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Sheahan Diamond Literature Technical Reference Compilation 2019


The Sheahan Diamond Literature Reference Compilation
The Sheahan Diamond Literature Reference Compilation is compiled by Patricia Sheahan who publishes on a monthly basis a list of new scientific articles related to diamonds as well as media coverage and corporate announcementscalled the Sheahan Diamond Literature Service that is distributed as a free pdf to a list of followers. Pat has kindly agreed to allow her work to be made available as an online digital resource at Kaiser Research Online so that a broader community interested in diamonds and related geology can benefit. The references are for personal use information purposes only; when available a link is provided to an online location where the full article can be accessed or purchased directly. Reproduction of this compilation in part or in whole without permission from the Sheahan Diamond Literature Service is strictly prohibited. Return to Diamond Resource Center
Sheahan Diamond Literature Reference Compilation - Scientific Articles by Author for all years
A-An Ao+ B-Bd Be-Bk Bl-Bq Br+ C-Cg Ch-Ck Cl+ D-Dd De-Dn Do+ E F-Fn Fo+ G-Gh Gi-Gq Gr+ H-Hd He-Hn Ho+ I J K-Kg Kh-Kn Ko-Kq Kr+ L-Lh
Li+ M-Maq Mar-Mc Md-Mn Mo+ N O P-Pd Pe-Pn Po+ Q R-Rh Ri-Rn Ro+ S-Sd Se-Sh Si-Sm Sn-Ss St+ T-Th Ti+ U V W-Wg Wh+ X Y Z
Sheahan Diamond Literature Reference Compilation - Media/Corporate References by Name for all years
A B C D-Diam Diamonds Diamr+ E F G H I J K L M N O P Q R S T U V W X Y Z
Tips for Users
Posted/Published Reference CodesThe SDLRC provides 3 types of references identified in the reference code. DS for scientific article, DM for a media article, and DC for a corporate announcement. Consider DS0512-0001. The DS stands for "diamond scientific". 05 stands for 2005, the year the reference was posted. 12 represents the month the reference was posted. For all years prior to 2015 the default month is 12. -0001 is the reference's identifier and it does not mean anything. The number below the refence code, ie 2015, is the year the article was published. Note that the posted year may sometimes be later than the published year.
Sort OrderReferences are sorted by the "author" name and when the reference was posted to the compilation.
Most RecentIf the reference code is highlighted yellow, the reference was made available through the most recent monthly compilation of new literature. Use this to check out new references. When new references are posted, we make it our priority to track down an online link and obtain an abstract. With regard to older references, tracking down an abstract and an online link is a work in progress.
Link to external location of article: If the title has a link, it means we have found a location online where you can either retrieve the full article free, or purchase access to it. The Sheahan Diamond Literature Service is not a technical article procurement service; if you want a restricted article, you must deal directly with the vendor who controls the copyright to the article.
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Monthly Sheahan Diamond Newsletters for 2019
January 2019 May 2019 September 2019
February 2019 June 2019 October 2019
March 2019 July 2019 November 2019
April 2019 August 2019 December 2019
2019 Technical Reference Compilation
Posted/
Published
AuthorTitleSourceRegionKeywords
DS201902-0254
2019
Abersteiner, A., Kamenetsky, V.S., Goemann, K., Giuliani, A., Howarth, G.H., Castillo-Oliver, M., Thompson, J., Kamenetsky, M., Cherry, A.Composition and emplacement of the Benfontein kimberlite sill complex ( Kimberley, South Africa): textural, petrographic and melt inclusion constraints.Lithos, Vol. 324-325, pp. 297-314.Africa, South Africadeposit - Benfontein

Abstract: The Benfontein kimberlite is a renowned example of a sill complex and provides an excellent opportunity to examine the emplacement and evolution of intrusive kimberlite magmas. We have undertaken a detailed petrographic and melt inclusion study of the Benfontein Upper, Middle and Lower sills. These sills range in thickness from 0.25 to 5?m. New perovskite and baddeleyite U/Pb dating produced ages of 85.7?±?4.4?Ma and 86.5?±?2.6?Ma, respectively, which are consistent with previous age determinations and indicate emplacement coeval with other kimberlites of the Kimberley cluster. The Benfontein sills are characterised by large variations in texture (e.g., layering) and mineral modal abundance between different sill levels and within individual samples. The Lower Sill is characterised by carbonate-rich diapirs, which intrude into oxide-rich layers from underlying carbonate-rich levels. The general paucity of xenogenic mantle material in the Benfontein sills is attributed to its separation from the host magma during flow differentiation during lateral spreading. The low viscosity is likely responsible for non-explosive emplacement of the Benfontein sills, while the rhythmic layering is attributed to multiple magma injections. The Benfontein sills are marked by the excellent preservation of olivine and groundmass mineralogy, which is composed of monticellite, spinel, perovskite, baddeleyite, ilmenite, apatite, calcite, dolomite along with secondary serpentine and glagolevite [NaMg6[Si3AlO10](OH,O)8•H2O]. This is the first time glagolevite is reported in kimberlites. Groundmass spinel exhibits atoll-textures and is composed of a magnesian ulvöspinel - magnetite (MUM) or chromite core, surrounded by occasional pleonaste and a rim of Mg-Al-magnetite. We suggest that pleonaste crystallised as a magmatic phase, but was resorbed back into the residual host melt and/or removed by alteration. Analyses of secondary inclusions in olivine and primary inclusions in monticellite, spinel, perovskite, apatite and interstitial calcite are largely composed of Ca-Mg carbonates and, to a lesser extent, alkali-carbonates and other phases. These inclusions probably represent the entrapment of variably differentiated parental kimberlite melts, which became progressively more enriched in carbonate, alkalis, halogens and sulphur during crystal fractionation. Carbonate-rich diapirs from the Lower Sill contain more exotic phase assemblages (e.g., Ba-Fe titanate, barite, ancylite, pyrochlore), which probably result from the extreme differentiation of residual kimberlite melts followed by physical separation and isolation from the parental carbonate-rich magma. It is likely that any alkali or halogen rich minerals crystallising in the groundmass were removed from the groundmass during syn-/post-magmatic alteration, or in the case of Na, remobilised to form secondary glagolevite. The Benfontein sill complex therefore provides a unique example of how the composition of kimberlites may be modified after magma emplacement in the upper crust.
DS201905-1014
2019
Abersteiner, A., Kamenetsky, V.S., Goemann, K., Golovin, A.V., Gornova, M.A.Polymineralic inclusions in kimberlite hosted megacrysts: implications for kimberlite melt evolution.Lithos, doi.101016/j.lithos .2019.04.004 42p.Canada, Northwest Territories, Russiadeposit - Diavik, Jericho, Leslie, Udachnaya East

Abstract: Megacrysts are large (cm to >20?cm in size) mantle-derived crystals, which are commonly entrained by kimberlite magmas, comprising of olivine, orthopyroxene, clinopyroxene, phlogopite, garnet, ilmenite and zircon as common phases. Numerous studies have shown megacrysts to contain polymineralic inclusions, which have been interpreted to represent entrapped kimberlite melt. To constrain the origin of these inclusions in megacrysts and their relationship to kimberlite magmatism, we present a detailed petrographic and geochemical study of clinopyroxene and olivine megacrysts and their hosted inclusions from the Diavik, Jericho, Leslie (Slave Craton, Canada) and Udachnaya-East (Siberian Craton, Russia) kimberlites. The studied megacrysts are between 1 and 3?cm in size and representative of both the Cr-rich and Cr-poor suites. Megacrysts contain two types of inclusions: i. Large (<0.5-5?mm in size) round-to-irregular shaped polymineralic inclusions, which are composed of minerals similar to the host kimberlite groundmass, and consist of olivine, calcite, spinel, perovskite, phlogopite and apatite (± serpentine, alkali-carbonates, alkali-chlorides, barite). ii. Swarms/trails of ‘micro melt inclusions’ (MMI; <1-5?µm in size), which surround polymineralic inclusions, veins and fractures, thereby forming a ‘spongy’ texture. MMIs generally contain multiphase assemblages similar to polymineralic inclusions as well as various additional phases, such as alkali-carbonates or alkali-chlorides, which are typically absent in polymineralic inclusions and the surrounding kimberlite groundmass. Textural and geochemical evidence suggests that polymineralic inclusions in megacrysts crystallised from kimberlite melt, which infiltrated along fracture/vein networks. The polymineralic inclusion assemblages resulted from disequilibria reactions between the host megacryst and infiltrating kimberlite melt, which was likely enhanced by rapidly changing conditions during magmatic ascent. The connectivity of polymineralic inclusions to the kimberlite groundmass via network veins/fractures suggests that they are susceptible to infiltrating post-emplacement fluids. Therefore, the vast majority of polymineralic inclusions are unlikely to represent ‘pristine’ entrapped kimberlite melt. In contrast, MMIs are isolated within megacrysts (i.e. not connected to fractures/veins and therefore shielded from post-magmatic fluids) and probably represent entrapped remnants of the variably differentiated kimberlite melt, which was more enriched in alkalis-Cl-S-CO2 than serpentinised polymineralic inclusions and the host rocks exposed at Earth's surface as kimberlites.
DS201902-0255
2019
Abersteiner, A., Kamenetsky, V.S., Goemann, K., Golovin, A.V., Sharygin, I.S., Giuliani, A., Rodemann, T., Spetsius, Z.V., Kamenetsky, M.Djerfisherite in kimberlites and their xenoliths: implications for kimberlite melt evolution.Contributions to Mineralogy and Petrology, Vol. 174, 8 22p. Africa, South Africa, Russia, Canada, Northwest Territoriesdeposit - Bultfontein, Roberts Victor, Udachnaya-East, Obnazhennaya, Vtorogodnitsa, Koala, Leslie

Abstract: Djerfisherite (K6(Fe,Ni,Cu)25S26Cl) occurs as an accessory phase in the groundmass of many kimberlites, kimberlite-hosted mantle xenoliths, and as a daughter inclusion phase in diamonds and kimberlitic minerals. Djerfisherite typically occurs as replacement of pre-existing Fe-Ni-Cu sulphides (i.e. pyrrhotite, pentlandite and chalcopyrite), but can also occur as individual grains, or as poikilitic phase in the groundmass of kimberlites. In this study, we present new constraints on the origin and genesis of djerfisherite in kimberlites and their entrained xenoliths. Djerfisherite has extremely heterogeneous compositions in terms of Fe, Ni and Cu ratios. However, there appears to be no distinct compositional range of djerfisherite indicative of a particular setting (i.e. kimberlites, xenoliths or diamonds), rather this compositional diversity reflects the composition of the host kimberlite melt and/or interacting metasomatic medium. In addition, djerfisherite may contain K and Cl contents less than the ideal formula unit. Raman spectroscopy and electron backscatter diffraction (EBSD) revealed that these K-Cl poor sulphides still maintain the same djerfisherite crystal structure. Two potential mechanisms for djerfisherite formation are considered: (1) replacement of pre-existing Fe-Ni-Cu sulphides by djerfisherite, which is attributed to precursor sulphides reacting with metasomatic K-Cl bearing melts/fluids in the mantle or the transporting kimberlite melt; (2) direct crystallisation of djerfisherite from the kimberlite melt in groundmass or due to kimberlite melt infiltration into xenoliths. The occurrence of djerfisherite in kimberlites and its mantle cargo from localities worldwide provides strong evidence that the metasomatising/infiltrating kimberlite melt/fluid was enriched in K and Cl. We suggest that kimberlites originated from melts that were more enriched in alkalis and halogens relative to their whole-rock compositions.
DS201910-2240
2019
Abeykoon, S., Frost, D.J., Laurenz, V., Miyajima, N.A new geothermometer based on the oxygen content of sulphide inclusions in diamonds.Goldschmidt2019, 1p. AbstractMantlegeothermometry

Abstract: Sulphides are the most common type of inclusions found in diamonds and are widely used to determine the timing and lithology of diamond formation. Typical inclusions are monosulfide solid solutions (MSS) in the Fe-Ni-S system with minor amounts of Cu, Co and Mo. Previous experimental studies show that oxygen partitions into sulphide melts but most importantly measurements of natural sulphide inclusions indeed show measureable oxygen concentrations. If the parameters that control sulphide oxygen concentration can be determined then they could be potentially used to understand formation conditions of diamonds. We performed a series of high pressure (3-11 GPa) and high temperature (1573-1973 K) experiments in order to parameterize the oxygen content in sulphides in equilibrium with a mantle peridotite assemblage relevant to diamond formation. Multi-anvil experiments were carried out in graphite capsules and a peridotite silicate composition was equilibrated with molten FeS for at least 5 hrs. Run products that contained mantle silicate minerals and quenched sulphide melts were analysed using the electron microprobe. In some cases Ir was added in sufficient quantities to saturate the sulphides and form an Fe-Ir alloy from which the oxygen fugacity could be accurately determined. We measured up to 16 weight % of FeO in our experimental sulphide melts at mantle conditions. Moreover, the content of oxygen in the sulphide is found to be not controlled by fO2 or fS2, which is in disagreement with previous experimental studies conducted at ambient pressure conditions. The experiments indicate that the oxygen concentration is mainly controlled by the FeO activity in coexisting silicate phases and the temperature. In order to fit the data and to account for the observed FeO dependence, we developed a thermodynamic model using an end-member equilibrium between olivine, pyroxene and FeO in the sulphide melt. Using this relationship with measurements of oxygen in natural sulphide inclusions in diamonds reveals temperatures for lithospheric diamond formation in the range of 1140 – 1410 ºC.
DS201910-2241
2019
Ackerman, L., Polak, L., Magna, T., Rapprich, V., Jana, D., Upadhyay, D.Highly siderophile element geochemistry and Re-Os isotopic systematics of carbonatites: insights from Tamil Nadu, India.Earth and Planetary Science letters, Vol. 520, pp. 175-187.Indiacarbonatites

Abstract: Carbonatite metasomatism has been widely implicated for worldwide mafic mantle suites but so far, no combined data have been available for highly siderophile element systematics (HSE - Os, Ir, Ru, Pt, Pd, Re) and Re-Os isotopic compositions in carbonatites themselves. We present the first systematic survey of the HSE and Re-Os isotopic compositions in a suite of well-characterized Neoproterozoic carbonatites, silicocarbonatites and associated silicate rocks (pyroxenites, monzogabbros, syenites) from south India in order to place constraints on the HSE systematics in carbonatite magmas, anchoring possible mantle sources of carbonatites and relationship to the ambient crustal lithologies as well as preliminary constraints on carbonatite metasomatism in Earth's mantle. The most plausible explanation for generally low HSE contents in calciocarbonatites from Tamil Nadu (?HSE < 1.22 ppb) involves a low-degree (<1%) partial melting of the mantle source producing sulfur-saturated carbonatitic magmas leaving behind sulfide phases retaining HSE. The new data also indicate a strong FeO control on the distribution of Os and Pt during segregation of carbonatite melt from its enriched mantle source and/or melt differentiation. The combined 187Re/188Os values (from 0.10 to 217), 187Os/188Os ratios (0.186-10.4) and initial ?Os values back-calculated to 800 Ma (from +0.1 to +6052) predict that most Tamil Nadu calciocarbonatites were plausibly derived from a carbonated peridotite source with <10% recycled component. This model would thus provide significant constraints on the origin/source of carbonatites, irrespective of their post-emplacement history. The unusual, volumetrically rare, Mg-Cr-rich silicocarbonatites (?HSE = 14-41 ppb) display almost identical HSE patterns with those of host pyroxenites and predominantly high Pt (up to 38 ppb), the origin of which remains unknown. Positive co-variations between Pt, Pd and Re, and the well-developed positive correlation between Pt and MgO in these Mg-Cr-rich silicocarbonatites argue for a source coming predominantly from the upper mantle. The Re-Os isotopic systematics agree with direct incorporation of enriched mantle-derived material into parental melts but variable incorporation of potassium-rich crustal materials is evidenced by highly positive ?Os800 Ma values for a sub-suite of Mg-Cr-rich silicocarbonatites, indicating intense fenitization. The highly radiogenic Os isotopic compositions of monzogabbros and a syenite argue for their derivation from crustal lithologies with no or only negligible contribution of mantle material. Collectively, low Ir, Ru, Pt and Pd contents found in the Tamil Nadu carbonatites appear to indicate the incapability to significantly modify the total budget of these elements in the Earth's mantle during carbonatite metasomatism. In contrast, very high Re/Os ratios found in some of the analyzed carbonatites, paralleled by extremely radiogenic 187Os/188Os signature, can produce large modification of the Re-Os isotopic composition of mantle peridotites during carbonatite melt percolation when high melt/rock ratios are achieved.
DS201910-2242
2019
Afanasiev, V.P., Nikolenko, E.I., Glushkova, N.V., Zolnikov, I.D.The new Massadou diamondiferous kimberlite field in Guinea.Geology of Ore Deposits, Vol. 61, 4, pp. 92-100.Africa, Guineadeposit - Massadou

Abstract: A new Massadou kimberlite field, was discovered in southeastern Guinea, near the town of Macenta. It consists of 16 poorly diamondiferous kimberlite dikes, ~1 m thick on average. The ore-controlling zone has a width of around 600 m, its orientation corresponds to the K-4 trend after S. Haggerty, and it is quite well detectable in satellite images. A thick laterite weathering profile has developed on the kimberlites. The main indicator minerals are pyrope, chromite, and ilmenite. Ilmenite grains have a zoned structure with a high-Fe core (hemoilmenite) overgrown by a parallel-columnar aggregate of Mg-ilmente rim resulting from interaction of the core phase with kimberlitic melt. The age of kimberlites is estimated as 140-145 Ma by analogy with those in adjacent areas. Dikes occur as an independent form of kimberlite magmatism in the Guinean-Liberian shield, rather than being roots of kimberlite pipes; therefore, the erosion cutout is relatively small and large-scale diamond placers should not be expected.
DS201909-2014
2019
Agashev, A.M.Geochemistry of garnet megacrysts from the Mir kimberlite pipe ( Yakutia) and the nature of protokimberlite melts.Doklady Earth Sciences, Vol. 486, 2, pp. 675-678.Russiadeposit -Mir

Abstract: The chemical compositions of garnets from a megacryst association of the Mir kimberlite pipe have been studied. By petrogenic elements, the garnet megacrysts can be classified as high-Ti and low-Cr pyrope. The megacryst TiO2 contents of the Mir pipe correlate inversely with the MgO and Cr2O3 contents. Modeling of the composition of garnets through a fractional crystallization process showed that the most suitable composition of the melts parental for the garnets of the megacryst association is picrite. The composition of garnets crystallized from the kimberlite does not correspond to the composition of the natural garnets from the Mir pipe. The kimberlites contain less Ti, Zr, Y, and HREEs, but are more enriched with strongly incompatible elements (LREEs, Th, U, Nb, Ta, and Ba) than the model composition of the melt suitable for crystallization of the garnet megacrysts.
DS201901-0001
2017
Agrosi, G., Tempesta, G., Della Ventura, G., Cestelli Guidi, M., Hutchison, M., Nimis, P., Nestola, F.Non-destructive in situ study of plastic deformation in diamonds: X-ray diffraction topography and uFTIR mapping of two super deep diamond crystals from Sao Luiz ( Juina, Brazil).Crystals MDPI, Vol. 7, 8, 11p. Doi.org/10. 3390/cryst7080233South 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.
DS201912-2766
2019
Agrosi, G., Tempesta, G., Mele, D., Caggiani, MC., Mangone, A., Della Ventura, G., Cestelli-Guidi, M., Allegretta, I., Hutchison, M.T., Nimis, P., Nestola, F.Multiphase inclusions associate with residual carbonate in a transition zone diamond from Juina, Brazil.Lithos, in press available, 31p. pdfSouth America, Brazildeposit - Juina

Abstract: Super-deep diamonds and their mineral inclusions preserve very precious information about Earth’s deep mantle. In this study, we examined multiphase inclusions entrapped within a diamond from the Rio Vinte e um de Abril, São Luiz area (Juina, Brazil), using a combination of non-destructive methods. Micro-Computed X-ray Tomography (µ-CXRT) was used to investigate the size, shape, distribution and X-Ray absorption of inclusions and mapping by micro X-ray Fluorescence (µ-XRF), µ-Raman Spectroscopy and micro-Fourier Transform Infrared Spectroscopy (µ-FTIR) were used to determine the chemical and mineralogical composition of the inclusions. Four large inclusions enclosed in the N-rich diamond core consist of dominant ferropericlase-magnesiowüstite and locally exsolved magnesioferrite. FTIR maps, obtained integrating the band at 1430 cm-1, show also the presence of carbonates. A fifth large inclusion (ca 100 µm) was remarkable because it showed a very unusual flask shape, resembling a fluid/melt inclusion. Based on µCXRT tomography and µ-Raman mapping, the flask-shaped inclusion is polyphase and consists of magnetite and hematite partly replacing a magnesiowüstite core and small-volume of gas/vacuum. µ-Raman spectra on the same inclusion revealed local features that are ascribed to post-spinel polymorphs, such as maohokite or xieite, which are stable at P = 18 GPa, and to huntite, a carbonate with formula CaMg3(CO3)4. This represents the first finding of maohokite and huntite in diamond. We interpret the composition of the inclusions as evidence of formation of ferropericlase-magnesiowüstite and diamond in a carbonate-rich environment at depths corresponding at least to the Transition Zone, followed by oxidation of ferropericlase-magnesiowüstite by reaction with relatively large-volume entrapped melt during diamond ascent.
DS201911-2507
2019
Akam, C., Simandl, G.J., Lett, R., Paradis, S., Hoshino, M., Kon, Y., Araoka, D., Green, C., Kodama, S., Takagi, T., Chaudhry, M.Comparison of methods for the geochemical determination of rare earth elements: Rock Canyon Creek REE-F-Ba deposit case study, SE British Columbia, Canada.Geochemistry: Exploration, Environment, Analysis, Vol. 19, pp. 414-430.Canada, British Columbiageochemistry

Abstract: Using Rock Canyon Creek REE-F-Ba deposit as an example, we demonstrate the need for verifying inherited geochemical data. Inherited La, Ce, Nd, and Sm data obtained by pressed pellet XRF, and La and Y data obtained by aqua regia digestion ICP-AES for 300 drill-core samples analysed in 2009 were compared to sample subsets reanalysed using lithium metaborate-tetraborate (LMB) fusion ICP-MS, Na2O2 fusion ICP-MS, and LMB fusion-XRF. We determine that LMB ICP-MS and Na2O2 ICP-MS accurately determined REE concentrations in SY-2 and SY-4, and provided precision within 10%. Fusion-XRF was precise for La and Nd at concentrations exceeding ten times the lower detection limit; however, accuracy was not established because REE concentrations in SY-4 were below the lower detection limit. Analysis of the sample subset revealed substantial discrepancies for Ce concentrations determined by pressed pellet XRF in comparison to other methods due to Ba interference. Samarium, present in lower concentrations than other REE compared, was underestimated by XRF methods relative to ICP-MS methods. This may be due to Sm concentrations approaching the lower detection limits of XRF methods, elemental interference, or inadequate background corrections. Aqua regia dissolution ICP-AES results, reporting for La and Y, are underestimated relative to other methods.
DS201908-1768
2019
Alberti, M., Arabas, A., Fursich, F.T., Andersen, N., Ziolkowski, P.The Middle to Upper Jurassic stable isotope record of Madagascar: linking temperature changes with plate tectonics during the break-up of Gondwana.Gondwana Research, Vol. 73, pp. 1-15.Africa, Madagascargeochemistry

Abstract: Stable isotope (d18O, d13C) analyses were performed on well preserved belemnites, oysters, and rhynchonellid brachiopods from the Middle to Upper Jurassic of the Morondava Basin in southern Madagascar. Both brachiopods and oysters indicate similar average temperatures of 18.7 to 19.3?°C in the Early Callovian, followed by a temperature decrease towards the Middle Oxfordian (13.9?°C) and a minimum in the Early Kimmeridgian (12.3?°C). In contrast, belemnites from the Oxfordian show lower average temperatures of 10.0?°C, which is likely caused by specific conditions for these organisms (e.g., different fractionation or life habits). Additionally, three oysters from the Upper Oxfordian and Lower Kimmeridgian were used for high-resolution stable isotope analyses. The data show seasonal fluctuations of >6?°C around averages between 14.4 and 14.7?°C. Latitudinal temperature gradients for the Callovian and Kimmeridgian are similar to today at the examined low latitudes of the southern hemisphere. The observed cooling of around 5?°C from the Callovian to the Oxfordian/Kimmeridgian can be attributed to a concurrent southward drift of Madagascar during the break-up of Gondwana. Thus, the study underlines the importance of considering palaeogeography in interpreting stable isotope data as well as the potential of detecting and timing palaeogeographic events by using stable isotope analyses.
DS201906-1266
2019
Alemayehu, M., Guo, F., Aulbach, S.Transformation of continental lithospheric mantle beneath the East African Rift: constraints from platinum group elements and Re-Os isotopes in mantle xenoliths from Ethiopia.Contributions to Mineralogy and Petrology, Vol. 174, 5, 27p.Africa, Ethiopiaxenoliths

Abstract: The behavior of sub-continental lithospheric mantle (SCLM) in extensional settings, up to successful rifting, plays an important role in geodynamics and in the global carbon cycle, yet the underlying processes and rates of lithosphere destruction remain poorly constrained. We determined platinum-group element (PGE: Os, Ir, Ru, Pt, and Pd) abundances and Re-Os-isotope systematics for well-characterized mantle xenoliths hosted in Cenozoic basalts from the northwestern plateau (Gundeweyn area) and southern rift zone (Dillo and Megado areas) of Ethiopia to provide new insights on the nature and timing of processes leading to the formation and transformation of the off-cratonic lithospheric mantle beneath the East Africa rift system (EARS). The whole-rock PGE concentrations are highly variable, with total PGE abundances ranging from 6.6 to 12.6 ppb for Gundeweyn, 11.5 to 23.3 ppb for Dillo, and 9.9 to 19.4 ppb for Megado mantle xenoliths. The 187Os/188Os ratios of the whole-rock mantle xenoliths vary from 0.1180 to 0.1287 for Gundeweyn, 0.1238 to 0.1410 for Dillo and 0.1165 to 0.1277 for Megado, compared to 0.130 for the Afar plume and?=?0.14 for the Kenya plume, with Re depletion ages up to 1.45 Ga for Gundeweyn, 0.64 Ga for Dillo, and 1.65 Ga for Megado mantle xenoliths. The regional differences between refertilizing agents recorded in mantle xenoliths from the plateau area and the rift systems reflect distinct tectonomagmatic settings: (1) low PGE abundances, with some retention of low 187Os/188Os in Gundeweyn peridotites, are ascribed to scavenging by early small-volume oxidizing melts, generated in the convecting mantle ahead of the arrival of the Afar plume. (2) Percolation of late-stage silicate/basaltic melts, associated with the arrival of hot mantle plume and lithosphere thinning in the rift setting, locally led to refertilization and sulfide precipitation and partial replenishment of the PGE (Dillo), with convecting mantle-like 187Os/188Os. Local enclaves of older, cryptically metasomatised mantle with unradiogenic Os (Megado) attest to the heterogeneous nature of melt-peridotite interaction at this stage (pervasive vs. focused melt flow). Highly depleted abundances of the compatible PGE are characteristic of SCLM affected by incipient rifting and percolation of oxidizing melts, here associated with the Afar and Kenya plume beneath the East Africa rift, and may be precursors to advanced degrees of lithosphere destruction/transformation.
DS201912-2767
2019
Alencastro, M.State - diamond sector relations in Angola, 1912-2002.Journal of Southern African Studies, Vol. 45, 5, pp. 805-820.Africa, South Africaeconomics

Abstract: Existing studies on mining in Angola are mostly concerned with its social and military underpinnings and tend to analyse the diamond sector as empirically distinct from the state. In addition, little attention has been paid to how they are bound together and what these interconnections mean for the nature of politics in Angola. This gap in the literature is significant because diamond companies produce far more than revenue and profits: for some 100?years, the diamond sector has governed, policed, defended and controlled the strategic, diamond-rich provinces of Lunda Sul and Lunda Norte. In order to fill this lacuna, this article offers a case study on the role of the diamond industry for the state in Angola from the creation of the first diamond company in 1917 to the end of the Angolan civil war in 2002. Drawing on a wide range of untapped official documents and on interviews, it argues that the diamond sector has functioned historically as the conduit through which the state projects its power and secures its interests in strategic but hostile territory.
DS201908-1769
2019
Alessio, B.L., Glorie, S., Collins, A.S., Jourdan, F., Jepson, G., Nixon, A., Siegfried, P.R., Clark, C.The thermo-tectonic evolution of the southern Congo craton margin as determined from apatite and muscovite thermochronology.Tectonophysics, Vol. 766, pp. 398-415.Africa, Zambia, Malawi, Mozambique, Tanzaniacraton

Abstract: The Southern Irumide Belt (SIB) of Zambia consists of predominantly Mesoproterozoic terranes that record a pervasive tectono-metamorphic overprint from collision between the Congo and Kalahari cratons in the final stages of Gondwana amalgamation. This study applies multi-method thermochronology to samples throughout southern Zambia to constrain the post-collisional, Phanerozoic thermo-tectonic evolution of the region. U-Pb apatite and 40Ar/39Ar muscovite data are used to constrain the cooling history of the region following Congo-Kalahari collision, and reveal ages of c. 550-450?Ma. Variations in the recorded cooling ages are interpreted to relate to localised post-tectonic magmatism and the proximity of analysed samples to the Congo-Kalahari suture. Apatite fission track data are used to constrain the low-temperature thermo-tectonic evolution of the region and identify mean central ages of c. 320-300, 210-200 and 120-110?Ma. Thermal modelling of these samples identifies a number of thermal events occurring in the region throughout the Phanerozoic. Carboniferous to Permian-Triassic heating is suggested to relate to the development of Karoo rift basins found throughout central Africa and constrain the timing of sedimentation in the basin. Permian to Jurassic cooling is identified in a number of samples, reflecting exhumation as a result of the Mauritanian-Variscan and Gondwanide orogenies. Subsequent cooling of the majority of samples occurs from the Cretaceous and persists until present, reflecting exhumation in response to larger scale rifting associated with the break-up of Gondwana. Each model reveals a later phase of enhanced cooling beginning at c. 30?Ma that, if not an artefact of modelling, corresponds to the development of the East African Rift System. The obtained thermochronological data elucidate the previously unconstrained thermal evolution of the SIB, and provides a refined regional framework for constraining the tectonic history of central Africa throughout the Phanerozoic.
DS201912-2768
2019
Alvaro, M., Mazzucchelli, M.L., Angel, R.J., Murri, M., Campmenosi, N., Scambelluri, M., Nestola, F., Korsakov, A., Tomilenko, A.A., Marone, F., Morana, M.Fossil subduction recorded by quartz from the coesite stability field. GeobarometryGeology, in press, 5p. PdfRussia, Yakutiadeposit - Mir

Abstract: Metamorphic rocks are the records of plate tectonic processes whose reconstruction relies on correct estimates of the pressures and temperatures (P-T) experienced by these rocks through time. Unlike chemical geothermobarometry, elastic geobarometry does not rely on chemical equilibrium between minerals, so it has the potential to provide information on overstepping of reaction boundaries and to identify other examples of non-equilibrium behavior in rocks. Here we introduce a method that exploits the anisotropy in elastic properties of minerals to determine the unique P and T of entrapment from a single inclusion in a mineral host. We apply it to preserved quartz inclusions in garnet from eclogite xenoliths hosted in Yakutian kimberlites (Russia). Our results demonstrate that quartz trapped in garnet can be preserved when the rock reaches the stability field of coesite (the high-pressure and high-temperature polymorph of quartz) at 3 GPa and 850 °C. This supports a metamorphic origin for these xenoliths and sheds light on the mechanisms of craton accretion from a subducted crustal protolith. Furthermore, we show that interpreting P and T conditions reached by a rock from the simple phase identification of key inclusion minerals can be misleading.
DS201910-2243
2019
Amrstrong, K., Frost, D.J., McCammon, C.A., Rubie, D.C., Boffa Ballaran, T.Deep magma ocean formation set the oxidation state of Earth's mantle.Science, Vol. 365, 6456, pp. 903-906.Mantleredox

Abstract: The composition of Earth’s atmosphere depends on the redox state of the mantle, which became more oxidizing at some stage after Earth’s core started to form. Through high-pressure experiments, we found that Fe2+ in a deep magma ocean would disproportionate to Fe3+ plus metallic iron at high pressures. The separation of this metallic iron to the core raised the oxidation state of the upper mantle, changing the chemistry of degassing volatiles that formed the atmosphere to more oxidized species. Additionally, the resulting gradient in redox state of the magma ocean allowed dissolved CO2 from the atmosphere to precipitate as diamond at depth. This explains Earth’s carbon-rich interior and suggests that redox evolution during accretion was an important variable in determining the composition of the terrestrial atmosphere.
DS201909-2015
2019
Andrews, G.D.M.The kimberlite factory: the volcanic nature of kimberlites.53rd Annual South-Central 71st Rocky Mtn GSA section meeting, 1p. AbstractMantlediamond genesis

Abstract: Although traditionally considered the realm of igneous petrologists and geochemists, kimberlites have received attention from physical volcanologists interested in how they are emplaced in the crust and how they can erupt. This presentation will review the evidence for the volcaniclastic (i.e. fragmental) nature of kimberlites from examples in Canada's Northwest Territories and in Pennsylvania. A growing body of evidence indicates that kimberlite magmas are gas-dominated (overwhelmingly CO2) suspensions of molten kimberlite liquid and crystals, usually olivines. The olivines, like other mineral phases and xenoliths, are entrained from the surrounding mantle peridotite wall-rock, rather than crystallized from the meager kimberlite liquid, and are, therefore, overwhelmingly xenocrystic. This crystal and rock fragment load is sampled and mechanically processed by a turbulent gas-jet before being immersed in a bath of kimberlite liquid: this is the kimberlite factory. As the gas-charged crack-tip propagates and ascends, new mantle is processed into the kimberlite factory. Each emplacement event records the passage of a kimberlite factory through the mantle and lithosphere. The Masontown kimberlite in Pennsylvania is a solitary hypabyssal kimberlite dyke but it preserves evidence of the passage of a single kimberlite factory. Although many kimberlites stall in the crust, many erupt explosively to produce indisputably volcaniclastic kimberlite lithofacies associated with diatremes. Open-pit mining of several diatremes in Canada reveals the complex temporal-spatial nature of different emplacement events within the same volcanic field, and the ubiquitous presence of hypabyssal kimberlite dykes that fed or attempted to feed explosive eruptions. Such explosive eruptions sustained tephra plumes that produced kimberlite fall deposits and pyroclastic density currents that produced kimberlite ignimbrites; both of which exited their source diatremes and inundated the surrounding landscape.
DS201907-1523
2019
Andrews, G.D.M., Russell, J.K., Cole, B.G.., Brown, S.R.The kimberlite factory: the volcanic nature of kimberlites.Joint 53rd Annual South-Central/53rd North Central/71st Rocky Mtn GSA section Meeting, 1p. AbstractMantlediamond genesis

Abstract: Although traditionally considered the realm of igneous petrologists and geochemists, kimberlites have received attention from physical volcanologists interested in how they are emplaced in the crust and how they can erupt. This presentation will review the evidence for the volcaniclastic (i.e. fragmental) nature of kimberlites from examples in Canada's Northwest Territories and in Pennsylvania. A growing body of evidence indicates that kimberlite magmas are gas-dominated (overwhelmingly CO2) suspensions of molten kimberlite liquid and crystals, usually olivines. The olivines, like other mineral phases and xenoliths, are entrained from the surrounding mantle peridotite wall-rock, rather than crystallized from the meager kimberlite liquid, and are, therefore, overwhelmingly xenocrystic. This crystal and rock fragment load is sampled and mechanically processed by a turbulent gas-jet before being immersed in a bath of kimberlite liquid: this is the kimberlite factory. As the gas-charged crack-tip propagates and ascends, new mantle is processed into the kimberlite factory. Each emplacement event records the passage of a kimberlite factory through the mantle and lithosphere. The Masontown kimberlite in Pennsylvania is a solitary hypabyssal kimberlite dyke but it preserves evidence of the passage of a single kimberlite factory. Although many kimberlites stall in the crust, many erupt explosively to produce indisputably volcaniclastic kimberlite lithofacies associated with diatremes. Open-pit mining of several diatremes in Canada reveals the complex temporal-spatial nature of different emplacement events within the same volcanic field, and the ubiquitous presence of hypabyssal kimberlite dykes that fed or attempted to feed explosive eruptions. Such explosive eruptions sustained tephra plumes that produced kimberlite fall deposits and pyroclastic density currents that produced kimberlite ignimbrites; both of which exited their source diatremes and inundated the surrounding landscape.
DS201902-0256
2018
Andrews, R.G.Earth is missing a huge part of its crust. Now we may know why. A fifth of the Earth's geologic history might have vanished because planet-wide glaciers buried the evidence.National Geographic, Dec. 31, United States, Arizonageomorphology

Abstract: The Grand Canyon is a gigantic geological library, with rocky layers that tell much of the story of Earth’s history. Curiously though, a sizeable layer representing anywhere from 250 million years to 1.2 billion years is missing. Known as the Great Unconformity, this massive temporal gap can be found not just in this famous crevasse, but in places all over the world. In one layer, you have the Cambrian period, which started roughly 540 million years ago and left behind sedimentary rocks packed with the fossils of complex, multicellular life. Directly below, you have fossil-free crystalline basement rock, which formed about a billion or more years ago. So where did all the rock that belongs in between these time periods go? Using multiple lines of evidence, an international team of geoscientists reckons that the thief was Snowball Earth, a hypothesized time when much, if not all, of the planet was covered in ice.
DS201901-0002
2018
Anthonis, A., Chapman, J., Smans, S., Bouman, M., De Corte, K.Fluorescence in diamond: new insights.Gems & Gemology, Sixth International Gemological Symposium Vol. 54, 3, 1p. Abstract p. 265-6.GlobalFluoresence

Abstract: The effect of fluorescence on the appearance of diamonds has been a subject of debate for many years (Moses et al., 1997). In the trade, fluorescence is generally perceived as an undesirable characteristic. Nearly 80% of diamonds graded at HRD Antwerp receive a “nil” fluorescence grade, while the remainder are graded as “slight,” “medium,” and “strong,” their value decreasing with level of fluorescence. To understand how fluorescence might change diamond appearance, a selection of 160 round brilliant-cut diamonds were investigated in detail. This study focused on the effect of thetic samples, it is possible that some of the observed phosphorescence does not involve boron impurities. In this paper we report on the results of combined fluorescence, phosphorescence, thermoluminescence, and quantitative charge transfer investigations undertaken on both HPHT and CVD synthetic diamond, with the objective of identifying which defects are involved in the fluorescence and phosphorescence processes.
DS201905-1015
2019
Antonelli, M.A., DePaolo, D.J., Chacko, T., Grew, E.S., Rubatto, D.Radiogenic Ca isotope confirms post-formation K depletion of lower crust.Geochemical Perspective Letters, Vol. 10, pp. 43-48. doi:10.7185/ geochemlet.1904Mantlexenoliths

Abstract: Heat flow studies suggest that the lower crust has low concentrations of heat-producing elements. This could be due to either (i) greater fractions of basaltic rock at depth or (ii) metamorphic depletion of radioactive elements from rocks with more evolved (andesitic to granodioritic) compositions. However, seismic data suggest that lower crust is not predominantly basaltic, and previous studies (using Pb and Sr isotopes) have shown that lower crustal rocks have experienced significant losses of U and Rb. This loss, however, is poorly constrained for K, which is inferred to be the most important source of radioactive heat in the earliest crust. Our high precision Ca isotope measurements on a suite of granulite facies rocks and minerals from several localities show that significant losses of K (~60 % to >95 %) are associated with high temperature metamorphism. These results support models whereby reduction of heat production from the lower crust, and consequent stabilisation of continental cratons in the Precambrian, are largely due to high temperature metamorphic processes. Relative changes in whole rock K/Ca suggest that 20-30 % minimum (granitic) melt removal can explain the K depletions.
DS201912-2769
2018
Anzolini, C.Depth of formation of super-deep diamonds.Plinius, No. 44, 8p. PdfMantlediamond genesis

Abstract: “Super-deep” diamonds are thought to have a sub-lithospheric origin (i.e., below ~300 km depth) because some of the mineral phases entrapped within them as inclusions are considered to be the products of retrograde transformation from lower-mantle or transition-zone precursors. CaSiO3-walstromite, the most abundant Ca-bearing mineral inclusion found in super-deep diamonds, is believed to derive from CaSiO3-perovskite, which is stable only below ~600 km depth, although its real depth of origin is controversial. The remnant pressure (Pinc) retained by an inclusion, combined with the thermoelastic parameters of the mineral inclusion and the diamond host, allows calculation of the entrapment pressure of the diamond-inclusion pair. Raman spectroscopy, together with X-ray diffraction, is the most commonly used method for measuring the Pinc without damaging the diamond host. In the present study we provide, for the first time, a calibration curve to determine the Pinc of a CaSiO3-walstromite inclusion by means of Raman spectroscopy without breaking the diamond. To do so, we performed high-pressure micro-Raman investigations on a CaSiO3-walstromite crystal under hydrostatic stress conditions within a diamond-anvil cell. We additionally calculated the Raman spectrum of CaSiO3-walstromite by ab initio methods both under hydrostatic and non-hydrostatic stress conditions to avoid misinterpretation of the results caused by the possible presence of deviatoric stresses causing anomalous shift of CaSiO3-walstromite Raman peaks. Last, we applied single-inclusion elastic barometry to estimate the minimum entrapment pressure of a CaSiO3-walstromite inclusion trapped in a natural diamond, which is ~9 GPa (~260 km) at 1800 K. These results suggest that the diamond investigated is certainly sub-lithospheric and endorse the hypothesis that the presence of CaSiO3-walstromite is a strong indication of super-deep origin.
DS201904-0714
2019
Anzolini, C., Nestola, F., Mazzucchelli, M.L., Alvaro, M., Nimis, P., Gianese, A., Morganti, S., Marone, F., Campione, M., Hutchison, M.T., Harris, J.W.Depth of diamond formation obtained from single periclase inclusions. SDD ( Super Deep Diamonds)Geology , Vol. 47, 3, pp. 219-222.South America, Brazil, Guyanadiamond genesis

Abstract: Super-deep diamonds (SDDs) are those that form at depths between ~300 and ~1000 km in Earth’s mantle. They compose only 1% of the entire diamond population but play a pivotal role in geology, as they represent the deepest direct samples from the interior of our planet. Ferropericlase, (Mg,Fe)O, is the most abundant mineral found as inclusions in SDDs and, when associated with low-Ni enstatite, which is interpreted as retrogressed bridgmanite, is considered proof of a lower-mantle origin. As this mineral association in diamond is very rare, the depth of formation of most ferropericlase inclusions remains uncertain. Here we report geobarometric estimates based on both elasticity and elastoplasticity theories for two ferropericlase inclusions, not associated with enstatite, from a single Brazilian diamond. We obtained a minimum depth of entrapment of 15.7 (±2.5) GPa at 1830 (±45) K (~450 [±70] km depth), placing the origin of the diamond-inclusion pairs at least near the upper mantle-transition zone boundary and confirming their super-deep origin. Our analytical approach can be applied to any type of mineral inclusion in diamond and is expected to allow better insights into the depth distribution and origin of SDDs.
DS201907-1524
2019
Anzolini, C., Wang, F., Harris, G.A., Locock, A.J., Zhang, D., Nestola, F., Peruzzo, L., Jacobsen, S.D., Pearson, D.G.Nixonite, Na2Ti6O13, a new mineral from a metasomatized mantle garnet pyroxenite from the western Rae Craton, Darby kimberlite field, Canada.American Mineralogist, in press available 26p.Canada, Nunavutdeposit - Darby

Abstract: Nixonite (IMA 2018-133), ideally Na2Ti6O13, is a new mineral found within a heavily-metasomatized pyroxenite xenolith from the Darby kimberlite field, beneath the west central Rae Craton, Canada. It occurs as microcrystalline aggregates, 15 to 40 µm in length. Nixonite is isostructural with jeppeite, K2Ti6O13, with a structure consisting of edge- and corner-shared titanium-centered octahedra that enclose alkali-metal ions. The Mohs hardness is estimated to be between 5 and 6 by comparison to jeppeite and the calculated density is 3.51(1) g/cm3. Electron microprobe wavelength-dispersive spectroscopic analysis (average of 6 points) yielded: Na2O 6.87, K2O 5.67 CaO 0.57, TiO2 84.99, V2O3 0.31, Cr2O3 0.04, MnO 0.01, Fe2O3 0.26, SrO 0.07, total 98.79 wt%. The empirical formula, based on 13 O atoms, is: (Na1.24K0.67Ca0.06)S1.97(Ti5.96V0.023Fe0.018)S6.00O13 with minor amounts of Cr and Mn. Nixonite is monoclinic, space group C2/m, with unit-cell parameters a = 15.3632(26) Å, b = 3.7782(7) Å, c = 9.1266(15) Å, ß = 99.35(15)º and V = 522.72(1) Å3, Z = 2. Based on the average of seven integrated multi-grain diffraction images, the strongest diffraction lines are [dobs in Å (I in %) (h k l)]: 3.02 (100) (3 1 0) , 3.66 (75) (1 1 0), 7.57 (73) (2 0 0), 6.31 (68) (2 0 -1), 2.96 (63) (3 1 -1), 2.96 (63) (2 0 -3) and 2.71 (62) (4 0 2). The five main Raman peaks of nixonite, in order of decreasing intensity, are at: 863, 280, 664, 135 and 113 cm-1. Nixonite is named after Peter H. Nixon, a renowned scientist in the field of kimberlites and mantle xenoliths. Nixonite occurs within a pyroxenite xenolith in a kimberlite, in association with rutile, priderite, perovskite, freudenbergite and ilmenite. This complex Na-K-Ti rich metasomatic mineral assemblage may have been produced by a fractionated Na-rich kimberlitic melt that infiltrated a mantle-derived garnet pyroxenite and reacted with rutile during kimberlite crystallization.
DS201901-0003
2018
Aremieva, I.M., Thybo, H., Cherepanova, Y.Isopycnicity of cratonic mantle restricted to kimberlite provinces.Earth and Planetary Science Letters, Vol. 505, pp. 162-172.Russia, Siberiacraton

Abstract: The isopycnicity hypothesis states that the lithospheric mantle of ancient platforms has a unique composition such that high density due to low lithosphere temperature is nearly compensated by low-density composition of old cratonic mantle. This hypothesis is supported by petrological studies of mantle xenoliths hosted in kimberlite magmas. However, the representativeness of the kimberlite sampling may be questioned, given that any type of magmatism is atypical for stable regions. We use EGM2008 gravity data to examine the density structure of the Siberian lithospheric mantle, which we compare with independent constraints based on free-board analysis. We find that in the Siberian craton, geochemically studied kimberlite-hosted xenoliths sample exclusively those parts of the mantle where the isopycnic condition is satisfied, while the pristine lithospheric mantle, which has not been affected by magmatism, has a significantly lower density than required by isopycnicity. This discovery allows us to conclude that our knowledge on the composition of cratonic mantle is incomplete and that it is biased by kimberlite sampling which provides a deceptive basis for the isopycnicity hypothesis.
DS201904-0715
2019
Armistead, S.E., Collins, A.S., Redaa, A., Gilbert, S., Jepson, G., Gillespie, J., Blades, M.L., Foden, J.D., Razakamana, T.Structural evolution and medium temperature thermochronology of central Madagascar: implications for Gondwana amalgamation.Journal of the Geological Society of London, in press available 25p.Africa, Madagascarthermochronology

Abstract: Madagascar occupied an important place in the amalgamation of Gondwana, and preserves a record of several Neoproterozoic events that can be linked to orogenesis of the East African Orogen. We integrate remote sensing and field data to unravel complex deformation in the Ikalamavony and Itremo domains of central Madagascar. The deformation sequence comprises a gneissic foliation (S1), followed by south to south-west directed, tight to isoclinal, recumbent folding (D2). These are overprinted by north-trending upright folds that formed during a ~E-W shortening event. Together these produced type 1 and type 2 fold interference patterns throughout the Itremo and Ikalamavony domains. Apatite U-Pb and muscovite and biotite Rb-Sr thermochronometers indicate that much of central Madagascar was thermally reset to at least ~500oC at c. 500 Ma. Deformation in west-central Madagascar occurred between c. 750 Ma and c. 550 Ma, and we suggest this deformation formed in response to the c. 650 Ma collision of Azania with Africa along the Vohibory Suture in southwestern Madagascar. In eastern Madagascar, deformation is syn- to post-550 Ma, which formed in response to the final closure of the Mozambique Ocean along the Betsimisaraka Suture that amalgamated Madagascar with the Dharwar Craton of India.
DS201906-1267
2019
Armitage, P.E.B.The Songwe Hill rare earths project, Malawi - geological observations on the recently announced mineral resource upgrade.3rd International Critical Metals Meeting held Edinburgh, 1p. Abstract p. 37.Africa, Malawideposit - Songwe Hill

Abstract: PDF link to the presentation.
DS201901-0004
2018
Artyushkov, E.V., Korikovsky, S.P., Massonne, H-J., Checkhovich, P.A.Recent crustal uplift of Precambrian cratons: key patterns and possible mechanisms.Russian Geology and Geophysics, Vol. 59, 11, pp. 1389-1409.Russiacraton

Abstract: Precambrian cratons cover about 70% of the total continental area. According to a large volume of geomorphological, geological, paleontological, and other data for the Pliocene and Pleistocene, these cratons have experienced a crustal uplift from 100-200 m to 1000-1500 m, commonly called the recent or Neotectonic uplift. Shortening of the Precambrian crust terminated half a billion years ago or earlier, and its uplift could not have been produced by this mechanism. According to the main models of dynamic topography in the mantle, the distribution of displacements at the surface is quite different from that of the Neotectonic movements. According to seismic data, there is no magmatic underplating beneath most of the Precambrian cratons. In most of cratonic areas, the mantle lithosphere is very thick, which makes its recent delamination unlikely. Asthenospheric replacement of the lower part of the mantle lithosphere beneath the Precambrian cratons might have produced only a minor part of their Neotectonic uplifts. Since the above mechanisms cannot explain this phenomenon, the rock expansion in the crustal layer is supposed to be the main cause of the recent uplift of Precambrian cratons. This is supported by the strong lateral nonuniformity of the uplift, which indicates that expansion of rocks took place at a shallow depth. Expansion might have occurred in crustal rocks that emerged from the lower crust into the middle crust with lower pressure and temperature after the denudation of a thick layer of surface rocks. In the dry state, these rocks can remain metastable for a long time. However, rapid metamorphism accompanied by expansion of rocks can be caused by infiltration of hydrous fluids from the mantle. Analysis of phase diagrams for common crustal rocks demonstrates that this mechanism can explain the recent crustal uplift of Precambrian cratons.
DS201909-2016
2019
Ashchepkov, I., Ivanov, A.S., Kostrovitsky, S.I., Vavilov, M.A., Vladykin, N., Babushkina, S.A., Tychkov, N.S., Medvedev, N.S.Mantle terranes of the Siberian craton: their interaction with plume melts based on thermobarometry and geochemistry of mantle xenocrysts.Solid Earth, Vol. 10, 2, pp. 197-245.Russia, Siberiamelting

Abstract: Variations of the structure and composition of mantle terranes in the terminology of the Siberian craton were studied using database (>60000) EPMA of kimberlite xenocrysts from the pipes of Yakutian kimberlite province (YKP) by a team of investigators from IGM, IGH, IEC and IGBM SB RAS and ALROSA company. The monomineral thermobarometry (Ashchepkov et al., 2010, 2014, 2017) Geochemistry of minerals obtained LA ICP MS was used to determine the protolith, melting degree, Type of the metasomatism . The mantle stratification commonly was formed by 6-7 paleosubduction slabs, separated by pyroxenite, eclogite, and metasomatic horizons and dunite lenses beneath kemberltes . We built mantle sections across the kimberlite field and transects of craton. Within the established tectonic terrains strengthening to thousands km (Gladkochub et al, 2006), the collage of microplates was determined at the mantle level. Under the shields of Anabar and Aldan lower SCLM consist of 3 -4 dunites dunites with Gar-Px-Ilm- Phl nests. Terranes framing protocratons like suture Khapchanskyare are saturated in eclogites and pyroxenites, sometimes dominated probably represent the ascending bodies of igneous eclogites intruding mantle lithosphere (ML). The ubiquitous pyroxenite layer at the level of 3.5-4.5 GPa originated in the early Archaean when melted eclogites stoped stoped subdction. Beneath the Early Archaean granite-greenstone terranes - Tunguskaya, Markhinskaya, Birektinskaya, Shary-Zhalgaiskaya (age to~3.8-3.0 GA) (Gladkochub et al., 2018) the SCLM is less depleted and often metasomatized having flat structures in some subterrains. Daldyn and Magan granulite-orthogneisic terranes have a layered and folded ML seen in N-S sections from Udachnaya to Krasnopresnenskaya less pronounced in latitudinal direction. From Daldyn to Alakit field increases the degree of Phl metasomatism and Cpx alkalinity. The most productive Aykhal and Yubleynaya pipes confined to the dunite core. Within the Magan terrane, the thin-layered SCLM have depleted base horizon. Granite-greenstone Markha terrane contains pelitic eclogites. Central and Northern craton parts show slight inclination of paleoslabs to West. The formation of SCLM in Hadean accompanied by submelting (Perchuk et al., 2018, Gerya, 2014.) had no deep roots. Ultrafine craton nuclei like Anabar shield was framed by steeper slab. During 3.8-3.0 GA craton keel growth in superplume periods (Condie, 2004) when melted eclogites and peridotites acquiring buoyancy of the sinking plate melted. For peridotites, the melting lines calculated from the experimental data (Herzberg, 2004) mainly lie near 5-6 GPA (Ionov et al., 2010; 2015). In classical works all geotherms are conductive (Boyd, 1973), but this is quite rare. The garnet pyroxene geotherms for (Ashchepkov et al., 2017) calculated with most reliable methods (Nimis, Taylor, 2000; McGregor , 1974; Brey Kohler, Nickel Green, 1985; Ashchepkov et al., 2010; 2017) give are sub-adiabatic and are formed during the melt percolation superplume vent often in presence of volatiles (Wyllie, Ryabchikov, 2000) and therefore, after superplumes trends P-Fe# of garnet are smoothed and change the tilts.
DS201911-2508
2019
Ashchepkov, I.V., Mevedev, N.S., Yudin, D.S., Ntaflos, T., Makovchuk, I.V., Ivanov, A.S., Kiseeva, E.Mantle columns beneath Kosomolskaya and Zarnitsa kimberlite pipes: xenolith study.Goldschmidt2019, 1p. AbstractRussiadeposit - Kosomolskaya, Zarnitsa

Abstract: Mantle xenolith from Komsomolskya and Zarnitsa pie were used for the reconstryctions of mantle columns beneath theses kimberlite pipes. Relatively fresh mantle xenolith from Zarnitsa and Komsomolskaya pipes we used for PTX reconstructions of mantle sections. In Zarnitsa dunites - harburgites with richterite, Phl-Ilm veins, sheared lherzolites, pyroxenites (with amphibole) and eclogites and deformed peridotites. Mg -rich Gar and Opx formed stepped P-Fe# trend, Fe- enriched Cpx with Ilm were created mostly by protkimberlites. Sub Ca garnets rarely show U spikes while Ti rich show Th, U, Ta, Nb, Zr and peaks Many minerals demonstrate Th enrichment due to carbonitites. In mantle of Komsomolskaya pipe Phl is wide spreadin periditites from lherzolites ti dunites and in eclogites. There are 6 intervals with sharp division at 5 GPa.Mg eclogites prevae in lower part while fe- enriched in middle part. The Fe# rise is detevcted in lower and upper parts of mantle section. The TRE spiderdiagrams of grnets shows U -pb subduction peaks But Cpx mainly show n Th- peak. The ages of eclogites ogive 500-600 Ma (one 1525 MA) which is much less than in Zarnitsa or Udachnaya having Proterozoic - Archean ages.
DS201906-1268
2019
Aubert, J., Finlay, C.C.Geomagnetic jerks and rapid hydromagnetic waves focusing at Earth's core surface.Nature Geoscience, Vol. 12, 5, pp. 393-398.Mantlegeophysics

Abstract: Geomagnetic jerks are abrupt changes in the second time derivative "the secular acceleration" of Earth’s magnetic field that punctuate ground observatory records. As their dynamical origin has not yet been established, they represent a major obstacle to the prediction of geomagnetic field behaviour for years to decades ahead. Recent jerks have been linked to short-lived, temporally alternating and equatorially localized pulses of secular acceleration observed in satellite data, associated with rapidly alternating flows at Earth’s core surface. Here we show that these signatures can be reproduced in numerical simulations of the geodynamo that realistically account for the interaction between slow core convection and rapid hydromagnetic waves. In these simulations, jerks are caused by the arrival of localized Alfvén wave packets radiated from sudden buoyancy releases inside the core. As they reach the core surface, the waves focus their energy towards the equatorial plane and along lines of strong magnetic flux, creating sharp interannual changes in core flow and producing geomagnetic jerks through the induced variations in magnetic field acceleration. The ability to numerically reproduce jerks offers a new way to probe the physical properties of Earth’s deep interior.
DS201901-0005
2018
Aulbach, S., Arndt, N.T.Ecologites as paleodynamic archives: evidence for warm ( not hot) and depleted ( but heterogeneous) Archean ambient mantle.Earth and Planetary Science Letters, Vol. 505, pp. 162-172.Mantleeclogites

Abstract: Some high-Mg eclogite xenoliths, entrained by kimberlites from the mantle lithospheres of ancient continental cores, and rare orogenic eclogites and ophiolites, exhumed or obducted during the closure of palaeo-ocean basins, have elemental and isotopic compositions indicative of protoliths that formed as little-differentiated melts erupted in ancient ocean floors. Despite metamorphism and, in part, partial melt loss, these samples of ancient mid-ocean ridge basalt and picrite retain a memory of the chemical and physical state of their protoliths' ambient convecting mantle sources. Published data show that, when filtered to exclude specimens with cumulate protoliths or showing evidence for later enrichment (metasomatism), the samples lack Y or Al 2 O 3 depletion relative to TiO 2 and MgO. This indicates melt segregation of the protolith predominantly from a garnet-free peridotite source and implies intersection of the solidus at low pressures (=3 GPa). Given the dependence of melt composition and volume on source composition (assumed to be similar to modern depleted mantle) and mantle potential temperature (T P), we calculate moderate average melt fractions F (~0.22 ± 0.01) from the Ti contents of the least differentiated samples in three sample suites with 2.6 to 2.9 Ga ages. This converts to T P of ~1410 ± 10 • C assuming a final pressure of melting of 0.5 GPa, melt productivity of 10%/GPa and mantle adiabat of 0.4 • C/km, and using a mantle solidus parameterisation. Though model-dependent, the results are in agreement with recent work advocating moderate Archaean mantle T P. Estimates drop to F = 0.19 and T P = 1380 • C at 1.9 Ga and F = 0.12 and T P = 1310 at 0.6 Ga, corresponding to a decrease in T P of only ~100 • C over the last 3 Ga. A less depleted mantle source yields higher F and T P , but the above estimates are in better agreement with qualitative evidence from Al 2 O 3 and Y, and with Nd-Hf and Sr isotope compositions of orogenic eclogite and granulite suites and mantle eclogites, respectively, which indicate that portions of the Meso-to Neoarchaean mantle were depleted. Moderate T P supports early plate strengthening and a possible transition to plate tectonics in the Mesoarchaean if not earlier. Moreover, moderate temperatures in Archaean subduction zones may have facilitated deep recycling of volatiles that would otherwise have been lost from subducting slabs at shallow depths.
DS201902-0257
2019
Aulbach, S., Heaman, L.M., Jacob, D., Viljoen, K.S.Ages and sources of mantle eclogites: ID-TIMS and in situ MC-ICPMS Pb-Sr isotope systematics of clinopyroxene.Chemical Geology, Vol. 503, pp. 15-28.Africa, South Africa, Zimbabwe, Sierra Leonedeposit - Lace, Orapa, Koidu

Abstract: Strontium and Pb isotopic compositions of clinopyroxene (cpx) in selected samples from three well-characterised eclogite suites with oceanic crustal protoliths (Lace/Kaapvaal craton, Orapa/Zimbabwe craton and Koidu/West African craton) were acquired by high-precision isotope dilution thermal ionisation mass spectrometry (ID-TIMS) and in situ multicollector-laser ablation-inductively-coupled plasma mass spectrometry (MC-LA-ICPMS). The aims of this study are twofold: (1) assess their utility to obtain formation or resetting age constraints and identify elemental signatures that enhance the chances of successful age dating, and (2) to confirm the veracity and utility of results obtained by novel MC-LA-ICPMS techniques. Strontium-Pb isotope systematics of eclogitic cpx measured in this study are decoupled and may reflect addition of unsupported radiogenic Sr during seawater alteration or interaction with oceanic sediments in subduction mélanges, and/or disturbance due to mantle metasomatism, to which the more incompatible Pb is more susceptible. Despite a complex history, subsets of samples yield meaningful model dates. Clinopyroxene fractions from Lace with high Pb contents (3-6?ppm), unradiogenic Pb isotopic compositions (206Pb/204Pb?=?13.57-13.52) and low 238U/204Pb (1.0-1.5) give single-stage model Pb dates of 2.90-2.84?Ga. In contrast, samples from Orapa plot to the right of the Geochron and do not yield meaningful Pb model ages. However, these data do define secondary isochrons that can be modelled to yield minimum age constraints on major events affecting the cratonic lithosphere. Within the uncertainties, the resultant 2.18?±?0.45?Ga age obtained for Koidu eclogites reflect disturbance of the Pb isotope system due to subduction beneath the craton linked to the Eburnean orogeny, while they retained their unradiogenic 87Sr/86Sr (0.7016). Similarly, the age for samples from Orapa (2.20?±?0.54?Ga) is interpreted as an overprint age related to Palaeoproterozoic accretion at the western craton margin. Gabbroic eclogites (Eu/Eu*?>?1) with plagioclase-rich protoliths having low time-integrated Rb/Sr and U/Pb retain the least radiogenic Sr and, in part, Pb. High model µ (9.0 to 9.1) for several eclogites from Lace with elevated LREE, Th and Pb abundances reflects ca. 3.0?Ga addition of a sedimentary component, possibly derived from reworking of a high-µ basaltic protocrust, as observed on other cratons. We suggest that sample targeting can be usefully guided by fast-throughput in situ LA-ICPMS techniques, which largely yield results identical to ID-TIMS, albeit at lower precision, and which can further help identify kimberlite contamination in the mineral separates used for solution work.
DS201906-1269
2019
Aulbach, S., Hofer, H.E., Gerdes, A.High Mg and Low Mg mantle eclogites from Koidu (West African Craton) linked by Neoproterozoic ultramafic melt metasomatism of subducted Archean plateau-like oceanic crust.Journal of Petrology, Vol. 60, 4, pp. 723-754.Africa, Sierra Leonedeposit - Koidu

Abstract: Bimineralic eclogites and pyroxenites (n?=?75?±?accessory rutile, ilmenite, sulphide, apatite) from the Koidu kimberlite (West African Craton) were investigated for mineral major and trace elements and mineral Sr-Nd isotope compositions to constrain (1) the nature and age of their basaltic to picritic protoliths, and (2) the effect, timing and source of mantle metasomatism. Consistent with published work, samples are grouped into low-Mg eclogites with Mg# from 0•49 to 0•73 (median 0•59; n?=?40) and high-Mg eclogites with Mg# from 0•60 to 0•88 (median 0•75; n?=?14), plus pyroxenites [clinopyroxene Na/(Na + Ca) <0•2; n?=?8] and gabbroic eclogites and pyroxenite (Eu/Eu* of reconstructed bulk-rocks >1•05; n?=?8), with five unclassifiable samples. Reconstructed low-Mg and gabbroic eclogites have major and trace element systematics (Eu/Eu*-heavy rare earth elements-Y) indicating crustal protolith crystallisation, confirming an origin as subducted oceanic crust. Their high FeO contents at MgO >~10?wt % require an Fe-rich source, the high melt productivity of which led to the formation of thicker crust, perhaps in a plateau-like setting. This is consistent with SiO2-MgO relationships indicating differentiation at ~0•5?GPa. Unradiogenic Sr in some clinopyroxene (87Sr/86Sr of 0•7010-0•7015), combined with light rare earth element (LREE) depletion relative to normal mid-ocean ridge basalt (N-MORB) for the majority of samples (average N-MORB-normalised Nd/Yb of unmetasomatised samples = 0•51), suggests eclogitisation and partial melt loss in the Neoarchaean, possibly coeval with and parental to 2•7?Ga overlying continental crust. Most reconstructed high-Mg eclogites and some pyroxenites formed by metasomatic overprinting of low-Mg eclogites and gabbroic eclogites, as indicated by the preservation of positive Eu anomalies in some samples, and by the Mg-poorer composition of included versus matrix minerals. Coupled enrichment in MgO, SiO2 and Cr2O3 and in incompatible elements (Sr, LREE, Pb, Th and U) is ascribed to metasomatism by a kimberlite-like, small-volume, carbonated ultramafic melt, mediated by addition of clinopyroxene from the melt (i.e. stealth metasomatism). Strontium-Nd isotope systematics suggest a Neoproterozoic age for this metasomatic event, possibly linked to Rodinia break-up, which facilitated intrusion of asthenospheric carbonated melts with an ocean island basalt-like 87Sr/86Sri of ~0•7035. Cretaceous kimberlite magmatism (including Koidu), with more radiogenic 87Sr/86Sr (~0•7065, intermediate between Kaapvaal kimberlites and orangeites), may have been partially sourced from associated Neoproterozoic metasomes. The presence of diamonds in low-Mg eclogites, but absence in high-Mg eclogites, indicates the diamond-destructive nature of this event. Nevertheless, the moderate proportion of affected eclogites (~35%) suggests preservation of a sizeable diamond-friendly mantle eclogite reservoir beneath Koidu.
DS201903-0497
2019
Aulbach, S., Sun, J., Tappe, S., Gerdes, A.Effects of multi-stage rifting and metasomatism on HSE 187 Os 188 Os systematics of the cratonic mantle beneath SW Greenland. KimberlitesContributions to Mineralogy and Petrology, Vol. 174, 23p.Europe, Greenlandmetasomatism

Abstract: We report highly siderophile element (HSE) abundances and Re-Os isotope compositions, obtained by isotope dilution induc-tively coupled plasma mass spectrometry, of olivine separates from a suite of multiply metasomatised peridotite xenoliths entrained in kimberlites from SW Greenland. Combined with petrographic and compositional observations on accessory base metal sulphides (BMS), the results reveal new insights into the chemical, physical and mineralogical effects of multi-stage rifting and associated melt percolation on the Archaean lithospheric mantle. Refertilised lherzolites are dominated by rare to frequent small (tens of µm) BMS inclusions in olivine, whereas modally metasomatised phlogopite-bearing lherzolite and wehrlites have higher proportions of more Ni-rich BMS, including abundant large interstitial grains (hundreds of µm). The olivine separates display depleted HSE systematics with Primitive Upper Mantle (PUM)-normalised Pd/Ir of 0.014-0.62, and have both depleted and enriched 187 Os/ 188 Os (0.1139-0.2724) relative to chondrite that are not correlated with 187 Re/ 188 Os. Four out of ten olivine separates retain similarly depleted Os corresponding to Re-depletion model ages of 2.1-1.8 Ga. They may reflect Palaeoproterozoic refertilisation (lherzolitisation) during Laurentia plate assembly, with re-introduction of clinopyroxene and Os-rich BMS into the originally refractory mantle lithosphere by asthenosphere-derived basaltic melts, followed by recrystallisation and occlusion in olivine. Unradiogenic Os is observed regardless of lithology, including from peridotites that contain abundant interstitial BMS. This reflects addition of Os-poor BMS (<< 1 ppm) during more recent wehrlitisation and phlogopite-introduction, and control of the Os isotopic signature by older Os-rich BMS that precipitated from the basaltic melt. Depletions in compatible HSE (< 0.5 × PUM for Ru, Ir, Os) in all, but one olivine separate reflect nugget effects (amount of depleted vs. metasomatic BMS inclusions) and/or loss due to sulphide dissolution into oxidising small-volume melts that invaded the lithosphere during recurrent rifting, the latter supported by similar depletions in published bulk peridotite data. Combined, these multiple metasomatic events destroyed all vestiges of Mesoarchaean or older inheritance in the olivine separates investigated here, and highlight that caution is needed when interpreting Proterozoic Os model ages in terms of Proterozoic lithosphere stabilisation.
DS201907-1525
2019
Aulbach, S., Symes, C., Chacko, T.Elemental and radiogenic isotope perspective on formation and transformation of cratonic lower crust: Central Slave craton ( Canada). DiavikGeochimica et Cosmochimica Acta, in press available, 42p.Canada, Northwest Territoriesdeposit -Diavik A154 N & S

Abstract: Kimberlite-borne granulite xenoliths provide rare insights into the age, chemical composition and tectonothermal evolution of the otherwise largely inaccessible deep cratonic crust. The formation and transformation of the lower continental crust (LCC) beneath the central Slave craton (Canada) is here illuminated using whole-rock trace-element and Sr-Nd isotope compositions of nine metabasaltic (MBG), one gabbroic (MGG) and two metasedimentary/hybrid (MSG) granulite xenoliths. On the one hand, published sulphide Re-Os and a few zircon U-Pb data indicate that at least a portion of the LCC beneath the central Slave craton has a Palaeoarchaean origin (~3.3?Ga), which apparently coincides with a period of juvenile crust and deep lithospheric mantle formation during plume impingement beneath the pre-existing cratonic nucleus. On the other hand, enrichment in Li, Sr, LREE, Pb and Th, but relative depletion in Ti, Hf and HREE, suggest formation of (picro)basaltic protoliths by partial melting of a subduction-modified garnet-bearing source, Crystallisation in the crust after fractionation of plagioclase is inidicated by their Sr and Eu negative anomalies, which are complementary to the positive anomalies in the MGG. Samarium-Nd isotopes in MBG and MGG show large scatter, but fall on Neo- or Mesoarchaean age arrays. These elemental systematics are suggested to fingerprint deserpentinisation fluids plus small amounts of sedimentary melt as the main contaminants of the mantle source, supporting the operation of at least regional and transient subduction at 3.3?Ga. Evidence for quasi-coeval plume impingement and subduction beneath the central Slave craton in the Mesoarchaean is reconcilable in a dynamic regime where vertical tectonics, though waning, was still active and plate interactions became increasingly important. Unradiogenic 87Sr/86Sr (down to 0.7017) is consistent with significant loss of Rb and probably other heat-producing elements (K, Th, U) plus H2O during Neoarchaean metamorphism, which helped to enhance LCC viscosity and stabilise the cratonic lithosphere.
DS201904-0716
2019
Aulbach, S., Tappe, S., Gerdes, A.Effects of multi-stage rifting and metasomatism on HSE-187Os/188Os systematic of the cratonic mantle beneath SW Greenland.Contributions to Mineralogy and Petrology, Vol. 174, 23p.Europe, Greenlandkimberlites

Abstract: We report highly siderophile element (HSE) abundances and Re-Os isotope compositions, obtained by isotope dilution inductively coupled plasma mass spectrometry, of olivine separates from a suite of multiply metasomatised peridotite xenoliths entrained in kimberlites from SW Greenland. Combined with petrographic and compositional observations on accessory base metal sulphides (BMS), the results reveal new insights into the chemical, physical and mineralogical effects of multi-stage rifting and associated melt percolation on the Archaean lithospheric mantle. Refertilised lherzolites are dominated by rare to frequent small (tens of µm) BMS inclusions in olivine, whereas modally metasomatised phlogopite-bearing lherzolite and wehrlites have higher proportions of more Ni-rich BMS, including abundant large interstitial grains (hundreds of µm). The olivine separates display depleted HSE systematics with Primitive Upper Mantle (PUM)-normalised Pd/Ir of 0.014-0.62, and have both depleted and enriched 187Os/188Os (0.1139-0.2724) relative to chondrite that are not correlated with 187Re/188Os. Four out of ten olivine separates retain similarly depleted Os corresponding to Re-depletion model ages of 2.1-1.8 Ga. They may reflect Palaeoproterozoic refertilisation (lherzolitisation) during Laurentia plate assembly, with re-introduction of clinopyroxene and Os-rich BMS into the originally refractory mantle lithosphere by asthenosphere-derived basaltic melts, followed by recrystallisation and occlusion in olivine. Unradiogenic Os is observed regardless of lithology, including from peridotites that contain abundant interstitial BMS. This reflects addition of Os-poor BMS (<
DS201912-2770
2019
Bachynski, R., Suchan, J., Suchan, D.Curiousity project - an update on a newly acquired diamondiferous kimberlite. LI-201 ( Ekati arena)Yellowknife Forum NWTgeoscience.ca, abstract Volume p. 5.Canada, Northwest Territoriesdeposit - Curiousity

Abstract: The Curiosity Property, located in the Slave Province to the southwest of Contwoyto Lake, is situated ~25 kilometers north of the Ekati Diamond Mine’s mineral rights. This newly acquired property hosts a known diamondiferous kimberlite, called “LI-201”, which was originally discovered in a 1997 diamond drill campaign. Multiple attempts have been made over the past twenty years to delineate the extent of the body using an assortment of traditional exploration methods, yet LI-201 continues to remain poorly understood in terms of its overall dimensions and diamond-bearing potential. As part of a ten-day exploration program in August 2019, 275 geochemical till samples and 170 biogeological samples were collected. Geochemical sampling along 100-meter spaced fences that are down-ice and approximately perpendicular to the main ice-flow direction were collected in an attempt to further prioritize key geophysical targets in the project area surrounding LI-201. In the vicinity of LI-201, geochemical and biogeological samples were collected as a pilot study in an attempt to investigate the potential microbial community’s response to the presence of kimberlite and to determine if a discernable relationship exists between soil geochemistry and microbial populations. Despite the inconclusive understanding of the kimberlitic body, historical samples of LI-201 show apparent geochemical endowment and bode well for the prospectivity of the project area as a whole. Currently, efforts are being made to compile, verify, and interpret historical data, in addition to integrating newly collected data and interpretations. At the time of presenting, only preliminary geochemical results will be available; microbiological results are pending. In the future, findings from this study will be used to assess the effectiveness of the microbiological method as a means of detecting the known footprint of LI-201, which may also offer insights to the true footprint of the kimberlitic body.
DS201902-0258
2018
Badro, J., Aubert, J., Hirose, K., Nomura, R., Blanchard, I., Borensztajn, S., Siebert, J.Magnesium partitioning between Earth's mantle and core and its potential to drive an early exsolution geodynamo.Geophysical Research Letters, Vol. 45, 24, pp. 13,240-13,248.Mantlegeodynamics

Abstract: We measure the incorporation of magnesium oxide (one of the main components of Earth's mantle) into iron (the main constituent Earth's core), using extremely high pressure and temperature experiments that mimic the conditions of Earth's mantle and core. We find that magnesium oxide dissolution depends on temperature but not on pressure, and on metal (i.e., core) composition but not silicate (i.e., mantle) composition. Our findings support the idea that magnesium oxide dissolved in the core during its formation will precipitate out during subsequent core cooling. The precipitation should stir the entire core to produce a magnetic field in Earth's distant past, at least as intense as the present-day field.
DS201909-2017
2019
Bai, T., Chen, W., Jiang, S-Y.Evolution of the carbonatite Mo-HREE deposits in the Lesser Qinling orogen: insights from in situ geochemical investigation of the calcite and sulfate. Huanglongpu, HuangshuianOre Geology Reviews, in press available, 38p. PdfChinacarbonatite
DS201907-1526
2019
Balaram, V.Rare earth elements: a review of applications, occurrence, exploration, analysis, recycling, and environmental impact.Geoscience Frontiers, Vol. 10, pp. 1285-1303.GlobalRare earths

Abstract: Rare earth elements (REE) include the lanthanide series elements (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) plus Sc and Y. Currently these metals have become very critical to several modern technologies ranging from cell phones and televisions to LED light bulbs and wind turbines. This article summarizes the occurrence of these metals in the Earth's crust, their mineralogy, different types of deposits both on land and oceans from the standpoint of the new data with more examples from the Indian subcontinent. In addition to their utility to understand the formation of the major Earth reservoirs, multi-faceted updates on the applications of REE in agriculture and medicine including new emerging ones are presented. Environmental hazards including human health issues due to REE mining and large-scale dumping of e-waste containing significant concentrations of REE are summarized. New strategies for the future supply of REE including recent developments in the extraction of REE from coal fired ash and recycling from e-waste are presented. Recent developments in individual REE separation technologies in both metallurgical and recycling operations have been highlighted. An outline of the analytical methods for their precise and accurate determinations required in all these studies, such as, X-ray fluorescence spectrometry (XRF), laser induced breakdown spectroscopy (LIBS), instrumental neutron activation analysis (INAA), inductively coupled plasma optical emission spectrometry (ICP-OES), glow discharge mass spectrometry (GD-MS), inductively coupled plasma mass spectrometry (including ICP-MS, ICP-TOF-MS, HR-ICP-MS with laser ablation as well as solution nebulization) and other instrumental techniques, in different types of materials are presented.
DS201902-0259
2019
Banerjee, A., Chakrabarti, R.A geochemical and Nd, Sr and stable Ca isotopic study of carbonatites and associated silicate rocks from the ~65 Ma old Ambadongar carbonatite complex and the Phenai Mata igneous complex, Gujarat, India: implications for crustal contamination, carbonate rLithos, in press available 56p.Indiacarbonatite

Abstract: Major, trace element concentrations and Nd, Sr and Ca stable isotopic compositions (d44/40Ca and d44/42Ca w.r.t. NIST SRM915a) of carbonatites and associated igneous silicate rocks from the ~65?Ma old Ambadongar carbonatite complex and the surrounding Phenai Mata igneous complex of western India are reported. Samples of fluorspar from Ambadongar and the Bagh Limestone and Sandstone, which are part of the country rocks at Ambadongar, have also been analysed. The Ambadongar carbonatites are primarily calcio- and ferro-carbonatites while the silicate rocks from these two complexes are alkaline and tholeiitic in composition. The d44/40Ca values of the carbonatites (0.58-1.1‰, n?=?7) and the associated igneous silicate rocks (0.50-0.92‰, n?=?14) show a broad range. The low K/Ca values of the carbonatites (<0.2) and silicate rocks (<2) along with their young eruption age (~65 Ma) rule out any effect of radiogenic 40Ca ingrowth due to decay of 40K on the d44/40Ca values. The lack of correlations between d44/40Ca and Mg# as well as La/Yb(N) values suggest that the variability in d44/40Ca is not controlled by the degree of partial melting. The d44/40Ca values of the carbonatites (0.58-1.1‰) overlap with that of the upper mantle/Bulk Silicate Earth and is mostly higher than the d44/40Ca value of the Bagh Limestone (0.66‰) suggesting that assimilation of these crustal limestones by the magma is unlikely to have caused the variability in d44/40Ca of the carbonatites. In plots of d44/40Ca versus eNd(t) and 87Sr/86Sr(t), the igneous silicate rocks from the Ambadongar and Phenai Mata complexes plot on a mixing trend between a primitive (plume) mantle source and the continental crustal basement suggesting the role of continental crustal contamination during eruption of the Reunion plume. While simple binary mixing calculations yield unrealistically high amounts of crustal contamination (40%), assimilation and fractional crystallization (AFC) models suggest up to 20% contribution from a heterogeneous basement for these igneous silicate rocks. The role of continental crustal contamination in the genesis of the igneous silicate rocks is further supported by their unradiogenic eNd(t), radiogenic 87Sr/86Sr(t) and low Ce/Pb values. In contrast, carbonatites plot away from the mixing trend between a primitive mantle (plume) source and continental crust in Ca-Sr-Nd isotopic diagrams suggesting that the Ca isotopic variability of carbonatites is not caused by continental crustal contamination. In contrast, the isotopic composition of the carbonatites can be explained by mixing of the plume end-member with up to 20% of ~160?Ma-old recycled carbonates suggesting their derivation from a highly heterogeneous, recycled carbonate-bearing plume mantle source. The composition of one carbonatite sample showing unusually high d44/40Ca and highly radiogenic 87Sr/86Sr(t) is explained by hydrothermal alteration which is also invoked for the formation of massive fluorspar deposits with high d44/40Ca (1.44‰) at Ambadongar. In a plot of d44/40Ca versus K/Rb, the carbonatites plot towards the phlogopite end-member (d44/40Ca?=?1‰, K/Rb?=?40-450) while the igneous silicate rocks plot towards the amphibole end-member (d44/40Ca?=?0.44‰, K/Rb >1000). Phlogopite, especially if F-rich, is stable at greater depths in the mantle compared to amphibole. Hence, the correlated d44/40Ca and K/Rb values of the carbonatites and associated igneous silicate rocks suggest the derivation of these carbonatites from a relatively deeper mantle source compared to the silicate rocks, both within the Reunion mantle plume. The origin of the carbonatites from the F-rich phlogopite-bearing mantle is also consistent with the occurrence of large fluorspar deposits within the Ambadongar carbonatite complex.
DS201902-0260
2019
Banerjee, A., Chakrabarti, R.A geochemical and Nd, Sr and stable Ca isotopic study of carbonatites and associated silicate rocks from the ~65 Ma old Ambadongar carbonatite complex and the Phenai Mata igneous complex, Gujarat, India: implications for crustal contamination, carbonate rLithos, Vol. 324, pp. 89-104.Africa, South Africadeposit - Ambadongar
DS201903-0498
2019
Banks, G.J., Walter, B.F., Marks, M.A.W., Siegfried, P.R.A workflow to define, map and name a carbonatite-alkaline igneous-associated REE-HFSE mineral system: a case study from SW Germany.MDPI, Vol. 9, 97, 28p. PdfGlobalREE

Abstract: Security of supply of “hi-tech” raw materials (including the rare earth elements (REE) and some high-field-strength elements (HFSEs)) is a concern for the European Union. Exploration and research projects mostly focus on deposit- to outcrop-scale description of carbonatite- and alkaline igneous-associated REE-HFSE mineralization. The REE-HFSE mineral system concept and approach are at a nascent stage, so developed further here. However, before applying the mineral system approach to a chosen REE-HFSE metallogenic province its mineral system extent first needs defining and mapping. This shifts a mineral system project’s foundation from the mineral system concept to a province’s mineral system extent. The mapped extent is required to investigate systematically the pathways and potential trap locations along which the REE-HFSE mass may be distributed. A workflow is presented to standardize the 4-D definition of a REE-HFSE mineral system at province-scale: (a) Identify and hierarchically organize a mineral system’s genetically related sub-divisions and deposits, (b) map its known and possible maximum extents, (c) name it, (d) discern its size (known mineral endowment), and (e) assess the favorability of the critical components to prioritize further investigations. The workflow is designed to generate process-based perspective and improve predictive targeting effectiveness along under-evaluated plays of any mineral system, for the future risking, comparing and ranking of REE-HFSE provinces and plays.
DS201909-2018
2019
Bannerjee, A., Chakrabarti, R.Geochemical and Nd-Sr-Ca isotopic compositions of carbonatites and alkaline igneous rocks from the Deccan Igneous Province: role of recycled carbonates, crustal assimilation and plume heterogeneity.Goldschmidt2019, 1p. AbstractIndiacarbonatite
DS201902-0261
2019
Baratoux, L., Soderlund, U., Ernst, R.E., de Roever, E., Jessell, M.W., Kamo, S., Naba, S., Perrouty, S., Metelka, V., Yatte, D., Grenholm, M., Diallo, D.P., Ndiaye, P.M., Dioh, E., Cournede, C., Benoit, M., Baratoux, D., Youbi, N., Rousse, S., BendaoudNew U-Pb baddeleyite ages of mafic dyke swarms of the West African and Amazonian cratons: implication for their configuration in supercontinents through time.Dyke Swarms of the World: a modern perspective, Srivastava et al. eds. Springer , pp. 263-314.Africa, West Africa, South Americageochronology

Abstract: Eight different generations of dolerite dykes crosscutting the Paleoproterozoic basement in West Africa and one in South America were dated using the high precision U-Pb TIMS method on baddeleyite. Some of the individual dykes reach over 300 km in length and they are considered parts of much larger systems of mafic dyke swarms representing the plumbing systems for large igneous provinces (LIPs). The new U-Pb ages obtained for the investigated swarms in the southern West African Craton (WAC) are the following (oldest to youngest): 1791?±?3 Ma for the N010° Libiri swarm, 1764?±?4 Ma for the N035° Kédougou swarm, 1575?±?5 for the N100° Korsimoro swarm, ~1525-1529 Ma for the N130° Essakane swarm, 1521?±?3 Ma for the N90° Sambarabougou swarm, 915?±?7 Ma for the N070° Oda swarm, 867?±?16 Ma for the N355° Manso swarm, 202?±?5 Ma and 198?±?16 Ma for the N040° Hounde swarm, and 200?±?3 Ma for the sills in the Taoudeni basin. The last ones are related to the Central Atlantic Magmatic Province (CAMP) event. The Hounde swarm is oblique to the dominant radiating CAMP swarm and may be linked with the similar-trending elongate Kakoulima intrusion in Guinea. In addition, the N150° Käyser swarm (Amazonian craton, South America) is dated at 1528?±?2 Ma, providing a robust match with the Essakane swarm in a standard Amazonia-West African craton reconstruction, and resulting in a combined linear swarm >1500 km by >1500 km in extent. The Precambrian LIP barcode ages of c. 1790, 1765-1750, 1575, 1520, 915. 870 Ma for the WAC are compared with the global LIP record to identify possible matches on other crustal blocks, with reconstruction implications. These results contribute to the refinement of the magmatic ‘barcode’ for the West African and Amazonian cratons, representing the first steps towards plausible global paleogeographic reconstructions involving the West African and Amazonian cratons.
DS201906-1270
2019
Barnett, M.J., Deady, E.A., Gregory, S.P., Palumbo-Roe, B.The role of biobased circular economy approach in sustainable critical metal extraction: the rare earth elements. Bioleaching3rd International Critical Metals Meeting held Edinburgh, Apr. 30-May 2.GlobalREE

Abstract: PDF link to presentation.
DS201906-1271
2019
Barry, P.H., de Moor, J.M., Giovannelli, D., Schrenk, M., Hummer, D.R., Lopez, T., Pratt, C.A., Alpizar Segua, Y., Battaglia, A., Beaudry, A., Bini, G., Cascante, M., d'Errico, G., di Carlo, M., Fattorini, D., Fullerton, K., H+Gazel, E., Gonzalez, G., HalForearc carbon sink reduces long term volatile recycling into the mantle.Nature , 588, 7753, p. 487.Mantlecarbon

Abstract: Carbon and other volatiles in the form of gases, fluids or mineral phases are transported from Earth’s surface into the mantle at convergent margins, where the oceanic crust subducts beneath the continental crust. The efficiency of this transfer has profound implications for the nature and scale of geochemical heterogeneities in Earth’s deep mantle and shallow crustal reservoirs, as well as Earth’s oxidation state. However, the proportions of volatiles released from the forearc and backarc are not well constrained compared to fluxes from the volcanic arc front. Here we use helium and carbon isotope data from deeply sourced springs along two cross-arc transects to show that about 91 per cent of carbon released from the slab and mantle beneath the Costa Rican forearc is sequestered within the crust by calcite deposition. Around an additional three per cent is incorporated into the biomass through microbial chemolithoautotrophy, whereby microbes assimilate inorganic carbon into biomass. We estimate that between 1.2 × 108 and 1.3 × 1010 moles of carbon dioxide per year are released from the slab beneath the forearc, and thus up to about 19 per cent less carbon is being transferred into Earth’s deep mantle than previously estimated.
DS201910-2244
2019
Basu, U., Powell, C.Pn tomography and anisotropy study of the Central United States.Journal of Geophysical Research: Solid Earth, Vol. 124, 7, pp. 7105-7119.United Statesgeophysics - seismic

Abstract: Detailed P wave velocity and anisotropy structure of the uppermost mantle below the central United States is presented based on a tomographic inversion of Pn traveltimes for earthquakes in the range 2 to 14°. Dense raypath coverage throughout the northern Mississippi Embayment is obtained using the Northern Embayment Lithosphere Experiment and U.S. Transportable Array data sets. A detailed analysis of the trade-off between velocity and anisotropy variations demonstrates that both are well resolved over most of the study area. Anomalously fast Pn velocities are identified below the northern Mississippi Embayment, centered on the New Madrid seismic zone. A prominent region of low velocity coincides with the southwestern margin of the Illinois basin. Pn anisotropy displays complex patterns and differs from absolute plate motion directions and SKS splitting directions. A circular pattern of fast anisotropy directions is centered on the New Madrid seismic zone and may be related to the presence of the mafic “rift pillow.”
DS201909-2019
2019
Bataleva, Y., Palyanov, Y., Borzdov, Y., Bayukov, O.Processes and conditions of the origin of Fe3+- bearing magnesiowustite under lithospheric mantle pressures and temperatures.Minerals, Vol. 9, 8, p. 474-MantleUHP

Abstract: An experimental study, implicated in the revealing of the conditions for the origin for Fe3+-bearing magnesiowüstite in the lithospheric mantle, was performed using Mössbauer spectroscopy of pre-synthesized samples. Experiments were carried out using a multi-anvil high-pressure split-sphere apparatus at 6.3-7.5 GPa, in the range of 1100-1650 °C in carbonate-metal, carbonate-oxide-metal, carbonate-oxide, carbide-oxide and carbonate-metal- sulphur systems. In three experimental series, oxygen fugacity gradient in the samples was created, which enabled the study of the processes of magnesiowüstite formation under oxidizing and reducing conditions (?logfO2 (FMQ) values from -1 to -5). It was established that Fe3+-bearing magnesiowüstite can form both in assemblage with oxidized phases, such as carbonate or with reduced ones—metal, carbides, sulphides, graphite and diamond. According to the Mössbauer spectroscopy, the composition of synthesized magnesiowüstite varied within a range of Fe3+/SFe values from 0 to 0.3, with IV and VI coordination of Fe3+ depending on P, T, fO2, x-parameters. It was established that Fe3+-bearing magnesiowüstite formation processes under upper mantle P,T-conditions include redox reactions, with magnesiowüstite being (1) reductant or (2) product of interaction, (3) crystallization processes of magnesiowüstite from an oxidized melt, where magnesiowüstite acts as a sink for ferric iron and (4) iron disproportionation.
DS201905-1016
2019
Bataleva, Y.V., Palyanov, Y.N., Borzdov, Y.M., Novoselov, I.D., Bayukov, O.A.An effect of reduced S-rich fluids on diamond formation under mantle- slab interaction.Lithos, Vol. 336-337, pp. 27-39.Mantlediamond genesis

Abstract: Experimental study, dedicated to understanding the effect of S-rich reduced fluids on the diamond-forming processes under subduction settings, was performed using a multi-anvil high-pressure split-sphere apparatus in Fe3C-(Mg,Ca)CO3-S and Fe0-(Mg,Ca)CO3-S systems at the pressure of 6.3?GPa, temperatures in the range of 900-1600?°C and run time of 18-60?h. At the temperatures of 900 and 1000?°C in the carbide-carbonate-sulfur system, extraction of carbon from cohenite through the interaction with S-rich reduced fluid, as well as C0-producing redox reactions of carbonate with carbide were realized. As a result, graphite formation in assemblage with magnesiowüstite, cohenite and pyrrhotite (±aragonite) was established. At higher temperatures (=1100?°C) formation of assemblage of Fe3+-magnesiowüstite and graphite was accompanied by generation of fO2-contrasting melts - metal-sulfide with dissolved carbon (Fe-S-C) and sulfide-oxide (Fe-S-O). In the temperature range of 1400-1600?°C spontaneous diamond nucleation was found to occur via redox interactions of carbide or iron with carbonate. It was established, that interactions of Fe-S-C and Fe-S-O melts as well as of Fe-S-C melt and magnesiowüstite, were ?0-forming processes, accompanied by disproportionation of Fe. These resulted in the crystallization of Fe3+-magnesiowüstite+graphite assemblage and growth of diamond. We show that a participation of sulfur in subduction-related elemental carbon-forming processes results in sharp decrease of partial melting temperatures (~300?°C), reducting the reactivity of the Fe-S-C melt relatively to FeC melt with respect to graphite and diamond crystallization and decrease of diamond growth rate.
DS201906-1272
2019
Bataleva, Y.V., Palyanov, Y.N., Borzdov, Y.M., Novoselov, I.D., Bayukov, O.A.An effect of reduced S rich fluids on diamond formation under mantle-slab interaction.Lithos, Vol. 336-337, pp. 27-39.Mantlediamond genesis

Abstract: Duplicate
DS201901-0006
2018
Bataleva, Yu.V., Palyanov, Yu.N., Borzdov, Yu.M., Bayukov, O.A., Sobolev, N.V.Experiment al modeling of Co forming processes involving cohenite and CO2 fluid in a silicate mantle.Doklady earth Sciences, Vol. 483, 1, pp. 1427-1430.Mantlepetrology

Abstract: Experimental studies were performed in the Fe3C-SiO2-(Mg,Ca)CO3 system (6.3 GP?, 1100-1500°C, 20-40 h). It is established that the carbide-oxide-carbonate interaction leads to the formation of ferrosilite, fayalite, graphite, and cohenite (1100 and 1200°?), as well as a Fe-C melt (1300°?). It is determined that the main processes in the system are decarbonation, redox-reactions of cohenite and a CO2-fluid, extraction of carbon from carbide, and crystallization of metastable graphite (± diamond growth), as well as the formation of ferriferous silicates. The interaction studied can be considered as a simplified model of the processes that occur during the subduction of oxidized crustal material to reduced mantle rocks.
DS201901-0007
2018
Bataleva, Yu.V., Palyanov, Yu.N., Borzdov, Yu.M., Novoselov, I.D., Bayukov, O.A., Sobolev, N.V.Conditions of formation of iron-carbon melt inclusions in garnet and orthopyroxene under P-T conditions of lithospheric mantle.Petrology, Vol. 26, 6, pp. 565-574.Mantlemetasomatism

Abstract: Of great importance in the problem of redox evolution of mantle rocks is the reconstruction of scenarios of alteration of Fe°- or Fe3C-bearing rocks by oxidizing mantle metasomatic agents and the evaluation of stability of these phases under the influence of fluids and melts of different compositions. Original results of high-temperature high-pressure experiments (P = 6.3 GPa, T = 1300-1500°?) in the carbide-oxide-carbonate systems (Fe3C-SiO2-(Mg,Ca)CO3 and Fe3C-SiO2-Al2O3-(Mg,Ca)CO3) are reported. Conditions of formation of mantle silicates with metallic or metal-carbon melt inclusions are determined and their stability in the presence of CO2-fluid representing the potential mantle oxidizing metasomatic agent are estimated. It is established that garnet or orthopyroxene and CO2-fluid are formed in the carbide-oxide-carbonate system through decarbonation, with subsequent redox interaction between CO2 and iron carbide. This results in the formation of assemblage of Fe-rich silicates and graphite. Garnet and orthopyroxene contain inclusions of a Fe-C melt, as well as graphite, fayalite, and ferrosilite. It is experimentally demonstrated that the presence of CO2-fluid in interstices does not affect on the preservation of metallic inclusions, as well as graphite inclusions in silicates. Selective capture of Fe-C melt inclusions by mantle silicates is one of the potential scenarios for the conservation of metallic iron in mantle domains altered by mantle oxidizing metasomatic agents.
DS201907-1527
2019
Batanova, V.G., Thompson, J.M., Danyushevsky, L.V., Portnyagin, M.V., Garbe-Schonberg, D., Hauri, E., Kimura, J-I., Chang, Q., Senda, R., Goemann, K., Chauvel, C., Campillo, S., Ionov, D.A., Sobolev,A.V.New olivine reference material for in situ microanalysis.Geostandards and Geoanalytical Research, in press available, 21p.Asia, Mongoliaolivine

Abstract: A new olivine reference material - MongOL Sh11-2 - for in situ analysis has been prepared from the central portion of a large (20 × 20 × 10 cm) mantle peridotite xenolith from a ~ 0.5 My old basaltic breccia at Shavaryn-Tsaram, Tariat region, central Mongolia. The xenolith is a fertile mantle lherzolite with minimal signs of alteration. Approximately 10 g of 0.5-2 mm gem quality olivine fragments were separated under binocular microscope and analysed by EPMA, LA-ICP-MS, SIMS and bulk analytical methods (ID-ICP-MS for Mg and Fe, XRF, ICP-MS) for major, minor and trace elements at six institutions world-wide. The results show that the olivine fragments are sufficiently homogeneous with respect to major (Mg, Fe, Si), minor and trace elements. Significant inhomogeneity was revealed only for phosphorus (homogeneity index of 12.4), whereas Li, Na, Al, Sc, Ti and Cr show minor inhomogeneity (homogeneity index of 1-2). The presence of some mineral and fluid-melt micro-inclusions may be responsible for the inconsistency in mass fractions obtained by in situ and bulk analytical methods for Al, Cu, Sr, Zr, Ga, Dy and Ho. Here we report reference and information values for twenty-seven major, minor and trace elements.
DS201909-2020
2019
Baudouin, C., France, L., Boulanger, M., Dalou, C., Devidal, J-L.New constraints on trace element partitioning between minerals and alkaline melts.Goldschmidt2019, 1p. AbstractGlobalalkaline rocks
DS201911-2509
2019
Baziotis, I., Xydous, S., Asimow, P.D., Mavrogonatos, C., Flemetakis, S., Klemme, S., Berndt, J.The potential of phosphorous in clinopyroxene as a geospeedometer: examples from mantle xenoliths.Geochimica et Cosmochimica Acta, Vol. 266, pp. 307-311.United States, California, Africa, Moroccometasomatism

Abstract: We investigate the potential to use concentrations and zoning patterns of phosphorus (P) in clinopyroxene as indicators of the rates of igneous and metasomatic processes, comparable to recent applications of P in olivine but applicable to more evolved rocks and lower temperatures of crystallization. Few high-P pyroxenes have been previously reported, and none have been analyzed in detail for the mechanism of P enrichment or the implications for mineral growth kinetics. Here, we report the discovery and characteristics of exotic phosphorus-rich secondary clinopyroxene in glassy pockets and veins in composite mantle xenoliths from the Cima Volcanic Field (California, USA) and the Middle Atlas Mountains (Morocco, West Africa). These glass-bearing xenoliths preserve evidence of melt infiltration events and the contrasting behavior of P in their pyroxene crystals constrains the different rates of reaction and extents of equilibration that characterized infiltration in each setting. We report optical petrography and chemical analysis of glasses and minerals for major elements by electron microprobe microanalyzer and trace elements by laser-ablation Inductively Coupled Plasma Mass Spectrometry. The Cima Volcanic Field specimen shows one end-member behavior, with unzoned P-rich clinopyroxene in a melt pocket. We attribute this occurrence to a slow crystallization process that occurred after the melt temperature reached near-equilibrium with the host rock and during which the P concentration in the melt was buffered by apatite saturation. In the Morocco xenolith, by contrast, clinopyroxene exhibits zonation with P increasing all the way to the rim, in contact with the glass. We ascribe this feature to a rapid growth process in which excess P was incorporated into the growing clinopyroxene from a diffusive boundary layer. We demonstrate quantitative agreement between the enrichment of P and other trace elements and their expected diffusion and partitioning behavior during rapid growth. We suggest that P has not been widely reported in clinopyroxene in large part because it has rarely been looked for and that its analysis offers considerable promise as a kinetic indicator both in xenoliths and volcanic rocks.
DS201909-2021
2019
Beard, C.D., Goodenough, K.M., Broom-Findlay, S., Borst, A.M., Roberts, N.M.W., Finch, A.A., Deady, E.A.Subducted sediments as a source of REE in mineralized post - collisional alkaline carbonatite systems.Goldschmidt2019, 1p. AbstractChinasubduction

Abstract: Many of the world's largest known REE deposits are associated with post-collisional alkaline-carbonatite magmatic complexes (e.g., the Minanning-Dechang belt, China). These systems are potassic to ultrapotassic in composition and contain LREE-dominated mineralisation associated with F and Ba-rich carbonatite breccias, carbonatite dykes and carbo-hydrothermal veins. They are typically emplaced through major shear zones during a period of 'relaxation' that postdates continental collision by up to 75 Ma. The subduction of sediment during continental collision is potentially a key control on the 'fertility' of the mantle source, and understanding the role of sediment is a crucial step towards better exploration models. However, the identification of sediment source components to alkaline systems has not been straightforward because their petrological complexity precludes traditional methods such as trace-element ratios and major-element modelling of crystal fractionation. We use a global database of Sr, Nd and Hf isotope compositions for alkaline and carbonatite systems, alongside geodynamic reconstructions to identify favourable source components for mineralisation and to provide direct information about the origin of the metals of interest. Subduction of shale and carbonate sequences is likely to introduce REE + HFSE and potentially mineralising ligands (F-, CO3 2-) into the mantle source for post-collisional alkaline systems; clastic sediments are poorer in these vital components. This research provides a framework through which the mineral exploration industry can identify tectonic environments that are predisposed to form REE mineralisation, providing regional-scale (100-1000 km) guidance especially for systems hidden beneath sedimentary cover.
DS201906-1273
2019
Beard, C.D., Goodenough, K.M., Deady, E.A.Deposit scale geomodels for REE and HFSE exploration in carbonatite and alkaline silicate magmatic systems.3rd International Critical Metals Meeting held Edinburgh, 1p.abstract p. 39.GlobalREE

Abstract: PDF link to presentation.
DS201911-2510
2019
Beaussier, S.J., Gerya, T.V., Burg, J-P.3D numerical modelling of the Wilson cycle: structural inheritance of alternating subduction polarity.N: Cycle Concepts in Plate Tectonics, editors Wilson and Houseman , Geological Society of London special publication 470, 439-461.Mantleplate tectonics

Abstract: Alternating subduction polarity along suture zones has been documented in several orogenic systems. Yet the mechanisms leading to this geometric inversion and the subsequent interplay between the contra-dipping slabs have been little studied. To explore such mechanisms, 3D numerical modelling of the Wilson cycle was conducted from continental rifting, breakup and oceanic spreading to convergence and self-consistent subduction initiation. In the resulting models, near-ridge subduction initiating with the formation of contra-dipping slab segments is an intrinsically 3D process controlled by earlier convergence-induced ridge swelling. The width of the slab segments is delimited by transform faults inherited from the rifting and ocean floor spreading stages. The models show that the number of contra-dipping slab segments depends mainly on the size of the oceanic basin, the asymmetry of the ridge and variations in kinematic inversion from divergence to convergence. Convergence velocity has been identified as a second-order parameter. The geometry of the linking zone between contra-dipping slab segments varies between two end-members governed by the lateral coupling between the adjacent slab segments: (1) coupled slabs generate wide, arcuate linking zones holding two-sided subduction; and (2) decoupled slabs generate narrow transform fault zones against which one-sided, contra-dipping slabs abut.
DS201906-1274
2019
Bedard, L.P., Desjardins, D., Matton, G.The importance of syenite enclaves in the evolution of the Saint-Honore alkaline complex.GAC/MAC annual Meeting, 1p. Abstract p. 60.Canada, QuebecCarbonatite

Abstract: The Saint-Honoré alkaline complex located near the Saguenay River (Grenville Province, Québec) has a syenite outer rim and concentric units of calcio-, magnesio- to ferro-carbonatite moving towards the centre. The Mg-carbonatite hosts a niobium deposit, and the Fe-carbonatite hosts a rare earth-rich zone at its centre. The Nb mineralization has a close spatial relationship to the syenite enclaves suggesting that the syenites may have played a critical role in concentrating the pyrochlore (Pcl). There are two forms of Nb mineralization: high- and low-grade. Low-grade mineralization is characterized by highly variable Pcl chemistry with higher U concentrations and a low abundance of fluoroapatite (Ap), whereas high-grade mineralization has a consistent Pcl chemistry (low-U), abundant Ap (with many acicular crystals) and more abundant phlogopite and magnetite. Some of the Pcl crystals have been altered to columbite by hydrothermal processes. It is interpreted that the metamict Pcl (rich in radioactive elements) was altered more readily than the Pcl having undamaged crystal structure. The high-grade mineralization is generally located near the syenite enclaves. Syenite enclaves (from a centimetre scale to several tens of metres in size) reacted with the carbonatite magma to produce a phlogopite rim. Ap is also abundant along the immediate contact between the enclaves and Mg-carbonatite. Large enclaves show hydro-fracturing by the carbonatite suggesting they were crystalline enough to be brittle. There are smaller textures (3-6 mm in diameter) that share many similarities with the syenite enclaves; however, these textures are rounded and could be interpreted as being related to liquid immiscibility. The interaction of carbonatite magma with syenite enclaves is interpreted to have started with abundant crystallization of acicular Ap which depleted the magma in F and lowered the magma's Nb-solubility. Pcl then crystallized in abundance in the vicinity of the syenite enclaves to create the economic Nb-rich zone.
DS201908-1770
2019
Behr, W.Role of major erosion events in Earth's dynamics.Nature , Vol. 570, 7759 pp. 38-39.Mantlegeomorphology

Abstract: A study provides evidence for the unconventional idea that the advent and evolution of plate tectonics on Earth were related to the rise of continents and to sediment accumulation at continental edges and in trenches.
DS201908-1771
2019
Behr, W.Sediment control on subduction plate speeds.Nature , Vol. 570, 7759, p. 38.Mantlesubduction

Abstract: Tectonic plate velocities predominantly result from a balance between the potential energy change of the subducting slab and viscous dissipation in the mantle, bending lithosphere, and slab-upper plate interface. A range of observations suggest that slabs may be weak, implying a more prominent role for plate interface dissipation than previously thought. The shallow thrust interface is commonly assumed to be weak due to an abundance of fluids and near-lithostatic pore fluid pressures, but little attention has been paid to the influence of the deeper, viscous interface. Here we show that the deep interface viscosity in subduction zones is strongly affected by the relative proportions of sedimentary to mafic rocks that are subducted to depth. Where sediments on the down-going plate are sparse, the deep interface is dominated by mafic lithologies that metamorphose to eclogites, which exhibit viscosities 1-2 orders of magnitude higher than the asthenospheric mantle, and reduce subduction plate speeds. In contrast, where sediments are abundant and subducted to depth, the deep interface viscosity is 1-2 orders of magnitude lower than the asthenospheric mantle, thus allowing significantly faster plate velocities. This correlation between subduction plate speed and deep sediment subduction may help explain dramatic accelerations (or decelerations) in convergence rates, such as the acceleration documented for India-Asia convergence during the mid-Cenozoic.
DS201911-2511
2019
Benaouda, R., Kraemer, D., Sitnikova, M., Goldmann, S., Bau, M.Thorium poor monzonite and columbite (Fe) mineralization in the Giebat Lafhouda carbonatite and its associated iron-oxide deposit of the Ouled Dlim Massif, south Morocco.Gondwana Research, Vol. 77, pp. 19-39.Africa, Moroccocarbonatite

Abstract: Recent exploration work in South Morocco revealed the occurrence of several carbonatite bodies, including the Paleoproterozoic Gleibat Lafhouda magnesiocarbonatite and its associated iron oxide mineralization, recognized here as iron-oxide-apatite (IOA) deposit type. The Gleibat Lafhouda intrusion is hosted by Archean gneiss and schist and not visibly associated with alkaline rocks. Metasomatized micaceous rocks occur locally at the margins of the carbonatite outcrop and were identified as glimmerite fenite type. Rare earth element (REE) and Nb mineralization is mainly linked to the associated IOA mineralization and is represented by monazite-(Ce) and columbite-(Fe) as major ore minerals. The IOA mineralization mainly consists of magnetite and hematite that usually contain large apatite crystals, quartz and some dolomite. Monazite-(Ce) is closely associated with fluorapatite and occurs as inclusions within the altered parts of apatite and along cracks or as separate phases near apatite. Monazite shows no zonation patterns and very low Th contents (<0.4?wt%), which would be beneficial for commercial extraction of the REE and which indicates monazite formation from apatite as a result of hydrothermal volatile-rich fluids. Similar monazite-apatite mineralization and chemistry also occurs at depth within the carbonatite, although the outcropping carbonatite is barren, suggesting an irregular REE ore distribution within the carbonatite body. The barren carbonatite contains some tiny unidentified secondary Nb-Ta-U phases, synchysite and monazite. Niobium mineralization is commonly represented by anhedral minerals of columbite-(Fe) which occur closely associated with magnetite-hematite and host up to 78?wt% Nb2O5, 7?wt% Ta2O5 and 1.6?wt% Sc2O3. This association may suggest that columbite-(Fe) precipitated by an interaction of Nb-rich fluids with pre-existing Fe-rich minerals or as pseudomorphs after pre-existing Nb minerals like pyrochlore. Our results most strongly suggest that the studied mineralization is economically important and warrants both, further research and exploration with the ultimate goal of mineral extraction.
DS201909-2022
2019
Benaouda, R., Kraemer, D., Sitnikova, M., Goldmann, S., Freitag, R., Bouali, A., Mouttaqi, A., El Haloui, R., Essaadaoui, M., Bau, M.Thorium-poor monazite and columbite-(Fe) mineralization in the Gleibat Lafhouda carbonatite and its associated iron-oxide-apatite deposit of the Ouled Dlim Massif, South Morocco.Gondwana Research, Vol. 77, pp. 19-39.Africa, MoroccoREE

Abstract: Recent exploration work in South Morocco revealed the occurrence of several carbonatite bodies, including the Paleoproterozoic Gleibat Lafhouda magnesiocarbonatite and its associated iron oxide mineralization, recognized here as iron-oxide-apatite (IOA) deposit type. The Gleibat Lafhouda intrusion is hosted by Archean gneiss and schist and not visibly associated with alkaline rocks. Metasomatized micaceous rocks occur locally at the margins of the carbonatite outcrop and were identified as glimmerite fenite type. Rare earth element (REE) and Nb mineralization is mainly linked to the associated IOA mineralization and is represented by monazite-(Ce) and columbite-(Fe) as major ore minerals. The IOA mineralization mainly consists of magnetite and hematite that usually contain large apatite crystals, quartz and some dolomite. Monazite-(Ce) is closely associated with fluorapatite and occurs as inclusions within the altered parts of apatite and along cracks or as separate phases near apatite. Monazite shows no zonation patterns and very low Th contents (<0.4?wt%), which would be beneficial for commercial extraction of the REE and which indicates monazite formation from apatite as a result of hydrothermal volatile-rich fluids. Similar monazite-apatite mineralization and chemistry also occurs at depth within the carbonatite, although the outcropping carbonatite is barren, suggesting an irregular REE ore distribution within the carbonatite body. The barren carbonatite contains some tiny unidentified secondary Nb-Ta-U phases, synchysite and monazite. Niobium mineralization is commonly represented by anhedral minerals of columbite-(Fe) which occur closely associated with magnetite-hematite and host up to 78?wt% Nb2O5, 7?wt% Ta2O5 and 1.6?wt% Sc2O3. This association may suggest that columbite-(Fe) precipitated by an interaction of Nb-rich fluids with pre-existing Fe-rich minerals or as pseudomorphs after pre-existing Nb minerals like pyrochlore. Our results most strongly suggest that the studied mineralization is economically important and warrants both, further research and exploration with the ultimate goal of mineral extraction.
DS201907-1528
2019
Bercovici, D., Mulyukova, E., Long, M.D.A simple toy model for coupled retreat and detachment of subducting slabs.Journal of Geodynamics, in press available, 15p.Mantleconvection

Abstract: Subducting slabs are the primary drivers of plate tectonics and mantle circulation, but can also undergo various instabilities that cause dramatic adjustments in tectonic evolution and motion. Slab rollback or trench retreat is possibly a dominant form of time dependence in the plate-mantle system, causing plates to shrink and the mantle to undergo complex flow patterns. Likewise, slab detachment can induce abrupt adjustments in both plate motions and vertical displacement of continents. The arrival or accumulation of continental crust over a subduction zone induces high stresses on the plate and slab that can trigger either rollback or detachment or both. However, these processes necessarily interact because of how stress is relieved and plate motions altered. Here we present a simple boundary-layer like model of coupled trench retreat and slab detachment, induced by continent accumulation, and with slab necking augmented by grain-damage self-weakening (to allow for abrupt necking). With this model we find that, with continental accumulation, initial rollback is at first modest. However, as the stress from continental accumulation peaks, it triggers abrupt slab detachment. The subsequent slab loss causes the plate to lose its primary motive force and to thus undergo a more dramatic and rapid rollback event. After the larger rollback episode, the contracted continental mass re-expands partially. Plausible grain-damage parameters and 40?km thick crust cause abrupt detachment and major rollback to occur after a few hundred million years, which means the plates remain stable for that long, in agreement with the typical age for most large plates. While the complexity of some field areas with a well documented history of detachment and rollback, such as the Mediterranean, taxes the sophistication of our toy model, other simpler geological examples, such as on the western North American plate, show that episodes of rollback can follow detachment.
DS201907-1529
2017
Berman, N., Couttenir, M., Rohner, D., Thoenig, M.This mine is mine! How minerals fuel conflict in Africa.American Economic Review, Vol. 107, 6, pp. 1564-1610. pdfAfricalegal

Abstract: We combine georeferenced data on mining extraction of 14 minerals with information on conflict events at spatial resolution of 0.5 degree x 0.5 degree for all of Africa between 1997 and 2010. Exploiting exogenous variations in world prices, we find a positive impact of mining on conflict at the local level. Quantitatively, our estimates suggest that the historical rise in mineral prices (commodity super-cycle) might explain up to one-fourth of the average level of violence across African countries over the period. We then document how a fighting group's control of a mining area contributes to escalation from local to global violence. Finally, we analyze the impact of corporate practices and transparency initiatives in the mining industry.
DS201912-2771
2019
Berrub, M.Diavik traditional knowledge panel.Yellowknife Forum NWTgeoscience.ca, abstract Volume p. 7.Canada, Northwest Territoriesdeposit - Diavik

Abstract: Diavik has a robust communities portfolio to ensure that our impacted communities are informed and trusted partners in the success of our operation. The Diavik Traditional Knowledge Panel has been in place since 2012 as a resource for developing and providing recommendations on a variety of operational and closure details. The Panel is comprised of a male elder, a female elder and a youth from each of the five Participation Agreement communities and, to date, have made 194 recommendations. Diavik will present on the benefits and opportunities that are created when we utilize traditional knowledge in our operations.
DS201906-1275
2019
Biemiller, J., Ellis, S., Mizera, M., Little, T., Wallace, L., Lavier, L.Tectonic inheritance following failed continental subduction: a model for core complex formation in cold, strong lithosphere.Tectonics, in press available, 22p.Mantlesubduction

Abstract: Inherited structural, compositional, thermal, and mechanical properties from previous tectonic phases can affect the deformation style of lithosphere entering a new stage of the Wilson cycle. When continental crust jams a subduction zone, the transition from subduction to extension can occur rapidly, as is the case following slab breakoff of the leading subducted oceanic slab. This study explores the extent to which geometric and physical properties of the subduction phase affect the subsequent deformation style and surface morphology of post subduction extensional systems. We focus on regions that transition rapidly from subduction to extension, retaining lithospheric heterogeneities and cold thermal structure inherited from subduction. We present numerical models suggesting that following failed subduction of continental crust (with or without slab breakoff), the extensional deformation style depends on the strength and dip of the preexisting subduction thrust. Our models predict three distinct extensional modes based on these inherited properties: (1) reactivation of the subduction thrust and development of a rolling-hinge detachment that exhumes deep crustal material in a domal structure prior to onset of an asymmetric rift; (2) partial reactivation of a low-angle subduction thrust, which is eventually abandoned as high-angle, “domino”-style normal faults cut and extend the crust above the inherited thrust; and (3) no reactivation of the subduction fault but instead localized rifting above the previous subduction margin as new rift-bounding, high-angle normal faults form. We propose that the first mode is well exemplified by the young, rapidly exhumed Dayman-Suckling metamorphic core complex that is exhuming today in Papua New Guinea.
DS201912-2772
2019
Bilak, G.S., Cummings, D., Elliott, B.Investigating the nature and origin of the Exeter Lake esker and its application in mineral exploration; a preliminary report.Yellowknife Forum NWTgeoscience.ca, abstract volume p. 9-10.Canada, Northwest Territorieseskers

Abstract: Eskers are long ridges of glaciofluvial sand and gravel frequently sampled during mineral exploration campaigns. Sampling of the 700 km long Exeter Lake esker by Chuck Fipke and Stu Blusson in the 1980s led directly to the discovery of the Lac De Gras kimberlite field and establishment of the diamond industry in the Northwest Territories. Despite their significant role in mineral exploration, the details surrounding eskers formation remain controversial (e.g. long-conduit vs. short-conduit models). In my coming research I will use a combination of geomorphological and provenance data to gain insight into the nature of the Exeter Lake esker and the origin of its sediment to help further define the parameters surrounding esker formation and their application in the mining industry. The geomorphology of the esker will be characterized in ArcMap using (1) the new Arctic DEM (2 m resolution), supplemented by (2) aerial imagery (3) GoPro footage of the entire esker collected during a low-level fly-over, (4) ground observations and short foot traverses made at regularly spaced intervals, and (5) locally collected drone footage. Morpho-sedimentary building block elements of the esker system will be identified and interpreted. Esker provenance will be studied using two sample suites. The first suite (112 samples) was collected at coarsely spaced intervals (15-20 km) along the entire length of the esker and contains pared till and esker-ridge samples from both the pebble and finer fractions. These samples will be used to ascertain whether dispersal trains—such as those emanating from the Dubawnt Supergroup—extend the entire length of the esker, considerably overshooting the till dispersal trains from which they were sourced, or whether they are more local in scale. Mud fractions (<63 microns) will be analyzed geochemically; this fraction has never been analyzed previously in similar studies, but could be more indicative of subglacial stream length. Zircon grains from the sand fraction will be analyzed using uranium-lead dating and correlated to diversely aged rock units along the esker system. Finally, the lithology of the pebbles will be analyzed and compared against previously mapped bedrock lithologies along the esker transect. The second suite (62 samples) was collected at closely spaced intervals (300-600 m) from various geomorphological expressions of the greater esker system near the edge of the Lac de Gras kimberlite indicator mineral (KIM) plume, as defined in the KIDD database. KIM concentrations from the samples will be compared with one another, and if the KIM train in the esker considerably overshoots that in the till, a long-conduit model may be more likely. Additionally, by comparing multiple expressions of the esker system any bias in the concentration of KIMs should be detected. Due to the novel approach and large dataset this study has the potential to provide considerable insight into the nature of esker systems and how they are deposited. With this knowledge, mining and exploration companies will be able reassess their esker datasets backed by a scientifically robust exploration model.
DS201906-1276
2019
Bindi, L., Camara, F., Griffin, W.L., Huang, J-X., Gain, S.E.M., Toledo, V., O'Reilly, S.Y.Discovery of the first natural hydride. Mt. CarmelAmerican Mineralogist, Vol. 104, pp. 611-614.Europe, Israelcrystallography

Abstract: Although hydrogen is the most abundant element in the solar system, the mechanisms of exchange of this element between the deep interior and surface of Earth are still uncertain. Hydrogen has profound effects on properties and processes on microscopic-to-global scales. Here we report the discovery of the first hydride (VH2) ever reported in nature. This phase has been found in the ejecta of Cretaceous pyroclastic volcanoes on Mt Carmel, N. Israel, which include abundant xenoliths containing highly reduced mineral assemblages. These xenoliths were sampled by their host magmas at different stages of their evolution but are not genetically related to them. The xenoliths are interpreted as the products of extended interaction between originally mafic magmas and CH4+H2 fluids, derived from a deeper, metal-saturated mantle. The last stages of melt evolution are recorded by coarse-grained aggregates of hibonite (CaAl12O19) + grossite (CaAl4O7) + V-rich spinels ± spheroidal to dendritic inclusions of metallic vanadium (V0), apparently trapped as immiscible metallic melts. The presence of V0 implies low oxygen fugacities and suggests crystallization of the aggregates in a hydrogen-rich atmosphere. The presence of such reducing conditions in the upper mantle has major implications for the transport of carbon, hydrogen and other volatile species from the deep mantle to the surface.
DS201911-2512
2019
Black, B.A., Gibson, S.A.Deep carbon and the life cycle of large igneous provinces.Elements, Vol. 15, pp. 319-324.Mantlecarbon

Abstract: Carbon is central to the formation and environmental impact of large igneous provinces (LIPs). These vast magmatic events occur over geologically short timescales and include voluminous flood basalts, along with silicic and low-volume alkaline magmas. Surface outgassing of CO2 from flood basalts may average up to 3,000 Mt per year during LIP emplacement and is subsidized by fractionating magmas deep in the crust. The large quantities of carbon mobilized in LIPs may be sourced from the convecting mantle, lithospheric mantle and crust. The relative significance of each potential carbon source is poorly known and probably varies between LIPs. Because LIPs draw on mantle reservoirs typically untapped during plate boundary magmatism, they are integral to Earth’s long-term carbon cycle.
DS201901-0008
2018
Blank, V.D., Churkin, V.D., Kulnitsky, B.A., Perezhogin, I.A., Kirichenko, A.N., Erohin, S.V., Sorokin, P.B., Popov, M.Y.Pressure induced transformation of graphite and diamond to onions.Crystals MDPI, Vol. 8, 2, 8p. Doi.org/10.3390/cryst8020068Russiacarbon nanotubes

Abstract: In this study, we present a number of experiments on the transformation of graphite, diamond, and multiwalled carbon nanotubes under high pressure conditions. The analysis of our results testifies to the instability of diamond in the 55-115 GPa pressure range, at which onion-like structures are formed. The formation of interlayer sp3-bonds in carbon nanostructures with a decrease in their volume has been studied theoretically. It has been found that depending on the structure, the bonds between the layers can be preserved or broken during unloading.
DS201902-0262
2018
Bo, T., Katz, R.F., Shorttle, O., Rudge, J.F.The melting column as a filter of mantle trace element heterogeneity.Geochemistry, Geophysics, Geosystems, Vol. 19, 12, pp. 4694-4721.Mantlemelting

Abstract: Basaltic lavas, created by melting the convecting mantle, show variability of concentration of trace element that are correlated with their affinity for the liquid phase during melting. The observed variability in lavas and melt inclusions carries information about heterogeneity in the mantle. The difficulty is to disentangle the contributions of source heterogeneity (i.e., spatial variability of mantle composition before melting) and process heterogeneity (i.e., spatial and temporal variability in melt transport). Here we develop an end-member model of the source heterogeneity and show that it is inadequate to explain observations.
DS201904-0717
2019
Bogdana-Radu, I., Harris, C., Moine, B.N., Costin, G., Cottin, J-Y.Subduction relics in the subcontinental lithospheric mantle evidence from variation in the delta 180 value of eclogite xenolths from the Kaapvaal craton.Contributions to Mineralogy and Petrology, Vol 174, https://doi.org/ 10.1007/s00410-019-1552-zAfrica, South Africadeposit - Roberts Victor, Jagersfontein

Abstract: Mantle eclogites are commonly accepted as evidence for ancient altered subducted oceanic crust preserved in the subcontinental lithospheric mantle (SCLM), yet the mechanism and extent of crustal recycling in the Archaean remains poorly constrained. In this study, we focus on the petrological and geochemical characteristics of 58 eclogite xenoliths from the Roberts Victor and Jagersfontein kimberlites, South Africa. Non-metasomatized samples preserved in the cratonic root have variable textures and comprise bimineralic (garnet (gt)-omphacite (cpx)), as well as kyanite (ky)- and corundum (cor)-bearing eclogites. The bimineralic samples were derived from a high-Mg variety, corresponding to depths of ~ 100-180 km, and a low-Mg variety corresponding to depths of ~ 180-250 km. The high-Al (ky-, cor-bearing) eclogites originated from the lowermost part of the cratonic root, and have the lowest REE abundances, and the most pronounced positive Eu and Sr anomalies. On the basis of the strong positive correlation between gt and cpx d18O values (r2 = 0.98), we argue that d18O values are unaffected by mantle processes or exhumation. The cpx and gt are in oxygen isotope equilibrium over a wide range in d18O values (e.g., 1.1-7.6‰ in garnet) with a bi-modal distribution (peaks at ~ 3.6 and ~ 6.4‰) with respect to mantle garnet values (5.1 ± 0.3‰). Reconstructed whole-rock major and trace element compositions (e.g., MgO variation with respect to Mg#, Al2O3, LREE/HREE) of bimineralic eclogites are consistent with their protolith being oceanic crust that crystallized from a picritic liquid, marked by variable degrees of partial melt extraction. Kyanite and corundum-bearing eclogites, however, have compositions consistent with a gabbroic and pyroxene-dominated protolith, respectively. The wide range in reconstructed whole-rock d18O values is consistent with a broadly picritic to pyroxene-rich cumulative sequence of depleted oceanic crust, which underwent hydrothermal alteration at variable temperatures. The range in d18O values extends significantly lower than that of present-day oceanic crust and Cretaceous ophiolites, and this might be due to a combination of lower d18O values of seawater in the Archaean or a higher temperature of seawater-oceanic crust interaction.
DS201905-1017
2019
Boger, S.D., Maas, R., Pastuhov, M., Macey, P.H., Hirdes, W., Schulte, B., Fanning, C.M., Ferreira, C.A.M., Jenett, T., Dallwig, R.The tectonic domains of southern and western Madagascar.Precambrian Research, Vol. 327, pp. 144-175.Africa, Madagascarplate tectonics

Abstract: Southern and western Madagascar is comprised of five tectonic provinces that, from northeast to southwest, are defined by the: (i) Ikalamavony, (ii) Anosyen, (iii) Androyen, (iv) Graphite and (v) Vohibory Domains. The Ikalamavony, Graphite and Vohibory Domains all have intermediate and felsic igneous protoliths of tonalite-trondhjemite-granodiorite-granite composition, with positive eNd, and low Sr and Pb isotopic ratios. All three domains are interpreted to be the products of intra-oceanic island arc magmatism. The protoliths of the Ikalamavony and Graphite Domains formed repectively between c. 1080-980?Ma and 1000-920?Ma, whereas those of the Vohibory Domain are younger and date to between c. 670-630?Ma. Different post-formation geologic histories tie the Vohibory-Graphite and Ikalamavony Domains to opposite sides of the pre-Gondwana Mozambique Ocean. By contrast, the Androyen and Anosyen Domains record long crustal histories. Intermediate to felsic igneous protoliths in the Androyen Domain are of Palaeoproterozoic age (c. 2200-1800?Ma), of tonalite-trondhjemite-granodiorite-granite composition, and show negative eNd, moderate to high 87Sr/86Sr and variable Pb isotopic compositions. The felsic igneous protoliths of the Anosyen Domain are of granitic composition and, when compared to felsic gneisses of the Androyen Domain, show consistently lower Sr/Y and markedly higher Sr and Pb isotope ratios. Like the Vohibory and Graphite Domains, the Androyen Domain can be linked to the western side of the Mozambique Ocean, while the Anosyen Domain shares magmatic and detrital zircon commonalities with the Ikalamavony Domain. It is consequently linked to the opposing eastern side of this ocean. The first common event observed in all domains dates to c. 580-520?Ma and marks the closure of the Mozambique Ocean. The trace of this suture lies along the boundary between the Androyen and Anosyen Domains and is defined by the Beraketa high-strain zone.
DS201905-1018
2019
Bohm, C.O., Hartlaub, R.P., Heaman, L.M., Cates, N., Guitreau, M., Bourdon, B., Roth, A.S.G., Mojzsis, S.J., Blichert-Toft, J.The Assean Lake Complex: ancient crust at the northwestern margin of the Superior Craton, Manitoba, Canada.Earths Oldest Rocks, researchgate.com Chapter 28, 20p. Pdf availableCanada, Manitobacraton

Abstract: This chapter describes the Assean Lake Complex (ALC) at ancient crust at the Northwestern margin of the Superior Craton, Manitoba, and Canada. An initial tectonic model for the Assean Lake area indicated that a regionally extensive high-strain zone running through the lake marks the suture between Archean high-grade crustal terranes of the Superior Craton to the southeast and Paleoproterozoic rocks of the Trans-Hudson Orogen to the northwest. Detailed geologic remapping combined with isotopic and geochemical studies led to a re-interpretation of the crust immediately north of the Assean Lake high-strain zone as Mesoarchean. The study area straddles the boundary between the Archean Superior Craton and the ca.1.90-1.84 Ga arc and marginal basin rocks of the Trans-Hudson Orogen, which represent the remains of ca. 1.83-1.76 Ga ocean closure and orogeny. It is indicated that the gneisses of the Split Lake Block consist primarily of meta-igneous protoliths of gabbroic to granitic composition. Tonalite and granodiorite are the most volumetrically dominant, but an anorthosite dome is also present in the northeast. Mapping, isotopic, and age data combined with high-resolution aero-magnetic data indicate that the Mesoarchean ALC is a crustal slice up to 10 km wide, and has a strike length of at least 50 km.
DS201903-0499
2019
Bologna, M.S., Dragone, G.N., Muzio, R., Peel, E., Nunez, Demarco, P., Ussami, N.Electrical structure of the lithosphere from Rio de la Plata craton to Parana Basin: amalgamation of cratonic and refertilized lithospheres in SW Gondwanaland.Tectonics, Vol. 38, 1, pp. 77-94.South America, Brazilcraton

Abstract: We conducted a magnetotelluric (MT) study from Paleoproterozoic Rio de la Plata Craton, in Uruguay, toward Paleozoic-Mesozoic Paraná Basin, in Brazil. The 850-km-long MT transect comprises 35 evenly spaced broadband electromagnetic soundings sites. In the Paraná Basin, 11 additional long-period measurements were acquired to extend the maximum depth of investigation. All data were inverted using two- and three-dimensional approaches obtaining the electrical resistivity structure from the surface down to 200 km. The Rio de la Plata Craton is >200-km thick and resistive (~2,000 Om). Its northern limit is electrically defined by a lithosphere scale lateral transition and lower crust conductive anomalies (1-10 Om) interpreted as a Paleoproterozoic suture at the southern edge of Rivera-Taquarembó Block. The latter is characterized by an approximately 100-km thick and moderate resistive (>500 Om) upper mantle. The Ibaré shear zone is another suture where an ocean-ocean subduction generated the 120-km thick and resistive (>1,000 Om) São Gabriel juvenile arc. Proceeding northward, a 70- to 80-km thick, 150-km wide, and inclined resistive zone is imaged. This zone could be remnant of an oceanic lithosphere or island arcs accreted at the southern border of Paraná Basin. The MT transect terminates within the southern Paraná Basin where a 150- to 200-km-thick less resistive lithosphere (<1,000 Om) may indicate refertilization processes during plate subduction and ocean closure in Neoproterozoic-Cambrian time. Our MT data support a tectonic model of NNE-SSW convergence for this segment of SW Gondwanaland.
DS201909-2023
2019
Bosco-Santos, A., Gilholy, W.P., Fouskas, F., Baldim, M., Oliveira, E.P.Ferruginous - euxinc - oxic: a three step redox change in the Neoarchean record.Goldschmidt2019, 1p. AbstractSouth America, Brazilcraton

Abstract: Much of the secular record of sulfur mass independet fractionation (S-MIF) is based on pyrites extracted from a limited number of formations from Western Australia and Southern Africa. Here we present multiproxy evidence for an episodic loss of S-MIF in sulfides from a 2.7 Ga sedimentary record in the São Francisco craton, Brazil. Based on combined proxies, we assigned three phases, in a continous drill core, that track evolving water column redox conditions and changes in ecology. In Phase-I, the stratigraphically older rocks, reactive iron ratios suggest ferruginous conditions. The pyrites have modest S-MIF values (D33S from -0.7 to 2.6‰) and the carbon isotope composition of the iron formations is indicative of carbon fixation by anoxygenic photosynthetic bacteria that oxidized Fe2+ (d13Corg from -27.7 to -17.5‰). Within Phase-II, an intermediate phase characterized by graphite schist, the iron ratios, expansion of the S-MIF (D33S from 2.15 to 3.4‰) and an excess of Mo relative to Corg suggest deposition in an anoxic environment with periodic development of euxinic conditions. Phase-III culminates in fully oxic conditions with a loss of S-MIF and emergence of sulfur mass dependent fractionation (S-MDF) with homogeneous d34S pyrite values (average = 3.3 ± 0.5‰). The loss of S-MIF in the Archean sulfides of Phase-III was interpreted as a response to increased oxygen levels that lead to an intensification of oxidative weathering. Based on the continous deposition within this drillcore, the development of more oxidizing conditions may have been relatively rapid, reinforcing the model that the transition from S-MIF to S-MDF can happen on rapid geological time scales and was recorded about 400 million years prior to the GOE in the Brazilian craton.
DS201904-0718
1991
Bossi, J., Campal, N., Civetta, L., Demarchi, G., Girardi, V.V., Mazzucchelli, M., Piccirillo, E.M., Rivalenti, G., Sinigol, S., Teixeira, W., Fragoso-Cesar, A.R.Petrological and geochronological aspects of the Precambrian mafic dyke swarm of Uruguay. IN: Eng. Note Date****BOL.IG-USP, Publ.Esp., Vol. 10, pp. 35-42.South America, Uruguaydykes

Abstract: The subparallel maflc dykes of the Aorida-Durazno-S.José region (SW Uruguay) trend N60-80W and vary in thickness from 0.6 to 50 m. They are part of the mafic dyke swarms intrudlng granitic-gnelssic basement that were mappecl by BOSSI et ai. (1989), In an ares approximately 200 km In length and 100 km in bresdth. Plagioclass, augite, subcalclc augite (plgeonite) and opaques are the maln components of the dykes. Orthopyroxene and oIlvine are very rare. Blotite and homblende are secondary minerais. Quartz-feldspar Intergrowths occur In the coarser gralnecl dykes. The characterlstlc textures are subophitic and intersertal.
DS201904-0719
2019
Boulard, E., Harmand, M., Guyot, F., Lelong, G., Morard, D., Cabaret, D., Boccato, S., Rosa, A.D., Briggs, R., Pascarelli, S., Fiquet, G.Ferrous iron under oxygen rich conditions in the deep mantle.Geophysical Research Letters, Vol. 46, 3, pp. 1348-1356.MantleUHP

Abstract: Iron oxides are important end-members of the complex materials that constitute the Earth's interior. Among them, FeO and Fe2O3 have long been considered as the main end-members of the ferrous (Fe2+) and ferric (Fe3+) states of iron, respectively. All geochemical models assume that high oxygen concentrations are systematically associated to the formation of ferric iron in minerals. The recent discovery of O22- peroxide ions in a phase of chemical formula FeO2Hx stable under high-pressure and high-temperature conditions challenges this general concept. However, up to now, the valences of iron and oxygen in FeO2Hx have only been indirectly inferred from a structural analogy with pyrite FeS2. Here we compressed goethite (FeOOH), an Fe3+-bearing mineral, at lower mantle pressure and temperature conditions by using laser-heated diamond-anvil cells, and we probed the iron oxidation state upon transformation of FeOOH in the pressure-temperature stability field of FeO2Hx using in situ X-ray absorption spectroscopy. The data demonstrate that upon this transformation iron has transformed into ferrous Fe2+. Such reduced iron despite high oxygen concentrations suggests that our current views of oxidized and reduced species in the lower mantle of the Earth should be reconsidered.
DS201906-1277
2019
Boulvais, P., Ntiharirizwa, S., Branquet, Y., Poujol, M., Moreli, C., Ntungwanayo, J., Midende, G.Geology and U-Th dating of the Gakara REE deposit.GAC/MAC annual Meeting, 1p. Abstract p. 64.Africa, BurundiREE

Abstract: The Gakara Rare Earth Elements (REE) deposit is one of the world’s highest grade REE deposits, likely linked to a carbonatitic magmatic-hydrothermal activity. It is located near Lake Tanganyika in Burundi, along the western branch of the East African Rift. Field observations suggest that the mineralized veins formed in the upper crust. Previous structures inherited from the Kibaran orogeny may have been reused during the mineralizing event. The paragenetic sequence and the geochronological data show that the Gakara mineralization occurred in successive stages in a continuous hydrothermal history. The primary mineralization in bastnaesite was followed by an alteration stage into monazite. The U-Th-Pb ages obtained on bastnaesite (602 ± 7 Ma) and on monazite (589 ± 8 Ma) belong to the Pan-African cycle. The emplacement of the Gakara REE mineralization most likely took place during a pre-collisional event in the Pan-African belt, probably in an extensional context.
DS201904-0720
2019
Bouman, M., Anthonis, A., Chapman, J., Smans, S., De Corte, K.The effect of blue fluorescence on the colour appearance of round brilliant cut diamonds.Journal of Gemology, Vol. 36, 4, pp. 298-315.Globaldiamond fluoresence
DS201904-0721
2019
Braithwaite, J., Stixrude, L.Melting of CaSiO3 perovskite at high pressure.Geophysical Research Letters, Vol. 46, 4, pp. 2037-2044.Mantlemelting

Abstract: Silicate melting is a major agent of thermal and chemical evolution of the Earth and other rocky planets. The melting temperature of Calcium silicate perovskite, a mineral that exists in Earth's lower mantle, is unknown over most of the pressure range that occurs in the mantle of Earth and super-Earth exoplanets. We use advanced quantum mechanical simulations to predict the melting temperature of this material. We find that the melting temperature increases with increasing pressure but at a rate that diminishes continuously. The liquid and crystal have very similar volumes in the deep portions of planetary mantles, supporting the view that crystals may float at great depth.
DS201908-1772
2019
Braukmuller, N., Wombacher, F., Funk, C., Munker, C.Earth's volatile element depletion pattern inherited from a carbonaceous chondrite-like source.Nature Geoscience, Vol. 12, 7, pp. 564-568.Mantlechondrite

Abstract: Earth’s volatile element abundances (for example, sulfur, zinc, indium and lead) provide constraints on fundamental processes, such as planetary accretion, differentiation and the delivery of volatile species, like water, which contributed to Earth becoming a habitable planet. The composition of the silicate Earth suggests a chemical affinity but isotopic disparity to carbonaceous chondrites—meteorites that record the early element fractionations in the protoplanetary disk. However, the volatile element depletion pattern of the silicate Earth is obscured by core formation. Another key problem is the overabundance of indium, which could not be reconciled with any known chondrite group. Here we complement recently published volatile element abundances for carbonaceous chondrites with high-precision sulfur, selenium and tellurium data. We show that both Earth and carbonaceous chondrites exhibit a unique hockey stick volatile element depletion pattern in which volatile elements with low condensation temperatures (750-500?K) are unfractionated from each other. This abundance plateau accounts for the apparent overabundance of indium in the silicate Earth without the need of exotic building materials or vaporization from precursors or during the Moon-forming impact and suggests the accretion of 10-15?wt% CI-like material before core formation ceased. Finally, more accurate estimates of volatile element abundances in the core and bulk Earth can now be provided.
DS201909-2024
2019
Braunger, S., Marks, M.A.W., Wenzel, T., Chmyz, L., Azzone, R.G., Markl, G.Carbonatite-alkaline silica rock complexes reflect highly oxidized conditions in their Upper Mantle source.Goldschmidt2019, 1p. AbstractMantlecarbonatite

Abstract: Alkaline complexes consist of variable mantle-derived silicate rocks, ranging from primitive alkali basalts, melilitites, nephelinites and basanites towards tephrites and more evolved phonolites, respectively their plutonic equivalents. This lithological variance is also expressed by a wide range of redox conditions that vary by several log units around the synthetic fayalite-magnetite-quartz (FMQ) buffer. However, only some of these complexes are characterized by the occurrence of carbonatites which must be related to specific formation conditions. Based on textural, mineralogical and geochemical observations, we calculated the redox conditions of carbonatites and associated silicate rocks for seven alkaline complexes (Kaiserstuhl, Sokli, Kovdor, Palabora, Magnet Cove, Oka, Jacupiranga) which are considered to represent typical carbonatite-alkaline silicate rock associations. In combination with a comprehensive literature review, we demonstrate that carbonatite-bearing alkaline complexes formed under highly oxidized conditions and hence, belong to the most oxidized alkaline rocks at all. This is consistent with the prerequisite of a carbonated mantle as the source region for carbonatite complexes, which requires redox conditions distinctively above that for mean lithospheric or asthenospheric mantle. Carbonatitemetasomatized peridotites also show high redox conditions and might not only reflect an interaction between peridotite and carbonatitic melts/fluids, but at least partly represent the carbonated mantle source for crustally emplaced carbonatite complexes. We therefore suggest that the oxidation state of carbonatites and associated silicate rocks provides direct information about an extraordinary oxidized parental mantle source.
DS201901-0009
2018
Breeding, C.M.Colored diamonds: the rarity and beauty of imperfection.Gems & Gemology, Sixth International Gemological Symposium Vol. 54, 3, 1p. Abstract p. 275.Globaldiamond color

Abstract: Diamond is often romanticized as a symbol of purity and perfection, with values that exceed all other gemstones. However, even the most flawless and colorless natural diamonds have atomic-level imperfections. Somewhat ironically, the rarest and most valuable gem diamonds are those that contain abundant impurities or certain atomic defects that produce beautiful fancy colors such as red, blue, or green—stones that can sell for millions of dollars per carat. Atomic defects can consist of impurities such as nitrogen or boron that substitute for carbon atoms in the diamond atomic structure (resulting in classifications such as type Ia, type Ib, type IIa, and type IIb) or missing or misaligned carbon atoms. Some defects are created during diamond growth, while others are generated over millions to billions of years as the diamond sits deep in the earth at high temperatures and pressures. Defects may be created when the diamond is rapidly transported to the earth’s surface or by interaction with radioactive fluids very near the earth’s surface. Each defect selectively absorbs different wavelengths of light to produce eye-visible colors. Absorptions from these color-producing defects (or color centers) are detected and identified using the gemological spectroscope or more sensitive absorption spectrometers such as Fouriertransform infrared (FTIR) or ultraviolet/visible/near-infrared (UV-Vis-NIR; figure 1). Some defects not only absorb light but also produce their own luminescence, called fluorescence. For example, the same defect that produces “cape” yellow diamonds also generates blue fluorescence when exposed to ultraviolet light. In some cases, the fluorescence generated by defects can be strong enough to affect the color of gem diamonds. With the exception of most natural white and black diamonds, where the color is a product of inclusions, colored diamonds owe their hues to either a single type of defect or a combination of several color centers. More than one type of defect can produce a particular color, however. Table 1 provides a list of the most common causes of color in diamond. Subtle differences in atomic defects can drastically affect a diamond’s color. For example, isolated atoms of nitrogen impurities usually produce strong yellow color (“canary” yellow diamonds). If those individual nitrogen atoms occur together in pairs, no color is generated and the diamond is colorless. If instead the individual nitrogen atoms occur adjacent to missing carbon atoms (vacancies), the color tends to be pink to red. Rearrangement of diamond defects is the foundation of using treatments to change the color of diamond. Identification of treatments and separation of natural and synthetic diamond requires a thorough understanding of the atomic-level imperfections that give rise to diamond color and value.
DS201909-2025
2019
Brooks, K.Layered intrusions: key to fundamental planetary processes. Description of book…. Comments.Geology Today, Vol. 35, 4, pp. 146-153.China, Canada, Africalayered complexes

Abstract: A large book entitled Layered Intrusions (edited by Bernard Charlier, Olivier Namur, Rais Latypov and Christian Tegner, Springer) has been published recently. This book (almost 750 pages) has 15 contributions by 36 experts in the field. While Part I deals with subjects such as geochronology, igneous layering, textures, silicate liquid immiscibility and behaviour of precious metals in these intrusions, Part II examines six examples that are reviewed by experts: Panzhihua (China), Sept Iles (Canada), Bushveld (South Africa), Kiglapait (Labrador), Ilímaussaq (Greenland) and ophiolitic magma chambers in the Canadian Appalachians. The publication of this book has led me to consider the geology of the most famous of them all-the Skaergaard Intrusion of Greenland-and my long history of studying it.
DS201906-1278
2019
Broom-Fendley, S., Smith, M., Andrade, M.B., Ray, S., Banks, D.A., Loye, E., Atencio, D., Pickles, J.R., Wall, F.Sulphate bearing monazite (Ce) from silicified dolomite carbonatite, Eureka, Namibia: substitution mechanisms, redox state and HREE enrichment.3rd International Critical Metals Meeting held Edinburgh, 1p. Abstract p. 51.Africa, Namibiadeposit - Eureka
DS201909-2026
2019
Brown, M., Johnson, T.Metamorphism and the evolution of subduction on Earth.American Mineralogist, Vol. 104, pp. 1065-1082.Mantlesubduction

Abstract: Subduction is a component of plate tectonics, which is widely accepted as having operated in a manner similar to the present-day back through the Phanerozoic Eon. However, whether Earth always had plate tectonics or, if not, when and how a globally linked network of narrow plate boundaries emerged are matters of ongoing debate. Earth's mantle may have been as much as 200-300 °C warmer in the Mesoarchean compared to the present day, which potentially required an alternative tectonic regime during part or all of the Archean Eon. Here we use a data set of the pressure (P), temperature (T), and age of metamorphic rocks from 564 localities that vary in age from the Paleoarchean to the Cenozoic to evaluate the petrogenesis and secular change of metamorphic rocks associated with subduction and collisional orogenesis at convergent plate boundaries. Based on the thermobaric ratio (T/P), metamorphic rocks are classified into three natural groups: high T/P type (T/P > 775 °C/GPa, mean T/P ~1105 °C/GPa), intermediate T/P type (T/P between 775 and 375 °C/GPa, mean T/P ~575 °C/GPa), and low T/P type (T/P < 375 °C/GPa, mean T/P ~255 °C/GPa). With reference to published thermal models of active subduction, we show that low T/P oceanic metamorphic rocks preserving peak pressures >2.5 GPa equilibrated at P-T conditions similar to those modeled for the uppermost oceanic crust in a wide range of active subduction environments. By contrast, those that have peak pressures <2.2 GPa may require exhumation under relatively warm conditions, which may indicate subduction of young oceanic lithosphere or exhumation during the initial stages of subduction. However, low T/P oceanic metamorphic rocks with peak pressures of 2.5-2.2 GPa were exhumed from depths where, in models of active subduction, the slab and overriding plate change from being decoupled (at lower P) to coupled (at higher P), possibly suggesting a causal relationship. In relation to secular change, the widespread appearance of low T/P metamorphism in the Neoproterozoic represents a “modern” style of cold collision and deep slab breakoff, whereas rare occurrences of low T/P metamorphism in the Paleoproterozoic may reveal atypical localized regions of cold collision. Low T/P metamorphism is not known from the Archean geological record, but the absence of blueschists in particular is unlikely to reflect secular change in the composition of the oceanic crust. In addition, the premise that the formation of lawsonite requires abnormally low thermal gradients and the postulate that oceanic subduction-related rocks register significantly lower maximum pressures than do continental subduction-related rocks, and imply different mechanisms of exhumation, are not supported. The widespread appearance of intermediate T/P and high T/P metamorphism at the beginning of the Neoarchean, and the subsequent development of a clear bimodality in tectono-thermal environments are interpreted to be evidence of the stabilization of subduction during a transition to a globally linked network of narrow plate boundaries and the emergence of plate tectonics.
DS201910-2245
2019
Brown, M., Johnson, T.E.Metamorphism and evolution of subduction on Earth.American Mineralogist, Vol. 104, 8, pp. 1065-1082.Mantlesubduction

Abstract: Subduction is a component of plate tectonics, which is widely accepted as having operated in a manner similar to the present-day back through the Phanerozoic Eon. However, whether Earth always had plate tectonics or, if not, when and how a globally linked network of narrow plate boundaries emerged are matters of ongoing debate. Earth's mantle may have been as much as 200-300 °C warmer in the Mesoarchean compared to the present day, which potentially required an alternative tectonic regime during part or all of the Archean Eon. Here we use a data set of the pressure (P), temperature (T), and age of metamorphic rocks from 564 localities that vary in age from the Paleoarchean to the Cenozoic to evaluate the petrogenesis and secular change of metamorphic rocks associated with subduction and collisional orogenesis at convergent plate boundaries. Based on the thermobaric ratio (T/P), metamorphic rocks are classified into three natural groups: high T/P type (T/P > 775 °C/GPa, mean T/P ~1105 °C/GPa), intermediate T/P type (T/P between 775 and 375 °C/GPa, mean T/P ~575 °C/GPa), and low T/P type (T/P < 375 °C/GPa, mean T/P ~255 °C/GPa). With reference to published thermal models of active subduction, we show that low T/P oceanic metamorphic rocks preserving peak pressures >2.5 GPa equilibrated at P-T conditions similar to those modeled for the uppermost oceanic crust in a wide range of active subduction environments. By contrast, those that have peak pressures <2.2 GPa may require exhumation under relatively warm conditions, which may indicate subduction of young oceanic lithosphere or exhumation during the initial stages of subduction. However, low T/P oceanic metamorphic rocks with peak pressures of 2.5-2.2 GPa were exhumed from depths where, in models of active subduction, the slab and overriding plate change from being decoupled (at lower P) to coupled (at higher P), possibly suggesting a causal relationship. In relation to secular change, the widespread appearance of low T/P metamorphism in the Neoproterozoic represents a “modern” style of cold collision and deep slab breakoff, whereas rare occurrences of low T/P metamorphism in the Paleoproterozoic may reveal atypical localized regions of cold collision. Low T/P metamorphism is not known from the Archean geological record, but the absence of blueschists in particular is unlikely to reflect secular change in the composition of the oceanic crust. In addition, the premise that the formation of lawsonite requires abnormally low thermal gradients and the postulate that oceanic subduction-related rocks register significantly lower maximum pressures than do continental subduction-related rocks, and imply different mechanisms of exhumation, are not supported. The widespread appearance of intermediate T/P and high T/P metamorphism at the beginning of the Neoarchean, and the subsequent development of a clear bimodality in tectono-thermal environments are interpreted to be evidence of the stabilization of subduction during a transition to a globally linked network of narrow plate boundaries and the emergence of plate tectonics.
DS201901-0010
2018
Brun, J-P., Sokoutis, D., Tirel, C., Gueydan, F., Beslier, M-O.Crustal versus mantle core complexes.Tectonophysics, Vol. 746, pp. 22-45.Mantlegeodynamics

Abstract: Deep crustal and mantle rocks are exhumed in core complex mode of extension in three types of structures: metamorphic core complexes, oceanic core complexes and magma poor passive margins. Using available analogue and numerical models and their comparison with natural examples, the present paper reviews the mechanical processes involved in these different types of extensional setting. Three main aspects are considered: i) the primary role of lithosphere rheology, ii) the lithosphere-scale patterns of progressive deformation that lead to the exhumation of deep metamorphic or mantle rocks and iii) the initiation and development of detachment zones. Crustal core complexes develop in continental lithospheres whose Moho temperature is higher than 750 °C with “upper crust-dominated” strength profiles. Contrary to what is commonly believed, it is argued from analogue and numerical models that detachments that accommodate exhumation of core complexes do not initiate at the onset of extension but in the course of progressive extension when the exhuming ductile crust reaches the surface. In models, convex upward detachments result from a rolling hinge process. Mantle core complexes develop in either the oceanic lithosphere, at slow and ultra-slow spreading ridges, or in continental lithospheres, whose initial Moho temperature is lower than 750 °C, with “sub-Moho mantle-dominated” strength profiles. It is argued that the mechanism of mantle exhumation at passive margins is a nearly symmetrical necking process at lithosphere scale without major and permanent detachment, except if strong strain localization could occur in the lithosphere mantle. Distributed crustal extension, by upper crust faulting above a décollement along the ductile crust increases toward the rift axis up to crustal breakup. Mantle rocks exhume in the zone of crustal breakup accommodated by conjugate mantle shear zones that migrate with the rift axis, during increasing extension.
DS201910-2246
2019
Bureau, H., Raepsat, V., Esteve, I., Armstrong, K., Manthilake, G.Replicate mantle diamonds.Goldschmidt2019, 1p. AbstractMantlediamond genesis

Abstract: Still today, diamond growth in the mantle is difficult to understand. It may implicate different processes but there is an agreement to involve fluids as diamonds parents. The composition of these fluids is supposed to be variable depending of the the settings and depths. Natural diamonds also exhibit dissolution features, possibly mantle-derived and not only due to kimberlite-induced resorption during magma ascent [1]. We present experimental results devoted to understand diamond growth versus dissolution mechanisms in the lithosphere. Experiments are performed using multianvil presses at 7 GPa, 1300-1675°C for a few hours (4 to 27 hrs). As starting materials we use mixtures of water, carbonates, natural lherzolite or MORB, graphite and diamonds seeds resulting in hydrous-carbonate-silicate fluids at high pressure and temperature. For similar pressure and temperature conditions, results show that diamonds are formed or dissolved in these fluids, depending on the redox conditions. Focussed ion beam preparations of the diamonds evidence that when they grow, they trap multi-phased inclusions similar to those observed in fibrous, coated and monocrystalline natural diamonds, in agreement with previous studies [2-4].
DS201910-2247
2019
Bussweiler, Y.Polymineralic inclusions in megacrysts as proxies for kimberlite melt evolution - a review.Minerals ( MDPI), Vol. 9, p. 530 - 20p.Mantlediamond inclusions

Abstract: Polymineralic inclusions in megacrysts have been reported to occur in kimberlites worldwide. The inclusions are likely the products of early kimberlite melt(s) which invaded the pre-existing megacryst minerals at mantle depths (i.e., at pressures ranging from 4 to 6 GPa) and crystallized or quenched upon emplacement of the host kimberlite. The abundance of carbonate minerals (e.g., calcite, dolomite) and hydrous silicate minerals (e.g., phlogopite, serpentine, chlorite) within polymineralic inclusions suggests that the trapped melt was more volatile-rich than the host kimberlite now emplaced in the crust. However, the exact composition of this presumed early kimberlite melt, including the inventory of trace elements and volatiles, remains to be more narrowly constrained. For instance, one major question concerns the role of accessory alkali-halogen-phases in polymineralic inclusions, i.e., whether such phases constitute a common primary feature of kimberlite melt(s), or whether they become enriched in late-stage differentiation processes. Recent studies have shown that polymineralic inclusions react with their host minerals during ascent of the kimberlite, while being largely shielded from processes that affect the host kimberlite, e.g., the assimilation of xenoliths (mantle and crustal), degassing of volatiles, and secondary alteration. Importantly, some polymineralic inclusions within different megacryst minerals were shown to preserve fresh glass. A major conclusion of this review is that the abundance and mineralogy of polymineralic inclusions are directly influenced by the physical and chemical properties of their host minerals. When taking the different interactions with their host minerals into account, polymineralic inclusions in megacrysts can serve as useful proxies for the multi-stage origin and evolution of kimberlite melt/magma, because they can (i) reveal information about primary characteristics of the kimberlite melt, and (ii) trace the evolution of kimberlite magma on its way from the upper mantle to the crust.
DS201908-1773
2019
Bussweiler, Y., Giuliani, A., Greig, A., Kjarsgaard, B.A., Petts, D., Jackson, S.E., Barrett, N., Luo, Y., Pearson, D.G.Trace element analysis of high-Mg olivine by LA-ICP-MS - characterization of natural olivine standards for matrix-matched calibration and application to mantle peridotites.Chemical Geology, Vol. 524, pp. 136-157.Mantleperidotite

Abstract: The trace element composition of olivine is becoming increasingly important in petrological studies due to the ubiquity of olivine in the Earth's upper mantle and in primitive magmatic rocks. The LA-ICP-MS method allows for the routine analysis of trace elements in olivine to sub-ppm levels, but a major drawback of this method is the lack of knowledge about possible downhole fractionation effects when non matrix-matched calibration is used. In this contribution, we show that matrix-matched (i.e., olivine-based) calibration is preferable for small laser spot sizes (<100?µm) due to significant laser-induced inter-element fractionation between olivine and commonly used silicate glass calibration materials, e.g., NIST SRM 612, GSD-1G and BHVO-2G. As a result, we present two Mg-rich natural olivine standards (355OL and SC-GB) that have been characterized by independent methods (EPMA, solution ICP-MS), and by LA-ICP-MS in four different laboratories. These natural olivines have been used 1) as primary standards for the matrix-matched calibration of olivine samples for most elements of interest (e.g., Li, Na, Al, P, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn), and 2) as secondary standards to assess the accuracy of results. Comparison of olivine- and silicate glass-calibrated results for natural peridotitic olivine reveals that matrix-matched calibration is essential when using small laser spot sizes (<100?µm) in order to mitigate downhole fractionation effects for certain elements, especially Na, P, Mn, Co, Ni and Zn. If matrix-matched calibration is not feasible, we recommend that spot sizes of =100?µm, laser fluence of =4.0?J/cm2, and total laser shot counts of =250 (e.g., 5?Hz repetition rate for 50?s) are used in order to minimize fractionation effects between olivine and silicate glass calibration materials. We demonstrate the applicability of matrix-matched calibration on olivine from a suite of different mantle peridotite xenoliths sampled by kimberlites and alkali basalts from on-craton and off-craton localities.
DS201906-1279
2019
Bussweiler, Y., Grutzner, T., Rohrbach, A., Klenne, S.New insights into cratonic mantle metasomatism from HP-HT reaction experiments between saline fluids and mantle rocks.GAC/MAC annual Meeting, 1p. Abstract p. 67.Mantlemetasomatism

Abstract: Saline (Cl-rich) fluids potentially play an important role as metasomatic agents in the lithospheric mantle. Natural evidence for deep saline fluids exists as inclusions within diamonds and within groundmass minerals in kimberlites. Previous experimental studies have investigated melting relations in the chloride-carbonate-silicate system at upper mantle conditions, but a systematic experimental study of how saline fluids react with the lithospheric mantle is still lacking. Here, we present high-pressure, high-temperature (HP-HT) reaction experiments between a saline fluid and different mantle rocks (lherzolite, harzburgite, eclogite) at conditions corresponding to the lower cratonic lithosphere. Experiments were performed over a P-T range of 3-6 GPa and 1050-1300 °C using a multi-anvil apparatus. Preliminary results show that the interaction between saline fluid and mantle rocks is very reactive, compared to reactions with silico-carbonate melts. The reaction between saline fluid and lherzolite at 4 GPa and 1200 °C leads to extensive melting. The restite consists mainly of olivine and garnet, whereas pyroxenes are only observed as rare inclusions within garnet. In contrast, reactions between saline fluid and eclogite at 4 GPa and 1200 °C also lead to melting, but the melt is more enriched in Si. The restite consists exclusively of garnet. The experimental results demonstrate how saline fluids react with different components of the lithospheric mantle and support evolutionary models of high density fluids within diamonds.
DS201901-0011
2018
Butler, J.E., Byrne, K.S., Wang, W., Post, J.E.Complex charge transfer in chameleon diamonds: a model of the color-change process,Gems & Gemology, Sixth International Gemological Symposium Vol. 54, 3, 1p. Abstract p. 303.Globaldiamond color

Abstract: A group of natural diamonds known as chameleon diamonds change color from green to yellow based on their exposure to light and heat. These diamonds also emit long-lived phosphorescence after UV excitation. We have observed the optical response of these diamonds to optical and thermal excitation and developed a model to explain the observed phenomena. A principal element of the model is the proposal of an acceptor state (figure 1), which should be observable in the near-infrared (NIR) region. Subsequently, we have observed the NIR absorption to this acceptor state, supporting our model of charge-transfer processes in these diamonds.
DS201909-2027
2019
Butvina, V.G., Vorobey, S.S., Safonov, O.G., Varlamov, D.A., Bondarenko, G.V., Shapovalov, Yu.B.Experimental study of the formation of chromium-bearing priderite and yimengite as products of modal mantle metasomatism.Doklady Earth Sciences, Vol. 486, 2, pp. 711-715.Mantlemetasomatism

Abstract: The results of experiments on the synthesis of exotic titanates (priderite and yimengite) simulating metasomatic conditions of alteration of the mantle minerals (chromite and ilmenite) are reported. Ba-free Cr-bearing priderite was synthesized for the first time. Experiments showed the possibility of crystallization of this mineral as a product of the reaction of high-Cr spinel and rutile with hydrous-carbonate fluid (melt) under the conditions of the upper mantle. In particular, the experimental data obtained provide an interpretation of the relationships between K?Cr priderite and carbonate-silicate inclusions in chromites from garnet peridotite of the Bohemian massif. Experimental study of the reaction of chromite and ilmenite with potassic hydrous-carbonate fluid (melt) shows the presence of both titanate phases (priderite and yimengite), the mineral indicators of mantle metasomatism. This provides direct evidence for the formation of yimengite and K?Cr priderite, as well as other titanates, due to mantle metasomatism of the upper mantle peridotite under the conditions of the highest activities of potassium.
DS201907-1530
2019
Byrnes, J.S., Bezada, M., Long, M.D., Benoit, M.H.The lithosphere beneath the central Appalachian Mountains: constraints from seismic attenuation beneath the MAGIC array.Earth and Planetary Science Letters, Vol. 519, pp. 297-307.United Statesgeophysics - seismics

Abstract: The passive margin of the eastern coast of the United States is known to be geologically active, with recently rejuvenated topography, intraplate seismicity, and volcanism of Eocene age. This study uses seismic data from the Mid-Atlantic Geophysical Integrative Collaboration (MAGIC) experiment to constrain lateral variations in the attenuation of teleseismic P waves beneath the central Appalachian Mountains to shed light on the structure and dynamics of the upper mantle at this “active” passive margin. We use a Monte Carlo approach to estimate variations in attenuation along with both data and model uncertainties. The quality factor of the upper mantle dramatically decreases over a distance of less than 50 km on the western side of the central Appalachian Mountains, where a low-velocity anomaly has been previously inferred. Extrinsic factors such as scattering or focusing are rejected as explanations for the observations on the basis of finite-difference waveform modeling experiments. The peak in attenuation beneath the crest of the Appalachian Mountains requires that near- to super-solidus conditions occur in the upper mantle and is co-located with volcanism of Eocene age. Our preferred interpretation is that the attenuation reflects the removal of the mantle lithosphere via delamination beneath the mountains, followed by ongoing small-scale convection.
DS201906-1280
2019
Campbell, D., Zurevinski, S., Elliott, B.Geochemistry and glacial dispersal patterns of kimberlite indicator minerals in the south Slave province, NT.GAC/MAC annual Meeting, 1p. Abstract p. 68.Canada, Northwest Territoriesgeochemistry

Abstract: Drift prospecting has been utilized throughout the Slave Province in the Northwest Territories for decades, where glaciation and erosion within the past 10 000 years has produced the dispersion of minerals from their original host to till in their surrounding areas. This study is part of the greater Slave Province geophysical, surficial materials and permafrost study: a Northwest Territories Geological Survey (NTGS) led government-academic-industry research program. The purpose of this particular research is to assess kimberlite indicator minerals (KIMs) for any potential signature that may coincide with glacial dispersal trains through quantitative mineralogical and geochemical analysis. The NTGS has recently published data on Southern Slave Province surficial materials, which is useful as a comparative tool in the analysis of potential dispersal trains. Samples were collected from surficial sediment at various targets throughout the 75N and M NTS zones. Sample locations were chosen based on their down-ice position with respect to known kimberlites and gravity anomalies previously identified by the NTGS. Samples were preferentially collected from active and recently inactive frost boils. Overall, twenty-one 10 kg samples were collected and examined for KIMs. Several samples contain KIMs in moderate to high concentrations. Positive identifications of Cr-pyrope, chromite, Mg-ilmenite, and Cr-diopside have been confirmed in preliminary analysis. Of the identified KIMs garnet is the most abundant at 78 %, followed by chromite at 13 %, ilmenite at 8.9 %, and Cr-diopside at 0.5 %. Quantitative analyses are reported on confirmed KIMs: Cr-pyrope, Mg-ilmenite, Cr-diopside, chromite, and olivine for each sample site. The results of the analyses will be used to make further insights into till and kimberlite geochemistry of the Southern Slave Province.
DS201909-2028
2019
Cangelosi, D., Broom-Fendley, S., Banks, D., Morgan, D., Yardley, B.LREE redistribution during hydrothermal alteration at the Okorusu carbonatite complex, Namibia.Mineralogical Magazine, in press available 54p. PdfAfrica, Namibiacarbonatite - Okorusu

Abstract: The Cretaceous Okorusu carbonatite, Namibia, includes diopside-bearing and pegmatitic calcite carbonatites, both exhibiting hydrothermally altered mineral assemblages. In unaltered carbonatite, REE, Sr and Ba are largely hosted by calcite and fluorapatite. However, in hydrothermally altered carbonatites, small (< 50 µm) parisite-(Ce) grains are the dominant REE host, while Ba and Sr are hosted in baryte, celestine, strontianite and witherite. Hydrothermal calcite has a much lower trace element content than the original, magmatic calcite. Despite the low REE contents of the hydrothermal calcite, the REE patterns are similar to those of parisite-(Ce), and magmatic minerals and mafic rocks associated with the carbonatites. These similarities suggest that hydrothermal alteration remobilised REE from magmatic minerals, predominantly calcite, without significant fractionation or addition from an external source. Ba and Sr released during alteration were mainly reprecipitated as sulfates. The breakdown of magmatic pyrite into Fe-hydroxide is inferred to be the main source of sulfate. The behaviour of sulfur suggests that the hydrothermal fluid was somewhat oxidising and it may have been part of a geothermal circulation system. Late hydrothermal massive fluorite replaced the calcite carbonatites at Okorusu and resulted in extensive chemical change, suggesting continued magmatic contributions to the fluid system.
DS201905-1019
2019
Canil, D., Grundy, R., Johnston, S.T.Thermal history of the Donjek harzburgite massif in ophiolite from Yukon, Canada with implications for the cooling of oceanic mantle lithosphere.Lithos, Vol. 328-329, pp. 33-42.Canada, Yukongeothermometry

Abstract: We examine the partial melting and the cooling history of a ~5?km section of mantle lithosphere preserved in the Donjek massif, part of a Permian ophiolite in the northern Cordillera of Yukon, Canada. The mantle rocks are depleted spinel harzburgite containing <3% clinopyroxene displaying steep rare-earth element (REE) chondrite-normalized profiles and low (Gd/Yb)n (0.02 to 0.07) compared to most other ophiolites. The REE patterns of clinopyroxene can be modeled as 16-20% partial melts of typical depleted mid-ocean ridge (MOR) mantle. The REE exchange between coexisting ortho- and clinopyroxene preserves temperatures (TREE) of 1150-1360?°C, some of the highest values recorded in ophiolites and abyssal peridotites, and show a positive correlation with CaMg exchange (solvus) temperatures (TBKN) of 900-970?°C. The harzburgite represents lithosphere formed at an initial melting temperature of ~ 1350?°C that cooled at rate of 10-1 to 10-4?°C/year as deduced by TREE values with cation diffusion and grain size data. The TREE temperatures and cooling rates for the Donjek massif show a regular systematic variation with depth from the crust-mantle transition along a trend similar to the Samail ophiolite of Oman, consistent with conductive heat transfer beneath a cool lower crust. High near-solidus temperatures and the cooling rates in the massif were a consequence of rapid obduction against oceanic crust along either a transform or low angle detachment soon after melt extraction. Final emplacement of the ophiolite as klippen on underlying continental crust occurred ~ 40?m.y. later.
DS201911-2513
2019
Capitanio, F.A., Nebel, O. Cawood, P.A., Weinberg, R.F.. Chouddhury, P.Reconciling thermal regimes and tectonics of the early Earth.Geology, Vol. 47, pp. 923-927.Mantlegeothermometry

Abstract: Thermomechanical models of mantle convection and melting in an inferred hotter Archean Earth show the emergence of pressure-temperature (P-T) regimes that resemble present-day plate tectonic environments yet developed within a non-plate tectonics regime. The models’ P-T gradients are compatible with those inferred from evolving tonalite-trondhjemite-granodiorite series rocks and the paired metamorphic belt record, supporting the feasibility of divergent and convergent tectonics within a mobilized, yet laterally continuous, lithospheric lid. “Hot” P-T gradients of 10-20 °C km-1 form along asymmetric lithospheric drips, then migrate to areas of deep lithospheric downwelling within ~300-500 m.y., where they are overprinted by high-pressure warm and, later, cold geothermal signatures, up to ~8 °C km-1. Comparisons with the crustal production and reworking record suggest that this regime emerged in the Hadean.
DS201910-2248
2019
Capitanio, F.A., Nebel, O., Cawood, P.A., Weinberg, R.F., Clos, F.Lithosphere differentiation in the early Earth controls Archean tectonics.Earth and Planetary Science letters, Vol. 525, 115755, 12p.Mantleplate tectonics

Abstract: The processes that operated on the early Earth and the tectonic regimes in which it was shaped are poorly constrained, reflecting the highly fragmentary rock record and uncertainty in geodynamic conditions. Most models of early Earth geodynamics invoke a poorly mobile lid regime, involving little or episodic movement of the lithosphere, above a convecting mantle. However, such a regime does not reconcile with the record of Archean tectonics, which displays contrasting environments associated with either non-plate tectonics or plate tectonics. Here, we propose a regime for the early Earth in which progressive melt extraction at sites of divergence led to the formation of large portions of stiffer lithospheric lid, called proto-plates. These proto-plates enabled stress propagation to be focussed at their margins, which were then the locus for extension as oppose to shortening, under-thrusting and thickening to form adjoining proto-cratons. We test this hypothesis embedding lithospheric stiffening during melt extraction in thermo-mechanical models of mantle convection, under conditions that prevailed in the Archean. We demonstrate the emergence of migrating, rigid proto-plates in which regions of prolonged focused compression coexist with remnants of the stagnant lid, thereby reproducing the widespread dichotomy proposed for the Archean tectonic record. These diverse tectonic modes coexist in a single regime that is viable since the Hadean and lasted until the transition to modern plate tectonics.
DS201903-0500
2019
Carneiro, C.de C., Juliani, C., Carreiro-Araujo, S.A., Monteiro, L.V.S., Crosta, A.P., Fernandes, C.M.D.New crustal framework in the Amazon craton based on geophysical data: evidence of deep east-west trending suture zones.IEEE.org , Vol. 16, 1, pp. 20-24.South America, Brazilcraton

Abstract: The Tapajós mineral province (TMP), in the Brazilian Amazon Craton, comprises NW-SE Paleoproterozoic insular magmatic arcs accreted to the Carajás Archean Province (CAP). We present new geological and geophysical data pointing toward a different evolutionary model for the TMP. Results obtained from magnetic data indicate that NNW-SSE trending structures occur at shallow crustal levels. Furthermore, an E-W structural framework shows up at 15.4 km depth, in disagreement with the accreted island arc orientation. These E-W structures are associated with north-dipping blocks, reflecting ductile compressive tectonics, similar to the tectonic setting found in the CAP. We interpret these E-W structures of the TMP as the continuity westwards of similar structures from the CAP, under the Paleoproterozoic volcanic rocks of the Uatumã Supergroup. Based on this evidence, we propose that Paleoproterozoic arcs have been formed in an Archean active continental margin, instead of in island arcs. This novel tectonic setting for the TMP has significant implications for the tectonic evolution and the metallogenic potential of the southern portion of the Amazon craton, particularly for Paleoproterozoic magmatic-hydrothermal (epithermal and porphyry) precious and base metal systems.
DS201901-0012
2018
Cartier, L.E., Ali, S.H., Krzemnicki, M.S.Blockchain, chain of custody and trace elements: an overview of tracking and traceability opoortunities in the gem industry.Journal of Gemmology, Vol. 36, 3, pp. 212-227.Globalblockchain

Abstract: Dr. Laurent Cartier and Dr. Saleem Ali of the Knowledge Hub recently co-authored an overview article on traceability in the gem and jewellery industry. This paper was published in the Journal of Gemmology and is entitled 'Blockchain, Chain of Custody and Trace Elements: An Overview of Tracking and Traceability Opportunities in the Gem Industry'. Recent developments have brought due diligence, along with tracking and traceability, to the forefront of discussions and requirements in the diamond, coloured stone and pearl industries. This article provides an overview of current trends and developments in the tracking and traceability of gems, along with an explanation of the terms used in this context. Further, the article discusses current initiatives in the sector and provides an introduction blockchain concepts.
DS201904-0722
2019
Cate, A.Machine learning for Prospectivity mapping? Not specific to diamondsPDAC Short Course, 56 ppts. PdfGlobaltarget - deposit
DS201904-0723
2017
Cate, A., Perozzi, L., Gloaguen, E., Blouin, M.Machine learning as a tool for geologists. Not specific to diamondsThe leading Edge, https://dx.doi.org/10.1190/tle36030064.1Globaldata sets

Abstract: Machine learning is becoming an appealing tool in various fields of earth sciences, especially in resources estimation. Six machine learning algorithms have been used to predict the presence of gold mineralization in drill core from geophysical logs acquired at the Lalor deposit, Manitoba, Canada. Results show that the integration of a set of rock physical properties — measured at closely spaced intervals along the drill core — with ensemble machine learning algorithms allows the detection of gold-bearing intervals with an adequate rate of success. Since the resulting prediction is continuous along the drill core, the use of this type of tool in the future will help geologists in selecting sound intervals for assay sampling and in modeling more continuous ore bodies during the entire life of a mine.
DS201902-0263
2018
Cavalcante, C., Hollanda, M.H., Vauchez, A., Kawata, M.How long can the middle crust remain partially molten during orogeny?Geology, Vol. 46, pp. 839-852.South America, Brazil, Africa, Congomelting

Abstract: Extensive partial melting of the middle to lower crustal parts of orogens, such as of the current Himalaya-Tibet orogen, significantly alters their rheology and imposes first-order control on their tectonic and topographic evolution. We interpret the late Proterozoic Araçuaí orogen, formed by the collision between the São Francisco (Brazil) and Congo (Africa) cratons, as a deep section through such a hot orogen based on U-Pb sensitive high-resolution ion microprobe (SHRIMP) zircon ages and Ti-in-zircon and Zr-in-rutile temperatures from the Carlos Chagas anatectic domain. This domain is composed of peraluminous anatexites and leucogranites that typically exhibit interconnected networks of garnet-rich leucosomes or a magmatic foliation. Zirconium-in-rutile temperatures range from 745 to 820 °C, and the average Ti-in-zircon temperature ranges from 712 to 737 °C. The geochronologic and thermometry data suggest that from 597 to 572 Ma this domain was partially molten and remained so for at least 25 m.y., slowly crystallizing between temperatures of ~815 and >700 °C. Significant crustal thickening must have occurred prior to 600 Ma, with initial continental collision likely before 620 Ma, a time period long enough to heat the crust to temperatures required for widespread partial melting at middle crustal levels and to favor a "channel flow" tectonic behavior.
DS201901-0013
2019
Cawood, P. A., Hawkesworth, C.J.Continental crustal volume, thickness and area, and their geodynamic implications.Gondwana Research, Vol. 66, pp. 116-125.Mantleplate tectonics

Abstract: Models of the volume of continental crust through Earth history vary significantly due to a range of assumptions and data sets; estimates for 3?Ga range from <10% to >120% of present day volume. We argue that continental area and thickness varied independently and increased at different rates and over different periods, in response to different tectonic processes, through Earth history. Crustal area increased steadily on a pre-plate tectonic Earth, prior to ca. 3?Ga. By 3?Ga the area of continental crust appears to have reached a dynamic equilibrium of around 40% of the Earth's surface, and this was maintained in the plate tectonic world throughout the last 3?billion?years. New continental crust was relatively thin and mafic from ca. 4-3?Ga but started to increase substantially with the inferred onset of plate tectonics at ca. 3?Ga, which also led to the sustained development of Earth's bimodal hypsometry. Integration of thickness and area data suggests continental volume increased from 4.5?Ga to 1.8?Ga, and that it remained relatively constant through Earth's middle age (1.8-0.8?Ga). Since the Neoproterozoic, the estimated crustal thickness, and by implication the volume of the continental crust, appears to have decreased by as much as 15%. This decrease indicates that crust was destroyed more rapidly than it was generated. This is perhaps associated with the commencement of cold subduction, represented by low dT/dP metamorphic assemblages, resulting in higher rates of destruction of the continental crust through increased sediment subduction and subduction erosion.
DS201901-0014
2018
Cawthorn, R.G.Lopolith - a 100 year-old term. Is it still definitive?South African Journal of Geology, Vol. 121, pp. 253-260.Globalterminology

Abstract: The definition of a lopolith as a large planar-convex (downward) intrusion was coined by F.F. Grout one hundred years ago for the proposed shape of the Duluth gabbro. Subsequent research has challenged the concept that it is a single body, and that it has the lateral extent (under Lake Superior) and shape originally proposed. Other large basic intrusions have shapes, especially for their lower contacts, that are difficult to constrain, and none can be convincingly shown to be of the proposed shape of a lopolith. Their inferred or proposed shapes range from wedge to funnel to planar shaped, with a rarely exposed vertical feeder, and with angles to the sides that vary from minimal to very steep, and variably contorted surface plan. If no intrusions fit the definition, should the term lopolith be discontinued?
DS201911-2514
2019
Cesare, B., Nestola, F., Johnson, T., Mugnaioli, E., Della Ventura, G., Peruzzo, L., Bartoli, O., Viti, C., Erickson, T.Garnet, the archetypal cubic mineral, grows tetragonal.Nature Research, doi.org/10.1038/s41598-019-51214-9Mantlegarnet

Abstract: Garnet is the archetypal cubic mineral, occurring in a wide variety of rock types in Earth’s crust and upper mantle. Owing to its prevalence, durability and compositional diversity, garnet is used to investigate a broad range of geological processes. Although birefringence is a characteristic feature of rare Ca-Fe3+ garnet and Ca-rich hydrous garnet, the optical anisotropy that has occasionally been documented in common (that is, anhydrous Ca-Fe2+-Mg-Mn) garnet is generally attributed to internal strain of the cubic structure. Here we show that common garnet with a non-cubic (tetragonal) crystal structure is much more widespread than previously thought, occurring in low-temperature, high-pressure metamorphosed basalts (blueschists) from subduction zones and in low-grade metamorphosed mudstones (phyllites and schists) from orogenic belts. Indeed, a non-cubic symmetry appears to be typical of common garnet that forms at low temperatures (<450?°C), where it has a characteristic Fe-Ca-rich composition with very low Mg contents. We propose that, in most cases, garnet does not initially grow cubic. Our discovery indicates that the crystal chemistry and thermodynamic properties of garnet at low-temperature need to be re-assessed, with potential consequences for the application of garnet as an investigative tool in a broad range of geological environments.
DS201905-1020
2019
Cesare, B., Nestola, F., Mugnaioli, E., Della Ventura, G., Peruzzo, L., Bartoli, O., Viti, C., Johnson, T., Erickson, T.I was not born cubic, said low temperature metamorphic garnet. Geophysical Research Abstracts EGRU2019-3091, Vol. 21, 3091, 1p.Europe, Alpsgarnet

Abstract: Garnet is the paradigmatic cubic mineral of metamorphic and igneous rocks, and is generally regarded as optically isotropic. Nonetheless, evident birefringence is observed, particularly in the rare CaFe 3+ hydrogarnets, which is attributed to the coexistence of two or more cubic phases. A weak birefringence, with rare examples of optical sector zoning, has also been documented in much more common Fe 2+-Mg-Mn garnets, but an adequate explanation for its cause is, so far, lacking. Here we show that optically anisotropic garnets are much more widespread than previously thought, both in blueschists and blueschist-facies rocks, as well as in lower greenschist-facies phyllites, but they are frequently overlooked when working with conventional, 30-µm-thick thin sections. Utilizing a multi-technique approach including optical microstructural analysis, BSEM, EMPA, EBSD, FTIR, TEM, EDT and single-crystal XRD, we demonstrate here that the birefringence in these garnets is related to their tetragonal symmetry, that it is not due to strain, and that crystals are twinned according to a merohedral law. We also show that the birefringent garnets from blueschists and phyllites are anhydrous, lacking any hydrogarnet component, and have compositions dominated by almandine (58-79%) and grossular (19-30%) with variable spessartine (0-21%) and very low pyrope (1-7%). Considering the widespread occurrence of optically anisotropic OH-free garnets in blueschists and phyllites, their common low-grade metamorphic origin, and the occurrence of optically isotropic garnets with similar Ca-rich almandine composition in higher-grade rocks, we conclude that garnet does not grow with cubic symmetry in low-temperature rocks (< 400 • C). The tetragonal structure appears to be typical of Fe-Ca-rich compositions, with very low Mg contents. Cubic but optically sector-zoned garnet in a lower amphibolite-facies metapelite from the eastern Alps suggests that preservation of tetragonal garnet is favored in rocks which did not progress to T> ˜500 • C, where transition to the cubic form, accompanied by change of stable chemical composition, would take place. Our data show that the crystal-chemistry of garnet, its thermodynamics and, in turn, its use in unravelling petrogenetic processes in cold metamorphic environments need to be reassessed.
DS201901-0015
2018
Chaika, I.F., Izokh, A.E.Dunites of Inagli massif ( Central Aldan), cumulates of lamproitic magma.Russian Geology and Geophysics, Vol. 59, 11, pp. 1450-1460.Russia, Aldanlamproite

Abstract: We consider a hypothesis for the origin of PGE-bearing ultramafic rocks of the Inagli massif (Central Aldan) through fractional crystallization from ultrabasic high-potassium magma. We studied dunites and wehrlites of the Inagli massif and olivine lamproites of the Ryabinovy massif, which is also included into the Central Aldan high-potassium magmatic area. The research is focused on the chemistry of Cr-spinels and the phase composition of Cr-spinel-hosted crystallized melt inclusions and their daughter phases. Mainly two methods were used: SEM-EDS (Tescan Mira-3), to establish different phases and their relationships, and EPMA, to obtain precise chemical data on small (2-100 µm) phases. The obtained results show similarity in chromite composition and its evolutionary trends for the Inagli massif ultramafites and Ryabinovy massif lamproites. The same has been established for phlogopite and diopside from crystallized melt inclusions from the rocks of both objects. Based on the results of the study, the conclusion is drawn that the ultramafic core of the Inagli massif resulted from fractional crystallization of high-potassium melt with corresponding in composition to low-titanium lamproite. This conclusion is consistent with the previous hypotheses suggesting an ultrabasic high-potassium composition of primary melt for the Inagli ultramafites.
DS201906-1281
2019
Chakhmouradian, A., Reid, K.Wekusko Lake dikes ( central Manitoba): long -overdue kimberlites, oddball carbonatites, or "a missing link?"GAC/MAC annual Meeting, 1p. Abstract p. 70.Canada, ManitobaCarbonatite

Abstract: Manitoba, with its 400 000 km2 of exposed Precambrian basement, remains the most conspicuous "white spot" on the map of Canadian kimberlites. The apparent absence of these rocks from the regional geological record seems all the more paradoxical, given the existence of large Phanerozoic kimberlite fields just across the provincial border in eastern Saskatchewan, and abundant evidence of mantle-derived carbonate-rich magmatism (carbonatites and ultramafic lamprophyres) across central Manitoba. Interestingly, rocks of this type were first identified in the Province in 1983 at Wekusko Lake, where they crosscut supracrustal assemblages of the Paleoproterozoic Flin Flon belt, and were tentatively logged as kimberlites. This interpretation, based to a large extent on their high Cr + Ni contents and the presence of indicator minerals in their modal composition, was challenged in subsequent research. Similar rocks have been recognized recently in similar settings south of Wekusko Lake. These discoveries expanded not only the area of known post-Paleoproterozoic mantle magmatism, but also the petrographic and geochemical spectrum of its products. The primary carbonate phase in these rocks is dolomite that shows a variable degree of subsolidus isotopic re-equilibration under CO2-rich conditions. Fluid-rock interaction was also responsible for the replacement of olivine, phlogopite and groundmass perovskite by secondary minerals and deposition of hydrothermal carbonates in fractures, although the relative timing of these processes with respect to dike emplacement is poorly understood at present. Notably, indicator minerals indistinguishable from those in bona fide kimberlites are common in all of the examined dikes. These recent discoveries may hold key to understanding the genetic relations between kimberlites and primitive carbonatites, and have practical implications for heavy-mineral-based diamond exploration.
DS201902-0264
2019
Chakraborty, T., Upadhyay, D., Ranjan, S., Pruseth, K.L., Nanda, J.K.The geological evolution of the Gangpur schist belt, eastern India: constraints on the formation of the greater Indian landmass of the Proterozoic.Journal of Metamorphic Geology, Vol. 37, 1, pp. 113-151.Indiageology

Abstract: The Central Indian Tectonic Zone (CITZ) is a Proterozoic suture along which the Northern and Southern Indian Blocks are inferred to have amalgamated forming the Greater Indian Landmass. In this study, we use the metamorphic and geochronological evolution of the Gangpur Schist Belt (GSB) and neighbouring crustal units to constrain crustal accretion processes associated with the amalgamation of the Northern and Southern Indian Blocks. The GSB sandwiched between the Bonai Granite pluton of the Singhbhum craton and granite gneisses of the Chhotanagpur Gneiss Complex (CGC) links the CITZ and the North Singhbhum Mobile Belt. New zircon age data constrain the emplacement of the Bonai Granite at 3,370 ± 10 Ma, while the magmatic protoliths of the Chhotanagpur gneisses were emplaced at c. 1.65 Ga. The sediments in the southern part of the Gangpur basin were derived from the Singhbhum craton, whereas those in the northern part were derived dominantly from the CGC. Sedimentation is estimated to have taken place between c. 1.65 and c. 1.45 Ga. The Upper Bonai/Darjing Group rocks of the basin underwent major metamorphic episodes at c. 1.56 and c. 1.45 Ga, while the Gangpur Group of rocks were metamorphosed at c. 1.45 and c. 0.97 Ga. Based on thermobarometric studies and zircon-monazite geochronology, we infer that the geological history of the GSB is similar to that of the North Singhbhum Mobile Belt with the Upper Bonai/Darjing and the Gangpur Groups being the westward extensions of the southern and northern domains of the North Singhbhum Mobile Belt respectively. We propose a three-stage model of crustal accretion across the Singhbhum craton - GSB/North Singhbhum Mobile Belt - GC contact. The magmatic protoliths of the Chhotanagpur Gneisses were emplaced at c. 1.65 Ga in an arc setting. The earliest accretion event at c. 1.56 Ga involved northward subduction and amalgamation of the Upper Bonai Group with the Singhbhum craton followed by accretion of the Gangpur Group with the Singhbhum craton-Upper Bonai Group composite at c. 1.45 Ga. Finally, continent-continent collision at c. 0.96 Ga led to the accretion of the CGC with the Singhbhum craton-Upper Bonai Group-Gangpur Group crustal units, synchronous with emplacement of pegmatitic granites. The geological events recorded in the GSB and other units of the CITZ only partially overlap with those in the Trans North China Orogen and the Capricorn Orogen of Western Australia, indicating that these suture zones are not correlatable.
DS201906-1282
2019
Chambers, E.L., Harmon, N., Keir, D., Rychert, C.A.Using ambient noise to image the northern East African Rift.Geochemistry, Geophysics, Geosystems, Vol. 20, 4, pp. 2091-2109.Africageophysics

Abstract: In Ethiopia, the African Continent is rifting apart to slowly form a new ocean basin, which will expand the Red Sea and the Gulf of Aden. How and why this rifting is occurring remains an important unanswered question in earth science. We know tectonic forces are partly responsible, but magmatism also seems a key ingredient for breaking up Africa. Here we use seismic images obtained from signals pulled out of noise, to understand the crustal structure of the region; In particular, how and where magma is stored in the crust, and its relationship to the different stages of continental breakup visible in the region. We find evidence for long-term melt storage in places where rifting is just beginning in southern Ethiopia; whereas in regions where the crust is thinner due to extensive rifting, magma erupts more regularly. The long-term storage of magma in unrifted crust may help to heat and weaken it, allowing rifting to accelerate and propagate further south. We are also able to image regions with hydrothermal fluids in the shallow parts of the crust in inactive fault zones. These results provide insight into the breakup process and the role magma plays at different stages of rifting.
DS201909-2029
2019
Chandra, J., Paul, D., Stracke, A., Chabaux, F., Granet, M.The origin of carbonatites from Amba Dongar within the Deccan Large Igneous Province.Journal of Petrology , Vol. 60, 6, pp. 1119--1134.Indiacarbonatite

Abstract: There are disparate views about the origin of global rift- or plume-related carbonatites. The Amba Dongar carbonatite complex, Gujarat, India, which intruded into the basalts of the Deccan Large Igneous Province (LIP), is a typical example. On the basis of new comprehensive major and trace element and Sr-Nd-Pb isotope data, we propose that low-degree primary carbonated melts from off-center of the Deccan-Réunion mantle plume migrate upwards and metasomatize part of the subcontinental lithospheric mantle (SCLM). Low-degree partial melting (~2%) of this metasomatized SCLM source generates a parental carbonated silicate magma, which becomes contaminated with the local Archean basement during its ascent. Calcite globules in a nephelinite from Amba Dongar provide evidence that the carbonatites originated by liquid immiscibility from a parental carbonated silicate magma. Liquid immiscibility at crustal depths produces two chemically distinct, but isotopically similar magmas: the carbonatites (20% by volume) and nephelinites (80% by volume). Owing to their low heat capacity, the carbonatite melts solidified as thin carbonate veins at crustal depths. Secondary melting of these carbonate-rich veins during subsequent rifting generated the carbonatites and ferrocarbonatites now exposed at Amba Dongar. Carbonatites, if formed by liquid immiscibility from carbonated silicate magmas, can inherit a wide range of isotopic signatures that result from crustal contamination of their parental carbonated silicate magmas. In rift or plume-related settings, they can, therefore, display a much larger range of isotope signatures than their original asthenosphere or mantle plume source.
DS201904-0724
2019
Chang, S-J, Ferreira, A.M.G.Inference of water content in the mantle transition zone near subducted slabs from anisotropy tomography.Geochemistry, Geophysics, Geosystems, Vol. 20, 2, pp. 1189-1201.Mantlesubduction

Abstract: Tectonic plates plunge into the mantle at trenches, carrying water from the oceans. Some of this water may go down to the mantle transition zone between 410- and 660-km depth, where minerals have a large water storage capacity. In this study, we use observations of seismic anisotropy, the directional dependency of seismic wave speed, which is sensitive to the water content in the mantle transition zone. We find that the mantle transition zone beneath some subduction zones is drier than previously thought.
DS201906-1283
2018
Chanturia, V.A., Dvoichenkova, G.P., Morozov, V.V., Kovalchuk, O.E., Podkamenny, Y.A., Yakolev, V.N.Experimental justification of luminophore composition for indication of diamonds in x-ray luminescence separation of kimberlite ore.Journal of Mineral Science, Vol. 54, 3, pp. 458-465.Russialuminescence

Abstract: Organic and inorganic luminophores of similar luminescence parameters as diamonds are selected. Indicators, based on the selected luminophores, are synthesized. Spectral and kinetic characteristics of luminophores are experimentally determined for making a decision on optimal compositions to ensure maximum extraction of diamonds in X-ray luminescence separation owing to extra recovery of non-luminescent diamond crystals. As the components of luminophore-bearing indicators, anthracene and K-35 luminophores are selected as their parameters conform luminescence parameters of diamonds detected using X-ray luminescence separator with standard settings.
DS201910-2249
2019
Chasse, M., Blanchard, M., Cabareta, D., Juhin, A., Vantelon, D., Griffin, W.L., O'Reilly, S.Y., Calas, G.Deciphering molecular-scale mechanisms covering scandium dynamics in the critical zone. Goldschmidt2019, in press available, 71 ppt.Australialaterites

Abstract: Scandium is often considered as immobile during chemical weathering, based on its low solubility. In contrast to other conservative (i.e. relatively immobile) elements incorporated into accessory minerals resistant to weathering (e.g. zirconium, thorium or niobium), the scarcity of scandium minerals indicates that the processes accounting for scandium's immobilisation are distinctive. However, the evolution of scandium speciation during weathering is unknown, limiting the understanding of the processes controlling its dynamics in the critical zone. Exceptional scandium concentrations in east Australian laterites provide the possibility of unravelling these mechanisms. We follow scandium speciation through thick lateritic profiles (> 30 m) using a multiscale mineralogical and spectroscopic approach involving electron microprobe, laser-ablation--inductively coupled plasma mass spectrometry, selective leaching and X-ray absorption near-edge structure spectroscopy, complemented by mass-transfer calculations. We show that the initial reservoir of scandium contained in the parent rock is preserved under reducing conditions occurring in the lowest horizons of the profiles. The dissolution of scandium-bearing clinopyroxene generates smectitic clays that immobilise and concentrate scandium. It is subsequently trapped in the lateritic duricrust by goethite. Scandium mobilisation appears in this horizon and increases upward as a result of the dissolution of goethite, possibly assisted by dissolved organic matter, and the precipitation of hematite. Molecular-scale analyses demonstrate that changes in speciation govern scandium dynamics, with substitution in smectitic clays and adsorption on iron oxyhydroxides playing a crucial role in scandium immobility in the saprolite and lower lateritic duricrust. The higher affinity of scandium for goethite relative to hematite drives scandium mobilisation in the upper lateritic duricrust, leading to its concentration downward in the lower lateritic duricrust. These successive mechanisms illustrate how the unique complexity of the critical zone leads to scandium concentrations that may form new types of world-class scandium deposits. Comparison with conservative elements and with rare-earth elements, expected to have similar geochemical properties, emphasizes the unique behaviour of scandium in the critical zone. While scandium remains immobile during the early stages of weathering, intense and long-term alteration processes, observed in lateritic contexts, lead to scandium mobilisation. This study highlights the dependence of scandium mobility on weathering conditions.
DS201910-2250
2019
Chauvel, C.Enigmatic origin of diamond-bearing rocks revealed. Overview of Woodhead's article.Nature, Vol. 573, pp. 498-499.Mantlediamond genesis

Abstract: Kimberlites are volcanic rocks that derive from deep in Earth’s mantle, but the nature of their source is uncertain. A study of this source’s evolution over two billion years provides valuable information about its properties.
DS201901-0016
2019
Chebotarev, D.A., Veksler, I.V., Wohlgemuth-Uberwasser, C., Doroshkevich, A.G., Koch-Muller, M.Experimental study of trace element distribution between calcite, fluorite and carbonatitic melt in the systemCaCO3+CaF2+Na2CO3+-Ca3(P04)2 at 100MPa.Contributions to Mineralogy and Petrology, Vol. 174, 4, doi.org/10. 1007/s00410-018-1530-x 13p.Mantlecarbonatite

Abstract: Here we present an experimental study of the distribution of a broad range of trace elements between carbonatite melt, calcite and fluorite. The experiments were performed in the CaCO3 + CaF2 + Na2CO3 ± Ca3(PO4)2 synthetic system at 650-900 °C and 100 MPa using rapid-quench cold-seal pressure vessels. Starting mixtures were composed of reagent-grade oxides, carbonates, Ca3(PO4)2 and CaF2 doped with 1 wt% REE-HFSE mixture. The results show that the distribution coefficients of all the analyzed trace elements for calcite and fluorite are below 1, with the highest values observed for Sr (0.48-0.8 for calcite and 0.14-0.3 for fluorite) and Y (0.18-0.3). The partition coefficients of REE gradually increase with increasing atomic number from La to Lu. The solubility of Zr, Hf, Nb and Ta in the synthetic F-rich carbonatitic melts, which were used in our experiments, is low and limited by crystallization of baddeleyite and Nb-bearing perovskite.
DS201901-0017
2018
Chen, M., Shu, J., Xie, X., Tan, D.Maohokite, a post-spinel polymorph of MgFe2O4 in shocked gneiss from the Xiuyan crater in China.Meteoritics & Planetary Science, doi.10.1111/ maps.13222 8p.Chinamineralogy

Abstract: Maohokite, a post-spinel polymorph of MgFe2O4, was found in shocked gneiss from the Xiuyan crater in China. Maohokite in shocked gneiss coexists with diamond, reidite, TiO2-II, as well as diaplectic glasses of quartz and feldspar. Maohokite occurs as nano-sized crystallites. The empirical formula is (Mg0.62Fe0.35Mn0.03)2+Fe3+2O4. In situ synchrotron X-ray microdiffraction established maohokite to be orthorhombic with the CaFe2O4-type structure. The cell parameters are a = 8.907 (1) Å, b = 9.937(8) Å, c = 2.981(1) Å; V = 263.8 (3) Å3; space group Pnma. The calculated density of maohokite is 5.33 g cm-3. Maohokite was formed from subsolidus decomposition of ankerite Ca(Fe2+,Mg)(CO3)2 via a self-oxidation-reduction reaction at impact pressure and temperature of 25-45 GPa and 800-900 °C. The formation of maohokite provides a unique example for decomposition of Fe-Mg carbonate under shock-induced high pressure and high temperature. The mineral and its name have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA 2017-047). The mineral was named maohokite after Hokwang Mao, a staff scientist at the Geophysical Laboratory, Carnegie Institution of Washington, for his great contribution to high pressure research.
DS201907-1532
2019
Chen, W., Liu, H-Y,m Jiang, S-Y., Simonetti, A., Xu, C., Zhang, W.The formation of the ore-bearing dolomite marble from the giant Bayan Obo REE-Nb-Fe deposit, Inner Mongolia: insights from micron-scale geochemical data.Mineralium Deposita, in press available, 16p.Asia, Mongoliadeposit - Bayan Obo

Abstract: The genesis of Earth’s largest rare earth element (REE) deposit, Bayan Obo (China), has been intensely debated, in particular whether the host dolomite marble is of sedimentary or igneous origin. The protracted (Mesoproterozoic to Paleozoic) and intricate (magmatic to metasomatic) geological processes complicate geochemical interpretations. In this study, we present a comprehensive petrographic and in situ, high-spatial resolution Sr-Pb isotopic and geochemical investigation of the host dolomite from the Bayan Obo marble. Based on petrographic evidence, the dolomite marble is divided into three facies including coarse-grained (CM), fine-grained (FM), and heterogeneous marble (HM). All carbonates are ferroan dolomite with high SrO and MnO contents (>?0.15 wt.%), consistent with an igneous origin. Trace element compositions of these dolomites are highly variable both among and within individual samples, with CM dolomite displaying the strongest LREE enrichment. In situ 206Pb/204Pb and 207Pb/204Pb ratios of the dolomite are generally consistent with mantle values. However, initial 208Pb/204Pb ratios define a large range from 35.45 to 39.75, which may result from the incorporation of radiogenic Pb released from decomposition of monazite and/or bastnäsite during Early Paleozoic metasomatism. Moreover, in situ Sr isotope compositions of dolomite indicate a large range (87Sr/86Sr?=?0.70292-0.71363). CM dolomite is characterized by a relatively consistent, unradiogenic Sr isotope composition (87Sr/86Sr?=?0.70295-0.70314), which is typical for Mesoproterozoic mantle. The variation of 87Sr/86Sr ratios together with radiogenic 206Pb/204Pb signatures for dolomite within FM and HM possibly represents recrystallization during Early Paleozoic metasomatism with the contribution of radiogenic Sr and Pb from surrounding host rocks. Therefore, our in situ geochemical data support a Mesoproterozoic igneous origin for the ore-bearing dolomite marble in the Bayan Obo deposit, which subsequently underwent intensive metasomatism during the Early Paleozoic.
DS201904-0725
2019
Chen, W., Ying, Y-C., Bai, T., Zhang, J-J., Jiang, S-Y., Zhao, K-D.In situ major and trace element analysis of magnetite from carbonatite related complexes: implications for petrogenesis and ore genesis.Ore Geology Reviews, Vol. 107, pp. 30-40.Chinacarbonatite

Abstract: Magnetite (Fe3O4) is one of the most common accessory minerals in magmatic rocks, and it can accommodate a wide variety of major, minor and trace elements that can be measured by laser ablation ICP-MS. In this study, we investigate the chemical compositions of magnetite from four carbonatite complexes (Oka, Mushgai Khudag, Hongcheon and Bayan Obo). The minor elements (Mg, Ti, Al, Mn) in magnetite vary significantly both within and between different complexes. High field strength elements (Zr, Hf, Nb, Ta, U, Th) are generally depleted in magnetite from carbonatite complexes, whereas K, Rb, Cs, Ca and P are commonly below detection limits. V and Zn display significant variations from tens to thousands of ppm. Co, Ni and Ga are present in ppm or tens of ppm, whereas Cu, Sr, Y, Ba and Pb are characterized by sub-ppm levels. Mo and Ge are identified at the ppm level, whereas a consistent concentration of 2-5?ppm is observed for Ge. The determined chemical compositions of magnetite from carbonatite complexes are quite distinguishable compared to those formed in silicate and sulfide melts. This is clearly shown using multielement variation diagrams, and the distinct signatures of carbonatite-related magnetite include strong positive anomalies of Mn and Zn and negative anomalies of Cu, Co and Ga. The discriminant diagrams of Ti vs. Zr?+?Hf, Ti vs. Nb?+?Ta and Ni/Cr vs. Ti are applicable for distinguishing magmatic and hydrothermal magnetite in carbonatite-related environments. In addition, the discriminant diagram of Zn/Co vs. Cu/Mo and Cu vs. Zr?+?Hf can be used to distinguish carbonatite-related magnetite from magnetite that formed in other environments.
DS201903-0501
2019
Chepurov, A., Faryad, S.W., Agashev, A.M.Experimental crystallization of a subcalcic Cr-rich pyrope in the presence of REE bearing carbonatite.Chemical Geology, carbonatite

Abstract: This paper focuses on formation of subcalcic Cr-rich garnet (up to 14.25?wt% Cr2O3) in the model ultramafic system corresponding to natural harzburgite with the presence of REE-bearing fluid phase. The experiments were carried out using a “split-sphere” type multi-anvil high-pressure apparatus (BARS) at a pressure of 5?GPa and a temperature of 1300?°C. Natural serpentine, chromite, corundum and REE-carbonatite were used as starting components. Crystallization of garnet occurred in subsolidus conditions by the reaction of orthopyroxene and spinel in the presence of fluid phase. Composition of fluid was controlled by interaction of water released by decomposition of serpentine with carbonate. By using different amounts of carbonatite (0.5 and 1.5?wt%) as a source of calcium and REE, subcalcic Cr-rich garnets with up to 3.5?wt% CaO were crystallized, which are typical for inclusions of harzburgitic paragenesis in natural diamonds. The experiments demonstrated that the rare earth elements (REE) released from the initial carbonatite were transported by the fluid and were incorporated into the newly formed garnet. The distribution of REE in garnet revealed a vivid enrichment toward the heavy REE (HREE), showing the pattern with a very steep slope. These results confirmed high partitioning of HREE into garnet. The present study indicates that the mantle carbonatites, which contain very high proportions of light REE (LREE) to HREE, can play an important role as source material in formation of REE-rich fluids to crystallize garnets with typical REE patterns in mantle peridotites.
DS201907-1533
2019
Cheskidov, V.I., Akishev, A.N., Sakantsev, G.G.Use of draglines in mining diamond ore deposits in Yakutia.Journal of Mining Science, Vol. 54, 4, pp. 628-637.Russia, Yakutiamining

Abstract: Potential ranges of use of draglines at steeply dipping diamond ore deposits in Yakutia are discussed. Technology of stripping with direct dumping and rehandling by draglines is substantiated for upper overburden layers. A variant of increasing height of stripping benches on haulage horizons through the use of draglines and crane lines is discussed. A resource saving technology is proposed for mining roundish and extended ore bodies with alternating advance of mining front and with internal dumping. The method of estimating efficient thickness of overburden in case of direct dumping is developed using the layer coefficient of overburden rehandling. Expediency of using blasting for displacement of broken overburden to internal dump is specified.
DS201908-1774
2019
Chmyz, L., Arnaud, N., Biondi, J.C., Azzone, R.G., Bosch, D.Hf-Pb isotope and trace element constraints on the origin of the Jacupiringa complex ( Brazil): insights into carbonatite genesis and multi-stage metasomatism of the lithospheric mantle.Gondwana Research, Vol. 71, pp. 16-27.South America, Brazilcarbonatite

Abstract: The Lower Cretaceous Jacupiranga complex, in the central-southeastern portion of the South American Platform, includes carbonatites in close association with silicate rocks (i.e. strongly and mildly silica-undersaturated series). Here we document the first hafnium isotope data on the Jacupiranga complex, together with new trace element and Pb isotope compositions. Even though liquid immiscibility from a carbonated silicate melt has been proposed for the genesis of several Brazilian carbonatites, isotopic and geochemical (e.g., Ba/La ratios, lack of pronounced Zr-Hf and Nb-Ta decoupling) information argues against a petrogenetic relationship between Jacupiranga carbonatites and their associated silicate rocks. Thus, an origin by direct partial melting of the mantle is considered. The isotopic compositions of the investigated silicate samples are coherent with a heterogeneously enriched subcontinental lithospheric mantle (SCLM) source of rather complex evolution. At least two metasomatic processes are constrained: (1) a first enrichment event, presumably derived from slab-related fluids introduced into the SCLM during Neoproterozoic times, as indicated by consistently old TDM ages and lamprophyre trace signatures, and (2) a Mesozoic carbonatite metasomatism episode of sub-lithospheric origin, as suggested by eNd-eHf values inside the width of the terrestrial array. The Jacupiranga parental magmas might thus derive by partial melting of distinct generations of metasomatic vein assemblages that were hybridized with garnet peridotite wall-rocks.
DS201905-1021
2019
Chmyz, L., Arnaud, N., Biondo, J.C., Azzone, R.G., Bosch, D.Hf-Pb isotope and trace element constraints on the origin of the Jacupiranga Complex ( Brazil): insights into carbonatite genesis and multi-stage metasomatism of the lithospheric mantle.Gondwana Research, Vol. 71, pp. 16-27.South America, Brazilcarbonatite

Abstract: The Lower Cretaceous Jacupiranga complex, in the central-southeastern portion of the South American Platform, includes carbonatites in close association with silicate rocks (i.e. strongly and mildly silica-undersaturated series). Here we document the first hafnium isotope data on the Jacupiranga complex, together with new trace element and Pb isotope compositions. Even though liquid immiscibility from a carbonated silicate melt has been proposed for the genesis of several Brazilian carbonatites, isotopic and geochemical (e.g., Ba/La ratios, lack of pronounced Zr-Hf and Nb-Ta decoupling) information argues against a petrogenetic relationship between Jacupiranga carbonatites and their associated silicate rocks. Thus, an origin by direct partial melting of the mantle is considered. The isotopic compositions of the investigated silicate samples are coherent with a heterogeneously enriched subcontinental lithospheric mantle (SCLM) source of rather complex evolution. At least two metasomatic processes are constrained: (1) a first enrichment event, presumably derived from slab-related fluids introduced into the SCLM during Neoproterozoic times, as indicated by consistently old TDM ages and lamprophyre trace signatures, and (2) a Mesozoic carbonatite metasomatism episode of sub-lithospheric origin, as suggested by eNd-eHf values inside the width of the terrestrial array. The Jacupiranga parental magmas might thus derive by partial melting of distinct generations of metasomatic vein assemblages that were hybridized with garnet peridotite wall-rocks.
DS201906-1284
2019
Chow, R., Fedortchouk, Y., Normandeau, P.Trace element partitioning between apatite and kimberlite-like melts: implications for volatile degassing and formation of different kimberlite facies.GAC/MAC annual Meeting, 1p. Abstract p. 71.Mantlekimberlites

Abstract: Primary melt composition of kimberlites remains poorly constrained due to the contamination from mantle and crustal rocks, loss of volatiles during emplacement, significant alteration, and the lack of any quenched melts. Additionally, kimberlite bodies have multiple morphologies of which their emplacement mechanism remains elusive. Apatite is a common accessory mineral in kimberlite. Its structure incorporates many trace elements of which partitioning depends on the composition of the melt. Concentrations of trace elements in kimberlitic apatite can help to assess the content of carbonate and silicate components in kimberlite melt. Apatite is also often used as an indicator mineral of magma degassing in igneous systems. As such, it should be applied to kimberlitic systems to study the volatile behaviour during emplacement. However, the existing estimates for the trace elements partitioning in apatite provide controversial estimates for carbonatitic melts and estimates for silicate melts use compositions very different than the composition of kimberlites. This study experimentally determines partition coefficients of trace elements and kimberlite-like melts. The experiments were done in piston cylinder apparatus at 1250-1350 °C and 1-2 Gpa. Partition coefficients for Nb, Sr, Rb, Zr, Sm, Cs, Hf, La, Yb, and Eu were examined in synthetic compositions representing evolved kimberlite melts: three lamproitic compositions (17-23 wt % SiO2 and 9-33 wt % CO2) and a composition modelled after a magmatic kimberlite (14-29 wt % SiO2 and 7-33 wt % CO2). The effects of melt composition, temperature, pressure, water, and oxygen fugacity have been tested. The obtained partition coefficients were applied to natural kimberlitic apatites from Ekati Mine (Canada) and Orapa cluster (Botswana) to model kimberlite melt composition. Observed variation in the presence, textures, and composition of natural apatites relative to depth in kimberlite pipes of differing lithologies is compared to experimental run products to infer crystallization conditions of different kimberlite bodies.
DS201912-2773
2019
Chow, R., Fedortchouk, Y., Normandeau, P.X.Trace element partitioning between apatite and kimberlite melts: implications to crystallization conditions of kimberlite magma.Yellowknife Forum NWTgeoscience.ca, abstract volume poster p.103.Mantlemagmatism

Abstract: Kimberlites are the deepest mantle magmas to reach the surface of the Earth and the hosts of the major primary diamond deposits. The enigmatic nature of kimberlites owning to poorly constrained triggers of kimberlite magmatism, melt composition, and crystallization conditions, are mostly limited by unknown content and composition of volatiles. The content and ratio of H2O and CO2 are important parameters of magma emplacement. They are essential for the mantle melting and rapid ascent of kimberlites. Volatiles also greatly affect diamond preservation in kimberlites during the ascent to the surface. Apatite has been used as an indicator of volatiles in different magmatic systems. Partitioning of trace elements between apatite and a melt is also sensitive to the carbonate component in the melt. This makes apatite potentially very useful indicator of evolution of melt composition and fluid during kimberlite ascent and emplacement. However, trace element partition coefficients between apatite and melts have been determined for compositions much more SiO2-rich than kimberlites, whereas coefficients in carbonate melts show large discrepancies. This study presents experimentally determined trace element partition coefficients (D) between apatite and synthetic analogues of kimberlite (SiO2 content ranging from 11 to 23 wt%) and carbonatite melts (SiO2 content <1 wt% and 4.5 wt%). The experiments were conducted in piston-cylinder apparatus at 1150o, 1250o, 1350o, at 1 and 2 GPa, and at oxygen fugacity -3.97, 0.27, 4.83 log units relative to fayalite-magnetite-quartz (FMQ) buffer. We demonstrate the increase of DREE for Rare Earth Elements (REE) with increase in SiO2 of the melt and the effect of apatite composition (natural Durango apatite vs. synthetic apatite) on D and substitution mechanism. We found no effect of temperature, pressure, water content, and oxygen fugacity on D in these low SiO2 melts. This allows us to use trace element content of natural apatite to examine the composition of kimberlite magma. We apply the results to apatite from two kimberlite classes: Class 1 composite kimberlite pipe from Orapa cluster (Botswana) with hypabyssal coherent and volcaniclastic kimberlite facies and Class 3 kimberlite pipes from Ekati Mine (Northwest Territories, Canada) filled with effusive coherent kimberlites in Leslie pipe and both volcaniclastic and coherent kimberlites in Boa pipe, and discuss how changes in SiO2 content of kimberlite melt affect apatite saturation. We further apply our experimentally determined DREE to model the composition of evolved kimberlite melt using published bulk rock and apatite compositions in kimberlites.
DS201912-2774
2019
Chowdbury, P., Dasgupta, R.Sulfur extraction via carbonated melts from sulfide bearing mantle lithologie - implications for deep sulfur cycle and mantle redox. ( mentions carbonatite and kimberlite)Geochimica et Cosmochimica Acta, in press, 61p. PdfMantlepetrology

Abstract: Transport of sulfur via mantle-derived partial melts from deep Earth to the surface reservoirs is a critical step in the deep global sulfur cycle. Given that sulfur is stored mostly in sulfide phases in mantle lithologies, the critical parameter is sulfur concentration at sulfide saturation (SCSS) of mantle-derived magmas. CO2?±?H2O-induced melting beneath oceanic and continental mantle produces incipient CO2-rich melts. Although, SCSS of silicate melts of a variety of compositions is extensively studied, the SCSS of carbonatitic and carbonated silicate melts have not received much attention. Here we present experiments in graphite capsules at pressures (P) of 2.5-6.0 GPa and temperatures (T) of 1350-1650?°C investigating the SCSS of carbonatitic and carbonated silicate melts. All experiments produced quenched Fe?±?Ni-sulfide melt blobs?+?carbonated melt matrix?±?ol?±?cpx?±?opx?±?gt, with melt composition on a CO2-free basis varying from 7 to 40 wt.% SiO2, 0.5 to 7 wt.% Al2O3, and 9 to 17 wt.% FeO* (total FeO). SCSS measured using EPMA increases with SiO2 and T but is not affected by P; the effect of composition being more pronounced than P-T. The composition of sulfide melt phase also affects SCSS. With increasing Ni in the molten sulfide phase, the SCSS changes from 2000 to 4000?ppm (Ni-free) to is 800-3000?ppm (33 wt.% Ni). Comparison of our measured SCSS with the existing SCSS models for nominally CO2-free silicate melts and with one study for carbonated melts show that these parameterizations fail to capture the sulfide saturation values in CO2-rich melts from our study. Using our new SCSS data and previous SCSS data for melt compositions that span the range from carbonatite to basalts via carbonated silicate melts, we develop a new empirical SCSS parameterization. Unlike a previous model, which suggested SCSS of carbonated melt is only affected by melt FeO* (other than P-T) and did not constrain how SCSS evolves from low-silica carbonatitic melt to low-CO2 basaltic melt, our new parameterization captured complex effects of many melt compositional parameters, including silica on SCSS. Using our new SCSS model, we constrained the efficiency of S extraction from the mantle beneath mid-oceanic ridges and continents via low-degree carbonated melts. Deep carbonated melts beneath ridges are expected to mobilize 5-15% of the initial sulfur before nominally-volatile-free peridotite melting begins. In continental mantle, deep kimberlitic melt can act as an agent to mildly enrich the shallow mantle in sulfide as it evolves to a carbonatitic melt upon reactive cooling. Application of our data to subduction zones suggests that low degree carbonatitic melt is not an efficient agent to extract residual sulfide from the subducting oceanic crust.
DS201901-0018
2018
CIMCIM Mineral Exploration Best Practice Guidelines.CIM , Nov. 23, 17p. Pdf Globalvaluation

Abstract: The CIM Mineral Exploration Best Practice Guidelines (the Exploration Guidelines) have been prepared to assist professional geoscientists and engineers to conduct consistently high-quality work in order to maintain public confidence. The Exploration Guidelines are meant to assist professional geoscientists and exploration practitioners in planning, supervising, and executing exploration programs. In Canada, there are generally two types of public resource reporting: “Disclosure”, as defined by NI 43-101, is the reporting of technical information to the public and market participants for securities legislation purposes where a Qualified Person (QP) must be involved, and reporting of exploration information for governmental agencies to support obligations under laws including the Mining Acts of each of the Provinces and Territories. The Exploration Guidelines are also relevant where the results will not be publicly reported but are intended for internal company use. While this document is intended as guidance for work conducted or supervised by geoscientists in Canada, many of the practices described herein can be adapted to mineral exploration activities in other countries. The Exploration Guidelines are not intended to inhibit original thinking, or to prevent the application of new approaches that may develop into fundamental components of successful mineral exploration programs. Rather than provide prescriptive solutions to specific issues, they include general guidelines for current professional practice and to demonstrate and defend the merits of new methods. These guidelines do not preclude individuals and companies from developing more detailed guidelines specific to their own requirements. The initial version of the Exploration Guidelines was prepared by the Canadian Institute of Mining and Metallurgy and Petroleum (CIM) Exploration Best Practices Committee and adopted by CIM Council on August 20, 2000. On January 9, 2018, CIM Council formed a new committee, the Mineral Resources and Reserves Committee (CIM MRMR Committee) with a mandate to, among other things, update the Exploration Best Practice Guidelines. The mandate for the committee was accepted by CIM Council on March 2, 2018. The new Exploration Guidelines document was adopted by the CIM Council on November 23, 2018.
DS201908-1775
2019
Cimen, O., Kuebler, C., Simonetti, S.S., Corcoran, L., Mitchell, R., Simonetti, A.Combined boron, radiogenic ( Nd, Pb, Sr) stable (C,O) isotopic and geochemical investigations of carbonatites from the Blue River region, British Columbia ( Canada): implications for mantle sources and recycling of crustal carbon.Chemical Geology, in press available, 59p. PdfCanada, British Columbiadeposit - Blue River

Abstract: This study reports the combined major, minor and trace element compositions, and stable (C, O), radiogenic (Nd, Pb, and Sr) isotopic compositions, and first d11B isotopic data for the Fir, Felix, Gum, and Howard Creek carbonatites from the Blue River Region, British Columbia (Canada). These sill-like occurrences were intruded into Late Proterozoic strata during rifting and extensional episodes during the Late Cambrian and Devonian -Mississippian, and subsequently deformed and metamorphosed to amphibolite grade in relation to a collisional-type tectonic environment. The carbonatites at Fir, Gum, and Felix contain both calcite and dolomite, whereas the carbonatite at Howard Creek contains only calcite. The dolomite compositions reported here are consistent with those experimentally determined by direct partial melting of metasomatized peridotitic mantle. The combined major and trace element compositions and d13CPDB (-5.37 to -4.85‰) and d18OSMOW (9.14 to 9.62‰) values for all the samples investigated are consistent with those for primary igneous carbonate and support their mantle origin. However, these signatures cannot be attributed to closed system melt differentiation from a single parental melt. The initial Nd, Pb, and Sr isotopic ratios are highly variable and suggest generation from multiple, small degree parental melts derived from a heterogeneous mantle source. The d11B values for carbonates from Felix, Gum, and Howard Creek vary between -8.67 and -6.36‰, and overlap the range for asthenospheric mantle (-7.1?±?0.9‰), whereas two samples from Fir yield heavier values of -3.98 and -2.47‰. The latter indicate the presence of recycled crustal carbon in their mantle source region, which is consistent with those for young (<300?Ma) carbonatites worldwide. The radiogenic and B isotope results for the Blue River carbonatites are compared to those from contrasting, anorogenic tectonic settings at Chipman Lake, Fen, and Jacupiranga, and indicate that similar upper mantle sources are being tapped for carbonatite melt generation. The pristine, mantle-like d11B values reported here for the Blue River carbonatites clearly demonstrate that this isotope system is robust and was not perturbed by post-solidification tectono-metamorphic events. This observation indicates that B isotope signatures are a valuable tool for deciphering the nature of the upper mantle sources for carbonates of igneous origin.
DS201909-2030
2019
Cimen, O., Kuebler, C., Simonetti, S.S., Corcoran, L., Mitchell, R., Simonetti, A.Combined boron, radiogenic (Nd, Pb, Sr), stable (C,O) isotopic and geochemical investigations of carbonatites from the Blue River region, British Columbia ( Canada): implications for mantle sources and recycling of crustal carbon.Chemical Geology, doi.org/10.1016/j.chemgeo.2019.07.015 59p.Canada, British Columbiacarbonatite - Blue River

Abstract: This study reports the combined major, minor and trace element compositions, and stable (C, O), radiogenic (Nd, Pb, and Sr) isotopic compositions, and first d11B isotopic data for the Fir, Felix, Gum, and Howard Creek carbonatites from the Blue River Region, British Columbia (Canada). These sill-like occurrences were intruded into Late Proterozoic strata during rifting and extensional episodes during the Late Cambrian and Devonian -Mississippian, and subsequently deformed and metamorphosed to amphibolite grade in relation to a collisional-type tectonic environment. The carbonatites at Fir, Gum, and Felix contain both calcite and dolomite, whereas the carbonatite at Howard Creek contains only calcite. The dolomite compositions reported here are consistent with those experimentally determined by direct partial melting of metasomatized peridotitic mantle. The combined major and trace element compositions and d13CPDB (-5.37 to -4.85‰) and d18OSMOW (9.14 to 9.62‰) values for all the samples investigated are consistent with those for primary igneous carbonate and support their mantle origin. However, these signatures cannot be attributed to closed system melt differentiation from a single parental melt. The initial Nd, Pb, and Sr isotopic ratios are highly variable and suggest generation from multiple, small degree parental melts derived from a heterogeneous mantle source. The d11B values for carbonates from Felix, Gum, and Howard Creek vary between -8.67 and -6.36‰, and overlap the range for asthenospheric mantle (-7.1?±?0.9‰), whereas two samples from Fir yield heavier values of -3.98 and -2.47‰. The latter indicate the presence of recycled crustal carbon in their mantle source region, which is consistent with those for young (<300?Ma) carbonatites worldwide. The radiogenic and B isotope results for the Blue River carbonatites are compared to those from contrasting, anorogenic tectonic settings at Chipman Lake, Fen, and Jacupiranga, and indicate that similar upper mantle sources are being tapped for carbonatite melt generation. The pristine, mantle-like d11B values reported here for the Blue River carbonatites clearly demonstrate that this isotope system is robust and was not perturbed by post-solidification tectono-metamorphic events. This observation indicates that B isotope signatures are a valuable tool for deciphering the nature of the upper mantle sources for carbonates of igneous origin.
DS201902-0265
2019
Cizkova, H., Bina, C.R.Linked influences on slab stagnation: interplay between lower mantle viscosity structure, phase transitions, and plate coupling.Earth and Planetary Science Letters, Vol. 509, 1, pp. 88-99.Mantlegeophysics - seismic

Abstract: An endothermic phase transition in mantle material at 660-km depth constitutes a barrier that in most cases prevents the direct penetration of subducted slabs. Seismic tomography shows that subducted material is in many subduction zones trapped at the bottom of the transition zone, just above the 660-km phase boundary. Recent tomographic models however also report subducted material that penetrates to the shallow lower mantle, and there it is observed to flatten at about 1000-km depth. Models of slab dynamics that generally assume sharp rheological transition at 660-km depth, however, mostly predict slab stagnation at the bottom of the transition zone. Multiple lines of evidence, including recent experiments, indicate that viscosity may gradually increase in the uppermost ~300 km of the lower mantle, rather than simply changing abruptly at the upper-lower mantle boundary. Here we present the results of a modeling study focused on the effects of rheological transition between upper and lower mantle material on slab deformation and stagnation. We test the effects of smoothing the viscosity increase over 300 km and shifting it to a depth of 1000 km or even deeper. We show that slab ability to penetrate to the lower mantle is mainly controlled by the trench migration rate, which in turn is affected by crustal viscosity. Coupling between the subducting and overriding plates thus plays a key role in controlling slab penetration to the lower mantle and stagnation in the deep transition zone or shallow lower mantle. Models with strong crust and consequently negligible rollback display penetration to the lower mantle without much hindrance and no stagnation above or below the 660-km interface, regardless of viscosity stratification in the shallow lower mantle. Models with weak crust are characterized by fast rollback, and penetration is very limited as slabs buckle horizontally and flatten above the 660-km boundary. Most interesting from the point of view of shallow lower mantle stagnation are models with intermediate crustal viscosity. Here rollback is efficient, though slower than in weak-crust cases. Horizontally lying slab segments are trapped in the transition zone if the sharp viscosity increase occurs at 660 km, but shifting the viscosity increase to 1000 km depth allows for efficient sinking of the flat-lying part and results in temporary stagnation below the upper-lower mantle boundary at about 1000 km depth.
DS201907-1534
2019
Coetzee, A., Kisters, A.F.M., Chevallier, L.Sill complexes in the Karoo LIP: emplacement controls and regional implications.Journal of African Earth Sciences, Vol. 158, available 14p. pdf Africa, South Africamagmatism

Abstract: Field and sub-surface data from the Victoria West sill complex in the Karoo Large Igneous Province (ca. 180 Ma) of South Africa are used to constrain the emplacement controls of the regional-scale sill complexes in the central Karoo basin. Cross-cutting relationships point to the presence of five distinct and successively emplaced saucer-shaped sills. Growth of the sill complex was achieved through magmatic underaccretion of magma batches below earlier sills and associated uplift of the overlying strata. The magmatic underaccretion suggests that earlier sills were fully crystallized during the emplacement of later magma pulses and that the rigid (high E) dolerites, in particular, acted as stress barriers that impeded further upward propagation of steep feeder sheets. The resulting nested structure of sills-in-sills within a confined area of less than 2000 km2 also suggests the reutilization of the same or similar feeder system even after full crystallization thereof. The emplacement controls of sills in the central Karoo through stress barriers implies that sill emplacement occurred under very low deviatoric stresses or in a mildly compressional stress regime prior to the break-up of Gondwana. The swap from earlier (184-180?Ma), mainly sill complexes to later (182-174?Ma) dykes and dyke swarms is indicative of a switch in the stress field during the early stages of Gondwana break-up. We speculate that loading, thermal subsidence and lithospheric flexure associated with the emplacement of the earlier, stacked and voluminous sill complexes in the Karoo basins may have determined the formation of the large Karoo dyke swarms, particularly when coinciding with deeper crustal structures. The original and inherited basin geometry and lithospheric structure is pivotal in the development of later Karoo magmatism.
DS201901-0019
2018
Cohen, H., Ruthstein, S.Evaluating the color and nature of diamonds via EPR spectroscopy.Gems & Gemology, Sixth International Gemological Symposium Vol. 54, 3, 1p. Abstract p. 276.Globaldiamond color

Abstract: Diamond characterization is carried out via a wide variety of gemological and chemical analyses. An important analytical tool for this purpose is spectroscopic characterization utilizing both absorption and emission measurements. The main techniques are UV-visible and infrared spectroscopy, though Raman as well as cathodoluminescence spectroscopy are also used. We have used electron paramagnetic resonance (EPR) spectroscopy to compare the properties of treated colored diamonds to the pretreated stones. The colors studied were blue, orange, yellow, green, and pink. The EPR technique determines radicals (atoms with unpaired electrons) and is very sensitive, capable of measuring concentrations as low as ~1 × 10–17 radicals/cm3. The results, shown in table 1, indicate that all the carbon radicals determined are affected by adjacent nitrogen atoms, with the spectra showing a hyperfine structure attributed to the presence of nitrogen. The highest concentration of radicals and hyperfine structures is observed in pink and orange treated diamonds. The results concerning nitrogen concentration were correlated with the infrared spectra, which determine the absorption peaks of the diamonds as well as those of the nitrogen contamination in their crystal structure.
DS201906-1285
2019
Coint, N., Dahlgren, S.Assessing the distribution of REE mineralization in Fe-dolomite carbonatite drill cores from the Fen complex, Telemark, southern Norway.GAC/MAC annual Meeting, 1p. Abstract p. 72.Europe, NorwayCarbonatite

Abstract: The Fen Complex is a 2 km-wide subcircular intrusion composed mainly of sovite, Fe-dolomite carbonatite, damtjernite (lamprophyre) and minor alkaline rocks such as nepheline syenite and ijolite, emplaced at 580 Ma through Mesoproterozoic orthogneisses forming the Fennoscandian Shield. Previous bulk-rock isotopic study indicates that the carbonatite magma originated in the upper mantle [(87Sr/86Sr)i = 0.7029] and underwent contamination during its ascent throughout the crust. This study focuses on two deep cores (1000 m and 700 m), drilled to assess the distribution of REE mineralizations in the Fe-dolomite carbonatite. Hyperspectral data, allowing investigators to log cores objectively and quantify lithologies, were acquired using a SisuRock Gen 2 system composed of three cameras gathering data in the following wavelengths: RGB, Near-Visible Short-Wave Infrared (VN-SWIR) and Long-Wave Infrared (LWIR). In addition, every meter of the first core and 500 m of the second one were analyzed for bulk-rock geochemistry to characterize the distribution of elements. In this study, we compare the results obtained by the imaging technique with the bulk-rock data and present preliminary results of the textural variations observed in rare-earth mineralizations. Preliminary results indicate that neither of the deep bore holes reached the fenitized host-rock and that the Fe-dolomite carbonatite continues at depth. In both cores, the dominant carbonate is Fe-rich dolomite, although calcite and Fe-Mg carbonate have been observed locally. REE-minerals, composed mainly of bastnäsite, parisite/synchisite and monazite, display variable textural relationships and often occur together in clusters associated with barite and minor Fe-oxides, sulfides (pyrite ± sphalerite) and locally thorite.
DS201907-1535
2019
Cole, B.G., Andrews, G.D.M., Brown, S.R., Prellwitz, H.The Masontown kimberlite, Fayette County, Pennsylvania: insights into emplacement processes by the characterization of xenocryst sizes and shapes using computed tomography.Joint 53rd Annual South-Central/53rd North Central/71st Rocky Mtn GSA section Meeting, Vol. 331 United States, Pennsylvaniadeposit - Masontown

Abstract: The late Jurassic Masontown dyke in Fayette County, SW Pennsylvania, preserves abundant rounded, mm to cm-diameter masses of olivine and serpentine cemented together in serpentine-rich kimberlite groundmass. Each mass is interpreted to be a partially serpentinized olivine xenocryst or peridotite xenocryst. Each rounded clast is jacketed by a distinct rim of serpentine; probably originally olivine. The (1) ubiquitous roundness of clasts and (2) the presence of distinct serpentine jackets around each clast, supports emplacement of the dyke by a 'kimberlite factory' (Brett et al., 2015). Due to the paucity of available samples, we have used non-destructive imaging by computed tomography (CT) at the National Energy Technology Lab in Morgantown, WV, to construct 3D models of the internal structure of hand samples loaned from the Smithsonian Institute's Museum of Natural History. MicroCT (1-3 micron resolution) and industrial CT (~15 microns resolution) serial scans processed in ImageJ and Blob3D allow for 3D characterizations of individual clasts, including their shape factors (sphericity, roughness, etc.) and sizes (i.e. crystal size distributions).
DS201909-2031
2019
Colombo, C.L., Vierire Conceicao, R., Grings, C.D.Implications for mantle heterogeneity and diamond preservation derived from RosaRio-6 kimberlite, south of Brazil.Goldschmidt2019, 1p. Poster abstractSouth America, Brazildeposit - RosaRio-6
DS201901-0020
2018
Coltice, N., Larrouturou, G., Debayle, E., Garnero, E.J.Interactions of scales of convection in the Earth's mantle.Tectonophysics, Vol. 746, pp. 669-677.Mantleconvection

Abstract: The existence of undulations of the geoid, gravity and bathymetry in ocean basins, as well as anomalies in heat flow, point to the existence of small scale convection beneath tectonic plates. The instabilities that could develop at the base of the lithosphere are sufficiently small scale (< 500 km) that they remain mostly elusive from seismic detection. We take advantage of 3D spherical numerical geodynamic models displaying plate-like behavior to study the interaction between large-scale flow and small-scale convection. We find that finger-shaped instabilities develop at seafloor ages > 60 Ma. They form networks that are shaped by the plate evolution, slabs, plumes and the geometry of continental boundaries. Plumes impacting the boundary layer from below have a particular influence through rejuvenating the thermal lithosphere. They create a wake in which new instabilities form downstream. These wakes form channels that are about 1000 km wide, and thus are possibly detectable by seismic tomography. Beneath fast plates, cold sinking instabilities are tilted in the direction opposite to plate motion, while they sink vertically for slow plates. These instabilities are too small to be detected by usual seismic methods, since they are about 200 km in lateral scale. However, this preferred orientation of instabilities below fast plates could produce a pattern of large-scale azimuthal anisotropy consistent with both plate motions and the large scale organisation of azimuthal anisotropy obtained from recent surface wave models.
DS201907-1536
2019
Condie, K.C., Puetz, S.J.Time series analysis of mantle cycles Part II: the geologic record in zircons, large igneous provinces and mantle lithosphere.Geoscience Frontiers, Vol. 10, pp. 1327-1336Mantleboundary

Abstract: Igneous and detrital zircons have six major U/Pb isotopic age peaks in common (2700 Ma, 1875 Ma, 1045 Ma, 625 Ma, 265 Ma and 90 Ma). For igneous rocks, each age peak is comprised of subpeaks with distinct geographic distributions and a subpeak age range per age peak =100 Myr. There are eight major LIP age peaks (found on = 10 crustal provinces) of which only four are in common to major detrital zircon age peaks (2715 Ma, 1875 Ma, 825 Ma, 90 Ma). Of the whole-rock Re depletion ages, 58% have corresponding detrital zircon age peaks and 55% have corresponding LIP age peaks. Ten age peaks are found in common to igneous zircon, detrital zircon, LIP, and Re depletion age time series (3225 Ma, 2875 Ma, 2145 Ma, 2085 Ma, 1985 Ma, 1785 Ma, 1455 Ma, 1175 Ma, 825 Ma, and 90 Ma), and these are very robust peaks on a global scale as recorded in both crustal and mantle rocks. About 50% of the age peaks in each of these time series correspond to predicted peaks in a 94-Myr mantle cycle, including four of the ten peaks in common to all four time series (2875 Ma, 1785 Ma, 825 Ma and 90 Ma). Age peak widths and subpeak ranges per age peak suggest that mantle events responsible for age peaks are <100 Myr and many <50 Myr in duration. Age peak geographic distributions show three populations (=1000 Ma, 2500-1000 Ma, =2500 Ma), with the number of new provinces in which age peaks are represented decreasing with time within each population. The breaks between the populations (at 2.5 Ga and 1 Ga) fall near the onsets of two transitions in Earth history. The First Transition may represent a change from stagnant-lid tectonics into plate tectonics and the Second Transition, the onset of subduction of continental crust. The major factor controlling geographic distribution of age peaks is the changing locations of orogeny. Before ~2 Ga, age subpeaks and peaks are housed in orogens within or around the edges of crustal provinces, mostly in accretionary orogens, but beginning at 1.9 Ga, collisional orogens become more important. The coincidence in duration between magmatic flare-ups in Phanerozoic arcs and duration of age subpeaks (10-30 Myr) is consistent with subpeaks representing periods of enhanced arc-related magmatism, probably caused by increased subduction flux. The correlation of isotopic age peaks between time series supports a cause and effect relationship between mantle plume activity, continental magma production at convergent margins, and crustal deformation. Correlation of over half of the detrital zircon age peaks (and six of the nine major peaks) with Re depletion age peaks supports an interpretation of the zircon peaks as crustal growth rather than selective preservation peaks.
DS201906-1286
2019
Cone, D., Kopylova, M., Swerjensky, D.Determining the origin of megacrysts from the Muskox kimberlite pipe, northwest Canada.GAC/MAC annual Meeting, 1p. Abstract p. 73.Canada, Northwest Territoriesdeposit - Muskox

Abstract: Megacrysts are mineral grains of garnet, clinopyroxene, orthopyroxene, ilmenite, olivine, phlogopite and zircon larger than 10 mm frequently observed in kimberlite occurrences across the world, with reported sizes commonly exceeding 10 cm. Despite their common occurrence and decades of research into their origin, megacryst petrogenesis is still a debated topic amongst petrologists. A strictly phenocrystal origin is doubted, with recent research suggesting a multi-stage model involving isobaric formation over a wide temperature range, followed by metasomatism of a protokimberlite fluid that replaces mantle minerals. Our project aims to contribute to ongoing research by modeling the metasomatism of the ambient peridotitic mantle affected by the fluid using major and trace element data obtained from megacrysts from the Jurassic Muskox kimberlite pipe of the Slave province of Canada. We report major element compositions of 24 megacryst samples of garnet, olivine, clinopyroxene and ilmenite and employ DEW (Deep Earth Water) modelling to establish the composition of the potential metasomatizing agent and mineral trends that result from the mantle metasomatism. This project has important implications for not only constraining the composition of the source fluids, but also understanding the reactions in the cratonic mantle leading to the kimberlite melt formation.
DS201907-1537
2019
Conover, E.Diamond detectors could aid the search for dark matter.sciencenews.org, June 17, 1p.Spacediamond morphology
DS201907-1538
2019
Conover, E.The search for mysterious dark matter underdogs steps up.sciencenews.org, Vol. 99, April 9, 1p.Spacediamond morphology
DS201904-0726
2019
Cook, T.Explaining the genesis of superdeep diamonds.EOS, 100, https://doi.org/101029 /2019EO117779Mantlediamond genesis

Abstract: Real-time tracking during diamond anvil cell experiments indicates reaction rates may control the unusual depth distribution of the extremely rare diamonds that form deep within Earth’s mantle.
DS201901-0021
2018
Copjakova, R., Kotkova, J.Composition of barium mica in multiphase solid inclusions fro orogenic garnet peridotites as evidence of mantle metasomatism in a subduction zone setting.Contributions to Mineralogy and Petrology, Vol. 173, 12, pp. 106-Mantlemetasomatism

Abstract: Multiphase solid inclusions in minerals formed at ultra-high-pressure (UHP) provide evidence for the presence of fluids during deep subduction. This study focuses on barian mica, which is a common phase in multiphase solid inclusions enclosed in garnet from mantle-derived UHP garnet peridotites in the Saxothuringian basement of the northern Bohemian Massif. The documented compositional variability and substitution trends provide constraints on crystallization medium of the barian mica and allow making inferences on its source. Barian mica in the multiphase solid inclusions belongs to trioctahedral micas and represents a solid solution of phlogopite KMg3(Si3Al)O10(OH)2, kinoshitalite BaMg3(Al2Si2)O10(OH)2 and ferrokinoshitalite BaFe3(Al2Si2)O10(OH)2. In addition to Ba (0.24-0.67 apfu), mica is significantly enriched in Mg ( X Mg 0.85 to 0.95), Cr (0.03-0.43 apfu) and Cl (0.04-0.34 apfu). The substitution vector involving Ba in the I-site which describes the observed chemical variability can be expressed as BaFeIVAlClK-1Mg-1Si-1(OH)-1. A minor amount of Cr and VIAl enters octahedral sites following a substitution vector VI(Cr,Al)2?VI(Mg,Fe)-3 towards chromphyllite and muscovite. As demonstrated by variable Ba and Cl contents positively correlating with Fe, barian mica composition is partly controlled by its crystal structure. Textural evidence shows that barian mica, together with other minerals in multiphase solid inclusions, crystallized from fluids trapped during garnet growth. The unusual chemical composition of mica reflects the mixing of two distinct sources: (1) an internal source, i.e. the host peridotite and its garnet, providing Mg, Fe, Al, Cr, and (2) an external source, represented by crustal-derived subduction-zone fluids supplying Ba, K and Cl. At UHP-UHT conditions recorded by the associated diamond-bearing metasediments (c. 1100 °C and 4.5 GPa) located above the second critical point in the pelitic system, the produced subduction-zone fluids transporting the elements into the overlying mantle wedge had a solute-rich composition with properties of a hydrous melt. The occurrence of barian mica with a specific chemistry in barium-poor mantle rocks demonstrates the importance of its thorough chemical characterization.
DS201901-0022
2018
Cordani, U.G., Ernesto, M., Da Silva Dias, M.A.F., de Alkmim, F.F., Medonca, C.A., Albrecht, R.Un pouco de historia: as Ciencias da Terra no Brasil colonial e no Imperio. ( IN PORT) History of Brazil gold and diamondsEstudos Avancados ( Ensino de Geosciencias na universidade), Vol. 32, (94), pp. 309-330. pdf available in PORT.South America, Brazilhistory
DS201902-0266
2018
Cracknell, A.P.The development of remote sensing in the last 40 years.International Journal of remote sensing, Vol. 39, 23, pp. 8387-8427.GlobalRemote sensing

Abstract: This editorial has its origins in a keynote presentation entitled ‘The Evolution of the Development of Remote Sensing Technologies - the Last 40 years’ which I gave at the 9th International Conference and Exhibition on Geospatial and Remote Sensing (9 IGRSM 2018) in Kuala Lumpur 24-25 April 2018 ‘Geospatial Enablement’. The editorial is not intended to be a definitive history of remote sensing from the beginning up to the day of its submission for publication. Rather it represents a personal account to try to enable present-day practitioners of remote sensing to gain a slight appreciation of what went before the time when they were introduced to the subject. The fun in our group in the 1980s was being able to explore many possible new applications of remote sensing, some of which turned out to be successful and some of which turned out to be failures - for various reasons. At a first glance it may seem that the list of references is woefully inadequate. However this is not an encyclopaedic review of remote sensing as it now is, but an attempt to recall some of the history of how we got here. The references are only meant to document some of the things that are said. For other information we assume that readers will consult whatever search engine, Google, etc., that they commonly use. I chose 40 years because it seemed to me that 1978 was a landmark year for remote sensing. In that year three very important new satellite systems were launched into space, the TIROS-N satellite with the AVHRR (Advanced Very High Resolution Radiometer) on board, the SEASAT satellite and the NIMBUS-7 satellite with the CZCS (Coastal Zone Colour Scanner) on board. In addition to all these, the third satellite in the Landsat programme (Landsat 3) was launched in March 1978. Of rather less importance, it was the year of my very first remote sensing project which involved attempting to use CZCS data to study water quality parameters; we learned the hard way about the difficulties involved in conducting field experiments on a rapidly changing environmental system simultaneously with satellite overflights. 1978 was also just before the launch of the International Journal of Remote Sensing (IJRS) in 1980 and so the initial work on the start up of the IJRS was being done in 1978. This editorial is therefore divided into three parts (a) Part 1 remote sensing before 1978, (b) Part 2 1978, the year of the launch of three very important polar-orbiting satellites and (c) Part 3 remote sensing since 1978. Textbooks sometimes define remote sensing to mean the observation of, or gathering of information about, a target by a device separated from it by some distance. In practice it is usually taken to be more restricted than that. It is sometimes claimed that the expression ‘remote sensing’ was coined by geographers at the U.S. Office of Naval Research in the 1960s at about the time that the use of ‘spy’ satellites was beginning to move out of the military sphere and into the civilian sphere. Remote sensing is often regarded as being synonymous with the use of artificial satellites, but there is an ongoing history of air photos that preceded the satellites and goes right up to the recent development of UAVs (drones) which are likely to supersede satellites in some areas
DS201901-0023
2018
Crameri, F., Lithgow-Bertelloni, C.Abrupt upper plate tilting during slab transition zone collision.Tectonophysics, Vol. 746, pp. 199-211.Mantlesubduction

Abstract: The sinking remnant of a surface plate crosses and interacts with multiple boundaries in Earth's interior. Here, we specifically investigate the prominent dynamic interaction of the sinking plate portion with the upper-mantle transition zone and its corresponding surface elevation signal. We unravel, for the first time, that the collision of the sinking slab with the transition zone induces a sudden, dramatic downward tilt of the upper plate towards the subduction trench. Unraveling this crucial interaction was only possible thanks to state-of-the-art numerical modelling and post-processing. The new model that is introduced here to study the dynamically self-consistent temporal evolution of subduction features accurate subduction-zone topography, robust single-sided plate sinking, stronger plates close to laboratory values, an upper-mantle phase transition, and simple continents at a free surface. To distinguish the impact of the new physical model features, three different setups are used: the simplest model setup includes a basic high-viscosity lower mantle, the second adds a 660-km phase transition, and the third includes, additionally, a continental upper plate. Common to all models is the clear topographic signal upon slab-transition-zone interaction: the upper plate tilts abruptly towards the subduction trench by about 0.05° and over around 10 Ma. This dramatic increase in upper-plate tilt can be related to the slab-induced excitation of the high-viscosity lower mantle, which introduces a wider flow pattern. A large change in horizontal extent of inundation of up to 900 km is observed as a direct consequence of the upper-plate tilting. Such an abrupt variation in surface topography and inundation extent should be clearly visible in temporal records of large-scale surface elevation and might explain continental tilting as observed in Australia since the Eocene and North America during the Phanerozoic.
DS201907-1539
2019
Crosta, A.P., Reimold, W.U., Vasconcelos, M.A.R., Hauser, N., Oliveira, G.J.G.Impact cratering: the South American record - Part 2. Brazil was covered in Part 1. Geochemistry, Vol. 79, pp. 191-220.South Americameteorite

Abstract: In the first part of this review of the impact record of South America, we have presented an up-to-date introduction to impact processes and to the criteria to identify/confirm an impact structure and related deposits, as well as a comprehensive examination of Brazilian impact structures. The current paper complements the previous one, by reviewing the impact record of other countries of South America and providing current information on a number of proposed impact structures. Here, we also review those structures that have already been discarded as not being formed by meteorite impact. In addition, current information on impact-related deposits is presented, focusing on impact glasses and tektites known from this continent, as well as on the rare K-Pg boundary occurrences revealed to date and on reports of possible large airbursts. We expect that this article will not only provide systematic and up-to-date information on the subject, but also encourage members of the South American geoscientific community to be aware of the importance of impact cratering and make use of the criteria and tools to identify impact structures and impact deposits, thus potentially contributing to expansion and improvement of the South American impact record.
DS201905-1022
2019
Crowell, R.Secrets from the New Madrid seismic zone's quaking past.EOS, https://doi.org/ 10.1029/2019EO120349 3p.United States, Arkansas, Missouri, Tennesseegeophysics, seismic
DS201905-1023
2019
Cutts, J.A., Smit, M.A., Kooijman, E., Schmitt, M.Two stage cooling and exhumation of deeply subducted continents.Tectonics, Vol. 38, 3, pp. 863-877.Mantlesubduction

Abstract: The burial and exhumation of continental crust during collisional orogeny exert a strong control on the dynamics of mountain belts and plateaus. Constraining the rates and style of exhumation of deeply buried crust has proven difficult due to complexities in the local geology and thermochronometric methods typically used. To advance this field, we applied trace-element and U-Pb laser ablation inductively coupled plasma mass spectrometry analyses to rutile from eclogite and amphibolite samples from the Western Gneiss Complex of Norway—an archetypal continental (ultra)high-pressure (UHP) terrane. Peak temperature and timing of midcrustal cooling were constrained for samples collected along a subduction- and exhumation-parallel transect, using Zr-in-rutile thermometry and U-Pb rutile geochronology, respectively. Peak temperatures decrease from 830 °C in the UHP domain to 730 °C at the UHP-HP transition, remain constant at 730 °C across most of the terrane, and decrease to 620 °C at the eclogite-out boundary. U-Pb results show that most of the terrane cooled through 500 °C at 380-375 Ma except for the lowest grade region, where cooling occurred approximately 20 million years earlier. The results indicate that exhumation was a two stage process, involving (1) flexural rebound and slab flattening at depth combined with foreland-directed extrusion, followed by (2) synchronous cooling below 500 °C across the, by then, largely flat-lying Western Gneiss Complex. The latter implies and requires relatively homogeneous mass removal across a large area, consistent with erosion of an overlying orogenic plateau. The Caledonides were at near-equatorial latitudes at the time. A Caledonian paleo-plateau thus may represent a so far unrecognized factor in Devonian and Carboniferous atmospheric circulation and climate forcing.
DS201910-2251
2019
Cutts, J.A., Smit, M.A., Spengler, D., Kooijman, E., van Roermund, H.L.M.Two billion years of mantle evolution in sync with global tectonic cycles.Earth and Planetary Science letters, Vol. 528, 115820 11p.Mantlecraton

Abstract: The continental crust and sub-continental lithospheric mantle (SCLM) are co-dependent reservoirs in terms of their geochemistry, tectonics, and long-term evolution. Obtaining insight into the mechanisms of lithosphere formation and differentiation requires robust constraint on the complex petrological history of mantle rocks. This has proven difficult as samples from the deep mantle are rare and, although many may have formed in the Archean, no such age has been obtained directly from mantle-derived silicate minerals. Lutetium-hafnium geochronology of garnet has the potential of overcoming this limitation. In this study, this technique was applied on fragments of the SCLM exposed in the Norwegian Caledonides. The chronologic record of these rocks is rich and extensive, yet it is difficult to interpret and is, in part, inconsistent. Our Lu-Hf results from supersilicic pyrope in dunite provide the first Archean internal isochron ages for mantle rocks. These ages are consistent with a period of juvenile crust formation worldwide and provide a record of deeply sourced mantle upwellings from >350 km depth. Results from fertile rock types indicate that melting and isotope re-equilibration occurred in sync with two Proterozoic supercontinent break-up events that are recorded in the Laurentian and Baltic lithospheres. Together, the results indicate that since its extraction during a period of rapid Archean crustal growth, the SCLM appears to have largely been at petro-physical and chemical stasis, with the exception of major episodes of continental break-up. The evolution of the SCLM is thus, highly punctuated and ultimately controlled by the Wilson cycle.
DS201910-2252
2019
Czas, J., Pearson, D.G., Stachel, T., Kjarsgaard, B.A., Read, G.A diamondiferous paleoproterozoic mantle root beneath the Sask craton ( western Canada).Goldschmidt2019, 1p. AbstractCanada, Saskatchewancraton

Abstract: Primary diamond deposits are typically restricted to the stable Archean cores of continents, an association known as Clifford’s rule. Archean to Palaeoproterozoic crustal ages (3.3 - 2.1 Ga) have been reported for the Sask Craton, a small terrane in Western Canada, which hosts the diamondiferous Cretaceous Fort à la Corne (FALC) Kimberlite Field. Yet the craton is enclosed by the Palaeoproterozoic (1.9 - 1.8 Ga) Trans Hudson Orogen (THO). In this study we evaluate the age and geochemistry (major, trace, and platinum group elements data, as well as Re-Os isotope systematics) of the lithospheric mantle root beneath the Sask Craton to assess the timing of craton formation and the potential role played by the THO in its evolution. The lithospheric mantle root is dominated by lherzolite with average olivine Mg# of 91.5, which is more fertile than observed in other cratons. Garnets from concentrate further highlight the rarity of harzburgite in the lithospheric mantle. Single clinopyroxene thermobarometry provides temperaturepressure constraints for the garnet-bearing lithospheric mantle (840 to 1250 °C and 2.7 to 5.5 GPa), indicative of a cool geotherm (38 mW/m2) and a large diamond window of ~100 km thickness (from ~120-220 km depth). Most of the studied xenoliths show evidence for melt metasomatism in their trace and major element compositions, while retaining platinum group element patterns expected for melt residues. 187Os/188Os compositions span a broad range from 0.1109 to 0.1507, corresponding to Re-depletion (TRD) ages between 2.4 to 0.3 Ga, with a main mode in the Palaeoproterozoic (2.4 to 1.7 Ga). With the absence of Archean ages, the main depletion and stabilisation of the Sask Craton occurred in the Palaeoproterozoic, closely associated with the Wilson cycle of the THO. From a diamond exploration perspective this indicates that major diamond deposits can be found on cratons that were stabilised in the Palaeoproterozoic.
DS201912-2775
2019
Czas, J., Pearson, G., Stachel, T., Kjarsgaard, B.A., Read, G.A Paleoproterozic diamond bearing lithospheric mantle root beneath the Archean Sask Craton.Lithos, 10.1016/j.lithos.2019.105301 63p. PdfCanada, Saskatchewancraton

Abstract: The recently recognised Sask Craton, a small terrane with Archean (3.3-2.5 Ga) crustal ages, is enclosed in the Paleoproterozoic (1.9-1.8 Ga) Trans Hudson Orogen (THO). Only limited research has been conducted on this craton, yet it hosts major diamond deposits within the Cretaceous (~106 to ~95 Ma) Fort à la Corne (FALC) Kimberlite Field. This study describes major, trace and platinum group element data, as well as osmium isotopic data from peridotitic mantle xenoliths (n = 26) from the Star and Orion South kimberlites. The garnet-bearing lithospheric mantle is dominated by moderately depleted lherzolite. Equilibration pressures and temperatures (2.7 to 5.5 GPa and 840 to 1250 °C) for these garnet peridotites define a cool geotherm indicative of a 210 km thick lithosphere, similar to other cratons worldwide. Many of the peridotite xenoliths show the major and trace element signatures of carbonatitic and kimberlitic melt metasomatism. The Re-Os isotopic data yield TRD (time of Re-depletion) model ages, which provide minimum estimates for the timing of melt depletion, ranging from 2.4 to 0.3 Ga, with a main mode spanning from 2.4 to 1.7 Ga. No Archean ages were recorded. This finding and the complex nature of events affecting this terrane from the Archean through the Palaeoproterozoic provide evidence that the majority of the lithospheric mantle was depleted and stabilised in the Palaeoproterozoic, significantly later than the Archean crust. The timing of the dominant lithosphere formation is linked to rifting (~2.2 Ga - 2.0 Ga), and subsequent collision (1.9-1.8 Ga) of the Superior and Hearne craton during the Wilson cycle of the Trans Hudson Orogen.
DS201903-0502
2019
da Silva, B.V., Hackspacher, P.C., Siqueira Riberio, M.C., Glasmacher, U.A., Goncalves, A.O., Doranti-Tiritan, C., de Godoy, D.F., Constantino, R.R.Evolution of the southwestern Angolan margin: episodic burial and exhumation is more realistic than long term denudation.International Journal of Earth Sciences, Vol. 108, pp. 89-113.Africa, Angolathermochronology

Abstract: There are two main points of view regarding how continental margins evolve. The first one argues that the present-day margins have been developed by long-term denudation since a major exhumation episode, probably driven by rifting or another relevant tectonic event. The second one argues that continental margins underwent alternating burial and exhumation episodes related to crustal tectonic and surface uplift and subsidence. To demonstrate that the proximal domain of the southwestern Angolan margin has evolved in a polycyclic pattern, we present a review of geological and thermochronological information and integrate it with new combined apatite fission-track and (U-Th)/He data from Early Cretaceous volcanic and Precambrian basement samples. We also provide hypotheses on the possible mechanisms able to support the vertical crustal movements of this margin segment, which are also discussed based on some modern rifting models proposed for Central South Atlantic. The central apatite fission-track ages range from 120.6?±?8.9 to 272.9?±?21.6 Ma, with the mean track lengths of approximately 12 µm. The single-grain apatite (U-Th)/He ages vary between 52.2?±?1 and 177.2?±?2.6 Ma. The integration of the thermochronological data set with published geological constraints supports the following time-temperature evolution: (1) heating since the Carboniferous-Permian, (2) cooling onset in the Early Jurassic, (3) heating onset in the Early Cretaceous, (4) cooling onset in the Mid- to Late Cretaceous, (5) heating onset in the Late Cretaceous, and (6) cooling onset in the Oligocene-Miocene. The thermochronological data and the geological constraints, support that the proximal domain of the southwestern Angolan margin was covered in the past by pre-, syn-, and post-rift sediments, which were eroded during succeeding exhumation events. For this margin segment, we show that a development based on long-term denudation is less realistic than one based on burial and exhumation episodes during the last 130 Myr.
DS201901-0024
2018
Dal Zilio, L., Faccenda, M., Capitanio, F.The role of deep subduction in supercontinent breakup.Tectonophysics, Vol. 746, pp. 312-324.Mantleplate tectonics

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.
DS201910-2253
2019
Dalton, H., Giuliani, A., Phillips, D., Hergt, J., O'Brien, H.Petrographic and geochemical variations in the Kaavi-Kuopio kimberlite field, Finland: the role of mantle assimilation.Goldschmidt2019, 1p. AbstractEurope, Finlanddeposit - Kaavi-Kuopio

Abstract: Kimberlites are silica-poor, volatile-rich (CO2 ± H2O), volcanic rocks that are often described as ‘hybrid’, because their parental magmas include abundant xenocrystic (crustand mantle-derived) components. Unravelling the influence of mantle assimilation on kimberlite melt compositions represents an outstanding question of kimberlite petrology. To address this issue, we have carried out a comprehensive geochemical and petrographic investigation of nine kimberlites from the Kaavi-Kuopio field in Finland, that were emplaced on the southern margin of the Karelian Craton in the Neoproterozoic (~550-600 Ma). Olivine is the dominant mineral phase in kimberlites (~50 vol.%) with cores mainly derived from the disaggregation of mantle peridotite. In contrast, olivine rims crystallise directly from the kimberlitic melt and their Mg# (Mg/(Mg+Fe)) typically show remarkable homogeneity within and between kimberlites of a single cluster and field (e.g., Lac de Gras). The Kaavi-Kuopio kimberlites appear to represent a unique case where there is a (statistically) significant difference between the average Mg# of olivine rims in different pipes (89.9 ± 0.2 to 88.5 ± 0.3). Importantly, the Mg# of olivine rims exhibit a strong correlation with the Mg# of olivine cores. Furthermore, the compositions of olivine cores (and rims) exhibit a strong correlation with those of spinel (e.g., Mg#, TiO2 contents). These geochemical variations correlate with the modal mineralogy of the kimberlites: for example, higher abundances of monticellite and lower abundances of ilmenite are associated with higher Mg# olivine. The robust relationship between entrained and assimilated lithospheric mantle material (i.e. olivine cores) and magmatic components (i.e. olivine rims, spinel, and other groundmass minerals) suggests that assimilation of lithospheric mantle has impacted the compositions of kimberlitic melts to a greater extent than previously recognised. These new data also suggest significant variations in the composition of the mantle lithosphere beneath the Kaavi-Kuopio kimberlites, which are spaced less than 10 km apart.
DS201911-2515
2019
Dalziel, I.W.D., Dewey, J.F.The classic Wilson Cycle revisited.IN: Cycle Concepts in Plate Tectonics, editors Wilson and Houseman , Geological Society of London special publication 470, pp. 18-38.Mantleplate tectonics

Abstract: In the first application of the developing plate tectonic theory to the pre-Pangaea world 50 years ago, attempting to explain the origin of the Paleozoic Appalachian-Caledonian orogen, J. Tuzo Wilson asked the question: ‘Did the Atlantic close and then reopen?’. This question formed the basis of the concept of the Wilson cycle: ocean basins opening and closing to form a collisional mountain chain. The accordion-like motion of the continents bordering the Atlantic envisioned by Wilson in the 1960s, with proto-Appalachian Laurentia separating from Europe and Africa during the early Paleozoic in almost exactly the same position that it subsequently returned during the late Paleozoic amalgamation of Pangaea, now seems an unlikely scenario. We integrate the Paleozoic history of the continents bordering the present day basin of the North Atlantic Ocean with that of the southern continents to develop a radically revised picture of the classic Wilson cycle The concept of ocean basins opening and closing is retained, but the process we envisage also involves thousands of kilometres of mainly dextral motion parallel with the margins of the opposing Laurentia and Gondwanaland continents, as well as complex and prolonged tectonic interaction across an often narrow ocean basin, rather than the single collision suggested by Wilson.
DS201911-2516
2019
Dantas de Araujo, A.J., Bongiolo, E.M., Avila, C.A.The southern Sao Francisco craton puzzle: insights from aerogeophysical and geological data.Journal of South American Earth Sciences, Vol. 94, 102203 14p. PdfSouth America, Brazilgeophysics - magnetics

Abstract: Accretionary orogens are considered as the result of the major crust production process, and terranes are accreted material representing distinctive assemblages regarding age and evolution. Scientific advances in the last years show that the southernmost São Francisco Craton includes Archean, Paleoproterozoic and Neoproterozoic areas. We used aerogeophysical data and field geology to understand the extension of individual pieces of this tectonic puzzle. We described five magnetometric lineaments. A-, B- and C-lineaments are related to dyke swarms of different ages. D- and E-lineaments represent regional-scale tectonic structures. In a tectonic perspective, we have identified the following terranes: (i) the Archean São Tiago crust (2.67?Ga), which is part of the São Francisco proto-craton; two Siderian juvenile arcs, represented by the (ii) Cassiterita (2.47?Ga) and the (iii) Resende Costa/Lagoa Dourada (2.36-2.35?Ga) orthogneisses; and two Rhyacian arcs, the (iv) juvenile Serrinha (2.22-2.20?Ga) and the continental Ritápolis (2.19-2.10?Ga) arcs. Tectonic terranes and five magnetic subdomains were identified on the basis of (i) association of shear zones/faults with quartz veins in the field; (ii) low- and high-intensity magnetic anomalies; (iii) sharp contrast in Euler solution intensities; and (iv) high-contrast in radioelement contents in the gammaspectrometric maps. Processing of aerogeophysical data permitted us to propose a new scenario on the evolution of the southern São Francisco Craton, and in particular of the Mineiro belt. The integration between aerogeophysical, new and compiled geologic information, provides a robust model for the understanding of individual tectonic pieces of the studied area.
DS201909-2032
2019
Dasgupta, P., Ray, A., Chakraborti, T.Geochemical characterisation of the Neoarchean newer dolerite dykes of the Bahalda region, Singhbhum craton, Odisha, India: implication for petrogenesis.Journal of Earth Science System, doi:10.1007/s12040- 019-1228-0Indiageochemistry

Abstract: The mafic dyke swarm, newer dolerite dykes (NDDs) intrudes the Archaean Singbhum granite of the Singhbhum craton, eastern India. The present investigation focuses on the petrography and geochemistry of 19 NNE-SSW to NE-SW trending NDDs in two sectors in the northern and south-western part of Bahalda town, Odisha, Singhbhum. Chondrite normalised rare earth element (REE) patterns show light REE (LREE) enrichment among majority of the 13 dykes while the remaining six dykes show a flat REE pattern. Critical analyses of some important trace element ratios like Ba/La, La/Sm, Nb/Y, Ba/Y, Sm/La, Th/La, La/Sm, Nb/Zr, Th/Zr, Hf/Sm, Ta/La and Gd/Yb indicate that the dolerite dykes originated from a heterogeneous spinel peridotite mantle source which was modified by fluids and melts in an arc/back arc setting. REE modelling of these dolerite dykes were attempted on LREE-enriched representative of NDD which shows that these dykes might have been generated by 5-25% partial melting of a modified spinel peridotite source which subsequently suffered around 30% fractional crystallisation of olivine, orthopyroxene and clinopyroxene. The reported age of ~2.75-2.8 Ma seems to be applicable for these dykes and this magmatism appears to be contemporaneous with major scale anorogenic granitic activity in the Singhbhum craton marking a major event of magmatic activity in eastern India.
DS201911-2517
2019
Davies, D.R., Valentine, A.P., Kramer, S.C., Rawlinson, N., Hoggard, M.J., Eakin, C.M., Wilson, C.R.Earth's multi-scale topographic response to global mantle flow.Nature Geosciences, Vol. 12, pp. 845-850.Mantlegeodynamics

Abstract: Earth’s surface topography is a direct physical expression of our planet’s dynamics. Most is isostatic, controlled by thickness and density variations within the crust and lithosphere, but a substantial proportion arises from forces exerted by underlying mantle convection. This dynamic topography directly connects the evolution of surface environments to Earth’s deep interior, but predictions from mantle flow simulations are often inconsistent with inferences from the geological record, with little consensus about its spatial pattern, wavelength and amplitude. Here, we demonstrate that previous comparisons between predictive models and observational constraints have been biased by subjective choices. Using measurements of residual topography beneath the oceans, and a hierarchical Bayesian approach to performing spherical harmonic analyses, we generate a robust estimate of Earth’s oceanic residual topography power spectrum. This indicates water-loaded power of 0.5?±?0.35?km2 and peak amplitudes of up to ~0.8?±?0.1?km at long wavelengths (~104?km), decreasing by roughly one order of magnitude at shorter wavelengths (~103?km). We show that geodynamical simulations can be reconciled with observational constraints only if they incorporate lithospheric structure and its impact on mantle flow. This demonstrates that both deep (long-wavelength) and shallow (shorter-wavelength) processes are crucial, and implies that dynamic topography is intimately connected to the structure and evolution of Earth’s lithosphere.
DS201911-2518
2019
de Almeida Morales, B.A., de Almeida, D.D.P.M., Koester, E., da Rocha, A.M.R., Dorneles, N.T., da Rosa, M.B., Martins, A.A.Mineralogy, whole-rock geochemistry and C, O isotopes from Passo Feio carbonatite, Sul-Riograndense shield, Brazil.Journal of South American Earth Sciences, Vol. 94, 102208 13p. PdfSouth America, Brazilcarbonatite

Abstract: Carbonatites are peculiar igneous rocks, consisting mainly of greater than 50% carbonate minerals, which arouse an economic interest due to the potentiality of high phosphate content and Light Rare Earth Elements (LREE) associated with their occurrence. The Passo Feio Carbonatite (PFC) is located 17?km Southwest of Caçapava do Sul city and constitutes NW dipping body, which is interposed with Passo Feio Formation metamorphic rocks. The PFC varies texturally from massive to foliated, being mainly composed of calcites and dolomites and on a smaller scale by apatites, phlogopites and tremolites. The opaque minerals correspond to hematites, magnetites, pyrites and barites, while the accessory minerals are represented by zircons, monazites- (Ce) and aeschynites- (Ce). Probably those REE mineral phases correspond to a hydrothermal stage, with the REE remobilization from apatites into those latter REE-rich mineral phases - this hypothesis is corroborated by geochemistry, mineral chemistry and microtextures found. Considering the results of mineral chemistry and taking into account the textural criteria, it was possible to classify carbonatite as an alvikite, with geochemical patterns that do not indicate economic potential for REE. However, soil geochemistry showed an important enrichment in REE, reflecting a probable concentration of monazites- (Ce) and aeschynites- (Ce), and because of this, it was possible to establish a zone in which the Passo Feio Carbonatite would probably be extended. In the stable isotope analyzes, the d13C values varied between -4.14 and -3.89‰ while those of d18O between 10.01 and 11.32‰ which can be attributed to the cooling of the magma itself, without suggesting metamorphic processes or subsequent changes. The deformation found in this carbonatite was probably developed in late-magmatic conditions, guided by tectonics associated with horizontal movements in shear zones. Thus, this work suggests that this carbonatite was the product of the reactivation of mantle sources, within a post-collision magmatic context of the Sul-Riograndense Shield.
DS201912-2776
2019
de Hoog, J.C.M., Tachel, T., Harris, J.W.Trace element geochemistry of diamond hosted olivine inclusions from the Akwatia mine, West African Craton: implications for diamond paragenesis and geothermobaromtry.Contributions to Mineralogy and Petrology, Vol. 174, 28p. PdfAfrica, Ghanadeposit - Akwatia

Abstract: Trace-element concentrations in olivine and coexisting garnets included in diamonds from the Akwatia Mine (Ghana, West African Craton) were measured to show that olivine can provide similar information about equilibration temperature, diamond paragenesis and mantle processes as garnet. Trace-element systematics can be used to distinguish harzburgitic olivines from lherzolite ones: if Ca/Al ratios of olivine are below the mantle lherzolite trend (Ca/Al??300 µg/g Ca or?>?60 µg/g Na are lherzolitic. Conventional geothermobarometry indicates that Akwatia diamonds formed and resided close to a 39 mW/m2 conductive geotherm. A similar value can be derived from Al in olivine geothermometry, with TAl-ol ranging from 1020 to 1325 °C. Ni in garnet temperatures is on average somewhat higher (TNi-grt?=?1115-1335 °C) and the correlation between the two thermometers is weak, which may be not only due to the large uncertainties in the calibrations, but also due to disequilibrium between inclusions from the same diamond. Calcium in olivine should not be used as a geothermobarometer for harzburgitic olivines, and often gives unrealistic P-T estimates for lherzolitic olivine as well. Diamond-hosted olivine inclusions indicate growth in an extremely depleted (low Ti, Ca, Na, high Cr#) environment with no residual clinopyroxene. They are distinct from olivines from mantle xenoliths which show higher, more variable Ti contents and lower Cr#. Hence, most olivine inclusions in Akwatia diamonds escaped the refertilisation processes that have affected most mantle xenoliths. Lherzolitic inclusions are probably the result of refertilisation after undergoing high-degree melting first. Trivalent cations appear to behave differently in harzburgitic diamond-hosted olivine inclusions than lherzolitic inclusions and olivine from mantle xenoliths. Some divalent chromium is predicted to be present in most olivine inclusions, which may explain high concentrations up to 0.16 wt% Cr2O3 observed in some diamond inclusions. Strong heterogeneity of Cr, V and Al in several inclusions may also result in apparent high Cr contents, and is probably due to late-stage processes during exhumation. However, in general, diamond-hosted olivine inclusions have lower Cr and V than expected compared to mantle xenoliths. Reduced Na activity in depleted harzburgites limits the uptake of Cr, V and Sc via Na-M3+ exchange. In contrast, Al partitioning in harzburgites is not significantly reduced compared to lherzolites, presumably due to uptake of Al in olivine by Al-Al exchange.
DS201911-2519
2019
de Meillon, L.The alluvial deposits of the Middle Orange River. Paleostone Miningwww.gssa.org Deposits of the Northern Cape , Oct. 10-11, 1p. AbstractAfrica, South Africaalluvials
DS201907-1540
2019
de Wit, M.In the world of diamonds, the Big and Beautiful size does matter!Junior Indaba held Johannesburg June 4, 35 ppts. PdfGlobaldiamonds notable
DS201902-0267
2019
Deales, J., Lenardic, A., Moore, W.Assessing the intrinsic uncertainty and structural stability of planetary models: 1) parameterized thermal/tectonic history models.Researchgate preprint, 21p. Pdf availableMantlegeothermometry

Abstract: Thermal history models, that have been used to understand the geological history of Earth, are now being coupled to climate models to map conditions that allow planets to maintain surface water over geologic time - a criteria considered crucial for life. However, the lack of intrinsic uncertainty assessment has blurred guidelines for how thermal history models can be used toward this end. A model, as a representation of something real, is not expected to be complete. Unmodeled effects are assumed to be small enough that the model maintains utility for the issue(s) it was designed to address. The degree to which this holds depends on how unmodeled factors affect the certainty of model predictions. We quantify this intrinsic uncertainty for several parameterized thermal history models (a widely used subclass of planetary models). Single perturbation analysis is used to determine the reactance time of different models. This provides a metric for how long it takes low amplitude, unmodeled effects to decay or grow. Reactance time is shown to scale inversely with the strength of the dominant feedback (negative or positive) within a model. A perturbed physics analysis is then used to determine uncertainty shadows for model outputs. This provides probability distributions for model predictions and tests the structural stability of a model. That is, do model predictions remain qualitatively similar, and within assumed model limits, in the face of intrinsic uncertainty. Once intrinsic uncertainty is accounted for, model outputs/predictions and comparisons to observational data should be treated in a probabilistic way.
DS201904-0727
2019
Decree, S., Demaiffe, D., Tack, L., Nimpagaritse, G., De Paepe, P., Bouvais, P., Debaille, V.The Neoproterozoic Upper Ruvubu alkaline plutonic complex ( Burundi) revisited: large scale syntectonic emplacement, magmatic differentiation and late stage circulations of fluids.Precambrian Research, Vol. 325, pp. 150-171.Africa, Burundicarbonatite

Abstract: The Upper Ruvubu Alkaline Plutonic Complex (URAPC) in Burundi consists of three separate intrusions, each with a specific emplacement age and petrological composition. Three main units are recognized: an outer unit with silica-saturated plutonic rocks (from gabbro to granite), an inner unit with silica-undersaturated plutonic rocks (feldspathoidal syenite with subordinate feldspathoidal monzonite and ijolite) and a carbonatitic body in the subsoil, known by drilling. The URAPC is quite large in size (~24?km long and up to 10?km wide). It is considered to have been intruded syntectonically in an overall extensional context, thanks to the kilometric shear zones that accommodated its emplacement. Radiometric ages from literature range from 748 to 705?Ma and point to structurally-controlled magmatic differentiation followed by long-lived circulations of late-stage fluids postdating the emplacement of a part of the undersaturated rocks and the carbonatites. In the north-western part of the outer unit, gabbro likely has been emplaced at a deeper structural level than the granite, which represents a more apical structural level of emplacement. This petrological, geochemical and isotopic (Sr-Nd-Hf) study concentrates on the processes that generated the URAPC: (i) fractional crystallization, evidenced by the chemical evolution trends of the major and trace elements, and by marked P, Ti and Ba anomalies in the trace element patterns; (ii) crustal assimilation/contamination, as shown by the wide range of Nd isotope compositions and the general increase of the Sr isotope ratios with increasing SiO2 contents, and (iii) late-magmatic/hydrothermal alteration inducing an increase of the Sr isotope composition without changing significantly the Nd isotope composition. The isotopic data are consistent with an asthenospheric mantle source, though less depleted than the Depleted Mantle (DM), contaminated by the Subcontinental Lithospheric Mantle (SCLM). The silicate and carbonate magmatic series are cogenetic. The outer unit is clearly more contaminated than the inner unit, whereas the carbonatitic body could have evolved by liquid immiscibility. The URAPC lies within East Africa’s Western Rift Valley, which is marked by 23 alkaline plutonic complexes. Their emplacement has been ascribed to reactivation of Proterozoic lithospheric weakness zones resulting from the breakup of the Neoproterozoic supercontinent Rodinia supercontinent.
DS201906-1287
2019
Dekkers, M.J.Extraordinary Polar wander during the Late Jurassic?EOS, Apr. 28, 3p.Globalgeophysics - gravity

Abstract: Knowing how much Earth’s rotation axis has moved in the geological past - the so-called "polar wander" - has important implications for understanding geological processes. For example, it exposes significant areas on Earth to rapidly changing climatic conditions. The polar shift is a consequence of the Earth responding to a changed center of gravity, caused by processes such as slab-break-off...(no abstract, good graphics)
DS201901-0025
2018
Deljanin, B., Chapman, J.Steps in screening and ID of laboratory-grown diamonds with synthetic diamond ID kit.Gems & Gemology, Sixth International Gemological Symposium Vol. 54, 3, 1p. Abstract p. 305-6.Globalsynthetics

Abstract: Laboratory-grown diamonds are created using either high-pressure, high-temperature (HPHT) or chemical vapor deposition (CVD). With the influx of manmade diamonds on the market over the past few years, instrument producers and labs have launched screening and detection instruments to help dealers and jewelers spot HPHTor CVD-grown specimens. Most standard instruments are inaccurate testers or just type I and type II screening devices that do not give a definite answer about diamond genesis. Over the last four annual Mediterranean Gemmological and Jewellery Conferences and more than 30 workshops given in 17 countries, we have assembled a portable new Synthetic Diamond Identification Kit. The kit comprises two portable instruments and two booklets: 1) A PL inspector (mini UV lamp with magnifier) to inspect laboratory-grown, treated, and natural diamonds using long- and short-wave fluorescence and phosphorescence 2) A 2017 handbook with images and explanation of longand short-wave reactions of diamonds of all types 3) A mini foldable polariscope with portable light to separate natural diamonds using characteristic birefringence patterns from HPHT and CVD diamonds 4) A 2010 handbook with images and explanations of crosspolarized filter reactions of diamonds of all types The combination of this kit with professional training could identify all HPHT-grown diamonds and most CVD-grown diamonds on the market, loose or mounted. Also available are melee and jewelry inspectors consisting of larger UV lamps with magnifiers designed for identification of small loose or mounted diamonds. Different diamond types and subtypes can exhibit different birefringence under cross-polarized filters. A clear majority of natural diamonds exhibit some degree of internal strain, with type II natural diamonds showing a weak “tatami” pattern. HPHTgrown diamonds are free of such strain, and CVD-grown diamonds show mostly coarse columnar patterns. Most natural diamonds have a strong reaction to long-wave UV; this reaction is usually weaker (mostly blue) at shorter wavelengths. Laboratory-grown diamonds generally exhibit more intense fluorescence with short-wave UV compared to long-wave UV, with a chalky coloring tinged with green or yellow. Most HPHT-grown diamonds also phosphoresce. If a diamond is free of inclusions, fluorescence is a reliable screening test to flag suspicious stones that should be further checked under cross-polarized filters (figure 1). In the case of some rare near-colorless clean CVD-grown diamonds that do not show fluorescence or have a birefringence pattern that is coarse but resembling tatami in type IIa and weak patterns in natural Ia diamonds, additional tests using advanced spectroscopy and strong short-wave UV light to observe growth patterns are needed to confirm diamond genesis.
DS201902-0268
2018
Demarco, E.Erosion has erased most of Earth's impact craters. Here are the survivors. History and list of craters.sciencenews.org, Dec. 18, 5p.Europe, Greenlandcrater
DS201909-2033
2019
Deng, J., Karki, B.B., Ghosh, D.B., Lee, K.K.M.First principles study of FeO2Hx solid and melt system at high pressures: implications for ultralow-velocity zones. ( Lower mantle may have a wet bottom** citation note) Journal of Geophysical Research: Solid Earth, Vol. 124, pp. 4566-4575.Mantleboundary

Abstract: Ultralow-velocity zones (ULVZs) are 5-40-km-thick patches lying above Earth's core-mantle boundary. They are characterized with anomalously low seismic velocities compared with the ambient mantle and may contain important clues on the thermochemical evolution of the Earth. A recent experimental study argued that ULVZs may be caused by the accumulation of pyrite-type FeO2Hx (P phase) at the bottom of the mantle. Here for the first time, we systematically study the thermoelastic properties of both FeO2Hx solid and liquid phases. We find that P phase is likely melted near the core-mantle boundary and thus cannot be the source of ULVZs. Furthermore, in order for the molten product of P phase to cause ULVZs, the dense and nearly inviscid melts must be dynamically stable and confined within the ULVZs, which requires that the mantle is highly viscous and/or convects vigorously.
DS201910-2254
2019
Dentith, M., Enkin, R.J., Morris, W., Adams, C., Bourne, B.Petrophysics and mineral exploration: a workflow for data analysis and a new interpretation framework. ( Not specific to diamonds)Geophysical Prospecting, htpps://doi.org/10.1111/1365-2478.12882Globalgeophysics - seismic

Abstract: As mineral exploration seeks deeper targets there will be a greater reliance on geophysical data and a better understanding of the geological meaning of the responses will be required, and this must be achieved with less geological control from drilling. Also, exploring based on the mineral system concept requires particular understanding of geophysical responses associated with altered rocks. Where petrophysical datasets of adequate sample size and measurement quality are available, physical properties show complex variations, reflecting the combined effects of various geological processes. Large datasets, analysed as populations, are required to understand the variations. We recommend the display of petrophysical data as frequency histograms as the nature of the data distribution is easily seen with this form of display. A petrophysical data set commonly contains a combination of overlapping sub-populations, influenced by different geological factors. To understand the geological controls on physical properties in hard rock environments it is necessary to analyse the petrophysical data not only in terms of the properties of different rock types. It is also necessary to consider the effects of processes such as alteration, weathering, metamorphism, and strain, and variables such as porosity and stratigraphy. To address this complexity requires that much more supporting geological information be acquired than is current practice. The widespread availability of field portable instruments means quantitative geochemical and mineralogical data can now be readily acquired, making it unnecessary to rely primarily on categorical rock classification schemes. The petrophysical data can be combined with geochemical, petrological and mineralogical data to derive explanations for observed physical property variations based not only on rigorous rock classification methods, but also in combination with quantitative estimates of alteration and weathering. To understand how geological processes will affect different physical properties it is useful to define three end-member forms of behaviour. Bulk behaviour depends on the physical properties of the dominant mineral components. Density and, to a lesser extent, seismic velocity show such behaviour. Grain and texture behaviour occur when minor components of the rock are the dominate controls on its physical properties. Grain size and shape control grain properties, and for texture properties the relative positions of these grains are also important. Magnetic and electrical properties behave in this fashion. Thinking in terms of how geological processes change the key characteristics of the major and minor mineralogical components allows the resulting changes in physical properties to be understood and anticipated.
DS201904-0728
2019
Desharnais, G.How machine learning will disrupt mining. The power and pitfalls of predictive algorithms.researchgate.net, 2p. PdfGlobaldata sets
DS201904-0729
2019
Desharnais, G., Paiement, J.P., Hatfield, D., Poupart, N.Mining BIG data: the future of exploration targeting using machine learning.PDAC Short Course, 5p. PdfGlobaldata sets
DS201912-2777
2019
Desrosiers, P., Ward, B.C., Sacco, D., Elliott, B.The effect of post depositional meltwater processes on kimberlite indicator mineral concentrations in glacial sediments.Yellowknife Forum NWTgeoscience.ca, abstract volume poster p.105-106.Canada, Northwest Territoriesdrift prospecting

Abstract: In the glaciated terrain of the Northwest Territories, successful diamond exploration projects depend on the implementation of drift prospecting. Drift prospecting combines surficial sediment sampling with an understanding of glacial sediment transport history so that geochemical anomalies can be properly interpreted. However, deglacial meltwater processes that may rework, erode, transport, and deposit previously emplaced till are commonly overlooked or misidentified in sample collection and data interpretation. Exactly how deglacial meltwater processes affect the concentration of kimberlite indicator minerals in glacial sediments is poorly understood. The aim of this study is to determine if syn- and post-depositional meltwater processes affect kimberlite indicator mineral concentrations and distributions. The study area is approximately 225 km2, located in the Winter Lake area, in the southern Slave region. This area was chosen for its multiple subglacial meltwater corridors with numerous meltwater related landforms adjacent to relatively unmodified till. It is a prospective area for kimberlites based on the kimberlite indicator minerals identified during previous till sampling programs. The project incorporates terrain mapping, fieldwork and geochemical analysis. Progress so far includes a desktop study using existing air photos and surficial maps of the region and fieldwork. Stereo image visualization and mapping software (Summit EvolutionTM) combined with digital air photos of the area were utilized to complete a preliminary 1:10 000 scale digital terrain map. Fieldwork was completed in the summer of 2019: the nature and distribution of surficial materials were described, ice flow indicators identified and recorded, and surficial material samples collected. Sampling targeted sediments that experienced varying degrees of meltwater modification; materials collected cover the spectrum from unmodified till to washed till to sorted glaciofluvial sand and gravel. Analysis and interpretation are ongoing. Clast shape and lithology analysis has been completed. Grain size analysis will be completed for the presentation. Samples have been sent to commercial labs for geochemical analysis of the silt and clay fraction as well as heavy mineral separation followed by picking of kimberlite, base metal and gold indicator minerals. Potential kimberlite indicator minerals will be analyzed by electron microprobe to verify the mineralogy; their chemistry will be related to diamond potential. The results of these analysis will not be available in time for the presentation. Field descriptions and photogrammetry indicate that many meltwater corridors contain hummocks and elongate ridges composed of diamicton that is sandier and contains less silt than an unmodified till. The morphology and directionality of these identified landforms suggest they are not esker segments. Comparison of grain size, clast shape and lithology data between till and modified sediments will be related to landform genesis. The observations of surficial materials, landforms and ice flow indicators are being used to update the preliminary 1:10 000 scale terrain map of the area, as well as to interpret the local glacial history of the study area. The results of this project will have significant implications in the planning and execution of diamond exploration programs in the Northwest Territories as well as in effectively interpreting the results of drift prospecting campaigns.
DS201901-0026
2018
D'Haenens-Johansson, U.F.S.The Lesedi La Rona and the Constellation - the puzzle of the large rough diamonds from Karowe.Gems & Gemology, Sixth International Gemological Symposium Vol. 54, 3, 1p. Abstract p. 273-4.Africa, Botswanadeposit - Karowe

Abstract: In November 2015, Lucara Diamond’s operation at the Karowe mine in Botswana gained notoriety due to the extraction of a series of large colorless diamonds, including the 1,109 ct Lesedi La Rona and the 812 ct Constellation. The Lesedi La Rona marks the largest gem diamond recovered since the Cullinan (3,106 ct) in 1905. The Constellation, considered to be the seventh-largest recorded diamond, attained the highest price ever paid for a rough, selling for $63.1 million ($77,649 per carat). Additionally, three other significant colorless diamonds were recovered during the same period, weighing 374, 296, and 183 ct. Due to the similarity in their external characteristics— which include cleavage faces—as well as their extraction locations and dates, it was suspected that these stones might have originated from a larger rough that had broken. Lucara demonstrated that the 374 ct diamond and the Lesedi La Rona fit together, yet a large cleavage plane is still unaccounted for. GIA was able to study several rough and/or faceted pieces of these five diamonds using a range of spectroscopic and imaging techniques to gain insight into the presence and distribution of point defects in these diamonds. Diamonds are commonly classified according to their nitrogen content measured by Fourier-transform infrared (FTIR) spectroscopy: Type I diamonds contain nitrogen in either isolated (Ib) or aggregated (IaAB) forms, while type II diamonds do not contain detectable nitrogen concentrations (IIa) but may contain boron (IIb). Analysis of faceted stones cut from the Lesedi La Rona indicates that the rough is a mixed-type diamond, containing both type IIa and pure type IaB regions. These types of diamonds, though exceedingly unusual, have been observed at GIA and reported by Delaunay and Fritsch (2017). The Constellation and the 374, 296, and 183 ct diamonds were determined to be type IaB, containing 20 ± 4 ppm B-aggregates (N4V), in agreement with the concentration for the type IaB pieces of the Lesedi La Rona. Pure type IaB diamonds such as these are actually quite rare, accounting for only 1.2% of a random suite of 5,060 large (>10 ct) D-to-Z diamonds submitted to GIA, whereas 24.6% were type II. Photoluminescence spectra further confirmed analogous defect content for the five large Karowe diamonds, with emissions from H4 (N4V2 0, 496 nm), H3 (NVN0, 503 nm), 505 nm, NV– (637 nm), and GR1 (V0, 741 nm) defects showing similar relative intensities and peak widths. Even for diamonds of the same type, parallel defect content and characteristics across such a variety of defects is unlikely for unrelated stones. The external morphologies of the diamonds showed primary octahedral, resorbed, and fractured faces, with the Constellation and the 296 ct diamond featuring fractures containing metallic inclusions and secondary iron oxide staining. Deep UV fluorescence (< 230 nm) imaging elucidated the internal growth structures of the samples. For the Constellation and the 374, 296, and 183 ct diamonds, at least two growth zones with differing blue fluorescence intensities were observed within single pieces. Combined with the spectroscopic data, these results provide compelling evidence that the Lesedi La Rona, the Constellation, and the 374, 296, and 183 ct diamonds from Karowe had comparable growth histories and likely originated from the same rough, with a combined weight of at least 2,774 ct.
DS201901-0027
2018
Diggle, P.L., D'Haenens-Johannsson, U.F.S., Wang, W., Newton, M.E.Diamond and diffraction limit: optical characterization of synthetic diamond.Gems & Gemology, Sixth International Gemological Symposium Vol. 54, 3, 1p. Abstract p. 265.GlobalDiamondView

Abstract: Diamond, known for its splendor in exquisite jewelry, has been synthesized since the 1950s. In the last six decades, the perfection of laboratory-grown single-crystal diamond has vastly improved through the research and development of two main synthesis techniques. One replicates Earth’s natural process, where the diamond is grown in the laboratory under conditions of diamond stability at high temperature and high pressure (HPHT). The other technique relies on the dissociation of methane (or other carbon-containing source gas) and hydrogen and the subsequent deposition of diamond at low pressures from the gaseous phase in a process known as chemical vapor deposition (CVD). In the latter case, diamond is not the stable form of carbon, but the kinetics in the CVD process are such that diamond wins out. Large gem-quality synthetic diamonds are now possible, and a 6 ct CVD (2018) and a 15.32 ct HPHT (2018) have been reported. It is of course possible to differentiate laboratory-grown from natural diamond based on how extended and point defects are incorporated into the crystal. Furthermore, treated diamond can be identified utilizing knowledge of how defects are produced and how they migrate and aggregate in both natural and synthetic diamond samples. Room-temperature confocal photoluminescence microscopy can be used to image the emission of light from defects in diamond with a spatial resolution limited only by the diffraction limit; a lateral spatial resolution approaching 300 nm is routinely achieved (figure 1). It is possible with this tool to identify point defects with concentrations less than 1 part per trillion (1011 cm–3). This talk will outline the experimental setup, how this tool has been used to identify the decoration of dislocations with point defects in CVD lab-grown diamond, and how different mechanisms for defect incorporation operate at growth sector boundaries in HPHT synthetic diamond.
DS201901-0028
2018
Dixon, N.A., Durham, W.B.Measurement of activation volume for creep of dry olivine at upper-mantle conditions.Journal of Geophysical Research: Solid Earth, Vol. 123, 10, pp. 8459-8473.Mantleolivine

Abstract: Olivine is the most abundant and among the weakest phases in Earth's upper mantle, and thus, its rheological properties play a critical role in governing thermal structure and convective flow in the upper mantle. A persistent obstacle to constraining the in situ flow properties of olivine by laboratory experiment has been the difficulty in resolving the effect of pressure, which is weak within the 0- to ~2-GPa pressure range of conventional laboratory deformation instruments but potentially strong over the 1- to ~14-GPa range of the upper mantle. Using a deformation-DIA, one of a new generation of bonafide deformation devices designed for operation to =10 GPa, we have deformed dry, polycrystalline San Carlos olivine in high-temperature creep with the singular intent of providing the best achievable measurement of activation volume V* and a comprehensive statement of uncertainty. Under strictly dry conditions, at constant temperature (1,373 K) and strain rate (1 × 10-5 s-1), varying only pressure (1.8 to 8.8 GPa), we measure V* = 15 ± 5 cm3/mol. We have reproduced the well-known mechanism change from [100]-slip to [001]-slip near 5 GPa and determined that, whatever the change in V* associated with the change in slip system, the effective value of 15 ± 5 cm3/mol is still accurate for modeling purposes in the 2- to 9-GPa pressure range. This is a substantial pressure effect, which in the absence of a temperature gradient would represent a viscosity increase from the top to bottom of the upper mantle of 5 ± 2 orders of magnitude.
DS201909-2034
2019
Djeddi, A., Parat, F., Bodinier, J-L., Ouzegane, K. Immiscibility and hybridization during progressive cooling of carbonatite and alkaline magmas ( in Oussal Terrane, western Hoggar).Goldschmidt2019, 1p. AbstractAfrica, Algeriacarbonatite

Abstract: Carbonatites and syenites from Ihouhaouene (2 Ga; In Ouzzal terrane, Hoggar, South of Algeria) have close spatial relationships. Their analogous mineral assemblages with diopside/hedenbergite (cpx), apatite, wollastonite +/- calcite and alkali-feldspar suggest that they were emplaced from a common igneous parental event. Carbonatites from In Ouzzal terrane are calciocarbonatites and form a continuous range of whole-rock major and trace element composition from Sipoor carbonatite (<20 wt.% SiO2; 24-36 wt.% CO2) to Si-rich carbonatite (20-35 wt.% SiO2; 11-24 wt.% CO2) then white syenite (52-58 wt.% SiO2; 0.1-6.5 wt.% CO2) and red syenite (57-65 wt.% SiO2; 0.1-0.4 wt.% CO2). Equilibrium calculations reveal that apatite (Ce/Lu= 1690-6182; Nb/Ta >50) and cpx (Ce/Lu= 49-234; Nb/Ta<10) from Si-rich carbonatites and white syenites crystallized from a REEenriched carbonate melt and an evolved silicate melt, respectively. Likewise, Si-poor carbonatites have a higher REE contents in calculated apatite equilibrium melts than in their cpx and a wide range of Nb/Ta ratios with a majority of subchondritic value (<10) that reflects the segregation of the carbonate fraction from an evolved parental melt. Otherwise, red syenites have similar REE contents in apatite and clinopyroxene equilibrium melts (Nb/Ta>10) suggesting an origin from homogeneous evolved melt batches. Both mineralogical and geochemical features reveal the intimate link between carbonatites and syenites and their cogenetic signature. Immiscibility and fractional crystallization processes modelling explain the trace element contents and low Nb/Ta ratio in minerals. These processes were partly counterbalanced by intermingling of partially crystallized melt fractions and hybridization of segregated minerals during the progressive cooling of a silico-carbonated mantle melt.
DS201902-0269
2019
Domeier, M., Torsvik, T.H.Full plate modelling in pre-Jurassic time.Geological Magazine, Vol. 156, 2, pp. 261-280.Mantleplate tectonics

Abstract: A half-century has passed since the dawning of the plate tectonic revolution, and yet, with rare exception, palaeogeographic models of pre-Jurassic time are still constructed in a way more akin to Wegener's paradigm of continental drift. Historically, this was due to a series of problems - the near-complete absence of in situ oceanic lithosphere older than 200 Ma, a fragmentary history of the latitudinal drift of continents, unconstrained longitudes, unsettled geodynamic concepts and a lack of efficient plate modelling tools - which together precluded the construction of plate tectonic models. But over the course of the last five decades strategies have been developed to overcome these problems, and the first plate model for pre-Jurassic time was presented in 2002. Following on that pioneering work, but with a number of significant improvements (most notably longitude control), we here provide a recipe for the construction of full-plate models (including oceanic lithosphere) for pre-Jurassic time. In brief, our workflow begins with the erection of a traditional (or ‘Wegenerian’) continental rotation model, but then employs basic plate tectonic principles and continental geology to enable reconstruction of former plate boundaries, and thus the resurrection of lost oceanic lithosphere. Full-plate models can yield a range of testable predictions that can be used to critically evaluate them, but also novel information regarding long-term processes that we have few (or no) alternative means of investigating, thus providing exceptionally fertile ground for new exploration and discovery.
DS201906-1288
2019
Dongre, A., Tappe, S.Kimberlite and carbonatite dykes within the Premier diatreme root ( Cullinan diamond mine, South Africa: new insights to mineralogical-genetic classifications and magma CO2 degassing.Lithos, Vol. 338-339, pp. 155-173.Africa, South Africadeposit - Cullinan

Abstract: The ca. 1153?Ma Premier kimberlite pipe on the Kaapvaal craton has been intruded by late-stage kimberlite and carbonatite magmas forming discrete 0.5 to 5?m wide dykes within the lower diatreme. On the basis of petrography and geochemistry, the fresh kimberlite dykes represent archetypal monticellite phlogopite kimberlite of Group-1 affinity. Their mineral compositions, however, show marked deviations from trends that are typically considered as diagnostic for Group-1 kimberlite in mineralogical-genetic classification schemes for volatile-rich ultramafic rocks. Groundmass spinel compositions are transitional between magnesian ulvöspinel (a Group-1 kimberlite hallmark feature) and titanomagnetite trends, the latter being more diagnostic for lamproite, orangeite (formerly Group-2 kimberlite), and aillikite. The Premier kimberlite dykes contain groundmass phlogopite that evolves by Al- and Ba-depletion to tetraferriphlogopite, a compositional trend that is more typical for orangeite and aillikite. Although high-pressure cognate and groundmass ilmenites from the Premier hypabyssal kimberlites are characteristically Mg-rich (up to 15?wt% MgO), they contain up to 5?wt% MnO, which is more typical for carbonate-rich magmatic systems such as aillikite and carbonatite. Manganese-rich groundmass ilmenite also occurs in the Premier carbonatite dykes, which are largely devoid of mantle-derived crystal cargo, suggesting a link to the kimberlite dykes by fractionation processes involving development of residual carbonate-rich melts and fluids. Although mineralogical-genetic classification schemes for kimberlites and related rocks may provide an elegant approach to circumvent common issues such as mantle debris entrainment, many of the key mineral compositional trends are not as robust for magma type identification as previously thought. Utilizing an experimentally constrained CO2-degassing model, it is suggested that the Premier kimberlite dykes have lost between 10 and 20?wt% CO2 during magma ascent through the cratonic lithosphere, prior to emplacement near the Earth's surface. Comparatively low fO2 values down to -5.6 ?NNO are obtained for the kimberlite dykes when applying monticellite and perovskite oxybarometry, which probably reflects significant CO2 degassing during magma ascent rather than the original magma redox conditions and those of the deep upper mantle source. Thus, groundmass mineral oxybarometry may have little value for the prediction of the diamond preservation potential of ascending kimberlite magmas. After correction for olivine fractionation and CO2-loss, there remains a wide gap between the primitive kimberlite and carbonatite melt compositions at Premier, which suggests that these magma types cannot be linked by variably low degrees of partial melting of the same carbonated peridotite source in the deep upper mantle. Instead, fractionation processes produced carbonate-rich residual melts/fluids from ascending kimberlite magma, which led to the carbonatite dykes within Premier pipe.
DS201906-1289
2019
Doroshkevich, A.G., Chebotarev, D.A., Sharygin, V.V., Prokopyev, I.R., Nikolenko, A.M.Petrology of alkaline silicate rocks and carbonatites of the Chuktukon massif, Chadobets upland, Russia: sources, evolution and relation to the Triassic Siberian LIP.Lithos, Vol. 332-333, pp. 245-260.Russiacarbonatites

Abstract: The petrogenesis of temporally and spatially associated carbonatitic and deeply derived carbonated alkaline silicate magmas provides an opportunity to gain insights into the nature of the deepest lithospheric mantle. The Chuktukon massif, which is part of the Chadobets alkaline ultramafic carbonatite complex (Chadobets upland, Siberian craton) is a carbonatite-melilitite-damtjernite intrusion, whose emplacement was coeval with the Siberian Traps large igneous province (LIP). In this study, the sources of the primary melts are examined, the petrogenetic evolution of the complex is reconstructed and the relationship with the Siberian LIP is also discussed. Isotopic and geochemical information indicate that the source for the Chuktukon primary melts was isotopically moderately depleted and the primary melts were formed by low degree partial melting of garnet carbonated peridotite. Hydrothermal processes caused 18 O- and 13 C- enrichment. The weathering process was accompanied by trace element re-distribution and enrichment of the weathering crust in Zn, Th, U, Nb, Pb and REE, relative to the Chuktukon rocks and a change in radiogenic (Sr, Nd) isotope compositions.
DS201905-1024
2019
Doroshkevich, A.G., Chebotarev, D.A., Sharygin, V.V.. Prokopyev, I.R., Nikolenko, A.M.Petrology of alkaline silicate rocks and carbonatites of the Chuktukon massif, Chadobets upland, Russia: sources, evolution and relation to the Triassic Siberian LIP.Lithos, Vol. 332-333, pp. 245-260.Russiacarbonatite

Abstract: The petrogenesis of temporally and spatially associated carbonatitic and deeply derived carbonated alkaline silicate magmas provides an opportunity to gain insights into the nature of the deepest lithospheric mantle. The Chuktukon massif, which is part of the Chadobets alkaline ultramafic carbonatite complex (Chadobets upland, Siberian craton) is a carbonatite-melilitite-damtjernite intrusion, whose emplacement was coeval with the Siberian Traps large igneous province (LIP). In this study, the sources of the primary melts are examined, the petrogenetic evolution of the complex is reconstructed and the relationship with the Siberian LIP is also discussed. Isotopic and geochemical information indicate that the source for the Chuktukon primary melts was isotopically moderately depleted and the primarymelts were formed by lowdegree partial melting of garnet carbonated peridotite. Hydrothermal processes caused 18O- and 13C- enrichment. The weathering process was accompanied by trace element re-distribution and enrichment of the weathering crust in Zn, Th, U, Nb, Pb and REE, relative to the Chuktukon rocks and a change in radiogenic (Sr, Nd) isotope compositions.
DS201901-0029
2018
Dransfield, M.H., Chen, T.Heli-borne gravity gradiometry in rugged terrain. (mentions Margaret Lake)Geophysical Prospecting, doi.org/10.1111/1365-2478.12736 Canada, Northwest Territoriesgeophysics
DS201907-1541
2019
Dransfield, M.H., Chen, T.Heli-borne gravity gradiometry in rugged terrain ( mentions Margaret Lake)Geophysical Prospecting, Vol. 67, 6, pp. 1626-1636.Global, Canada, Northwest Territoriesgeophysics - graviometry

Abstract: For airborne gravity gradiometry in rugged terrain, helicopters offer a significant advantage over fixed-wing aircraft: their ability to maintain much lower ground clearances. Crucially, this provides both better signal-to-noise and better spatial resolution than is possible with a fixed-wing survey in the same terrain. Comparing surveys over gentle terrain at Margaret Lake, Canada, and over rugged terrain at Mount Aso, Japan, demonstrates that there is some loss of spatial resolution in the more rugged terrain. The slightly higher altitudes forced by rugged terrain make the requirements for terrain correction easier than for gentle terrain. Transforming the curvature gradients measured by the Falcon gravity gradiometer into gravity and the complete set of tensor components is done by a Fourier method over gentle terrain and an equivalent source method for rugged terrain. The Fourier method is perfectly stable and uses iterative padding to improve the accuracy of the longer wavelengths. The equivalent source method relies on a smooth model inversion, and the source distribution must be designed to suit the survey design.
DS201905-1025
2019
Drenth, B.J., Grauchm V.J.S.Finding the gap in America's magnetic maps. ( Apr. 16, 2019)EOS, https://spaces.hightail. com/receive/ 2jvDHdtWRrUnited States, Arkansas, Missouri, Tennesseegeophysics, magnetic
DS201903-0503
2019
Drewitt, J.W.E., Walter, M.J., Zhang, H., McMahon, S.C., Edwards, D., Heinen, B.J., Lord, O.T., Anzellini, S., Kleppe, A.K.The fate of carbonate in oceanic crust subducted into Earth's lower mantle.Earth and Planetary Science Letters, Vol. 511, pp. 213-222.MantleBridgemanite

Abstract: We report on laser-heated diamond anvil cell (LHDAC) experiments in the FeO-MgO-SiO2-CO2 (FMSC) and CaO-MgO-SiO2-CO2 (CMSC) systems at lower mantle pressures designed to test for decarbonation and diamond forming reactions. Sub-solidus phase relations based on synthesis experiments are reported in the pressure range of ~35 to 90 GPa at temperatures of ~1600 to 2200 K. Ternary bulk compositions comprised of mixtures of carbonate and silica are constructed such that decarbonation reactions produce non-ternary phases (e.g. bridgmanite, Ca-perovskite, diamond, CO2-V), and synchrotron X-ray diffraction and micro-Raman spectroscopy are used to identify the appearance of reaction products. We find that carbonate phases in these two systems react with silica to form bridgmanite ±Ca-perovskite + CO2 at pressures in the range of ~40 to 70 GPa and 1600 to 1900 K in decarbonation reactions with negative Clapeyron slopes. Our results show that decarbonation reactions form an impenetrable barrier to subduction of carbonate in oceanic crust to depths in the mantle greater than ~1500 km. We also identify carbonate and CO2-V dissociation reactions that form diamond plus oxygen. On the basis of the observed decarbonation reactions we predict that the ultimate fate of carbonate in oceanic crust subducted into the deep lower mantle is in the form of refractory diamond in the deepest lower mantle along a slab geotherm and throughout the lower mantle along a mantle geotherm. Diamond produced in oceanic crust by subsolidus decarbonation is refractory and immobile and can be stored at the base of the mantle over long timescales, potentially returning to the surface in OIB magmas associated with deep mantle plumes.
DS201903-0504
2019
Driscoll, P.Geodynamics recharged. Nature Geoscience, Vol. 12, pp. 83-84.MantleGeophysics - magnetics

Abstract: Transition from a weak and erratic geomagnetic field to a more stable one around 560 million years ago, inferred from palaeomagnetic measurements, suggests that the inner core may have solidified around that time, much later than thought.
DS201909-2035
2019
Driscoll, P.E., Du, Z.Geodynamo conductivity limits.Geophysical Research Letters, Vol. 46, 14, pp. 7982-7989.Mantlegeophysics

Abstract: In a metal, as in Earth's core, the thermal and electrical conductivities are assumed to be correlated. In a planetary dynamo this implies a contradiction: that both electrical conductivity, which makes it easier to induce current and magnetic field, and conductive heat transport, which hinders thermal convection, should increase simultaneously. Here we show that this contradiction implies that the magnetic induction rate peaks at a particular value of electrical and thermal conductivity and derive the low- and high-conductivity limits for thermal dynamo action. A dynamo regime diagram is derived as a function of electrical conductivity and temperature for Earth's core that identifies four distinct dynamo regimes: no dynamo, thermal dynamo, compositional dynamo, and thermocompositional dynamo. Estimates for the temperature-dependent electrical conductivity of the core imply that the geodynamo may have come close to its high-conductivity “no dynamo” limit prior to inner core nucleation, consistent with recent paleomagnetic observations.
DS201905-1026
2019
Dsmit, K.V., Stachel, T., Luth, R.W., Stern, R.A.Evaluating mechanisms for eclogitic diamond growth: an example from Zimmi Neoproterozoic diamonds ( West African Craton).Chemical Geology, doi.org/10,1016/j.chem geo.2019.04.014 37p.Africa, Sierra Leonedeposit - Zimmi

Abstract: Here we present SIMS data for a suite of Zimmi sulphide-bearing diamonds that allow us to evaluate the origin and redox-controlled speciation of diamond-forming fluids for these Neoproterozoic eclogitic diamonds. Low d13C values below -15‰ in three diamonds result from fluids that originated as carbon in the oceanic crust, and was recycled into the diamond-stable subcratonic lithospheric mantle beneath Zimmi during subduction. d13C values between -6.7 and -8.3‰ in two diamonds are within the range for mantle-derived carbon and could reflect input from mantle fluids, serpentinised peridotite, or homogenised abiogenic and/or biogenic carbon (low d13C values) and carbonates (high d13C values) in the oceanic crust. Diamond formation processes in eclogitic assemblages are not well constrained and could occur through redox exchange reactions with the host rock, cooling/depressurisation of CHO fluids or during H2O-loss from CHO fluids. In one Zimmi diamond studied here, a core to rim trend of decreasing d13C (-23.4 to -24.5‰) and decreasing [N] is indicative of formation from reduced CH4-bearing fluids. Unlike mixed CH4-CO2 fluids near the water maximum, isochemical diamond precipitation from such reduced CHO fluids will only occur during depressurisation (ascent) and should not produce coherent fractionation trends in single diamonds that reside at constant depth (pressure). Furthermore, due to a low relative proportion of the total carbon in the fluid being precipitated, measurable carbon isotopic variations in diamond are not predicted in this model and therefore cannot be reconciled with the 1‰ internal core-to- rim variation. Consequently, this Zimmi eclogitic diamond showing a coherent trend in d13C and [N] likely formed through oxidation of methane by the host eclogite, although the mineralogical evidence for this process is currently lacking.
DS201910-2255
2019
Du, Z., Deng, J., Miyazaki, Y., Mao, H-k., Karki, B.B., Lee, K.K.M.Fate of hydrous Fe-silicate melt in Earth's deep mantle.Geophysical Research Letters, Vol. 46, doi.org/ 10.1029/ 2019GL083633Mantlemelting

Abstract: Planetary-scale melting is ubiquitous after energetic impacts early in Earth's history. Therefore, determining key melt properties, such as density, is of great significance to better understand Earth's formation and subsequent evolution. In this study, we performed state-of-art first-principles molecular dynamics simulations to examine the density of deep mantle melts, namely, hydrous Fe-rich silicate melts. We find that such hydrous melts can be gravitationally stable near Earth's core-mantle boundary given their likely high iron content. This has great implications for Earth's thermochemical evolution, as well as Earth's volatile cycle.
DS201911-2520
2019
Du, Z., Deng, J., Miyazaki, Y., Mao, H-K., Karki, B.B., Lee, K.K.M.Fate of hydrous Fe-rich silicate melt in Earth's deep mantle.Geophysical Research Letters, Vol. 46, 16, pp. 9466-9473.Mantlewater

Abstract: Planetary-scale melting is ubiquitous after energetic impacts early in Earth's history. Therefore, determining key melt properties, such as density, is of great significance to better understand Earth's formation and subsequent evolution. In this study, we performed state-of-art first-principles molecular dynamics simulations to examine the density of deep mantle melts, namely, hydrous Fe-rich silicate melts. We find that such hydrous melts can be gravitationally stable near Earth's core-mantle boundary given their likely high iron content. This has great implications for Earth's thermochemical evolution, as well as Earth's volatile cycle.
DS201904-0730
2019
Duncombe, J.The unsolved mystery of the Earth blobs.EOS, 100, https://doi.org/10.1029/ 2019EO117193Mantletomography

Abstract: Researchers peering into Earth’s interior found two continent-sized structures that upend our picture of the mantle. What could their existence mean for us back on Earth’s surface?
DS201910-2256
2019
Dymshits, A., Sharygin, I., Yakolev, I., Malovets, V.Thermal state and composition of the lithospheric mantle beneath the Upper Muna kimberlite field, Yakutia.Goldschmidt2019, 1p. AbstractRussia, Yakutiadeposit - Upper Muna

Abstract: Mantle xenoliths brought up by kimberlitic magmas are the main source of data on the composition and physical conditions of cratonic mantle. Temperature varioations in a complete lithospheric mantle section (80-200 km) of the Siberian craton beneath the Upper Muna kimberlite filed are estimated based 49 peridotite xenolith and 330 Cpx grains from the Komsomolskaya-Magnitnaya pipe. Pressure and temperature estimates closely follow the 34.5 mW/m2 conductive geotherm. Thermal lithospere thickness is of ~ 220 km, and “diamond window” in the Paleozoic is ~75 km thick (Fig.1). Olivine compositions range in Mg# from 82 to 94 and the majority of olivenes has very high Mg# > 93. Garnets compositions mainlly follow to harzburgite-dunite and lherzolite trends plotted as Cr2O3 vs CaO. The composition of the minerals indicated the extremly depleted lithospheric mantle beneath the Upper-Muna kimberlite field. Figure 1: Model palaeogeotherms calculated using the program FITPLOT. Komsomolskaya-Magnitnaya - our data, Novinka and Udachaya are from Z16 [1]
DS201901-0030
2018
Eaton-Magana, S.Summary of CVD lab-grown diamonds seen at the GIA laboratory.Gems & Gemology, Sixth International Gemological Symposium Vol. 54, 3, 1p. Abstract p. 269-270..United Statessynthetics

Abstract: While chemical vapor deposition (CVD) diamond growth technology has progressed significantly in recent years, with improvements in crystal size and quality, the use of these goods in the jewelry trade is still limited. Not all CVD-grown gem diamonds are submitted to GIA for grading reports, and they only account for about 0.01% of GIA’s annual diamond intake (both D–Z equivalents and fancy color; Eaton-Magaña and Shigley, 2016). The CVD process involves diamond growth at moderate temperatures (700–1300°C) but very low pressures of less than 1 atmosphere in a vacuum chamber (e.g., Angus and Hayman, 1988; Nad et al., 2015). This presentation summarizes the quality factors and other characteristics of the CVD-grown material submitted to GIA (e.g., figure 1) and discusses new research and products. Today the CVD process is used to produce high-color (as well as fancy-color) and high-clarity type II diamonds up to several carats in size. The majority of the CVD material seen at GIA consists of near-colorless (G–N equivalent) with colorless (D–F equivalent) and various “pink” hues. Additionally, CVD material is constantly setting new size milestones, with the announcement of an approximately 6 ct round brilliant earlier this year (Davis, 2018). However, the attainable sizes among CVD products are dwarfed by those from the HPHT process, with 15.32 ct as the current record for a faceted gem (Ardon and Eaton-Magaña, 2018). One particular challenge for gemologists (albeit very rarely encountered) comes from the lab-grown/natural hybrids (figure 2) that have been submitted to and documented by gemological laboratories (e.g., Moe et al., 2017; Tang et al., 2018). In these specimens, the grower places a natural diamond into the CVD reactor as the seed plate, with both components retained in the faceted gem. If the manufacturer is using a colorless natural type Ia diamond as a seed plate for near-colorless CVD growth, the hybrid cannot undergo any post-growth HPHT treatment, as this would radically alter the natural seed by turning the natural diamond yellow. If the manufacturer is creating a CVD overgrowth layer on a faceted natural diamond, the intent is to either add weight to a diamond that may be near a weight boundary or to achieve a color change, typically to blue. These hybrid products also make it more difficult to infer a diamond’s history based solely on its diamond type. The CVD process has also created some unique gems that have not been duplicated among natural, treated, or HPHT-grown diamonds. These include CVD-grown diamonds with a high concentration of silicon impurities, which create a pink to blue color shift. In those samples, a temporary effect was activated by UV exposure, which precipitated a charge transfer between negative and neutral silicon-vacancy centers (D’Haenens-Johansson et al., 2015). Also recently seen are type IIb CVD goods. Some that were submitted by clients had a low boron concentration (3 ppb, with G-equivalent color and 1.05 carat weight). Meanwhile, some research samples produced by a manufacturer in China and fashioned as flat plates had dark bluish coloration and very high boron concentration (2500 ppb and higher). Also among that suite of flat-plate CVD samples was one with a black color caused by extremely high amounts of nitrogen-vacancy centers. Although new CVD products are continually being manufactured and introduced to the trade, the laboratory-grown diamonds examined to date by GIA can be readily identified.
DS201903-0505
2018
Eaton-Magana, S., Ardon, T., Smit, K.V., Breeding, C.M., Shigley, J.E.Natural color pink, purple, red and brown diamonds: band of many colors.Gems & Gemology, Vol. 54, 4, pp. 352-377.Global, Australiadiamond colour

Abstract: Diamond is one of Earth’s most extraordinary materials. It represents the pinnacle for several material and physical properties. As a gem, however, it is the near-perfect examples—diamonds attaining the D-Flawless distinction—and those with imperfections resulting in a vibrant or surprising color that create the most enduring impressions. Fancy-color natural diamonds are among the most highly valued gemstones due to their attractiveness and great rarity. The 18.96 ct Winston Pink Legacy, with a color grade of Fancy Vivid pink, recently made history by selling at over $50 million, its $2.6 million per carat price an all-time high for a pink diamond (Christie’s, 2018).
DS201907-1531
2019
Ecclestone, C.Rare Earths .. Sunset for China's REE dominance.Hallgartenco.com, June 5, 21p. PdfChinaREE
DS201905-1027
2019
Ekimov, E.A., Kondrin, M.V., Krivobok, V.S., Khomich, A.A., Vlasov, I.I., Khmelnitskiy, R.A.Effect of Si, Ge and Sn dopant elements on structure and photoluminescence of nano- and microdiamonds synthesized from organic compounds.Diamond & Related Materials, Vol. 93, pp. 75-83.Globalluminescence

Abstract: HPHT synthesis of diamonds from hydrocarbons attracts great attention due to the opportunity to obtain luminescent nano- and microcrystals of high structure perfection. Systematic investigation of diamond synthesized from the mixture of hetero-hydrocarbons containing dopant elements Si or Ge (C24H20Si and C24H20Ge) with a pure hydrocarbon - adamantane (C10H16) at 8?GPa was performed. The photoluminescence of SiV- and GeV- centers in produced diamonds was found to be saturated when Si and Ge contents in precursors exceed some threshold values. The presence of SiC or Ge as second phases in diamond samples with saturated luminescence indicates that ultimate concentrations of the dopants were reached in diamond. It is shown that SiC inclusions can be captured by growing crystals and be a source of local stresses up to 2?GPa in diamond matrix. No formation of Ge-related inclusions in diamonds was detected, which makes Ge more promising as a dopant in the synthesis method. Surprisingly, the synthesis of diamonds from the C24H20Sn hetero-hydrocarbon was ineffective for SnV- formation: only fluorescence of N-and Si-related color centers was detected at room temperature. As an example of great potential for the synthesis method, mass synthesis of 50-nm diamonds with GeV- centers was realized at 9.4?GPa. Single GeV- production in individual nanodiamond was demonstrated.
DS201904-0731
2019
Elazar, O., Frost, D., Navon, O., Kessel, R.Melting H2O and CO2 bearing eclogite at 4-6 GPa and 900-1200 C: implications for the generation of diamond forming fluids.Geochimica et Cosmochimica Acta, in press available 47p.Mantlemelting, subduction
DS201906-1290
2019
Elazar, O., Frost, D., Navon, O., Kessel, R.Melting H2O and CO2 bearing eclogite at 4-6 Gpa and 900-1200C: implications for the generation of diamond forming fluids.Geochimica et Cosmochimica Acta, Vol. 255, pp. 69-87.Mantlediamond genesis

Abstract: Eclogites play a significant role in geodynamic processes, transferring large amounts of basaltic material and volatiles (chiefly CO2 and H2O species) into the earth's mantle via subduction. Previous studies of eclogite melting focused on two end member systems: either carbonated or hydrous eclogites. Here we focus on the hydrous carbonated eclogitic system in order to define the position of its solidus and determine the near solidus fluid and melt compositions at 4-6?GPa and 900-1200?°C. Experiments were performed on a rocking multi-anvil press. The total dissolved solids in the equilibrated fluids were analyzed following the cryogenic technique using a LA-ICP-MS. H2O and CO2 content were determined by mass balance calculations. Solid phases were chemically characterized using an EPMA. Garnet and clinopyroxene are present in all experiments, assembling the eclogitic rock. A carbonate phase was detected at all temperatures at 4?GPa and at temperatures below 1200?°C at 5 and 6?GPa. Coesite was observed at all pressures below 1200?°C. The solidus was crossed between 1000 and 1100?°C at 4 and 5?GPa. At 6?GPa we observed a relatively smooth decrease in the H2O and CO2 content of the fluid phase with rising temperature, suggesting the presence of a supercritical fluid. The second critical endpoint is thus defined in this system at ~5.5?GPa and 1050?°C. The composition of fluids and melts reported in this study indicates that the hydrous carbonated eclogite system is a plausible source-rock for high density fluids (HDFs) found in microinclusions in diamonds, specifically for the intermediate compositions along the array spanned between low-Mg carbonatitic HDFs and hydrous-silicic ones. Our results suggest that the whole array reflects melting in a heterogeneous mantle. Melting of water-rich eclogite produces silicic HDFs, carbonate-rich zones will produce carbonatitc HDFs, while source-rocks with varying H2O/CO2 ratios produce intermediate compositions.
DS201906-1291
2019
Elliott, H.A.L., Broom-Fendley, S., Wall, F.Fenite exploration criteria surrounding carbonatite hosted critical metal deposits.3rd International Critical Metals Meeting held Edinburgh, 1p. Abstract p. 38.Europe, Finlanddeposit - Sokli
DS201903-0506
2019
Emry, E.L., Shen, Y., Nyblade, A.A., Flinders, A., Bao, X.Upper mantle Earth structure in Africa from full wave ambient noise tomography.Geochemistry, Geophysics, Geosystems, Vol. 20, 1, pp. 120-147.Africatomography

Abstract: We use advanced seismic imaging techniques (full-waveform tomography), constrained by data from background (ambient) seismic noise to image the upper mantle beneath the African continent and search for low-velocity structures (hot spots) that might coincide with regions of volcanism, surface uplift, and continental rifting, particularly along the East African Rift. We also searched for high-velocity structures (old, rigid blocks) that could influence how warm, buoyant material flows within the Earth's upper mantle. Our seismic tomography method allowed us to obtain a clear image of structure beneath parts of Africa where no or very few seismometers are located (such as the Sahara Desert and the Congo Basin). Our results provide indications for segmented secondary (or shallow) upwellings in the upper mantle beneath East Africa, as opposed to earlier models suggesting one large, continuous plume within the upper mantle. Our results also suggest that the one large, rigid, cratonic block previously imaged beneath the Congo region may instead be composed of smaller, distinct blocks. These results provide insight into the factors that control continental rifting along East Africa and provide new testable models that help us to understand the relationships between upper mantle flow, rifting, volcanism, surface uplift, and sedimentation records.
DS201901-0031
2018
Engwicht, N. The local translation of global norms: the Sierra Leonean diamond market.Conflict, Security and Develoment, Vol. 18, 6, pp. 463-492.Africa, Sierra Leoneeconomics

Abstract: Shortcomings in natural resource governance leading to economic mismanagement, political clientelism, underdevelopment and civil conflict, have caused an increase in global norms of ‘good governance’ of natural resource sectors. As a result, a growing number of global governance initiatives are targeting conflict-prone natural resource sectors. Whether these regulatory efforts stand a chance of being successful depends on their implementation in producer countries. As the transnational regulatory framework aimed at curbing the trade in conflict minerals is expanding, this article investigates the local translation of global norms of resource governance. Drawing on the ‘local-to-global’ research perspective developed in this special issue and norm diffusion theories, the article examines one of the most prominent cases of governance reform targeting conflict-affected natural resource sectors: The Sierra Leonean diamond market. Based on extensive field research, the article analyses the implementation of KPCS requirements on the national and subnational level of governance institutions. It evaluates the accomplishments, the challenges and the local adaption to and (formal and informal) interpretation of KPCS norms.
DS201907-1542
2019
Eppelbaum, L.V., Kutasov, I.M.Well drilling in permafrost regions: dynamics of the thawed zone.Polar Research, Vol. 20, 3351 9p. PdfGlobalpermafrost

Abstract: In the cold regions, warm mud is usually used to drill deep wells. This mud causes formation thawing around wells, and as a rule is an uncertain parameter. For frozen soils, ice serves as a cementing material, so the strength of frozen soils is significantly reduced at the ice-water transition. If the thawing soil cannot withstand the load of overlying layers, consolidation will take place, and the corresponding settlement can cause significant surface shifts. Therefore, for long-term drilling or oil/gas production, the radius of thawing should be estimated to predict platform stability and the integrity of the well. It is known that physical properties of formations are drastically changed at the thawing-freezing transition. When interpreting geophysical logs, it is therefore important to know the radius of thawing and its dynamics during drilling and shut-in periods. We have shown earlier that for a cylindrical system the position of the phase interface in the Stefan problem can be approximated through two functions: one function determines the position of the melting-temperature isotherm in the problem without phase transitions, and the second function does not depend on time. For the drilling period, we will use this approach to estimate the radius of thawing. For the shut-in period, we will utilize an empirical equation based on the results of numerical modelling.
DS201908-1776
2019
Ernst, R.E., Liikane, D.A., Jowitt, S.M., Buchan, K.L., Blanchard, J.A.A new plumbing system framework for mantle plume related continental large igneous provinces and their mafic ultramafic intrusions.Journal of Volcanology and Geothermal Research, in press available 34p. PdfGlobalmantle plumes, hotspots

Abstract: The magmatic components of continental Large Igneous Provinces (LIPs) include flood basalts and their plumbing system of giant mafic dyke swarms (radiating, linear, and the recently discovered circumferential type), mafic sill provinces, a lower crustal magmatic underplate, mafic-ultramafic (M-UM) intrusions, associated silicic magmatism, and associated carbonatites and kimberlites. This paper proposes a new plumbing system framework for mantle plume-related continental LIPs that incorporates all of these components, and provides a context for addressing key thematic aspects such as tracking magma batches "upstream" and "downstream" and their geochemical evolution, assessing the setting of M-UM intrusions and their economic potential, interpreting deep magmatic component identified by geophysical signatures, and estimating magnitudes of extrusive and intrusive components with climate change implications. This plumbing system model, and its associated implications, needs to be tested against the rapidly improving LIP record.
DS201909-2036
2019
Ernst, R.E., Wang, Q., Mishenina, Y.Linking paleo-surface characteristics and deep crustal processes caused by mantle plumes.Acta Geologica Sinica, Mantlehotspots

Abstract: Buoyant upwellings from the deep mantle (mantle plumes) can arrive at the base of the lithosphere and generate large igneous province (LIP) magmatism which is emplaced throughout the crustal profile, from a deep-crustal magmatic underplate to intra-crustal dykes, sills, and layered intrusions, and surface volcanism. The presence of mantle plumes, has a direct influence on deep crustal magmatism, metamorphism, and dynamics. In this contribution we provide an overview of the links between mantle plumes and their surface expression and atmospheric influence. We consider three aspects: 1) the distribution of associated large igneous provinces (LIPs) and especially their volcanic expression; 2) topographic changes (domal and annular) associated with the flattening of the mantle plume head at the base of the lithosphere, and also development of triple junction rifting; and 3) dramatic climatic excursions in both atmosphere and oceans as recorded by compositional changes in sedimentary rocks and in weathering characteristics. The goal of this investigation is to address the inverse situation:using the characteristics observed at the Earth’s surface and their timing to infer the existence and location of paleo-mantle plumes, and thus infer their deep crustal effects.
DS201904-0732
2019
Esteve, C., Schaeffer, A.J., Audet, P.Upper mantle structure underlying the diamondiferous Slave craton from teleseismic body-wave tomography. Lac de GrasTectonophysics, in press available, 27p.Canada, Northwest Territoriesgeophysics - seismics

Abstract: Cratons are, by definition, the most tectonically stable and oldest parts of the continental lithosphere on Earth. The Archean Slave craton is located in the northwestern part of the Canadian Shield. The propensity of diamondiferous kimberlite pipes in the central Slave craton raises many questions regarding their structural environment and source. Here, we provide the most robust teleseismic P and S body wave tomography models over the Slave craton region based on 20,547 P-wave delay times, 6,140 direct S-wave delay times and 3,381 SKS delay times. The P-wave model reveals an alternating pattern of relative positive and negative anomalies over a fine broad scale region within the central Slave craton. Furthermore, the P-wave model revealed two fine structures located in the lithosphere beneath the Lac de Gras kimberlite cluster, with relatively slow anomalies (B - C) that extend from 75 km to 350 km depths with an apparent dip to the north. These relatively slow P- and S-wave anomalies are associated with metasomatised regions within the lithosphere. The S-wave model displays a slow S-wave anomaly lying from 300 km depth to the transition zone beneath the central Slave craton. This anomaly is located beneath the Lac de Gras kimberlite cluster. We suggest that this anomaly is not the cause of the actual kimberlites at the surface since last eruption occurred 75-45 Ma ago but may be related to a potential kimberlite magma ascent in the asthenosphere.
DS201909-2037
2019
Estrade, G., Marquis, E., Smith, M., Goodenough, K.,Nason, P.REE concentration processes in ion absorption deposits: evidence from the Ambohimirahavavy alkaline complex in Madagascar.Ore Geology Reviews, in press available, 21p. pdfAfrica, MadagascarREE
DS201904-0733
2019
Evans, R.L., Elsenbeck, J., Zhu, J., Abdelsalam, M.G., Sarafian, E., Mutamina, D., Chilongola, F., Atekwana, E.A., Jones, A.G.Structure of the lithosphere beneath the Barotse basin, western Zambia, from magnetotelluric data.Tectonics, Vol. 38, 2, pp. 666-686.Africa, Zambiageophysics

Abstract: A magnetotelluric survey in the Barotse Basin of western Zambia shows clear evidence for thinned lithosphere beneath an orogenic belt. The uppermost asthenosphere, at a depth of 60-70 km, is highly conductive, suggestive of the presence of a small amount of partial melt, despite the fact that there is no surface expression of volcanism in the region. Although the data support the presence of thicker cratonic lithosphere to the southeast of the basin, the lithospheric thickness is not well resolved and models show variations ranging from ~80 to 150 km in this region. Similarly variable is the conductivity of the mantle beneath the basin and immediately beneath the cratonic lithosphere to the southeast, although the conductivity is required to be elevated compared to normal lithospheric mantle. In a general sense, two classes of model are compatible with the magnetotelluric data: one with a moderately conductive mantle and one with more elevated conductivities. This latter class would be consistent with the impingement of a stringer of plume-fed melt beneath the cratonic lithosphere, with the melt migrating upslope to thermally erode lithosphere beneath the orogenic belt that is overlain by the Barotse Basin. Such processes are potentially important for intraplate volcanism and also for development or propagation of rifting as lithosphere is thinned and weakened by melt. Both models show clear evidence for thinning of the lithosphere beneath the orogenic belt, consistent with elevated heat flow data in the region.
DS201903-0507
2019
Evans, R.L., Elsenbeck, J., Zhu, J., Abelsalam, M.G., Sarafian, E., Mutamina, D., Chilongola, F., Atekwan, E., Jones, A.G.Structure of the lithosphere beneath the Barotse Basin, western Zambia from magnetotelluric data.Tectonics, in press available Africa, Zambiamelting

Abstract: A magnetotelluric survey in the Barotse Basin of western Zambia shows clear evidence for thinned lithosphere beneath an orogenic belt. The uppermost asthenosphere, at a depth of 60-70 km, is highly conductive, suggestive of the presence of a small amount of partial melt, despite the fact that there is no surface expression of volcanism in the region. Although the data support the presence of thicker cratonic lithosphere to the southeast of the basin, the lithospheric thickness is not well resolved and models show variations ranging from ~80 to 150 km in this region. Similarly variable is the conductivity of the mantle beneath the basin and immediately beneath the cratonic lithosphere to the southeast, although the conductivity is required to be elevated compared to normal lithospheric mantle. In a general sense, two classes of model are compatible with the magnetotelluric data: one with a moderately conductive mantle and one with more elevated conductivities. This latter class would be consistent with the impingement of a stringer of plume-fed melt beneath the cratonic lithosphere, with the melt migrating upslope to thermally erode lithosphere beneath the orogenic belt that is overlain by the Barotse Basin. Such processes are potentially important for intraplate volcanism and also for development or propagation of rifting as lithosphere is thinned and weakened by melt. Both models show clear evidence for thinning of the lithosphere beneath the orogenic belt, consistent with elevated heat flow data in the region.
DS201907-1543
2019
Even-Zohar, C., Narvekar, P.The 2018 diamond pipeline: faking the diamond dream. Thediamondloupe, May 7p. Pdf availableGlobaldiamond pipeline

Abstract: Last year the diamond pipeline pretty well succeeded in Faking the Diamond Dream. Some of the largest companies discovered that defaulting on debts of hundreds of millions of dollars had become the new source of value. Lenders tried to recover lost value by suing clients - some of whom responded in kind. Court appointed forensic investigators revealed the myriad of fake corporate conduits established to facilitate carefully premeditated roundtripping, money laundering, banking and trading frauds, and schemes to syphon (other people's) money out of the diamond pipeline. Banks en masse were recusing themselves from future participation in the diamond pipeline. Selling undisclosed synthetic diamonds, especially in smaller goods, continues to remain the new source of value for some. This was the year in which De Beers betrayed its own slogans and revealed its ambitions to become a huge lab-grown gem diamond supplier, undercutting competitor pricing well before it sold its very first Lightbox stone. For the squeezed mid-stream of the diamond pipeline to succeed, it needed to fake the diamond dream. Or else. Or else - what? Some exasperated players came to believe that if you are a decent, honest, hardworking player, fully respecting all the treasured ethical, moral and legal norms, when you take pride in honoring commitments to fellow players, clients, suppliers, banks, etc. - then you most likely did not make money and were eroding your equity. Planning one's exit out of the business or "compromise" (and criminalize yourself) by joining the Diamond Dream Fakers too often seem the more viable option.
DS201907-1544
2019
Extance, A.Perovskites on trial. The reality behind solar power's next star material. Companies say they are close to commercializing cheap perovskite films that could diisrupt solar power - but are they too optimistic?Nature, Vol. 570, June 27, pp. 429-432.Globalperovskites
DS201904-0734
2019
Faccenda, M., Ferreira, A.M.G., Tisato, N., Lithgow-Bertelloni, C., Stixrude, L., Pennacchioni, G.Extrinsic elastic anisotropy in a compositionally heterogeneous Earth's mantle.Journal of Geophysical Research: Solid Earth, https://doi,org/ 10.1029/2018JB016482Mantleanistropy

Abstract: Several theoretical studies indicate that a substantial fraction of the measured seismic anisotropy could be interpreted as extrinsic anisotropy associated with compositional layering in rocks, reducing the significance of strain-induced intrinsic anisotropy. Here we quantify the potential contribution of grain-scale and rock-scale compositional anisotropy to the observations by (i) combining effective medium theories with realistic estimates of mineral isotropic elastic properties and (ii) measuring velocities of synthetic seismic waves propagating through modeled strain-induced microstructures. It is shown that for typical mantle and oceanic crust subsolidus compositions, rock-scale compositional layering does not generate any substantial extrinsic anisotropy (<1%) because of the limited contrast in isotropic elastic moduli among different rocks. Quasi-laminated structures observed in subducting slabs using P and S wave scattering are often invoked as a source of extrinsic anisotropy, but our calculations show that they only generate minor seismic anisotropy (<0.1-0.2% of Vp and Vs radial anisotropy). More generally, rock-scale compositional layering, when present, cannot be detected with seismic anisotropy studies but mainly with wave scattering. In contrast, when grain-scale layering is present, significant extrinsic anisotropy could exist in vertically limited levels of the mantle such as in a mid-ocean ridge basalt-rich lower transition zone or in the uppermost lower mantle where foliated basalts and pyrolites display up to 2-3% Vp and 3-6% Vs radial anisotropy. Thus, seismic anisotropy observed around the 660-km discontinuity could be possibly related to grain-scale shape-preferred orientation. Extrinsic anisotropy can form also in a compositionally homogeneous mantle, where velocity variations associated with major phase transitions can generate up to 1% of positive radial anisotropy.
DS201912-2778
2019
Falck, H., Elliott, B., Cairns, S., Powell, L.NWT mineral exploration and mining overview 2019.Yellowknife Forum NWTgeoscience.ca, abstract volume p. 27.Canada, Northwest Territorieseconomics

Abstract: In spite of a poor year for sales of rough diamonds globally, diamond mining continues to provide a foundation for the NWT economy. Gahcho Kué mine, which has been operating slightly ahead of plan, announced the discovery of the diamondiferous Wilson kimberlite within the current mine plan area. Consistently high forecasts for zinc demand have encouraged both the rejuvenation of Pine Point by Osisko Metals Inc. and NorZinc Ltd.’s ongoing efforts to bring Prairie Creek into production. Gold prices have been buoyed by safe-haven sentiment after concerns over economic growth, tariffs and trade wars with China. Advanced projects have benefited with an improving investment climate encouraging on-going exploration by Nighthawk Gold Corp. and TerraX Minerals Inc. However, many smaller projects were suspended as the companies were not able to raise sufficient funds on in the investment market. This was particularly true for the commodities targeting green energy and battery technologies. Most of the projects focusing on lithium, cobalt and vanadium started the year strongly but were dormant by the summer. A notable exception was the reactivation of Avalon’s Nechalacho project with an infusion of resources from Cheetah Resources of Australia. One of the indicators of exploration activity – claims staked vs. lapsed – continued an upward trend that began in 2017. In 2018, a total of 268 claims covering 184,985 hectares were added and 70 claims covering 58, 876 hectares were released. In the first three quarters of 2019, 120 claims covering 45,000 Ha were added but a nearly equivalent area 55,000 Ha in 85 claims and leases were cancelled. There are also 37 active Prospecting Permits this year. New staking included large areas in the Mackenzie Mountains, the additional ground at Pine Point, re-staking of claims in the Lac de Gras region and expansion of claims in the Yellowknife area. In 2019-2020, the Government of Northwest Territories invested nearly $1 million in grassroots mineral exploration through the Mining Incentive Program. This funding was dispersed to 19 exploration projects comprising twelve prospectors and seven companies. The Mineral Resources Act has passed the legislature marking the NWT’s first-ever stand-alone Act governing mining in the territory.
DS201905-1028
2018
Farahbakhsh, E., Chandra, R., Olierook, H.K.H., Scalzo, R., Clark, C., Reddy, S.M., Muller, R.D.Computer vision based framework for extracting geological lineaments from optical remote sensing data.arXiv.1810,02320vl, researchgate 17p.Australialineaments
DS201902-0270
2018
Farre-de-Pablo, J., Proenza, J.A., Gonzales-Jimenez, J.M., Garcia-Casco, A., Colas, V., Roque-Rossell, J., Camprubi, A., Sanchez-Navas, A.A shallow origin for diamonds in ophiolitic chromitites.Geology, Vol. 46, pp. 75-78.Mexico, Pueblaophiolite

Abstract: Recent findings of diamonds in ophiolitic peridotites and chromitites challenge our traditional notion of Earth mantle dynamics. Models attempting to explain these findings involve incorporation of diamonds into chromite near the mantle transition zone. However, the occurrence of metastable diamonds in this context has not been considered. Here, we report for the first time in situ microdiamonds in chromite from ophiolitic chromitite pods hosted in the Tehuitzingo serpentinite (southern Mexico). Here, diamonds occur as fracture-filling inclusions along with quartz, clinochlore, serpentine, and amorphous carbon, thus indicating a secondary origin during the shallow hydration of chromitite. Chromite chemical variations across the diamond-bearing healed fractures indicate formation during the retrograde evolution of chromitite at temperatures between 670 °C and 515 °C. During this stage, diamond precipitated metastably at low pressure from reduced C-O-H fluids that infiltrated from the host peridotite at the onset of serpentinization processes. Diamond was preserved as a result of fracture healing at the same temperature interval in which the chromite alteration began. These mechanisms of diamond formation challenge the idea that the occurrence of diamond in ophiolitic rocks constitutes an unequivocal indicator of ultrahigh-pressure conditions.
DS201909-2038
2019
Farre-de-Pblo, J., Proenza, J.A., Gonzalez-Jiminez, J.M., Garcia-Casco, A., Colas, V., Roque-Rosell, J., Camprubi, A., Sanchez-Navas, A.A shallow origin for diamonds in ophiolitic chromitites. Geology, Vol. 47, pp. e477-478.North America, Mexicomicrodiamonds

Abstract: Recent findings of diamonds in ophiolitic peridotites and chromitites challenge our traditional notion of Earth mantle dynamics. Models attempting to explain these findings involve incorporation of diamonds into chromite near the mantle transition zone. However, the occurrence of metastable diamonds in this context has not been considered. Here, we report for the first time in situ microdiamonds in chromite from ophiolitic chromitite pods hosted in the Tehuitzingo serpentinite (southern Mexico). Here, diamonds occur as fracture-filling inclusions along with quartz, clinochlore, serpentine, and amorphous carbon, thus indicating a secondary origin during the shallow hydration of chromitite. Chromite chemical variations across the diamond-bearing healed fractures indicate formation during the retrograde evolution of chromitite at temperatures between 670 °C and 515 °C. During this stage, diamond precipitated metastably at low pressure from reduced C-O-H fluids that infiltrated from the host peridotite at the onset of serpentinization processes. Diamond was preserved as a result of fracture healing at the same temperature interval in which the chromite alteration began. These mechanisms of diamond formation challenge the idea that the occurrence of diamond in ophiolitic rocks constitutes an unequivocal indicator of ultrahigh-pressure conditions.
DS201903-0508
2019
Fedortchouk, Y.A new approach to understanding diamond surface features based on a review of experimental and natural diamond studies.Earth-Science Reviews, 10.1016/j.earscirev .2019.02.013 56p.Canada, Northwest Territories, Africa, Botswanadiamond morphology

Abstract: Diamonds originate deep in the Earth's mantle since billions of years ago. Through their long history diamonds accumulate information about the Earth's evolution, and preserve it owing to their extreme chemical and mechanical stability. The surface of natural diamonds shows a variety of growth and dissolution features, which reflect the diversity of conditions in the mantle and in kimberlite magma, providing an important clue for understanding the deep regions of subcratonic mantle. However, such studies are hampered by an absence of a systematic approach for studying diamond surface features and morphology. This review integrates studies of natural diamonds with the results of diamond dissolution experiments to explore the origin of the most typical resorption features of diamonds and the information they provide. It uses detailed studies of over ~ 3500 diamonds from eight kimberlite bodies in the Northwest Territories in Canada and Orapa kimberlite cluster in Botswana, and the data from diamond dissolution experiments covering a pressure range of between 0.1?MPa - 7.5?GPa, temperature range of between 900?°C - 1750?°C, and over 12 log units of oxygen fugacity values. Examining the effects of these parameters on diamond resorption morphology shows that the shape and size of the etch pits depends on the temperature and H2O:CO2 ratio in the fluid, whereas pressure affects the efficiency of diamond crystal shape transformation from octahedral into rounded resorbed forms. The effect of pressure on the physical properties of the reacting fluid / melt controls the character of diamond etching. A comparison between the experimentally-induced and naturally occurring diamond resorption demonstrates a clear difference between the features developed in kimberlite magma and features inherited from the mantle source. Kimberlite-induced resorption on diamonds shows a strong correlation with the geology and emplacement mode of the hosting kimberlite unit. Low-relief surfaces develop on diamonds from pyroclastic kimberlites in all kimberlite classes, whereas surface features on diamonds from coherent kimberlites differ between kimberlite localities and often show corrosive character. Diamond resorption morphology can offer a robust method to better understand emplacement processes in different kimberlite localities, which are a matter of significant debate. The proposed here classification scheme for diamond resorption features is based on the features observable under a stereomicroscope. It helps differentiating resorption produced in the mantle source from that in the kimberlite magma and assigning diamond resorption to a particular mode of kimberlite emplacement, or a mantle metasomatic event.
DS201901-0032
2018
Fedortchouk, Y., Liebske, C., McCammon, C.Diamond destruction and growth during mantle metasomatism: an experimental study of diamond resorption features.Earth and Planetary Science Letters, Vol. 506, pp. 493-506.Mantlemetasomatism

Abstract: Most diamonds found in kimberlites show complex patterns of growth and dissolution (resorption) surface features. Populations of diamonds from within single kimberlite bodies commonly contain a large diversity of diamond surface forms, some of which are a result of dissolution in kimberlite magma and others are inherited from the mantle. Morphological studies of natural diamonds differentiated features produced during dissolution in kimberlite magma and during mantle metasomatism. The former features were experimentally reproduced at 1 3 GPa and used to infer the presence and composition of magmatic fluid in different kimberlites. However, the mantle-derived resorption features have not been reproduced experimentally and the composition and origins of their formative solvents are unknown. Here we report the results of diamond dissolution experiments conducted in a multi-anvil apparatus at 6 GPa and 1200 to 1500 °C in synthetic CaO MgO SiO2 CO2 H2O system. The experiments produced very different diamond resorption morphologies in COH fluid, in silicate-saturated fluid, and in silicate and carbonate melts. Dissolution in SiO2-free COH fluid developed rounded crystal forms with shallow negative trigons, striations and hillocks, which are commonly observed on natural diamonds and are similar in 6 GPa and in 1 3 GPa experiments. However, silicate-saturated fluid produced very different resorption features that are rarely observed on natural diamonds. This result confirms that natural, SiO2-poor fluid-induced resorption develops under the comparatively low-pressures of kimberlite ascent, because at mantle pressures the high content of SiO2 in fluids would produce features like those from the silicate-saturated experiments. Comparison of the experimental products from this study to natural diamond resorption features from the literature suggests that natural diamonds show no record of dissolution by fluids during mantle metasomatism. Diamond resorption morphologies developed in experiments with silicate carbonate melts closely resemble many of the mantle-derived resorption features of natural diamonds, whose diversity can result from variable SiO2 concentration in carbonatitic melts and temperature variation. The experimental results imply that metasomatism by fluids does not dissolve diamond, whereas metasomatism by melts is diamond-destructive. The repetitive growth-dissolution patterns of natural diamonds could be due to diamond growth from fluids in harzburgitic lithologies followed by its dissolution in partial melts.
DS201904-0735
2019
Ferreira, A.M.G., Faccenda, M., Sturgeon, W., Chang, S-J., Schardong, L.Ubiquitous lower mantle anisotropy beneath subduction zones.Nature Geoscience, Vol. 32, pp. 301-306.Mantlesubduction

Abstract: Seismic anisotropy provides key information to map the trajectories of mantle flow and understand the evolution of our planet. While the presence of anisotropy in the uppermost mantle is well established, the existence and nature of anisotropy in the transition zone and uppermost lower mantle are still debated. Here we use three-dimensional global seismic tomography images based on a large dataset that is sensitive to this region to show the ubiquitous presence of anisotropy in the lower mantle beneath subduction zones. Whereas above the 660?km seismic discontinuity slabs are associated with fast SV anomalies up to about 3%, in the lower mantle fast SH anomalies of about 2% persist near slabs down to about 1,000-1,200?km. These observations are consistent with 3D numerical models of deformation from subducting slabs and the associated lattice-preferred orientation of bridgmanite produced in the dislocation creep regime in areas subjected to high stresses. This study provides evidence that dislocation creep may be active in the Earth’s lower mantle, providing new constraints on the debated nature of deformation in this key, but inaccessible, component of the deep Earth.
DS201901-0033
2018
Fisher, D.Addressing the challenges of detecting synthetic diamonds.Gems & Gemology, Sixth International Gemological Symposium Vol. 54, 3, Fall 1p. Abstract p. 263-4Globalsynthetics

Abstract: The dream of growing synthetic diamonds existed for many centuries before it was achieved in the 1950s. The development of techniques to identify synthetic diamonds and enable their reliable separation from natural diamonds has not had the luxury of centuries to work with. Since the early reports on the characteristics of laboratory-grown stones, scientists have been working steadily to establish and improve the means of detection. For many years the De Beers Group has been developing equipment for rapidly screening and testing for potential synthetic and treated diamonds as part of a strategy aimed at maintaining consumer confidence in natural untreated diamonds. This work has been underpinned by extensive research into defects in natural and synthetic diamond, either conducted within De Beers’ own facilities or through financial and practical support of research in external institutions. Key to any detection technique for synthetic diamonds is a fundamental understanding of the differences between them and natural diamonds. This could take the form of differences in the atomic impurity centers or differences in the spatial distributions of these centers brought about by very significant distinctions in the growth environments. The former was used in the development of the Dia - mondSure instrument that, among other things, detects variance differences in the absorption spectra due to the presence or absence of the N3 feature. This absorption is from a nitrogen-related defect that is usually only produced in nitrogen-containing diamonds by extended periods at relatively high temperatures—that is, conditions generally experienced by natural diamonds. Growth-related differences in impurity distributions can be very accurately imaged using the DiamondView instrument. Short-wave ultraviolet (UV) light is used to excite luminescence from a very thin layer of diamond near the surface to give images free from the blurring encountered with more common longer-wavelength excitation sources. DiamondView has, since its launch, provided the benchmark for the detection of synthetic diamonds. A number of approaches involving absorption features have been developed, including the use of almost complete absorption in the ultraviolet region of the spectrum to indicate that a diamond is not synthetic. The UV absorption is produced by the A center (two adjacent nitrogen atoms) and is rarely encountered in as- grown synthetic diamonds. The main form of nitrogen in synthetic diamonds is a single substitutional nitrogen atom that absorbs in both the ultraviolet and visible regions to produce yellow color. The combination of UV absorption and no strong yellow color is therefore restricted to natural diamond. However, treatment of nitrogen-containing synthetic diamonds is capable of generating A centers, but generally does not produce a colorless stone. This effect accounts for the careful color ranges often applied to instruments relying on UV absorption for screening. This also highlights one of the limitations of absorption spectroscopy: When smaller stones are tested, the amount of absorption decreases and the technique becomes less reliable. In recent years we have seen a shift to smaller sizes (below 0.01 ct) in the synthetic diamonds being offered for sale to the jewelry market, and screening techniques have had to evolve to address this situation and the limitations of absorption-based approaches. Testing melee-sized diamonds, as well as introducing technical challenges around the measurement technique, has also led to the introduction of greater automation. In 2014 the De Beers Group introduced the first automated melee screening instrument (AMS1), which combined the measurement technique from Dia - mondSure with automated feeding and dispensing of stones in the range of 0.20 to 0.01 ct. While this instrument was well received and effectively addressed concerns around synthetic melee-sized stones in the trade at the time, there soon came calls for improvements— a faster instrument capable of measuring smaller stones, no restrictions on cut, and a lower referral rate for natural diamonds. These requirements proved impossible to meet with the limitations imposed by absorption measurements, and a new technique based on time-resolved spectroscopy was developed. This resulted in the AMS2 instrument, launched in March 2017. The AMS2 processes stones at a speed of one stone per second, 10 times faster than the AMS1. It measures round brilliants down to 0.003 ct (0.9 mm dia - meter) and can be used on other cuts for stones of 0.01 ct and above. The measurement technique itself has been incorporated into the SYNTHdetect (figure 1, left), an instrument launched in September 2017 that allows manual observation of the time-resolved emission. Besides providing the same testing capability as AMS2 (figure 1, right) for loose stones, various holders allow testing of mounted stones in a wide range of configurations. The benefit of this approach is that stones tested loose using AMS2 will generate a broadly consistent result when mounted on SYNTHdetect. Changes in growth processes for synthetic diamonds have also led to the gradual introduction of new characteristics. High - pressure, high-temperature (HPHT) synthetics have tended to be fairly consistent in their growth-related luminescence patterns, while significant variations in the features associated with chemical vapor deposition (CVD) synthetics have been observed. These continue to be well documented and have led to the gradual evolution of the DiamondView instrument and the way in which it is used. Post-growth treatment of synthetic diamonds can be applied for a number of reasons: improvement in the color, modification of the atomic defects to make the stones look more like a natural diamond, and removal of a characteristic that could be used to identify a synthetic diamond. The motivation for the latter two treatments can only be described as fraudulent. The challenge in developing detection instruments and techniques is to ensure that they are as robust as possible in the face of such challenges. Treatment techniques will rarely have any effect on the growth patterns associated with synthetic diamonds, and it is therefore very difficult to treat synthetics in a way that would make them undetectable using the DiamondView. Screening instruments tend to be based on a single technique, and it is important that the approach adopted not be vulnerable to simpler forms of treatment. This has been of primary concern to the De Beers Group in the development of our own screening instruments. It has also been necessary in certain cases to withhold detailed information about detection techniques where disclosure of this would lead to undermining of the detection technique itself. The De Beers Group continues to invest heavily in growth and treatment research in order to develop the next generation of instruments and techniques that will assist the trade in maintaining detection capability to support consumer confidence. The Group is uniquely placed in the industry to address these challenges due to its collaboration with Element Six (world leaders in synthesis of diamond for industrial and technical applications) and its indepth knowledge of the properties of natural diamonds with known provenance from its own mines.
DS201904-0736
2019
Fitzpayne, A., Giuliani, A., Harris, C., Thomassot, E., Cheng, C., Hergt, J.Evidence for subduction related signatures in the southern African lithosphere from the N-O isotopic composition of metasomatic mantle minerals.Geochimica et Cosmochimica Acta, in press available 21p.Africa, South Africadeposit - Bultfontein

Abstract: Current understanding of the fate of subducted material (and related fluids) in the deep Earth can be improved by combining major and trace element geochemistry with stable isotopic compositions of mantle rocks or minerals. Limited isotopic fractionation during high temperature processes means that significant deviations from mantle-like isotope ratios in mantle rocks probably result from recycling of surficial material. To determine the effects and origins of mantle metasomatic fluids/melts, new d15N and d18O data have been collected for thirteen mantle xenoliths - harzburgites, wehrlites, lherzolites, and MARID (Mica-Amphibole-Rutile-Ilmenite-Diopside) rocks - from the Bultfontein kimberlite (Kimberley, South Africa), which show varying degrees of metasomatism. The d18O values of olivine and orthopyroxene in phlogopite-free harzburgites match the mantle composition (d18Oolivine?=?+5.2?±?0.3‰; d18Oorthopyroxene?=?+5.7?±?0.3‰; 2?s.d.), consistent with previous inferences that harzburgites were formed by interaction with ancient silica-rich melts unrelated to subduction processes. Wehrlite samples display mineral compositional characteristics (e.g., low La/Zr in clinopyroxene) resembling those of other products of kimberlite melt metasomatism, such as PIC (Phlogopite-Ilmenite-Clinopyroxene) rocks. The inferred interaction with kimberlite melts may be responsible for O isotopic disequilibrium between clinopyroxene and olivine (?18O?=?+0.2‰) in the wehrlites of this study. In contrast with broadly mantle-like d18O values, the d15N value of phlogopite in a wehrlite sample (+5.9‰) differs from the mantle composition (d15N?=?-5?±?2‰). This unusual N isotopic composition in kimberlite-related mantle products might indicate that a recycled crustal component occurred in the source of the Kimberley kimberlites, or was assimilated during interaction with the lithospheric mantle. Similar major and trace element characteristics in clinopyroxene from phlogopite-lherzolite and MARID samples suggest metasomatism by fluids of similar composition. Lherzolite and MARID clinopyroxene d18O values (as low as +4.4‰) extend below those reported in mantle peridotites (i.e. d18Oclinopyroxene?=?+5.6?±?0.3‰; 2?s.d.), and strong negative correlations are found between mineral d18O values and major element compositions (e.g., Na2O contents in clinopyroxene). Furthermore, phlogopite d15N values (+4 to +7‰) in the studied lherzolite and MARID samples are higher than mantle values. Combined, the low d18O-high d15N isotopic signatures of MARID and lherzolite samples suggest progressive mantle metasomatism by a melt containing a recycled oceanic crust (eclogitic) component. This study demonstrates that progressive enrichment of the subcontinental lithospheric mantle may be inextricably linked to plate tectonics via recycling of subducted crustal material into the deep mantle.
DS201902-0271
2019
Fitzpayne, A., Giuliani, A., Maas, R., Hergt, J., Janney, P., Phillips, D.Progressive metasomatism of the mantle by kimberlite melts: Sr-Nd-Hf-Pb isotope compositions of MARID and PIC minerals.Earth and Planetary Science Letters, Vol. 506, pp. 15-26.Africa, South Africadeposit - Newlands, Kimberley, Bultfontein

Abstract: MARID (Mica-Amphibole-Rutile-Ilmenite-Diopside) and PIC (Phlogopite-Ilmenite-Clinopyroxene) rocks occur as mantle-derived xenoliths in kimberlites and other alkaline volcanic rocks. Both rock types are alkaline and ultramafic in composition. The H2O and alkali metal enrichments in MARID and PIC rocks, reflected in abundant phlogopite, have been suggested to be caused by extreme mantle metasomatism. Radiogenic (Sr-Nd-Hf-Pb) isotope and trace element compositions for mineral separates from MARID (clinopyroxene and amphibole) and PIC (clinopyroxene only) samples derived from Cretaceous kimberlites (Kimberley) and orangeites (Newlands) from South Africa are used here to examine the source(s) of mantle metasomatism. PIC clinopyroxene is relatively homogeneous, with narrow ranges in initial isotopic composition (calculated to the emplacement age of the host Bultfontein kimberlite; 87Sr/86Sri: 0.7037-0.7041; eNdi: +3.0 to +3.6; eHfi: +2.2 to +2.5; 206Pb/204Pbi: 19.72-19.94) similar to kimberlite values. This is consistent with PIC rocks representing peridotites modified by intense metasomatic interaction with kimberlite melts. The MARID clinopyroxene and amphibole separates () studied here display broader ranges in isotope composition (e.g., 87Sr/86Sri: 0.705-0.711; eNdi: -11.0 to -1.0; eHfi: -17.9 to -8.5; 206Pb/204Pbi: 17.33-18.72) than observed in previous studies of MARID rocks. The Nd-Hf isotope compositions of kimberlite-derived MARID samples fall below the mantle array (?eHfi between -13.0 and -2.4), a feature reported widely for kimberlites and other alkaline magmas. We propose that such displacements in MARID minerals result from metasomatic alteration of an initial “enriched mantle” MARID composition (i.e., 87Sr/86Sri = 0.711; eNdi = -11.0; eHfi = -17.9; and 206Pb/204Pbi = 17.3) by the entraining kimberlite magma (87Sr/86Sr; eNd; eHf; 206Pb/204Pb). A model simulating the flow of kimberlite magma through a mantle column, thereby gradually equilibrating the isotopic and chemical compositions of the MARID wall-rock with those of the kimberlite magma, broadly reproduces the Sr-Nd-Hf-Pb isotope compositions of the MARID minerals analysed here. This model also suggests that assimilation of MARID components could be responsible for negative ?eHfi values in kimberlites. The isotopic composition of the inferred initial MARID end-member, with high 87Sr/86Sr and low eNd, eHf, and 206Pb/204Pb, resembles those found in orangeites, supporting previous inferences of a genetic link between MARID-veined mantle and orangeites. The metasomatic agent that produced such compositions in MARID rocks must be more extreme than the EM-II mantle component and may relate to recycled material that experienced long-term storage in the lithospheric mantle.
DS201910-2257
2019
Fitzpayne, A., Giuliani, A., Maas, R., Hergt, J., Janney, P., Phillips, D.Progressive metasomatism of the mantle by kimberliitic melts: Sr-Nd-Hf-Pb isotopic composition of MARID and PIC minerals.Goldschmidt2019, 1p. AbstractMantlemetasomatism

Abstract: MARID (Mica-Amphibole-Rutile-Ilmenite-Diopside) and PIC (Phlogopite-Ilmenite-Clinopyroxene) rocks occur as mantle-derived xenoliths in kimberlites and other alkaline volcanic rocks. Both rock types are alkaline and ultramafic in composition. The H2O and alkali metal enrichments in MARID and PIC rocks, reflected in abundant phlogopite, have been suggested to be caused by extreme mantle metasomatism. Radiogenic (Sr-Nd-Hf-Pb) isotope and trace element compositions for mineral separates from MARID (clinopyroxene and amphibole) and PIC (clinopyroxene only) samples derived from Cretaceous kimberlites (Kimberley) and orangeites (Newlands) from South Africa are used here to examine the source(s) of mantle metasomatism. PIC clinopyroxene ( n = 4 ) is relatively homogeneous, with narrow ranges in initial isotopic composition (calculated to the emplacement age of the host Bultfontein kimberlite; 87Sr/86Sri: 0.7037-0.7041; eNdi: +3.0 to +3.6; eHfi: +2.2 to +2.5; 206Pb/204Pbi: 19.72-19.94) similar to kimberlite values. This is consistent with PIC rocks representing peridotites modified by intense metasomatic interaction with kimberlite melts. The MARID clinopyroxene ( n = 9 ) and amphibole separates ( n = 11 ) studied here display broader ranges in isotope composition (e.g., 87Sr/86Sri: 0.705-0.711; eNdi: -11.0 to -1.0; eHfi: -17.9 to -8.5; 206Pb/204Pbi: 17.33-18.72) than observed in previous studies of MARID rocks. The Nd-Hf isotope compositions of kimberlite-derived MARID samples fall below the mantle array (?eHfi between -13.0 and -2.4), a feature reported widely for kimberlites and other alkaline magmas. We propose that such displacements in MARID minerals result from metasomatic alteration of an initial “enriched mantle” MARID composition (i.e., 87Sr/86Sri = 0.711; eNdi = -11.0; eHfi = -17.9; and 206Pb/204Pbi = 17.3) by the entraining kimberlite magma (87Sr/86Sr ~ i 0.704 ; eNd ~ i + 3.3 ; eHf ~ i + 2.3 ; 206Pb/204Pb ~ i 19.7 ). A model simulating the flow of kimberlite magma through a mantle column, thereby gradually equilibrating the isotopic and chemical compositions of the MARID wall-rock with those of the kimberlite magma, broadly reproduces the Sr-Nd-Hf-Pb isotope compositions of the MARID minerals analysed here. This model also suggests that assimilation of MARID components could be responsible for negative ?eHfi values in kimberlites. The isotopic composition of the inferred initial MARID end-member, with high 87Sr/86Sr and low eNd, eHf, and 206Pb/204Pb, resembles those found in orangeites, supporting previous inferences of a genetic link between MARID-veined mantle and orangeites. The metasomatic agent that produced such compositions in MARID rocks must be more extreme than the EM-II mantle component and may relate to recycled material that experienced long-term storage in the lithospheric mantle.
DS201912-2779
2020
Fitzpayne, A., Prytulak, J., Giuliani, A., Hergt, J.Thallium isotope composition of phlogopite in kimberlite hosted MARID and PIC mantle xenoliths.Chemical Geology, Vol. 531, 14p. PdfMantlemetasomatism

Abstract: MARID (Mica-Amphibole-Rutile-Ilmenite-Diopside) and PIC (Phlogopite-Ilmenite-Clinopyroxene) rocks are rare mantle xenoliths entrained by kimberlites. Their high phlogopite modes (15 to ~100 vol.%) and consequent enrichments in alkali metals and H2O suggest a metasomatic origin. Phlogopite also has high concentrations (>0.2 µg/g) of thallium (Tl) relative to mantle abundances (<3 ng/g). Thallium isotope ratios have proven useful in tracing the input of Tl-rich materials, such as pelagic sediments and altered oceanic crust, to mantle sources because of their distinct isotopic compositions compared to the peridotitic mantle. This study presents the first Tl isotopic compositions of well-characterised phlogopite separates from MARID and PIC samples to further our understanding of their genesis. The PIC rocks in this study were previously interpreted as the products of kimberlite melt metasomatism, whereas the radiogenic and stable N-O isotope systematics of MARID rocks suggest a parental metasomatic agent containing a recycled component. The e205Tl values of phlogopite in both PIC (-2.7 ± 0.8; 2 s.d., n = 4) and MARID samples (-2.5 ± 1.3; 2 s.d., n = 21) overlap with the estimated mantle composition (-2.0 ± 1.0). PIC phlogopite Tl contents (~0.4 µg/g) are suggestive of equilibrium with kimberlite melts (0.1-0.6 µg/g Tl), based on partitioning experiments in other silica-undersaturated melts. Kimberlite Tl-e205Tl systematics suggest their genesis does not require a recycled contribution: however, high temperature-altered oceanic crust cannot be ruled out as a component of the Kimberley kimberlites’ source. Mantle-like e205Tl values in MARID samples also seem to contradict previous suggestions of a recycled contribution towards their genesis. Recycled components with isotopic compositions close to mantle values (e.g., high temperature-altered oceanic crust) are still permitted. Moreover, mass balance mixing models indicate that incorporation into the primitive mantle of 1-30% of a low temperature-altered oceanic crust + continental crust recycled component or 1-50% of continental crust alone could be accommodated by the Tl-e205Tl systematics of the MARID parental melt. This scenario is consistent with experimental evidence and existing isotopic data. One PIC phlogopite separate has an extremely light Tl isotopic composition of -9.9, interpreted to result from kinetic isotopic fractionation. Overall, phlogopite is the main host mineral for Tl in metasomatised mantle and shows a very restricted range in Tl isotopic composition, which overlaps with estimates of the mantle composition. These results strongly suggest that negligible high temperature equilibrium Tl isotopic fractionation occurs during metasomatism and reinforces previous estimates of the mantle’s Tl isotopic composition.
DS201911-2521
2019
Flament, N.The deep roots of Earth's surface.Nature Geosciences, Vol. 12, pp. 787-788.Mantleconvection

Abstract: The structure of the lithosphere is key to reconciling the dynamic topography predicted by mantle convection models with residual topography derived from observations, suggest analyses of both models and data.
DS201912-2780
2019
Foley, S.F., Yaxley, G.M., Kjarsgaard, B.A.Kimberlites: from source to surface, insights from experiments.Elements, Vol. 15, 6, pp.Mantlepetrology
DS201905-1029
2019
Forster, M.W.Subduction zone metasomatism and its consequences for potassium rich magmatism and deep nitrogen cycling. ( mentions salty kimberlites Udachnaya)Ph.d Thesis Macquarie University, researchgate.com 250p. Pdf availableMantlelamproites

Abstract: In total, subduction zones span 40,000 km across Earth’s surface and recycle an average thickness of 500 m of sediment. During burial and heating these sediments eventually start melting at T >675 °C, following which Si-rich hydrous melts infiltrate the peridotites of the mantle wedge above the subducting slab. In this thesis, a high-pressure experimental approach is used to examine the reaction of sediments and peridotites at 2-6 GPa in subduction zones and its consequences on the generation of K-rich magmatism and on deep nitrogen cycling. All experiments are conducted in a layered arrangement, where the depleted peridotite is placed above the sediments in a 1:1 ratio. At 2-3 GPa, the reaction of melts of sediment with depleted peridotite, simulating the fore-arc of a subduction zone, leads to the formation of layered phlogopite pyroxenites and selective incorporation of major and trace elements in these metasomatic layers. Partial melting of these phlogopite pyroxenites produces melts rich in K2O (>9 wt%) with K/Na >>2 and a trace element pattern comparable to “orogenic lamproites”. At similar pressures, the reaction of hydrous mantle melts with depleted peridotites produces metasomatic layers that show K/Na ~1 and a trace element pattern that closely resembles “anorogenic lamproites”. In both cases, K-enrichment is facilitated by the crystallization of an eclogitic residue rich in Na, poor in K, and consequently with low K/Na. At 4-6 GPa, the reaction of melts of sediment with depleted peridotite is does not produce mica, instead resulting in alkali chlorides with K/Na ratios similar to saline fluid inclusions in diamonds. Besides the chlorides, magnesite also crystallises in the peridotite. Both phases are important ingredients for the generation of salty kimberlites such as Udachnaya East. The change in metasomatic style from mica- to chloride formation between 3 to 4 GPa corresponds to the depth of the mid-lithospheric discontinuity, a zone of low seismic velocities that is found intermittently beneath all continents at a depth of 80-100 km. The subduction of sediment is the main mechanism that recycles nitrogen back to Earth’s mantle. The partitioning of nitrogen between fluid and melt (DN(Fluid/Melt)) and fluid and bulk residue (melt+mica) (DN(Fluid/Bulk)) was found to increase linearly with temperature normalized to pressure. Using the new partition coefficients, the amount of N recycled to Earth’s mantle since the onset of subduction is calculated as 50 ±6 %.
DS201909-2039
2019
Forster, M.W., Foley, S.F., Alard, O., Buhre, S.Partitioning of nitrogen during melting and recycling in subduction zones and the evolution of atmospheric nitrogen.Chemical Geology, in press available 31p. PdfMantlesubduction, metasomatism

Abstract: The subduction of sediment connects the surface nitrogen cycle to that of the deep Earth. To understand the evolution of nitrogen in the atmosphere, the behavior of nitrogen during the subduction and melting of subducted sediments has to be estimated. This study presents high-pressure experimental measurements of the partitioning of nitrogen during the melting of sediments at sub-arc depths. For quantitative analysis of nitrogen in minerals and glasses, we calibrated the electron probe micro-analyzer on synthetic ammonium feldspar to measure nitrogen concentrations as low as 500?µg?g-1. Nitrogen abundances in melt and mica are used together with mass balance calculations to determine DN(Mica/Melt), DN(Fluid/Mica), and DN(Fluid/Melt). Calculated partition coefficients correspond to expected values for NH4+, which behaves similarly to Rb+ due to its nearly identical size. Nitrogen partitioning between fluid and melt (DN(Fluid/Melt)) and fluid and bulk residue (melt+mica) (DN(Fluid/Bulk)) increase linearly with temperature normalized to pressure. This linear relationship can be used to calculate DN(Fluid/Melt) and DN(Fluid/Bulk) for slab melts from 800 to 1200?°C following: and [nasty equation that did not copy]. We used these partition coefficients to quantify the amount of N recycled into the mantle as 50?±?6% of today's atmospheric N. Depending on the rate of mantle N degassing we calculated 4 different scenarios for atmospheric pN2 evolution. All 4 scenarios estimate pN2 to be 8-12% higher at the beginning of the Phanerozoic. These estimates diverge towards the past due to uncertainties in the mechanism and magnitude of N degassing from the mantle. Assuming degassing of N in the past was close to modern degassing rates from MORB, pN2 was up to 40% higher at the onset of plate tectonics at 3-4?Ga. However, degassing rates were probably higher than this: assuming 10× and 20× times higher rates at the onset of plate tectonics leads to pN2 within 20% of modern values. If N degassing from the mantle is increased to 40× the modern MORB rate, pN2 in the Archean would have been 50% lower than today's, which is in accordance with observations from paleoatmospheric studies.
DS201907-1545
2019
Forster, M.W., Foley, S.F., Marschall, H.R., Alard, O., Buhre, S.Melting of sediments in the deep mantle produces saline fluid inclusions in diamonds.Science Advances, Vol. 5, 5, eaau 2620 7p.Mantlediamond inclusions

Abstract: Diamonds growing in the Earth’s mantle often trap inclusions of fluids that are highly saline in composition. These fluids are thought to emerge from deep in subduction zones and may also be involved in the generation of some of the kimberlite magmas. However, the source of these fluids and the mechanism of their transport into the mantle lithosphere are unresolved. Here, we present experimental results showing that alkali chlorides are stable solid phases in the mantle lithosphere below 110 km. These alkali chlorides are formed by the reaction of subducted marine sediments with peridotite and show identical K/Na ratios to fluid inclusions in diamond. At temperatures >1100°C and low pressures, the chlorides are unstable; here, potassium is accommodated in mica and melt. The reaction of subducted sediments with peridotite explains the occurrence of Mg carbonates and the highly saline fluids found in diamonds and in chlorine-enriched kimberlite magmas.
DS201905-1030
2019
Forster, M.W., Prelevic, D., Buhre, S., Mertz-Kraus, R., Foley, S.F.An experimental study of the role of partial melts of sediments versus mantle melts in the sources of potassic magmatism.Journal of Asian Earth Sciences, Vol. 177, pp. 76-88.Mantlelamproite

Abstract: Potassium-rich lavas with K/Na of >2 are common in orogenic and anorogenic intraplate magmatic provinces. However, in the primitive mantle, the concentration of Na exceeds that of K by 10 times. The source of K-rich lavas thus needs to be either K-enriched or Na-depleted to account for high K/Na ratios. The geochemical and isotopic compositions of high 87Sr/86Sr post-collisional lavas show that their mantle source contains a recycled crustal component. These highly K-enriched lavas with crustal like trace element patterns are termed “orogenic lamproites” and are compositionally distinct from K-rich “anorogenic lamproites” that show lower 87Sr/86Sr and a trace element pattern that resembles that of primary mantle melts. For both groups the processes of K-enrichment within their source are uncertain and are thought to be linked to melts of sedimentary rocks for “orogenic lamproites” and low-degree melts of ultramafic mantle rocks for “anorogenic lamproites”. In both cases, metasomatism of the mantle lithosphere is the precursor to K-rich magmatism. In this study we experimentally determine the effects of mantle metasomatism by sediment- and hydrous mantle melts. The experiments simulate the interaction of refractory lithospheric mantle and metasomatizing melt in a 2-layer reaction experiment. The sediment/dunite reaction experiments lead to formation of a strongly K-enriched phlogopite-pyroxenite layer sandwiched between the two starting materials. The low temperature of the sediment/dunite reaction runs at <1000?°C simulates a fore-arc subduction environment, in which the melts of sediment are consumed during interaction with dunite as the temperature is below the solidus of the produced phlogopite-pyroxenites. The hydrous mantle melt/dunite reaction run is simulated by reacting a hydrated basanite with dunite. Since the temperature of the reaction is higher than the solidus of the resulting phlogopite-pyroxenites (1200?°C), the hydrous melt is not consumed but flows further, increasing in K2O and K/Na as it reacts with the refractory peridotite. In both cases, melts are enriched in K and K/Na increases by crystallizing a low K and low K/Na eclogitic residue. Compositions of glass and phlogopite from both types of reactions are comparable to glasses and phlogopites found within post-collisional lavas. Since the enrichment of K within the reaction zone is strongly controlled by the formation of low K/Na and low-K residues, metasomatic enrichment of the mantle lithosphere in K does not need a highly K-enriched metasomatic agent.
DS201912-2781
2019
Forster. M.W., Prelevic, D., Buhre, S., Mertz-Kraus, R., Foley, S.F.An experimental study of the role of partial melts of sediments versus mantle melts in the sources of potassic magmatism.Journal of Asian Earth Sciences, Vol. 177, pp. 76-88.Mantlemetasomatism

Abstract: Potassium-rich lavas with K/Na of >2 are common in orogenic and anorogenic intraplate magmatic provinces. However, in the primitive mantle, the concentration of Na exceeds that of K by 10 times. The source of K-rich lavas thus needs to be either K-enriched or Na-depleted to account for high K/Na ratios. The geochemical and isotopic compositions of high 87Sr/86Sr post-collisional lavas show that their mantle source contains a recycled crustal component. These highly K-enriched lavas with crustal like trace element patterns are termed “orogenic lamproites” and are compositionally distinct from K-rich “anorogenic lamproites” that show lower 87Sr/86Sr and a trace element pattern that resembles that of primary mantle melts. For both groups the processes of K-enrichment within their source are uncertain and are thought to be linked to melts of sedimentary rocks for “orogenic lamproites” and low-degree melts of ultramafic mantle rocks for “anorogenic lamproites”. In both cases, metasomatism of the mantle lithosphere is the precursor to K-rich magmatism. In this study we experimentally determine the effects of mantle metasomatism by sediment- and hydrous mantle melts. The experiments simulate the interaction of refractory lithospheric mantle and metasomatizing melt in a 2-layer reaction experiment. The sediment/dunite reaction experiments lead to formation of a strongly K-enriched phlogopite-pyroxenite layer sandwiched between the two starting materials. The low temperature of the sediment/dunite reaction runs at <1000?°C simulates a fore-arc subduction environment, in which the melts of sediment are consumed during interaction with dunite as the temperature is below the solidus of the produced phlogopite-pyroxenites. The hydrous mantle melt/dunite reaction run is simulated by reacting a hydrated basanite with dunite. Since the temperature of the reaction is higher than the solidus of the resulting phlogopite-pyroxenites (1200?°C), the hydrous melt is not consumed but flows further, increasing in K2O and K/Na as it reacts with the refractory peridotite. In both cases, melts are enriched in K and K/Na increases by crystallizing a low K and low K/Na eclogitic residue. Compositions of glass and phlogopite from both types of reactions are comparable to glasses and phlogopites found within post-collisional lavas. Since the enrichment of K within the reaction zone is strongly controlled by the formation of low K/Na and low-K residues, metasomatic enrichment of the mantle lithosphere in K does not need a highly K-enriched metasomatic agent.
DS201903-0509
2010
Francke, J.Applications of GPR in mineral resource applications. Mentions kimberliteIEEE.org * note date , 5p.Globalgeophysics - GPR

Abstract: Since the commercialisation of ground penetrating radar (GPR) in the 1970s, radar technology has been employed for niche applications in the mining industry. Although reliant on electrically resistive environments, GPR has gained acceptance in recent years as a standard exploration method for a number of deposit types, ranging from paleochannel delineation to iron ore mapping and kimberlite imaging. Numerous case studies have been published on GPR's applications to specific mineral exploration projects. Provided herein is an overview of commercialised GPR applications for surface mineral resource evaluations, covering examples of alluvial channels, nickel and bauxitic laterites, iron ore deposits, mineral sands, coal, kimberlite and massive sulphide examples.
DS201911-2522
2018
Frankfurter, R., Kardas-Nelson, M., Benton, A., Barrie, M.B., Dibba, Y., Farmer, P., Richardson, E.T.Indirect rule redux: the political economy of diamond mining and its relation to the Ebola outbreak in Kono district, Sierra Leone.Review of African Political Economy, Vol. 45, no. 158, pp. 522-540.Africa, Sierra Leonehistory

Abstract: This article explores the relationship between the 2014-2016 Ebola outbreak and the political economy of diamond mining in Kono District, Sierra Leone. The authors argue that foreign companies have recycled colonial strategies of indirect rule to facilitate the illicit flow of resources out of Sierra Leone. Drawing on field research conducted during the outbreak and in its aftermath, they show how this ‘indirect rule redux’ undermines democratic governance and the development of revenue-generation institutions. Finally, they consider the linkages between indirect rule and the Ebola outbreak, vis-à-vis the consequences of the region’s intentionally underdeveloped health care infrastructure and the scaffolding of outbreak containment onto the paramount chieftaincy system.
DS201912-2782
2019
Frezzotti, M.L.Diamond growth from organic compounds in hydrous fluids deep within the Earth.Nature Communications, 10:4952 9p. PdfMantlesubduction

Abstract: At subduction zones, most diamonds form by carbon saturation in hydrous fluids released from lithospheric plates on equilibration with mantle rocks. Although organic molecules are predicted among dissolved species which are the source for carbon in diamonds, their occurrence is not demonstrated in nature, and the physical model for crustal diamond formation is debated. Here, using Raman microspectroscopy, I determine the structure of carbon-based phases inside fluid inclusions in diamond-bearing rocks from the Alps. The results provide direct evidence that diamond surfaces are coated by sp2-, and sp3-bonded amorphous carbon and functional groups of carboxylic acids (e.g., carboxyl, carboxylate, methyl, and methylene), indicating the geosynthesis of organic compounds in deep hydrous fluids. Moreover, this study suggests diamond nucleation via metastable molecular precursors. As a possible scenario, with carbon saturation by reduction of carboxylate groups, I consider tetrahedral H-terminated C groups as templates for the growth of sp3-structured carbon.
DS201902-0272
2019
Friedrich, A.M.Palaeogeological hiatus surface mapping: a tool to visualize vertical motion of the continents.Geological Magazine, Vol. 156, 2, pp. 308-319.Mantletomography

Abstract: Dynamic topography is a well-established consequence of global geodynamic models of mantle convection with horizontal dimensions of >1000 km and amplitudes up to 2 km. Such physical models guide the interpretation of geological records on equal dimensions. Continent-scale geological maps therefore serve as reference frames of choice to visualize erosion/non-deposition as a proxy for long-wavelength, low-amplitude vertical surface motion. At a resolution of systems or series, such maps display conformable and unconformable time boundaries traceable over hundreds to thousands of kilometres. Unconformable contact surfaces define the shape and size of time gap (hiatus) in millions of years based on the duration of time represented by the missing systems or series. Hiatus for a single system or series base datum diminishes laterally to locations (anchor points) where it is conformable at the mapped resolution; it is highly dependent upon scale. A comparison of hiatus area between two successive system or series boundaries yields changes in location, shape, size and duration, indicative of the transient nature of vertical surface motion. As a single-step technique, it serves as a quantitative proxy for palaeotopography that can be calibrated using other geological data. The tool magnifies the need for geological mapping at the temporal resolution of stages, matching process rates. The method has no resolving power within conformable regions (basins) but connects around them. When applied to marine seismic sections that relate to rock record, not to time, biostratigraphic and radiometric data from deep wells are needed before hiatus areas - that relate to time - can be mapped.
DS201903-0510
2019
Frigo, C., Stalder, R., Ludwig, T.OH defects in coesite and stishovite during ultrahigh-pressure metamorphism of continental crust. Dora Massif, KochetavPhysics and Chemistry of Minerals, Vol. 46, pp. 77-89.Russia, Europe, AlpsUHP

Abstract: The high-pressure silica polymorphs coesite and stishovite were synthesized under water-saturated conditions from a natural granitic composition doped with Li and B. Experiments were performed in a Multi-Anvil apparatus between 4 and 9.1 GPa and 900 and 950 °C, based on the conditions of a subducting continental crust as realistic for the ultrahigh-pressure metamorphic units Dora Maira and Kochetav massifs. Run products consisted of coesite/stishovite?+?kyanite?±?phengite?±?omphacite, and quench material. The synthesized silica polymorphs were successively analyzed by infrared spectroscopy, electron microprobe, and Secondary-Ion Mass Spectrometry (SIMS). No hydrous defects were observed in coesite synthesized at 4 GPa and 900 °C, whereas coesite grown at higher pressures revealed a triplet of infrared absorptions bands at 3575, 3523, and 3459 cm-?1, two minor bands at 3535 and 3502 cm-?1, and a small band at 3300 cm-?1 that was only visible at 7.7 GPa. The total amount of Al was charge-balanced by H and the other monovalent cations. However, the band triplet could not be associated with AlOH defects, while the band doublet was inferred to BOH defects and the small band probably corresponded to interstitial H. Stishovite displayed one dominant band at 3116 cm-?1 with a shoulder at 3170 cm-?1, and a minor band at 2665 cm-?1, probably all associated with AlOH defects. BOH defects were not observed in stishovite, and LiOH defects were neither observed in coesite nor stishovite, probably because of preferentially partition of Li in other phases such as omphacite. The total amount of defect protons increased with pressure and with metal impurity concentrations. The general increase in OH defects in silica polymorphs with increasing pressure (this study) contrasted the negative pressure trend of OH in quartz observed previously from the same starting material, and revealed an incorporation minimum of OH in silica polymorphs around the quartz/coesite phase transition.
DS201906-1292
2019
Frost, B.B., Frost, C.The Wyoming province, a long-lived craton on the periphery of Laurentia.GAC/MAC annual Meeting, 1p. Abstract p. 91.United States, Canadacraton

Abstract: The Wyoming craton is one of the three cratons, Wyoming, Slave, and Nain, with Hadean roots that lie on the margins of Laurentia. The Wyoming and Slave provinces show many similarities, most notably a widespread supracrustal sequence that formed around 2.86 Ga. It is possible that the two cratons rifted apart at 2.86 Ga and docked onto Laurentia as separate entities in the Paleoproterozoic. The Wyoming province is characterized by elevated 207Pb/204Pb indicative of cratons that have a Hadean origin. The earliest rocks contain 3.8 to 4.0 Ga detrital and xenocrystic zircon grains. The 3.82 Ga xenocrystic zircon grains from 3.4 Ga tonalitic gneisses in the Granite Mountains have Hf isotopic compositions requiring Hadean precursors. The transition from tonalitic to granodioritic plutonism is diachronous; it occurs around 3.3 Ga in the Granite Mountains and around 2.85 Ga in the Bighorn Mountains. Granitic plutonism since 2.85 Ga is dominantly magnesian and calc-alkalic, compositionally identical to Phanerozoic arc magmas. The Teton Range, on the western margin of the province, records the earliest Himalayan orogeny on Earth at 2.7 Ga, further evidence that much of the Wyoming Province was constructed by processes similar to those operating in the Phanerozoic. The latest structural and metamorphic event in the evolution of the craton was accretion of crustal fragments along structures that trend broadly NE-SW at 2.62 Ga. The latest major magmatic event was the intrusion of the peraluminous granites of the Mount Owen batholith in the Teton Range at 2.55 Ga. The Wyoming craton was accreted to Laurentia in the Paleoproterozoic, probably during the later stages of the Trans-Hudson orogeny.
DS201905-1031
2019
Fulop, A., Kopylova, M., Kurszlaukis, S., Hilchie, L., Ellemers, P.A reply to the comment by Germon et al. on the Petrography of the Snap Lake kimberlite dyke ( Northwest Territories, Canada) and its interaction with country rock granitoids.Journal of Petrology, Vol. 60, 3, pp. 661-671.Canada, Northwest Territoriesdeposit - Snap Lake
DS201901-0034
2018
Fulop, A., Kopylova, M., Kurszlaukis, S., Hilchie, L., Ellemers, P., Squibb, C.Petrography of Snap Lake kimberlite dyke ( Northwest Territories, Canada) and its interaction with country rock granitoids.Journal of Petrology, Vol. 59, 12, pp. 2493-2518.Canada, Northwest Territoriesdeposit - Snap Lake

Abstract: Carbonate-rich intrusions in contact with felsic rocks theoretically should show the effects of interaction between the two rock types, due to their contrasting compositions. In reality, though, such interaction is rarely reported at kimberlite contacts. We present the first documented case of lithological and mineralogical zonation at the margin of a kimberlite, the Snap Lake dyke, in contact with the wall-rock granitoid. Our detailed petrographic, mineralogical and geochemical study shows that the fresh hypabyssal kimberlite consists of olivine macrocrysts and microcrysts, and phlogopite macrocrysts set in a groundmass of serpentinized monticellite, phlogopite, spinel, perovskite and apatite, with interstitial lizardite and calcite. This typical Group I kimberlite mineralogy does not match the bulk-rock composition, which resembles a Group II micaceous kimberlite. The mismatch between the chemical and mineralogical properties is ascribed to contamination by granitoid xenoliths and metasomatic reactions with the felsic country rocks, the Snap Lake kimberlite has extremely low bulk-Ca compared to other documented Group I kimberlites. Reaction with deuteric H2O and CO2 has led to Ca removal, serpentinization of olivine, replacement of calcite by dolomite, alteration of perovskite and decomposition of apatite. Adjacent to the contact with the host granitoid and in haloes around granitoid clasts, poikilitic phlogopite and lizardite are replaced by subsolidus phlogopite and a multiphase phyllosilicate composed of phlogopite+?lizardite+?chlorite+?talc. A modified isocon analysis accounts for felsic xenolith assimilation and isolates metasomatic changes. Enrichment of altered kimberlites in Si owes solely to xenolith incorporation. The metasomatic ingress of granitoid-derived Al for a limited distance inside the dyke was counteracted by a flux of Mg and Fe to the granitoid. Metasomatic changes in K and Ca tend to be positive in all lithologies of kimberlite and in the granitoids implying distal transport. The combination of xenolith digestion with metasomatic element transport is expected in hybrid zones where kimberlite magmas interact with felsic wall-rocks.
DS201909-2040
2019
Gaillard, E., Nabyl, Z., Tuduri, J., Di Carlo, I., Melleton, J., Bailly, L.The effects of F, Cl, P and H2O on the immiscibility and rare metals partitioning between carbonate and phonolite melts.Goldschmidt2019, 1p. AbstractGlobalcarbonatite - REE

Abstract: Carbonatite and alkaline magma constitute one of the principal resources of rare metals (REE, Nb, Ti, Zr). Carbonatite rare metals enrichment is mainly considered as the result of hydrothermal or supergen processes. However, the magmatic processes linked to carbonatites genesis and differentiation are still debated and whether these processes can significantly impact on the rare metal concentrations remains unclear. Experimental studies have shown that immiscibility processes between carbonate and silicate melts can lead to both REE enrichments and depletions in carbonatites. Anionic species (F, Cl, P or S) and water may impact both melt compositions and expand the immiscibility gap. Morever, anionic species are assumed to play an important role in REE behaviour in carbonate melts [1]. Indeed, halogens may occur in carbonatites as immiscible salt melts in melt inclusions [2] and primary REE- fluoride minerals have been identified as magmatic phases in carbonatites. Such occurrences thus question on the role of salt (carbonate, phosphate, fluoride and chloride) melts in REE and other rare metals partitioning. F, Cl, P and also H2O may all significantly increase the window of primary REE enrichment in carbonatites. Here we present high pressure and high temperature experiments made in piston-cylinder (850 to 1050°C, 8kb) simulating the immiscibility between carbonate and differentiated alkaline melts. We added F, Cl, P and H2O in order to assess the effect of salts and water on the immiscibility gap and on the rare metals partitoning between carbonatite and evolved silicate melts. The partitioning data are analysed using LA-ICP-MS, nano-SIMS, FTIR and RAMAN. The characterization of rare metal partition coefficients allow to determine the relative importance of F, Cl, P and H2O on carbonatites rare metal enrichments at evolved magmatic stage.
DS201905-1032
2014
Gaillou, E., Rossman, G.R.Color in natural diamonds .. The beauty of defects. Note date ***Rocks & Minerals, 12p.Globaldiamond colour

Abstract: In its pure form, diamond is colorless. However, in nature (or even when made in laboratories), diamonds are never composed of 100 percent carbon atoms. Even colorless diamonds will contain some defects: missing carbon atoms or containing trace amounts of nitrogen or hydrogen, for example. When present in certain atomic arrangements and concentrations, most minor components cause absorption of specific wavelengths of light, giving rise to color. The color in diamond is not source specific, even if some mines are known to produce more of certain colors, such as blue diamonds from the Premiere mine in South Africa, or brown and pink diamonds from the Argyle mine in Australia. Virtually every single diamond mine could produce any kind of colored diamond. At auction, record prices for gems are currently held by pink and blue diamonds: for example, $2,155,332 per carat for a 24.78-carat Fancy vivid pink diamond (sold at Sotheby's in 2010) and $1.8 million per carat for a 5.3-carat Fancy deep blue diamond (sold at Bonhams in London in April 2013).
DS201910-2258
2019
Gain, S.E., Griffin, W.L., Saunders, M., Shaw, J.A., Toledo, V.A showcase of analytical techniques: native vanadium in hibonite and chromium in corundum: ultra-high contents under reducing conditions. Two posters Shefa Gems Microscopy and Microanalysis ( M&M)Co. Conference, Sept. 9, posters 1 p. eachEurope, Israeldeposit - Kishon

Abstract: The Microscopy and Microanalysis (M&M) conference in Portland Oregon, USA is one of the biggest microscopy conferences in the world and this year it hosted its largest meeting in history with over 3,300 participants, up to 20 parallel sessions and over 600 posters. The two posters were presented by Sarah E.M. Gain who is from the University of Western Australia where she trains and supports researchers in Microscopy, Characterisation and Microanalysis. Sarah discussed some of the unique gem material collected from Shefa Gems’ exploration activity in the Kishon Mid Reach and Rakefet Magmatic Complex, analysed using a range of microscopy and microanalysis techniques. She also discussed the scientific importance of this material.The first poster looked at hibonite (a Ca-Al-oxide) with inclusions of vanadium metal. The second poster looked at, Cr corundum (ruby), which is unusual due to the extremely high Cr levels and the inclusions of Cr metal.
DS201906-1293
2019
Gain, S.E.M., Greau, Y., Henry, H., Belousova, E., Dainis, I., Griffin, W.L., O'Reilly, S.Y.Mud Tank zircon: long term evaluation of a reference material for U-Pb dating, Hf-isotope analysis and trace element analysis. ( Carbonatite)Geostandards and Geoanalytical Research, in press available, 16p.Australiadeposit - Mud Tank

Abstract: Zircon megacrysts from the Mud Tank carbonatite, Australia, are being used in many laboratories as a reference material for LA-ICP-MS U-Pb dating and trace element measurement, and LA-MC-ICP-MS determination of Hf isotopes. We summarise a database of > 10000 analyses of Mud Tank zircon (MTZ), collected from 2000 to 2018 during its use as a secondary reference material for simultaneous U-Pb and trace element analysis, and for Hf-isotope analysis. Trace element mass fractions are highest in dark red-brown stones and lowest in colourless and gem-quality ones. Individual unzoned grains can be chemically homogeneous, while significant variations in trace element mass fraction are associated with oscillatory zoning. Chondrite-normalised trace element patterns are essentially parallel over large mass fraction ranges. A Concordia age of 731.0 ± 0.2 Ma (2s, n = 2272) is taken as the age of crystallisation. Some grains show lower concordant to mildly discordant ages, probably reflecting minor Pb loss associated with cooling and the Alice Springs Orogeny (450-300 Ma). Our weighted mean 176Hf/177Hf is 0.282523 ± 10 (2s, n = 9350); the uncertainties on this ratio reflect some heterogeneity, mainly between grains. A few analyses suggest that colourless grains have generally lower 176Hf/177Hf. MTZ is a useful secondary reference material for U-Pb and Hf-isotope analysis, but individual grains need to be carefully selected using CL imaging and tested for homogeneity, and ideally should be standardised by solution analysis.
DS201904-0737
2019
Gaina, C., Niocaill, C.M., Conrad, C.P., Steinberger, B., Svensen, H.H.Linking plate tectonics and volcanism to deep Earth dynamics - a tribute to Torsvik.Tectonophysics, in press available 6p.Mantlegeodynamics
DS201904-0738
2019
Galli, A., Grassi, D., Sartori, G., Gianola, O., Burg, J-P., Schmidt, M.W.Jurassic carbonatite and alkaline magmatism in the Ivrea zone ( European Alps) related to the breakup of Pangea.Geology, Vol. 47, 3, pp. 199-202..Europecarbonatite

Abstract: We report on pipe-like bodies and dikes of carbonate rocks related to sodic alkaline intrusions and amphibole mantle peridotites in the Ivrea zone (European Southern Alps). The carbonate rocks have bulk trace-element concentrations typical of low-rare earth element carbonatites interpreted as cumulates of carbonatite melts. Faintly zoned zircons from these carbonate rocks contain calcite inclusions and have trace-element compositions akin to those of carbonatite zircons. Laser ablation-inductively coupled plasma-mass spectrometry U-Pb zircon dating yields concordant ages of 187 ± 2.4 and 192 ± 2.5 Ma, coeval with sodic alkaline magmatism in the Ivrea zone. Cross-cutting relations, ages, as well as bulk and zircon geochemistry indicate that the carbonate rocks are carbonatites, the first ones reported from the Alps. Carbonatites and alkaline intrusions are comagmatic and were emplaced in the nascent passive margin of Adria during the Early Jurassic breakup of Pangea. Extension caused partial melting of amphibole-rich mantle domains, yielding sodic alkaline magmas whose fractionation led to carbonatite-silicate melt immiscibility. Similar occurrences in other rifts suggest that small-scale, sodic and CO2-rich alkaline magmatism is a typical result of extension and decompression-driven reactivation of amphibole-bearing lithospheric mantle during passive continental breakup and the evolution of magma-poor rifts.
DS201911-2523
2019
Gao, Y., Yin, P.Determination of crystallite size of nanodiamond by raman spectroscopy.Diamond & Related Materials, Vol. 99, 107524Globalnanodiamond

Abstract: Although the phonon confinement model (PCM) was claimed to be successfully used to accurately calculate the size of larger Si nanocrystals, quantitative size characterization by Raman spectra still remains a challenge in the case of nanodiamonds due to its complexity. Here, we find that a local-mode model of Raman spectra developed recently can be employed to determine the bond number of the ordered diamond core in nanodiamonds, and then furtherly determine the size of nanodiamonds. The Raman lines of nanodiamonds of 3.0?nm, 2.0?nm, 2.2?nm, 3.3?nm, 3.7?nm 4.42?nm and 6.3?nm are calculated. Results are in good agreement with the measured Raman spectra. It not only provides a new approach to predict the size of nanodiamonds accurately by Raman spectra, but also helps to clarify issues in Raman spectra of nanodiamond and other carbon nanomaterials.
DS201903-0511
2018
Garanin, K.Alrosa - world top diamond producer.7th Symposio Brasleiro de geologia do diamante, 54p ppts AvailableRussiaoverview
DS201906-1294
2019
Gem News InternationalColombian emeralds and Mozambican rubies from Fura Gems….. Comments from Fura GemsGems & Gemology, Vol. 55, 1, pp. 125-126.South America, Columbiaemerald
DS201906-1295
2019
Gem News InternationalPotentate's Montana sapphire mine: an interview with Warren Boyd.Gems & Gemology, Vol. 55, 1, pp. 134.United States, Montanasapphire

Abstract: The history of the American West is told in stories of frontiersmen seeking fortune in gold and other precious metals. It was serendipity when these intrepid adventurers arrived in western Montana and discovered strange, shiny pebbles—sapphires—while looking for gold. Little did they know the gem wealth they had uncovered with the sapphires, which were simply a nuisance to the gold miners at first. More than 100 years later, this legacy of mining is carried on by several small-scale miners across Montana, and with the arrival of Potentate Mining at the Rock Creek sapphire deposit. We had the chance to sit down in Tucson with Potentate’s director of marketing, Warren Boyd, for an update on their mining activities and their plans to find a place for Montana sapphires in the market...(No abstract - full article)
DS201904-0739
2019
Gems & JewelleryMazarin's passion for diamonds left to Louis IVX by Cardinal Mazarin. ( Sancy)Gems&Jewellery, Vol. 28, 1. pp. 32-38.Europe, Francehistory
DS201911-2524
2019
Gerocs, T.The transformation of African-Russian economic relations in the multipolar world-system.Review of African Political Economy, Vol. 46, pp. 317-335.Africa, RussiaNews item - economics

Abstract: Despite the historical legacy of the Soviet Union, the Russian Federation’s economic presence in Africa today is minuscule in comparison to that of the West or China. The aim of this Briefing is to provide a framework for the trajectory of African-Russian economic ties in the changing international environment. Although the economic, trade and investment affairs could develop more complementarity, it is still an open question whether African countries benefit from the deepening economic ties or whether these inhibit local socio-economic development.
DS201911-2525
2019
Gerya, T.Geodynamics of the Early Earth: quest for the missing paradigm.Geology, Vol. 47, pp. 1006-1007.Mantlegeodynamics

Abstract: In contrast to modern-day plate tectonics, geodynamics of the early Earth presents a unique challenge, as currently there is no consensus on a global paradigm concerning the mantle dynamics and lithosphere tectonics in the Precambrian (Benn et al., 2006; Gerya, 2014). This challenge is mainly due to the severe objective restrictions of obtaining geological and/or geophysical observations constraining Earth’s surface and interior dynamics back in geological time (Fig. 1). The subject of geodynamics can be schematically represented by the time-depth diagram (see Fig. 1) covering the entire Earth’s history and interior. In theory, the entire diagram should be "covered" by data points characterizing the physical-chemical state of Earth at different depths, for different moments in geological time. However, in practice, observations are only available along two axes: (1) geophysical data for Earth’s internal structure at all ranges of depths, but only for the very short present-day time, and (2) the geological record preserved in rocks formed over a broad range of geological times, but only at a very shallow depth range. As a result, the importance of well-constrained geological and geophysical data, and thoroughly studied present-day geodynamic regime (modern-style plate tectonics) is almost unavoidably exaggerated and "stretched" toward the Precambrian Earth. This "plate tectonics trap" can only be avoided by further calibrating our geological intuition on the basis of numerical geodynamic modeling that integrates available geological, geochemical, petrological, and geochronological records (Gerya, 2014).
DS201911-2526
2019
Giampouras, M., Garrido, C.J., Zwicker, J., Vadillo, I., Smrzka, D., Bach, W., Peckmann, J., Jemenez, P., Benavente, J., Garcia-Ruiz, J.M.Geochemistry and mineralogy of serpentinization driven hyperalkaline springs in the Ronda peridotite.Lithos, doi 10.1016/j.lithos.2019.105215, 75p. PdfEurope, Spaindeposit - Ronda

Abstract: We present a detailed study of the water geochemistry, mineralogy and textures in serpentinization-related hyperalkaline springs in the Ronda peridotites. Ronda waters can be classified into hyperalkaline fluids and river waters that are broadly similar to Ca2+-OH- and Mg2+-HCO3- water types described in serpentinite-hosted alkaline springs elsewhere. At the discharge sites of the fluids (fractures or human made outlets) and ponds along the fluid flow paths, the fluids are hyperalkaline (10.9 < pH < 12) and characterized by low Mg and high Na, K, Ca, and Cl concentrations. River waters, occurring near the spring sites, are mildly alkaline (8.5 < pH < 8.9) and enriched in Mg and DIC compared to Na, K, Ca and Cl. The chemistry of Ronda Mg-HCO3 river waters is likely due to the hydrolysis of ferromagnesian peridotite minerals in equilibrium with the atmosphere by infiltrated meteoric water and shallow groundwater in the serpentinized peridotite. The Ronda Ca-OH hyperalkaline fluids are generated by the combination of low temperature serpentinization reactions from infiltrated surface Mg-HCO3 river waters —or Ca-HCO3 waters from near karst aquifers— and deep carbonate precipitation isolated from atmospheric CO2. Mass balance calculations indicate that the weathering of Ca-bearing peridotite silicates such as diopside is a feasible source of Ca in Ronda Ca-OH hyperalkaline fluids; however, it requires steady-state dissolution rates substantially greater than those determined experimentally. Travertine, crystalline crusts and sediment deposits are the main types of solid precipitates observed in Ronda hyperalkaline spring sites. Calcite and aragonite, minor dolomite and Mg-Al-rich clays are the main minerals in the spring sites. As illustrated in the Baños del Puerto spring site, (i) calcite-dominated precipitation is due to hyperalkaline fluid uptake of atmospheric CO2 during discharge, and (ii) aragonite-dominated precipitation is due to mixing of Ca-OH hyperalkaline fluids with Mg- HCO3 river waters. Aragonite and dolomite contents increase away from the springs and toward the river waters that uniquely reflects the effect of Mg ions on the precipitation of aragonite versus calcite. Other potential factors controlling the precipitation of these CaCO3 polymorphs are the Mg/Ca ratio, the CO2 content, and the temperature of the fluids. Dolomite forms during lithification of travertine due to periodic flooding of river water combined with subsequent evaporation.
DS201912-2783
2019
Gibbs, W.W.A new form of pure carbon dazzles and attracts.Science, Vol. 366, 6467, pp. 782-783.Mantlecarbon

Abstract: A "happy accident" has yielded a new, stable form of pure carbon made from cheap feedstocks, researchers say. Like diamond and graphene, two other guises of carbon, the material seems to have extraordinary physical properties. It is harder than stainless steel, about as conductive, and as reflective as a polished aluminum mirror. Perhaps most surprising, the substance appears to be ferromagnetic, behaving like a permanent magnet at temperatures up to 125°C. The discovery, announced in a talk here at the International Symposium on Clusters and Nanomaterials, could lead to lightweight coatings, medical products, and novel electronic devices. The news has elicited both excitement and caution among the dozens of researchers attending the meeting. Experts note that carbon is much lighter than other ferromagnetic elements such as manganese, nickel, and iron. Moreover, carbon is nontoxic in the body—which could mean the substance could be used for making biosensors or drug-delivery carriers.
DS201903-0512
2018
Gibsher, A.Mineral inclusions in Siberian diamonds: mineralogy, geochemistry and application to diamond exploration.7th Symposio Brasleiro de geologia do diamante, 22 ppts. Pdf availableRussia, Siberiadiamond inclusions
DS201909-2041
2019
Giebel, R.J., Marks, M.A.W., Gauert, C.D.K., Markl, G.A model for the formation of carbonatite-phoscorite assemblages.Goldschmidt2019, 1p. AbstractGlobalcarbonatite

Abstract: A detailed electron microprobe study has been carried out on the compositional variations of mica and apatite from carbonatites, phoscorites and associated pyroxenites (and fenites) of the Loolekop deposit, Palabora Carbonatite Complex (South Africa). Mica in pyroxenites and fenites is Mg-rich biotite, whilst micas in carbonatites and phoscorites are compositionally diverse including phlogopite, Ba-rich phlogopite (up to 30% kinoshitalite component), IVAl-rich phlogopite (up to 30% eastonite component) and tetraferriphlogopite. The various types of phlogopites are interpreted as orthomagmatic phases, whereas tetraferriphlogopite precipitation was a late-magmatic to hydrothermal process that additionally introduced REE into the system. Orthomagmatic apatite is generally REE- and Sr-poor fluorapatite and does not show large compositional differences between rock types. Apatite associated with the late-stage tetraferriphlogopite mineralization reaches higher levels of REE (up to 4.9?wt%), Si (up to 1.5?wt% SiO2), Sr (up to 2.6?wt% SrO) and Na (up to 1.0?wt% Na2O). The compositional variation of micas and apatites, which is affiliated with distinct rock types, reflects the multi-stage evolution of the Loolekop deposit and provides detailed insight into the relationships of the carbonatite-phoscorite assemblage. The obtained data support the separation of phoscorite and carbonatite by immiscibility from a common parental magma, which may happen due to a decrease of temperature and/or pressure during the ascent of the magma. This results in a density contrast between the carbonatitic and phoscoritic components that will lead to descending phoscorite accumulations at the outer zones of the magma channel and a jet-like ascent (further promoted by its extremely low viscosity) of the carbonatite magma. The genetic model deduced here explains the peculiar association of carbonatites, phoscorites and silicate rocks in many alkaline complexes worldwide.
DS201902-0273
2019
Giebel, R.J., Marks, M.A.W., Gauert, C.K., Markl, G.A model for the formation of carbonatite-phoscorite assemblages based on the compositonal variations of mica and apatite from the Palabora carbonatite complex, South AfricaLithos, Vol. 324, pp. 68-73.Europe, Azoresdeposit - Palabora

Abstract: A detailed electron microprobe study has been carried out on the compositional variations of mica and apatite from carbonatites, phoscorites and associated pyroxenites (and fenites) of the Loolekop deposit, Palabora Carbonatite Complex (South Africa). Mica in pyroxenites and fenites is Mg-rich biotite, whilst micas in carbonatites and phoscorites are compositionally diverse including phlogopite, Ba-rich phlogopite (up to 30% kinoshitalite component), IVAl-rich phlogopite (up to 30% eastonite component) and tetraferriphlogopite. The various types of phlogopites are interpreted as orthomagmatic phases, whereas tetraferriphlogopite precipitation was a late-magmatic to hydrothermal process that additionally introduced REE into the system. Orthomagmatic apatite is generally REE- and Sr-poor fluorapatite and does not show large compositional differences between rock types. Apatite associated with the late-stage tetraferriphlogopite mineralization reaches higher levels of REE (up to 4.9?wt%), Si (up to 1.5?wt% SiO2), Sr (up to 2.6?wt% SrO) and Na (up to 1.0?wt% Na2O). The compositional variation of micas and apatites, which is affiliated with distinct rock types, reflects the multi-stage evolution of the Loolekop deposit and provides detailed insight into the relationships of the carbonatite-phoscorite assemblage. The obtained data support the separation of phoscorite and carbonatite by immiscibility from a common parental magma, which may happen due to a decrease of temperature and/or pressure during the ascent of the magma. This results in a density contrast between the carbonatitic and phoscoritic components that will lead to descending phoscorite accumulations at the outer zones of the magma channel and a jet-like ascent (further promoted by its extremely low viscosity) of the carbonatite magma. The genetic model deduced here explains the peculiar association of carbonatites, phoscorites and silicate rocks in many alkaline complexes worldwide.
DS201909-2042
2019
Giebel, R.J., Parsapoor, A., Walter, B.F., Braunger, S., Marks, M.A.W.Evidence for magma-wall rock interaction in carbonatites from the Kaiserstuhl volcanic complex ( southwest Germany).Journal of Petrology , Vol. 60, 6, pp. 1163-1194.Europe, Germanycarbonatite

Abstract: The mineralogy and mineral chemistry of the four major sövite bodies (Badberg, Degenmatt, Haselschacher Buck and Orberg), calcite foidolite/nosean syenite xenoliths (enclosed in the Badberg sövite only) and rare extrusive carbonatites of the Kaiserstuhl Volcanic Complex in Southern Germany provide evidence for contamination processes in the carbonatitic magma system of the Kaiserstuhl. Based on textures and composition, garnet and clinopyroxene in extrusive carbonatites represent xenocrysts entrained from the associated silicate rocks. In contrast, forsterite, monticellite and mica in sövites from Degenmatt, Haselschacher Buck and Orberg probably crystallized from the carbonatitic magma. Clinopyroxene and abundant mica crystallization in the Badberg sövite, however, was induced by the interaction between calcite foidolite xenoliths and the carbonatite melt. Apatite and micas in the various sövite bodies reveal clear compositional differences: apatite from Badberg is higher in REE, Si and Sr than apatite from the other sövite bodies. Mica from Badberg is biotite- and comparatively Fe2+-rich (Mg# = 72-88). Mica from the other sövites, however, is phlogopite (Mg# up to 97), as is typical of carbonatites in general. The typical enrichment of Ba due to the kinoshitalite substitution is observed in all sövites, although it is subordinate in the Badberg samples. Instead, Badberg biotites are strongly enriched in IVAl (eastonite substitution) which is less important in the other sövites. The compositional variations of apatite and mica within and between the different sövite bodies reflect the combined effects of fractional crystallization and carbonatite-wall rock interaction during emplacement. The latter process is especially important for the Badberg sövites, where metasomatic interaction released significant amounts of K, Fe, Ti, Al and Si from earlier crystallized nosean syenites. This resulted in a number of mineral reactions that transformed these rocks into calcite foidolites. Moreover, this triggered the crystallization of compositionally distinct mica and clinopyroxene crystals around the xenoliths and within the Badberg sövite itself. Thus, the presence and composition of clinopyroxene and mica in carbonatites may be useful indicators for contamination processes during their emplacement. Moreover, the local increase of silica activity during contamination enabled strong REE enrichment in apatite via a coupled substitution involving Si, which demonstrates the influence of contamination on REE mineralization in carbonatites.
DS201912-2784
2019
Gilfillan, S.M.V., Gyore, D., Flude, S., Johnson, G., Bond, C.E., Hicks, N., Lister, R., Jones, D.G., Kremer, Y., Hazeldine, R.S., Stuart, F.M.Noble gases confirm plume related mantle degassing beneath southern Africa.Nature Communications, Vol. 10, 1, 10.1038/s41467-019-1244-6Africa, South Africaplumes

Abstract: Southern Africa is characterised by unusually elevated topography and abnormal heat flow. This can be explained by thermal perturbation of the mantle, but the origin of this is unclear. Geophysics has not detected a thermal anomaly in the upper mantle and there is no geochemical evidence of an asthenosphere mantle contribution to the Cenozoic volcanic record of the region. Here we show that natural CO2 seeps along the Ntlakwe-Bongwan fault within KwaZulu-Natal, South Africa, have C-He isotope systematics that support an origin from degassing mantle melts. Neon isotopes indicate that the melts originate from a deep mantle source that is similar to the mantle plume beneath Réunion, rather than the convecting upper mantle or sub-continental lithosphere. This confirms the existence of the Quathlamba mantle plume and importantly provides the first evidence in support of upwelling deep mantle beneath Southern Africa, helping to explain the regions elevation and abnormal heat flow.
DS201911-2527
2019
Gilloly, T., Coltice, N., Wolf, C.An anticipation experiment for plate tectonics. Boundaries.Tectonics, in press availableMantleplate tectonics

Abstract: Although plate tectonics has pushed the frontiers of geosciences in the past 50 years, it has legitimate limitations and among them we focus on both the absence of dynamics in the theory, and the difficulty of reconstructing tectonics when data is sparse. In this manuscript, we propose an anticipation experiment, proposing a singular outlook on plate tectonics in the digital era. We hypothesize that mantle convection models producing self-consistently plate-like behavior will capture the essence of the self-organisation of plate boundaries. Such models exist today in a preliminary fashion and we use them here to build a database of mid-ocean ridge and trench configurations. To extract knowledge from it we develop a machine learning framework based on Generative Adversarial Networks (GANs) that learns the regularities of the self-organisation in order to fill gaps of observations when working on reconstructing a plate configuration. The user provides the distribution of known ridges and trenches, the location of the region where observations lack, and our digital architecture proposes a horizontal divergence map from which missing plate boundaries are extracted. Our framework is able to prolongate and interpolate plate boundaries within an unresolved region, but fails to retrieve a plate boundary that would be completely contained inside of it. The attempt we make is certainly too early because geodynamic models need improvement and a larger amount of geodynamic model outputs, as independent as possible, is required. However, this work suggests applying such an approach to expand the capabilities of plate tectonics is within reach.
DS201904-0740
2019
Giovanardi, T., Girardi, V.A.V., Teixeira, W., Mazzucchelli, M.Mafic dyke swarms at 1882, 535 and 200 Ma in the Carajas region Amazonian Craton: Sr-Nd isotopy, trace element geochemistry and inferences on their origin and geological settings.Journal of South American Earth Sciences, Vol. 92, pp. 197-208.South America, Brazilcraton

Abstract: The Carajás-Rio Maria region, together with the Rio Maria domain of the Central Amazonian province, comprises the eastern margin of the Amazonian Craton with the Neoproterozoic Araguaia belt. This region hosts several basaltic dyke swarms whose UPb baddeleyite ages highlighted three intrusive events at 1882, 535 and 200?Ma. New geochemical and SrNd isotopic data were obtained for the different groups of the Carajás dykes allowing new insights on i) the mantle source composition beneath the Carajás region through time and ii) the geodynamic setting of the intrusive events. The 1882?Ma swarm is coeval to the Uatumã SLIP event which is one of the oldest intraplate events of the proto-Amazonian craton. Trace elements and isotopic values suggest that the dyke parent melt for those dykes have a crustal component derived from a sedimentary source similar to GLOSS (GLObal Subducting Sediment compositions). This is consistent with the emplacement of the dykes in a supra-subduction setting or in a post-collisional setting. Trace and isotopic values of the 535?Ma dyke swarm are consistent with an enriched mantle source from EMII component. These geochemical features suggest an enrichment of the mantle from an oceanic lithosphere poor in sediments, different to that of the 1882?Ma source. The age of this swarm matches magmatic activity during a post-collisional extensive-transtensive event recorded in the marginal Araguaia belt after the amalgamation of the Amazonian Craton to the Western Gondwana during Neoproterozoic. The 200?Ma dyke swarm which is related to the CAMP (Central Atlantic Magmatic Province) and opening of the Atlantic Ocean shows trace element composition similar to Atlantic E-MORB. The coupled isotopic values are consistent with an enriched mantle source with EMII component. These particular geochemical features suggest that the plume activity responsible for the CAMP near the rifting zone has not affected the mantle beneath the Carajás region.
DS201905-1033
2019
Giuliani, A., Martin, L.A.J., Soltys,A., Griffin, W.L.Mantle like oxygen isotopes in kimberlites determined by in situ SIMS analyses of zoned olivine.Geochimica et Cosmochimica Acta, in press available, 19p.Africa, South Africa, Canada, South America, Brazildeposit - Lac de Gras, Paranaiba

Abstract: Kimberlites are the deepest melts produced on Earth that are erupted at the surface and can therefore provide unique insights into the composition and evolution of the mantle. Radiogenic isotopes provide ambiguous evidence for the occurrence of recycled crustal material in kimberlite sources. Oxygen isotopes can fractionate significantly only in the shallow crust, and thus represent a powerful tracer of subducted material in the sources of kimberlite. To constrain the oxygen isotope composition of kimberlite melts, we have examined olivine grains in eleven Cretaceous to Eocene archetypal kimberlites from southern Africa, Lac de Gras (Canada) and Alto Paranaiba (Brazil), which exhibit radiogenic isotope evidence for recycled crustal material in their sources including highly radiogenic Pb isotopes and Nd-Hf isotope compositions deviating below the mantle array. Olivine grains are commonly zoned between a mantle-derived xenocrystic core and one or more magmatic overgrowths, i.e. occasional internal zones, ubiquitous rims and rare rinds (moving outward from the core). The oxygen isotope composition of different olivine zones was determined in situ within separated olivine grains by secondary ion mass spectrometry (SIMS) after point selection using back-scattered electron (BSE) images combined with major and minor element analyses. With the exception of a few cores, the d18O values of different olivine zones do not deviate from typical mantle olivine values of 5.18?±?0.28‰ (Mattey et al., 1994). There are no correlations between oxygen isotopes and major/minor element compositions for internal zones and rims from individual localities or in the entire dataset. This indicates that the oxygen isotope composition of kimberlite melts is not affected by melt differentiation to the point of olivine rim crystallisation. However, olivine rinds from the Koala kimberlite (Canada) display an inverse correlation between d18O and Mn-Ca concentrations, with d18O values extending below the mantle range, which is probably due to carbonate fractionation, CO2 degassing and/or assimilation of serpentine-rich material after kimberlite emplacement in the upper crust. The mantle-like d18O composition of olivine internal zones and rims suggests that assimilation of mantle material and liberation of a CO2-rich phase during ascent in the mantle do not significantly modify the original d18O signature of kimberlite melts. Modelling of oxygen isotope fractionation shows that up to 15 wt% of CO2 can be lost by kimberlites en route to the upper crust. Our results combined with mass balance calculations indicate that only a limited amount (<5-10 wt%) of recycled crustal material could occur in the source of kimberlites from southern Africa, Lac de Gras and Alto Paranaiba, or that the recycled material had an oxygen isotope composition similar to the mantle.
DS201912-2785
2019
Giuliani, A., Pearson, D.G.Kimberlites: from deep Earth to diamond mines. An introduction.Elements, Vol. 15, 6, pp.Mantlediamond genesis
DS201901-0035
2017
Goes, S., Agrusta, R., van Hunen, J., Garel, F.Subduction - transition zone interaction: a review.Geosphere, Vol. 13, 3, pp. 644-664.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.
DS201910-2259
2019
Golovin, A.V., Sharygin, I., Korsakov, A.V., Kamenetsky, V.S., Abersteiner, A.Can primitive kimberlite melts be alkali-carbonate liquids: composition of the melt snapshots preserved in deepest mantle xenoliths.Journal of Raman Spectroscopy, in press available, 19p. PdfRussiadeposit - Udachnaya

Abstract: The study of kimberlite rocks is important as they provide critical information regarding the composition and dynamics of the continental mantle and are the principal source of diamonds. Despite many decades of research, the original compositions of kimberlite melts, which are thought to be derived from depths > 150 km, remain highly debatable due to processes that can significantly modify their composition during ascent and emplacement. Snapshots of the kimberlite-related melts were entrapped as secondary melt inclusions hosted in olivine from sheared peridotite xenoliths from the Udachnaya-East pipe (Siberian craton). These xenoliths originated from 180- to 220-km depth and are among the deepest derived samples of mantle rocks exposed at the surface. The crystallised melt inclusions contain diverse daughter mineral assemblages (>30 mineral species), which are dominated by alkali-rich carbonates, sulfates, and chlorides. The presence of aragonite as a daughter mineral suggests a high-pressure origin for these inclusions. Raman-mapping studies of unexposed inclusions show that they are dominated by carbonates (>65 vol.%), whereas silicates are subordinate (<13 vol.%). This indicates that the parental melt for the inclusions was carbonatitic. The key chemical features of this melt are very high contents of alkalis, carbon dioxide, chlorine, and sulfur and extremely low silica and water. Alkali-carbonate melts entrapped in xenolith minerals likely represent snapshots of the primitive kimberlite melt. This composition is in contrast with the generally accepted notion that kimberlites originated as ultramafic silicate water-rich melts. Experimental studies revealed that alkali-carbonate melts are a very suitable diamond-forming media. Therefore, our findings support the idea that some diamonds and kimberlite magmatism may be genetically related.
DS201905-1034
2019
Golovin, A.V., Sharygin, I.S., Kamenetsky, V.S., Korsakov, A.V., Yaxley, G.M.Alkali-carbonate melts from the base of cratonic lithospheric mantle: links to kimberlites.Chemical Geology, Vol. 483, pp. 261-274.Russia, Yakutiadeposit - Udachnaya -East

Abstract: Identification of the primary compositions of mantle-derived melts is crucial for understanding mantle compositions and physical conditions of mantle melting. However, these melts rarely reach the Earth's surface unmodified because of contamination, crystal fractionation and degassing, processes that occur almost ubiquitously after melt generation. Here we report snapshots of the melts preserved in sheared peridotite xenoliths from the Udachnaya-East kimberlite pipe, in the central part of the Siberian craton. These xenoliths are among the deepest mantle samples and were delivered by kimberlite magma from 180-230?km depth interval, i.e. from the base of the cratonic lithosphere. The olivine grains of the sheared peridotites contain secondary inclusions of the crystallized melt with bulk molar (Na?+?K)/Ca?~?3.4. Various Na-K-Ca-, Na-Ca-, Na-Mg-, Ca-Mg- and Ca-carbonates, Na-Mg-carbonates with additional anions, alkali sulphates and halides are predominant among the daughter minerals in secondary melt inclusions, whereas silicates, oxides, sulphides and phosphates are subordinate. These inclusions can be considered as Cl-S-bearing alkali-carbonate melts. The presence of aragonite, a high-pressure polymorph of CaCO3, among the daughter minerals suggests a mantle origin for these melt inclusions. The secondary melt inclusions in olivine from the sheared peridotite xenoliths and the melt inclusions in phenocrystic olivines from the host kimberlites demonstrate similarities, in daughter minerals assemblages and trace-element compositions. Moreover, alkali-rich minerals (carbonates, halides, sulphates and sulphides) identified in the studied melt inclusions are also present in the groundmass of the host kimberlites. These data suggests a genetic link between melt enclosed in olivine from the sheared peridotites and melt parental to the Udachnaya-East kimberlites. We suggest that the melt inclusions in olivine from mantle xenoliths may represent near primary, kimberlite melts. These results are new evidence in support of the alkali-carbonate composition of kimberlite melts in their source regions, prior to the kimberlite emplacement into the crust, and are in stark contrast to the generally accepted ultramafic silicate nature of parental kimberlite liquids.
DS201907-1546
2019
Gorce, J.S., Caddick, M.J., Bodnar, R.J.Thermodynamic contraints on carbonate stability and carbon volatility during subduction.Earth and Planetary Science Letters, Vol. 519, pp. 213-222.Mantlecarbon cycle

Abstract: The breakdown of carbonate minerals at high pressure is frequently cited as an important mechanism that leads to carbon release from subducted rocks. However, carbonate minerals in the subducting slab are predicted to be stable to depths that are greater than arc-generating magma depths of approximately 150 km, implying that breakdown of carbonate phases in dehydrated MORB may not be a major contributor to arc volcano carbon budgets. To account for this discrepancy, previous studies have suggested that addition of H2O-rich fluids promotes the breakdown of carbonate-rich lithologies, thus generating volatile C species that could be incorporated into arc magmas. Here, we explore the feasibility of H2O-mediated decarbonation with a simple thermodynamic model. We calculate equilibrium mineral assemblages and accompanying fluid H2O/CO2 ratios for typical subducted lithologies, assuming a range of subduction zone geotherms, and explore the implications of addition of external fluids that are generated from deserpentinization of ultramafic lithologies at various stages. Results suggest that the liberation of C along volcanic arcs is facilitated by either the breakdown of carbonate minerals due to thermodynamically favorable conditions in hotter subduction systems, or by the breakdown of carbonate minerals during periods of higher fluid productivity associated with deserpentinization at appropriate depths along colder subduction geotherms. A comparison of C fluxes measured at volcanic arcs shows that colder subduction zones generate higher C fluxes, implying that the depth at which deserpentinization reactions occur strongly controls the availability of aqueous fluids for slab decarbonation, and that fluid availability represents the dominant control on carbon volatility during subduction.
DS201901-0036
2018
Gorczyk, W., Mole, D.R., Barnes, S.J.Plume lithosphere interaction at craton margins throughout Earth history.Tectonophysics, Vol. 746, pp. 678-694.Mantlecraton

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.
DS201911-2528
2019
Goss, H.This is how the world moves.EOS, 100, doi.org/10.1029/2019EO134611Globalgeophysics
DS201912-2786
2019
Gostlin, K., Brenton, K., Liu, W., Clark, L.Gahcho Kue mine update.Yellowknife Forum NWTgeoscience.ca, abstract volume p. 57.Canada, Northwest Territoriesdeposit - Gahcho Kue

Abstract: Gahcho Kué Mine is owned as a joint venture between Mountain Province Diamonds Inc. and De Beers Canada Inc. Located about 280 km northeast of Yellowknife, it is Canada’s newest diamond mine and the world’s largest in the last 14 years. After two years of construction, commercial operations began in September 2016. As the mine enters into its fourth year of operation, De Beers is pleased to provide an update on the current mine operations, updated mine plan, safety, environment, and social performance.
DS201906-1296
2019
Gouza, M., Paton, D.A.The role of inherited lithospheric heterogeneities in defining the crustal architecture of rifted margins and the magmatic budget during continental breakup.Geochemistry, Geophysics, Geosystems, Vol. 20, 4, pp. 1836-1853.Mantlemagmatism

Abstract: During the final stage of continental rifting, stretching localizes in the future distal domain where lithospheric necking occurs resulting in continental breakup. In magma-poor margins, the lithospheric necking is accompanied by crustal hyperextension, serpentinization, and exhumation of mantle lithosphere in the continent-ocean transition domain. In magma-rich margins, the necking is accomplished by the emplacement of large amounts of volcanics in the continental-ocean transition, in the form of seaward dipping wedges of flood basalts (seaward dipping reflections). This study examines the factors controlling the final crustal architecture observed in rifted margins and the magmatic budget during continental breakup, using observations from the Labrador Sea. The latter shows magma-rich breakup with seaward dipping reflections documented in the north and magma-poor breakup with a wide domain of exhumed serpentinized mantle recorded in the south. The pre-rift strength of the lithosphere, defined by the inherited thermal structure, composition, and thickness of the lithospheric layers, controls the structural evolution during rifting. While variations in the magmatic budget associated with breakup are controlled primarily by the interaction between the pre-rift inheritance, the timing and the degree of mantle melting, in relation to lithospheric thinning and mantle hydration.
DS201910-2260
2019
Graf, C., Sandner, T., Woodland, A., Hofer, H., Seitz, H-M., Pearson, G., Kjarsgaard, B.Metasomatism, oxidation state of the mantle beneath the Rae craton, Canada.Goldschmidt2019, 1p. AbstractCanadacraton

Abstract: The Rae craton is an important part of the Canadian Shield and was amalgamated to the Slave craton at ?? 1.9 Ga [1]. Recent geophysical and geochemical data indicate a protracted geodynamic history [1, 2]. Even though the oxidation state of the Earth’s mantle has an important influence of fluid compositions and melting behavior, no data on the oxidation state of the Rae’s mantle are available. The aims of this study were to 1) determine the oxidation state (ƒO2) of the lithosphere beneath the Rae craton, 2) link these results to potential metasomatic overprints and 3) compare the geochemical evolution with the Slave craton. We studied 5 peridotite xenoliths from Pelly Bay (central craton) and 22 peridotites from Somerset Island (craton margin). Pelly Bay peridotites give T < 905°C and depths of ??80- 130 km. Garnets have depleted or “normal” REE patterns, the latter samples recording fO2 values ??0.5 log units higher. The deeper samples are more enriched and oxidised. Peridotites from Somerset Island record T ??825-1190°C, a ?logfO2 ranging from ?? FMQ - FMQ-3.6 from a depth interval of ??100-150 km. Garnets exhibit two REE signatures - sinusoidal and “normal” - indicating an evolutionary sequence of increasing metasomatic re-enrichment and a shift from fluid to melt dominated metasomatism. Compared to the Slave craton, the Rae mantle is more reduced at ??80km but becomes up to 2 log units more oxidised (up to ??FMQ-1) at ??100-130 km. Similar oxidising conditions can be found >140 km in the Slave mantle [3]. Especially under Somerset Island, the lithospheric mantle has contrasting fO2 and metasomatic overprints in the same depth range, which may represent juxtaposed old and rejuvenated domains [2].
DS201901-0037
2018
Grantham, G., Eglinton, B., Macey, P.H., Ingram,B., Radeneyer, M., Kaiden, H., Manhica, V.The chemistry of Karoo age andesitic lavas along the northern Mozambique coast, southern Africa and possible implications for Gondwana breakup.South African Journal of Geology, Vol. 121, pp. 271-286.Africa, Mozambiquegeodynamics

Abstract: Major, trace, radiogenic isotope and stable isotope data from lavas along the northeastern coast of Mozambique are described. The whole rock composition data demonstrate that the rocks are dominantly andesitic with compositions typical of calc-alkaline volcanic rocks from arc environments. SHRIMP U/Pb data from zircons indicate that the zircons are xenocrystic, having ages of between 500 Ma and 660 Ma, with the age of the lava constrained by Rb/Sr data at ~184 Ma. Strontium, Nd and Pb radiogenic isotope data support an interpretation of extensive mixing between a Karoo age basaltic magma (dolerite) from Antarctica and continental crust similar in composition to the Mozambique basement. Oxygen isotope data also imply a significant crustal contribution to the lavas. Possible tectonic settings for the lavas are at the margin of a plume or from a locally restricted compressional setting during Gondwana breakup processes.
DS201903-0513
2018
Greaux, S., Yamada, A.Density variations of Cr-rich garnets in the upper mantle inferred from the elasticity of uvarovite garnet.Comptes Rendu Geoscience, doi.org/10.16/ j.crte.2018.09.012 9p.MantleUHP

Abstract: The thermoelastic parameters of Ca3Cr2Si3O12 uvarovite garnet were examined in situ at high pressure up to 13 GPa and high temperature up to 1100 K by synchrotron radiation energy-dispersive X-ray diffraction within a 6-6-type multi-anvil press apparatus. A least-square fitting of room T data to a third-order Birch-Murnaghan (BM3) EoS yielded K0 = 164.2 ± 0.7 GPa, V0 = 1735.9 ± 0.3 Å3 (K’0 fixed to 4.0). P-V-T data were fitted simultaneously by a modified HT-BM3 EoS, which gave the isothermal bulk modulus K0 = 163.6 ± 2.6 GPa, K’0 = 4.1 ± 0.5, its temperature derivative (?K0,T/?T)P = -0.014 ± 0.002 GPa K-1, and the thermal expansion coefficients a0 = 2.32 ± 0.13 ×10-5 K-1 and b0 = 2.13 ± 2.18 ×10-9 K-2 (K’0 fixed to 4.0). Our results showed that the Cr3+ enrichment in natural systems likely increases the density of ugrandite garnets, resulting in a substantial increase of mantle garnet densities in regions where Cr-rich spinel releases chromium through a metasomatic reaction.
DS201905-1035
2019
Greaux, S., Yamada, A.Density variations of Cr-rich garnets in the upper mantle inferred from the elasticity of uvarovite garnet.Comptes Rendus Geoscience, in press available 9p.Mantlegarnets

Abstract: The thermoelastic parameters of Ca3Cr2Si3O12 uvarovite garnet were examined in situ at high pressure up to 13 GPa and high temperature up to 1100 K by synchrotron radiation energy-dispersive X-ray diffraction within a 6-6-type multi-anvil press apparatus. A least-square fitting of room T data to a third-order Birch-Murnaghan (BM3) EoS yielded K0 = 164.2 ± 0.7 GPa, V0 = 1735.9 ± 0.3 Å3 (K’0 fixed to 4.0). P-V-T data were fitted simultaneously by a modified HT-BM3 EoS, which gave the isothermal bulk modulus K0 = 163.6 ± 2.6 GPa, K’0 = 4.1 ± 0.5, its temperature derivative (?K0,T/?T)P = -0.014 ± 0.002 GPa K-1, and the thermal expansion coefficients a0 = 2.32 ± 0.13 ×10-5 K-1 and b0 = 2.13 ± 2.18 ×10-9 K-2 (K’0 fixed to 4.0). Our results showed that the Cr3+ enrichment in natural systems likely increases the density of ugrandite garnets, resulting in a substantial increase of mantle garnet densities in regions where Cr-rich spinel releases chromium through a metasomatic reaction.
DS201910-2261
2019
Gress, M.U., Smit, K.V., Chinn, I., Wang, W., Davies, G.R., Kornneef, J.M.Spectroscopic characteristics of Botswanan diamonds and their potential relationship with age.De Beers Diamond Conference, Not availableAfrica, Botswanadiamond growth zones
DS201905-1036
2019
Grewal, D.S., Dasgupta, R., Holems, A.K., Costin, G., Li, Y., Tsuno, K.The fate of nitrogen during core-mantle separation on Earth.Geochimica et Cosmochimica Acta, Vol. 251, pp. 87-115.Mantlenitrogen

Abstract: Nitrogen, the most dominant constituent of Earth’s atmosphere, is critical for the habitability and existence of life on our planet. However, its distribution between Earth’s major reservoirs, which must be largely influenced by the accretion and differentiation processes during its formative years, is poorly known. Sequestration into the metallic core, along with volatility related loss pre- and post-accretion, could be a critical process that can explain the depletion of nitrogen in the Bulk Silicate Earth (BSE) relative to the primitive chondrites. However, the relative effect of different thermodynamic parameters on the alloy-silicate partitioning behavior of nitrogen is not well understood. Here we present equilibrium partitioning data of N between alloy and silicate melt () from 67 new high pressure (P?=?1-6?GPa)-temperature (T?=?1500-2200?°C) experiments under graphite saturated conditions at a wide range of oxygen fugacity (logfO2?~??IW -4.2 to -0.8), mafic to ultramafic silicate melt compositions (NBO/T?=?0.4 to 2.2), and varying chemical composition of the alloy melts (S and Si contents of 0-32.1?wt.% and 0-3.1?wt.%, respectively). Under relatively oxidizing conditions (~?IW -2.2 to -0.8) nitrogen acts as a siderophile element ( between 1.1 and 52), where decreases with decrease in fO2 and increase in T, and increases with increase in P and NBO/T. Under these conditions remains largely unaffected between S-free conditions and up to ~17?wt.% S content in the alloy melt, and then drops off at >~20?wt.% S content in the alloy melt. Under increasingly reduced conditions (<~?IW -2.2), N becomes increasingly lithophile ( between 0.003 and 0.5) with decreasing with decrease in fO2 and increase in T. At these conditions, fO2 along with Si content of the alloy under the most reduced conditions (<~?IW -3.0), is the controlling parameter with T playing a secondary role, while, P, NBO/T, and S content of the alloy have minimal effects. A multiple linear least-squares regression parametrization for based on the results of this study and previous studies suggests, in agreement with the experimental data, that fO2 (represented by Si content of the alloy melt and FeO content of the silicate melt), followed by T, has the strongest control on . Based on our modeling, to match the present-day BSE N content, impactors that brought N must have been moderately to highly oxidized. If N bearing impactors were reduced, and/or there was significant disequilibrium core formation, then the BSE would be too N-rich and another mechanism for N loss, such as atmospheric loss, would be required.
DS201904-0741
2019
Grewal, D.S., Dasgupta, R., Holmes, A.K., Costin, G., Li, Y., Tsuno, K.The fate of nitrogen during core-mantle seperation on Earth.Geochimica et Cosmochimica Acta, Vol. 251. pp. 87-115.Mantlenitrogen

Abstract: Nitrogen, the most dominant constituent of Earth’s atmosphere, is critical for the habitability and existence of life on our planet. However, its distribution between Earth’s major reservoirs, which must be largely influenced by the accretion and differentiation processes during its formative years, is poorly known. Sequestration into the metallic core, along with volatility related loss pre- and post-accretion, could be a critical process that can explain the depletion of nitrogen in the Bulk Silicate Earth (BSE) relative to the primitive chondrites. However, the relative effect of different thermodynamic parameters on the alloy-silicate partitioning behavior of nitrogen is not well understood. Here we present equilibrium partitioning data of N between alloy and silicate melt () from 67 new high pressure (P?=?1-6?GPa)-temperature (T?=?1500-2200?°C) experiments under graphite saturated conditions at a wide range of oxygen fugacity (logfO2?~??IW -4.2 to -0.8), mafic to ultramafic silicate melt compositions (NBO/T?=?0.4 to 2.2), and varying chemical composition of the alloy melts (S and Si contents of 0-32.1?wt.% and 0-3.1?wt.%, respectively). Under relatively oxidizing conditions (~?IW -2.2 to -0.8) nitrogen acts as a siderophile element ( between 1.1 and 52), where decreases with decrease in fO2 and increase in T, and increases with increase in P and NBO/T. Under these conditions remains largely unaffected between S-free conditions and up to ~17?wt.% S content in the alloy melt, and then drops off at >~20?wt.% S content in the alloy melt. Under increasingly reduced conditions (<~?IW -2.2), N becomes increasingly lithophile ( between 0.003 and 0.5) with decreasing with decrease in fO2 and increase in T. At these conditions, fO2 along with Si content of the alloy under the most reduced conditions (<~?IW -3.0), is the controlling parameter with T playing a secondary role, while, P, NBO/T, and S content of the alloy have minimal effects. A multiple linear least-squares regression parametrization for based on the results of this study and previous studies suggests, in agreement with the experimental data, that fO2 (represented by Si content of the alloy melt and FeO content of the silicate melt), followed by T, has the strongest control on . Based on our modeling, to match the present-day BSE N content, impactors that brought N must have been moderately to highly oxidized. If N bearing impactors were reduced, and/or there was significant disequilibrium core formation, then the BSE would be too N-rich and another mechanism for N loss, such as atmospheric loss, would be required.
DS201902-0274
2019
Grewal, D.S., Dasgupta, R., Sun, C., Tsuno, K., Costin, G.Delivery of carbon, nitrogen, and sulfur to the silicate Earth by a giant impact.Science Advances, Vol. 5, 1, Jan. 23, 10.1126/sciadv.aau3669 13p.Mantlecrater

Abstract: Earth’s status as the only life-sustaining planet is a result of the timing and delivery mechanism of carbon (C), nitrogen (N), sulfur (S), and hydrogen (H). On the basis of their isotopic signatures, terrestrial volatiles are thought to have derived from carbonaceous chondrites, while the isotopic compositions of nonvolatile major and trace elements suggest that enstatite chondrite-like materials are the primary building blocks of Earth. However, the C/N ratio of the bulk silicate Earth (BSE) is superchondritic, which rules out volatile delivery by a chondritic late veneer. In addition, if delivered during the main phase of Earth’s accretion, then, owing to the greater siderophile (metal loving) nature of C relative to N, core formation should have left behind a subchondritic C/N ratio in the BSE. Here, we present high pressure-temperature experiments to constrain the fate of mixed C-N-S volatiles during core-mantle segregation in the planetary embryo magma oceans and show that C becomes much less siderophile in N-bearing and S-rich alloys, while the siderophile character of N remains largely unaffected in the presence of S. Using the new data and inverse Monte Carlo simulations, we show that the impact of a Mars-sized planet, having minimal contributions from carbonaceous chondrite-like material and coinciding with the Moon-forming event, can be the source of major volatiles in the BSE.
DS201902-0275
2018
Griffin, W.L., Gain, S.E.M., Bindi, L., Toledo, V., Camara, F., Saunders, M., O'Reilly, S.Y.Carmeltazite, ZrAl2Ti4011, a new mineral trapped in corundum from volcanic rocks of Mt Carmel, northern Israel.Minerals ( mdpi.com), Vol. 8, 12, 11p. PdfEurope, Israelmineralogy

Abstract: The new mineral species carmeltazite, ideally ZrAl2Ti4O11, was discovered in pockets of trapped melt interstitial to, or included in, corundum xenocrysts from the Cretaceous Mt Carmel volcanics of northern Israel, associated with corundum, tistarite, anorthite, osbornite, an unnamed REE (Rare Earth Element) phase, in a Ca-Mg-Al-Si-O glass. In reflected light, carmeltazite is weakly to moderately bireflectant and weakly pleochroic from dark brown to dark green. Internal reflections are absent. Under crossed polars, the mineral is anisotropic, without characteristic rotation tints. Reflectance values for the four COM wavelengths (Rmin, Rmax (%) (? in nm)) are: 21.8, 22.9 (471.1); 21.0, 21.6 (548.3), 19.9, 20.7 (586.6); and 18.5, 19.8 (652.3). Electron microprobe analysis (average of eight spot analyses) gave, on the basis of 11 oxygen atoms per formula unit and assuming all Ti and Sc as trivalent, the chemical formula (Ti3+3.60Al1.89Zr1.04Mg0.24Si0.13Sc0.06Ca0.05Y0.02Hf0.01)S=7.04O11. The simplified formula is ZrAl2Ti4O11, which requires ZrO2 24.03, Al2O3 19.88, and Ti2O3 56.09, totaling 100.00 wt %. The main diffraction lines, corresponding to multiple hkl indices, are (d in Å (relative visual intensity)): 5.04 (65), 4.09 (60), 2.961 (100), 2.885 (40), and 2.047 (60). The crystal structure study revealed carmeltazite to be orthorhombic, space group Pnma, with unit-cell parameters a = 14.0951 (9), b = 5.8123 (4), c = 10.0848 (7) Å, V = 826.2 (1) Å3, and Z = 4. The crystal structure was refined to a final R1 = 0.0216 for 1165 observed reflections with Fo > 4s(Fo). Carmeltazite exhibits a structural arrangement similar to that observed in a defective spinel structure. The name carmeltazite derives from Mt Carmel (“CARMEL”) and from the dominant metals present in the mineral, i.e., Titanium, Aluminum and Zirconium (“TAZ”). The mineral and its name have been approved by the IMA Commission on New Minerals, Nomenclature and Classification (2018-103).
DS201903-0514
2019
Griffin, W.L., Gain, S.E.M., Huang, J-X., Saunders, M., Shaw, J., Toledo, V., O'Reilly, S.Y.A terrestrial magmatic hibonite-grossite-vanadium assemblage: desilication and extreme reduction in a volcanic plumbing system, Mount Carmel, Israel.American Mineralogist, Vol. 104, pp. 207-219.Europe, Israelmelting

Abstract: Hibonite (CaAl12O19) is a constituent of some refractory calcium-aluminum inclusions (CAIs) in carbonaceous meteorites, commonly accompanied by grossite (CaAl4O7) and spinel. These phases are usually interpreted as having condensed, or crystallized from silicate melts, early in the evolution of the solar nebula. Both Ca-Al oxides are commonly found on Earth, b