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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 B-Bq Br+ C D E F G-Gq Gr+ H I J K-Km Kn+ L M-Md Me+ N O P Q R S-Sg Sh+ T U V W X Y Z
Sheahan Diamond Literature Reference Compilation - Media/Corporate References by Name for all years
A B C D-Di Di+ 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
DS1712-2667
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.
DS1707-1298
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.
DS1708-1588
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.
DS1708-1589
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].
DS1707-1299
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.
DS1708-1563
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
DS1708-1564
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).
DS1709-1949
2017
Abritis, A., McCook, A.Cash bonuses for peer reviewed papers go global. Overview citing China 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.
DS1707-1300
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 d13CV-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.
DS1710-2209
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
DS1711-2497
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.
DS1701-0001
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
DS1708-1590
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.
DS1708-1591
2017
Agashev, A.Geochemistry of Mirny field kimberlites, Siberia.11th. International Kimberlite Conference, PosterRussia, Siberiadeposit - Mirny
DS1705-0806
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.
DS1712-2668
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.
DS1712-2669
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.
DS1704-0615
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.
DS1706-1061
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).
DS1706-1062
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.
DS1707-1301
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.
DS1709-1950
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.
DS1703-0396
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; 2s), 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.
DS1707-1302
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.
DS1704-0616
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.
DS1712-2670
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.
DS1705-0807
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.
DS1707-1303
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.
DS1712-2671
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
DS1701-0002
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 d26Mg and d56Fe of garnet peridotites from these two cratons. d26Mg of whole rocks varies from -0.243‰ to -0.204‰ with an average of -0.225 ± 0.037‰ (2s, n = 19), and d56Fe from -0.038‰ to 0.060‰ with an average of -0.003 ± 0.068‰ (2s, 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 d26Mg 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 d26Mg and d56Fe, 2s) 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 d26Mg and d56Fe 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 d26Mg and much lighter d56Fe, 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.
DS1702-0192
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 d26Mg and d56Fe of garnet peridotites from these two cratons. d26Mg of whole rocks varies from -0.243 to -0.204 with an average of -0.225 ± 0.037 (2s, n = 19), and d56Fe from -0.038‰ o 0.060 with an average of -0.003 ± 0.068 (2s, 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 d26Mg 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 d26Mg and d56Fe, 2s) 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 d26Mg and d56Fe 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 d26Mg and much lighter d56Fe, 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.
DS1704-0617
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 d26Mg and d56Fe of garnet peridotites from these two cratons. d26Mg of whole rocks varies from -0.243‰ to -0.204‰ with an average of -0.225 ± 0.037‰ (2s, n = 19), and d56Fe from -0.038‰ 0.060 with an average of -0.003 ± 0.068‰ (2s, 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 d26Mg 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 d26Mg and d56Fe, 2s) 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 d26Mg and d56Fe 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 d26Mg and much lighter d56Fe, 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.
DS1709-1951
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 d18O 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.
DS1707-1304
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.
DS1710-2210
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.
DS1711-2498
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
DS1711-2499
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.
DS1709-1952
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)]dTKTR(T,P=0)=KTR,0[V0V(T)]dT and K'TR(T,P=0)=K'TR,0[V(T)V0]d'KTR'(T,P=0)=KTR,0'[V(T)V0]d', 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 aV0 = 2.666(9) × 10-5 K-1, ?E=484(6)?E=484(6), dTdT = 5.77(8), and d'd' = -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.
DS1712-2672
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.
DS1712-2673
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.
DS1708-1592
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 (ß-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.
DS1704-0618
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.
DS1709-1953
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.
DS1709-1954
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 eHf(t) values that trend toward an evolved signature at c. 2500 Ma. The c. 2500 Ma population shows a wide range of eHf(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 eHf(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.
DS1708-1593
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
DS1710-2211
2017
Armstrong, J.P., Gababotse, J.Karowe diamond mine.11th International Kimberlite Field Trip Guide, Sept. 19p. PdfAfrica, Botswanadeposit - Karowe
DS1708-1594
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
DS1712-2674
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.
DS1705-0808
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.
DS1703-0397
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.
DS1711-2500
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.
DS1708-1595
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
DS1709-1955
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.
DS1710-2212
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 d18O 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 d18O 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 d18O 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.
DS1709-1956
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 d18O 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 d18O 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 d18O 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.
DS1709-1957
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+/SFe ratio and d18 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+/SFe 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+/SFe 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+/SFe, nor does garnet d18OVSMOW (5.14 to 6.21‰) point to significant seawater alteration. Median bulk-rock Fe3+/SFe 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.
DS1704-0619
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.
DS1704-0620
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.
DS1702-0193
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.
DS1708-1596
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
DS1708-1597
2017
Banas, A.Yellow and white diamonds from the Qilalugaq kimberlites: two generations of diamond growth.11th. International Kimberlite Conference, PosterCanada, Nunavutdeposit - Qilalugaq
DS1709-1958
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.
DS1708-1598
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.
DS1710-2213
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
DS1712-2675
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.
DS1707-1305
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.
DS1710-2214
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.
DS1709-1959
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.
DS1709-1960
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 d15N 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.
DS1708-1565
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.
DS1701-0003
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.
DS1702-0194
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.
DS1707-1306
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.
DS1711-2501
2015
Begg, G.C., Griffin, W.L., O'Reilly, S.Y., Natapov, L.Geoscience data 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.
DS1709-1961
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.
DS1707-1307
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 µ-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
DS1707-1308
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.
DS1705-0809
2017
Benaouda, R., Holzheid, A., Schenk, V., Badra, L., Ennaciri, A.Magmatic evolution of the Jbel Boho alkaline complex in the Bou Azzer inlier ( 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 SLREE = 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.
DS1708-1566
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.
DS1702-0195
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.
DS1708-1599
2017
Bezzola, M.The geology and evaluation of the Kelvin kimberlite pipe, NWT, Canada.11th. International Kimberlite Conference, PosterCanada, Northwest Territoriesdeposit - Kelvin
DS1706-1063
2017
Bianchini, G., Bodinier, J-L., Braga, R., Wilson, M.Crust-mantle and lithosphere-Asthenosphere boundaries.Geological Society of America, SPE 526, 200p.Mantlebook
DS1708-1567
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
DS1702-0196
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.
DS1708-1600
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
DS1708-1601
2017
Bobrov, A.V.Sodium-bearing phases in the transition zone and uppermost lower mantle: experimental and natural data.11th. International Kimberlite Conference, PosterMantlemineralogy
DS1710-2215
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 d18O 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 eHf-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.
DS1702-0197
2017
Boniface, N.Crystal chemistry of pyrochlore from the Mesozoic Panda 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.
DS1709-1962
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.
DS1705-0810
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.
DS1710-2216
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.-
DS1707-1309
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.
DS1708-1602
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
DS1710-2217
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.
DS1706-1064
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.
DS1708-1603
2017
Brett, C.Petrology of the White River diamondiferous Paleoproterozoic intrusive rocks.11th. International Kimberlite Conference, PosterCanada, Ontariodeposit - White River
DS1708-1604
2017
Brey, G.The birth, growth and ageing of the Kaapvaal subcratonic mantle.11th. International Kimberlite Conference, OralAfrica, Southern AfricaSubduction, metasomatism
DS1709-1963
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.
DS1707-1310
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.
DS1701-0004
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.
DS1709-1964
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.
DS1712-2676
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) data 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 (d18O + 3 to + 5‰VSMOW and d13C - 3.5 to - 3.2‰VPDB). In contrast, dolomite in the same samples has similar d13C values but much higher d18O, 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 d18O 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: d18O + 7.7 to + 10.3‰ and d13C -5.2 to -6.0‰; 87Sr/86Sr 0.70296-0.70298) is not directly linked with the REE mineralisation.
DS1711-2502
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.
DS1709-1965
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 µm 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 µm) 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.
DS1707-1311
2017
Buikin, A.I., Kogarko, L.N., Hopp, J., Trieloff, M.Light noble gas data 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.
DS1708-1605
2017
Bulanova, G.Natural diamond growth conditions recorded by their internal structure.11th. International Kimberlite Conference, PosterTechnologydiamond morphology
DS1705-0811
2017
Bullock, E.Diamonds in the Sky.lithographie.org, No. 19, pp. 128-131.TechnologyBook - meteorites
DS1705-0812
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.
DS1709-1966
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 d13C 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.
DS1709-1967
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.
DS1708-1606
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
DS1710-2218
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
DS1708-1607
2017
Burnham, A.The nitrogen budget of subducted crust.11th. International Kimberlite Conference, PosterMantlenitrogen
DS1706-1065
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.
DS1709-1968
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].
DS1708-1608
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
DS1708-1609
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.
DS1705-0813
2017
Butler, J.E., Feigelson, B.N.Laboratory-Grown Diamonds.lithographie.org, No. 19, pp. 114-127.TechnologyBook - synthetics
DS1712-2677
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 (d18O) 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 d18O may have resulted from fractionation of deep magma ocean phases, as has been proposed to explain lithophile and siderophile isotope compositions of Archaean komatiites.
DS1708-1610
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 -
DS1711-2503
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.
DS1702-0198
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.
DS1708-1657
2017
Campebll, D., Puumala, M., Eichenberg, D., Riemer, W., Wahl, R.Diamond field trip Marathon-White Ricer area. Guidebook, 15p. Pdf availableCanada, Ontarioguidebook
DS1711-2504
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.
DS1709-1969
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.
DS1705-0814
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.
DS1711-2505
2017
Carreras, I.M.Minerales "exoticos" en chromititas ofioliticas de Tehuitzingo ( Estado de Puebla, Mexico)Thesis, Universitat de Barcelona *** SPA, 77p. PdfMexicochromites
DS1709-1970
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.
DS1702-0199
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.
DS1708-1611
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
DS1708-1612
2017
Castillo Oliver, M.Metasomatism evolution of the SCLM beneath the Lunda Norte province ( NE Angola).11th. International Kimberlite Conference, PosterAfrica, Angolametasomatism
DS1711-2506
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.
DS1702-0200
2017
Cayer, E., Winterburn, P., Barrett, E.Direct detection of drift concealed kimberlites using surface geochemistry and landscape 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 (dCe, dEu) and hydrothermal overprint (dY) 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.
DS1710-2219
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
DS1710-2220
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.
DS1707-1312
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.
DS1707-1313
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.
DS1702-0201
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.
DS1702-0202
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.
DS1706-1066
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.
DS1705-0815
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
DS1705-0816
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.
DS1701-0005
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.
DS1702-0203
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 (<- 1%) at comparable depths. The P velocity increases from - 0.5% above 70 km depth to 1.5% at 330 km depth beneath southern Alberta, which provides compelling evidence for a deep, structurally complex Hearne craton. In comparison, the lithosphere is substantially thinner beneath the adjacent Buffalo Head Terrane (160 km) and Medicine Hat Block (200 km). These findings are consistent with earlier theories of tectonic assembly in this region, which featured distinct Archean and Proterozoic plate convergences between the Hearne craton and its neighboring domains. The highly variable, bimodally distributed craton thicknesses may also reflect different lithospheric destruction processes beneath the western margin of Laurentia.
DS1705-0817
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.
DS1705-0818
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
DS1705-0819
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 µm 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.
DS1705-0820
2017
Chapman, J.Argyle Diamonds.lithographie.org, No. 19, pp. 104-109.AustraliaBook - Argyle
DS1705-0821
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.
DS1709-1971
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.
DS1712-2678
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.
DS1708-1613
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
DS1712-2679
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.
DS1702-0204
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
DS1709-1972
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.
DS1707-1314
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.
DS1708-1614
2017
Chinn, I.Stable isotope data and Ftir analyses of diamonds from the Orapa mine: a clear subduction signature.11th. International Kimberlite Conference, OralAfrica, Botswanadeposit - Orapa
DS1707-1315
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.
DS1708-1615
2017
Choi, E.Mineralogy, geochemistry, and petrogenesis of Paleoproterozoic alkaline magmas in the Yilgarn Craton, western Australia.11th. International Kimberlite Conference, PosterAustraliaalkaline rocks
DS1709-1973
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 µm) and compositionally non titaniferous, and (b) large macrocrysts (>100 µm) having replacement cores having distinctly Ti-rich (TiO2 up to 28.51 wt %) compositions. Spinel is an abundant phase varying from <20 to >300 µm 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.
DS1710-2221
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.
DS1711-2507
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.
DS1702-0205
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
DS1705-0822
2017
Collins, A.T.Comment on the apparent anomalous reflectance of a Sumitomo synthetic diamond.Journal of Gemmology, Vol. 35, 5, p. 450.TechnologySynthetics
DS1703-0398
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?
DS1711-2508
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?
DS1701-0006
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.
DS1707-1316
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.
DS1709-1974
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.
DS1703-0399
2017
Cook, T.Fingerprinting the source of fore-arc fluids.EOS Transaction of AGU, https://doi.org/10.1029/2017EO067201MantleSubduction
DS1706-1067
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.
DS1701-0007
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.
DS1702-0206
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.
DS1704-0621
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.
DS1712-2680
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
DS1706-1068
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,…
DS1710-2222
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.
DS1712-2681
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.
DS1709-1975
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].
DS1708-1616
2017
Czas, J.Diamond brecciation and annealing accompanying major metasomatism in eclogite xenoliths from the Sask craton, Canada.11th. International Kimberlite Conference, OralCanada, Saskatchewanmetasomatism
DS1709-1976
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(a,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.
DS1708-1617
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
DS1707-1317
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.
DS1708-1568
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.
DS1710-2223
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
DS1708-1618
2017
Daniels, L.The magnitude of termites to the future of kimberlite exploration in Botswana.11th. International Kimberlite Conference, OralAfrica, Botswanatermites
DS1709-1977
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.
DS1708-1619
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
DS1708-1620
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.
DS1712-2682
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
DS1702-0207
2017
Davy, A.The Murowa kimberlites, Zimbabwe.PDAC 2017, March 6, 1p. AbstractAfrica, ZimbabweDeposit - Murowa
DS1708-1621
2017
Davy, A.The diamond size/frequency and size/quality distribution in the Argyle AK1 lamproite.11th. International Kimberlite Conference, OralAustraliadeposit - Argyle
DS1702-0208
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.
DS1708-1622
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
DS1708-1623
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
DS1702-0209
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 Catalao I Carbonatite complex in Brazil: new Sr-Nd and C-O isotopic data 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 d18O in carbonates. This is interpreted here as the result of the interaction of previously-formed dolomite carbonatites with carbo-hydrothermal fluids.
DS1711-2509
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.
DS1708-1624
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
DS1707-1318
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.
DS1702-0210
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.
DS1705-0823
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
DS1708-1625
2017
Delgaty, J.Ontario's newest kimberlite cluster - the Pagwachuan cluster.11th. International Kimberlite Conference, PosterCanada, Ontariodeposit - Pagawachuan
DS1712-2683
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.
DS1709-1978
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
DS1704-0622
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.
DS1710-2224
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.
DS1708-1626
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
DS1708-1627
2017
Diering, M.Generation of 3D kimberlite pipe models for resource classification and mine planning data sources, procedures and guidelines.11th. International Kimberlite Conference, OralTechnologymodels
DS1701-0008
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.
DS1709-1979
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.
DS1705-0824
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.
DS1708-1628
2017
Dongre, A.Ultramafic lamprophyre from the Wajrakarur kimberlite field of southern India and its petrogenetic significance.11th. International Kimberlite Conference, PosterIndiadeposit - Wajrakarur
DS1707-1319
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.
DS1709-1980
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.
DS1702-0211
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.
DS1708-1629
2017
Draper, J.C.M.Ilmenite generations in orangeite from Banankoro, Guinea: implications for exploration.11th. International Kimberlite Conference, PosterAfrica, Guineadeposit - Banankoro
DS1707-1320
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.
DS1701-0009
2016
Earth ExplorerMagnetic inversion results for Ngamiland 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.
DS1702-0212
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 µm, which increased to 3 µm after 1200 °C and 14 µm 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.
DS1708-1569
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.
DS1712-2684
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.
DS1703-0400
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
DS1704-0623
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.
DS1704-0624
1969
Egorov, L.S.Melilitic rocks of the Meimecha Kotui Province, Northern Siberia. ***IN RUSNedra Publishing House, Leningrad., 249p. *** in RUSRussiaMelilites
DS1709-1981
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.
DS1708-1630
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
DS1709-1982
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
DS1707-1321
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 (eSr1395 = - 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.
DS1702-0213
2017
Eppelbaum, L., Kutasov, I., Pilchin, A.Markers of thermal conditions within lithosphere. Lecture Notes in Earth Science Systems, Pt. 6.4, 51p. pdfMantleGeothermometry
DS1702-0214
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.
DS1703-0401
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.
DS1710-2225
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.
DS1708-1631
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
DS1709-1983
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.
DS1708-1632
2017
Farr, H.Melt evolution of the Finsch orangeite, South Africa.11th. International Kimberlite Conference, OralAfrica, South Africadeposit - Finsch
DS1708-1633
2017
Farr, H.Petrography and geochronology of the Nxau kimberlites, north-west Botswana.11th. International Kimberlite Conference, PosterAfrica, Botswanadeposit - Nxau
DS1711-2510
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
DS1708-1634
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.
DS1708-1635
2017
Fedortchouk, Y.Diamond surface features and metasomatic processes in subcratonic mantle.11th. International Kimberlite Conference, PosterMantlemetasomatism
DS1710-2226
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.
DS1707-1322
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.
DS1708-1636
2017
Fei, Y.Stability of Fe3+ bearing majorite in the Earth's mantle.11th. International Kimberlite Conference, OralMantlemajorite
DS1709-1984
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.
DS1703-0402
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.
DS1711-2511
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.
DS1705-0825
2017
Fershtater, G.B., Yudalevich, Z.A.Mantle metasomatism and magma formation in continental lithosphere: data on xenoliths in alkali basalts from the Makhtesh Ramon, Negrev Desert, Israel.Petrology, Vol. 25, 2, pp. 181-205.Asia, IsraelBasanites
DS1708-1637
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”).
DS1708-1638
2017
Fitzpayne, A.Multiple metasomatic events recorded in MARID xenoliths.11th. International Kimberlite Conference, PosterMantlemetasomatism
DS1708-1639
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
DS1701-0010
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.
DS1707-1323
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.
DS1712-2685
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.
DS1711-2512
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.
DS1709-1985
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.
DS1711-2513
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.
DS1708-1571
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.
DS1706-1069
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.
DS1701-0011
2016
Fschroeder-Frerkes, F., Woodland, A.B., Uenver-Thiele, I., Klimm, K., Knapp, N.Ca-Eskola incorporation 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.
DS1708-1640
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
DS1708-1641
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
DS1707-1324
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.
DS1705-0826
2017
Funk, M.T.Diamond Heists.lithographie.org, No. 19, pp. 132-137.GlobalBook - theft
DS1708-1642
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
DS1705-0827
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.
DS1708-1643
2017
Gainer, D.The geology of the Faraday 3 kimberlite, NWT, Canada.11th. International Kimberlite Conference, PosterCanada, Northwest Territoriesdeposit - Faraday 3
DS1710-2227
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.
DS1706-1070
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.
DS1701-0012
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.
DS1703-0403
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.
DS1707-1325
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.
DS1706-1071
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.
DS1708-1644
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
DS1708-1645
2017
Garanin, K.Zarya diamond deposit, Yakutian Province, Russia.11th. International Kimberlite Conference, PosterRussia, Yakutiadeposit - Zarya
DS1708-1646
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
DS1705-0828
2017
Garanin, V.K., Kriulina, G.Y.Diamonds in Russia. ( discoveries)lithographie.org, No. 19, pp. 94-103.RussiaBook - history
DS1703-0404
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
DS1708-1647
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.
DS1708-1648
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
DS1709-1986
2017
Gem notesDiamond with concentric inclusionsGems & Gemology, p. 228.Technologydiamond inclusions
DS1712-2700
2017
Gems & GemologyHigh quality diamond from Brazilian kimberlite. Lab notes - LipariGems & Gemology, Vol. 53, 3, p. 360.South America, Brazil, Bahiadeposit - Brauna
DS1705-0829
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.
DS1706-1072
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.
DS1708-1570
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.
DS1709-1987
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.
DS1709-1988
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
DS1707-1326
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.
DS1708-1649
2017
Gilika, O.Building a geometallurgical model for Orapa mine, Botswana.11th. International Kimberlite Conference, PosterAfrica, Botswanadeposit - Orapa
DS1705-0830
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 eNd(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.
DS1708-1650
2017
Giuliani, A.Olivine zoning and the evolution of kimberlite systems.11th. International Kimberlite Conference, OralGlobalolivine
DS1708-1651
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
DS1709-1989
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-µ (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.
DS1707-1327
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 d18O composition of the BK bulk carbonate fraction is above the mantle range, whereas the d13C 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 d18O 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.
DS1707-1328
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 d ¹³C of 2–3‰ occur across the contacts between distinct zones. Generally, d¹³C within the diamond cores varies only by 1–2‰, in rare cases up to 3.3‰. d¹³C 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 d¹³C across the diamond growth zones are sharp with no evidence of diffusive relaxation.
DS1712-2686
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 eNd(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.
DS1705-0831
2017
Glas, M.Diamond Studies.lithographie.org, No. 19, pp. 36-39.TechnologyBook - review
DS1709-1990
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.
DS1707-1329
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.
DS1704-0625
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
DS1704-0626
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
DS1707-1330
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.
DS1712-2687
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.
DS1710-2228
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.
DS1711-2514
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.
DS1706-1073
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.
DS1708-1652
2017
Goodarzi, P.Oxygen fugacity as a control on the distribution of diamond in the sub-cratonic lithospheric mantle.11th. International Kimberlite Conference, PosterMantleBlank
DS1709-1991
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
DS1709-1992
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 Ditrau 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.
DS1709-1993
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.
DS1706-1074
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.
DS1707-1331
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.
DS1706-1075
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.
DS1705-0832
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.
DS1708-1653
2017
Greaney, A.Chalcophile elements in the mantle.11th. International Kimberlite Conference, PosterMantlechalcophile
DS1710-2229
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.
DS1704-0627
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
DS1708-1654
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 35.7µg) 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 1013O 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 (d13C 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.
DS1708-1655
2017
Gress, M.Variation in diamond growth events recorded in Botswanan diamonds.11th. International Kimberlite Conference, PosterAfrica, Botswanadiamond morphology
DS1705-0833
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 35.7µg) 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 1013O 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 (d13C 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.
DS1708-1656
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
DS1708-1658
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
DS1708-1659
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
DS1708-1660
2017
Gu, T.1aB diamond and its geological implications.11th. International Kimberlite Conference, PosterAfrica, Botswanadeposit - Karowe
DS1709-1994
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; eNdi= -6.8 to -4.7; 176Hf/177Hf = 0.28248–0.28249; eHfi= -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 (d13C = -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.
DS1707-1332
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)S2.02(Nb1.68Ti0.29Zr0.02Sn0.01)S2.00O6.00(F0.92O0.08)S1.00 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.
DS1708-1661
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.
DS1708-1662
2017
Haggerty, S.Relation between micro- and macro-diamonds: myth, myopia or both?11th. International Kimberlite Conference, PosterTechnologymicrodiamonds
DS1701-0013
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.
DS1709-1995
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.
DS1711-2515
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?
DS1703-0405
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
DS1704-0628
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.
DS1708-1663
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
DS1706-1076
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.
DS1708-1664
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
DS1712-2688
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.
DS1706-1077
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
DS1708-1665
2017
Harte, B.Tracing lithsophere melt compositions using polymict peridotites11t