloom at 2.61-2.55 Ga. This stabilization probably represents the final differentiation of early crust into a relatively homogeneous, uniformly thin (35-42 km), tonalite-trondhjemite-granodiorite crust with pyroxenite layers near the Moho atop depleted lithospheric mantle. Peak thermo-tectonic events at 1.86-1.7 Ga broadly metasomatized, mineralized and recrystallized mantle and lower crustal rocks, apparently making mantle peridotite more ‘fertile’ and more conductive by introducing or concentrating sulfides or graphite at 80-120 km depths. This metasomatism may have also weakened the lithosphere or made it more susceptible to tectonic or chemical erosion. Late Cretaceous flattening of Farallon lithosphere that included the Shatsky Rise conjugate appears to have weakened, eroded and displaced the base of the Wyoming craton below 140-160 km. This process replaced the old re-fertilized continental mantle with relatively young depleted oceanic mantle.
DS201710-2266
2017
Sobolev, N.V., Schertle, H-P., Neuser, R.D., Tomilenko, A.A., Kuzmin, D.V., Loginova, A.M., Tolstov, A.V., Kostrovitsky, S.I., Yakovlev, D.A., Oleinikov, O.B.Formation and evolution of hypabyssal kimberlites from the Siberian craton: part 1 - new insights from cathodluminescence of the carbonates. Anabar and Olenek areaJournal of Asian Earth Sciences, Vol. 145, pt. B, pp. 670-678.Russia, Siberiadeposit - Kuranakh, Kharamay
DS201705-0876
2017
Sokol, A.G., Kruk, A.N., Palynov, Y.N., Sobolev, N.V.Stability of phlogopite in ultrapotassic kimberlite-like systems at 5.5-7.5 Gpa.Contributions to Mineralogy and Petrology, in press available 22p.MantleMetasomatism, magmatism, carbonatite

Abstract: Hydrous K-rich kimberlite-like systems are studied experimentally at 5.5-7.5 GPa and 1200-1450 °C in terms of phase relations and conditions for formation and stability of phlogopite. The starting samples are phlogopite-carbonatite-phlogopite sandwiches and harzburgite-carbonatite mixtures consisting of Ol + Grt + Cpx + L (±Opx), according to the previous experimental results obtained at the same P-T parameters but in water-free systems. Carbonatite is represented by a K- and Ca-rich composition that may form at the top of a slab. In the presence of carbonatitic melt, phlogopite can partly melt in a peritectic reaction at 5.5 GPa and 1200-1350 °C, as well as at 6.3-7.0 GPa and 1200 °C: 2Phl + CaCO3 (L)?Cpx + Ol + Grt + K2CO3 (L) + 2H2O (L). Synthesis of phlogopite at 5.5 GPa and 1200-1350 °C, with an initial mixture of H2O-bearing harzburgite and carbonatite, demonstrates experimentally that equilibrium in this reaction can be shifted from right to left. Therefore, phlogopite can equilibrate with ultrapotassic carbonate-silicate melts in a ? 150 °C region between 1200 and 1350 °C at 5.5 GPa. On the other hand, it can exist but cannot nucleate spontaneously and crystallize in the presence of such melts in quite a large pressure range in experiments at 6.3-7.0 GPa and 1200 °C. Thus, phlogopite can result from metasomatism of peridotite at the base of continental lithospheric mantle (CLM) by ultrapotassic carbonatite agents at depths shallower than 180-195 km, which creates a mechanism of water retaining in CLM. Kimberlite formation can begin at 5.5 GPa and 1350 °C in a phlogopite-bearing peridotite source generating a hydrous carbonate-silicate melt with 10-15 wt% SiO2, Ca# from 45 to 60, and high K enrichment. Upon further heating to 1450 °C due to the effect of a mantle plume at the CLM base, phlogopite disappears and a kimberlite-like melt forms with SiO2 to 20 wt% and Ca# = 35-40.
DS201708-1768
2017
Soltys, A.Apatite from Kimberley kimberlites ( South Africa): petrography and mineral chemistry.11th. International Kimberlite Conference, PosterAfrica, South Africadeposit - Kimberley

Abstract: The petrogenesis of kimberlites is commonly obscured by interaction with hydrothermal fluids, including deuteric (late-magmatic) and/or groundwater components. To provide new constraints on the modification of kimberlite rocks during fluid interaction and the fractionation of kimberlite magmas during crystallisation, we have undertaken a detailed petrographic and geochemical study of a hypabyssal sample (BK) from the Bultfontein kimberlite (Kimberley, South Africa). Sample BK consists of abundant macrocrysts (N1 mm) and (micro-) phenocrysts of olivine and lesser phlogopite, smaller grains of apatite, serpentinised monticellite, spinel, perovskite, phlogopite and ilmenite in a matrix of calcite, serpentine and dolomite. As in kimberlites worldwide, BK olivine grains consist of cores with variable Mg/Fe ratios, overgrown by rims that host inclusions of groundmass phases (spinel, perovskite, phlogopite) and have constant Mg/Fe, but variable Ni, Mn and Ca concentrations. Primary multiphase inclusions in the outer rims of olivine and in Fe-Ti-rich (‘MUM’) spinel are dominated by dolomite, calcite and alkali carbonates with lesser silicate and oxide minerals. Secondary inclusions in olivine host an assemblage of Na-K carbonates and chlorides. The primary inclusions are interpreted as crystallised alkali-Si-bearing Ca-Mg-rich carbonate melts, whereas secondary inclusions host Na-K-rich C-O-H-Cl fluids. In situ Sr-isotope analyses of groundmass calcite and perovskite reveal similar 87Sr/86Sr ratios to perovskite in the Bultfontein and the other Kimberley kimberlites, i.e. magmatic values. The ?18O composition of the BK bulk carbonate fraction is above the mantle range, whereas the ?13C values are similar to those of mantle-derived magmas. The occurrence of different generations of serpentine and occasional groundmass calcite with high 87Sr/86Sr, and elevated bulk carbonate ?18O values indicate that the kimberlite was overprinted by hydrothermal fluids, which probably included a significant groundwater component. Before this alteration the groundmass included calcite, monticellite, apatite and minor dolomite, phlogopite, spinel, perovskite and ilmenite. Inclusions of groundmass minerals in olivine rims and phlogopite phenocrysts show that olivine and phlogopite also belong to the magmatic assemblage. We therefore suggest that the crystallised kimberlite was produced by an alkali-bearing, phosphorus-rich, silica-dolomitic melt. The alkali-Si-bearing Ca-Mg-rich carbonate compositions of primary melt inclusions in the outer rims of olivine and in spinel grains with evolved compositions (MUM spinel) support formation of these melts after fractionation of abundant olivine, and probably other phases (e.g., ilmenite and chromite). Finally, the similarity between secondary inclusions in kimberlite olivine of this and other worldwide kimberlites and secondary inclusions in minerals of carbonatitic, mafic and felsic magmatic rocks, suggests trapping of residual Na-K-rich C-O-H-Cl fluids after groundmass crystallisation. These residual fluids may have persisted in pore spaces within the largely crystalline BK groundmass and subsequently mixed with larger volumes of external fluids, which triggered serpentine formation and localised carbonate recrystallisation.
DS201708-1769
2017
Soltys, A.Primitive melt composition of the Bultfontein kimberlite ( South Africa).11th. International Kimberlite Conference, PosterAfrica, South Africadeposit - Bultfontein
DS201705-0877
2017
Sommer, H., Jacob, D.E., Stern, R.A., Petts, D., Mattey, D.P., Pearson, D.G.Fluid induced transition from banded kyanite to bimineralic eclogite and implications for the evolution of cratons.Geochimica et Cosmochimica Acta, in press available 55p.Africa, South AfricaDeposit - Roberts Victor

Abstract: Heterogeneous, modally banded kyanite-bearing and bimineralic eclogites from the lithospheric mantle, collected at the Roberts Victor Diamond mine (South Africa), show a reaction texture in which kyanite is consumed. Geothermobarometric calculations using measured mineral compositions in Perple_X allowed the construction of a P-T path showing a steep, cool prograde metamorphic gradient of 2 °C/km to reach peak conditions of 5.8 GPa and 890 °C for the kyanite eclogite. The kyanite-out reaction formed bimineralic eclogite and is probably an integral part of the mineralogical evolution of most archetypal bimineralic eclogites at Roberts Victor and potentially elsewhere. The kyanite-out reaction occured at close to peak pressure (5.3 GPa) and was associated with a rise in temperature to 1380 °C. Mass balance calculations show that upon breakdown, the kyanite component is fully accommodated in garnet and omphacite via a reaction system with low water fugacity that required restricted fluid influx from metasomatic sources. The ?18O values of garnets are consistently higher than normal mantle values. Each sample has its characteristic trend of ?18O variance between garnets in the kyanite-bearing sections and those in the bimineralic parts covering a range between 5.1‰ and 6.8‰. No systematic change in O-isotope signature exists across the sample population. Differences in garnet trace element signatures between differing lithologies in the eclogites are significant. Grossular-rich garnets coexisting with kyanite have strong positive Eu-anomalies and low Gd/Yb ratios, while more pyrope-rich garnets in the bimineralic sections have lost their positive Eu-anomaly, have higher Gd/Yb ratios and generally higher heavy rare earth element contents. Garnets in the original kyanite-bearing portions thus reflect the provenance of the rocks as metamorphosed gabbros/troctolites. The kyanite-out reaction was most likely triggered by a heating event in the subcratonic lithosphere. As kyanite contains around 100 ppm of H2O it is suggested that the kyanite-out reaction, once initiated by heating and restricted metasomatic influx, was promoted by the release of water contained in the kyanite. The steep (high-P low-T) prograde P-T path defining rapid compression at low heating rates is atypical for subduction transport of eclogites into the lithospheric mantle. Such a trajectory is best explained in a model where strong lateral compression forces eclogites downward to higher pressures, supporting models of cratonic lithosphere formation by lateral collision and compression.
DS201709-2056
2017
Sommer, H., Jacob, D.E., Stern, R.A., Petts, D., Mattey, D.P., Pearson, D.G.Fluid induced transition from banded kyanite to bimineralic eclogite and implications for the evolution of cratons.Goldschmidt Conference, abstract 1p.Africa, South Africadeposit - Roberts Victor

Abstract: Heterogeneous, modally banded kyanite-bearing and bimineralic eclogites from the lithospheric mantle, collected at the Roberts Victor Diamond mine (South Africa), show a reaction texture in which kyanite is consumed. Geothermobarometric calculations using measured mineral compositions in Perple_X allowed the construction of a P-T path showing a steep, cool prograde metamorphic gradient of 2 °C/km to reach peak conditions of 5.8 GPa and 890 °C for the kyanite eclogite. The kyanite-out reaction formed bimineralic eclogite and is probably an integral part of the mineralogical evolution of most archetypal bimineralic eclogites at Roberts Victor and potentially elsewhere. The kyanite-out reaction occured at close to peak pressure (5.3 GPa) and was associated with a rise in temperature to 1380 °C. Mass balance calculations show that upon breakdown, the kyanite component is fully accommodated in garnet and omphacite via a reaction system with low water fugacity that required restricted fluid influx from metasomatic sources. The ?18O values of garnets are consistently higher than normal mantle values. Each sample has its characteristic trend of ?18O variance between garnets in the kyanite-bearing sections and those in the bimineralic parts covering a range between 5.1‰ and 6.8‰. No systematic change in O-isotope signature exists across the sample population. Differences in garnet trace element signatures between differing lithologies in the eclogites are significant. Grossular-rich garnets coexisting with kyanite have strong positive Eu-anomalies and low Gd/Yb ratios, while more pyrope-rich garnets in the bimineralic sections have lost their positive Eu-anomaly, have higher Gd/Yb ratios and generally higher heavy rare earth element contents. Garnets in the original kyanite-bearing portions thus reflect the provenance of the rocks as metamorphosed gabbros/troctolites. The kyanite-out reaction was most likely triggered by a heating event in the subcratonic lithosphere. As kyanite contains around 100 ppm of H2O it is suggested that the kyanite-out reaction, once initiated by heating and restricted metasomatic influx, was promoted by the release of water contained in the kyanite. The steep (high-P low-T) prograde P-T path defining rapid compression at low heating rates is atypical for subduction transport of eclogites into the lithospheric mantle. Such a trajectory is best explained in a model where strong lateral compression forces eclogites downward to higher pressures, supporting models of cratonic lithosphere formation by lateral collision and compression.
DS201707-1370
2017
Song, W., Xu, C., Chakhmouradian, A.R., Kynicky, J., Huang, K., Zhang, Z.Carbonatites of Tarim ( NW China): first evidence of crustal contribution in carbonatites from large igneous province.Lithos, Vol. 282-283, pp. 1-9.China, Mongoliacarbonatite - Tarim

Abstract: Many carbonatites are associated both spatially and temporally with large igneous provinces (LIPs), and considered to originate from a mantle plume source lacking any contribution from recycled crustal materials. Here, we report an occurrence of carbonatite enriched in rare-earth elements (REE) and associated with the Tarim LIP in northwestern China. The Tarim LIP comprises intrusive and volcanic products of mantle plume activity spanning from ~ 300 to 280 Ma. The carbonatites at Wajilitage in the northwestern part of Tarim are dominated by calcite and dolomite varieties, and contain abundant REE minerals (principally, monazite and REE-fluorcarbonates). Th–Pb age determination of monazite yielded an emplacement age of 266 ± 5.3 Ma, i.e. appreciably younger than the eruption age of flood basalts at ~ 290 Ma. The carbonatites show low initial 87Sr/86Sr (0.7037–0.7041) and high ?Nd(t) (1.2–4) values, which depart from the isotopic characteristics of plume-derived basalts and high-Mg picrites from the same area. This indicates that the Wajilitage carbonatites derived from a mantle source isotopically distinct from the one responsible for the voluminous (ultra)mafic volcanism at Tarim. The carbonatites show ?26MgDSM3 values (? 0.99 to ? 0.65‰) that are significantly lower than those in typical mantle-derived rocks and rift carbonatites, but close to marine sediments and orogenic carbonatites. We propose that the carbonatites in the Tarim LIP formed by decompressional melting of recycled sediments mixed with the ambient mantle peridotite. The enriched components in the Tarim plume could be accounted for by the presence of recycled sedimentary components in the subcontinental mantle.
DS201705-0878
2017
Song, WL, Xu, C., Chakhmouradian, A.R., Kynicky, J., Huang, K., Zhang, ZL.Carbonatites of Tarim ( NW China): first evidence of crustal contribution in carbonatites from a large igneous province.Lithos, Vol. 282-283, pp. 1-9.ChinaCarbonatite, subduction

Abstract: Many carbonatites are associated both spatially and temporally with large igneous provinces (LIPs), and considered to originate from a mantle plume source lacking any contribution from recycled crustal materials. Here, we report an occurrence of carbonatite enriched in rare-earth elements (REE) and associated with the Tarim LIP in northwestern China. The Tarim LIP comprises intrusive and volcanic products of mantle plume activity spanning from ~ 300 to 280 Ma. The carbonatites at Wajilitage in the northwestern part of Tarim are dominated by calcite and dolomite varieties, and contain abundant REE minerals (principally, monazite and REE-fluorcarbonates). Th-Pb age determination of monazite yielded an emplacement age of 266 ± 5.3 Ma, i.e. appreciably younger than the eruption age of flood basalts at ~ 290 Ma. The carbonatites show low initial 87Sr/86Sr (0.7037-0.7041) and high ?Nd(t) (1.2-4) values, which depart from the isotopic characteristics of plume-derived basalts and high-Mg picrites from the same area. This indicates that the Wajilitage carbonatites derived from a mantle source isotopically distinct from the one responsible for the voluminous (ultra)mafic volcanism at Tarim. The carbonatites show ?26MgDSM3 values (? 0.99 to ? 0.65‰) that are significantly lower than those in typical mantle-derived rocks and rift carbonatites, but close to marine sediments and orogenic carbonatites. We propose that the carbonatites in the Tarim LIP formed by decompressional melting of recycled sediments mixed with the ambient mantle peridotite. The enriched components in the Tarim plume could be accounted for by the presence of recycled sedimentary components in the subcontinental mantle.
DS201708-1770
2017
Southam, G.Microbial response to the presence of buried kimberlite pipes in the Attwapiskat region, northern Ontario: bacteria-kimberlite interactions.11th. International Kimberlite Conference, PosterCanada, Ontario, AttawapiskatMicrobiology
DS201704-0648
2017
Sparks, R.S.J., Cashman, K.V.Dynamic magma systems: implications for forecasting volcanic activity.Elements, Vol. 13, 1, pp. 35-40.MantleMagmatism

Abstract: Magma systems that supply volcanoes can extend throughout the crust and consist of mush (melt within a crystalline framework) together with ephemeral magma accumulations. Within a crystal-rich mush, slow processes of melt segregation and heat loss alternate with fast processes of destablisation and magma transport. Magma chambers form by two mechanisms: incremental magma intrusion into sub-solidus rocks or the segregation and rapid merging of melt-rich layers within mush regions. Three volcanic states reflect alternations of slow and fast processes: dormancy, unrest and eruption. Monitoring needs to detect processes of melt and fluid movements in the lower and middle crust during destabilisation to improve forecasting.
DS201710-2267
2017
Spencer, C.J., Roberts, N.M.W., Santosh, M.Growth, destruction, and preservation of Earth's continental crust.Earth-Science Reviews, Vol. 172, pp. 87-106.Mantlegeodynamics

Abstract: From the scant Hadean records of the Jack Hills to Cenozoic supervolcanoes, the continental crust provides a synoptic view deep into Earth history. However, the information is fragmented, as large volumes of continental crust have been recycled back into the mantle by a variety of processes. The preserved crustal record is the balance between the volume of crust generated by magmatic processes and the volume destroyed through return to the mantle by tectonic erosion and lower crustal delamination. At present-day, the Earth has reached near-equilibrium between the amount of crust being generated and that being returned to the mantle at subduction zones. However, multiple lines of evidence support secular change in crustal processes through time, including magma compositions, mantle temperatures, and metamorphic gradients. Though a variety of isotopic proxies are used to estimate crustal growth through time, none of those currently utilized are able to quantify the volumes of crust recycled back into the mantle. This implies the estimates of preserved continental crust and growth curves derived therefrom represent only a minimum of total crustal growth. We posit that from the Neoarchean, the probable onset of modern-day style plate tectonics (i.e. steep subduction), there has been no net crustal growth (and perhaps even a net loss) of the continental crust. Deciphering changes from this equilibrium state through geologic time remains a continual pursuit of crustal evolution studies.
DS201707-1371
2017
Spetius, Z.V., Cliff, J., Griffin, W.L., O'Reilly, S.Y.Carbon isotopes of eclogite hosted diamonds from the Nyurbinskaya kimberlite pipe, Yakutia: the metasomatic origin of diamonds.Chemical Geology, Vol. 455, pp. 131-147.Russia, Yakutiadeposit - Nyurbinskaya

Abstract: Carbon isotope compositions and the distribution of nitrogen and hydrogen in diamonds from 18 eclogites from Nurbinskaya kimberlites were studied in situ in polished plates. Cathodoluminescence images show that most of the diamonds have complex growth structures with distinctive core, intermediate and rim zones. In some diamonds the cores display dissolution features, and intermediate growth zones are separated from the cores by narrow rounded oscillatory zones. At least three crystals show interrupted multistage diamond growth; variations in ?13C of 2–3‰ occur across the contacts between distinct zones. Generally, ?13C within the diamond cores varies only by 1–2‰, in rare cases up to 3.3‰. ?13C values are usually lower in the intermediate zones and drop further towards the rims by up to 3‰. High-resolution SIMS profiles show that variations in ?13C across the diamond growth zones are sharp with no evidence of diffusive relaxation. Diamonds with predominantly tangential octahedral growth have a wide range in ?13C from ? 15.2‰ up to 9.0‰ (± 0.4‰), and their nitrogen (N) contents vary between 30 and 1500 at. ppm. Six diamonds show little internal variation along the isotopic profiles with changes in ?13C of only 0.3–0.9‰ around mean values ranging from ? 6‰ to ? 3‰. Five crystals are isotopically heavy, with relatively homogeneous ?13C up to 9‰. FTIR data show markedly different N concentrations and nitrogen aggregation states between major growth zones. This implies that the diamonds in eclogitic xenoliths from Nyurbinskaya pipe grew in multiple and interrupted growth events, probably from fluids enriched in K and H. The wide variations of ?13C in the studied eclogitic diamonds and identification of their anomalously positive ?13C values, combined with the wide range of high ?18O in garnets from the diamondiferous xenoliths of the Nyurbinskaya pipe, which are mostly outside of the mantle range, suggest a crustal contribution to the parental mantle-related fluids forming diamonds in these xenoliths and indicate the complex metasomatic evolution of the lithospheric mantle beneath the Nakynsky kimberlite field.
DS201709-2057
2017
Spivak, A.V., Litvin, Y.A., Dubrovinsky, L.S.Evolution of the lower mantle magma and diamond forming melts ( Experiment at 24-26 Gpa).Goldschmidt Conference, abstract 1p.Technologypetrology

Abstract: Experimental studies of phase relations in the oxide–silicate system MgO–FeO–SiO2 at 24 GPa show that the peritectic reaction of bridgmanite controls the formation of stishovite as a primary in situ mineral of the lower mantle and as an effect of the stishovite paradox. The stishovite paradox is registered in the diamond-forming system MgO–FeO–SiO2–(Mg–Fe–Ca–Na carbonate)–carbon in experiments at 26 GPa as well. The physicochemical mechanisms of the ultrabasic–basic evolution of deep magmas and diamondforming media, as well as their role in the origin of the lower mantle minerals and genesis of ultradeep diamonds, are studied.
DS201706-1105
2017
St. Onge, M.R., Harrison, J.C., Paul, D., Tella, S., Brent, T.A., Jauer, C.D., MacleanTectonic map of Arctic Canada (TeMAC): a first derivative product from Canada in 3-D geological compilation work.GAC annual meeting, 1p. AbstractCanadatectonics
DS201708-1771
2017
Stachel, T.The Victor diamond mine ( Superior craton, Canada) - A new paradigm for exploration in unconventional settings.11th. International Kimberlite Conference, OralCanada, Ontario, Attawapiskatdeposit - Victor
DS201707-1372
2017
Stachel, T., Chack, T., Luth, R.W.Carbon isotopoe fractionation during diamond growth in depleted peridotite: counterintuitive insights from modeling water-maximum CHO fluids as multi-compnent systems.Earth and Planetary Science Letters, Vol. 473, pp. 44-51.Africa, Zimbabwedeposit - Marange

Abstract: Because of the inability of depleted cratonic peridotites to effectively buffer oxygen fugacities when infiltrated by CHO or carbonatitic fluids, it has been proposed recently (Luth and Stachel, 2014) that diamond formation in peridotites typically does not occur by rock-buffered redox reactions as previously thought but by an oxygen-conserving reaction in which minor coexisting CH4 and CO2 components in a water-rich fluid react to form diamond (CO2 + CH4 = 2C + 2H2O). In such fluid-buffered systems, carbon isotope fractionation during diamond precipitation occurs in the presence of two dominant fluid carbon species. Carbon isotope modelling of diamond precipitation from mixed CH4CH4- and CO2-bearing fluids reveals unexpected fundamental differences relative to diamond crystallization from a single carbon fluid species: (1) irrespective of which carbon fluid species (CH4 or CO2) is dominant in the initial fluid, diamond formation is invariably associated with progressive minor (<1‰) enrichment of diamond in 13C as crystallization proceeds. This is in contrast to diamond precipitation by rock-buffered redox processes from a fluid containing only a single carbon species, which can result in either progressive 13C enrichment (CO2 or carbonate fluids) or View the MathML sourceC13 depletion (CH4 fluids) in the diamond. (2) Fluid speciation is the key factor controlling diamond ?13C?13C values; as XCO2 (XCO2 = CO2/[CO2 + CH4]) in the initial fluid increases from 0.1 to 0.9 (corresponding to an increase in fO2fO2 of 0.8 log units), the carbon isotope composition of the first-precipitated diamond decreases by 3.7‰. The tight mode in ?13C of ?5 ±1‰?5 ±1‰ for diamonds worldwide places strict constraints on the dominant range of XCO2 in water-rich fluids responsible for diamond formation. Specifically, precipitation of diamonds with ?13C values in the range ?4 to ?6‰ from mantle-derived fluids with an average ?13C value of ?5‰ (derived from evidence not related to diamonds) requires that diamond-forming fluids were relatively reduced and had methane as the dominant carbon species (XCO2 = 0.1–0.5). Application of our model to a recently published set of in-situ carbon isotope analyses for peridotitic diamonds from Marange, Zimbabwe (Smit et al., 2016), which contain CH4 fluid inclusions, allows us to perfectly match the observed co-variations in ?13C?13C, ?15N?15N and N content and at the same time explain the previously counter-intuitive observation of progressive View the MathML sourceC13 enrichment in diamonds that appear to have grown from a fluid with methane as the dominant carbon species. Similarly, the almost complete absence in the published record of progressive View the MathML sourceC13 depletion trends within diamonds likely reflects ubiquitous precipitation from CH4- and CO2-bearing water-rich fluids, rather than diamond formation exclusively by carbonate-bearing and CH4-free oxidized fluids or melts.
DS201709-2058
2017
Stachel, T., Harris, J.W., Hunt, L., Muehlenbachs, K., Kobussen, A., EIMFArgyle diamonds - how subduction along the Kimberley Craton edge generated the World's biggest diamond deposit.Economic Geology, 50p. By permission of authorAustraliadeposit - Argyle

Abstract: Based on the mineral inclusion content, diamonds from the Argyle Mine, Western Australia, derive primarily (~90%) from eclogitic sources with a minor peridotitic contribution from both harzburgitic and lherzolitic lithologies. The eclogitic inclusions cover a large compositional range and show in part unusually high concentrations of mantle incompatible elements (P, Ti, Na and K). Coherent trends in major elements (e.g., of Ti or Na versus Mg-number) suggest that the eclogitic diamond source was created by a single process, namely igneous fractionation. Calculated bulk rock REEN patterns match a section of oceanic crust reaching from lavas and sheeted dykes to upper gabbros. Positive Eu anomalies for garnet and clinopyroxene, with calculated bulk rock REEN patterns similar to upper (non-layered) gabbros, are strong evidence for plagioclase accumulation, which is characteristic for the gabbroic portions of oceanic crust. Linking previously published oxygen isotope analyses of eclogitic garnet inclusions with their major element composition reveals a correlation between ?18O (mean of +7.2‰) and Na content, consistent with coupled 18O and Na enrichment during low temperature alteration of oceanic crust. The carbon isotopic composition of Argyle eclogitic diamonds forms a normal distribution around a ?13C value of -11‰, indicative of mixing and homogenization of mantle and crustal (organic matter) derived carbon prior to diamond precipitation. Previously published noble gas data on Argyle diamonds support this two component model. Inclusion and nitrogen-in-diamond based thermometry indicate an unusually hot origin of the eclogitic diamond suite, indicative of derivation from the lowermost 25 km (about 180-205 km depth) of the local lithospheric mantle. This is consistent with emplacement of an oceanic protolith during subduction along the Kimberley Craton margin, likely during the Halls Creek Orogeny (about 1.85 Ga). For Argyle eclogitic diamonds the relationship between the rate of platelet degradation and mantle residence temperature indicates that both temperature and strain play an important role in this process. Therefore, ubiquitous platelet degradation and plastic deformation of Argyle diamonds are consistent with derivation from a high temperature environment (softening the diamond lattice) close to the lithosphere-asthenosphere boundary (inducing strain). In combination, the Argyle data set represents a uniquely strong case for a subduction origin of an eclogitic diamond source followed by mixing of mantle and crustal components during diamond formation. Some lherzolitic inclusions show a similarity in incompatible element enrichments (elevated P, Na and K) to the eclogitic suite. The presence of a mildly majoritic lherzolitic garnet further supports a link to eclogitic diamond formation, as very similar majoritic components were found in two eclogitic garnet inclusions. The carbon isotopic composition of peridotitic diamonds shows a mode between -5 to -4 ‰ and a tail extending towards the eclogitic mode (-11 ‰). This suggests the presence of multiple generations of peridotitic diamonds, with indications for an origin linked to the eclogitic suite being restricted to diamonds of lherzolitic paragenesis. Argyle diamonds – how subduction along the Kimberley Craton edge generated the world's biggest diamond deposit.
DS201705-0879
2017
Staebler, G.A., Mitchell, C.Lands Immemorial.lithographie.org, No. 19, pp. 4-9.IndiaBook - history
DS201709-2059
2017
Stagno, V., Kono, Y., Greaux, S., Kebukawa, Y., Stopponi, V., Scarlato, P., Lustrino, M., Irifune, T.From carbon in meteorites to carbonatite rocks on Earth.Goldschmidt Conference, abstract 1p.Globalcarbonatite

Abstract: The composition of the early Earth’s atmosphere is believed to result from significant magma outgassing during the Archaean eon. It has been widely debated whether the oxygen fugacity (fo2) of the Earth’s mantle has remained constant over the last ~3.8 Ga to levels where volatiles were mostly in their mobile form [1,2], or whether the mantle has experienced a gradual increase of its redox state [3]. Both hypotheses raise fundamental questions on the effect of composition of the early Earth’s accreting material, the origin and availability of primordial carbon in Earth’s interior, and the migration rate of CO2-rich magmas. In addition, the occurrence in nature of carbonatites (or silicate-carbonatitic rocks), diamonds and carbides indicate a dominant control of the mantle redox state on the volatile speciation over time and, maybe, on mechanisms of their formation, reaction and migration through the silicate mantle. A recent model has been developed that combines both experimental results on the fo2 of preserved carbonaceous chondrites at high pressure and thermodynamic predictions of the the temporal variation of the mantle redox state, with the CO2-bearing magmas that could form in the early asthenospheric mantle. Since any variation in melt composition is expected to cause significant changes in the physical properties (e.g., viscosity and density), the migration rate of these magmas has been determined using recent in situ viscosity data on CO2-rich melts with the falling sphere technique. Our results allow determining the composition of CO2- bearing magmas as function of the increasing mantle redox state over time, and the mechanisms and rate for exchange of carbon between mantle reservoirs.
DS201708-1772
2017
Stamm, N.The petrology and mineralogy of the kimberlite blow in Letseng la Terae: implications for its parental magma.11th. International Kimberlite Conference, PosterAfrica, Lesothodeposit - Letseng la terae
DS201709-2060
2017
Stamm, N., Schmidt, M.W.Asthenospheric kimberlites: volatile contents and bulk compositions at 7 Gpa.Earth and Planetary Science Letters, Vol. 474, pp. 309-321.Canada, Nunavutdeposit - Jericho

Abstract: During ascent, kimberlites react with the lithospheric mantle, entrain and assimilate xenolithic material, loose volatiles and suffer from syn- and post-magmatic alteration. Consequently, kimberlite rocks deviate heavily from their primary melt. Experiments at 7 GPa, 1300–1480?°C, 10–30 wt% CO2 and 0.46 wt% H2O on a proposed primitive composition from the Jericho kimberlite show that saturation with a lherzolitic mineral assemblage occurs only at 1300–1350?°C for a carbonatitic melt with <8 wt% SiO2 and >35 wt% CO2. At asthenospheric temperatures of >1400?°C, where the Jericho melt stays kimberlitic, this composition saturates only in low-Ca pyroxene, garnet and partly olivine. We hence forced the primitive Jericho kimberlite into multiple saturation with a lherzolitic assemblage by adding a compound peridotite. Saturation in olivine, low- and high-Ca pyroxene and garnet was obtained at 1400–1650 °C (7 GPa), melts are kimberlitic with 18–29 wt% SiO2 + Al2O3, 22.1–24.6 wt% MgO, 15–27 wt% CO2 and 0.4–7.1 wt% H2O; with a trade-off of H2O vs. CO2 and temperature. Melts in equilibrium with high-Ca pyroxene with typical mantle compositions have ?2.5 wt% Na2O, much higher than the commonly proposed 0.1–0.2 wt%. The experiments allow for a model of kimberlite origin in the convective upper mantle, which only requires mantle upwelling that causes melting at the depth where elemental carbon (in metal, diamond or carbide) converts to CO2 (at ?250 km). If primary melts leading to kimberlites contain a few wt% H2O, then adiabatic temperatures of 1400–1500?°C would yield asthenospheric mantle melts that are kimberlitic (>18 wt% SiO2 + Al2O3) but not carbonatitic (<10 wt% SiO2 + Al2O3) in composition, carbonatites only forming 100–200?°C below the adiabat. These kimberlites represent small melt fractions concentrating CO2 and H2O and then acquire part of their chemical signature by assimilation/fractionation during ascent in the subcratonic lithosphere.
DS201707-1373
2017
Stanley, C.Lithogeochemical classification of igneous rocks using Streckeisen ternary diagrams.Geochemistry: Exploration, Environment, Analysis, Vol. 17, 2, pp. 63-91.Technologyclassification

Abstract: Mineral deposit models strategically guide exploration. The lithologies from which these models are built have genetic connotations. Thus, rock classification must be accurate to ensure that mineral exploration is effective and successful. Rock classification is based on mineral proportions, and these are commonly determined by: (1) visual inspection, which is subject to large errors; (2) point counting, which is tedious and time-consuming; (3) image analysis of stained slabs or polished thin sections, which is expensive and constrained by the availability of appropriate stains; and (4) image analysis of spectrometric data, which is expensive. These features make rock classification difficult and undermine its quality, thereby negatively impacting geological conclusions and mineral exploration results. A novel alternative procedure for igneous rock classification involves using whole rock lithogeochemical data for classification on Streckeisen ternary diagrams. This approach employs several calculations that transform: (1) mass-based element concentrations (the original lithogeochemical data produced by the laboratory) sequentially into (2) unstandardized (do not sum to unity) molar element numbers; (3) unstandardized molar mineral numbers; (4) unstandardized volume mineral numbers; and finally (5) standardized (closed; sum to unity) volume mineral concentrations that estimate the mineral modes in rocks. These mineral mode estimates can then be plotted on (projected onto) Streckeisen ternary diagrams, to classify the rocks in the normal manner. This new approach has advantages over conventional classification strategies, in that it is relatively inexpensive, adaptable to all forms of igneous rocks, quantitative, accurate, and precise. Required petrographic information necessary to conduct such a classification includes only knowledge of chemical formulae of the ‘essential’ mineral assemblage. Essential minerals are, here, considered those minerals having concentrations exceeding 5% in 5% of the rocks under consideration. This criterion allows this lithogeochemical classification procedure to be applicable to a wide variety of igneous rocks. This lithogeochemical classification procedure has additional applications beyond the classification of plutonic igneous rocks. For example, if an essential mineral assemblage can be identified or hypothesized, classification of felsic or mafic volcanic rocks can also be achieved. Additionally, an essential mineral assemblage does not have to consist exclusively of igneous minerals. As a result, conversion from molar element numbers to molar mineral numbers can be undertaken using many mineral assemblages. This allows analogous lithogeochemical classification to be undertaken for almost any rock type (e.g. clastic sedimentary rocks, using the calculated proportions of quartz, feldspar, and clay minerals). Consequently, lithogeochemical calculation of the essential mineral modes in rocks can be used to establish mineral zoning maps in space or time, allowing exploration geoscientists to create down-hole logs depicting hydrothermal alteration mineral abundances, or surface maps of hydrothermal alteration zones on a mineral property. To demonstrate this new procedure, results from classifications of metaluminous, peraluminous, and alkaline felsic plutonic and volcanic rocks, and mafic and ultramafic plutonic and volcanic rocks are compared with mineral modes acquired by independent means (visual estimates, point counts, image analysis, spectrometry). These case studies demonstrate that the proposed lithogeochemical classification procedure is as or more accurate than conventional classification methods. Furthermore, because lithogeochemical samples are far larger, and thus more representative than the surfaces used to estimate mineral modes by conventional means, this lithogeochemical classification procedure is also far more precise. The resulting classification is thus especially effective when working with fine-grained rocks where mineral identification and volume estimation is difficult.
DS201705-0880
2017
Stanley, J., Flowers, R.Dating kimberlite emplacement with zircon and perovskite ( U-Th) /He geochronology.European Geosciences Union General Assembly 2017, Vienna April 23-28, 1p. 18924 AbstractAfricaGeochronology

Abstract: Kimberlites provide rich information about the composition and evolution of cratonic lithosphere. Accurate geochronology of these eruptions is key for discerning spatiotemporal trends in lithospheric evolution, but kimberlites can sometimes be difficult to date with available methods. We explored whether (U-Th)/He dating of zircon and perovskite can serve as reliable techniques for determining kimberlite emplacement ages. We obtained zircon and/or perovskite (U-Th)/He (ZHe, PHe) dates from 16 southern African kimberlites. Most samples with abundant zircon yielded reproducible ZHe dates (?15% dispersion) that are in good agreement with published eruption ages. The majority of dated zircons were xenocrystic. Zircons with reproducible dates were fully reset during eruption or resided at temperatures above the ZHe closure temperature prior to entrainment in the kimberlite magma. Not dating hazy and radiation damaged grains can help avoid anomalous results for more shallowly sourced zircons that underwent incomplete damage annealing and/or partial He loss during the eruptive process. All seven kimberlites dated with PHe yielded reproducible (?15% dispersion) and reasonable results. We conducted two preliminary perovskite 4He diffusion experiments, which suggest a PHe closure temperature of >300°C. Perovskite in kimberlites is unlikely to be xenocrystic and its relatively high temperature sensitivity suggests that PHe dates will typically record emplacement rather than postemplacement processes. ZHe and PHe geochronology can effectively date kimberlite emplacement and provide useful complements to existing techniques.
DS201708-1773
2017
Steifenhofer. J.The suitability of microdiamonds for local (blocked) resource estimation - opportunities and challenges.11th. International Kimberlite Conference, OralTechnologymicrodiamonds
DS201707-1374
2016
Stiefenhofer, J., Thurston, M.L., Rose, D.M., Chinn, I.L., Ferreira, J.J.Principles of using microdiamonds for resource estimation: 1 - the impact of mantle and kimberlite processes.Canadian Institute of Mining and Metallurgy, Vol. 7, 4, pp. 216-239.Globalmicrodiamonds

Abstract: Concerns around the use of micro-diamonds for resource estimation have been raised by some workers because: 1) multiple diamond populations are present in many parts of the mantle source region, 2) small diamonds in kimberlite could be exposed to proportionately greater levels of resorption and modification, and 3) euhedral micro-diamonds could crystallize immediately prior to kimberlite eruption. This paper addresses these concerns and discusses the geology of the mantle and the principal diamond host rocks, the impact of mantle processes, compares micro- and macro-diamond properties and features, and outlines several steps that can be undertaken to identify and mitigate the risk of resorption of diamond and its impact on the diamond grade size relationship.
DS201712-2731
2017
Stokes, L.Kennady delivers Faraday resources.Diamonds In Canada Magazine, Northern Miner, Nov. pp. 17-18.Canada, Northwest Territoriesdeposit - Farady
DS201709-2061
2017
Sun, J., Liu, C-Z., Kostrovisky, S.I., Wu, F-Y., Yang, J-H., Chu, Z., Yang, Y-H.Constraints from peridotites in the Obnazhennaya kimberlite.Goldschmidt Conference, abstract 1p.Russiadeposit - Obnazhennaya

Abstract: The characteristics of the sub-continental lithospheric mantle (SCLM) post-date the Siberian plume event (250 Ma) is still unclear; nearly all published data for mantle xenoliths are from a single kimberlite erupt before he Siberian plume (Udachnaya). We report major elements of the whole rock, trace elements data of clinopyroxene and Re-Os isotope and PGE concentration of mantle xenoliths from the Obnazhennaya kimberlite pipe (160 Ma). The Obnazhennaya mantle xenoliths, including spinel harzburgites, spinel dunites, spinel lherzolites, spinel-garnet lherzolite. The spinel harzburgites and dunites have refractory compositions, with 0.23-1.35 wt.% Al2O3, 0.41-3.11 wt.% CaO and 0.00-0.09 wt.% TiO2. Clinopyroxenes in harzburgites and dunites have lower Na2O but higher Cr2O3 contents. Modeling of the Y and Yb contents in clinopyroxenes indicates that the spinel harzburgites and dunites have been subjected to ca. 12-17% degrees of partial melting. The spinel harzburgites and dunites have 187Os/188Os of 0.11227-0.11637, giving a TRD age of 1.6-2.2 Ga. This suggests that old cratonic mantle still existed beneath the Obnazhennaya. In contrast, the lherzolites (both spinel- and spinel-garnet-) have more fertile compositions, containing 2.16-6.55 wt.% Al2O3, 2.91-7.55 wt.% CaO and 0.04-0.15 wt.% TiO2. Both spinel and spinelgarnet lherzolites have more radiogenic 187Os/188Os ratios (0.11931-0.17627), enriched P-PGEs. The higher Al2O3 and Os content and depleted IPGE character of these lherzolites suggest that they were not juvenile mantle accreted by Siberian mantle plume but the refertilized ancient mantle. Therefore, our result suggest that the cratonic mantle beneath the Obnazhennaya has not been replaced by juvenile mantle during the Siberian mantle plume.
DS201709-2062
2017
Sun, J., Liu, C-Z., Kostrovisky, S.I., Wu, F-Y., Yang, J-H., Chu, Z., Yang, Y-H.Composition of the lithospheric mantle in the northern Siberian craton: constraints from the peridotites in the Obnazhennaya kimberlite.Goldschmidt Conference, abstract 1p.Russia, Siberiadeposit - Obnazhennaya

Abstract: The characteristics of the sub-continental lithospheric mantle (SCLM) post-date the Siberian plume event (250 Ma) is still unclear; nearly all published data for mantle xenoliths are from a single kimberlite erupt before he Siberian plume (Udachnaya). We report major elements of the whole rock, trace elements data of clinopyroxene and Re-Os isotope and PGE concentration of mantle xenoliths from the Obnazhennaya kimberlite pipe (160 Ma). The Obnazhennaya mantle xenoliths, including spinel harzburgites, spinel dunites, spinel lherzolites, spinel-garnet lherzolite. The spinel harzburgites and dunites have refractory compositions, with 0.23-1.35 wt.% Al2O3, 0.41-3.11 wt.% CaO and 0.00-0.09 wt.% TiO2. Clinopyroxenes in harzburgites and dunites have lower Na2O but higher Cr2O3 contents. Modeling of the Y and Yb contents in clinopyroxenes indicates that the spinel harzburgites and dunites have been subjected to ca. 12-17% degrees of partial melting. The spinel harzburgites and dunites have 187Os/188Os of 0.11227-0.11637, giving a TRD age of 1.6-2.2 Ga. This suggests that old cratonic mantle still existed beneath the Obnazhennaya. In contrast, the lherzolites (both spinel- and spinel-garnet-) have more fertile compositions, containing 2.16-6.55 wt.% Al2O3, 2.91-7.55 wt.% CaO and 0.04-0.15 wt.% TiO2. Both spinel and spinelgarnet lherzolites have more radiogenic 187Os/188Os ratios (0.11931-0.17627), enriched P-PGEs. The higher Al2O3 and Os content and depleted IPGE character of these lherzolites suggest that they were not juvenile mantle accreted by Siberian mantle plume but the refertilized ancient mantle. Therefore, our result suggest that the cratonic mantle beneath the Obnazhennaya has not been replaced by juvenile mantle during the Siberian mantle plume.
DS201706-1106
2017
Sun, S., Hou, G., Hari, K.R., Liu, S., Guan, S.Mechanism of Paleo-Mesoproterozic rifts related to breakup of Columbia supercontinent: a paleostress field modeling.Journal of Geodynamics, Vol. 107, pp. 46-60.China, Indiacraton

Abstract: The Paleo-Mesoproterozoic Zhongtiao aulacogen in the North China Craton and Cuddapah basin in the Indian Craton, have both been interpreted as intra-continental rift formed by a mantle plume that led to the breakup of Columbia supercontinent, but the mechanism has not been completely deciphered. In this paper, the mechanism of the Zhongtiao aulacogen and Cuddapah basin related to initial breakup of Columbia has been evaluated with 2D elastic finite element models of the North China Craton and the Indian Craton. The trajectories of the horizontal maximum principal compressive stress of the best-fit model fit well with the trends of dyke swarms in the North China Craton and the Indian Craton. When the other three models generated were compared with the best-fit model, it can be found that a mantle plume beneath the Zhongtiao and Cuddapah areas played the most vital role in developing the Zhongtiao aulacogen, Cuddapah basin and initial breakup of Columbia supercontinent. The boundary subduction forces, including the northern margin of the NCC, the northwest and southwest margins of the Indian Craton are indispensable factors for the rifting and breakup, whereas the mechanical properties have little influence on these modeling results. The initial breakup of Columbia supercontinent might have been resulted from the coupling between a mantle plume upwelling and some plate tectonic forces.
DS201701-0034
2016
Surgutanova, E.A., Agashev, A.M., Demonterova, E.I., Golovin, A.V., Pokhilenko, N.P.Sr and Nd isotope composition of deformed peridotite xenoliths from Udachnaya kimberlite pipe.Doklady Earth Sciences, Vol. 471, 1, pp. 1104-1207.RussiaDeposit - Udachnaya

Abstract: New results of Rb-Sr and Sm-Nd isotope analyses have been obtained on samples of deformed peridotite xenoliths collected from the Udachnaya kimberlite pipe (Yakutia). The data obtained imply two main stages of metasomatic alteration of the lithospheric mantle base matter in the central part of the Siberian Craton. Elevated ratios of Sr isotopes may be considered as evidence of an ancient stage of metasomatic enrichment by a carbonatite melt. The acquired Nd isotope composition together with the geochemistry of the deformed peridotite xenoliths suggests that the second stage of metasomatic alteration took place shortly before formation of the kimberlite melt. The metasomatic agent of this stage had a silicate character and arrived from an asthenosphere source, common for the normal OIB type (PREMA) and the Group-I kimberlite.
DS201705-0881
2017
Tabassum, N., Kohn, S., Smith, C., Bulanova, G.The water concentations and OH in corporation mechanism of silicate inclusions in diamonds. What information do they provide?European Geosciences Union General Assembly 2017, Vienna April 23-28, 1p. 16735 AbstractAustralia, Canada, Russia, IndiaDiamond inclusions
DS201711-2529
2017
Tamarova, A.P., Bobrov, A.V., Sirotkina, E.A., Bindi, L., Irifune, T.Melting of model pyrolite under the conditions of the transition zone.Proceedings of XXXIV held Aug. 4-9. Perchuk International School of Earth Sciences, At Miass, Russia, 1p. AbstractMantlemelting
DS201708-1774
2017
Tappe, S.Evolution of kimberlite magmatism on the dynamic Earth.11th. International Kimberlite Conference, OralMantlemagmatism
DS201707-1375
2017
Tappe, S., Brand, N.B., Stracke, A., van Acken, D., Liu, C-Z., Strauss, H., Wu, F-Y., Luguet, A., Mitchell, R.H.Plates or plumes in the origin of kimberlites: U/pb perovskite and Sr-Nd-Hf-Os-C-O isotope contraints from the Superior craton ( Canada).Chemical Geology, Vol. 455, pp. 57-83.Canadadeposit - Renard, Wemndiji

Abstract: Neoproterozoic kimberlite, ultramafic lamprophyre, and carbonatite magmatic activity was widespread across the Canadian-Greenland Shield. Models to explain the preponderance of this deeply-derived CO2-rich magmatism between 680–540 Ma range from impingement of multiple mantle plumes to rifting activity linked to the breakout of the Laurentian plate from the Rodinia supercontinent configuration. We add to the debate about the origin of kimberlite magmas and evaluate possible mantle sources of the 655 Ma ‘diamond-rich’ Renard (new SIMS U/Pb perovskite ages) and 629 Ma ‘barren’ Wemindji kimberlites on the eastern Superior craton in Quebec, Canada. Our Sr-Nd-Hf and carbon isotope data (87Sr/86Sri = 0.70241–0.70442; ?Ndi = + 0.2 to + 4.8; ?Hfi = + 0.3 to + 6.5; ?13C = ? 5.6 to ? 3.9‰) suggest a common and moderately depleted convecting upper mantle source region for both the Renard and Wemindji kimberlites, which occur 400 km apart in the interior of the Superior craton. In contrast, the low Os isotope ratios (187Os/188Osi = 0.11078–0.12620; ?Osi = ? 13.7 to ? 1.6) and unfractionated chondritic relative HSE abundances (Os, Ir, Ru, Pt, Pd, Re) indicate significant involvement of ancient refractory cratonic mantle material in kimberlite magma formation. Our model calculations suggest that for both the diamond-rich Renard and the barren Wemindji kimberlite magmas up to 30% of the Os was derived from refractory cratonic peridotites. This material might have been assimilated by originally more CO2-rich carbonated silicate melts derived from the asthenosphere. We also show that the geochemical and Sr-Nd-Hf-Os isotopic compositions of the Renard and Wemindji kimberlites do not require significant input from melts derived from olivine-poor cratonic mantle lithologies such as MARID-type veins and pyroxenites/eclogites. This contrasts with the petrogenesis of deeply-derived volatile-rich potassic magmas found along the peripheries of cratons (e.g., ultramafic lamprophyres, kamafugites, and olivine lamproites), a setting where abundant non-peridotitic components have been added to the lithospheric mantle over the course of continent evolution. Provided that CO2-rich melts, such as proto-kimberlites, occur near the solidus of volatile-fluxed peridotites, no excess mantle heat is required in their formation. This important but often overlooked constraint, together with the observation that there exist no spatial or temporal relationships between the Superior craton kimberlites and Large Igneous Provinces during the Late Neoproterozoic, suggests that kimberlite magmatic activity was tectonically controlled. In our preferred model, ubiquitous CO2-rich proto-kimberlite melts form during volatile-controlled redox melting processes at ambient mantle temperatures in a thermal boundary layer directly beneath thick cratonic lithosphere. The success rate of ‘evolving’ hybrid kimberlite magmas reaching Earth’s surface increases when tensile stresses propagate into the > 200 km thick keels of continental lithosphere. These conditions are frequently met during fast and changing plate motions associated with the assembly and breakup of supercontinents.
DS201705-0882
2017
Tappe, S., Romer, R.L., Stracke, A., Steenfelt, A., Smart, K.A., Muehlenbachs, K., Torsvik, T.H.Sources and mobility of carbonate melts beneath cratons, with implications for deep carbon cycling, metasomatism and rift initiation.Earth and Planetary science Letters, Vol. 466, pp. 152-167.MantleMetasomatism, magma, carbonatite

Abstract: Kimberlite and carbonatite magmas that intrude cratonic lithosphere are among the deepest probes of the terrestrial carbon cycle. Their co-existence on thick continental shields is commonly attributed to continuous partial melting sequences of carbonated peridotite at >150 km depths, possibly as deep as the mantle transition zone. At Tikiusaaq on the North Atlantic craton in West Greenland, approximately 160 Ma old ultrafresh kimberlite dykes and carbonatite sheets provide a rare opportunity to study the origin and evolution of carbonate-rich melts beneath cratons. Although their Sr-Nd-Hf-Pb-Li isotopic compositions suggest a common convecting upper mantle source that includes depleted and recycled oceanic crust components (e.g., negative ??Hf??Hf coupled with View the MathML source>+5‰?7Li), incompatible trace element modelling identifies only the kimberlites as near-primary low-degree partial melts (0.05-3%) of carbonated peridotite. In contrast, the trace element systematics of the carbonatites are difficult to reproduce by partial melting of carbonated peridotite, and the heavy carbon isotopic signatures (?3.6 to View the MathML source?2.4‰?13C for carbonatites versus ?5.7 to View the MathML source?3.6‰?13C for kimberlites) require open-system fractionation at magmatic temperatures. Given that the oxidation state of Earth's mantle at >150 km depth is too reduced to enable larger volumes of ‘pure’ carbonate melt to migrate, it is reasonable to speculate that percolating near-solidus melts of carbonated peridotite must be silicate-dominated with only dilute carbonate contents, similar to the Tikiusaaq kimberlite compositions (e.g., 16-33 wt.% SiO2). This concept is supported by our findings from the North Atlantic craton where kimberlite and other deeply derived carbonated silicate melts, such as aillikites, exsolve their carbonate components within the shallow lithosphere en route to the Earth's surface, thereby producing carbonatite magmas. The relative abundances of trace elements of such highly differentiated ‘cratonic carbonatites’ have only little in common with those of metasomatic agents that act on the deeper lithosphere. Consequently, carbonatite trace element systematics should only be used with caution when constraining carbon mobility and metasomatism at mantle depths. Regardless of the exact nature of carbonate-bearing melts within the mantle lithosphere, they play an important role in enrichment processes, thereby decreasing the stability of buoyant cratons and promoting rift initiation - as exemplified by the Mesozoic-Cenozoic breakup of the North Atlantic craton.
DS201712-2732
2017
Tappert, R., Tappert, M.C.Novel kimberlite exploration tools: delineating country rock hydration associated with kimberlites using Vis-SWIR hyper spectral point dat a collected from drill core.45th. Annual Yellowknife Geoscience Forum, p. 78 abstractCanada, Northwest Territories, Saskatchewandeposit - Kelvin, Faraday, Pikoo

Abstract: Many kimberlite ore bodies are relatively small and the presence of overburden can make it challenging to intersect a kimberlite target during exploration drilling. If kimberlite is not intersected during drilling, it can be difficult to decide whether an existing kimberlite body has been missed or whether the geophysical target was not kimberlite. A preliminary spectroscopic study conducted in 2017 provides evidence that kimberlites with sizes exceeding 30 meters hydrate the adjacent country rock. The detection of such ‘hydration halos’ in barren country rock drill cores can provide crucial evidence for the existence of nearby undiscovered kimberlites. To gain a better understanding about the size and morphology of hydration halos around different kimberlite ore bodies, hyperspectral point data were collected from drill cores comprised of crustal rocks recovered in close proximity to known kimberlites (e.g., Kelvin, Farraday, and Pikoo kimberlites). The information obtained as a result of this study will likely serve as a foundation for the development of a rapid, low-cost kimberlite exploration tool that can help evaluate kimberlite potential in areas where kimberlite was not intersected during drilling.
DS201710-2268
2017
Tauzin, B., Kim, S., Kennett, B.L.N.Pervasive seismic low-velocity zones within stagnant plates in the mantle transition zone: thermal or compositional origin?Earth and Planetary Science Letters, Vol. 477, pp.Mantlegeophysics - seismics

Abstract: We exploit conversions between P and S waves for large-scale, high-resolution imaging of the mantle transition zone beneath Northwest Pacific and the margin of Eastern Asia. We find pervasive reflectivity concentrated in two bands with apparent wave-speed reduction of ?2% to ?4% about 50 km thick at the top of the transition zone and 100 km thick at the bottom. This negative reflectivity associated with the scattered-waves at depth is interpreted jointly with larger-scale mantle tomographic images, and is shown to delineate the stagnant portions of the subducted Pacific plate in the transition zone, with largely positive shear-wave velocity contrasts. The upper reflectivity zone connects to broad low-velocity regions below major intra-plate volcanoes, whereas the lower zone coincides locally with the occurrence of deep-focus earthquakes along the East Asia margin. Similar reflectivity is found in Pacific Northwest of the USA. We demonstrate that the thermal signature of plates alone is not sufficient to explain such features. Alternative explanations for these reflective zones include kinetic effects on olivine phase transitions (meta-stability), compositional heterogeneities within and above stagnant plates, complex wave-propagation effects in the heterogeneous slab structure, or a combination of such factors. We speculate that part of the negative reflectivity is the signature of compositional heterogeneities, as revealed by numerous other studies of seismic scattering throughout the mantle, and that such features could be widespread across the globe.
DS201708-1775
2017
Terbrugge, P.Vertical pit mining - an alternative to open pit mining for massive/shallow orebodies.11th. International Kimberlite Conference, OralAfrica, South Africamining - open pit

Abstract: The concept of vertical pit mining has developed as an alternative mining method for the exploitation from surface of small, vertical or near vertical, massive orebodies to depths of approximately 100 m where ore extraction can become uneconomical due to high stripping ratios. Support of the sidewalls is ensured with systematic anchoring depending on the condition of the insitu rock mass together with the installation of mesh and shotcrete in order to prevent small-scale ravelling and spalling which, with the pit at depth, can prove hazardous to operations at the base of the pit. Hoisting of the ore is carried out either by a vertical A Frame hoist at the crest of the pit, which requires tramming of ore at the base of the pit to the hoist. Alternatively, a Blondin Cableway system, which allows for loading of kibbles at any location within the pit, negating the need for a tram to the hoist located on the side of the pit, can be utilised. For various reasons the technique has been successfully applied to the mining of a chrome deposit in Zimbabwe to a depth of 95m and a kimberlite pit in West Africa where the pit was terminated at a depth of 85m due to a sidewall failure. Feasibility studies for two further vertical pits were conducted for orebodies in South Africa and Australia, kimberlite and nickel respectively, but due to economic considerations, have not been mined.
DS201708-1776
2017
Thomassot, E.The Archean sedimentary sulfur recycling under the Kaapvaal craton revisited from 4S- isotopic compositions in sulfide inclusions in diamonds from Kimberley Pool.11th. International Kimberlite Conference, OralAfrica, South Africadeposit - Kimberley Pool
DS201709-2063
2017
Thomassot, E., Pearson, D.G., Kitayama, Y., Deloule, E.Sulfur isotope signature 33S/34S and 36S of sea water altered Archean oceanic crust in Siberia eclogite.Goldschmidt Conference, abstract 1p.Russia, Siberiaeclogites

Abstract: Eclogite xenoliths brought to the surface by kimberlites are high pressure mafic rocks whose origin (magmatic vs crustal) remains debated. In addition to disagreement on how to interpret eclogite compositions, mantle metasomatism overprints the mineralogy and geochemistry of some of these rocks, making the question of their protolith undoubtedly more complex. In this contribution we aim to test the robustness of multiple S-isotope signatures in highly metasomatized eclogitic sulfides. We selected 12 interstitial sulfides from Mir (n=4) and Udachnaya (n=8) eclogites, intergrown with garnet and omphacite. We analysed their lead (including Pb204) and S-isotope (32S, 33S, 34S and 36S) compositions, insitu, using a Cameca ims 1280. The samples consist of complex assemblages of pyrrhotite pentlandite intergrowth with K- and Cl-rich sulfides (djerfisherite) invaded by veinlets of alteration minerals (mainly chlorite). All our samples display internal zoning in Pb concentration (118 ppm to 4.2 wt%) but are homogeneous in isotopic compositions (e.g. 208Pb/204Pb = 38.09 ± 0.35‰). Pb-Pb ages of eclogitic sulfides are modern and undoubtedly reflect the metasomatic overprint by a Cl- and K-rich kimberlitic melt (consistent with the presence of djerfisherite). Sulfur isotope signatures of these sulfide (G34S = -1.3‰ ±2‰) fall within the canonical mantle range and cannot be distinguished from the composition of sulfides in the kimberlite (-1.4 ±2.2‰, Kitayama et al., 2016). Furthermore, Mir and Udachanaya eclogitic sulfides carry the largest mass independant fractionation (MIF) ever reported in mantle rocks. The overall trend reveals negative ?33S (down to - 1.1‰) associated to positive ?36S (up to 3‰). This observed correlation between ?33S and ?36S is consistent with the composition of sulfate aerosols formed in the Archean by photolysis reactions and likely dissolved in the ocean [4]. Our results indicate that multiple sulfur isotopes survive intense metasomatism (because isotope fractionation does not create S-MIF), and provide further evidence that the protoliths of Siberian eclogites were mafic rocks altered by seawater in the Archean.
DS201711-2530
2017
Thompson, S.E.Diamond crystals… The diamond in the rough that stays that way.Lapidary Journal, Vol. 71, 5, pp. 50-51.Technologydiamond morphology
DS201705-0883
2017
Thoresen, L.Archaeogemmology and ancient literary sources on gems and their origins.Romisch-Germanisches Zentralmuseum Leibniz-Forschungsinstitut fur Archaologie Mainz International Conference Oct. 20-22, 2015, pp. 155-217.Africa, EuropeGemology - gemstones

Abstract: Archaeology and discoveries of new gemstones and new gem sources in recent decades attest to the need for critical review and updating of literature in translation concerning gems of the ancient world. The origins and identities of gemstones used in ancient glyptic have been inferred almost exclusively from literary descriptions available in secondary or even tertiary sources after now-lost ancient original texts. To date, no epigraphical or philological study has verified the ancient gem cutters’repertoire of materials against empirical gemological examination of extant material in public or private collections. However, such objective data should improve interpretation of literary source material that is often fragmentary or contains descriptions fraught with lexical ambiguities and contradictions. A carefully qualified perspective is needed. Whether in original form or in translation, manuscripts, from antiquity to the present day, reflect some degree of current knowledge about geography and gems in the contemporary world of the author/epigrapher/translator. Contemporary knowledge attributed to earlier cultures is an unwitting bias that frequently eludes both translators and scholars. Together with critical examination of the imprint of authorial bias, a gemological review of extant material is discussed in relation to the important treatises on gemstone nomenclature, identity, and geographic origin.
DS201706-1107
2017
Thorleifson, L.H.Geological mapping in the US.GAC annual meeting, 1p. AbstractUnited Statesmap
DS201702-0243
2017
Tian, Z-Z., Liu, J., Xia, Q-K., Ingrin, J., Hao, Y-T., Depecker, C.Water concentraion profiles in natural mantle orthopyroxenes: a geochronometer for long annealing of xenoliths within magma.Geology, Vol. 45, 1, pp. 87-90.ChinaBasanites, Foidites

Abstract: Both mantle-derived clinopyroxene and orthopyroxene are generally homogeneous in water concentration, while water content in the coexisting olivine is affected by partial or complete loss during the ascent of the hosting magma. Here, we report the first record of water content profiles (higher water in the cores than in the rims) in natural orthopyroxene grains in peridotite xenoliths hosted by Cenozoic alkali basalts in Tianchang volcano, eastern China. The water contents of the coexisting clinopyroxene grains are homogeneous and are twice that measured in the cores of orthopyroxene grains, confirming previous chemical equilibrium between the two pyroxenes. The olivines (ol) are nearly dry (?0 ppm). These observations demonstrate that H diffusion in mantle orthopyroxene (opx) is faster than in clinopyroxene (cpx), and the relative mobility of H in each mineral phase could be quantified as: Graphic (where is the chemical diffusion coefficient of hydrogen). Combining this with experimental diffusion coefficients from the literature, we infer that (1) the xenoliths remained in contact with the magma below 900 °C for several months, and (2) clinopyroxene remains the more reliable recorder of water from depth, and orthopyroxene should be used more cautiously but can be considered with olivine for tracing slow transport and cooling of magma.
DS201708-1777
2017
Timmerman, S.Relation between fluid end-members and noble gases in South African diamonds.11th. International Kimberlite Conference, OralAfrica, South Africadiamond inclusions

Abstract: Fibrous diamond growth zones can contain abundant high density fluid inclusions (HDFs) and these provide the most direct information on the source and composition of diamond-forming fluids. Four different fluid end-members have been defined; silicic, low-Mg carbonatitic, high-Mg carbonatitic, and saline. Continuous arrays exist between the silicic and low-Mg carbonatitic end-member and between the saline and high-Mg carbonatitic end-member. Different processes have been proposed to explain the two major element compositional arrays, but the origin of and relation between the various fluid end-members is still uncertain. In this study we provide new constraints on the evolution and origin of these diamond-forming fluids by combining noble gas systematics with ?13C, N concentrations, and fluid inclusion compositions.
DS201708-1778
2017
Timmerman, S.Formation of unusual yellow Orapa diamonds.11th. International Kimberlite Conference, PosterAfrica, Botswanadeposit - Orapa
DS201703-0434
2017
Timmerman, S., Koornneef, J.M., Chinn, I.L., Davies, G.R.Dated eclogitic diamond growth zones reveal variable recycling of crustal carbon through time.Earth and Planetary Science Letters, Vol. 463, pp. 178-188.Africa, BotswanaDeposit - Lethakane

Abstract: Monocrystalline diamonds commonly record complex internal structures reflecting episodic growth linked to changing carbon-bearing fluids in the mantle. Using diamonds to trace the evolution of the deep carbon cycle therefore requires dating of individual diamond growth zones. To this end Rb-Sr and Sm-Nd isotope data are presented from individual eclogitic silicate inclusions from the Orapa and Letlhakane diamond mines, Botswana. ?13C?13C values are reported from the host diamond growth zones. Heterogeneous 87Sr/86Sr ratios (0.7033-0.7097) suggest inclusion formation in multiple and distinct tectono-magmatic environments. Sm-Nd isochron ages were determined based on groups of inclusions with similar trace element chemistry, Sr isotope ratios, and nitrogen aggregation of the host diamond growth zone. Diamond growth events at 0.14±0.090.14±0.09, 0.25±0.040.25±0.04, 1.1±0.091.1±0.09, 1.70±0.341.70±0.34 and 2.33±0.022.33±0.02 Ga can be directly related to regional tectono-magmatic events. Individual diamonds record episodic growth with age differences of up to 2 Ga. Dated diamond zones have variable ?13C?13C values (?5.0 to ?33.6‰ vs PDB) and appear to imply changes in subducted material over time. The studied Botswanan diamonds are interpreted to have formed in different tectono-magmatic environments that involve mixing of carbon from three sources that represent: i) subducted biogenic sediments (lightest ?13C?13C, low 87Sr/86Sr); ii) subducted carbonate-rich sediments (heavy ?13C?13C, high 87Sr/86Sr) and iii) depleted upper mantle (heavy ?13C?13C, low 87Sr/86Sr). We infer that older diamonds from these two localities are more likely to have light ?13C?13C due to greater subduction of biogenic sediments that may be related to hotter and more reduced conditions in the Archaean before the Great Oxidation Event at 2.3 Ga. These findings imply a marked temporal change in the nature of subducted carbon beneath Botswana and warrant further study to establish if this is a global phenomenon.
DS201711-2531
2017
Timms, N.E., Erickson, T.M., Zanetti, M.R., Pearce, M.A., Cayron, C., Cavosie, A.J., Reddy, S.M., Wittman, A., Carpenter, P.K.Cubic zirconia in >2370 C impact melt records Earth's hottest crust.Earth and Planetary Science Letters, Vol. 478, pp. 52-58.Canada, QuebecMistastin crater

Abstract: Bolide impacts influence primordial evolution of planetary bodies because they can cause instantaneous melting and vaporization of both crust and impactors. Temperatures reached by impact-generated silicate melts are unknown because meteorite impacts are ephemeral, and established mineral and rock thermometers have limited temperature ranges. Consequently, impact melt temperatures in global bombardment models of the early Earth and Moon are poorly constrained, and may not accurately predict the survival, stabilization, geochemical evolution and cooling of early crustal materials. Here we show geological evidence for the transformation of zircon to cubic zirconia plus silica in impact melt from the 28 km diameter Mistastin Lake crater, Canada, which requires super-heating in excess of 2370?°C. This new temperature determination is the highest recorded from any crustal rock. Our phase heritage approach extends the thermometry range for impact melts by several hundred degrees, more closely bridging the gap between nature and theory. Profusion of >2370?°C superheated impact melt during high intensity bombardment of Hadean Earth likely facilitated consumption of early-formed crustal rocks and minerals, widespread volatilization of various species, including hydrates, and formation of dry, rigid, refractory crust.
DS201709-2064
2017
Tomilenko, A.A., Dublansky, Yu.V., Kuzmin, D.V., Sobolev, N.V.Isotope compositions of C and O of magmatic calcites from the Udachnaya-East pipe kimberlite, Yakutia.Doklady Earth Sciences, Vol. 475, 1, pp. 828-831.Russia, Yakutiadeposit - Udachnaya-East

Abstract: It has been demonstrated for the first time that the isotopic compositions of carbon (?13C) in magmatic calcites from the Udachnaya–East pipe kimberlite groundmass varies from–2.5 to–1.0‰ (V-PDB), while those of oxygen (?18O) range from 15.0 to 18.2‰ (V-SMOW). The obtained results imply that during the terminal late magmatic and postmagmatic stages of the kimberlite pipe formation, the carbonates in the kimberlite groundmass became successively heavier isotopically, which indicates the hybrid nature of the carbonate component of the kimberlite: it was formed with contributions from mantle and sedimentary marine sources.
DS201710-2269
2017
Tomilenko, A.A., Kuzmin, D.V., Bulbak, T.A., Sobolev, N.V.Primary melt and fluid inclusions in regenerated crystals and phenocrysts of olivine from kimberlites of the Udachnaya-East pipe, Yakutia: the problem of the kimberlite melt.Doklady Earth Sciences, Vol. 475, 2, pp. 949-952.Russiadeposit - Udachnaya-East

Abstract: The primary melt and fluid inclusions in regenerated zonal crystals of olivine and homogeneous phenocrysts of olivine from kimberlites of the Udachnaya-East pipe, were first studied by means of microthermometry, optic and scanning electron microscopy, electron and ion microprobe analysis (SIMS), inductively coupled plasma mass-spectrometry (ICP MSC), and Raman spectroscopy. It was established that olivine crystals were regenerated from silicate-carbonate melts at a temperature of ~1100°C.
DS201709-2065
2017
Tomlinson, E.L., Kamber, B.C., Hoare, C.V., Stead, C.V., Ildefonse, B.An exsolution origin for Archaean mantle garnet.Goldschmidt Conference, abstract 1p.Mantlegarnet

Abstract: It is now well established that the cratonic sub-continental lithospheric mantle (SCLM) represents a residue of extensively melted fertile peridotite. The widespread occurrence of garnet in the Archaean SCLM remains a paradox because many experiments agree that garnet is exhausted beyond c. 20% melting. It has been suggested that garnet may have formed by exsolution from Al-rich orthopyroxene [1,2,3]. However, the few examples of putative garnet exsolution in cratonic samples remain exotic and have not afforded a link to garnet that occurs as distinct grains in granular harzburgite. We present crystallographic (EBSD), petrographic and chemical (SEM-EDS and LA-ICP-MS) data for an exceptionally well-preserved orthopyroxene megacryst juxtaposed against granular harzburgite. Garnet lamellae within the megacryst show crystallographic continuity and have a strong fabric relative to the host orthopyroxene, strongly indicating that the megacryst formed by exsolution. Garnet lamellae are sub-calcic Cr-pyropes with sinusoidal rare earth element patterns, while the orthopyroxene host is high-Mg enstatite; the reconstructed precursor is clinoestatite. The megacryst shows evidence for disintegrating into granular peridotite, and garnet and orthopyroxene within the granular peridotite are texturally and chemically identical to equivalent phases in the megacryst. Collectively, this evidence supports a common origin for the granular and exsolved portions of the sample. The compositions of the exsolved Cr pyrope and enstatite are typical of harzburgites and depleted lherzolites from the SCLM. Furthermore, garnet inclusions within orthopyroxene in several granular peridotites exhibit the same fabric as those in the exsolved megacryst. We hypothesise that clinoenstatite was a common phase in cratonic SCLM and that exsolution is the likely origin of many sub-calcic garnets in depleted peridotites.
DS201707-1376
2017
Trela, J., Gazel, E., Sobolev, A.V., Moore, L., Bizimis, M.The hottest lavas of the Phanerozoic and the survival of Archean reservoirs.Nature Geoscience, Vol. 10, 6, pp. 451-456.Mantleplumes

Abstract: Large igneous provinces and some hotspot volcanoes are thought to form above thermochemical anomalies known as mantle plumes. Petrologic investigations that support this model suggest that plume-derived melts originated at high mantle temperatures (greater than 1,500?°C) relative to those generated at ambient mid-ocean ridge conditions (about 1,350?°C). Earth’s mantle has also cooled appreciably during its history and the temperatures of modern mantle derived melts are substantially lower than those produced during the Archaean (2.5 to 4.0 billion years ago), as recorded by komatiites (greater than 1,700?°C). Here we use geochemical analyses of the Tortugal lava suite to show that these Galapagos-Plume-related lavas, which formed 89 million years ago, record mantle temperatures as high as Archaean komatiites and about 400?°C hotter than the modern ambient mantle. These results are also supported by highly magnesian olivine phenocrysts and Al-in-olivine crystallization temperatures of 1,570 ± 20?°C. As mantle plumes are chemically and thermally heterogeneous, we interpret these rocks as the result of melting the hot core of the plume head that produced the Caribbean large igneous province. Our results imply that a mantle reservoir as hot as those responsible for some Archaean lavas has survived eons of convection in the deep Earth and is still being tapped by mantle plumes.
DS201711-2532
2017
Trela, J., Gazel, E., Sobolev, A.V., Moore, L., Bizimis, M., Jicha, B., Batanova, V.G.The hottest lavas of the Phanerozoic and the survival of deep Archean reservoirs.Nature Geoscience, Vol. 10, pp. 451-456.Mantlegeodynamics - plumes

Abstract: Large igneous provinces and some hotspot volcanoes are thought to form above thermochemical anomalies known as mantle plumes. Petrologic investigations that support this model suggest that plume-derived melts originated at high mantle temperatures (greater than 1,500?°C) relative to those generated at ambient mid-ocean ridge conditions (about 1,350?°C). Earth’s mantle has also cooled appreciably during its history and the temperatures of modern mantle derived melts are substantially lower than those produced during the Archaean (2.5 to 4.0 billion years ago), as recorded by komatiites (greater than 1,700?°C). Here we use geochemical analyses of the Tortugal lava suite to show that these Galapagos-Plume-related lavas, which formed 89 million years ago, record mantle temperatures as high as Archaean komatiites and about 400?°C hotter than the modern ambient mantle. These results are also supported by highly magnesian olivine phenocrysts and Al-in-olivine crystallization temperatures of 1,570 ± 20?°C. As mantle plumes are chemically and thermally heterogeneous, we interpret these rocks as the result of melting the hot core of the plume head that produced the Caribbean large igneous province. Our results imply that a mantle reservoir as hot as those responsible for some Archaean lavas has survived eons of convection in the deep Earth and is still being tapped by mantle plumes.
DS201701-0035
2016
Tretiakova, I.G., Belousova, E.A., Malkovets, V.G., Griffin, W.L., Piazolo, S., Pearson, N.J., O'Reilly, S.Y., Nishido, H.Recurrent magmatic activity on a lithosphere scale structure: crystallization and deformation in kimberlitic zircons.Gondwana Research, Vol. 42, pp. 126-132.RussiaDeposit - Nubinskaya

Abstract: Kimberlites are not only the most economically important source of diamonds; they also carry unique information encapsulated in rock fragments entrained as the magma traverses the whole thickness of the lithosphere. The Nurbinskaya pipe in the Siberian kimberlite province (Russia) is one of several intruded along the Vilyui Rift, a major terrane boundary. The pipe contains three populations of mantle-derived zircon xenocrysts: Archean (mean age 2709 ± 9 Ma), Devonian (mean age 371 ± 2.3 Ma), and a subset of grains with evidence of brittle deformation and rehealing, and a range of ages between 370 and 450 Ma. The Hf-isotope, O-isotope and trace-element signatures of the last group provide a link between the Archean and Devonian events, indicating at least three episodes of magmatic activity and zircon crystallization in the lithosphere beneath the pipe. The emplacement of the Nurbinskaya pipe ca 370 Ma ago was only the youngest activity in a magma plumbing system that has been periodically reactivated over at least 2.7 billion years, controlled by the lithosphere-scale structure of the Vilyui Rift.
DS201708-1779
2017
Tretiakova, L.Impact-metasomatic origin of mircodiamonds from Kundy-Kol deposit, north Kazakhstan.11th. International Kimberlite Conference, PosterRussia, Kazakhstanmicrodiamonds
DS201708-1780
2017
Tretiakova, L.History of natural diamond formation based on defects characteristics detected by spectroscopic methods.11th. International Kimberlite Conference, PosterTechnologyspectroscopy
DS201708-1781
2017
Tretyachenko, V.Main mineralogical petrological features of Early-hercynian volcanic complexs of Archangelsk kimberlite-picrite region, NW Russia.11th. International Kimberlite Conference, PosterRussia, Kola Peninsuladeposit - Archangel
DS201706-1108
2017
Trommelen, M.S., Gauthier, M., Kelly, S.E., Hodder, T.J., Wang, Y., Ross, M.Till composition inheritance and overprinting in the Hudson Bay Lowland and across the Precambrian shield.GAC annual meeting, 1p. AbstractCanada, Manitobageochemistry

Abstract: The goal of this work is to determine the effect of multiple glaciations on till composition, in a zone of transition from a multi-till stratigraphy within the Hudson Bay Lowland (HBL) to a single till stratigraphy over the Precambrian shield. The study area, in NE Manitoba, has access to numerous sections that expose multiple tills, in addition to interglacial and postglacial sediments. Sequences of thick till are not easily separated into different units, despite previous field attempts to define four named tills. The compositional transition to thin till overlying the Precambrian Shield in the west is also not well understood. Yet, the two different settings were affected by the same 3+ glacial cycles. The wide range in eastern- and/or northeastern-sourced calcareous clast concentrations, and ‘locally’-sourced shield clast concentrations, combined with variable concentrations of northern-sourced clasts, suggests that the tills of northeastern Manitoba are ‘provenance’ hybrids. Local tills result from the net effect of multiple glacial processes that underwent spatiotemporal variability. Mixed provenance applies not only to surface tills, but to the subsurface tills as well. Preliminary results suggest that carbonate transport across the shield was continuous throughout several glacial cycles, but the bulk of transport likely occurred prior to the most recent glacial cycle. Current work has established a northern-Manitoba ice-flow history using the erosional and depositional record, which encompasses 5 to 7 phases. This new compilation is used in conjunction with ‘till-clast’ stratigraphy and ‘till-geochemistry’ stratigraphy, to identify a new provenance framework for tills in northeastern Manitoba.
DS201702-0244
2017
Tsay, A., Zajacz, Z., Ulmer, P., Sanchez-Valle, C.Mobility of major and trace elements in the eclogite-fluid system and element fluxes upon slab dehydration.Geochimica et Cosmochimica Acta, Vol. 198, pp. 70-91.MantleSubduction

Abstract: The equilibrium between aqueous fluids and allanite-bearing eclogite has been investigated to constrain the effect of temperature (T) and fluid composition on the stability of allanite and on the mobility of major and trace elements during the dehydration of eclogites. The experiments were performed at 590-800 °C and 2.4-2.6 GPa, and fluids were sampled as synthetic fluid inclusions in quartz using an improved entrapment technique. The concentrations and bulk partition coefficients were determined for a range of major (Mg, Ca, Na, Fe, Al, Ti) and 16 trace elements as a function of T and fluid composition. The results reveal a significant effect of T on element partitioning between the fluids and the solid mineral assemblage. The partition coefficients increase by more than an order of magnitude for most of the major and trace elements, and several orders of magnitude for light rare-earth elements (LREE) from 590 to 800 °C. The addition of various ligand species into the fluid at 700 °C results in distinctive trends on element partitioning. The concentrations and corresponding partition coefficients of most of the elements are enhanced upon addition of NaF to the fluid. In contrast, NaCl displays a nearly opposite effect by suppressing the solubilities of major elements and consequently affecting the mobility of trace elements that form stable complexes with alkali-(alumino)-silicate clusters in the fluid, e.g. high field strength elements (HFSE). The results further suggest that fluids in equilibrium with orthopyroxene and/or diopsidic clinopyroxene are peralkaline (ASI ?0.1-0.7), whereas fluids in equilibrium with omphacitic pyroxene are more peraluminous (ASI ?1.15). Therefore, natural aqueous fluids in equilibrium with eclogite at about 90 km depth will be slightly peraluminous in composition. Another important finding of this study is the relatively high capacity of aqueous fluids to mobilize LREE, which may be even higher than that of hydrous melts.
DS201703-0435
2017
Tschirhart, V., Jefferson, C.W., Morris, W.A.Basement geology beneath the northeast The lon Basin, Nunavut: insights from integrating new gravity, magnetic and geological data.Geophysical Prospecting, Vol. 65, 2, pp. 617-636.Canada, NunavutGeophysics - Thelon Basin

Abstract: Current models for unconformity-associated uranium deposits predict fluid flow and ore deposition along reactivated faults in >1.76 Ga basement beneath Mesoproterozoic siliciclastic basins. In frontier regions such as the Thelon Basin in the Kivalliq region of Nunavut, little is known about the sub-basin distribution of units and structures, making exploration targeting very tenuous. We constructed a geological map of the basement beneath the unconformity by extrapolating exposed features into the subsurface. The new map is constrained by detailed geological, geophysical, and rock property observations of outcrops adjacent to the basin and by aeromagnetic and gravity data over the geophysically transparent sedimentary basin. From rock property measurements, it is clear that the diverse magnetic and density characteristics of major rock packages provide quantitative three-dimensional constraints. Gravity profiles forward modelled in four cross sections define broad synforms of the Amer Belt and Archean volcanic rocks that are consistent with the structural style outside the basin. Major lithotectonic entities beneath the unconformity include: supracrustal rocks of the Archean Woodburn Lake group and Marjorie Hills meta sedimentary gneiss and associated mixed granitoid and amphibolitic gneiss; the Amer Mylonite Zone and inferred mafic intrusions oriented parallel and sub-parallel; other igneous intrusions of 2.6 Ga, 1.83 Ga, and 1.75 Ga vintage; and the <2.3 Ga to >1.84 Ga Amer Group. Four main brittle regional fault arrays (040°-060°, 075°-90°, 120°, and 150°) controlled development and preservation of the basin. The reactivated intersections of such faults along fertile basement units such as the Rumble assemblage, Marjorie Hills assemblage, Nueltin igneous rocks, and Pitz formation are the best targets for uranium exploration.
DS201702-0245
2016
Tual, L., Pitra, P., Moller, C.P-T evolution of Precambrian eclogite in the Sveconorwegian orogen, SW Sweden.Journal of Metamorphic Geology, In press availableEurope, SwedenEclogite

Abstract: Conditions of the prograde, peak-pressure and part of the decompressional P-T path of two Precambrian eclogites in the eastern Sveconorwegian orogen have been determined using the pseudosection approach. Cores of garnet from a Fe-Ti-rich eclogite sample record a first prograde and syn-deformational stage along a Barrovian geothermal gradient from ~670 °C and 7 kbar to 710 °C and 8.5 kbar. Garnet rims grew during further burial to 16.5-19 kbar at ~850-900 °C, along a steep dP/dT gradient. The pseudosection model of a kyanite-bearing eclogite sample of more magnesian bulk composition confirms the peak conditions. Matrix reequilibration associated with subsequent near-isothermal decompression and partial exhumation produced plagioclase-bearing symplectites replacing kyanite and clinopyroxene and is estimated at 850-870 °C and 10-11 kbar. The validity of the pseudosections is discussed in detail. It is shown that in pseudosection modelling the fractionation of FeO in accessory sulphides may cause a significant shift of field boundaries (here displaced by up to 1.5 kbar and 70 °C) and must not be neglected. Fast burial, exhumation and subsequent cooling are supported by the steepness of both the prograde and the decompressional P-T paths as well as the preservation of garnet growth zoning and the symplectitic reaction textures. These features are compatible with deep tectonic burial of the eclogite-bearing continental crust as part of the underthrusting plate (Eastern Segment, continent Baltica) in a collisional setting that led to an effectively doubled crustal thickness and subsequent exhumation of the eclogites through tectonic extrusion. Our results are in accordance with regional structural and petrologic relationships, which demonstrate foreland-vergent partial exhumation of the eclogite-bearing nappe along a basal thrust zone and support a major collisional stage at c. 1 Ga. We argue that the similarities between Sveconorwegian and Himalayan eclogite occurrences emphasize the modern style of Grenvillian-aged tectonics.
DS201709-2066
2016
Tukker, H., Holder, A., Swarts, B., van Strijp, T., Grobler, E.The CCUT block cave design for Culli nan diamond mine.South African Institute of Mining and Metallurgy, Vol. 116, 8, pp. 715-723.Africa, South Africadeposit - Cullinan
DS201707-1377
2017
Turner, M., Turner, S., Blatter, D., Maury, R., Perfit, M., Yogodzinski, G.Water contents of clinopyroxenes from sub-arc mantle peridotitesIsland Arc, in press available 2p.Europe, Francemassif

Abstract: One poorly constrained reservoir of the Earth's water budget is that of clinopyroxene in metasomatised, mantle peridotites. This study presents reconnaissance Sensitive High-Resolution, Ion Microprobe–Stable Isotope (SHRIMP–SI) determinations of the H2O contents of (dominantly) clinopyroxenes in rare mantle xenoliths from four different subduction zones, i.e. Mexico, Kamchatka, Philippines, and New Britain (Tabar-Feni island chain) as well as one intra-plate setting (western Victoria). All of the sub-arc xenoliths have been metasomatised and carry strong arc trace element signatures. Average measured H2O contents of the pyroxenes range from 70 ppm to 510?ppm whereas calculated bulk H2O contents range from 88 ppm to 3?737?ppm if the variable presence of amphibole is taken into account. In contrast, the intra-plate, continental mantle xenolith from western Victoria has higher water contents (3?447?ppm) but was metasomatised by alkali and/or carbonatitic melts and does not carry a subduction-related signature. Material similar to the sub-arc peridotites can either be accreted to the base of the lithosphere or potentially be transported by convection deeper into the mantle where it will lose water due to amphibole breakdown.
DS201712-2733
2017
Ugalde, H., Furlan, A., Veglio, E., Milkereit, B., Mirza, A.M., Elliott, B.Airborne MAG/EM dat a integration of Slave Province kimberlites, Northwest Territories.45th. Annual Yellowknife Geoscience Forum, p. 82 abstractCanada, Northwest Territoriesgeophysics

Abstract: As part of the Slave Province Geophysical, Surficial Materials and Permafrost Study, the Northwest Territories Geological Survey (NTGS) commissioned high resolution geophysical surveys in the Slave Geological Province (SGP). The high resolution aeromagnetic survey was flown from February to April 2017 and comprise 87,600 line-km of data flown at 100 m line spacing and nominal aircraft terrain clearance was 60 m with drape flying over the Central Slave craton block. The horizontal gradient magnetic and frequency domain EM (FDEM) survey was flown from February to March 2017 acquired at 75 m line spacing over 6 other blocks with nominal terrain clearance of 60 m to maintain bird height of 25 m, covering 4,580 line-km (Munn Lake, Margaret Lake, Zyena Lake, Lac de Gras West, Big Blue and Mackay Lake). The objective of this work is to develop multi-parameter models to help mineral exploration and mining companies better understand the range of geophysical signatures associated with kimberlites in the SGP. A regular geophysical-based approach for kimberlite exploration usually involves inverting geophysical data with limited geological input. In this contribution we present different ways of looking at the geophysical data and try to obtain a more thorough geological understanding out of it. The workflow starts with a complete GIS compilation of all the ancillary data available in the area: previous industry reports, geology, remote sensing, topographic layers. Secondly, we compute a number of interpretation sub-products from the total magnetic intensity data (tilt derivatives, analytic signal, and other edge detection routines). The next stage involves the computation of a susceptibility distribution from the FDEM data (Tschirhart et al, 2015). With this we are able to generate a magnetic model of the near surface susceptibility distributions, which are then subtracted from the observed data. The resultant map shows anomalous sources that could be associated to either remanent magnetization and/or deeper sources. Following the work of Sterritt (2006), post-emplacement alteration is ubiquitous in kimberlite pipes. Alteration results in production of secondary oxide minerals and alteration of primary oxide minerals to phases with different magnetic susceptibilities (e.g. non-magnetic iron oxides). This can lead to a dramatic increase of magnetic susceptibility due to serpentinization (Clark, 1997). On the other hand, remanent magnetization can change the polarity of the observed magnetic anomalies or even completely remove the expected signature due to an equal but opposite combination of remanent and induced magnetic components. Therefore, a thorough compilation of petrophysical and mineralogical data over kimberlites and altered rocks in the vicinity of known occurrences is critical for the geological understanding of the existing geophysical data. This contribution will show some preliminary processing and compilation work completed over the Slave province kimberlites using the newly acquired geophysical data.
DS201705-0884
2017
Ugapeva, S., Goryainov, S., Afanasiev, V., Ponkratov, K.Raman mapping of mechanical stress field in diamond around a chromite inclusion.European Geosciences Union General Assembly 2017, Vienna April 23-28, 1p. 11676 AbstractTechnologyDiamond inclusions
DS201710-2270
2017
Umino, S., Knayama, K., Kitamura, K., Tamura, A., Ishizuka, A., Senda, R., Arai, S.Did boninite originate from the heterogeneous mantle with reycled ancient slab?Island Arc, Sept. 28, 3p.Mantlesubduction

Abstract: Boninites are widely distributed along the western margin of the Pacific Plate extruded during the incipient stage of the subduction zone development in the early Paleogene period. This paper discusses the genetic relationships of boninite and antecedent protoarc basalt magmas and demonstrates their recycled ancient slab origin based on the T-P conditions and Pb-Hf-Nd-Os isotopic modeling. Primitive melt inclusions in chrome spinel from Ogasawara and Guam islands show severely depleted high-SiO2, MgO (high-silica) and less depleted low-SiO2, MgO (low-silica and ultralow-silica) boninitic compositions. The genetic conditions of 1?346?°C at 0.58?GPa and 1?292?°C at 0.69?GPa for the low- and ultralow-silica boninite magmas lie on adiabatic melting paths of depleted mid-ocean ridge basalt mantle with a potential temperature of 1?430?°C in Ogasawara and of 1?370?°C in Guam, respectively. This is consistent with the model that the low- and ultralow-silica boninites were produced by remelting of the residue of the protoarc basalt during the forearc spreading immediately following the subduction initiation. In contrast, the genetic conditions of 1?428?°C and 0.96?GPa for the high-silica boninite magma is reconciled with the ascent of more depleted harzburgitic source which pre-existed below the Izu-Ogasawara-Mariana forearc region before the subduction started. Mixing calculations based on the Pb-Nd-Hf isotopic data for the Mariana protoarc basalt and boninites support the above remelting model for the (ultra)low-silica boninite and the discrete harzburgite source for the high-silica boninite. Yb-Os isotopic modeling of the high-Si boninite source indicates 18-30?wt% melting of the primitive upper mantle at 1.5-1.7?Ga, whereas the source mantle of the protoarc basalt, the residue of which became the source of the (ultra)low-Si boninite, experienced only 3.5-4.0?wt% melt depletion at 3.6-3.1?Ga, much earlier than the average depleted mid-ocean ridge basalt mantle with similar degrees of melt depletion at 2.6-2.2?Ga.
DS201710-2271
2017
Unsworth, J.Diamond aggregate sorting apparatus. ( recognizes boart from a gemstone).Materials World Magazine , Patent but.ly/2ss32Q4 1p.Technologysorting machine
DS201709-2067
2017
Upadhyay, D., Ranjan, S., Abhinay, K., Pruseth, K.L., Nanda, J.K.India-Antarica connection: constraints from deformed alkaline rocks and carbonatites.Goldschmidt Conference, abstract 1p.Indiacarbonatites

Abstract: Deformed Alkaline Rocks and Carbonatites (DARCs) are markers of suture zones where continents have rifted apart and later amalgamated [1]. Petrological and geochronological data indicates that parts of India and East Antarctica may have been involved in several episodes of collision and breakup during the assembly of past supercontinents [2]. DARCs at the eastern margin of the Eastern Ghats Province (EGP) in India preserve the record of these amalgamation and breakup events. It is thought that the Napier Complex of East Antarctica collided with the Dharwar Craton of India at ca. 1.60 Ga forming the central and eastern Indian shield [3]. New zircon U-Pb ages from DARCs at the EGP margin show that the alkaline complexes (Kamakhyanagar: 1350±14 Ma Rairakhol: 1379±6 Ma; Khariar: 1478±5 Ma; Koraput: 1387±34 Ma; Kunavaram: 1360±5 Ma; Jojuru: 1352±6 Ma) were emplaced in a narrow time interval. The alkaline magmatism marks an episode of rifting in the Indo-Antarctic continental fragment, correlatable with breakup of the Columbia supercontinent. Metamorphic zircon from the alkaline rocks furnish age populations at 917-950 Ma, 792- 806 Ma and 562-569 Ma. The 917-950 Ma ages are correlated with the closure of an oceanic basin between the Ruker Terrane of East Antarctica and the Indian Shield during the assembly of the Rodinia supercontinent. This led to the collision of the Ruker Terrane with the combined India-Napier Complex producing the Grenville-age EGPRayner Complex orogen [2, 3]. The 792-806 Ma ages record the disintegration of Rodinia when Greater India started to break away from East Antarctica [4]. In the early Paleozoic, India reconverged towards Antarctica and Australia during Gondwanaland assembly. The 562-569 Ma zircon ages date the resulting collisions during Pan-African orogenesis.
DS201710-2272
2017
Upadhyay, D., Ranjan, S., Abhinay, K., Pruseth, K.L., Nanda, J.K.India-Antarctica connection: constraints from deformed alkaline rocks and carbonatites.Goldschmidt Conference, 1p. AbstractIndiacarbonatites

Abstract: Re-Os and platinum group element analyses are reported for peridotite xenoliths from the 533 Ma Venetia kimberlite cluster situated in the Limpopo Mobile Belt, the Neoarchaean collision zone between the Kaapvaal and Zimbabwe Cratons. The Venetian xenoliths provide a rare opportunity to examine the state of the cratonic lithosphere prior to major regional metasomatic disturbance of Re-Os systematics throughout the Phanerozoic. The 32 studied xenoliths record Si-enrichment that is characteristic of the Kaapvaal lithospheric mantle and can be subdivided into five groups based on Re-Os analyses. The most pristine group I samples (n = 13) display an approximately isochronous relationship and fall on a 3.28 ± 0.17 Ga (95 % conf. int.) reference line that is based on their mean TMA age. This age overlaps with the formation age of the Limpopo crust at 3.35-3.28 Ga. The group I samples derive from ?50 to ?170 km depth, suggesting coeval melt depletion of the majority of the Venetia lithospheric mantle column. Group II and III samples have elevated Re/Os due to Re addition during kimberlite magmatism. Group II has otherwise undergone a similar evolution as the group I samples with overlapping 187Os/188Os at eruption age: 187Os/188OsEA, while group III samples have low Os concentrations, unradiogenic 187Os/188OsEA and were effectively Re-free prior to kimberlite magmatism. The other sample groups (IV and V) have disturbed Re-Os systematics and provide no reliable age information. A strong positive correlation is recorded between Os and Re concentrations for group I samples, which is extended to groups II and III after correction for kimberlite addition. This positive correlation precludes a single stage melt depletion history and indicates coupled remobilisation of Re and Os. The combination of Re-Os mobility, preservation of the isochronous relationship, correlation of 187Os/188Os with degree of melt depletion and lack of radiogenic Os addition puts tight constraints on the formation and subsequent evolution of Venetia lithosphere. First, melt depletion and remobilisation of Re and Os must have occurred within error of the 3.28 Ga mean TMA age. Second, the refractory peridotites contain significant Re despite recording >40 % melt extraction. Third, assuming that Si-enrichment and Re-Os mobility in the Venetia lithospheric mantle were linked, this process must have occurred within ?100 Myr of initial melt depletion in order to preserve the isochronous relationship. Based on the regional geological evolution, we propose a rapid recycling model with initial melt depletion at ?3.35 Ga to form a tholeiitic mafic crust that is recycled at ?3.28 Ga, resulting in the intrusion of a TTG suite and Si-enrichment of the lithospheric mantle. The non-zero primary Re contents of the Venetia xenoliths imply that TRD model ages significantly underestimate the true depletion age even for highly depleted peridotites. The overlap of the ?2.6 Ga TRD ages with the time of the Kaapvaal-Limpopo collision is purely fortuitous and has no geological significance. Hence, this study underlines the importance of scrutiny if age information is to be derived from whole rock Re-Os analyses.
DS201707-1378
2017
Urann, B.M.Fluorine and chlorine in mantle minerals and the halogen budget of the Earth's mantle.Contributions to Mineralogy and Petrology, Vol. 172, 51-Mantleperidotite

Abstract: The fluorine (F) and chlorine (Cl) contents of arc magmas have been used to track the composition of subducted components, and the F and Cl contents of MORB have been used to estimate the halogen content of depleted MORB mantle (DMM). Yet, the F and Cl budget of the Earth’s upper mantle and their distribution in peridotite minerals remain to be constrained. Here, we developed a method to measure low concentrations of halogens (?0.4 µg/g F and ?0.3 µg/g Cl) in minerals by secondary ion mass spectroscopy. We present a comprehensive study of F and Cl in co-existing natural olivine, orthopyroxene, clinopyroxene, and amphibole in seventeen samples from different tectonic settings. We support the hypothesis that F in olivine is controlled by melt polymerization, and that F in pyroxene is controlled by their Na and Al contents, with some effect of melt polymerization. We infer that Cl compatibility ranks as follows: amphibole > clinopyroxene > olivine ~ orthopyroxene, while F compatibility ranks as follows: amphibole > clinopyroxene > orthopyroxene ? olivine, depending on the tectonic context. In addition, we show that F, Cl, Be and B are correlated in pyroxenes and amphibole. F and Cl variations suggest that interaction with slab melts and fluids can significantly alter the halogen content of mantle minerals. In particular, F in oceanic peridotites is mostly hosted in pyroxenes, and proportionally increases in olivine in subduction-related peridotites. The mantle wedge is likely enriched in F compared to un-metasomatized mantle, while Cl is always low (<1 µg/g) in all tectonic settings studied here. The bulk anhydrous peridotite mantle contains 1.4–31 µg/g F and 0.14–0.38 µg/g Cl. The bulk F content of oceanic-like peridotites (2.1–9.4 µg/g) is lower than DMM estimates, consistent with F-rich eclogite in the source of MORB. Furthermore, the bulk Cl budget of all anhydrous peridotites studied here is lower than previous DMM estimates. Our results indicate that nearly all MORB may be somewhat contaminated by seawater-rich material and that the Cl content of DMM could be overestimated. With this study, we demonstrate that the halogen contents of natural peridotite minerals are a unique tool to understand the cycling of halogens, from ridge settings to subduction zones.
DS201702-0246
2017
Ustinov, V.Diamond potential of Angola: results of co-operation of Alrosa and Endiama.PDAC 2017, March 6, 1p. AbstractAfrica, AngolaExploration review
DS201708-1782
2017
Ustinov, V.Kimberlite field of Angola: structural control and diamond presence.11th. International Kimberlite Conference, PosterAfrica, Angoladeposit - Angola
DS201708-1783
2017
Ustinov, V.Models of reflection of kimberlite pipes of north east of Botswana in eolian haloes of dispersion.11th. International Kimberlite Conference, PosterAfrica, Botswanageochemistry
DS201704-0649
2017
Ustinov, V.N.Terriginous diamond-bearing rocks of the Siberian, East-European and African platforms. IN RUS***Nauka ***in RUS, 531p. Index of chapters available in english 3p. PdfRussiaBook - 9 chapters * titles descriptions in english
DS201703-0436
2017
Van Acken, D., Luguet, A., Pearson, D.G., Nowell, G.M., Fonseca, R.O.C., Nagel, T.J., Schulz, T.Mesoarchean melting and Neoarchean ro Paleoproterozoic metasomatism during the formation of the cratonic mantle keel beneath West Greenland.Geochimica et Cosmochimica Acta, Vol. 203, pp. 37-53.Europe, GreenlandCraton
DS201702-0247
2016
Van Avendonk, H.J.A, Davis, J.K., Harding, J.L.Decrease in oceanic crustal thickness since the break up of Pangea.Nature Geoscience, Vol. 10, pp. 58-61.MantleTectonics

Abstract: Earth’s mantle has cooled by 6-11?°C every 100 million years since the Archaean, 2.5 billion years ago. In more recent times, the surface heat loss that led to this temperature drop may have been enhanced by plate-tectonic processes, such as continental breakup, the continuous creation of oceanic lithosphere at mid-ocean ridges and subduction at deep-sea trenches. Here we use a compilation of marine seismic refraction data from ocean basins globally to analyse changes in the thickness of oceanic crust over time. We find that oceanic crust formed in the mid-Jurassic, about 170 million years ago, is 1.7?km thicker on average than crust produced along the present-day mid-ocean ridge system. If a higher mantle temperature is the cause of thicker Jurassic ocean crust, the upper mantle may have cooled by 15-20?°C per 100 million years over this time period. The difference between this and the long-term mantle cooling rate indeed suggests that modern plate tectonics coincide with greater mantle heat loss. We also find that the increase of ocean crustal thickness with plate age is stronger in the Indian and Atlantic oceans compared with the Pacific Ocean. This observation supports the idea that upper mantle temperature in the Jurassic was higher in the wake of the fragmented supercontinent Pangaea due to the effect of continental insulation.
DS201703-0451
2016
Van Avendonk, H.J.A, Davis, J.K., Harding, J.L.Decrease in oceanic crustal thickness since the break up of Pangea.Nature Geoscience, Vol. 10, pp. 58-61.MantleTectonics

Abstract: Earth’s mantle has cooled by 6-11?°C every 100 million years since the Archaean, 2.5 billion years ago. In more recent times, the surface heat loss that led to this temperature drop may have been enhanced by plate-tectonic processes, such as continental breakup, the continuous creation of oceanic lithosphere at mid-ocean ridges and subduction at deep-sea trenches. Here we use a compilation of marine seismic refraction data from ocean basins globally to analyse changes in the thickness of oceanic crust over time. We find that oceanic crust formed in the mid-Jurassic, about 170 million years ago, is 1.7?km thicker on average than crust produced along the present-day mid-ocean ridge system. If a higher mantle temperature is the cause of thicker Jurassic ocean crust, the upper mantle may have cooled by 15-20?°C per 100 million years over this time period. The difference between this and the long-term mantle cooling rate indeed suggests that modern plate tectonics coincide with greater mantle heat loss. We also find that the increase of ocean crustal thickness with plate age is stronger in the Indian and Atlantic oceans compared with the Pacific Ocean. This observation supports the idea that upper mantle temperature in the Jurassic was higher in the wake of the fragmented supercontinent Pangaea due to the effect of continental insulation.
DS201705-0885
2017
van den Heuvel, Q., Matveev, S., Drury, M., Gress, M., Chinn, I., Davies, G.Genesis of diamond inclusions: an integrated cathodluminescence ( CL) and electron backscatter diffraction (EBSD) study on eclogitic and peridotitic inclusions and their diamond host.European Geosciences Union General Assembly 2017, Vienna April 23-28, 1p. 6564 AbstractAfrica, BotswanaDeposit - Jwaneng, Letlhakane
DS201710-2273
2017
Van der Meer, Q., Klaver, M., Reisberg, L., Riches, A. J.V., Davies, G.R.Preservation of an Archean whole rock Re-Os isochron for the Venetia lithospheric mantle: evidence for rapid crustal recycling and lithosphere stabilization at 3.3 Ga.Geochimica et Cosmochimica Acta, Vol. 216, pp. 242-263.Africa, South Africadeposit - Venetia
DS201709-2068
2017
van der Meer, Q.H.A., Klaver, M., Reisberg, L., Riches, A.J.V., Davies, G.R.Preservation of an Archaean whole rock Re-Os isochron for the Venetia lithospheric mantle: evidence for rapid crustal recycling and lithospheric stabilization at 3.3 Ga.Geochimica et Cosmochimica Acta, in press available, 22p.Africa, South Africadeposit - Venetia

Abstract: Re-Os and platinum group element analyses are reported for peridotite xenoliths from the 533 Ma Venetia kimberlite cluster situated in the Limpopo Mobile Belt, the Neoarchaean collision zone between the Kaapvaal and Zimbabwe Cratons. The Venetian xenoliths provide a rare opportunity to examine the state of the cratonic lithosphere prior to major regional metasomatic disturbance of Re-Os systematics throughout the Phanerozoic. The 32 studied xenoliths record Si-enrichment that is characteristic of the Kaapvaal lithospheric mantle and can be subdivided into five groups based on Re-Os analyses. The most pristine group I samples (n = 13) display an approximately isochronous relationship and fall on a 3.28 ± 0.17 Ga (95 % conf. int.) reference line that is based on their mean TMA age. This age overlaps with the formation age of the Limpopo crust at 3.35–3.28 Ga. The group I samples derive from ?50 to ?170 km depth, suggesting coeval melt depletion of the majority of the Venetia lithospheric mantle column. Group II and III samples have elevated Re/Os due to Re addition during kimberlite magmatism. Group II has otherwise undergone a similar evolution as the group I samples with overlapping 187Os/188Os at eruption age: 187Os/188OsEA, while group III samples have low Os concentrations, unradiogenic 187Os/188OsEA and were effectively Re-free prior to kimberlite magmatism. The other sample groups (IV and V) have disturbed Re-Os systematics and provide no reliable age information. A strong positive correlation is recorded between Os and Re concentrations for group I samples, which is extended to groups II and III after correction for kimberlite addition. This positive correlation precludes a single stage melt depletion history and indicates coupled remobilisation of Re and Os. The combination of Re-Os mobility, preservation of the isochronous relationship, correlation of 187Os/188Os with degree of melt depletion and lack of radiogenic Os addition puts tight constraints on the formation and subsequent evolution of Venetia lithosphere. First, melt depletion and remobilisation of Re and Os must have occurred within error of the 3.28 Ga mean TMA age. Second, the refractory peridotites contain significant Re despite recording >40 % melt extraction. Third, assuming that Si-enrichment and Re-Os mobility in the Venetia lithospheric mantle were linked, this process must have occurred within ?100 Myr of initial melt depletion in order to preserve the isochronous relationship. Based on the regional geological evolution, we propose a rapid recycling model with initial melt depletion at ?3.35 Ga to form a tholeiitic mafic crust that is recycled at ?3.28 Ga, resulting in the intrusion of a TTG suite and Si-enrichment of the lithospheric mantle. The non-zero primary Re contents of the Venetia xenoliths imply that TRD model ages significantly underestimate the true depletion age even for highly depleted peridotites. The overlap of the ?2.6 Ga TRD ages with the time of the Kaapvaal-Limpopo collision is purely fortuitous and has no geological significance. Hence, this study underlines the importance of scrutiny if age information is to be derived from whole rock Re-Os analyses.
DS201709-2069
2016
Van Niekirk, L.M., Olivier, A., Armstrong, J., Sikwa, N.A.Pioneering large diamond recovery at Karowe diamond mine.South African Institute of Mining and Metallurgy, Vol. 116, 8, pp. 709-714.Africa, Botswanadeposit - Karowe

Abstract: Historically, the recovery of large diamonds in conventional treatment plant flow sheets has been associated with dense media separation (DMS). This is attributed mainly to DMS's highly efficient and proven track record in the concentration and separation of ores with variable solids densities. In most instances, DMS has been utilized as a pre-concentration step ahead of any recovery plant, due to its ability and versatility in reducing feed within a specific size range to manageable volumes for downstream X-ray processing and subsequent diamond recovery. The benefit of using carbon-signature-based detection equipment for retrieving large stones upfront in the flow sheet not only equates to earlier recovery of diamonds from the system, but also lessens the exposure of diamond-bearing ore to additional materials handling, pumping, and/or crushing, which has been known to damage or even break diamonds and decrease revenue.
DS201708-1581
2017
Van Rythoven, A.D., Schulze, D.J., Hauri, E.H., Wang, J., Shirey, S.Intra-crystal co-variations of carbon isotopes and nitrogen contents in diamond from three north american cratons. A54 south ( Diavik) Slave craton; Lynx dike Superior craton ; Kelsey Lake Wyoming cratonChemical Geology, in press available 54p.Canada, Northwest Territories, Quebec, United States, Coloradodeposit, A54, Lynx, Kelsey Lake

Abstract: Eighteen diamond samples from the A154 South kimberlite pipe (Diavik Mine), Slave Craton, Northwest Territories (Canada); sixteen diamond samples from the Lynx kimberlite dyke, Superior Craton, Quebec (Canada) and twelve diamond samples from the Kelsey Lake kimberlite pipe, Wyoming Craton, Colorado (USA), were cut through the core-zones, polished, imaged by cathodoluminescence (CL), and analyzed by secondary ion mass spectrometry (SIMS) for carbon isotope composition and nitrogen abundance. Twenty Kelsey Lake diamond plates, including the twelve crystals analyzed by SIMS, were analyzed by Fourier transform infrared spectrometry (FTIR) for nitrogen concentration and aggregation state. Diamond samples from Diavik and Kelsey Lake have average ?13CPDB and nitrogen contents (atomic ppm) similar to those found by earlier studies: averaging between ? 3.9‰ and 486 ppm, and ? 7‰ and 308 ppm, respectively. Samples from the Lynx dyke, investigated for the first time, are substantially different, having ?13C = ?1.2‰ and nitrogen content = 32 ppm (averages). All three localities have examples of significant variations in nitrogen content (> 100 ppm) within single stones. Carbon isotope variation within individual stones is relatively minor (< 2‰). In terms of nitrogen aggregation, samples from the Kelsey Lake kimberlite are dominated by zones of Type IaA, but mixed-type and Type IaB (less common) stones also occur. For the majority of samples, overall intra-diamond zonations of nitrogen abundances and carbon isotope ratios are not in agreement with modeled trends for single-event Rayleigh fractionation of diamond from fluid under nitrogen-compatible conditions at 1100 °C. The involvement of fluids from subducted crustal reservoirs with exceptionally light, and in the case of Lynx samples, exceptionally heavy ?13CPDB values is necessary to explain the observed growth histories of all the samples studied here.
DS201704-0650
2016
Varas-Reu, M.I., Garrido, C.J., Marchesi, C., Bodinier, J-L., Frets, E., Bosch, D., Tommasi, A., Hidas, K., Targuisti, K.Refertilization processes of the subcontinental lithospheric mantle: the record of the Beni Bousera orogenic peridotite ( Rif Belt, northern Morocco).Journal of Petrology, Vol. 57, 11-12, pp. 2251-2270.Africa, MoroccoDeposit - Beni Bousera

Abstract: Correlations between major and minor transition elements in tectonically emplaced orogenic peridotites have been ascribed to variable degrees of melt extraction and melt-rock reaction processes, leading to depletion or refertilization. To elucidate how such processes are recorded in the subcontinental lithospheric mantle, we processed a large geochemical dataset for peridotites from the four tectono-metamorphic domains of the Beni Bousera orogenic massif (Rif Belt, northern Morocco). Our study reveals that variations in bulk-rock major and minor elements, Mg-number and modal mineralogy of lherzolites, as well as their clinopyroxene trace element compositions, are inconsistent with simple partial melting and mainly resulted from different reactions between melts and depleted peridotites. Up to 30% melting at <3 GPa and cryptic metasomatism can account for the geochemical variations of most harzburgites. In Grt-Sp mylonites, melting and melt-rock reactions are masked by tectonic mixing with garnet pyroxenites and subsolidus re-equilibration. In the rest of the massif, lherzolites were mostly produced by refertilization of a refractory protolith (Mg-number = 91, Ol = 70%, Cpx/Opx = 0.4) via two distinct near-solidus, melt- rock reactions: (1) clinopyroxene and orthopyroxene precipitation and olivine consumption at melt/rock ratios <0.75 and variable mass ratio between crystallized minerals and infiltrated melt ®, which are recorded fairly homogeneously throughout the massif; (2) dissolution of orthopyroxene and precipitation of clinopyroxene and olivine at melt/rock ratios <1 and R = 0.2-0.3, which affected mainly the Arie` gite-Seiland and Seiland domains. The distribution of secondary lherzolites in the massif suggests that the first refertilization reaction occurred prior to the differentiation of the Beni Bousera mantle section into petro-structural zones, whereas the second reaction was associated with the development of the tectono-metamorphic domains. Our data support a secondary, refertilization-related origin for most lherzolites in orogenic peridotite massifs.
DS201707-1379
2017
Vasilev, Yu.R., Gora, M.P., Kuzmin, D.V.Petrology of foiditic and meymechitic volcanism in the Maimecha - Kotui province ( Polar Siberia).Russian Geology and Geophysics, Vol. 58, pp. 659-673.Russia, Siberiaalkaline - Maimecha

Abstract: Comparative analysis of ultramafic meymechites of the Maimecha Suite and alkaline volcanics of the Ary-Dzhang Suite (foidites (nephelinites, analcimites, limburgites, etc.) and melilitites) has shown their consanguinity, which indicates their relationship with the same magmatic system periodically producing large amounts of alkaline ultramafic melts. We have studied the petrogeochemical and mineralogical compositions of rocks and melt inclusions in the hosted olivines. The rocks of the Maimecha and Ary-Dzhang Suite differ considerably in MgO content, which is well explained by the accumulation of olivine. The inclusions in olivines from the meymechites and the rocks of the Ary-Dzhang Suite correspond in composition to foidites. The trace and rare-earth element patterns are similar both in the foidites and meymechites and in the melt inclusions: They show negative anomalies of Rb and K and positive anomalies of Nb and Ta. The ratios of indicator elements (Nb/Ta, Ba/La, Ta/La, etc.) in the rocks of the Maimecha and Ary-Dzhang Suite are constant and almost independent of their Mg# values. The La/Yb ratio in the foidites is significantly higher than that in the meymechites and in the melt inclusions from their olivines, which indicates that the rocks of the Ary-Dzhang Suite resulted from the fractionation of highly magnesian alkaline picritoid melt.
DS201701-0036
2017
Verma, K.Precambrian plate tectonic setting of Africa from multidimensional discrimination diagrams.Journal of African Earth Sciences, Vol. 125, pp. 137-150.AfricaTectonics

Abstract: New multi-dimensional discrimination diagrams have been used to identify plate tectonic setting of Precambrian terrains. For this work, nine sets of new discriminant-function based multi-dimensional discrimination diagrams were applied for thirteen case studies of Precambrian basic, intermediate and acid magmas from Africa to highlight the application of these diagrams and probability calculations. The applications of these diagrams indicated the following results: For northern Africa: to Wadi Ghadir ophiolite, Egypt indicated an arc setting for Neoproterozoic (746 ± 19 Ma). For South Africa: Zandspruit greenstone and Bulai pluton showed a collision and a transitional continental arc to collision setting at about Mesoarchaean and Neoarchaean (3114 ± 2.3 Ma and 2610-2577 Ma); Mesoproterozoic (1109 ± 0.6 Ma and 1100 Ma) ages for Espungabera and Umkondo sills were consistent with an island arc setting. For eastern Africa, Iramba-Sekenke greenstone belt and Suguti area, Tanzania showed an arc setting for Neoarchaean (2742 ± 27 Ma and 2755 ± 1 Ma). Chila, Bulbul-Kenticha domain, and Werri area indicated a continental arc setting at about Neoproterozoic (800-789 Ma); For western Africa, Sangmelima region and Ebolowa area, southern Cameroon indicated a collision and continental arc setting, respectively for Neoarchaean (?2800-2900 Ma and 2687-2666 Ma); Finally, Paleoproterozoic (2232-2169 Ma) for Birimian supergroup, southern Ghana a continental arc setting; and Paleoproterozoic (2123-2108 Ma) for Katiola-Marabadiassa, Côte d'Ivoire a transitional continental arc to collision setting. Although there were some inconsistencies in the inferences, most cases showed consistent results of tectonic settings. These inconsistencies may be related to mixed ages, magma mixing, crustal contamination, degree of mantle melting, and mantle versus crustal origin.
DS201702-0248
2016
Verplanck, P.L., Hitzman, M.W.Rare earth and critical elements in ore deposits.Reviews in Economic Geology, Vol. 18, 365p. $ 72. CD/pdf/printGlobalBook - rare earth

Abstract: This special volume provides a comprehensive review of the current state of knowledge for rare earth and critical elements in ore deposits. The first six chapters are devoted to rare earth elements (REEs) because of the unprecedented interest in these elements during the past several years. The following eight chapters describe critical elements in a number of important ore deposit types. These chapters include a description of the deposit type, major deposits, critical element mineralogy and geochemistry, processes controlling ore-grade enrichment, and exploration guides. This volume represents an important contribution to our understanding of where, how, and why individual critical elements occur and should be of use to both geoscientists and public policy analysts.
DS201702-0249
2016
Verplanck, P.L., Mariano, A.N., Mariano, A. Jr.Rare earth element ore geology of carbonatites.Reviews in Economic Geology, Vol. 18, pp. 5-32.GlobalCarbonatite
DS201704-0651
2017
Vertriest, W., Pardieu, V.Update on gemstone mining in northern Mozambique. RubyGems & Gemology, Vol. 52, 4, pp. 404-409.Africa, MozambiqueGemstones - ruby

Abstract: Northern Mozambique (figure 1) has gained attention for its rubies since a major discovery near Montepuez in 2009 (see McClure and Koivula, 2009; Pardieu and Lomthong, 2009; Pardieu and Chauvire, 2012; Pardieu et al., 2009, 2013; Hsu et al., 2014). Until the arrival of Gemfields in 2012, nearly all the production from this deposit came from unlicensed miners, known as garimpeiros. Between 2012 and 2016, Gemfields became a force in the ruby trade, supplying the market through regular auctions in Singapore and Jaipur. In 2016, two new players acquired ruby mining licenses around Montepuez: Mustang Resources and Metals of Africa. During a summer 2016 GIA field expedition, we visited these new sites. We also spent time at the Gemfields operation, in order to follow the development of what is already the world’s largest ruby mine. We also visited an interesting new pink spinel and tourmaline deposit near Ocua.
DS201711-2533
2017
Veter, M., Foley, S.F., Mertz-Kraus, R., Groschopf, N.Trace elements in olivine of ultramafic lamprophyres controlled by phlogopite rich mineral assemblages in the mantle source.Lithos, Vol. 292-293, pp. 81-95.Mantlelamprophyres

Abstract: Carbonate-rich ultramafic lamprophyres (aillikites) and associated rocks characteristically occur during the early stages of thinning and rifting of cratonic mantle lithosphere, prior to the eruption of melilitites, nephelinites and alkali basalts. It is accepted that they require volatile-rich melting conditions, and the presence of phlogopite and carbonate in the source, but the exact source rock assemblages are debated. Melts similar to carbonate-rich ultramafic lamprophyres (aillikites) have been produced by melting of peridotites in the presence of CO2 and H2O, whereas isotopes and trace elements appear to favor distinct phlogopite-bearing rocks. Olivine macrocrysts in aillikites are usually rounded and abraded, so that it is debated whether they are phenocrysts or mantle xenocrysts. We have analyzed minor and trace element composition in olivines from the type aillikites from Aillik Bay in Labrador, Canada. We characterize five groups of olivines: [1] mantle xenocrysts, [2] the main phenocryst population, and [3] reversely zoned crystals interpreted as phenocrysts from earlier, more fractionated, magma batches, [4] rims on the phenocrysts, which delineate aillikite melt fractionation trends, and [5] rims around the reversely zoned olivines. The main phenocryst population is characterized by mantle-like Ni (averaging 3400 ?g g? 1) and Ni/Mg at Mg# of 88-90, overlapping with phenocrysts in ocean island basalts and Mediterranean lamproites. However, they also have low 100 Mn/Fe of 0.9-1.3 and no correlation between Ni and other trace elements (Sc, Co, Li) that would indicate recycled oceanic or continental crust in their sources. The low Mn/Fe without high Ni/Mg, and the high V/Sc (2-5) are inherited from phlogopite in the source that originated by solidification of lamproitic melts at the base of the cratonic lithosphere in a previous stage of igneous activity. The olivine phenocryst compositions are interpreted to result from phlogopite and not high modal pyroxene in the source. The presence of kimberlites and ultramafic lamprophyres of Mesozoic age in Greenland indicates the persistence of a steep edge to the cratonic lithosphere at a time when this had been removed from the western flank in Labrador.
DS201711-2534
2017
Vidal, O., Rostom, F., Francois, C., Giraud, G.Global trends in metal consumption and supply: the raw material-energy nexus.Elements, Vol. 13, pp. 319-324.Globalresources

Abstract: The consumption of mineral resources and energy has increased exponentially over the last 100 years. Further growth is expected until at least the middle of the 21st century as the demand for minerals is stimulated by the industrialization of poor countries, increasing urbanization, penetration of rapidly evolving high technologies, and the transition to low-carbon energies. In order to meet this demand, more metals will have to be produced by 2050 than over the last 100 years, which raises questions about the sustainability and conditions of supply. The answers to these questions are not only a matter of available reserves. Major effort will be required to develop new approaches and dynamic models to address social, economic, environmental, geological, technological, legal and geopolitical impacts of the need for resources.
DS201705-0886
2016
Viezzoli, A.Tli Kwi Cho shootout. IV GeophysicsSEG Annual Meeting Dallas, 67 ppt.Canada, Northwest TerritoriesDeposit - Tli Kwi Cho
DS201703-0437
2017
Viezzoli, A., Kaminskiy, V., Fiandaca, G.Modeling induced polarization effects in helicopter time domain electromagnetic data: synthetic case studies. ( kimberlite simulated)Geophysics, Vol. 82, 2, pp. E31-E50.TechnologyGeophysics - IP, EM

Abstract: We have developed a synthetic multiparametric modeling and inversion exercise undertaken to study the robustness of inverting airborne time-domain electromagnetic (TDEM) data to extract Cole-Cole parameters. The following issues were addressed: nonuniqueness, ill posedness, dependency on manual processing and the effect of constraints, and a priori information. We have used a 1D layered earth model approximation and lateral constraints. Synthetic simulations were performed for several models and the corresponding Cole-Cole parameters. The possibility to recover these models by means of laterally constrained multiparametric inversion was evaluated, including recovery of chargeability distributions from shallow and deep targets based on analysis of induced polarization (IP) effects, simulated in airborne TDEM data. Different scenarios were studied, including chargeable targets associated with the conductive and resistive environments. In particular, four generic models were considered for the exercise: a sulfide model, a kimberlite model, and two generic models focusing on the depth of investigation.
DS201708-1784
2017
Vines, M.Discovery of an orangeite magmatic event in the central Kalahari: implications for the origin of southern African kimberlites.11th. International Kimberlite Conference, PosterAfrica, South Africa, Botswanaorangeite
DS201712-2734
2017
Wagner, A.Everything you ever wanted to know about perovskite, Earth's most abundant type of mineral - that we almost never see.Sciencemag.org, Nov. 17, videoTechnologyperovskite

Abstract: Perovskite is one of the most common crystal structures on the planet, but why is it so interesting to researchers from many scientific disciplines? Science looks into the properties of this odd cube of atoms, and what cutting-edge research is being performed on its many varieties.
DS201701-0037
2016
Walker, R.T., Telfer, M., Kahle, R.L., Dee, M.W., Kahle, J-L., Schwenninger, J-L., Sloan, R.A., Watts, A.B.Rapid mantle driven uplift along the Angolan margin in the Quaternary.Nature Geoscience, Vol. 9, pp. 909-914.Africa, AngolaTectonics

Abstract: Mantle flow can cause the Earth’s surface to uplift and subside, but the rates and durations of these motions are, in general, poorly resolved due to the difficulties in making measurements of relatively small vertical movements (hundreds of metres) over sufficiently large distances (about 1,000?km). Here we examine the effect of mantle upwelling through a study of Quaternary uplift along the coast of Angola. Using both optically stimulated luminescence on sediment grains, and radiocarbon dating of fossil shells, we date a 25?m coastal terrace at about 45 thousand years old, when sea level was about 75?m lower than today, indicating a rapid uplift rate of 1.8-2.6?mm?yr?1 that is an order of magnitude higher than previously obtained rates averaged over longer time periods. Automated extraction and correlation of coastal terrace remnants from digital topography uncovers a symmetrical uplift with diameter of more than 1,000?km. The wavelength and relatively short timescale of the uplift suggest that it is associated with a mantle process, possibly convective upwelling, and that the topography may be modulated by rapid short-lived pulses of mantle-derived uplift. Our study shows that stable continental regions far from the effects of glacial rebound may experience rapid vertical displacements of several millimetres per year.
DS201710-2274
2017
Walker, S.Diamond miners respond… Suffering from lower jewelry demand over much of past 10 years, the world's diamond industry picked up last year.Engineering and Mining Journal, Sept. pp. 58-66.Globalindustry - overview

Abstract: Since the last occasion when E&MJ took an in-depth look at the world diamond industry (September 2011, pp.54-63), the world’s diamond producers have continued the process of restructuring that began in the early 2000s when De Beers began to relinquish its traditional role of industry custodian. In the intervening period, statistics compiled by the Kimberley Process Certification Scheme (KPCS) indicate that producers responded in no mean way to reduced consumer demand, particularly in the aftermath of the 2008 global economic downturn, with output fluctuating within a fairly narrow band between 2009 and 2015, and only showing signs of picking up again last year.
DS201711-2535
2017
Wall, F., Rollat, A., Pell, R.S.Responsible sourcing for critical metals.Elements, Vol. 13, pp. 313-318.Globalresources, REE

Abstract: Most critical raw materials, such as the rare-earth elements (REEs), are starting products in long manufacturing supply chains. Unlike most consumers, geoscientists can become involved in responsible sourcing, including best environmental and social practices, because geology is related to environmental impact factors such as energy requirements, resource efficiency, radioactivity and the amount of rock mined. The energy and material inputs and the emissions and waste from mining and processing can be quantified, and studies for REEs show little difference between ‘hard rocks’, such as carbonatites, and easily leachable ion-adsorption clays. The reason is the similarity in the embodied energy in the chemicals used for leaching, dissolution and separation.
DS201709-2070
2017
Wall., F., Al Ali, S., Rollinson, G., Fitzpatrick, R., Dawes, W., Broom-Fendley, S.Geochemistry and mineralogy of rare earth processing.Goldschmidt Conference, abstract 1p.Africa, Malawicarbonatite - Songwe Hill

Abstract: The geochemistry and mineralogy of REE deposits is diverse, from carbonatite-related deposits, alkaline rocks, mineral sands and ion adsorption clays to potential by-products of phosphate and bauxite, and reuse of waste materials. Despite the large number of prospects that have been explored recently, very little additional REE production has started. A major challenge is to design effective, cost-efficient and environmentally-friendly processing and extraction. Processing flow sheets have to be constructed carefully for each deposit. Translating geochemistry and mineralogy studies, including quantitative mineralogy results, into processing characteristics can be illustrated using results from the Songwe Hill carbonatite, Malawi. Combining results with other published data then allows us to make some general conclusions about the common REE ore minerals and their geological environment, including the REE fluorcarbonate series, monazite and xenotime. The use of chemicals for REE extraction is often the largest environmental burden to mitigate. A new issue is that certain REE, such as Ce, are in oversupply, and are not being recovered in some proposed processing flowsheets. It will be important to understand the environmental and commercial implications of this development.
DS201705-0887
2017
Wallace, T.C. Jr.Colorado Diamonds. (Sloan and Kelsey Lake)lithographie.org, No. 19, pp. 110-113.United States, Colorado PlateauBook - history, deposits
DS201704-0652
2017
Walpole, J., Wookey, J., Kendall, J-M., Masters, T-G.Seismic anisotropy and mantle flow below subducting slabs.Earth and Planetary Science Letters, Vol. 465, pp. 155-167.MantleSubduction

Abstract: Subduction is integral to mantle convection and plate tectonics, yet the role of the subslab mantle in this process is poorly understood. Some propose that decoupling from the slab permits widespread trench parallel flow in the subslab mantle, although the geodynamical feasibility of this has been questioned. Here, we use the source-side shear wave splitting technique to probe anisotropy beneath subducting slabs, enabling us to test petrofabric models and constrain the geometry of mantle fow. Our global dataset contains 6369 high quality measurements - spanning ?40,000?km?40,000?km of subduction zone trenches - over the complete range of available source depths (4 to 687?km) - and a large range of angles in the slab reference frame. We find that anisotropy in the subslab mantle is well characterised by tilted transverse isotropy with a slow-symmetry-axis pointing normal to the plane of the slab. This appears incompatible with purely trench-parallel flow models. On the other hand it is compatible with the idea that the asthenosphere is tilted and entrained during subduction. Trench parallel measurements are most commonly associated with shallow events (source depth <50?km<50?km) - suggesting a separate region of anisotropy in the lithospheric slab. This may correspond to the shape preferred orientation of cracks, fractures, and faults opened by slab bending. Meanwhile the deepest events probe the upper lower mantle where splitting is found to be consistent with deformed bridgmanite.
DS201702-0250
2017
Wambeke, T., Benndorf, J.A simulation based geostatistical approach to real-time reconciliation of the grade control model.Mathematical Geosciences, Vol. 49, 1, pp. 1-37.TechnologyGeostatistics - not specific to diamonds

Abstract: One of the main challenges of the mining industry is to ensure that produced tonnages and grades are aligned with targets derived from model-based expectations. Unexpected deviations, resulting from large uncertainties in the grade control model, often occur and strongly impact resource recovery and process efficiency. During operation, local predictions can be significantly improved when deviations are monitored and integrated back into the grade control model. This contribution introduces a novel realization-based approach to real-time updating of the grade control model by utilizing online data from a production monitoring network. An algorithm is presented that specifically deals with the problems of an operating mining environment. Due to the complexity of the material handling process, it is very challenging to formulate an analytical approximation linking each sensor observation to the grade control model. Instead, an application-specific forward simulator is built, translating grade control realizations into observation realizations. The algorithm utilizes a Kalman filter-based approach to link forward propagated realizations with real process observations to locally improve the grade control model. Differences in the scale of support are automatically dealt with. A literature review, following a detailed problem description, presents an overview of the most recent approaches to solving some of the practical problems identified. The most relevant techniques are integrated and the resulting mathematical framework is outlined. The principles behind the self-learning algorithm are explained. A synthetic experiment demonstrates that the algorithm is capable of improving the grade control model based on inaccurate observations on blended material streams originating from two extraction points.
DS201703-0438
2017
Wang, E.Timing of the initial collision between the Indian and Asian continents.Science China Earth Sciences, Vol. 60, 10p.Asia, IndiaSubduction

Abstract: There exist three mainstream opinions regarding the timing of the initial collision between the Indian and Eurasian continents, namely, 65±5, 45±5, and 30±5 Ma. Five criteria are proposed for determining which tectonic event was related to the initial collision between India and Asia: the rapid decrease in the rate of plate motion, the cessation of magmatic activity originating from the subduction of oceanic crust, the end of sedimentation of oceanic facies, the occurrence of intracontinental deformation, and the exchange of sediments sourced from two continents. These criteria are used to constrain the nature of these tectonic events. It is proposed that the 65±5 Ma tectonic event is consistent with some of the criteria, but the upshot of this model is that the magmatic activity originating from the Tethyan subduction since the Mesozoic restarted along the southern margin of the Asian continent in this time after a brief calm, implying that the subduction of the Neotethys slab was still taking place. The magmatic activity that occurred along the southern margin of the Asian continent had a 7-Myr break during 72-65 Ma, which in this study is interpreted as having resulted from tectonic transformation from subduction to transform faulting, indicating that the convergence between the Indian and Asian continents was once dominated by strike-slip motion. The 30±5 Ma tectonic event resulted in the uplift of the Tibetan Plateau, which was related to the late stage of the convergence between these two continents, namely, a hard collision. The 45±5 Ma tectonic event is in accordance with most of the criteria, corresponding to the initial collision between these two continents.
DS201703-0439
2016
Wang, H., Li, J., Zhang, H., Xu, L., Li, W.The absolute paleoposition of the North Chin a block during the middle Ordovician.Science China Earth Sciences, Vol. 59, 3, pp. 573-582.ChinaCraton, North China

Abstract: Present-day hot spots and Phanerozoic large igneous provinces (LIPs) and kimberlites mainly occur at the edges of the projections of Large Low Shear Wave Velocity Provinces (LLSVPs) on the earth’s surface. If a plate contains accurately dated LIPs or kimberlites, it is possible to obtain the absolute paleoposition of the plate from the LIP/kimberlite and paleomagnetic data. The presence of Middle Ordovician kimberlites in the North China Block provides an opportunity to determine the absolute paleoposition of the block during the Middle Ordovician. In addition to paleobiogeographical information and the results of previous work on global plate reconstruction for the Ordovician Period, we selected published paleomagnetic data for the North China Block during the Middle Ordovician and determined the most reasonable absolute paleoposition of the North China Block during the Middle Ordovician: paleolatitude of approximately 16.6°S to 19.1°S and paleolongitude of approximately 10°W. The block was located between the Siberian Plate and Gondwana, close to the Siberian Plate. During the Cambrian and Ordovician periods, the North China Block may have moved toward the Siberian Plate and away from the Australian Plate.
DS201702-0251
2017
Wang, H., van Hunen, J., Pearson, D.G.Making Archean cratonic roots by lateral compression: a two stage thickening and stabilization model.Tectonophysics, in press available, 10p.MantleCraton, tectonics

Abstract: Archean tectonics was capable of producing virtually indestructible cratonic mantle lithosphere, but the dominant mechanism of this process remains a topic of considerable discussion. Recent geophysical and petrological studies have refuelled the debate by suggesting that thickening and associated vertical movement of the cratonic mantle lithosphere after its formation are essential ingredients of the cratonization process. Here we present a geodynamical study that focuses on how the thick stable cratonic lithospheric roots can be made in a thermally evolving mantle. Our numerical experiments explore the viability of a cratonization process in which depleted mantle lithosphere grows via lateral compression into a > 200-km thick, stable cratonic root and on what timescales this may happen. Successful scenarios for craton formation, within the bounds of our models, are found to be composed of two stages: an initial phase of tectonic shortening and a later phase of gravitational self-thickening. The initial tectonic shortening of previously depleted mantle material is essential to initiate the cratonization process, while the subsequent gravitational self-thickening contributes to a second thickening phase that is comparable in magnitude to the initial tectonic phase. Our results show that a combination of intrinsic compositional buoyancy of the cratonic root, rapid cooling of the root after shortening, and the long-term secular cooling of the mantle prevents a Rayleigh-Taylor type collapse, and will stabilize the thick cratonic root for future preservation. This two-stage thickening model provides a geodynamically viable cratonization scenario that is consistent with petrological and geophysical constraints.
DS201707-1380
2016
Wang, H., van Hunen, J., Pearson, D.G.Making Archean cratonic roots by lateral compression: a two stage thickening and stabilization model.Tectonophysics, in press availableMantlecraton

Abstract: Archean tectonics was capable of producing virtually indestructible cratonic mantle lithosphere, but the dominant mechanism of this process remains a topic of considerable discussion. Recent geophysical and petrological studies have refuelled the debate by suggesting that thickening and associated vertical movement of the cratonic mantle lithosphere after its formation are essential ingredients of the cratonization process. Here we present a geodynamical study that focuses on how the thick stable cratonic lithospheric roots can be made in a thermally evolving mantle. Our numerical experiments explore the viability of a cratonization process in which depleted mantle lithosphere grows via lateral compression into a > 200-km thick, stable cratonic root and on what timescales this may happen. Successful scenarios for craton formation, within the bounds of our models, are found to be composed of two stages: an initial phase of tectonic shortening and a later phase of gravitational self-thickening. The initial tectonic shortening of previously depleted mantle material is essential to initiate the cratonization process, while the subsequent gravitational self-thickening contributes to a second thickening phase that is comparable in magnitude to the initial tectonic phase. Our results show that a combination of intrinsic compositional buoyancy of the cratonic root, rapid cooling of the root after shortening, and the long-term secular cooling of the mantle prevents a Rayleigh-Taylor type collapse, and will stabilize the thick cratonic root for future preservation. This two-stage thickening model provides a geodynamically viable cratonization scenario that is consistent with petrological and geophysical constraints.
DS201710-2275
2017
Wang, H.S., et al.The elemental abundances ( with uncertainties) of the most Earth-like planet.Icarus, 10.1016/ j.icarus. 2017.08.024Mantlechemical composition

Abstract: To first order, the Earth as well as other rocky planets in the Solar System and rocky exoplanets orbiting other stars, are refractory pieces of the stellar nebula out of which they formed. To estimate the chemical composition of rocky exoplanets based on their stellar hosts' elemental abundances, we need a better understanding of the devolatilization that produced the Earth. To quantify the chemical relationships between the Earth, the Sun and other bodies in the Solar System, the elemental abundances of the bulk Earth are required. The key to comparing Earth's composition with those of other objects is to have a determination of the bulk composition with an appropriate estimate of uncertainties. Here we present concordance estimates (with uncertainties) of the elemental abundances of the bulk Earth, which can be used in such studies. First we compile, combine and renormalize a large set of heterogeneous literature values of the primitive mantle (PM) and of the core. We then integrate standard radial density profiles of the Earth and renormalize them to the current best estimate for the mass of the Earth. Using estimates of the uncertainties in i) the density profiles, ii) the core-mantle boundary and iii) the inner core boundary, we employ standard error propagation to obtain a core mass fraction of 32.5±0.3 wt%. Our bulk Earth abundances are the weighted sum of our concordance core abundances and concordance PM abundances. Our concordance estimates for the abundances of Mg, Sn, Br, B, Cd and Be are significantly lower than previous estimates of the bulk Earth. Our concordance estimates for the abundances of Na, K, Cl, Zn, Sr, F, Ga, Rb, Nb, Gd, Ta, He, Ar, and Kr are significantly higher. The uncertainties on our elemental abundances usefully calibrate the unresolved discrepancies between standard Earth models under various geochemical and geophysical assumptions.
DS201712-2735
2017
Wang, L., Wang, S-J., Brown, M., Zhang, J-F., Feng, P., Jin, Z.M.On the survival of intergranular coesite in UHP eclogite.Journal of Metamorphic Geology, in press availableChinaUHP

Abstract: Coesite is typically found as inclusions in rock-forming or accessory minerals in ultrahigh-pressure (UHP) metamorphic rocks. Thus, the survival of intergranular coesite in UHP eclogite at Yangkou Bay (Sulu belt, eastern China) is surprising and implies locally ‘dry’ conditions throughout exhumation. The dominant structures in the eclogites at Yangkou are a strong D2 foliation associated with tight-to-isoclinal F2 folds that are overprinted by close-to-tight F3 folds. The coesite-bearing eclogites occur as rootless intrafolial isoclinal F1 fold noses wrapped by a composite S1-S2 foliation in interlayered phengite-bearing quartz-rich schists. To evaluate controls on the survival of intergranular coesite we determined the number density of intergranular coesite grains per cm2 in thin section in two samples of coesite eclogite (phengite absent) and threee samples of phengite-bearing coesite eclogite (2-3 vol.% phengite), and measured the amount of water in garnet and omphacite in these samples, and also in two samples of phengite-bearing quartz eclogite (6-7 vol.% phengite, coesite absent). As coesite decreases in the mode, the amount of primary structural water stored in the whole rock, based on the nominally anhydrous minerals (NAMs), increases from 107/197 ppm H2O in the coesite eclogite to 157-253 ppm H2O in the phengite-bearing coesite eclogite to 391/444 ppm H2O in the quartz eclogite. In addition, there is molecular water in the NAMs and modal water in phengite. If the primary concentrations reflect differences in water sequestered during the late prograde evolution, the amount of fluid stored in the NAMs at the metamorphic peak was higher outside of the F1 fold noses. During exhumation from UHP conditions, where NAMs became H2O saturated, dehydroxylation would have generated a free fluid phase. Interstitial fluid in a garnet-clinopyroxene matrix at UHP conditions has dihedral angles >60°, so at equilibrium fluid will be trapped in isolated pores. However, outside the F1 fold noses strong D2 deformation likely promoted interconnection of fluid and migration along the developing S2 foliation, enabling conversion of some or all of the intergranular coesite into quartz. By contrast, the eclogite forming the F1 fold noses behaved as independent rigid bodies within the composite S1-S2 foliation of the surrounding phengite-bearing quartz-rich schists. Primary structural water concentrations in the coesite eclogite are so low that H2O saturation of the NAMs is unlikely to have occurred. This inherited drier environment in the F1 fold noses was maintained during exhumation by deformation partitioning and strain localization in the schists, and the fold noses remained immune to grain-scale fluid infiltration from outside allowing coesite to survive. The amount of inherited primary structural water and the effects of strain partitioning are important variables in the survival of coesite during exhumation of deeply subducted continental crust. Evidence of UHP metamorphism may be preserved in similar isolated structural settings in other collisional orogens.
DS201708-1785
2017
Wang, Q.Hydrogen of the lithospheric mantle in the northern Slave craton ( Canada): constraints from combined FTIR and EBSD measurements on peridoite xenoliths.11th. International Kimberlite Conference, PosterCanada, Northwest Territoriesperidotite
DS201706-1109
2017
Wang, Y., Foley, S.F., Prelevic, D.Potassium rich magmatism from a phlogopite free source.Geology, Vol. 45, 5, pp. 467-470.Europe, Serbiamelting

Abstract: The generation of strongly potassic melts in the mantle is generally thought to require the presence of phlogopite in the melting assemblage. In the Mediterranean region, trace element and isotope compositions indicate that continental crustal material is involved in the generation of many potassium-rich lavas. This is clearest in ultrapotassic rocks like lamproites and shoshonites, for which the relevant chemical signals are less diluted by extensive melting of peridotite. Furthermore, melting occurs here in young lithosphere, so the continental crust was not stored for a long period of time in the mantle before reactivation. We have undertaken two types of experiments to investigate the reaction between crust and mantle at 1000-1100 °C and 2-3 GPa. In the first, continental crustal metasediment (phyllite) and depleted peridotite (dunite) were juxtaposed as separate blocks, whereas in the second, the same rock powders were intimately mixed. In the first series, a clear reaction zone dominated by orthopyroxene was formed between dunite and phyllite but no hybridized melt could be found, whereas analyzable pools of hybridized melt occurred throughout the charges in the second series. Melt compositions show high abundances of Rb (100-220 ppm) and Ba (400-870 ppm), and consistent ratios of Nb/Ta (10-12), Zr/Hf (34-42), and Rb/Cs (28-34), similar to bulk continental crust. These experiments demonstrate that melts with as much as 5 wt% K2O may result from reaction between melts of continent-derived sediment and depleted peridotite at shallow mantle depths without the need for phlogopite or any other potassic phase in the residue.
DS201707-1381
2017
Wang, Y., Prelevic, D., Buhre, S., Foley, S.F.Constraints on the sources of post-collisional K rich magmatism: the roles of continental clastic sediemtns and terrigenous blueschists.Chemical Geology, Vol. 455, pp. 192-207.Mantlemagmatism

Abstract: The possible role of continental sediments in the generation of potassium-enriched lavas of the Alpine-Himalayan belt depends on their melting behaviour either during subduction or during post-collisional relaxation. Although usually classed as orogenic lavas, these volcanic rocks may result from re-melting of newly formed mantle lithosphere 30–40 million years after collision ends, and can thus be considered as the first stage of intraplate volcanism. The potassic component in these volcanics is characterized by a high Th/La signature for which there are two competing explanations: melting of subducted continental clastic sediments, and the involvement of lawsonite blueschists in the protoliths to the melting assemblages. Here, we report on a series of high-pressure experiments at 1–3 GPa and 900 to 975 °C on the melting behaviour of natural phyllite from Serbia, which serves as a proxy for Balkan upper continental crust. Hydrous granitic melts are present in all runs (68 wt% SiO2, ~ 4–5 wt% K2O, Mg# < 54 and ~ 5 wt% H2O). Garnet, quartz/coesite, plagioclase, K-feldspar, biotite/phengite, clinopyroxene and sillimanite/kyanite, and accessory phases including zircon, rutile, ilmenite, apatite and monazite occur in the charges. LA-ICP-MS analyses establish that the melts are extremely enriched in LILE (except for Sr), Th and U, but depleted in Nb and Zr, with LREE higher than HREE. Accessory phases accommodate several trace elements, especially HFSE and REE. Partition coefficients for some trace elements between residue and crustal melts are close to 1, contrasting strongly with melts of peridotite. Our dataset indicates that the direct melting of upper continental crust alone would generate siliceous, high-K magmas with enriched LILE, Th and U, but cannot explain the high Th/La fingerprint of K-rich lavas of the Alpine-Himalayan orogenic belt. We demonstrate that the Alpine-Himalayan orogenic volcanics attribute their unusual trace element geochemistry to the involvement of lawsonite blueschists that are imbricated together with extremely depleted fore-arc peridotites to form new lithosphere in the source region. There is no need or evidence for deep subduction in which a succession of additional reactions would only serve to modify and dilute the high Th/La signature.
DS201705-0888
2017
Warren, C.Plate tectonics: when ancient continents collide. Trans Hudson areaNature Geoscience, Vol. 10, pp. 245-246.Canada, NunavutTectonics

Abstract: The geological record preserves scant evidence for early plate tectonics. Analysis of eclogites - metamorphic rocks formed in subduction zones — in the Trans-Hudson mountain belt suggests modern-style subduction may have operated 1,800 million years ago.
DS201707-1382
2017
Warren, C.When ancient continents collide.Nature Geoscience, Vol. 10, 4, pp. 245-246.Mantleplate tectonics

Abstract: The geological record preserves scant evidence for early plate tectonics. Analysis of eclogites - metamorphic rocks formed in subduction zones - in the Trans-Hudson mountain belt suggests modern-style subduction may have operated 1,800 million years ago.
DS201708-1786
2017
Webb, K.Magmaclasts in kimberlite.11th. International Kimberlite Conference, PosterTechnologykimberlite classification
DS201706-1110
2017
Weidendorfer, D., Schmidt, M.W., Mattsson, H.B.A common origin of carbonatite magmas.Geology, Vol. 45, 6, pp. 507-510.Africa, Tanzaniacarbonatite - Oldoinyo Lengai

Abstract: The more than 500 fossil Ca-carbonatite occurrences on Earth are at odds with the only active East African Rift carbonatite volcano, Oldoinyo Lengai (Tanzania), which produces Na-carbonatite magmas. The volcano's recent major explosive eruptions yielded a mix of nephelinitic and carbonatite melts, supporting the hypothesis that carbonatites and spatially associated peralkaline silicate lavas are related through liquid immiscibility. Nevertheless, previous eruption temperatures of Na-carbonatites were 490-595 °C, which is 250-450 °C lower than for any suitable conjugate silicate liquid. This study demonstrates experimentally that moderately alkaline Ca-carbonatite melts evolve to Na-carbonatites through crystal fractionation. The thermal barrier of the synthetic Na-Ca-carbonate system, held to preclude an evolution from Ca-carbonatites to Na-carbonatites, vanishes in the natural system, where continuous fractionation of calcite + apatite leads to Na-carbonatites, as observed at Oldoinyo Lengai. Furthermore, saturating the Na-carbonatite with minerals present in possible conjugate nephelinites yields a parent carbonatite with total alkali contents of 8-9 wt%, i.e., concentrations that are realistic for immiscible separation from nephelinitic liquids at 1000-1050 °C. Modeling the liquid line of descent along the calcite surface requires a total fractionation of ?48% calcite, ?12% apatite, and ?2 wt% clinopyroxene. SiO2 solubility only increases from 0.2 to 2.9 wt% at 750-1200 °C, leaving little leeway for crystallization of silicates. The experimental results suggest a moderately alkaline parent to the Oldoinyo Lengai carbonatites and therefore a common origin for carbonatites related to alkaline magmatism.
DS201708-1582
2017
Weidendorfer, D., Schmidt, M.W., Mattsson, H.B.A common origin of carbonatite magmas.Geology, Vol. 45, 6, pp. 507-510.Africa, Tanzaniacarbonatites

Abstract: The more than 500 fossil Ca-carbonatite occurrences on Earth are at odds with the only active East African Rift carbonatite volcano, Oldoinyo Lengai (Tanzania), which produces Na-carbonatite magmas. The volcano’s recent major explosive eruptions yielded a mix of nephelinitic and carbonatite melts, supporting the hypothesis that carbonatites and spatially associated peralkaline silicate lavas are related through liquid immiscibility. Nevertheless, previous eruption temperatures of Na-carbonatites were 490–595 °C, which is 250–450 °C lower than for any suitable conjugate silicate liquid. This study demonstrates experimentally that moderately alkaline Ca-carbonatite melts evolve to Na-carbonatites through crystal fractionation. The thermal barrier of the synthetic Na-Ca-carbonate system, held to preclude an evolution from Ca-carbonatites to Na-carbonatites, vanishes in the natural system, where continuous fractionation of calcite + apatite leads to Na-carbonatites, as observed at Oldoinyo Lengai. Furthermore, saturating the Na-carbonatite with minerals present in possible conjugate nephelinites yields a parent carbonatite with total alkali contents of 8–9 wt%, i.e., concentrations that are realistic for immiscible separation from nephelinitic liquids at 1000–1050 °C. Modeling the liquid line of descent along the calcite surface requires a total fractionation of ?48% calcite, ?12% apatite, and ?2 wt% clinopyroxene. SiO2 solubility only increases from 0.2 to 2.9 wt% at 750–1200 °C, leaving little leeway for crystallization of silicates. The experimental results suggest a moderately alkaline parent to the Oldoinyo Lengai carbonatites and therefore a common origin for carbonatites related to alkaline magmatism.
DS201712-2736
2017
Weis, U., Schwager, B., Stoll, B., Nohl, U., Karlowski, P., Leisgang, I., Zwillich, F., Joachum, K.P.Geostandards and Geoanalytical Research bibliographic review 2016 ( geoanalyses, controls)Geostandards and Geoanalyical Review, Nov. 17, in press availableTechnologyreview

Abstract: This bibliographic review covers the research contained in twenty-one scientific journals with important contributions to geoanalysis and related scientific fields (Table 1, Figure 1). The relevance of well characterised reference materials (RMs) used as calibration materials or quality control samples for precise and accurate analyses is widely known and has often been described, for example, by Jochum and Enzweiler (2014).
DS201708-1787
2017
Weiss, Y.Fluid-rich Micro inclusions in diamonds open windows to large mantle processes.11th. International Kimberlite Conference, OralMantlediamond inclusions
DS201708-1788
2017
Weiss, Y.Ages of mantle metasomatism from the U-Th-He systematics of diamond forming C-O-H fluids.11th. International Kimberlite Conference, PosterMantlemetasomatism
DS201708-1789
2017
Weiss, Y.Thermo-chemical conditions of Mesozoic metasomatism at the southwestern Kaapvaal SCLM.11th. International Kimberlite Conference, PosterAfrica, South Africametasomatism
DS201705-0889
2017
Weiss, Y., Goldstein, S., Class, C., Winckler, G.A billion years of metasomatic alteration of the Kaapvaal SCLM encapsulated in fribrous diamonds.European Geosciences Union General Assembly 2017, Vienna April 23-28, 1p. 11122 AbstractAfrica, South AfricaDeposit - De Beers-pool, Finsch
DS201701-0038
2016
White, N.Surface sculpting by hidden agents.Nature Geoscience, Vol. 9, pp. 867-9.Africa, AngolaTectonics

Abstract: Tectonic plate interiors are often regarded as relatively inactive. Yet, reconstructions of marine terrace uplift in Angola suggest that underlying mantle flow can rapidly warp Earth's surface far from obviously active plate boundaries.
DS201712-2737
2017
Wickham, A.P., Winterburn, P.A.Surface till geochemistry and lithogeochemical exploration for a concealed kimberlite.45th. Annual Yellowknife Geoscience Forum, p. 118 abstract posterCanada, Northwest Territoriesdeposit - Kelvin, Kennady
DS201709-2071
2017
Wicks, J.K., Jackson, J.M., Struhahn, W., Zhang, D.Sound velocity and sensity of magnesiowustites: implications for ultralow velocity zone topography.Geophysics Research Letters, Vol. 44, 5, pp. 2148-2158.Mantlegeophysics - seismics

Abstract: We explore the effect of Mg/Fe substitution on the sound velocities of iron-rich (Mg1 ? xFex)O, where x = 0.84, 0.94, and 1.0. Sound velocities were determined using nuclear resonance inelastic X-ray scattering as a function of pressure, approaching those of the lowermost mantle. The systematics of cation substitution in the Fe-rich limit has the potential to play an important role in the interpretation of seismic observations of the core-mantle boundary. By determining a relationship between sound velocity, density, and composition of (Mg,Fe)O, this study explores the potential constraints on ultralow-velocity zones at the core-mantle boundary.
DS201710-2276
2017
Wiedenbeck, M., Lian, D.Secondary ion mass spectrometry analyses of diamond and moissanite in ophiolite.Acta Geologica Sinica, Vol. 91, s1, p.44 abstractEurope, Albaniamoissanites

Abstract: The Cameca 1280-HR large geometry SIMS instrument is a highly versatile analytical tool which can support a broad range of geochemical applications. Research using the Potsdam 1280 instrument focuses primarily on isotope ratio determinations in geomaterials. Optimized measurement protocols have already been established for ?18O determinations in zircon, and we are also working towards routine oxygen isotope determinations for quartz, calcite, mica, apatite and titanite. The primary challenge in developing such measurement systems are the identification and characterization of suitable reference materials (RMs), and this is made particularly challenging due to the matrix dependent ion yields of the SIMS ion source. Here we wish to report our progress towards establishing new analytical protocols for the determination of ?13C in both diamond and moissanite. In the case of diamond, our facility possesses three natural RMs with which we are able to produce data with a typical analytical repeatability of ?0.15 ‰ (1sd). An inter-comparison of our three diamond RMs demonstrates an overall data quality of better than 0.5‰ in terms of systematic offset between the various materials characterized using gas source mass spectrometry (Palot et al., 2012). A single such ?13C determination in diamond requires 80 s of data acquisition and involves a test portion mass of ?400 pg of material. In-house diamond reference materials for ?15N calibration allow us to measure this isotopic system to a total analytical uncertainty of ± 1.6 ‰ (1sd) at nitrogen concentrations reaching down to 250 ?g/g. Due to the relatively low abundance of nitrogen in diamonds, such isotope ratio determinations require around 9 minutes of data collection. With respect to ?13C determinations in moissanite, we use a kimberlitic SiC as calibrant (Mathez et al., 1995), on which we achieve a repeatability of ?0.2 ‰ (1sd) on a ?350 pg test portion mass. Total data acquisition time for such measurements is 80 s. We are currently in the process of developing a second moissanite RM based on a synthetic, coarse-grained powder. We will also investigate this new material for its ?30Si characteristics.
DS201707-1383
2017
Wiedendorfer, D., Schmidt, M.W., Mattsson B.A common origin of carbonatite magmas. Oldoinyo LengaiGeology, Vol. 45, 6, pp. 507-510.Africa, Tanzaniacarbonatite

Abstract: The more than 500 fossil Ca-carbonatite occurrences on Earth are at odds with the only active East African Rift carbonatite volcano, Oldoinyo Lengai (Tanzania), which produces Na-carbonatite magmas. The volcano’s recent major explosive eruptions yielded a mix of nephelinitic and carbonatite melts, supporting the hypothesis that carbonatites and spatially associated peralkaline silicate lavas are related through liquid immiscibility. Nevertheless, previous eruption temperatures of Na-carbonatites were 490–595 °C, which is 250–450 °C lower than for any suitable conjugate silicate liquid. This study demonstrates experimentally that moderately alkaline Ca-carbonatite melts evolve to Na-carbonatites through crystal fractionation. The thermal barrier of the synthetic Na-Ca-carbonate system, held to preclude an evolution from Ca-carbonatites to Na-carbonatites, vanishes in the natural system, where continuous fractionation of calcite + apatite leads to Na-carbonatites, as observed at Oldoinyo Lengai. Furthermore, saturating the Na-carbonatite with minerals present in possible conjugate nephelinites yields a parent carbonatite with total alkali contents of 8–9 wt%, i.e., concentrations that are realistic for immiscible separation from nephelinitic liquids at 1000–1050 °C. Modeling the liquid line of descent along the calcite surface requires a total fractionation of ?48% calcite, ?12% apatite, and ?2 wt% clinopyroxene. SiO2 solubility only increases from 0.2 to 2.9 wt% at 750–1200 °C, leaving little leeway for crystallization of silicates. The experimental results suggest a moderately alkaline parent to the Oldoinyo Lengai carbonatites and therefore a common origin for carbonatites related to alkaline magmatism.
DS201709-2072
2017
Wilson, D., Amos, R., Blowes, D., Langman, J., Smith, L., Sego, D.Diavik waste rock project: scale up of a reactive transport conceptual model for temperature and sulfide dependent geochemical evolution.Goldschmidt Conference, abstract 1p.Canada, Northwest Territoriesdeposit, Diavik
DS201709-2073
2017
Wilson, G., Kilius, L.R., Rucklidge, J.C., Zhao, X-L.Trace element analysis of mineral grains using accelerator mass spectrometry - from sampling to interpretation.Nuclear instruments and methods in Physics Research Section B , Vol. 123 ( 1-4) pp. 579-582.Technologyspectrometry

Abstract: A brief overview is provided of the uses of AMS in mineral analysis, emphasizing the selection of appropriate samples. Simple guidelines are given for judging the suitability of a set of samples (and the type of problem that they pose) for AMS, as opposed to other methods of in-situ analysis. Optimal interpretation of the AMS data requires that the method be employed in conjunction with a range of other types of information. These include textural and mineralogical observations obtained with petrographic or scanning electron microscopes, plus in-situ chemical data for areas of the target typically 1–250 ?m in diameter, obtained by some combination of complementary techniques, such as electron, proton or ion microprobe analysis (EPM, PIXE and SIMS, respectively).
DS201709-2074
2017
Wisznewska, J., et al.Central European carbonatites under cover: insights for mineral exploration from Tajno alkaline intrusions, NE Poland.Goldschmidt Conference, abstract 1p.Europe, Polandcarbonatite, Tajno

Abstract: The Carboniferous sub-platform Tajno alkaline-carbonatite intrusion is located within a narrow alkaline magmatic belt, which trends E–W from SW Lithuania to NE Poland, along the southern rim of the Mesoproterozoic A–type Mazury Complex. The Tajno pluto–volcanic massif comprises clinopyroxenite cumulates and syenites that are crosscut by carbonatite veins of variable thickness. An emplacement age for the carbonatite has been obtained based on zircon U–Pb and pyrrhotite Re–Os from albitites crosscut by the intrusion. Both ages cluster at 354–345Ma, which corresponds to the Tournaisian Epoch of the Early Carboniferous Period. The carbonatite is 5 to 20Ma younger than the Kola Province, Russian Federation [1]. The current Tajno pluto-volcanic massif lies under ~600m of a Meso–Cenozoic cover. Carbonatite igneous systems are formed by processes of partial melting in metasomatised lithospheric mantle, and are associated with mantle plumes. This implies that a specific geochemical footprint may be spread throughout the host rocks and overlying sedimentary cover by post–emplacement processes. This is of key importance for carbonatite mineral exploration under cover. The Tajno carbonatitic veins do not contain typical accessory minerals (e.g. pyrochlore, perovskite, zirconolite, baddeleyite) that are classically found in other carbonatites. Instead, REE-bearing minerals such as burbankite, parisite, synchysite and bastnaesite are common. This explains its low Nb content. By contrast, fluorite is abundant as cement in the carbonatite breccia.This new study of alkaline-carbonatite rock assemblages is focused on: (1) characterise Tajno's isotopic, REE and HFSE footprint based on petrographic and geochemical observations of apatite and titanite; and (2) increase the understanding of Tajno–type carbonatitic intrusions in the region, and determine if such intrusions can be detected under the sedimentary cover by geochemical techniques. [1] Demaiffe et al.,(2013) The Journal of Geology 12, (1), 91–104 Central European carbonatites under cover: insights for mineral exploration from the Tajno alkaline intrusions, NE Poland.
DS201702-0252
2017
Witze, A.Evidence falls into place for once and future supercontinents.Science News, Vol. 191, no. 1, p. 18-22.MantleSubduction
DS201710-2277
2017
Witze, A.Oldest traces of life on Earth may lurk in Canadian rocks. SaglekNature, Sept. 27 3p.Canada, Labradorgeochronology
DS201710-2278
2017
Wolfe, A.P., Reyes, A.V., Royer, D.L., Greenwood, D.R., Doria, G., Gagen, M.H., Siver, P.A., Westgate, J.A.Middle Eocene CO2 and climate reconstructed from the sediment fill of a subarctic kimberlite Maar.Geology , Vol. 45, 7, pp. 619-622.Canada, Northwest Territoriesdeposit - Giraffe

Abstract: Eocene paleoclimate reconstructions are rarely accompanied by parallel estimates of CO2 from the same locality, complicating assessment of the equilibrium climate response to elevated CO2. We reconstruct temperature, precipitation, and CO2 from latest middle Eocene (ca. 38 Ma) terrestrial sediments in the posteruptive sediment fill of the Giraffe kimberlite in subarctic Canada. Mutual climatic range and oxygen isotope analyses of botanical fossils reveal a humid-temperate forest ecosystem with mean annual temperatures (MATs) more than 17 °C warmer than present and mean annual precipitation ?4× present. Metasequoia stomatal indices and gas-exchange modeling produce median CO2 concentrations of ?630 and ?430 ppm, respectively, with a combined median estimate of ?490 ppm. Reconstructed MATs are more than 6 °C warmer than those produced by Eocene climate models forced at 560 ppm CO2. Estimates of regional climate sensitivity, expressed as ?MAT per CO2 doubling above preindustrial levels, converge on a value of ?13 °C, underscoring the capacity for exceptional polar amplification of warming and hydrological intensification under modest CO2 concentrations once both fast and slow feedbacks become expressed.
DS201708-1790
2017
Woodhead, J.Tracking continental scale modification of the Earth's mantle using zircon megacrysts.11th. International Kimberlite Conference, PosterMantlezircon

Abstract: Metasomatism, the chemical alteration of rocks by a variety of melts and fluids, has formed a key concept in studies of the Earth’s mantle for decades. Metasomatic effects are often inferred to be far-reaching and yet the evidence for their occurrence is usually based upon individual hand specimens or suites of rocks that display considerable heterogeneity. In rare cases, however, we are offered insights into larger-scale chemical modifications that occur in the mantle. Here we utilise the Lu–Hf systematics of zircon megacrysts erupted in kimberlite magmas to discern two temporally and compositionally discrete metasomatic events in the mantle beneath southern Africa, each having an influence extending over an area exceeding one million km2. These data provide unambiguous evidence for metasomatic processes operating at continental scales and seemingly unperturbed by the age and composition of the local lithospheric mantle. The most recent of these events may be associated with the major Jurassic-Karoo magmatism in southern Africa.
DS201708-1583
2017
Woodhead, J., Hergt, J., Guiliani, A., Phillips, D., Maas, R.Tracking continental style scale modification of the Earth's mantle using zircon megacrysts. KimberlitesGeochemical Perspectives Letters, Vol. 4, pp. 1-6.Africa, South Africa, Zimbabwemetasomatism, geochronology

Abstract: Metasomatism, the chemical alteration of rocks by a variety of melts and fluids, has formed a key concept in studies of the Earth’s mantle for decades. Metasomatic effects are often inferred to be far-reaching and yet the evidence for their occurrence is usually based upon individual hand specimens or suites of rocks that display considerable heterogeneity. In rare cases, however, we are offered insights into larger-scale chemical modifications that occur in the mantle. Here we utilise the Lu–Hf systematics of zircon megacrysts erupted in kimberlite magmas to discern two temporally and compositionally discrete metasomatic events in the mantle beneath southern Africa, each having an influence extending over an area exceeding one million km2. These data provide unambiguous evidence for metasomatic processes operating at continental scales and seemingly unperturbed by the age and composition of the local lithospheric mantle. The most recent of these events may be associated with the major Jurassic-Karoo magmatism in southern Africa.
DS201703-0440
2017
Wu, F-Y.,Mitchell, R.H., Li, Q-L., Zhang, C., Yang, Y-H.Emplacement age and isotopic composition of the Prairie Lake carbonatite complex, northwestern Ontario, Canada.Geological Magazine, Vol. 154, 2, pp. 217-236.Canada, OntarioCarbonatite

Abstract: Alkaline rock and carbonatite complexes, including the Prairie Lake complex (NW Ontario), are widely distributed in the Canadian region of the Midcontinent Rift in North America. It has been suggested that these complexes were emplaced during the main stage of rifting magmatism and are related to a mantle plume. The Prairie Lake complex is composed of carbonatite, ijolite and potassic nepheline syenite. Two samples of baddeleyite from the carbonatite yield U-Pb ages of 1157.2±2.3 and 1158.2±3.8 Ma, identical to the age of 1163.6±3.6 Ma obtained for baddeleyite from the ijolite. Apatite from the carbonatite yields the same U-Pb age of ~1160 Ma using TIMS, SIMS and laser ablation techniques. These ages indicate that the various rocks within the complex were synchronously emplaced at about 1160 Ma. The carbonatite, ijolite and syenite have identical Sr, Nd and Hf isotopic compositions with a 87Sr/86Sr ratio of ~0.70254, and positive ?Nd(t)1160 and ?Hf(t)1160 values of ~+3.5 and ~+4.6, respectively, indicating that the silicate and carbonatitic rocks are co-genetic and related by simple fractional crystallization from a magma derived from a weakly depleted mantle. These age determinations extend the period of magmatism in the Midcontinent Rift in the Lake Superior area to 1160 Ma, but do not indicate whether the magmatism is associated with passive continental rifting or the initial stages of plume-induced rifting.
DS201709-2075
2017
Wu, M., Du, X., Tse, J.S., Pan, Y.Viscosity of carbonate melts at high pressures and temperatures.Goldschmidt Conference, abstract 1p.Mantlecarbon

Abstract: Knowledge about the viscosity and other transport properties of CaCO3 melts at high pressures and temperatures relevant to the Earth’s mantle is critically important for understanding the deep carbon cycle [1,2]. We have conducted First-Principles Molecular Dynamics Calculations of CaCO3 melts up to 52.5 GPa and 3000 K to provide atomistic insights into the mechanisms of diffusion and viscosity. Our calculated viscosities of CaCO3 melts at low pressures are in good agreement with those from experiments. In particular, viscosity is almost constant at low pressures but increases linearly with pressure above 10 GPa. The ultralow viscosity of CaCO3 melts at low pressures [1] is readily attributed to the uncorrelated diffusion of Ca2+ and CO3 2- ions (Fig. 1). In contrast, the motions of the Ca2+ cations and CO3 2- anions at pressures >10 GPa become increasingly correlated (Fig. 1), leading to higher viscosities. Compared to water, the viscosity of CaCO3 melts is not anomalously low. Rather, the viscosity of water is anomalously high, because water molecules are strongly H-bonded and behave like polymers.
DS201710-2279
2017
Wu, W., Yang, J., Ma, C., Milushi, I., Lian, D., Tian, Y.Discovery and significance of diamonds and moissanites in chromitites within the Skenderbeu Massif of the Mirdita zone ophiolite, west Albania.Acta Geologica Sinica, Vol. 91, 3, pp. 882-897.Europe, Albaniamoissanites

Abstract: In recent years diamonds and other unusual minerals (carbides, nitrides, metal alloys and native elements) have been recovered from mantle peridotites and chromitites (both high-Cr chromitites and high-Al chromitites) from a number of ophiolites of different ages and tectonic settings. Here we report a similar assemblage of minerals from the Skenderbeu massif of the Mirdita zone ophiolite, west Albania. So far, more than 20 grains of microdiamonds and 30 grains of moissanites (SiC) have been separated from the podiform chromitite. The diamonds are mostly light yellow, transparent, euhedral crystals, 200-300 ?m across, with a range of morphologies; some are octahedral and cuboctahedron and others are elongate and irregular. Secondary electron images show that some grains have well-developed striations. All the diamond grains have been analyzed and yielded typical Raman spectra with a shift at ?1325 cm?1. The moissanite grains recovered from the Skenderbeu chromitites are mainly light blue to dark blue, but some are yellow to light yellow. All the analyzed grains have typical Raman spectra with shifts at 766 cm?1, 787 cm?1, and 967 cm?1. The energy spectrums of the moissanites confirm that the grains are composed entirely of silicon and carbon. This investigation expands the occurrence of diamonds and moissanites to Mesozoic ophiolites in the Neo-Tethys. Our new findings suggest that diamonds and moissanites are present, and probably ubiquitous in the oceanic mantle and can provide new perspectives and avenues for research on the origin of ophiolites and podiform chromitites.
DS201708-1791
2017
Wudrick, M.Age of the lithospheric mantle beneath the Karowe diamond mine.11th. International Kimberlite Conference, OralAfrica, BotswanaDeposit - Karowe
DS201707-1384
2017
Wyman, D.Do cratons preserve evidence of stagnant lid tectonics?Geoscience Frontiers, in press available 15p.Canada, Ontariomantle plumes

Abstract: Evidence for episodic crustal growth extending back to the Hadean has recently prompted a number of numerically based geodynamic models that incorporate cyclic changes from stagnant lid to mobile lid tectonics. A large part of the geologic record is missing for the times at which several of these cycles are inferred to have taken place. The cratons, however, are likely to retain important clues relating to similar cycles developed in the Mesoarchean and Neoarchean. Widespread acceptance of a form of plate tectonics by ?3.2 Ga is not at odds with the sporadic occurrence of stagnant lid tectonics after this time. The concept of scale as applied to cratons, mantle plumes and Neoarchean volcanic arcs are likely to provide important constraints on future models of Earth's geodynamic evolution. The Superior Province will provide some of the most concrete evidence in this regard given that its constituent blocks may have been locked into a stagnant lid relatively soon after their formation and then assembled in the next global plate tectonic interval. Perceived complexities associated with inferred mantle plume – volcanic arc associations in the Superior Province and other cratons may be related to an over estimation of plume size. A possible stagnant lid episode between ?2.9 Ga and ?2.8 Ga is identified by previously unexplained lapses in volcanism on cratons, including the Kaapvaal, Yilgarn and Superior Province cratons. If real, then mantle dynamics associated with this episode likely eliminated any contemporaneous mantle plume incubation sites, which has important implications for widespread plumes developed at ?2.7 Ga and favours a shallow mantle source in the transition zone. The Superior Province provides a uniquely preserved local proxy for this global event and could serve as the basis for detailed numerical models in the future.
DS201704-0653
2017
Xia, J., Qin, L., Shen, J., Carlson, R.W., Ionov, D.A., Mock, T.D.Chromium isotope heterogeneity in the mantle.Earth and Planetary Science Letters, Vol. 464, pp. 103-115.MantleGeochronology

Abstract: To better constrain the Cr isotopic composition of the silicate Earth and to investigate potential Cr isotopic fractionation during high temperature geological processes, we analyzed the Cr isotopic composition of different types of mantle xenoliths from diverse geologic settings: fertile to refractory off-craton spinel and garnet peridotites, pyroxenite veins, metasomatised spinel lherzolites and associated basalts from central Mongolia, spinel lherzolites and harzburgites from North China, as well as cratonic spinel and garnet peridotites from Siberia and southern Africa. The ?53CrNIST 979 values of the peridotites range from ?0.51±0.04‰?0.51±0.04‰ (2SD) to +0.75±0.05‰+0.75±0.05‰ (2SD). The results show a slight negative correlation between ?53Cr and Al2O3 and CaO contents for most mantle peridotites, which may imply Cr isotopic fractionation during partial melting of mantle peridotites. However, highly variable Cr isotopic compositions measured in Mongolian peridotites cannot be caused by partial melting alone. Instead, the wide range in Cr isotopic composition of these samples most likely reflects kinetic fractionation during melt percolation. Chemical diffusion during melt percolation resulted in light Cr isotopes preferably entering into the melt. Two spinel websterite veins from Mongolia have extremely light ?53Cr values of ?1.36±0.04‰?1.36±0.04‰ and ?0.77±0.06‰?0.77±0.06‰, respectively, which are the most negative Cr isotopic compositions yet reported for mantle-derived rocks. These two websterite veins may represent crystallization products from the isotopically light melt that may also metasomatize some peridotites in the area. The ?53Cr values of highly altered garnet peridotites from southern Africa vary from ?0.35±0.04‰?0.35±0.04‰ (2SD) to +0.12±0.04‰+0.12±0.04‰ (2SD) and increase with increasing LOI (Loss on Ignition), reflecting a shift of ?53Cr to more positive values by secondary alteration.
DS201702-0253
2016
Xie, Y., Hou, Z., Goldfarb, R.J., Guo, X., Wang, L.Rare earth element deposits in China.Reviews in Economic Geology, Vol. 18, pp. 115-136.ChinaREE deposits

Abstract: China is the world’s leading rare earth element (REE) producer and hosts a variety of deposit types. Carbonatite-related REE deposits, the most significant deposit type, include two giant deposits presently being mined in China, Bayan Obo and Maoniuping, the first and third largest deposits of this type in the world, respectively. The carbonatite-related deposits host the majority of China’s REE resource and are the primary supplier of the world’s light REE. The REE-bearing clay deposits, or ion adsorption-type deposits, are second in importance and are the main source in China for heavy REE resources. Other REE resources include those within monazite or xenotime placers, beach placers, alkaline granites, pegmatites, and hydrothermal veins, as well as some additional deposit types in which REE are recovered as by-products. Carbonatite-related REE deposits in China occur along craton margins, both in rifts (e.g., Bayan Obo) and in reactivated transpressional margins (e.g., Maoniuping). They comprise those along the northern, eastern, and southern margins of the North China block, and along the western margin of the Yangtze block. Major structural features along the craton margins provide first-order controls for REE-related Proterozoic to Cenozoic carbonatite alkaline complexes; these are emplaced in continental margin rifts or strike-slip faults. The ion adsorption-type REE deposits, mainly situated in the South China block, are genetically linked to the weathering of granite and, less commonly, volcanic rocks and lamprophyres. Indosinian (early Mesozoic) and Yanshanian (late Mesozoic) granites are the most important parent rocks for these REE deposits, although Caledonian (early Paleozoic) granites are also of local importance. The primary REE enrichment is hosted in various mineral phases in the igneous rocks and, during the weathering process, the REE are released and adsorbed by clay minerals in the weathering profile. Currently, these REE-rich clays are primarily mined from open-pit operations in southern China. The complex geologic evolution of China’s Precambrian blocks, particularly the long-term subduction of ocean crust below the North and South China blocks, enabled recycling of REE-rich pelagic sediments into mantle lithosphere. This resulted in the REE-enriched nature of the mantle below the Precambrian cratons, which were reactivated and thus essentially decratonized during various tectonic episodes throughout the Proterozoic and Phanerozoic. Deep fault zones within and along the edges of the blocks, including continental rifts and strike-slip faults, provided pathways for upwelling of mantle material.
DS201709-2076
2017
Xiong, F., Yang, J., Robinson, P.T., Dilek, Y., Milushi, I., Xu, X., Zhou, W., Zhang, Z., Rong, H.Diamonds discovered from high-Cr podiform chromitites from Bulqiza, eastern Mirdita ophiolite, Albania.Acta Geologica Sinica, Vol. 91, 2, pp. 455-468.Europe, Albaniadiamonds in chromitites

Abstract: Various combinations of diamond, moissanite, zircon, corundum, rutile and titanitehave been recovered from the Bulqiza chromitites. More than 10 grains of diamond have been recovered, most of which are pale yellow to reddish–orange to colorless. The grains are all 100–300 ?m in size and mostly anhedral, but with a range of morphologies including elongated, octahedral and subhedral varieties. Their identification was confirmed by a characteristic shift in the Raman spectra between 1325 cm?1 and 1333 cm?1, mostly at 1331.51 cm?1 or 1326.96 cm?1. This investigation extends the occurrence of diamond and moissanite to the Bulqiza chromitites in the Eastern Mirdita Ophiolite. Integration of the mineralogical, petrological and geochemical data of the Bulqiza chromitites suggests their multi–stage formation. Magnesiochromite grains and perhaps small bodies of chromitite formed at various depths in the upper mantle, and encapsulated the ultra–high pressure, highly reduced and crustal minerals. Some oceanic crustal slabs containing the magnesiochromite and their inclusion were later trapped in suprasubduction zones, where they were modified by tholeiitic and boninitic arc magmas, thus changing the magnesiochromite compositions and depositing chromitite ores in melt channels.
DS201710-2280
2017
Xiong, Q., Griffin, W.L., Huang, J-X., Gain, S.E.M., Toledo, V., Pearson, N.J., O'Reilly, S.Y.Super reduced assemblages in "ophiolitic" chromitites and peridotites: the view from Mount Carmel.European Journal of Mineralogy, Vol. 29, 4, pp. 557-570.Europe, Israelmineralogy

Abstract: Ultrahigh-pressure (UHP) materials (e.g., diamond, high-pressure polymorph of chromite) and super-reduced (SuR) phases (e.g., carbides, nitrides, silicides and native metals) have been identified in chromitites and peridotites of the Tibetan and Polar-Urals ophiolites. These unusual assemblages suggest previously unrecognized fluid- or melt-related processes in the Earth’s mantle. However, the origin of the SuR phases, and in particular their relationships with the UHP materials in the ophiolites, are still enigmatic. Studies of a recently recognized SuR mineral system from Cretaceous volcanics on Mt Carmel, Israel, suggest an alternative genesis for the ophiolitic SuR phases. The Mt Carmel SuR mineral system (associated with Ti-rich corundum xenocrysts) appears to reflect the local interaction of mantle-derived CH4 ± H2 fluids with basaltic magmas in the shallow lithosphere (depths of ?30-100 km). These interactions produced desilication of the magma, supersaturation in Al2O3 leading to rapid growth of corundum, and phase assemblages requiring local oxygen fugacity (fO2) gradually dropping to ?11 log units below the iron-wüstite (IW) buffer. The strong similarities between this system and the SuR phases and associated Ti-rich corundum in the Tibetan and Polar-Urals ophiolites suggest that the ophiolitic SuR suite probably formed by local influx of CH4 ± H2 fluids within previously subducted peridotites (and included chromitites) during their rapid exhumation from the deep upper mantle to lithospheric levels. In the final stages of their ascent, the recycled peridotites and chromitites were overprinted by a shallow magmatic system similar to that observed at Mt Carmel, producing most of the SuR phases and eventually preserving them within the Tibetan and Polar-Urals ophiolites.
DS201702-0254
2017
Xu, B., Griffin, W.L., Xiong, Q., Hou, Z-Q, O'Reilly, S.Y., Guo, Z., Pearson, N.J., Greau, Y., Yang, Z-M., Zheng, Y-C.Ultrapotassic rocks and xenoliths from South Tibet: contrasting styles of interaction between lithospheric mantle and asthenosphere during continental collision.Geology, Vol. 45, 1, pp. 51-54.China, TibetUPR - metasomatism

Abstract: Widespread Miocene (24-8 Ma) ultrapotassic rocks and their entrained xenoliths provide information on the composition, structure, and thermal state of the sub-continental lithospheric mantle in southern Tibet during the India-Asia continental collision. The ultrapotassic rocks along the Lhasa block delineate two distinct lithospheric domains with different histories of depletion and enrichment. The eastern ultrapotassic rocks (89°E-92°E) reveal a depleted, young, and fertile lithospheric mantle (87Sr/86Srt = 0.704-0.707 [t is eruption time]; Hf depleted-mantle model age [TDM] = 377-653 Ma). The western ultrapotassic rocks (79°E-89°E) and their peridotite xenoliths (81°E) reflect a refractory harzburgitic mantle refertilized by ancient metasomatism (lavas: 87Sr/86Srt = 0.714-0.734; peridotites: 87Sr/86Srt = 0.709-0.716). These data integrated with seismic tomography suggest that upwelling asthenosphere was diverted away from the deep continental root beneath the western Lhasa block, but rose to shallower depths beneath a thinner lithosphere in the eastern part. Heating of the lithospheric mantle by the rising asthenosphere ultimately generated the ultrapotassic rocks with regionally distinct geochemical signatures reflecting the different nature of the lithospheric mantle.
DS201705-0890
2017
Xu, C., Kynicky, J., Tao, R., Liu, X., Zhang, L., Pohanka, M., Song, W., Fei, Y.Recovery of an oxidized majorite inclusion from Earth's deep asthenosphere.Science Advances, Vol. 3, 4, e1601589MantleEclogite

Abstract: Minerals recovered from the deep mantle provide a rare glimpse into deep Earth processes. We report the first discovery of ferric iron-rich majoritic garnet found as inclusions in a host garnet within an eclogite xenolith originating in the deep mantle. The composition of the host garnet indicates an ultrahigh-pressure metamorphic origin, probably at a depth of ~200 km. More importantly, the ferric iron-rich majoritic garnet inclusions show a much deeper origin, at least at a depth of 380 km. The majoritic nature of the inclusions is confirmed by mineral chemistry, x-ray diffraction, and Raman spectroscopy, and their depth of origin is constrained by a new experimental calibration. The unique relationship between the majoritic inclusions and their host garnet has important implications for mantle dynamics within the deep asthenosphere. The high ferric iron content of the inclusions provides insights into the oxidation state of the deep upper mantle.
DS201708-1792
2017
Xu, J.Ilmenite as a recorder of the kimberlite history from mantle to surface: examples from Indian kimberlites.11th. International Kimberlite Conference, PosterIndiailmenite
DS201708-1793
2017
Xu, J.Magma mingling at the Menominee pipe, USA? Contributions from texture and chemistry.11th. International Kimberlite Conference, PosterUnited States, Michigandeposit - Menominee
DS201702-0255
2016
Yamato, P., Brun, J.P.Metamorphic record of catastrophic pressure drop in subduction zones.Nature Geoscience, Vol. 10, pp. 46-50.MantleSubduction

Abstract: When deeply buried in subduction zones, rocks undergo mineral transformations that record the increase of pressure and temperature. The fact that high-pressure metamorphic parageneses are found at the Earth’s surface proves that rock burial is followed by exhumation. Here we use analysis of available data sets from high-pressure metamorphic rocks worldwide to show that the peak pressure is proportional to the subsequent decompression occurring during the initial stage of retrogression. We propose, using a simple mechanical analysis, that this linear relationship can be explained by the transition from burial-related compression to extension at the onset of exhumation. This major switch in orientation and magnitude of principal tectonic stresses leads to a catastrophic pressure drop prior to actual rock ascent. Therefore, peak pressures are not necessarily, as commonly believed, directly dependent on the maximum burial depth, but can also reflect a change of tectonic regime. Our results, which are in agreement with natural data, have significant implications for rock rheology, subduction zone seismicity, and the magnitudes of tectonic pressures sustained by rocks. Current views of subduction dynamics could be reconsidered in that perspective.
DS201702-0256
2017
Yang, X., Lai, X., Pirajno, F., Liu, Y., Mingxing, L., Sun, W.Genesis of the Bayan Obo Fe_REE-Nb formation in Inner Mongolia, North Chin a craton: a perspective review.Precambrian Research, Vol. 288, pp. 39-71.ChinaDeposit - Bayan Obo

Abstract: The Bayan Obo deposit in Inner Mongolia, North China Craton (NCC) is the largest rare-earth element (REE) resource in the world. Due to the complex element and mineral compositions and the activity of several geological events, the ore-forming mechanism is still controversial. Previous models are reviewed here to provide information for further investigation on the Bayan Obo deposit. In this study, we summarize all different types of Fe-REE-Nb mineralization using field observations and microscope work, in which we recognize 9 types of Fe-REE-Nb ores in the Bayan Obo ore district. By compiling and re-evaluating a large number of published geochemical data, this paper provides solid evidence that the Bayan Obo deposit formed through interaction between sedimentary rocks and carbonatite magmatism. From the results of our review, it can be conjectured that the formation of iron ores was originated from sedimentation (Pt1), whereas the formation of REE mineralized dolomite might be related to interaction and reaction between the carbonatite magmas and/or associated fluids with sedimentary carbonate rocks, with the REE-bearing carbonatite magmas having undergone intense fractionation enrichment process. The C-O-S-Fe-Mg isotopes indicate that the REE-Nb mineralization was derived from metasomatism (fenitic alteration) of sedimentary carbonate. A new model is proposed for this unique REE-Nb mineralization, which is related to the subduction of Siberian Craton beneath the North China Craton since Early Paleozoic period. We interpret that the Bayan Obo Fe-REE-Nb ore deposits and their massive barren host, H8 dolomite, were generated as a result of interaction of fluids expelled from a subcontinental lithospheric mantle (SCLM)-derived carbonatite magma with sedimentary carbonates.
DS201702-0257
2017
Yin, Z., Jiang, C., Chen, M., Lu, F., Quanli, C.Inclusions of a-quartz, albite and olivine in a mantle diamond.Gondwana Research, in press available, 29p.ChinaDeposit - Shengli no. 1

Abstract: Mineral inclusions in diamonds have been used to track potential information on the Earth's deep mantle. Here we report results from a detailed study on the mineral inclusions in a ca. 0.28 ct diamond from the Shengli No. 1 kimberlite in Mengyin County, Shandong Province, eastern China. Our study reveals the presence of ?-quartz, albite and olivine in the diamond. At an inferred depth of ca. 165 km for the diamond crystallization, the inclusions of ?-quartz and albite suggest the possible involvement of deep subducted crustal material, traces of which were captured during the diamond growth and magma migration.
DS201709-2077
2017
Ying, Y., Chen, W., Lu, J., Jiang, S-Y., Yang, Y.In situ U-Th-Pb ages of the Miaoya carbonatite complex in the South Qinling orogenic belt, central China.Lithos, in press available, 57p.Chinacarbonatite - Miaoya

Abstract: The Miaoya carbonatite complex in the South Qinling orogenic belt hosts one of the largest rare earth element (REE)-Nb deposits in China that is composed of carbonatite and syenite. The emplacement age of the complex and the geochronological relationship between the carbonatite and syenite have long been debated. In this study, in situ U-Th-Pb ages have been obtained for the constituent minerals zircon, monazite and columbite from carbonatite and syenite of the Miaoya complex, together with their chemical and isotopic compositions. In situ trace element compositions for zircon from carbonatite and syenite are highly variable. The zircon displays slightly heavy REE (HREE)-enriched chondrite-normalized patterns with no Eu anomaly and various light REE (LREE) contents. In situ Th-Pb dating for zircon from the Miaoya complex by laser ablation ICP-MS yields ages of 442.6 ± 4.0 Ma (n = 53) for syenite and 426.5 ± 8.0 Ma (n = 23) for carbonatite. Monazite from carbonatite and syenite shows similar chondrite-normalized REE patterns and yields a consistent Th-Pb age of ~ 240 Ma. Based on petrographic and chemical composition, columbite from the carbonatite can be identified into two groups. The columbite dispersed within carbonatite is characterized by slightly LREE-enriched chondrite-normalized REE patterns, whereas columbite associated with apatite is characterized by LREE-depleted trends. Columbite has been further determined to have a weighted mean 206Pb/238U age of 232.8 ± 4.5 Ma (n = 9) using LA-ICP-MS. Detailed geochronological and chemical investigations suggest that there were two major episodes of magmatic/metasomatic activities in the formational history of the Miaoya carbonatite complex. The early alkaline magmatism emplaced in the Silurian was related to the opening of the Mianlue Ocean, whereas the late metasomatism or hydrothermal overprint occurred during the Triassic South Qinling orogeny. The latter serves as the major ore formation period for both REE (e.g., monazite) and Nb (e.g., columbite).
DS201708-1794
2017
Yi-Xiang, C.Tracing Mg-rich fluids by Mg-O isotopes at slab-mantle interface in continental subduction zones: insights from the Mg-metasomatic rocks in western and eastern11th. International Kimberlite Conference, PosterChinaSubduction, metasomatism

Abstract: Fluids are important for mass transfer at the slab–mantle interface in subduction zones. However, it is usually difficult to trace fluids from specific sources in a subducting slab, especially those derived from dehydration of serpentinite. Coesite-bearing whiteschist at Dora-Maira in the Western Alps is characterized by strong Mg enrichment relative to the country rocks, which requires infiltration of Mg-rich fluids into the supracrustal rock. In order to constrain the origin of such Mg-rich fluids, we have performed an integrated study of whole-rock Mg and O isotopes, zircon U–Pb ages and O isotopes for the whiteschist and related rocks. Zircons in the whiteschist show two groups of U–Pb ages at ?262 Ma and ?34 Ma, respectively, for relict and newly grown domains. The Permian U–Pb ages of relict magmatic domains are consistent with the protolith age of host metagranite, suggesting that their common protolith is the Permian granite. The Tertiary U–Pb ages occur in coesite-bearing metamorphic domains, consistent with the known age for ultrahigh-pressure metamorphism. The metamorphic domains have ?18O values of ‰5.8–6.8‰, whereas the relict magmatic domains have high ?18O values of ‰?10‰. Such high ?18O values are also characteristic of the metagranite, indicating that the whiteschist protolith underwent metasomatism by metamorphic fluids with low ?18O value of f ‰?2–4‰. The whiteschist mostly has whole-rock ?26Mg values of ?0.07 to 0.72‰, considerably higher than country-rock ?26Mg values of ?0.54 to ‰?0.11‰. Thus, the metamorphic fluids are not only rich in Mg but also heavy in Mg isotopes. They were probably derived from the breakdown of Mg-rich hydrous minerals such as talc and antigorite in serpentinite at the slab–mantle interface in the subduction channel. Therefore, the dehydration of mantle wedge serpentinite during the subduction and exhumation of continental crust can provide the Mg-rich fluids responsible for the metasomatism of crustal rocks at subarc depths.
DS201708-1584
2015
Yosizawa, K., Kennett, B.L.N.The lithosphere asthenosphere transition and radial anisotropy beneath the Australian continent.Geophysical Research Letters, Vol. 42, 10. pp. 3829-3846.Australiageophysics, seismic

Abstract: A new 3-D S wave speed model for the Australian region derived from multimode surface waves allows us to examine the nature of the lithosphere-asthenosphere transition (LAT) and its relation to radial anisotropy. In eastern Phanerozoic Australia the estimated depths of the LAT tie well with those from receiver functions. However, in the Archean and Proterozoic lithosphere in western and central Australia, the LAT derived from the surface wave model is generally much deeper than the discontinuities recognized from receiver functions and shows a smooth transition. There is significant radial anisotropy (SH?>?SV) in the upper lithosphere as well as in the LAT and the underlying asthenosphere. Strong anisotropy in the asthenosphere reflects the effects of present shear flow in the mantle beneath the continent. The lateral variation of lithospheric anisotropy correlates well with the suture zones between cratonic blocks, representing frozen anisotropy associated with the ancient tectonics of Australia.
DS201706-1111
2017
Yuryeva, O.P., Rakhmanova, M.I., Zedgenizov, D.A.Nature of type 1aB diamonds from the Mir kimberlite pipe (Yakutia): evidence from spectroscopic observation.Physics and Chemistry of Minerals, in press available 13p.Russia, Yakutiadeposit - Mir
DS201711-2536
2017
Yuryeva, O.P., Rakhmanova, M.I., Zedgenizov, D.A.Nature of type IaB diamonds from the Mir kimberlite pipe ( Yakutia): evidence from spectroscopic observation.Physics and Chemistry of Minerals, Vol. 44, 9, pp. 655-667.Russia, Yakutiadeposit - Mir

Abstract: In this study, the specific features of structural defects of type IaB diamonds from the Mir kimberlite pipe (Yakutian diamondiferous province) have been characterized using FTIR and photoluminescence spectroscopy. Mineral inclusions in these diamonds [olivine (Ol), orthopyroxene (OPx), chromite (Chr), sulphide (Sf)] correspond to associations of peridotite rocks at the base of the lithosphere. Nitrogen content in type IaB diamonds shows significant variations, suggesting different growth media and/or several growth stages. A specific feature of these diamonds is the absence or very small amount of platelets, which may be related to annealing during their long-term residence at the temperatures of the base of the lithosphere. All studied diamonds show the presence of hydrogen defects that are active in IR spectra with an intense line at 3107 cm?1, and additional weaker lines at 3085 and 3237 cm?1, which correlated with high nitrogen content. Type IaB diamonds are also characterized by the presence of nitrogen-nickel luminescence centres S2, S3 and 523.2 nm. This feature distinguishes them from superdeep diamonds with extreme nitrogen aggregation states, which clearly attest to different growth conditions and crystallization media of type IaB diamonds from the Mir kimberlite pipe.
DS201706-1112
2017
Zaitsev, A.N., Britvin, S.N., Kearsley, A., Wenzel, T., Kirk, C.Jorgkellerite, a new layered phosphate-carbonate mineral from Oldoinyo Lengai volcano, Gregory rift, northern Tanzania.Mineralogy and Petrology, Vol. 111, 3, pp. 373-381.Africa, Tanzaniamineralogy

Abstract: Jörgkellerite, ideally Na3Mn3+ 3(PO4)2(CO3)O2•5H2O, is a new layered phosphate-carbonate from the Oldoinyo Lengai volcano in the Gregory Rift (northern Tanzania). The mineral occurs as spherulites, up to 200 ?m in diameter, consisting of plates up to 10 ?m in thickness in shortite-calcite and calcite carbonatites. Jörgkellerite is brown with a vitreous lustre and has a perfect micaceous cleavage on {001}, Mohs hardness is 3. The calculated density is 2.56 g/cm3. Jörgkellerite is uniaxial (-), ? = 1.700(2), ? = 1.625(2) (Na light, 589 nm) with distinct pleochroism: O = dark brown, E = light brown. The empirical formula of the mineral (average of 10 electron microprobe analyses) is (Na2.46K0.28Ca0.08Sr0.04Ba0.02)?2.88(Mn3+ 2.39Fe3+ 0.56)?2.95((PO4)1.95(SiO4)0.05))?2.00(CO3)(O1.84(OH)0.16)?2.00•5H2O. The oxidation state of Mn has been determined by XANES. Jörgkellerite is trigonal, space group P-3, a = 11.201(2) Å, c = 10.969(2) Å, V = 1191.9(7) Å3 and Z = 3. The five strongest powder-diffraction lines [d in Å, (I/I o), (hkl)] are: 10.970 (100) (001), 5.597 (15) (002), 4.993 (8) (111), 2.796 (14) (220) and 2.724 (20) (004). The crystal structure is built up of the layers composed of disordered edge-sharing [MnO6] octahedra. Each fourth Mn site in octahedral layer is vacant that results in appearance of ordered system of hexagonal "holes" occupied by (CO3) groups. The overall composition of the layer can be expressed as [Mn3O8(CO3)]. These manganese-carbonate layers are linked in the third dimension by (PO4) tetrahedra and Na-polyhedra. The origin of jörgkellerite is related to low-temperature oxidative alteration of gregoryite-nyerereite carbonatites.
DS201706-1113
2017
Zaitsev, A.N., Zhitova, E.S., Spratt, J., Zolotarev, A.A., Krivovichev, S.V.Isolueshite, NaNb03, from the Kovdor carbonatite, Kola Peninsula, Russia: composition, crystal structure and possible formation scenarios.Neues Jahrbuch fur Mineralogie, Vol. 194, 2, pp. 165-173.Russia, Kola Peninsuladeposit - Kovdor

Abstract: Isolueshite, a cubic complex oxide with the formula NaNbO3, occurs as euhedral crystals 0.4 - 0.7 mm in size in calcite carbonatite, Kovdor ultrabasic-alkaline complex (Kola, Russia). Average composition of isolueshite, based on 40 analyses by wavelength-dispersive electron microprobe is (Na0.84Ca0.07Sr0.01La0.01Ce0.01)?0.95(Nb0.90Ti0.11)?1.01O3. Minor and trace elements are Ti (4.1- 6.8 wt.% TiO2), REEs (1.8 - 4.0 wt.% REE2O3), Ca (1.7- 3.3 wt.% CaO), Zr (0.1- 0.8 wt.% ZrO2), Sr (0.3 - 0.4 wt.% SrO), Th (0.1- 0.5 wt.% ThO2), Fe (0.1- 0.2 wt.% Fe2O3) and Ta (0.1 wt.% Ta2O5). The crystal structure of isolueshite was refined to an agreement index (R1) of 0.028 for 82 unique reflections with |F0| ? 4 ?(F). The mineral is cubic, Pm3-m, a = 3.9045(5) Å and V = 59.525(13) Å3. The diffraction pattern of the crystal contains only regular and strong Bragg reflections with no signs of diffuse scattering. There are two sites in the crystal structure: A is 12-coordinated (A-O = 2.556(3) Å) and located at the corners of the cubic primitive cell and B is situated in the center of the unit-cell and has an octahedral coordination. The crystal-chemical formula based on the structure refinement is (Na0.84(1)Ca0.16(1))(Nb0.88(1)Ti0.12(1))O3. We suggest that isolueshite is a quenched (kinetically favored) polymorph of lueshite that formed as a result of rapid crystallization due to the sudden drop in temperature and/or pressure.
DS201701-0039
2015
Zajac, I.S.John Jambor's contributions to the mineralogy of the Strange Lake peralkaline complex, Quebec-Labrador, Canada.The Canadian Mineralogist, Vol. 53, pp. 885-894.Canada, LabradorRare earths

Abstract: The Strange Lake peralkaline complex is one of the world's largest deposits of yttrium, heavy rare-earth elements, and zirconium. The Precambrian intrusive body of peralkaline granitic rocks in central Labrador is extensively mineralized but mineralogically complex. It is a pleasure to acknowledge John Jambor's important contributions to the understanding of the unusual and varied mineralization. He was first to identify and characterize the potentially economic minerals: gittinsite, widespread at Strange Lake but otherwise an uncommon zirconosilicate, and the unusual acid-soluble zircon, which are the main sources of Strange Lake zirconium. He also identified the previously unknown mineral gerenite-(Y), and provided better characterization of kainosite-(Y) and of the complex gadolinite-datolite species which, collectively, account for most of the yttrium and heavy rare-earths. In all, his identification and characterization of these minerals were invaluable to understanding of the peralkaline complex, particularly the late-stage alteration that affected it and generated its economically important minerals, making them amenable to effective metallurgical processes.
DS201705-0891
2017
Zartman, R.E., Kogarko, L.N.Lead isotopic evidence for interaction between plume and lower crust during emplacement of peralkine Lovozero rocks and related rare-metal deposits, East Fennoscandia, Kola Peninsula, Russia.Contributions to Mineralogy and Petrology, Vol. 172, 32p.Russia, Kola PeninsulaCarbonatite

Abstract: The Lovozero alkaline massif—an agpaitic nepheline syenite layered intrusion—is located in the central part of the Kola Peninsula, Russia, and belongs to the Kola ultramafic alkaline and carbonatitic province (KACP) of Devonian age. Associated loparite and eudialyte deposits, which contain immense resources of REE, Nb, Ta, and Zr, constitute a world class mineral district. Previous Sr, Nd, and Hf isotope investigations demonstrated that these rocks and mineral deposits were derived from a depleted mantle source. However, because the Sr, Nd, and Hf abundances in the Kola alkaline rocks are significantly elevated, their isotopic compositions were relatively insensitive to contamination by the underlying crustal rocks through which the intruding magmas passed. Pb occurring in relatively lower abundance in the KACP rocks, by contrast, would have been a more sensitive indicator of an acquired crustal component. Here, we investigate the lead isotopic signature of representative types of Lovozero rocks in order to further characterize their sources. The measured Pb isotopic composition was corrected using the determined U and Th concentrations to the age of the crystallization of the intrusion (376?±?28 Ma, based on a 206Pb/204Pb versus 238U/204Pb isochron and 373?±?9 Ma, from a 208Pb/204Pb versus 232Th/204Pb isochron). Unlike the previously investigated Sr, Nd, and Hf isotopes, the lead isotopic composition plot was well outside the FOZO field. The 206Pb/204Pb values fall within the depleted MORB field, with some rocks having lower 207Pb/204Pb but higher 208Pb/204Pb values. Together with other related carbonatites having both lower and higher 206Pb/204Pb values, the combined KACP rocks form an extended linear array defining either a?~2.5-Ga secondary isochron or a mixing line. The projection of this isotopic array toward the very unradiogenic composition of underlying 2.4-2.5-Ga basaltic rocks of the Matachewan superplume and associated Archean granulite facies country rock provides strong evidence that this old lower crust was the contaminant responsible for the deviation of the Lovozero rocks from a presumed original FOZO lead isotopic composition. Evaluating the presence of such a lower crustal component in the Lovozero rock samples suggests a 5-10% contamination by such rocks. Contamination by upper crustal rock is limited to only a negligible amount.
DS201708-1795
2017
Zdislav, S.Petrogenetic evidence and FTIR dat a constraints on the origin of diamonds in xenoliths from Yubileynaya and Komsomolskaya pipes, Yakutia.11th. International Kimberlite Conference, PosterRussiadeposit - Jubileynaya, Komsomolskaya
DS201708-1796
2017
Zdislav, S.Oxygen isotopes of garnets in Diamondiferous eclogites from the Udachnaya pipe, Yakutia: evidence for their origin.11th. International Kimberlite Conference, PosterRussiadeposit - Udachnaya
DS201701-0040
2017
Zhang, J., Liu, Y-S., Ling, W., Gao, S.Pressure dependent compatibility of iron in garnet: insights into the proigin of ferropicrite melt mantle, China.Geochimica et Cosmochimica Acta, Vol. 197, pp. 356-377.ChinaPicrite

Abstract: Iron-rich silicate melts in the Earth’s deep mantle have been seismologically and geochemically inferred in recent years. The origin of local enrichments in iron and low-velocity seismic anomalies that have been detected in dense mantle domains are critical to understanding the mantle’s evolution, which has been canonically explained by long-term chemical reactions between the Earth’s silicate mantle and its liquid iron outer core. However, the Pleistocene alkaline ferropicrites (?0.73 Ma) from Wudi, North China, show chemical and Sr-Nd-Os isotopic features that suggest derivation from the preferential melting of silica-deficient eclogite, a lithology of delaminated mafic lower continental crust that had stagnated at mid-upper mantle depths during the Mesozoic decratonization of the North China block. These rocks are characterized by substantial enrichment in iron (14.9-15.2 wt% Fe2O3), relative depletion in silica (40-41 wt% SiO2) and decoupled Y and heavy rare earth element (HREE) compositions. These ferropicrites have particularly higher Y/Yb ratios than the other Cenozoic basalts from North China. The pressure-dependent compatibility of Fe, Y and Yb in eclogitic garnet can adequately explain the Fe-enrichment and Y-HREE decoupling of the Wudi ferropicrites and indicates that the eclogites were melted at pressures of 5-8 GPa, as also constrained by previous high-P-T experiments. This melting depth ties together a seismically imaged high-velocity anomaly that extends from 150 km to 350 km in depth under the study area, which has been commonly interpreted as evidence for the stagnation of the missing, delaminated continental lithosphere. Our findings provide an alternative mechanism to produce an extremely iron-rich mantle reservoir in addition to core-mantle interaction. Iron-rich silicate melts that form by this process are likely to be denser than the ambient mantle peridotite (and therefore drive flow downward) and may play a more significant role in the deep-mantle geophysical and geochemical diversities than previously considered.
DS201704-0654
2016
Zhang, S., Pell, J.Conodonts and their colour alteration index values from carbonate xenoliths in four kimberlites on the Hall Peninsula, Baffin Island, Nunavut.Canada-Nunavut Geoscience Office, pp. 1-12.Canada, Nunavut, Baffin IslandDeposit - Chidliak
DS201708-1797
2017
Zhang, S-B.Oxidation of lithospheric mantle beneath Tanzania by melt reaction.11th. International Kimberlite Conference, PosterAfrica, Tanzaniamelting
DS201708-1585
2017
Zhang, S-H., Zhao, Y., Li, Q-L., Zhao-Chu, C., Zhen, Y.First identification of baddleleyite related/linked to contact metamorphism from carbonatites in the world's largest REE deposit, Bayan Obo in north Chin a craton.Lithos, Vol 284, pp. 654-665.Chinacarbonatite, Bayan Obo

Abstract: Baddeleyite has been recognized as a key mineral to determine the crystallization age of silica-undersaturated igneous rocks. Here we report a new occurrence of baddeleyite identified from REE-Nb-Th-rich carbonatite in the world's largest REE deposit, Bayan Obo, in the North China Craton (China). U-Th-Pb dating of three baddeleyite samples yields crystallization ages of 310–270 Ma with the best estimated crystallization age of ca. 280 Ma. These ages are significantly younger than the ca. 1300 Ma Bayan Obo carbonatites, but broadly coeval to nearby Permian granitoids intruding into the carbonatites. Hence, the Bayan Obo baddeleyite did not crystallize from the carbonatitic magma that led to the formation of the Bayan Obo carbonatites and related REE-Nb-Th deposit. Instead, it crystallized from hydrothermal fluids and/or a reaction involving zircon and dolomite during contact metamorphism related to the Permian granitoid emplacement. This is in agreement with the results of electron microprobe analysis that show humite inclusions in baddeleyite, since humite is a typical magnesian skarn mineral and occurs in close proximity to the intrusive contacts between carbonatites and granitoids. Our results show that baddeleyite can be used for dating hydrothermal and contact metamorphic processes.
DS201703-0441
2017
Zhang, S-H., Zhao, Y., Liu, Y.A precise zircon Th-Pb age of carbonatite sills from the world's largest Bayan Obo deposit: implications for timing and genesis of REE-Nb mineralization.Precambrian Research, Vol. 291, pp. 202-219.ChinaDeposit - Bayan Obo

Abstract: The Bayan Obo in the northern North China Craton (NCC) is the world’s largest light rare earth element (LREE) deposit and is hosted in carbonatite sills emplaced into sedimentary rocks of the Bayan Obo Group. However, the timing and genesis of the Bayan Obo deposit has been highly controversial for many decades. Here we report a precise zircon 208Pb/232Th age of 1301 ± 12 Ma (N = 47, mean square of weighted deviates [MSWD] = 2.2) for a REE-Nb-rich carbonatite sill from the Bayan Obo deposit. Zircon morphology, trace element compositions and mineral inclusions demonstrate that these zircons were crystallized from REE-Nb-rich carbonatitic magmas and their ages represent the timing of carbonatites and REE-Nb mineralization. The newly obtained age of ca. 1.30 Ga is consistent with field observations of the Bayan Obo REE-Nb deposit and successfully explains why the carbonatites and REE-Nb mineralization in the Bayan Obo deposit occurred mainly in the Jianshan Formation and that no carbonatites and REE-Nb mineralization were identified from the rocks overlying the Jianshan Formation. The new results demonstrate that the Bayan Obo REE-Nb deposit is a product of mantle-derived carbonatite magmatism at ca. 1.30 Ga. Field relations show that emplacement of the Bayan Obo carbonatites was accompanied by pre-magmatic uplift that is considered to be related to rift-to-drift transition. The Bayan Obo carbonatites and REE-Nb deposit are spatially and temporally linked with the newly identified 1.33-1.30 Ga Yanliao large igneous province (LIP) in the northern NCC and were related to continental rifting that have led to breakup of the NCC from the Columbia (Nuna) supercontinent.
DS201702-0258
2016
Zhimulev, E.I., Sonin, V.M., Afanasiev, V.P., Chepuov, A.I., Pokhilenko, N.P.Fe-S melt as a likely solvent of diamond under mantle conditions.Doklady Earth Sciences, Vol. 471, 2, pp. 1277-1279.MantleDiamond morphology

Abstract: The first results of experimental study of diamond dissolution in a S-bearing Fe melt at high P-T parameters are reported and the morphology of partially dissolved crystals is compared with that of natural diamonds. Our results show that under the experimental conditions (4 GPa, 1400°C), flat-faced octahedral diamond crystals are transformed into curve-faced octahedroids with morphological features similar to those of natural diamonds.
DS201705-0892
2017
Zhimulev, E.I., Sonin, V.M., Afanasiev, V.P., Chepurov, A.I., Pokhilenko, N.P.Fe-S melt as a likely solvent of diamond under mantle conditions.Doklady Earth Sciences, Vol. 471, 2, pp. 1277-1279.MantleDiamond morphology

Abstract: The first results of experimental study of diamond dissolution in a S-bearing Fe melt at high P-T parameters are reported and the morphology of partially dissolved crystals is compared with that of natural diamonds. Our results show that under the experimental conditions (4 GPa, 1400°C), flat-faced octahedral diamond crystals are transformed into curve-faced octahedroids with morphological features similar to those of natural diamonds.
DS201708-1586
2017
Zhou, Z-G., Wang, G-S., Di, Y-J., Gu, Y-C., Zhang, D., Zhu, W-P., Liu, C-F., Wu, C., Li, H-Y., Chen, L-Z.Discovery of Mesoproterozoic kimberlite from Dorbed Banner Inner Mongolia and its tectonic significance.Geological Journal, pp. 1-13.Asia, Mongoliadeposit - Longtou Shan

Abstract: Porphyritic olivine kimberlitic breccia, discovered in the Dörbed Banner of Inner Mongolia, Western China, is referred to as Longtou Shan Kimberlite in our study. This kimberlite occurs as a pipe in the Halahuogete Formation of Bayan Obo Group. Zircon U–Pb ages of Longtou Shan Kimberlite reveals a Mesoproterozoic age of ~1,552 Ma, constraining the deposition age of Halahuogete Formation to the Mesoproterozoic. Compared with Mesoproterozoic kimberlite of the ancient landmass, it can be inferred that the North China Craton is a member of the Ur ancient continent of the Columbia supercontinent. Furthermore, according to the tectonic background of the Bayan Obo Group, we raise this possibility that “Bayan Obo Aulacogen” should be renamed the “Bayan Obo Continental Rift.”
DS201711-2537
2017
Zhu, R., Zhang, H., Zhu, G., Meng, H., Fan, H., Yang, J., Wu, F., Zhang, Z.Craton destruction and related resources.International Journal of Earth Sciences, Vol. 106, 7, pp. 2233-2257.Chinacraton

Abstract: Craton destruction is a dynamic event that plays an important role in Earth’s evolution. Based on comprehensive observations of many studies on the North China Craton (NCC) and correlations with the evolution histories of other cratons around the world, craton destruction has be defined as a geological process that results in the total loss of craton stability due to changes in the physical and chemical properties of the involved craton. The mechanisms responsible for craton destruction would be as the follows: (1) oceanic plate subduction; (2) rollback and retreat of a subducting oceanic plate; (3) stagnation and dehydration of a subducting plate in the mantle transition zone; (4) melting of the mantle above the mantle transition zone caused by dehydration of a stagnant slab; (5) non-steady flow in the upper mantle induced by melting, and/or (6) changes in the nature of the lithospheric mantle and consequent craton destruction caused by non-steady flow. Oceanic plate subduction itself does not result in craton destruction. For the NCC, it is documented that westward subduction of the paleo-Pacific plate should have initiated at the transition from the Middle-to-Late Jurassic, and resulted in the change of tectonic regime of eastern China. We propose that subduction, rollback and retreat of oceanic plates and dehydration of stagnant slabs are the main dynamic factors responsible for both craton destruction and concentration of mineral deposits, such as gold, in the overriding continental plate. Based on global distribution of gold deposits, we suggest that convergent plate margins are the most important setting for large gold concentrations. Therefore, decratonic gold deposits appear to occur preferentially in regions with oceanic subduction and overlying continental lithospheric destruction/modification/growth.
DS201709-2078
2017
Zhu, R-N, Ni, P., Ding, J-Y., Wang, D-Z., Ju, Y., Kang, N.Petrography, chemical composition, and Raman spectra of chrome spinel: constraints on the diamond potential of the no. 30 pipe kimberlite in Wafandian, North Chin a Craton.Ore Geology Reviews, in press available, 40p.Chinadeposit - No. 30 Wafangdian

Abstract: Conventional diamond exploration seldom searches directly for diamonds in rock and soil samples. Instead, it focuses on the search for indicator minerals like chrome spinel, which can be used to evaluate diamond potential. Chrome spinels are preserved as pristine minerals in the early Paleozoic (?465 Ma), hydrothermally altered, Group I No. 30 pipe kimberlite that intruded the Neoproterozoic Qingbaikou strata in Wafangdian, North China Craton (NCC). The characteristics of the chrome spinels were investigated by petrographic observation (BSE imaging), quantitative chemical analysis (EPMA), and Raman spectral analysis. The results show that the chrome spinels are mostly sub-rounded with extremely few grains being subhedral, and these spinels are macrocrystic, more than 500 µm in size. The chrome spinels also have compositional zones: the cores are classified as magnesiochromite as they have distinctly chromium-rich (Cr2O3 up to 66.56 wt%) and titanium-poor (TiO2 < 1 wt%) compositions; and the rims are classified as magnetite as they have chromium-poor and iron-rich composition. In the cores of chrome spinels, compositional variations are controlled by Al3+-Cr3+ isomorphism, which results in a strong Raman spectra peak (A1g mode) varying from 690 cm?1 to 702.9 cm?1. In the rims of chrome spinel, compositional variations result in the A1g peak varying from 660 cm?1 to 672 cm?1. The morphology and chemical compositions indicate that the chrome spinels are mantle xenocrysts. The cores of the spinel are remnants of primary mantle xenocrysts that have been resorbed, and the rims were formed during kimberlite magmatism. The compositions of the cores are used to evaluate the diamond potential of this kimberlite through comparison with the compositions of chrome spinels from the Changmazhuang and No. 50 pipe kimberlites in the NCC. In MgO, Al2O3 and TiO2 versus Cr2O3 plots, the chrome spinels from the Changmazhuang and No. 50 pipe kimberlites are mostly located in the diamond stability field. However, only a small proportion of chrome spinels from No. 30 pipe kimberlite have same behavior, which indicates that the diamond potential of the former two kimberlites is greater than that of the No. 30 pipe kimberlite. This is also supported by compositional zones in the spinel grains: there is with an increase in Fe3+ in the rims, which suggests that the chrome spinels experienced highly oxidizing conditions. Oxidizing conditions may have been imparted by fluids/melts that have a great influence on diamond destruction. Here, we suggest that chrome spinel compositions can be a useful tool for identifying the target for diamond potential in the North China Craton.
DS201706-1114
2017
Zhu, Y-S., Yang, J-H., Sun- J-F., Wang, H.Zircon Hf-0 isotope evidence for recycled oceanic and continental crust in the sources of alkaline rocks.Geology, Vol. 45, 5, pp. 407-410.Mantlealkaline rocks
DS201708-1798
2017
Zhuk, V.Continuity of kimberley-type pyroclastic kimberlite phases within Renard 2 over 1,000 m depth - insights to the geological and emplacement model, Superior craton, Canada.11th. International Kimberlite Conference, OralCanada, QuebecDeposit - Renard 2
DS201706-1115
2017
Zi, J-W., Gregory, C.J., Rasmussen, B., Sheppard, S., Muhling, J.R.Using monazite geochronology to test the plume model for carbonatites: the example of Gifford Creek carbonatite complex, Australia.Chemical Geology, Vol. 463, pp. 50-60.Australiacarbonatite

Abstract: Carbonatites are carbonate-dominated igneous rocks derived by low-degree partial melting of metasomatized mantle, although the geodynamic processes responsible for their emplacement into the crust are disputed. Current models favor either reactivation of lithospheric structures in response to plate movements, or the impingement of mantle plumes. Geochronology provides a means of testing these models, but constraining the age of carbonatites and related metasomatic events is rarely straightforward. We use in situ U-Th-Pb analysis of monazite by SHRIMP to constrain the emplacement age and hydrothermal history of the rare earth element-bearing Gifford Creek Carbonatite Complex in Western Australia, which has been linked to plume magmatism at ca. 1075 Ma. Monazite in carbonatites and related metasomatic rocks (fenites) from the carbonatite complex dates the initial emplacement of the carbonatite at 1361 ± 10 Ma (n = 22, MSWD = 0.91). The complex was subjected to multiple stages of magmatic/hydrothermal overprinting from ca. 1300 Ma to 900 Ma during later regional tectonothermal events. Carbonatite emplacement at ca. 1360 Ma appears to be an isolated igneous event in the region, and occurred about 300 million years before intrusion of the ca. 1075 Ma Warakurna large igneous province, thus precluding a genetic connection. The Gifford Creek Carbonatite Complex occurs within a major crustal suture, and probably formed in response to reactivation of this suture during plate reorganization. Our study demonstrates the veracity of monazite geochronology in determining the magmatic and hydrothermal histories of a carbonatite complex, critical for evaluating competing geodynamic models for carbonatites. The approach involving in situ SHRIMP U-Th-Pb dating of monazite from a wide spectrum of rocks in a carbonatite complex is best suited to establishing the intrusive age and hydrothermal history of carbonatites.
DS201708-1587
2017
Zi, J-W., Gregory, C.J., Rasmussen, B., Sheppard, S., Muhling, J.R.Using monazite geochronology to test the plume model for carbonatites: the example of Gifford Creek carbonatite complex, Australia.Chemical Geology, Vol. 463, pp. 50-60.Australiacarbonatites, Gifford Creek

Abstract: Carbonatites are carbonate-dominated igneous rocks derived by low-degree partial melting of metasomatized mantle, although the geodynamic processes responsible for their emplacement into the crust are disputed. Current models favor either reactivation of lithospheric structures in response to plate movements, or the impingement of mantle plumes. Geochronology provides a means of testing these models, but constraining the age of carbonatites and related metasomatic events is rarely straightforward. We use in situ U-Th-Pb analysis of monazite by SHRIMP to constrain the emplacement age and hydrothermal history of the rare earth element-bearing Gifford Creek Carbonatite Complex in Western Australia, which has been linked to plume magmatism at ca. 1075 Ma. Monazite in carbonatites and related metasomatic rocks (fenites) from the carbonatite complex dates the initial emplacement of the carbonatite at 1361 ± 10 Ma (n = 22, MSWD = 0.91). The complex was subjected to multiple stages of magmatic/hydrothermal overprinting from ca. 1300 Ma to 900 Ma during later regional tectonothermal events. Carbonatite emplacement at ca. 1360 Ma appears to be an isolated igneous event in the region, and occurred about 300 million years before intrusion of the ca. 1075 Ma Warakurna large igneous province, thus precluding a genetic connection. The Gifford Creek Carbonatite Complex occurs within a major crustal suture, and probably formed in response to reactivation of this suture during plate reorganization. Our study demonstrates the veracity of monazite geochronology in determining the magmatic and hydrothermal histories of a carbonatite complex, critical for evaluating competing geodynamic models for carbonatites. The approach involving in situ SHRIMP U-Th-Pb dating of monazite from a wide spectrum of rocks in a carbonatite complex is best suited to establishing the intrusive age and hydrothermal history of carbonatites.
DS201712-2738
2017
Zimnisky, P. .Diamond market slows after strong recovery. A market update for the second half of 2017.Diamonds In Canada Magazine, Northern Miner, Nov. pp. 15-16.Globalmarkets
DS201703-0442
2017
Zubkov, V.I., Solomnikova, A.V., Post, J.E., Gaillou, E., Butler, J.E.Characterization of electronic properties of natural type 11b diamonds.Diamond and Related Materials, Vol. 72, pp. 87-93.TechnologyDiamonds - type 11b

Abstract: Precision admittance spectroscopy measurements were carried out over wide temperature and frequency ranges for a set of natural single crystal type IIb diamond samples. Peaks of conductance spectra vs. temperature and frequency were used to compute the Arrhenius plots, and activation energies were derived from these plots. The capacitance-voltage profiling was used to estimate the majority charge carrier concentration and its distribution into depth of the samples. Apparent activation energies between 315 and 325 meV and the capture cross section of about 10? 13 cm2 were found for samples with uncompensated boron concentrations in the range of 1 to 5 × 1016 cm? 3 (0.06-0.3 ppm). The obtained boron concentrations are in good coincidence with FTIR results for the samples. Also, a reason for the difference between the observed admittance activation energy and the previously reported ionization energy for the acceptor boron in diamond (0.37 eV) is proposed.
 
 

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