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Sheahan Diamond Literature Technical Reference Compilation 2020


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.
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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.
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Monthly Sheahan Diamond Newsletters for 2020
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April 2020 August 2020 December 2020
2020 Technical Reference Compilation
Posted/
Published
AuthorTitleSourceRegionKeywords
DS202005-0717
2020
Abdel Halim, A.H., Helmy, H.H., Elhaddad, M.A., El-Mahallawi, M., Mogessie, A.Petrology of a Neoproteroxoic mantle peridotite-chromitite association from Abu Dahr area, eastern Egypt Desert, Egypt: infiltration of boninitic melt in highly depleted harzburgite.Journal of African Earth Sciences, Vol. 165, 18p. PdfAfrica, EgyptBoninite

Abstract: Peridotites of Abu Dahr represent the main litho-unit of a Neoproterozoic dismembered ophiolite sequence and are among the best-preserved and well-exposed mantle rocks in South Eastern Desert of Egypt. Here, we present new geochemical and mineral chemical data for peridotites and associated pyroxenites and for chromitites and their platinum-group minerals to constrain their petrogenesis and geotectonic setting. The Abu Dahr ophiolite mantle section consists mainly of harzburgites, cut by pyroxenite dykes and containing dunite-chromitite lenses. The harzburgites are composed of olivine, orthopyroxene, spinel and minor clinopyroxene (?1.0 vol %) and amphibole. Olivine from harzburgites is highly magnesian (Fo 91-93) and Cr-spinel shows a wide-range of Cr2O3 and Al2O3 contents. The enstatite component of orthopyroxene decreases from harzburgite (En = 90-91) to orthopyroxenite (En = 84-87). Amphiboles are represented by magnesiohornblende and tschermakite. The chromitites are massive to disseminated and composed of magnesiochromite with high Cr# (83-93) and Mg# (66-79), and low TiO2 (<0.1 wt%) content. Solid inclusions in chromite include olivine, orthopyroxene and hornblende. Laurite (RuS2) is the most common PGM detected in the investigated chromitite samples and forms micrometer-size inclusions in fresh chromite. Various Ni-sulfides are found both in fresh chromite and along serpentine veinlets. Harzburgites have a refractory composition with a very low Al2O3 (0.4-0.8 wt%) and CaO (0.2-1.6 wt%) contents and high bulk-rock Mg# (89-92). Geochemical data suggest that the Abu Dahr peridotites are highly depleted SSZ peridotites formed in a forearc mantle wedge setting by high degrees of hydrous partial melting and emplaced as a result of the collision of the intra-oceanic arc with the Beitan gneisses. The podiform chromitites and orthopyroxenites were formed due to impregnation of mantle wedge harzburgites by boninitic melt. The highly depleted nature of the harzburgite is responsible for the small reserves of chromite ore at Abu Dahr and in the South Eastern Desert in general.
DS202007-1120
2020
Abe, N., Surour, A.A., Madani, A.A., Arai, S.Metasomatized peridotite xenoliths from the Cretaceous rift related Natash volcanics and their bearing on the nature of the lithospheric mantle beneath the southern part of the eastern desert of Egypt.Lithos, in press available , 47p. PdfAfrica, Asia, Egyptperidotites

Abstract: Highly carbonated mantle xenoliths have been found in rift-related alkaline basalts at the Wadi Natash area in the southern part of the Eastern Desert of Egypt. Although all olivine and most orthopyroxene was replaced by carbonate and/or quartz, textural and mineral chemical features show that they are plagioclase-free spinel peridotites (lherzolite to harzburgite). Cr and Mg numbers (Cr#, Mg#) of Cr-spinel vary from 0.06 to 0.45 and 0.73 to 0.81, respectively. The correlation between Cr# and Mg# of the Cr-spinel in the studied xenoliths is weakly negative and its TiO2 content is slightly higher than in abyssal peridotite that was not affected by melt injection. The chemistry of ortho- and clinopyroxene suggests enstatite and chromian diopside compositions, respectively, with distinct signatures of a sub-continental mantle source. In particular, the Na2O contents (>1.0?wt%) and AlVI/AlIV ratios (1.2-2.6) of chromian diopside suggest such an origin. Two-pyroxene geothermometry indicates a temperature of about 900?°C, which is slightly lower than that of ordinary spinel peridotite xenoliths from other rift zones. It is evident that the studied peridotite xenoliths had experienced mantle processes (e.g. decompression melting, magma upwelling and metasomatism) at higher pressure than abyssal peridotites. The trace-element chemistry of clinopyroxene, e.g. high LREE/HREE ratios {(Ce/Yb)n?=?7}, high LREE contents (>3.6?ppm and up to 30.0?ppm Ce) and high Sr between >85.6?ppm and 466?ppm, indicates metasomatic alteration of the peridotite. Clinopyroxene in one sample has very low Ti/Eu and high LREE/HREE ratios. Clinopyroxene with (Ce/Yb)n higher than 3-4 and Ti/Eu ratio lower than 1500 may have experienced carbonatite or carbonate-rich melt metasomatism prior to their incorporation into the host basalt. The basalt itself is almost devoid of any carbonatization and hence the studied mantle peridotites were carbonatized before the generation of the basaltic magma but following an earlier event of K-metasomatism as indicated by the presence of phlogopite. The studied peridotites from the Wadi Natash area were altered by a carbonate-rich melt during a rifting stage. The results of the present paper indicate that the Natash basalts with their peridotite xenoliths extruded along transversal fractures of the NW-trending Nuqra-Kom Ombo-Kharit continental rift on its western shoulder in the south Eastern Desert of Egypt.
DS202003-0329
2020
Abersteiner, A., Kamenetsky, V.S., Goemann, K.A genetic study of olivine crystallization in the Mark kimberlite ( Canada) revealed by zoning and melt inclusions.Lithos, In press available 46p. pdf.Canada, Northwest Territoriesdeposit - Mark

Abstract: Elucidating the composition of primary kimberlite melts is essential to understanding the nature of their source, petrogenesis, rheology, transport and ultimately the origin of diamonds. Kimberlite rocks are typically comprised of abundant olivine (~2560 vol%), which occurs as individual grains of variable size and morphology, and includes xenocrysts and zoned phenocrysts. Zoning patterns and inclusions in olivine can be used to decipher the petrogenetic history of kimberlites, starting from their generation in the mantle through to emplacement in the crust. This study examines well-preserved, euhedral, zoned olivine crystals from the Mark kimberlite (Lac de Gras, Canada). Olivine typically consists of xenocrystic cores, which are homogeneous in composition but vary widely between grains (Fo88.193.6). These cores are in turn surrounded by (in order of crystallisation) magmatic rims and Mg-rich rinds (Fo95.398.1). In addition, we document a new type of olivine zone (‘outmost rind’) that overgrows Mg-rich rinds. Crystal and melt/fluid inclusions are abundant in olivine and preserve a record of kimberlite melt evolution. For the first time in the studies of kimberlite olivine, we report primary melt inclusions hosted in Mg-rich olivine rinds. In addition, we observe that pseudosecondary melt/fluid inclusions are restricted to interior olivine zones (cores, rims) and are considered to have formed prior to rind formation. Pseudosecondary melt/fluid inclusions are inferred to have been entrapped at depth, as evidenced by measured densities in thermometric experiments of CO2 and decrepitation haloes, indicating a minimum entrapment pressure of ~200450 MPa (or ~615 km). Both primary and pseudosecondary melt inclusions in olivine have daughter minerals dominated by CaMg and K-Na-Ba-Sr-bearing carbonates, K-Na-chlorides along with subordinate silicates (e.g., phlogopite, monticellite), Fe-Mg-Al-Ti-spinel, perovskite, phosphates and sulphates/sulphides and periclase. In addition to phases reported in primary melt inclusions, pseudosecondary melt inclusions contain more diverse and exotic daughter mineral assemblages, where they contain phases such as tetraferriphlogopite Ba- or K-sulphates, kalsilite and Na-phosphates. The daughter mineral assemblages are consistent with a silica-poor, alkali dolomitic carbonatite melt. We demonstrate that the different types of inclusions in olivine can assist in constraining the timing of multi-stage olivine growth and the composition of the crystallising melt. The large variance in olivine zoning patterns, morphologies and Ni distribution (i.e. both coupling with and decoupling from Fo) indicates that olivine in the studied Mark kimberlite samples represent an accumulation of olivine, where olivine was derived from successive stages of the ascending magma and/or from multiple, but related pulses of magma. Primary and pseudosecondary melt/fluid inclusions in olivine indicate that a variably differentiated silica-poor, halogen-bearing, alkali-dolomitic melt crystallised and transported olivine in the Mark kimberlite.
DS202008-1365
2020
Abersteiner, A., Kamenetsky, V.S., Goemann, K., Kjarsgaard, B.A., Fedortchouk, Y., Ehrig, K., Kamenetsky, M.Evolution of kimberlite magmas in the crust: a case study of groundmass and mineral hosted inclusions in the Mark kimberlite ( Lac de Gras, Canada).Lithos, in press available, 55p. PdfCanada, Northwest Territoriesdeposit - Mark

Abstract: Kimberlites are the surface manifestation of deeply-derived (>150 km) and rapidly ascended magmas. Fresh kimberlite rocks are exceptionally rare, as most of them are invariably modified by pervasive deuteric and/or post-magmatic fluids that overprint the original mineralogy. In this study, we examined fresh archetypal kimberlite from the Mark pipe (Lac de Gras, Canada), which is characterised by well-preserved olivine and groundmass minerals. The sequence of crystallisation of the parental melt and its major compositional features, including oxygen fugacity, were reconstructed using textural relationships between magmatic minerals, their zoning patterns and crystal/melt/fluid inclusions. Crystal and multiphase primary, pseudosecondary and secondary melt/fluid inclusions in olivine, Cr-diopside, spinel, perovskite, phlogopite/kinoshitalite, apatite and calcite preserve a record of different stages of kimberlite melt evolution. Melt/fluid inclusions are generally more depleted in silica and more enriched in alkalis (K, Na), alkali-earth (Ba, Sr) and halogens (Cl, F) relative to the whole-rock composition of the Mark kimberlite. These melt/fluid inclusion compositions, in combination with presence of elevated CaO (up to 1.73 wt%), in Mg-rich olivine rinds, crystallisation of groundmass kinoshitalite, carbonates (calcite, Sr-Ba-bearing) and alkali-enriched rims around apatite suggest that there was progressive enrichment in CO2, alkalis and halogens in the evolving parental melt. The Mark kimberlite groundmass is characterised by the following stages of in-situ crystallisation: (1) olivine rims around xenocrystic cores + Cr-spinel/TIMAC. (2) Mg-rich olivine rinds around olivine rims/cores + MUM-spinel (followed by pleonaste and Mg-magnetite) + monticellite (+ partial resorption of olivine, along with the formation of ferropericlase and CO2 as a result of decarbonation reactions) + perovskite + apatite. (3) Olivine outmost rinds, which are coeval with phlogopite/kinoshitalite + apatite + sulphides + carbonate (calcite, Ba-Sr-Na-bearing varieties). In addition, oxygen fugacity of the Mark kimberlite was constrained by olivine-chromite, perovskite and monticellite oxygen barometry and showed that the parental melt became progressively more oxidised in response to fractional crystallisation. (4) Deuteric (i.e. late-stage magmatic) and/or post-magmatic (i.e. external fluids) alteration of magmatic minerals (e.g., olivine, monticellite, ferropericlase) and crystallisation of mesostasis serpentine, K-bearing chlorite and brucite (i.e. replacement of ferropericlase). The absence of any alkali (Na, K) and halogen (F, Cl) rich groundmass minerals in the Mark kimberlite may be attributed to these elements becoming concentrated in the late-stage melt where they potentially formed unstable, water-soluble carbonates (such as those observed in melt inclusions). Consequently, these minerals were most likely removed from the groundmass by deuteric and/or post-magmatic alteration.
DS202007-1121
2020
Abramov, S.S., Rass, I.T., Kononkova, N.N.Fenites of the Miaskite carbonatite complex in the Vishnevye Mountains, southern Urals, Russia: origin of the metasomatic zoning and thermodynamic simulations of the processes.Petrology, Vol. 28, 3, pp. 298-323. pdfRussia, Uralscarbonatite

Abstract: Mineral zoning in fenites around miaskite intrusions of the Vishnevye Mountains complex can be interpreted as a magmatic-replacement zonal metasomatic aureole (in D.S. Korzhinskii’s understanding): the metasomatic transformations of the fenitized gneisses under the effect of deep alkaline fluid eventually resulted in the derivation of nepheline syenite eutectic melt. Based on the P-T-fO2 parameters calculated from the composition of minerals coexisting in the successive zones, isobaric-isothermal fO2-aSiO2 and µNa2O-µAl2O3 sections were constructed with the Perplex program package to model how the fenites interacted with H2O-CO2 fluid (in the Na-K-Al-Si-Ca-Ti-Fe-Mg-O-H-C system). The results indicate that the fluid-rock interaction mechanisms are different in the outer (fenite) and inner (migmatite) parts of the zonal aureole. Its outer portion was dominated by desilication of rocks, which led, first, to quartz disappearance from these rocks and then to an increase in the Al# of the coexisting minerals (biotite and clinopyroxene). In the inner part of the aureole, fenite transformations into biotite-feldspathic metasomatic rocks and nepheline migmatite were triggered by an increase in the Na and Al activities in the system alkaline H2O-CO2 fluid-rock. As a consequence, the metasomatites were progressively enriched in Al2O3 and alkalis, and these transformations led to the development of biotite in equilibrium with K-Na feldspar and calcite at the sacrifice of pyroxene. The further introduction of alkalis led to the melting of the biotite-feldspathic metasomatites and the origin of nepheline migmatites. The simulated model sequence of metasomatic zones that developed when the gneiss was fenitized and geochemical features of the successive zones (differences in the LILE and REE concentrations in the rocks and minerals of the fenitization aureole and the Sm-Nd isotope systematics of the rocks of the alkaline complex) indicate that the source of the fluid responsible for the origin of zonal fenite-miaskite complexes may have been carbonatite, a derivative of mantle magmas, whereas the miaskites were produced by metasomatic transformations of gneisses and subsequent melting under the effect of fluid derived from carbonatite magmas.
DS202010-1824
2020
Abramov, S.S., Rass, I.T., Kononkova, N.N.Fenites of the Miasite-carbonatite complex in the Vishevye Mountains, southern Urals, Russia: origin of the metasomatic zoning and thermodynamic simulations of the processes.Petrology, Vol. 28, 3, pp. 263-286.Russia, Uralscarbonatite

Abstract: Mineral zoning in fenites around miaskite intrusions of the Vishnevye Mountains complex can be interpreted as a magmatic-replacement zonal metasomatic aureole (in D.S. Korzhinskii’s understanding): the metasomatic transformations of the fenitized gneisses under the effect of deep alkaline fluid eventually resulted in the derivation of nepheline syenite eutectic melt. Based on the P-T-fO2 parameters calculated from the composition of minerals coexisting in the successive zones, isobaric-isothermal fO2-aSiO2 and µNa2O-µAl2O3 sections were constructed with the Perplex program package to model how the fenites interacted with H2O-CO2 fluid (in the Na-K-Al-Si-Ca-Ti-Fe-Mg-O-H-C system). The results indicate that the fluid-rock interaction mechanisms are different in the outer (fenite) and inner (migmatite) parts of the zonal aureole. Its outer portion was dominated by desilication of rocks, which led, first, to quartz disappearance from these rocks and then to an increase in the Al# of the coexisting minerals (biotite and clinopyroxene). In the inner part of the aureole, fenite transformations into biotite-feldspathic metasomatic rocks and nepheline migmatite were triggered by an increase in the Na and Al activities in the system alkaline H2O-CO2 fluid-rock. As a consequence, the metasomatites were progressively enriched in Al2O3 and alkalis, and these transformations led to the development of biotite in equilibrium with K-Na feldspar and calcite at the sacrifice of pyroxene. The further introduction of alkalis led to the melting of the biotite-feldspathic metasomatites and the origin of nepheline migmatites. The simulated model sequence of metasomatic zones that developed when the gneiss was fenitized and geochemical features of the successive zones (differences in the LILE and REE concentrations in the rocks and minerals of the fenitization aureole and the Sm-Nd isotope systematics of the rocks of the alkaline complex) indicate that the source of the fluid responsible for the origin of zonal fenite-miaskite complexes may have been carbonatite, a derivative of mantle magmas, whereas the miaskites were produced by metasomatic transformations of gneisses and subsequent melting under the effect of fluid derived from carbonatite magmas.
DS202005-0718
2020
Afanasiev, V.P., Pokhilenko, N.P., Egorova, E.O., Lindenblot, E.S.The most ancient diamond crystals of the Siberian platform. Lamproites Morgogor Creek .. Ebelyakh River.Doklady Earth Sciences, Vol. 489, 2, pp. 1409-1412. pdf Russia, Siberiadiamond alluvials

Abstract: Based on a study of diamond grains from placers of the northeastern Siberian Platform, it is shown that certain types of diamonds (rounded dodecahedroids, diamonds of the II and V?VII varieties, according to the classification by Yu.L. Orlov) could have originated from Precambrian sources. “Ancient” diamonds also differ in terms of their sedimentological history: those of varieties V?VII, despite the maximum abrasion resistance, have the maximum degree of rounding, reflecting their more long-term sedimentological history, and, therefore, their ore bodies were likely the most ancient.
DS202006-0908
2020
Afanasiev, V.P., Pokhilenko, N.P., Grinenko, V.S., Kostin, A.V., Malkovets, V.G., Oleinikov, O.B.Kimberlitic magmatism in the south western flank of the Vilui basin. ( pyrope from Kenkeme River catchment) Jurassic-Cretaceous barren kimberlites.Doklady Earth Science, Vol. 490, 2, pp. 51-54.Russiageochronology

Abstract: We have analyzed 141 grains of pyrope from Neogene sediments in a quarry of construction materials, in the Kenkeme River catchment, along its left-side tributary (Chakiya River), about 60 km northwest of Yakutsk city. The mineral chemistry patterns of pyropes are typical of Jurassic-Cretaceous barren kimberlites, like the pipes of Obnazhennaya or Muza, but are uncommon to diamondiferous Middle Paleozoic kimberlites. The results allow identifying the magmatic event and placing time constraints on kimberlite magmatism in the southeastern flank of the Vilui basin, which was part of the Late Jurassic-Early Cretaceous tectonic-magmatic event in northeastern Asia.
DS202005-0719
2020
Agashev, A.M., Chervyakovskaya, M.V., Serov, I.V., Tolstov, A.V., Agasheva, E.V., Votyakov, S.L.Source rejuvenation vs. re-heating: constraints on Siberian kimberlite origin from U-Pb and Lu-Hf isotope compositions and geochemistry of mantle zircons. ( Silurian, Devonian, Triassic, Jurassic)Lithos, Vol. 364-365, 10p. PdfRussia, Siberiadeposit - Druzhba, Choumurdakh

Abstract: We have studied a suite of mantle zircons from several differently aged pipes of the Siberian kimberlite province via UPb and LuHf isotope analyses and trace element compositions. The UPb ages we obtained confirmed four main episodes (Silurian, Devonian, Triassic and Jurassic) of kimberlite activity on the Siberian craton. The Druzhba pipe had two populations of zircons dating from the Silurian and Devonian, respectively. The geochemical features of our suite of mantle zircons show low concentrations of U, Th and heavy rare earth elements (REEs), positive Ce anomalies, and weak or absent Eu anomalies, which is in accord with the mantle-derived nature of the zircon. Despite having broadly similar geochemistry, zircons from differently aged kimberlites had some clear differences arising from variations in the composition of the protokimberlite metasomatic melt and from peculiarities of fractional crystallization. The Th/U ratios were highest in the Silurian zircons and sharply decreased toward the Devonian. The Triassic zircons had elevated and highly variable Ce/Nb ratios with low and nearly constant Th/U ratios. Zircons from Siberian kimberlites with different UPb ages showed systematic variations in their initial Hf isotope compositions. The oldest Silurian kimberlite field, Chomurdakh, had two zircon populations: Silurian zircons, with ?Hft values in the range of +2.8 to +5.9 units, and Devonian zircons, with ?Hft values in the range of +1.6 to +2.0 units. Zircons from the Devonian field kimberlites were in the range of +5.6 to +9.6 ?Hft units. The Triassic kimberlitic zircons had the most juvenile Hf isotope composition, at +9.3 to +11.2 ?Hft units, while the Jurassic zircons had +6.9 ?Hft units. The combination of the UPb and LuHf isotope data suggests a periodic rejuvenation of the lithospheric mantle roots by low-volume melts from the asthenospheric mantle, resulting shortly after in kimberlite emplacements. Some Devonian and Jurassic kimberlites may have been melted by re-heating the Silurian and Triassic age sources, respectively, about 60 Myr after they were formed.
DS202009-1605
2020
Amsellem, E., Moynier, F., Bertrand, H., Bouyon, A., Mata, J., Tappe, S., Day, J.M.D.Calcium isotopic evidence for the mantle sources of carbonatites. ( Oldoinyo Lengai)Science Advances, Vol. 6, eaba3269 June 3, 7p. PdfGlobal, Africa, Tanzaniacarbonatites

Abstract: The origin of carbonatites-igneous rocks with more than 50% of carbonate minerals-and whether they originate from a primary mantle source or from recycling of surface materials are still debated. Calcium isotopes have the potential to resolve the origin of carbonatites, since marine carbonates are enriched in the lighter isotopes of Ca compared to the mantle. Here, we report the Ca isotopic compositions for 74 carbonatites and associated silicate rocks from continental and oceanic settings, spanning from 3 billion years ago to the present day, together with O and C isotopic ratios for 37 samples. Calcium-, Mg-, and Fe-rich carbonatites have isotopically lighter Ca than mantle-derived rocks such as basalts and fall within the range of isotopically light Ca from ancient marine carbonates. This signature reflects the composition of the source, which is isotopically light and is consistent with recycling of surface carbonate materials into the mantle.
DS202007-1122
2020
Amsellem, E., Moynier, F., Betrand, H., Bouyon, A., Mata, J., Tappe, S., Day, J.M.D.Calcium isotopic evidence for the mantle source of carbonatites.Science Adavances, Vol. 6, 63 eaba3269 6p. PdfMantlecarbonatite

Abstract: The origin of carbonatites—igneous rocks with more than 50% of carbonate minerals—and whether they originate from a primary mantle source or from recycling of surface materials are still debated. Calcium isotopes have the potential to resolve the origin of carbonatites, since marine carbonates are enriched in the lighter isotopes of Ca compared to the mantle. Here, we report the Ca isotopic compositions for 74 carbonatites and associated silicate rocks from continental and oceanic settings, spanning from 3 billion years ago to the present day, together with O and C isotopic ratios for 37 samples. Calcium-, Mg-, and Fe-rich carbonatites have isotopically lighter Ca than mantle-derived rocks such as basalts and fall within the range of isotopically light Ca from ancient marine carbonates. This signature reflects the composition of the source, which is isotopically light and is consistent with recycling of surface carbonate materials into the mantle.
DS202011-2026
2020
Anenburg, M.Rare earth mineral diversity controlled by REE pattern shapes.Mineralogical Magazine, doi.10.1180/mgm.2020.70 11p. PdfMantleREE

Abstract: The line connecting rare earth elements (REE) in chondrite-normalised plots can be represented by a smooth polynomial function using ? shape coefficients as described by O'Neill (2016). In this study, computationally generated ? combinations are used to construct artificial chondrite-normalised REE patterns that encompass most REE patterns likely to occur in natural materials. The dominant REE per pattern is identified, which would lead to its inclusion in a hypothetical mineral suffix, had this mineral contained essential REE. Furthermore, negative Ce and Y anomalies, common in natural minerals, are considered in the modelled REE patterns to investigate the effect of their exclusion on the relative abundance of the remainder REE. The dominant REE in a mineral results from distinct pattern shapes requiring specific fractionation processes, thus providing information on its genesis. Minerals dominated by heavy lanthanides are rare or non-existent, even though the present analysis shows that REE patterns dominated by Gd, Dy, Er and Yb are geologically plausible. This discrepancy is caused by the inclusion of Y, which dominates heavy REE budgets, in mineral name suffixes. The focus on Y obscures heavy lanthanide mineral diversity and can lead to various fractionation processes to be overlooked. Samarium dominant minerals are known, even though deemed unlikely by the computational model, suggesting additional fractionation processes that are not well described by ? shape coefficients. Positive Eu anomalies only need to be moderate in minerals depleted in the light REE for Eu to be the dominant REE, thus identifying candidate rocks in which the first Eu dominant mineral might be found. Here, I present an online tool, called ALambdaR that allows interactive control of ? shape coefficients and visualisation of resulting REE patterns.
DS202010-1825
2020
Anenburg, M., Mavrogenes, J.A., Bennett, V.C.The fluorapatite P-REE-Th vein deposit at Nolans Bore: genesis by carbonatite metasomatism.Journal of Petrology, Vol. 61, 1, egaa003 42p. PdfAustralia, Northern Territorydeposit - Nolans Bore

Abstract: Nolans Bore is a rare earth element (REE) ore deposit in the Reynolds Range, Aileron Province, Northern Territory, Australia. It consists primarily of fluorapatite and alteration products thereof, surrounded by a diopside-dominated selvage. Previously considered to form via hydrothermal fluids, we now suggest that the deposit formed by a metasomatic reaction between a mantle-derived carbonatite and granulite-facies felsic host rocks, after peak metamorphism. REE patterns of fluorapatite are strongly light REE (LREE) enriched, convex with maxima at Ce to Nd, and contain a weak negative Eu anomaly. Textural and geochemical properties of the fluorapatite are consistent with its formation from a carbonatite liquid. Sinusoidal REE patterns in diopside along with strong Yb-Lu enrichment relative to coexisting titanite are suggestive of derivation from a Ca-rich carbonatite. Likewise, hyalophane present in the selvages forms by reaction of a BaCO3 component in the carbonatite with K-feldspar in the silicate host rocks. The overall morphology of Nolans Bore is consistent with carbonatite-silicate reaction experiments, with the carbonatite itself migrating elsewhere owing to the open-system nature of Nolans Bore. Ekanite veins in massive fluorapatite zones and allanite-epidote crusts on fluorapatite in contact with the diopside selvages formed by hydrothermal fluids exsolved from the carbonatite. Minor interstitial calcite was not igneous but was the last mineral to crystallize from the carbonatite-exsolved fluid. Y/Ho ratios qualitatively trace the transition from mantle-dominated igneous minerals to later low-temperature hydrothermal minerals. Rb-Sr and Sm-Nd analyses of unaltered minerals (fluorapatite, allanite, calcite) show that the carbonatite had homogeneous initial 87Sr/86Sr?˜?0•7054 and eNd?˜?-4 at 1525?Ma, the best age estimate of the mineralization. Fluorapatite-allanite Sm-Nd dating results in an age of 1446?±?140?Ma, consistent with forming soon after the end of the Chewings Orogeny. Neodymium depleted mantle model ages are older than 2?Ga, indicating the presence of recycled crustal material within the source. We suggest that the carbonatite was sourced from a mantle enriched by subduction of LREE-rich oceanic crustal rocks, marine sediments, and phosphorites, potentially from the south, or the Mount Isa area to the east. Nolans Bore represents the root zone of a now-eroded carbonatite. Other Nolans-type deposits (Hoidas Lake, Canada and Kasipatnam, India) are similarly hosted within siliceous granulite-facies rocks in regions with a long tectonic history, suggesting common processes that led to the formation of all three deposits. The REE-rich compositions of the mid-crustal Nolans Bore fluorapatite are the cumulates hypothesized to cause REE depletion in some unmineralized carbonatites. The rocks at Nolans Bore demonstrate that carbonatites, previously thought to be mostly unreactive, can undergo modification and modify the composition of the silicate rocks which they encounter, forming an ‘antiskarn’. At igneous temperatures, the resulting mineral assemblage (other than fluorapatite) consists of diopside and titanite, both of which are common in granulite-facies rocks. Therefore, carbonatite metasomatism can remain unnoticed if the resulting assemblage does not contain distinctively carbonatitic minerals.
DS202011-2027
2020
Anenburg, M., Mavrogenes, J.A., Frigo, C., Wall, F.Rare earth element mobility in and around carbonatites controlled by sodium, potassium, and silica.Science Advances, Vol. 6, 11p. 10.1126/sciadv.abb6570 pdfGlobalcarbonatites, REE

Abstract: Carbonatites and associated rocks are the main source of rare earth elements (REEs), metals essential to modern technologies. REE mineralization occurs in hydrothermal assemblages within or near carbonatites, suggesting aqueous transport of REE. We conducted experiments from 1200°C and 1.5 GPa to 200°C and 0.2 GPa using light (La) and heavy (Dy) REE, crystallizing fluorapatite intergrown with calcite through dolomite to ankerite. All experiments contained solutions with anions previously thought to mobilize REE (chloride, fluoride, and carbonate), but REEs were extensively soluble only when alkalis were present. Dysprosium was more soluble than lanthanum when alkali complexed. Addition of silica either traps REE in early crystallizing apatite or negates solubility increases by immobilizing alkalis in silicates. Anionic species such as halogens and carbonates are not sufficient for REE mobility. Additional complexing with alkalis is required for substantial REE transport in and around carbonatites as a precursor for economic grade-mineralization.
DS202009-1606
2020
Anzolini, C., Marquardt, K., Stagno, V., Nestola, F.Evidence for complex iron oxides in the deep mantle from FeNi(Cu) inclusions in superdeep diamondsProceedings of the National Academy of Sciences, pnas.org/cgi/doi.10.1073 /pnas.2004269117 7p. PdfMantlediamond inclusions

Abstract: The recent discovery in high-pressure experiments of compounds stable to 24-26 GPa with Fe4O5, Fe5O6, Fe7O9, and Fe9O11 stoichiometry has raised questions about their existence within the Earth’s mantle. Incorporating both ferric and ferrous iron in their structures, these oxides if present within the Earth could also provide insight into diamond-forming processes at depth in the planet. Here we report the discovery of metallic particles, dominantly of FeNi (Fe0.71Ni0.24Cu0.05), in close spatial relation with nearly pure magnetite grains from a so-called superdeep diamond from the Earth’s mantle. The microstructural relation of magnetite within a ferropericlase (Mg0.60Fe0.40)O matrix suggests exsolution of the former. Taking into account the bulk chemistry reconstructed from the FeNi(Cu) alloy, we propose that it formed by decomposition of a complex metal M oxide (M4O5) with a stoichiometry of (Fe3+2.15Fe2+1.59Ni2+0.17Cu+0.04)S = 3.95O5. We further suggest a possible link between this phase and variably oxidized ferropericlase that is commonly trapped in superdeep diamond. The observation of FeNi(Cu) metal in relation to magnetite exsolved from ferropericlase is interpreted as arising from a multistage process that starts from diamond encapsulation of ferropericlase followed by decompression and cooling under oxidized conditions, leading to the formation of complex oxides such as Fe4O5 that subsequently decompose at shallower P-T conditions.
DS202007-1123
2020
Anzolini, C., Siva-Jothy, W., Locock, A.J., Nestola, F., Balic-Zunic, T., Alvaro, M., Stachel, T., Pearson, D.G.Heamanite-(Ce) (K0.5Ce0.5)Ti03 Mineralogical Magazine reports CNMNC Newsletter , No. 55, Vol. 84, https://doi.org/ 10.1180/mgm. 2020.39Canada, Northwest Territoriesdeposit - Gahcho Kue
DS202011-2028
2020
Apen, F.E., Rudnick, R.L., Cottle, J.M., Kylander-Clark, A.R.C., Blondes, M.S., Piccoli, P.M., Seward, G.Four dimensional thermal evolution of the East African Orogen: accessory phase petrochronology of crustal profiles through the Tanzanian Craton and Mozambique belt, northeastern Tanzania.Contributions to Mineralogy and Petrology, Vol. 175, 97, 30p. PdfAfrica, Tanzaniacraton

Abstract: U-Pb petrochronology of deep crustal xenoliths and outcrops across northeastern Tanzania track the thermal evolution of the Mozambique Belt and Tanzanian Craton following the Neoproterozoic East African Orogeny (EAO) and subsequent Neogene rifting. At the craton margin, the upper-middle crust record thermal quiescence since the Archean (2.8-2.5 Ga zircon, rutile, and apatite in granite and amphibolite xenoliths). The lower crust of the craton documents thermal pulses associated with Neoarchean ultra-high temperature metamorphism (ca. 2.64 Ga,?>?900 °C zircon), the EAO (600-500 Ma rutile), and fluid influx during rifting (?650 °C (above Pb closure of rutile and apatite) at the time of eruption. Zoned titanite records growth during cooling of the lower crust at 550 Ma, followed by fluid influx during slow cooling and exhumation (0.1-1 °C/Myr after 450 Ma). Permissible lower-crustal temperatures for the craton and orogen suggest variable mantle heat flow through the crust and reflect differences in mantle lithosphere thickness rather than advective heating from rifting.
DS202010-1826
2020
Armistead, S.E., Collins, A.S., Redaa, A., Jepson, G., Gillespie, J., Gilbert, S., Blades, M.L., Foden, J.D., RazakMnN, T.Structural evolution and medium temperature thermochronology of central Madagascar: implications for Gondwana amalagamation.Journal of the Geological Society, Vol. 177, pp. 784-798.Africa, Madagascargeothermometry

Abstract: Madagascar occupied an important place in the amalgamation of Gondwana and preserves a record of several Neoproterozoic events that are linked to orogenesis of the East African Orogen. In this study, we integrate remote sensing, field data and thermochronology 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 SW-directed, tight to isoclinal, recumbent folding (D2). These are overprinted by north-trending upright folds that formed during an approximately east-west shortening event (D3). Together these produced type 1 and type 2 fold interference patterns throughout the Itremo and Ikalamavony domains. We show that the Itremo and Ikalamavony domains were deformed together in the same orogenic system, which we interpret as the c. 630 Ma collision of Azania with Africa along the Vohibory Suture in southwestern Madagascar. In eastern Madagascar, deformation is syn- to post-550 Ma, and probably formed in response to final closure of the Mozambique Ocean along the Betsimisaraka Suture that amalgamated Madagascar with the Dharwar Craton of India. Apatite U-Pb and novel laser ablation triple quadrupole inductively coupled plasma mass spectrometry (LA-QQQ-ICP-MS) muscovite and biotite Rb-Sr thermochronology indicates that much of central Madagascar cooled through c. 500°C at c. 500 Ma.
DS202009-1607
2020
Arnould, M., Coltice, N., Flament, N., Mallard, C.Plate tectonics and mantle controls on plume dynamics.Earth and Planetary Science Letters, Vol. 547, 15p. PdfMantlegeodynamics

Abstract: Mantle plumes provide valuable information about whole-mantle convection: they originate at the core-mantle boundary, cross Earth's mantle and interact with the lithosphere. For instance, it has been proposed that the mobility/stability of plumes depends on plume intrinsic properties, on how slabs interact with the basal boundary layer, on mantle flow, or on their proximity to mid-ocean ridges. Here, we use 3D-spherical models of mantle convection generating self-consistent plate-like behaviour to investigate the mechanisms linking tectonics and mantle convection to plume dynamics. Our models produce fully-dynamic mantle plumes that rise vertically with deflection and present excess temperatures, rising speeds, buoyancy and heat fluxes comparable to observations. In the absence of plate tectonics, plumes are stable and their lifetime exceeds hundreds of million years. With plate tectonics, plumes are more mobile, and we identify four physical mechanisms controlling their stability. 1/ Fixed plumes are located at saddle points of basal mantle flow. 2/ Plumes moving at speeds between 0.5-1 cm yr-1 are slowly entrained by passive mantle flow. 3/ Fast plume motions between 2-5 cm yr-1 lasting several tens of million years are caused by slab push. 4/ Plumes occasionally drift at speeds >5 cm yr-1 over <10 Myr through plume merging. We do not observe systematic anchoring of plumes to mid-oceanic ridges. Independent of the presence of a dense basal layer, plate-like regimes decrease the lifetime of plumes compared to stagnant-lid models. Plume age, temperature excess or buoyancy flux are not diagnostic of plume lateral speed. The fraction of plumes moving by less than 0.5 cm yr-1 is >25%, which suggests that fixed hotspot reference frames can be defined from carefully selected hotspot tracks.
DS202008-1366
2020
Artyushkov, E.V., Kolka, V.V., Chekhovich, P.A.The occurrence of lower viscosity layer in the crust of old cratons as a cause of the strongly differentiated character of postglacial uplift.Doklady Earth Sciences, Vol. 492, pp. 351-355.Europe, Fennoscandia, Kola Peninsula, Karelia, Canadacraton

Abstract: Rapid glacio-isostatic rebound in Fennoscandia and Canada that is nonuniform in time and space indicates that there is a layer with strongly decreased viscosity at shallow crustal depths. The upper boundary of the layer is near the depth of 15 km, which corresponds to the maximum depth of earthquake hypocenters in the Precambrian cratons of the Kola Peninsula and Karelia. The position of the lower boundary is less distinct; however, most likely it is located near the base of the crust. The formation of such a layer in the Pliocene-Quaternary occurred due to infiltration of a large volume of mantle fluids into the crust. In many regions, this has led to retrograde metamorphism with rock expansion and a strong decrease in rocks viscosity.
DS202009-1608
2019
Arzamastev, A., Stepanova, A.V., Samsonov, A.V., Erofeev, K.G.Mafic magmatism of northeastern Fennoscandia ( 2.06-1.86 Ga) geochemistry of volcanic rocks and correlation with dike complexes.Stratigraphy and Geological Correlation, Vol. 28, 1, pp. 1-34.Europe, Fennoscandiamagmatism

Abstract: The comprehensive geochemical and isotopic-geochronological study of Early Proterozoic volcanic rocks in structure of the Polmak-Pechenga-Imandra-Varzuga belt and dikes and sills of the Murmansk and Kola-Norwegian terranes is conducted. Abundant swarms of mafic dikes (2.06-1.86 Ga) are established in the northwestern frame of the belt, including swarms of metadolerites (2060 ± 6 Ma), ferropicrites and gabbronorites (1983 ± 5 Ma), and poikilophitic dolerites (1860 ± 4 Ma). The comparison of volcanic rocks of the Pechenga and Imandra-Varzuga structures shows asynchronous change in volcanism style, with a significant time lapse. The geochemical features of volcanic rocks of the Tominga Formation are typical of those of continental magmatism and can hardly be correlated with those of the Pilguyarvi Formation. According to isotopic-geochronological data, depleted mantle melts in the Pechenga and Imandra-Varzuga zones intruded at 2010-1970 and 1970-1980 Ma, respectively. The analysis of the conditions of formation of volcanic series shows that Neoarchean lithospheric mantle, which produced melts with low Zr/Nb ratios, was a source for primary melts of the Kuetsjarvi Formation of the Pechenga structure and their homologs of the Imandra-Varzuga structure. In contrast, the volcanic rocks of the Kolasjoki Formation, which were weakly contaminated with crustal material, and the related Ilmozero Formation, as well as the metadolerite dikes of the Kirkenes region, were sourced mostly from asthenosphere with separation of melt above the garnet stability depth. The formation of the volcanic rocks of the Pilguyarvi Formation is related, judging from the geochemical data, to two asthenospheric sources different in depth, which produced tholeiitic and ferropicritic melts.
DS202010-1827
2020
Ashchepkov, I., Medvedev, N., Vladykin, N., Ivanov, A., Downes, H.Thermobarometry and geochemistry of mantle xenoliths from Zapolyarnaya pipe, Upper Muna field, Yakutia: implications for mantle layering, interaction with plume melts and diamond grade.Minerals, Vol. 10, 9, 740 10.3390/ min10090755 29p. PdfRussia, Yakutiadeposit - Zapplyarnaya

Abstract: Minerals from mantle xenoliths in the Zapolyarnaya pipe in the Upper Muna field, Russia and from mineral separates from other large diamondiferous kimberlite pipes in this field (Deimos, Novinka and Komsomolskaya-Magnitnaya) were studied with EPMA and LA-ICP-MS. All pipes contain very high proportions of sub-calcic garnets. Zapolyarnaya contains mainly dunitic xenoliths with veinlets of garnets, phlogopites and Fe-rich pyroxenes similar in composition to those from sheared peridotites. PT estimates for the clinopyroxenes trace the convective inflection of the geotherm (40-45 mW•m-2) to 8 GPa, inflected at 6 GPa and overlapping with PT estimates for ilmenites derived from protokimberlites. The Upper Muna mantle lithosphere includes dunite channels from 8 to 2 GPa, which were favorable for melt movement. The primary layering deduced from the fluctuations of CaO in garnets was smoothed by the refertilization events, which formed additional pyroxenes. Clinopyroxenes from the Novinka and Komsomolskaya-Magnitnaya pipes show a more linear geotherm and three branches in the P-Fe# plot from the lithosphere base to the Moho, suggesting several episodes of pervasive melt percolation. Clinopyroxenes from Zapolyarnaya are divided into four groups according to thermobarometry and trace element patterns, which show a stepwise increase of REE and incompatible elements. Lower pressure groups including dunitic garnets have elevated REE with peaks in Rb, Th, Nb, Sr, Zr, and U, suggesting mixing of the parental protokimberlitic melts with partially melted metasomatic veins of ancient subduction origin. At least two stages of melt percolation formed the inclined PT paths: (1) an ancient garnet semi-advective geotherm (35-45 mW•m-2) formed by volatile-rich melts during the major late Archean event of lithosphere growth; and (2) a hotter megacrystic PT path (Cpx-Ilm) formed by feeding systems for kimberlite eruptions (40-45 mW•m-2). Ilmenite PT estimates trace three separate PT trajectories, suggesting a multistage process associated with metasomatism and formation of the Cpx-Phl veinlets in dunites. Heating associated with intrusions of protokimberlite caused reactivation of the mantle metasomatites rich in H2O and alkali metals and possibly favored the growth of large megacrystalline diamonds.
DS202010-1828
2011
Ashchepkov, I.V.Program of the mantle thermometers and barometers: usage for reconstructions and calibration of PT methods.Vestnik Otdelenia nauk o Zemle RAN *** ENG, Vol. 3, doi:10.2205/2011NZ000138, 5p. Pdf * note dateMantlegeobarometry, peridotites

Abstract: Original monomineral thermobarometers for mantle peridotites for clinopyroxene, garnet, chromite and ilmenites for the mantle peridotites were statistically calibrated on the PT estimates for mantle peridotites [Ashchepkov et al., 2010] were tested using the mineral phases obtained in high pressure experiments with the natural peridotites (380 runs) [Brey et al.,1990; 2008 etc] and eclogites (240 runs)[Dasgupta et al., 2006 etc]. In the original program of that written on FORTRAN are assembled the most reliable methods of mineral thermometers (45) and barometers (36) and oxybarometers (5), including original monomineral and methods [Ashchepkov, 2003 Ashchepkov et al., 2008; 2009; 2010; 2011] for the mantle peridotites bases on the compositions of on clinopyroxene, garnet, chromite and ilmenite. Program reads the text files, which converted from Excel. Original data include standard silicate compositions for 12 components in standard order. The text file includes 15 columns of 8 symbols. The first is file name which is the same for all the minerals in the association. The second is indicator symbol for phases. E- enstatite, D - diopside, O-olivine, S-spinel, G- garnet, I -ilmenite, A- amphibole, F - phlogopite, P-plagioclase, L- liquid, R- bulk rock. Then follow oxides: SiO2, TiO2, Al2O3, Cr2O3, FeO, MnO, MgO, CaO, Na2O, K2O, NiO, V2O3 written with 2-3 decimals. The last column may contain description of the mineral or association up to 64 symbols. Monomineral methods use calculated values for Fe#Ol or Fe#Cpx. The input from console includes file name (8 symbols) (A8), then amount of PT pairs of numbers thermometers and barometers (2I2) and one for FO2 method. Program allows input of the iteration numbers (to 25 by default). It allow to choose whether to use the calculated Fe3+ for the minerals and also. It is possible also to put fixed values of T and P (default 1000o C and 40 kbar ).
DS202011-2029
2001
Ashchepkov, I.V., Afanasiev, V.P., Pokhilenko, N.P., Sobolev, N.V., Vladykin, N.V., Saprykin, A.I., Khmelnikova, O.S., Anoshin, G.N.Small note on the composition of Brazilian mantle. *** NOTE DATERevista Brasileira de Geociencas*** ENG, Vol. 31, 4, pp. 653-660. pdfSouth America, Brazilkimberlites

Abstract: Garne ts from couc eru ratc from the vargcm l kimberl ite pipe show a long compos itional range and reveallong lincar tre nds within the lherzolite field in a Cr~Ol - CaO% dia gram (Sobolcv et til. 1974) (lip (0 11% MgO). fon ned by grains of different dimensions with fcw deviations to harzburg itcs . Larger grains (fraction +3) arc higher in CaO with less Cr~01 (to 5.5%). TIle Cr20 1 freq uen cy reduc es in hyperbo lic function for each fraction . IImenites reve;1142-56% Ti0 2l..'Olllpositionai range with linear FeO - MgO correhuions but 3(4) separate groups for A I ~01 suggest different proport ion of co-prccipimted gimlet , probably due to polybn ric Irncnonanon. lncreasing Cr~O l nnd r"t..-Q% conte nt (fractionation uegn:e ) with red ucing TiO~ is in accord with Ar c mod el.. Ganict xenolith fnnnldnin II pipe with large Ga r- Cpxgrains and fine Mica-Curb bearing mat rix refer to 60 kbcr and 35 mv/m2 gcothcrm . 11displays enr iched trace c lement pat ter ns but not completely equilibrated compositions for Ga r anti Cpx. sugges ting low degree me lting of rela tively fertile mantle. St udied uuuc rinlmay s uggcsrmcrasomu tized, relat ively fertile and irre gularly heated mantle bene ath Sombcrn Bra zil as found by (Carvalho & Lccnnrdos 1997).
DS202010-1829
2013
Ashchepkov, I.V., Alymova, N.V., Loginova, A.M., Vladykin, N.V., Kuligin, S.S., Mityukhin, S.I., Stegnitsky, Y.B., Prokopiev, S.A., Salikhov, R.F., Palessky, V.S., Khmelnikova, O.S.Picroilmenites in Yakutian kimberlites: variations and genetic models. Solid Earth Discussions, Vol. 5, pp. 1-75. pdf * note dateRussia, Yakutiapicroilmenites

Abstract: Major and trace element variations in picroilmenites from Late Devonian kimberlite pipes in Siberia reveal similarities within the region in general, but show individual features for ilmenites from different fields and pipes. Empirical ilmenite thermobarometry (Ashchepkov et al., 2010), as well as common methods of mantle thermobarometry and trace element geochemical modeling, shows long compositional trends for the ilmenites. These are a result of complex processes of polybaric fractionation of protokimberlite melts, accompanied by the interaction with mantle wall rocks and dissolution of previous wall rock and metasomatic associations. Evolution of the parental magmas for the picroilmenites was determined for the three distinct phases of kimberlite activity from Yubileynaya and nearby Aprelskaya pipes, showing heating and an increase of Fe# (Fe# = Fe / (Fe + Mg) a.u.) of mantle peridotite minerals from stage to stage and splitting of the magmatic system in the final stages. High-pressure (5.5-7.0 GPa) Cr-bearing Mg-rich ilmenites (group 1) reflect the conditions of high-temperature metasomatic rocks at the base of the mantle lithosphere. Trace element patterns are enriched to 0.1-10/relative to primitive mantle (PM) and have flattened, spoon-like or S- or W-shaped rare earth element (REE) patterns with Pb > 1. These result from melting and crystallization in melt-feeding channels in the base of the lithosphere, where high-temperature dunites, harzburgites and pyroxenites were formed. Cr-poor ilmenite megacrysts (group 2) trace the high-temperature path of protokimberlites developed as result of fractional crystallization and wall rock assimilation during the creation of the feeder systems prior to the main kimberlite eruption. Inflections in ilmenite compositional trends probably reflect the mantle layering and pulsing melt intrusion during melt migration within the channels. Group 2 ilmenites have inclined REE enriched patterns (10-100)/PM with La / Ybn ~ 10-25, similar to those derived from kimberlites, with high-field-strength elements (HFSE) peaks (typical megacrysts). A series of similar patterns results from polybaric Assimilation + fractional crystallization (AFC) crystallization of protokimberlite melts which also precipitated sulfides (Pb < 1) and mixed with partial melts from garnet peridotites. Relatively low-Ti ilmenites with high-Cr content (group 3) probably crystallized in the metasomatic front under the rising protokimberlite source and represent the product of crystallization of segregated partial melts from metasomatic rocks. Cr-rich ilmenites are typical of veins and veinlets in peridotites crystallized from highly contaminated magma intruded into wall rocks in different levels within the mantle columns. Ilmenites which have the highest trace element contents (1000/PM) have REE patterns similar to those of perovskites. Low Cr contents suggest relatively closed system fractionation which occurred from the base of the lithosphere up to the garnet-spinel transition, according to monomineral thermobarometry for Mir and Dachnaya pipes. Restricted trends were detected for ilmenites from Udachnaya and most other pipes from the Daldyn-Alakit fields and other regions (Nakyn, Upper Muna and Prianabarie), where ilmenite trends extend from the base of the lithosphere mainly up to 4.0 GPa. Interaction of the megacryst forming melts with the mantle lithosphere caused heating and HFSE metasomatism prior to kimberlite eruption.
DS202007-1124
2020
Ashchepkov, I.V., Vladykin, N.V., Kalashnyk, H.A., Medvedev, N.S., Saprykin, A.I., Downes, H., Khmelnikova, O.S.Incompatible element enriched mantle lithosphere beneath kimberlitic pipes in Priazovie Ukrainian shield: volatile enriched focused melt flow and connection to mature crust?International Geology Review, in press available 24p. PdfEurope, Ukrainedeposit - Priazovie

Abstract: Major, minor and trace element compositions of mantle xenocrysts from Devonian kimberlite pipes in the Priazovie give an insight into the mantle structure beneath the SE Ukranian Shield and its evolution. Garnets yield low temperature conditions as determined by monomineral thermobarometry. The mantle lithosphere is sharply divided at 4.2 GPa, marked by a high temperature Cpx-Ilm-Phl trend, eclogites and changes in pyrope geochemistry. Seven layers are detected: Ist layer at 2.5-1 GPa is enriched mantle (Fe#Ol ~ 0.11 - 0.14) with Gar- pyroxenites and Sp peridotites; IInd at 2.5-3.2 GPa - Gar-Sp (Fe#Ol 0.08 - 0.10) peridotite. IIId at 4.3-3.2 GPa is formed of Archaean- Proterozoic peridotites with Fe#Ol ~0.07 - 0.095. IVth at 3.2-5 GPa- contains pyroxenitic Gar with higher Ca, eclogites, Chr and Cpx (Fe#Ol ~0.10 - 0.125); Vth at 5.8 - 5 GPa is marked by sub-Ca garnets, Cr-rich chromites and Mg-Cr ilmenites; VIth layer at 5.8-6.8 GPa contains Fe-enriched pyropes, almandines and Cr-Mg ilmenites near the lithosphere base; VIIth layer > 6.8 GPa consists of ‘hot’ Fe-rich garnets. Garnets show increasing enrichment in LREE, LILE, Hf, Zr with decreasing pressure. Primitive garnets have round REE patterns; depleted ones have S-type patterns inflected at Nd. Garnets from 6.5 to 3 GPa show increasing La/Ybn, Zr-Hf, LILE. Peridotitic clinopyroxenes have inclined linear trace element patterns rounded from La to Pr with high LILE and HFSE levels. The Fe-rich group (reacted with eclogites) shows bell-shaped irregular patterns with LILE close to the LREE levels. A possible reason for LILE (HFSE and) enrichment of the upper part of the mantle is subduction metasomatsm in Archaean times (with participation of mature continental sediments) activated by plumes at 1.8 Ga and earlier which produced pervasive focused melt flow with remelting of mica-amphibole metasomatites giving continuous REE and LILE enrichment in mantle lithologies from 5.8 to 2.5 GPa.
DS202004-0497
2020
Ashfold, M.N.R., Goss, J.P., Green, B., May, P.W., Newton, M.E., Peaker, C.V.Nitrogen in diamond.Chemical Reviews, Vol. 120, 4, 10.1021/ acs.chemrev.9b00578 50p. PdfGlobalHPHT, CVD, synthetics

Abstract: Nitrogen is ubiquitous in both natural and laboratory-grown diamond, but the number and nature of the nitrogen-containing defects can have a profound effect on the diamond material and its properties. An ever-growing fraction of the supply of diamond appearing on the world market is now lab-grown. Here, we survey recent progress in two complementary diamond synthesis methods: high pressure high temperature (HPHT) growth and chemical vapor deposition (CVD), how each is allowing ever more precise control of nitrogen incorporation in the resulting diamond, and how the diamond produced by either method can be further processed (e.g., by implantation or annealing) to achieve a particular outcome or property. The burgeoning availability of diamond samples grown under well-defined conditions has also enabled huge advances in the characterization and understanding of nitrogen-containing defects in diamond alone and in association with vacancies, hydrogen, and transition metal atoms. Among these, the negatively charged nitrogen-vacancy (NV-) defect in diamond is attracting particular current interest in account of the many new and exciting opportunities it offers for, for example, quantum technologies, nanoscale magnetometry, and biosensing.
DS202001-0001
2019
Ashwal, L.D.Wandering continents of the Indian ocean.South African Journal of Geology, Vol. 122, 4, pp. 397-420.IndiaGondwana

Abstract: On the last page of his 1937 book "Our Wandering Continents" Alex Du Toit advised the geological community to develop the field of "comparative geology", which he defined as "the study of continental fragments". This is precisely the theme of this paper, which outlines my research activities for the past 28 years, on the continental fragments of the Indian Ocean. In the early 1990s, my colleagues and I were working in Madagascar, and we recognized the need to appreciate the excellent geological mapping (pioneered in the 1950s by Henri Besairie) in a more modern geodynamic context, by applying new ideas and analytical techniques, to a large and understudied piece of continental crust. One result of this work was the identification of a 700 to 800 Ma belt of plutons and volcanic equivalents, about 450 km long, which we suggested might represent an Andean-type arc, produced by Neoproterozoic subduction. We wondered if similar examples of this magmatic belt might be present elsewhere, and we began working in the Seychelles, where late Precambrian granites are exposed on about 40 of the >100 islands in the archipelago. Based on our new petrological, geochemical and geochronological measurements, we built a case that these ~750 Ma rocks also represent an Andean-type arc, coeval with and equivalent to the one present in Madagascar. By using similar types of approaches, we tracked this arc even further, into the Malani Igneous Province of Rajasthan, in northwest India. Our paleomagnetic data place these three entities adjacent to each other at ~750 Ma, and were positioned at the margins, rather than in the central parts of the Rodinia supercontinent, further supporting their formation in a subduction-related continental arc. A widespread view is that in the Neoproterozoic, Rodinia began to break apart, and the more familiar Gondwana supercontinent was assembled by Pan-African (~500 to 600 Ma) continental collisions, marked by the highly deformed and metamorphosed rocks of the East African Orogen. It was my mentor, Kevin Burke, who suggested that the present-day locations of Alkaline Rocks and Carbonatites (called "ARCs") and their Deformed equivalents (called "DARCs"), might mark the outlines of two well-defined parts of the Wilson cycle. We can be confident that ARCs formed originally in intracontinental rift settings, and we postulated that DARCs represent suture zones, where vanished oceans have closed. We also found that the isotopic record of these events can be preserved in DARC minerals. In a nepheline syenite gneiss from Malawi, the U-Pb age of zircons is 730 Ma (marking the rifting of Rodinia), and that of monazites is 522 Ma (marking the collisional construction of Gondwana). A general outline of how and when Gondwana broke apart into the current configuration of continental entities, starting at about 165 Ma, has been known for some time, because this record is preserved in the magnetic properties of ocean-floor basalts, which can be precisely dated. A current topic of active research is the role that deep mantle plumes may have played in initiating, or assisting, continental fragmentation. I am part of a group of colleagues and students who are applying complementary datasets to understand how the Karoo (182 Ma), Etendeka (132 Ma), Marion (90 Ma) and Réunion (65 Ma) plumes influenced the break-up of Gondwana and the development of the Indian Ocean. Shortly after the impingement of the Karoo plume at 182 Ma, Gondwana fragmentation began as Madagascar + India + Antarctica separated from Africa, and drifted southward. Only after 90 Ma, when Madagascar was blanketed by lavas of the Marion plume, did India begin to rift, and rapidly drifted northward, assisted by the Marion and Deccan (65 Ma) plumes, eventually colliding with Asia to produce the Himalayas. It is interesting that a record of these plate kinematics is preserved in the large Permian - Eocene sedimentary basins of western Madagascar: transtensional pull-apart structures are dextral in Jurassic rocks (recording initial southward drift with respect to Africa), but change to sinistral in the Eocene, recording India’s northward drift. Our latest work has begun to reveal that small continental fragments are present in unexpected places. In the young (max. 9 Ma) plume-related, volcanic island of Mauritius, we found Precambrian zircons with ages between 660 and 3000 Ma, in beach sands and trachytic lavas. This can only mean that a fragment of ancient continent must exist beneath the young volcanoes there, and that the old zircons were picked up by ascending magmas on their way to surface eruption sites. We speculate, based on gravity inversion modelling, that continental fragments may also be present beneath the Nazareth, Saya de Malha and Chagos Banks, as well as the Maldives and Laccadives. These were once joined together in a microcontinent we called “Mauritia”, and became scattered across the Indian Ocean during Gondwana break-up, probably by mid-ocean ridge “jumps”. This work, widely reported in international news media, allows a more refined reconstruction of Gondwana, suggests that continental break-up is far more complex than previously perceived, and has important implications for regional geological correlations and exploration models. Our results, as interesting as they may be, are merely follow-ups that build upon the prescient and pioneering ideas of Alex Du Toit, whose legacy I appreciatively acknowledge.
DS202004-0498
2019
Ashwal, L.D.Wandering continents of the Indian Ocean. DARC's.South African Journal of Geology, Vol. 122, 4, pp. 397-420.Indiaalkaline, carbonatites

Abstract: On the last page of his 1937 book “Our Wandering Continents” Alex Du Toit advised the geological community to develop the field of “comparative geology”, which he defined as “the study of continental fragments”. This is precisely the theme of this paper, which outlines my research activities for the past 28 years, on the continental fragments of the Indian Ocean. In the early 1990s, my colleagues and I were working in Madagascar, and we recognized the need to appreciate the excellent geological mapping (pioneered in the 1950s by Henri Besairie) in a more modern geodynamic context, by applying new ideas and analytical techniques, to a large and understudied piece of continental crust. One result of this work was the identification of a 700 to 800 Ma belt of plutons and volcanic equivalents, about 450 km long, which we suggested might represent an Andean-type arc, produced by Neoproterozoic subduction. We wondered if similar examples of this magmatic belt might be present elsewhere, and we began working in the Seychelles, where late Precambrian granites are exposed on about 40 of the >100 islands in the archipelago. Based on our new petrological, geochemical and geochronological measurements, we built a case that these ~750 Ma rocks also represent an Andean-type arc, coeval with and equivalent to the one present in Madagascar. By using similar types of approaches, we tracked this arc even further, into the Malani Igneous Province of Rajasthan, in northwest India. Our paleomagnetic data place these three entities adjacent to each other at ~750 Ma, and were positioned at the margins, rather than in the central parts of the Rodinia supercontinent, further supporting their formation in a subduction-related continental arc. A widespread view is that in the Neoproterozoic, Rodinia began to break apart, and the more familiar Gondwana supercontinent was assembled by Pan-African (~500 to 600 Ma) continental collisions, marked by the highly deformed and metamorphosed rocks of the East African Orogen. It was my mentor, Kevin Burke, who suggested that the present-day locations of Alkaline Rocks and Carbonatites (called “ARCs”) and their Deformed equivalents (called “DARCs”), might mark the outlines of two well-defined parts of the Wilson cycle. We can be confident that ARCs formed originally in intracontinental rift settings, and we postulated that DARCs represent suture zones, where vanished oceans have closed. We also found that the isotopic record of these events can be preserved in DARC minerals. In a nepheline syenite gneiss from Malawi, the U-Pb age of zircons is 730 Ma (marking the rifting of Rodinia), and that of monazites is 522 Ma (marking the collisional construction of Gondwana). A general outline of how and when Gondwana broke apart into the current configuration of continental entities, starting at about 165 Ma, has been known for some time, because this record is preserved in the magnetic properties of ocean-floor basalts, which can be precisely dated. A current topic of active research is the role that deep mantle plumes may have played in initiating, or assisting, continental fragmentation. I am part of a group of colleagues and students who are applying complementary datasets to understand how the Karoo (182 Ma), Etendeka (132 Ma), Marion (90 Ma) and Réunion (65 Ma) plumes influenced the break-up of Gondwana and the development of the Indian Ocean. Shortly after the impingement of the Karoo plume at 182 Ma, Gondwana fragmentation began as Madagascar + India + Antarctica separated from Africa, and drifted southward. Only after 90 Ma, when Madagascar was blanketed by lavas of the Marion plume, did India begin to rift, and rapidly drifted northward, assisted by the Marion and Deccan (65 Ma) plumes, eventually colliding with Asia to produce the Himalayas. It is interesting that a record of these plate kinematics is preserved in the large Permian - Eocene sedimentary basins of western Madagascar: transtensional pull-apart structures are dextral in Jurassic rocks (recording initial southward drift with respect to Africa), but change to sinistral in the Eocene, recording India’s northward drift. Our latest work has begun to reveal that small continental fragments are present in unexpected places. In the young (max. 9 Ma) plume-related, volcanic island of Mauritius, we found Precambrian zircons with ages between 660 and 3000 Ma, in beach sands and trachytic lavas. This can only mean that a fragment of ancient continent must exist beneath the young volcanoes there, and that the old zircons were picked up by ascending magmas on their way to surface eruption sites. We speculate, based on gravity inversion modelling, that continental fragments may also be present beneath the Nazareth, Saya de Malha and Chagos Banks, as well as the Maldives and Laccadives. These were once joined together in a microcontinent we called "Mauritia", and became scattered across the Indian Ocean during Gondwana break-up, probably by mid-ocean ridge "jumps". This work, widely reported in international news media, allows a more refined reconstruction of Gondwana, suggests that continental break-up is far more complex than previously perceived, and has important implications for regional geological correlations and exploration models. Our results, as interesting as they may be, are merely follow-ups that build upon the prescient and pioneering ideas of Alex Du Toit, whose legacy I appreciatively acknowledge.
DS202008-1367
2020
Aulbach, S.Temperature dependent rutile solubility in garnet and clinopyroxene from mantle eclogite: implications for continental crust formation and V-based oxybarometry. ( kimberlite)Journal of Petrology, , https://doi.org/10. 1093/petrology/egaa065Mantleoxygen fugacity

Abstract: Despite its accessory mineral status in metabasaltic rocks, rutile controls the whole-rock Ti, Nb and Ta budget. These are key elements used to trace fluid- and melt-mediated mass transfer across the mantle-crust boundary. Rutile also contains significant amounts of the redox-sensitive element V, which is increasingly used to estimate oxygen fugacity. Kimberlite-borne mantle eclogite xenoliths, which are frequently rutile-bearing, have been interpreted as residues from the extraction of silicic partial melt similar in composition to the average continental crust. Published mineral compositions for eclogite xenoliths from various cratons combined with geothermobarometrical calculations show that TiO2 contents in garnet and clinopyroxene increase with increasing temperature of last residence in the lithospheric mantle, while apparent clinopyroxene-garnet distribution coefficients decrease. This implies that (1) increasing TiO2 contents in eclogitic garnet or clinopyroxene are not a signature of increasing metasomatism with depth, (2) whole-rock eclogites reconstructed without rutile will increasingly underestimate TiO2, Nb and Ta contents with decreasing temperature, and (3) low-temperature eclogites are more likely to contain free rutile. Only about a third of the ~250 samples considered here would have whole-rock TiO2 contents (reconstructed with calculated rutile modes) required for rutile saturation during subduction and partial melting. If there is a role for subducting oceanic crust now sampled as mantle eclogite, the characteristic Ti-Nb-Ta depletion in continental crust may require fluid-dominated processes, where these elements are not efficiently mobilised.
DS202009-1609
2020
Aulbach, S.Temperature-dependent rutile solubility in garnet and clinopyroxene from mantle eclogite: implications for continental crust formation and V-based oxybarometer.Journal of Petrology, in press available, 89p. PdfMantleeclogite

Abstract: Despite its accessory mineral status in metabasaltic rocks, rutile controls the whole-rock Ti, Nb and Ta budget. These are key elements used to trace fluid- and melt-mediated mass transfer across the mantle-crust boundary. Rutile also contains significant amounts of the redox-sensitive element V, which is increasingly used to estimate oxygen fugacity. Kimberlite-borne mantle eclogite xenoliths, which are frequently rutile-bearing, have been interpreted as residues from the extraction of silicic partial melt similar in composition to the average continental crust. Published mineral compositions for eclogite xenoliths from various cratons combined with geothermobarometrical calculations show that TiO2 contents in garnet and clinopyroxene increase with increasing temperature of last residence in the lithospheric mantle, while apparent clinopyroxene-garnet distribution coefficients decrease. This implies that (1) increasing TiO2 contents in eclogitic garnet or clinopyroxene are not a signature of increasing metasomatism with depth, (2) whole-rock eclogites reconstructed without rutile will increasingly underestimate TiO2, Nb and Ta contents with decreasing temperature, and (3) low-temperature eclogites are more likely to contain free rutile. Only about a third of the ~250 samples considered here would have whole-rock TiO2 contents (reconstructed with calculated rutile modes) required for rutile saturation during subduction and partial melting. If there is a role for subducting oceanic crust now sampled as mantle eclogite, the characteristic Ti-Nb-Ta depletion in continental crust may require fluid-dominated processes, where these elements are not efficiently mobilised.
DS202004-0499
2020
Aulbach, S., Masuyeau, M., Gerdes, A., Garber, J.M.Ultramafic carbonated melt- and-auto -metasomatism in mantle eclogites: compositional effects and geophysical consequences.Geochemistry, Geophysics, Geosystems, in press available, 41p. PdfMantleeclogites
DS202006-0909
2020
Aulbach, S., Symes, C., Chacko, T.Elemental and radiogenic isotope perspective on formation and transformation of cratonic lower crust: Central Slave craton ( Canada).Geochimica et Cosmochimica Acta, Vol. 278, pp. 78-83.Canada, Northwest Territorieskimberlites

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.
DS202006-0910
2020
Aulbach, S., Viljoen, K.S., Gerdes, A.Diamondiferous and barren eclogites and pyroxenites from the western Kaapvaal craton record subduction processes and mantle metasomatism respectively.Lithos, in press available 52p. PdfAfrica, South Africadeposit - Doomkloof-Sover

Abstract: Mineral major and trace elements combined with Sr isotopes of clinopyroxene are used to unravel the origins and evolution of mantle eclogite and pyroxenite xenoliths from the Doornkloof-Sover orangeite dike (western Kaapvaal craton), and to investigate the generation and destruction of diamond in these rocks. Two different eclogite types are present: (1) MgO-poor eclogites (MgO?=?7.3 to 14.5?wt%; n?=?43) with accessory diamond ± corundum and kyanite; garnet grossular content (median Ca#?=?0.25) and clinopyroxene jadeite content (0.39). Reconstructed bulk rocks are LREE-depleted (median La 0.29?ppm) and have low median Cr2O3 (0.06?wt%) and incompatible trace-element contents (e.g. Sr, Zr, Ba, Pb, Th), and high Li and transition metal abundances. Some are characterised by stepped REE patterns or steep slopes in the MREE, similar to eclogites affected by interaction with dehydration fluids generated in subduction zones. These fluids may also have deposited diamond in typically reducing eclogite assemblages at diamond-stable pressures. (2) MgO-rich eclogites and pyroxenites (MgO?=?14.0 to 20.0?wt%; n?=?29), which are barren and enriched in LREE (median La 1.39?ppm), Cr2O3 (0.25?wt%) and incompatible trace elements, with lower Li and transition metal abundances than the MgO-poor group. These are typical signatures of carbonated ultramafic melt metasomatism in the mantle lithosphere. Strontium isotopic compositions vary widely in both groups, but high Cr2O3 and Ba contents are dominantly associated with 87Sr/86Sr?>?0.7055. This reflects interaction with metasomatic agents remobilised from ancient lithospheric metasomes, which eventually gave rise to regional orangeite magmatism. The presence of strong positive Eu anomalies in both groups, including two pyroxenites, requires low-pressure igneous protoliths, presumably derived from a ca. 3?Ga spreading ridge, as reported for other eclogite materials from the western Kaapvaal craton. Based on the proportions of MgO-poor and -rich eclogites and pyroxenites, approximately 40% of the diamond inventory were destroyed by mantle metasomatism centred at ~135?±?15?km depth, overlapping a low-velocity anomaly (mid-lithospheric discontinuity). Two diamondiferous orangeites =20?km from Doornkloof-Sover contain significantly different eclogite xenolith populations: At Newlands, MgO-poor diamondiferous eclogites are present in addition to barren MgO-rich ones and pyroxenite, suggesting that the host orangeite sampled a source region equally affected by diamond-destructive mantle metasomatism, whereas at Bellsbank, all eclogites are MgO-poor and LREE-depleted. This may explain higher diamond grades reported for this locality compared to Newlands or Doornkloof-Sover.
DS202008-1368
2019
Aulbach, S., Woodand, A.B., Stern, R.A., Vasileyev, P., Heaman, L.M., Viljoen, K.S.Evidence for a dominantly reducing Archean ambient mantle from two redox proxies, and low oxygen fugacity of deeply subducted oceanic crust. Nature Research Scientific Reports, Vol. 9:20190 doir.org/10.38 /s41598-019-55743-1, 11p. PdfMantleeclogite

Abstract: Oxygen fugacity (ƒO2) is an intensive variable implicated in a range of processes that have shaped the Earth system, but there is controversy on the timing and rate of oxidation of the uppermost convecting mantle to its present ƒO2 around the fayalite-magnetite-quartz oxygen buffer. Here, we report Fe3+/SFe and ƒO2 for ancient eclogite xenoliths with oceanic crustal protoliths that sampled the coeval ambient convecting mantle. Using new and published data, we demonstrate that in these eclogites, two redox proxies, V/Sc and Fe3+/SFe, behave sympathetically, despite different responses of their protoliths to differentiation and post-formation degassing, seawater alteration, devolatilisation and partial melting, testifying to an unexpected robustness of Fe3+/SFe. Therefore, these processes, while causing significant scatter, did not completely obliterate the underlying convecting mantle signal. Considering only unmetasomatised samples with non-cumulate and little-differentiated protoliths, V/Sc and Fe3+/SFe in two Archaean eclogite suites are significantly lower than those of modern mid-ocean ridge basalts (MORB), while a third suite has ratios similar to modern MORB, indicating redox heterogeneity. Another major finding is the predominantly low though variable estimated ƒO2 of eclogite at mantle depths, which does not permit stabilisation of CO2-dominated fluids or pure carbonatite melts. Conversely, low-ƒO2 eclogite may have caused efficient reduction of CO2 in fluids and melts generated in other portions of ancient subducting slabs, consistent with eclogitic diamond formation ages, the disproportionate frequency of eclogitic diamonds relative to the subordinate abundance of eclogite in the mantle lithosphere and the general absence of carbonate in mantle eclogite. This indicates carbon recycling at least to depths of diamond stability and may have represented a significant pathway for carbon ingassing through time.
DS202002-0161
2019
Aulbach, S., Woodland, A.B., Stern, R.A., Vasilyev, P., Heaman, L.M., Viljoen, K.S.Evidence for a dominantly reducing Archaean ambient mantle from two redox proxies, and low oxygen fugacity of deeply subducted oceanic crust.Nature Research Scientific Reports, https://doi.org/10.1038/ s41598-019-55743-1 11p. PdfMantlemelting, redox

Abstract: Privacy Policy. You can manage your preferences in 'Manage Cookies'. Oxygen fugacity (fO2) is an intensive variable implicated in a range of processes that have shaped the Earth system, but there is controversy on the timing and rate of oxidation of the uppermost convecting mantle to its present fO2 around the fayalite-magnetite-quartz oxygen buffer. Here, we report Fe3+/SFe and ƒf2 for ancient eclogite xenoliths with oceanic crustal protoliths that sampled the coeval ambient convecting mantle. Using new and published data, we demonstrate that in these eclogites, two redox proxies, V/Sc and Fe3+/SFe, behave sympathetically, despite different responses of their protoliths to differentiation and post-formation degassing, seawater alteration, devolatilisation and partial melting, testifying to an unexpected robustness of Fe3+/SFe. Therefore, these processes, while causing significant scatter, did not completely obliterate the underlying convecting mantle signal. Considering only unmetasomatised samples with non-cumulate and little-differentiated protoliths, V/Sc and Fe3+/SFe in two Archaean eclogite suites are significantly lower than those of modern mid-ocean ridge basalts (MORB), while a third suite has ratios similar to modern MORB, indicating redox heterogeneity. Another major finding is the predominantly low though variable estimated fO2 of eclogite at mantle depths, which does not permit stabilisation of CO2-dominated fluids or pure carbonatite melts. Conversely, low-fO2 eclogite may have caused efficient reduction of CO2 in fluids and melts generated in other portions of ancient subducting slabs, consistent with eclogitic diamond formation ages, the disproportionate frequency of eclogitic diamonds relative to the subordinate abundance of eclogite in the mantle lithosphere and the general absence of carbonate in mantle eclogite. This indicates carbon recycling at least to depths of diamond stability and may have represented a significant pathway for carbon ingassing through time.
DS202004-0500
2020
Ba, M.H., Ibough, H., Lo, K., Youbi, N., Jaffal, M., Ernst, R.E., Niang, A.J., Dia, I., Abdeina, E.H., Bensalah, M.K., Boumehdi, M.A., Soderlund, U.Spatial and temporal distribution patterns of Precambrian mafic dyke swarms in northern Mauritania ( West African Craton): analysis and results fro remote sensing interpretation, geographical information systems ( GIS), Google Earth TM images, and regionaArabian Journal of Geosciences, Vol. 13, , 209 orchid.org/ 0000-002-3287-9537Africa, Mauritaniacraton

Abstract: We used remote sensing, geographical information systems, Google Earth™ images, and regional geology in order to (i) improve the mapping of linear structures and understand the chronology of different mafic dyke swarms in the Ahmeyim area that belongs to the Archean Tasiast-Tijirit Terrane of the Reguibat Shield, West African craton, NW Mauritania. The spatial and temporal distributions with the trends of the dyke swarms provide important information about geodynamics. The analysis of the mafic dyke swarms map and statistical data allow us to distinguish four mafic dyke swarm sets: a major swarm trending NE-SW to NNE-SSW (80%) and three minor swarms trending EW to ENE-WSW (9.33%), NW-SE to WNW-ESE (9.06%), and NS (1.3%). The major swarms extend over 35 km while the minor swarms do not exceed 13 km. The Google Earth™ images reveal relative ages through crossover relationships. The major NE-SW to NNE-SSW and the minor NS swarms are the oldest generations emplaced in the Ahemyim area. The NW-SE-oriented swarm dykes which are cutting the two former swarms are emplaced later. The minor E-W to WSW-ENE swarms are probably the youngest. A precise U-Pb baddeleyite age of 2733?±?2 Ma has been obtained for the NNE-SSW Ahmeyim Great Dyke. This dyke is approximately 1500 m wide in some zone and extends for more than 150 km. The distinct mafic dyke swarms being identified in this study can potentially be linked with coeval magmatic events on other cratons around the globe to identify reconstructed LIPs and constrain continental reconstructions.
DS202003-0330
2019
Badukhinov, L.D., Spetius, Z.V.. Kislov, E.V., Ivanov, A.S., Monkhorov, R.V.Parageneses of garnet inclusions in diamonds from Yakutia kimberlites based on Raman and IR spectroscopy data. Udachnaya, Zapolyarnaya, Komolskaya, Yuibeyana, Aikhal, Mir, Mayskaya.Geology of Ore Deposits, Vol. 61, 7, pp. 606-612. pdfRussia, Yakutiadiamond inclusions
DS202001-0002
2019
Ball, P.Black diamonds.Nature Materials, Vol. 18, pp. 1266-1277.Globalnanodiamond
DS202002-0162
2020
Barras, C.New signs of a shielding magnetic field found in Earth's oldest rock crystals ( zircons) Tarduno researcherScience, doi:101126/science.aba9499Mantlegeophysics - magnetics
DS202001-0003
2019
Barron, L.M., Barron, B.J., Sutherland, F.L.Re-appraisal of published nitrogen aggregation results in diamonds from Copeton, New South Wales.Australian Journal of Earth Sciences, Vol. 67, 1, pp. 151-152.Australia, New South Walesdeposit - Copeton
DS202009-1610
2020
Bassoo, R., Befus, K.S., Liang, P., Forman, S.L., Sharman, G.Deciphering the enigmatic origin of Guyana's diamonds.The American Mineralogist, in press available 59p. PdfSouth America, Guyanadiamond crystallography

Abstract: Diamonds have long been mined from alluvial terrace deposits within the rainforest of Guyana, South America. No primary kimberlite deposits have been discovered in Guyana, nor has there been previous studies on the mineralogy and origin of the diamonds. Paleoproterozoic terranes in Guyana are prospective to diamond occurrences because the most productive deposits are associated spatially with the eastern escarpment of the Paleoproterozoic Roraima Supergroup. Geographic proximity suggests that the diamonds are detrital grains eroding from the <1.98 Ga conglomerates, metamorphosed to zeolite and greenschist facies. The provenance and paragenesis of the alluvial diamonds are described using a suite of placer diamonds from different locations across the Guiana Shield. Guyanese diamonds are typically small, and those in our collection range from 0.3 to 2.7 mm in diameter; octahedral and dodecahedral, with lesser cubic and minor macle forms. The diamonds are further subdivided into those with abraded and non-abraded surfaces. Abraded diamonds show various colors in cathodoluminescence whereas most non-abraded diamonds appear blue. In all populations, diamonds are predominantly colorless, with lesser brown to yellow and very rare white. Diamonds are predominantly Type IaAB and preserve moderate nitrogen aggregation and total nitrogen concentrations ranging from trace to ~1971 ppm. The kinetics of nitrogen aggregation indicate mantle-derived residence temperatures of 1124 ± 100 ºC, assuming residence times of 1.3 Ga and 2.6 Ga for abraded and non-abraded diamonds respectively. The diamonds are largely sourced from the peridotitic to eclogitic lithospheric upper mantle based on both d13C values of -5.82 ± 2.45‰ (VPDB-LSVEC) and inclusion suites predominantly comprised of forsterite, enstatite, Cr-pyrope, chromite, rutile, clinopyroxene, coesite, and almandine garnet. Detrital, accessory minerals are non-kimberlitic. Detrital zircon geochronology indicates diamondiferous deposits are predominantly sourced from Paleoproterozoic rocks of 2079 ± 88 Ma.
DS202012-2204
2020
Bassoo, R., Refus, K.S.Finders Keepers: Crater of Diamonds Gems & Gemology, Vol. 56, 2, summer pp. 311-314. United States, Arkansasdeposit - Crater of diamonds

Abstract: There’s only one place on earth where the general public can prospect for diamonds directly from a primary kimberlite pipe: Crater of Diamonds State Park. This park is nestled among the pines, 100 miles off the interstate near the town of Murfreesboro, Arkansas. It boasts a network of scenic walking trails, picnic sites, and campsites. At its Diamond Discovery Center, visitors can learn about the local geology. Staff are also on hand to identify any minerals that are taken home, per their "finders, keepers" policy. The park is an ideal spot for a field trip. The state also hosts many other unusual igneous rocks, including carbonatite, lamprophyre, and lamproite. With this in mind, our university petrology class piled into a van to visit Arkansas and learn about mantle-derived magmas and associated volcanism. As a side quest, we wanted to try prospecting.
DS202005-0720
2019
Bateman , M.The Handbook of Luminescence Dating. ...dating techniques, including optically and infrared simulated luminescence and thermoluminescence applications.Whiitles Publishing Dunbeith Scotland ( Reviewed in Geoscience Canada Vol. 46, pp. 195-196., 416p. $ 163.00 GlobalLuminescence

Abstract: Luminescence dating is now widely applied by scientists working in Quaternary geology and archaeology to obtain ages for events as diverse as past earthquakes, desertification and cave occupation sites. Using quartz or feldspar minerals found in almost ubiquitous sand and finer sediments, luminescence can provide ages from over 500,000 years ago to modern. Written by some of the foremost experts in luminescence dating from around the world, this book takes a new approach. It explains what luminescence can and can’t do, what and where to sample, types of measurements available and how to interpret and analyse ages once they are measured. It is accordingly for scientists who require luminescence ages for their research rather than those scientists developing the luminescence technique or making their own luminescence measurements. The background to the technique is explained in simple terms so that the range of potential applications, limits and issues can be understood. The book helps scientists plan where and what to sample to optimise the successful application of luminescence and stemming from that the chronologies that can be constructed. The Handbook sets out the challenges and limitations when applying luminescence dating in different environmental and archaeological settings and gives practical advice on how issues might be avoided in sampling, or mitigated by requesting different laboratory measurement approaches or analysis. Guidance is provided on how luminescence ages can be interpreted and published as well as how they can be used within chronological frameworks. With luminescence dating continuing to develop, information on more experimental approaches is given which may help expand the range of chronological challenges to which luminescence dating can be routinely applied
DS202006-0911
2020
Baudouin, C., France, L., Boulanger, M., Dalou, C., Devidal, J-L.Trace element partitioning between clinopyroxene and alkaline magmas: parametrization and role of M1 site on HREE enrichment in clinopyroxenes.Contributions to Mineralogy and Petrology, Vol. 175, 15p. PdfAfrica, Tanzaniadeposit - Oldoinyo Lengai

Abstract: Trace element partitioning between minerals and liquids provides crucial constraints on igneous processes. We quantified trace element concentrations in clinopyroxene (Cpx) phenocrysts and their phonolite melt inclusions from the 2007-08 eruption of Oldoinyo Lengai (Tanzania), and report Cpx-melt partition coefficients (D) and corresponding partitioning equations for rare earth elements (REE) and high field strength elements (HFSE) in alkaline magmas. Heavy REE (HREE: Er, Tm, Yb, Lu) are enriched relative to middle REE in alkaline Cpx and display a specific partitioning behavior that is characteristic of alkaline systems. HFSE (Ti, Zr, Hf) and HREE have similar D values (DHf?=?0.25; DLu?=?0.4) that are significantly higher than MREE (DSm?=?0.06). High DHREE/DMREE are strongly correlated with the high values of DZr and DHf relative to the low DMREE values. In this study, REE partitioning between phonolite melt and Cpx is not consistent with standard models assuming incorporation of all REE in the Cpx M2 site, but rather highlights HREE substitution in both the M1 and M2 sites. Here we highlight the preferential incorporation of HREE in the VI-coordinated M1 site, whereas light REE and MREE remain mostly distributed in the VIII-coordinated M2 site. REE partitioning is strongly dependent on Cpx chemistry: the ideal ionic radius and HREE incorporation in the M1 site increase with increasing Fe3+ content and decrease with increasing Mg2+ and AlVI content. In our study, we focus on alkaline evolved magmas, and update existing models to obtain adequate DHREE for alkaline evolved melts. We provide equations to quantify REE and HFSE partitioning, and HREE enrichment in Cpx that are based on Cpx major element composition and temperature. We propose a new model based on the lattice strain approach that predicts HREE partitioning between Cpx and alkaline magmas. The knowledge of the melt composition or of the trace element contents is not required to obtain DREE from the new model. An improved parameterization of HFSE partitioning between Cpx and phonolite and trachy-phonolite melts is also provided herein. We discuss the potential implications of the new data on our understanding of REE deposits that are commonly associated with igneous alkaline complexes.
DS202005-0721
2020
Bauer, A.M., Reimink, J.R., Chacko, T., Foley, B.J., Shirey, S.B., Pearson, D.G.Hafnium isotopes in zircons document the gradual onset of mobile-lid tectonics. ( Pilbara, Zimbabwe, Slave, Singhbhum, Rae, Wyoming, Jack HillsGeochemical Perspectives Letters, Vol. 14, pp. 1-6.GlobalTectonics

Abstract: The tectonic regime of the early Earth has proven enigmatic due to a scarcity of preserved continental crust, yet how early continents were generated is key to deciphering Earth’s evolution. Here we show that a compilation of data from 4.3 to 3.4 Ga igneous and detrital zircons records a secular shift to higher 176Hf/177Hf after ~3.8-3.6 Ga. This globally evident shift indicates that continental crust formation before ~3.8-3.6 Ga largely occurred by internal reworking of long-lived mafic protocrust, whereas later continental crust formation involved extensive input of relatively juvenile magmas, which were produced from rapid remelting of oceanic lithosphere. We propose that this secular shift in the global hafnium isotope record reflects a gradual yet widespread transition from stagnant-lid to mobile-lid tectonics on the early Earth.
DS202004-0501
2020
BBC NewsDiamond samples in Canada reveal size of lost continent. Chidliak and UBC Kopylovabbc.com, March 20, 1/2p.Canada, Baffin Islandcraton
DS202002-0163
2019
Beard, C.D., van Hinsberg, V.J., Stix, J., Wilke, M.Clinopyroxene melt trace element partitioning in sodic alkaline magmas.Journal of Petrology, in press available 92p. PdfEurope, Canary IslandsREE

Abstract: Clinopyroxene is a key fractionating phase in alkaline magmatic systems, but its impact on metal enrichment processes, and the formation of REE + HFSE mineralisation in particular, is not well understood. To constrain the control of clinopyroxene on REE + HFSE behaviour in sodic (per)alkaline magmas, a series of internally heated pressure vessel experiments was performed to determine clinopyroxene-melt element partitioning systematics. Synthetic tephriphonolite to phonolite compositions were run H2O-saturated at 200?MPa, 650-825?C with oxygen fugacity buffered to log f O2 ˜ ?QFM + 1 or log f O2 ˜ ?QFM +5. Clinopyroxene-glass pairs from basanitic to phonolitic fall deposits from Tenerife, Canary Islands, were also measured to complement our experimentally-derived data set. The REE partition coefficients are 0.3-53, typically 2-6, with minima for high-aegirine clinopyroxene. Diopside-rich clinopyroxenes (Aeg5-25) prefer the MREE and have high REE partition coefficients (DEuup to 53, DSmup to 47). As clinopyroxene becomes more Na- and less Ca-rich (Aeg25-50), REE incorporation becomes less favourable, and both the VIM1 and VIIIM2 sites expand (to 0.79 Å and 1.12 Å), increasing DLREE/DMREE. Above Aeg50 both M sites shrink slightly and HREE (VIri= 0.9 Å ˜ Y) partition strongly onto the VIM1 site, consistent with a reduced charge penalty for REE3+ ? Fe3+ substitution. Our data, complemented with an extensive literature database, constrain an empirical model that predicts trace element partition coefficients between clinopyroxene and silicate melt using only mineral major element compositions, temperature and pressure as input. The model is calibrated for use over a wide compositional range and can be used to interrogate clinopyroxene from a variety of natural systems to determine the trace element concentrations in their source melts, or to forward model the trace element evolution of tholeiitic mafic to evolved peralkaline magmatic systems.
DS202002-0164
2020
Belley, P.M., Groat, L.A.Metamorphosed carbonate platforms and controls on the genesis of sapphire, gem spinel, and lapis Lazuli: insight from the Lake Harbour Group, Nunavut, Canada and implications for gem exploration.Ore Geology Reviews, Vol. 116, 10p. PdfCanada, Nunavutgemstones

Abstract: Baffin Island's Lake Harbour Group (LHG), a Paleoproterozoic granulite facies metasedimentary sequence rich in carbonates, contains occurrences of the gemstones sapphire (corundum), spinel (including vivid blue, cobalt-enriched spinel), and lapis lazuli (haüyne-bearing rock). Most occurrences of these gem minerals are uniquely metasedimentary (carbonates and calc-silicate rock), while a few spinel occurrences formed from metasomatic reactions between Si-Al-rich rock (syenogranite or gneiss) and marble. The metasedimentary corundum, spinel, and haüyne occurrences have similar protoliths: primarily dolomitic marls with a high Al/Si relative abundance (interpreted as sandy mud to clay siliciclastic fraction in the protolith). Kimmirut-type sapphire deposits formed via a multi-step metamorphic process under three different and specific P-T conditions. Lapis lazuli formation required the presence of evaporites to provide Na and possibly S for the blue mineral haüyne. In addition to high Al/Si calc-silicate rocks, spinel also occurs in impure dolomitic marbles with very low K/Al. Potential for Kimmirut-type sapphire deposits is expected to be restricted to metacarbonate sequences proximal to the thrust fault separating the LHG from the Narsajuaq Arc, where retrograde upper amphibolite facies mineralization is most pervasive. Spinel and Kimmirut-type sapphire deposits are expected to be found in dolomitic marble sequences rich in calc-silicate layers. The potential occurrence of lapis lazuli is more difficult to predict but deposits could be identified thanks to large geographical footprints and their color. Similar gem occurrences or deposits to those in the LHG may be found in other metacarbonate-bearing terranes with similar metamorphic conditions (and for Kimmirut-type sapphire, a similar metamorphic history). Aerial hyperspectral and photographic surveys are well-suited to gemstone exploration on southern Baffin Island thanks to excellent rock exposure with minimal sediment or plant/lichen cover. Spectral mapping of dolomite-, diopside-, phlogopite-, and scapolite-rich domains in LHG metacarbonate sequences using airborne hyperspectral data is expected to provide exploration targets. Remote sensing exploration could be used in other metacarbonate-bearing, upper amphibolite to granulite facies metamorphic terranes found in polar climates, arid climates, or at high elevation in mountainous regions where such rocks are well exposed with minimal vegetative cover.
DS202008-1369
2020
Benoaouda, R., Kraemer, D., Sitnikova, M., Goldmann, S., Schwarz-Schampera, U., Errami, A., Mouttaqi, A., Bau, M.Discovery of high grade REE-Nb-Fe mineralization associated with calcio-carbonatite in south Morocco.Ore Geology Reviews, in press available, 43p. PdfAfrica, Moroccocarbonatite

Abstract: The recently discovered REE and Nb mineralization in the Twihinat area in the western part of the Oulad Dlim Massif (Adrar Souttouf) in South Morocco is linked to a Cretaceous calciocarbonatite intrusion which was likely formed in an intracontinental rift setting and crops out locally within a ring structure that mainly consists of massive Fe-oxide mineralization and silica breccia. The carbonatite shows intensively metasomatized zones, which contain bastnaesite and pyrochlore-group minerals as the main REE and Nb ore minerals. They are usually associated with apatite, quartz and Fe-oxides, or trapped in calcite voids, suggesting a secondary ore formation. Within the associated Fe-oxide mineralization, pyrochlore and monazite-(Ce) are the main ore minerals occurring closely associated with quartz and magnetite or hematite. The silica breccia also shows significant subsequent infill of barite, bastnaesite-(Ce) and hydrated ceriopyrochlore, which was identified by EPMA and Raman spectroscopy. Bastnaesite commonly forms prismatic aggregates whereas pyrochlore and ceriopyrochlore usually display subhedral grains along tiny fractures. Structural and textural relationships clearly indicate epigenetic ore formation induced by multiple stages of hydrothermal fluid flow and fracturing. Ore precipitation likely resulted from interaction between low-pH mineralizing hydrothermal fluids and the wall-rock. The latter efficiently buffered the acidity of the fluids and allowed significant amounts of REE and Nb ore minerals to precipitate. Trace element ICP-MS analyses show very high REE and Nb concentrations of up to 0.76 wt% SREE and 0.21 wt% Nb in carbonatite and up to 3 wt% SREE and 1.3 wt% Nb in the associated silica and Fe-oxide mineralization. The results clearly demonstrate that the Twihinat REE-Nb deposits are significant and represent a potential new high-grade resource for these critical metals.
DS202007-1125
2020
Berkesi, M., Bali, E., Bodnar, R.J., Szabo, A., Guzmics, T.Carbonatite and highly peralkaline nephelinitie melts from Oldoinyo Lengai volcano, Tanzania: the role of natrite-normative fluid degassing.Gondwana Research, Vol. 85, pp. 76-83. pdfAfrica, Tanzaniadeposit - Oldoinyo Lengai

Abstract: Oldoinyo Lengai, located in the Gregory Rift in Tanzania, is a world-famous volcano owing to its uniqueness in producing natrocarbonatite melts and because of its extremely high CO2 flux. The volcano is constructed of highly peralkaline [PI = molar (Na2O + K2O)/Al2O3 > 2-3] nephelinite and phonolites, both of which likely coexisted with carbonate melt and a CO2-rich fluid before eruption. Results of a detailed melt inclusion study of the Oldoinyo Lengai nephelinite provide insights into the important role of degassing of CO2-rich vapor in the formation of natrocarbonatite and highly peralkaline nephelinites. Nepheline phenocrysts trapped primary melt inclusions at 750-800 °C, representing an evolved state of the magmas beneath Oldoinyo Lengai. Raman spectroscopy, heating-quenching experiments, low current EDS and EPMA analyses of quenched melt inclusions suggest that at this temperature, a dominantly natritess-normative, F-rich (7-14 wt%) carbonate melt and an extremely peralkaline (PI = 3.2-7.9), iron-rich nephelinite melt coexisted following degassing of a CO2 + H2O-vapor. We furthermore hypothesize that the degassing led to re-equilibration between the melt and liquid phases that remained and involved 1/ mixing between the residual (after degassing) alkali carbonate liquid and an F-rich carbonate melt and 2/ enrichment of the coexisting nephelinite melt in alkalis. We suggest that in the geological past similar processes were responsible for generating highly peralkaline silicate melts in continental rift tectonic settings worldwide.
DS202002-0165
2019
Bezada, M.J., Smale, J.Lateral variations in lithospheric mantle structure control the location of intracontinental seismicity in Australia.Geophysical Research Letters, Vol. 46, 22, pp. 12862-12869.Australiageophysics - seismic

Abstract: Despite decades of study, the mechanisms that lead to the localization of intracontinental seismicity remain vigorously debated. We find a very strong correlation between the attenuation of teleseismic P waves and the occurrence of intraplate seismicity in Australia. The regions with the highest attenuation host ~2 orders of magnitude more earthquakes per unit of area than the least attenuating regions. We argue that the attenuation we observe is produced by lateral variations in the thickness and/or viscosity of the lithospheric mantle and further suggest that the correlation we document implies that lithospheric mantle structure exerts first-order controls on the localization of intraplate seismicity.
DS202005-0722
2020
Bhaskar Rao, Y.J., Kumar, T.V., Screeenivas, B., Babu, E.V.S.S.K.A review of Paleo- to Neoarchean crust evolution in the Dharwar craton, southern India and the transition towards a plate tectonic regime.Episodes ( IUGS), Vol. 43, 1, pp. 51-68.Indiacraton

Abstract: An emerging view is that Earth’s geodynamic regime witnessed a fundamental transition towards plate tectonics around 3.0 Ga (billion years). However, the manifestations of this change may have been diachronous and craton-specific. Here, we review geological, geophysical and geochronological data (mainly zircon U-Pb age-Hf isotope compositions) from the Dharwar craton representing over a billion year-long geologic history between ~3.5 and 2.5 Ga. The Archean crust comprises an oblique section of ~12 km from middle to deep crust across low- to mediumgrade granitegreenstone terranes, the Western and Eastern Dharwar Cratons (WDC and EDC), and the highgrade Southern Granulite Terrain (SGT). A segment of the WDC preserving Paleo- to Mesoarchean gneisses and greenstones is characterised by ‘dome and keel’ structural pattern related to vertical (sagduction) tectonics. The geology of the regions with dominantly Neoarchean ages bears evidence for convergent (plate) tectonics. The zircon U-Pb age-Hf isotope data constrain two major episodes of juvenile crust accretion involving depleted mantle sources at 3.45 to 3.17 Ga and 2.7 to 2.5 Ga with crustal recycling dominating the intervening period. The Dharwar craton records clear evidence for the operation of modern style plate tectonics since ~2.7 Ga.
DS202009-1611
2020
Bhaskar Rao, Y.J., Kumar, T.V., Sreenivas, B., Babu, E.V.S.S.K.A review of Paleo to Neoarchean crustal evolution in the Dharwar craton, southern Indian and the transition towards a plate tectonic regime.Episodes, Vol. 43, 1, pp. 51-68.Indiacraton

Abstract: An emerging view is that Earth’s geodynamic regime witnessed a fundamental transition towards plate tectonics around 3.0 Ga (billion years). However, the manifestations of this change may have been diachronous and craton-specific. Here, we review geological, geophysical and geochronological data (mainly zircon U-Pb age-Hf isotope compositions) from the Dharwar craton representing over a billion year-long geologic history between ~3.5 and 2.5 Ga. The Archean crust comprises an oblique section of ~12 km from middle to deep crust across low- to mediumgrade granitegreenstone terranes, the Western and Eastern Dharwar Cratons (WDC and EDC), and the highgrade Southern Granulite Terrain (SGT). A segment of the WDC preserving Paleo- to Mesoarchean gneisses and greenstones is characterised by ‘dome and keel’ structural pattern related to vertical (sagduction) tectonics. The geology of the regions with dominantly Neoarchean ages bears evidence for convergent (plate) tectonics. The zircon U-Pb age-Hf isotope data constrain two major episodes of juvenile crust accretion involving depleted mantle sources at 3.45 to 3.17 Ga and 2.7 to 2.5 Ga with crustal recycling dominating the intervening period. The Dharwar craton records clear evidence for the operation of modern style plate tectonics since ~2.7 Ga.
DS202009-1612
2020
Bidgood, A.K., Parsons, A.J., Lloyd, G.E., Wtares, D.J., Goddard, R.M.EBSD-based criteria for coesite-to-quartz transformation.Journal of Metamorphic Geology, doi.org/10/111/jmg.12566Mantlecoesite

Abstract: Ultrahigh-pressure (UHP) metamorphism observed in continental terranes implies that continental crust can subduct to ~40 kbar before exhuming to the surface. This process is one of the least understood and widely debated parts of the orogenic cycle. The dominantly felsic composition of UHP continental terranes means that many petrology-based techniques for determining peak pressures and temperatures are often not possible. In such cases, the detection of UHP conditions depends on the preservation of coesite, a rarely preserved mineral in exhumed UHP terranes as it rapidly transforms to quartz on decompression. Consequently, the qualitative identification of palisade quartz microstructures that form during the retrograde transformation of coesite to quartz is often used to identify UHP terranes. In this study, we conduct EBSD and misorientation analysis of palisade quartz inclusions in the coesite-bearing pyrope quartzite from the Dora Maira massif in the Alps, and matrix-scale palisade quartz in the Polokongka La granite from Tso Morari in the Ladakh Himalaya, in order to quantitatively define crystallographic characteristics of quartz after coesite. The repeatability of our observations in two unrelated occurrences of UHP rocks supports our interpretation that the following features provide a systematic and predictable set of criteria to identify the coesite to quartz transition: (1) Quartz crystallographic orientations define spatially and texturally distinct subdomains of palisade quartz grains with ‘single crystal’ orientations defined by distinct c-axis point-maxima. (2) Adjacent subdomains are misorientated with respect to each other by a misorientation angle/axis of 90°/. (3) Within each subdomain, palisade quartz grain boundaries commonly have intra- and inter-granular misorientations of 60°/[0001], consistent with the dauphiné twin law. Our observations imply that the coesite-to-quartz transformation is crystallographically controlled by the epitaxial nucleation of palisade quartz on the former coesite grain, specifically on potential coesite twin planes such as (101) and (021).
DS202012-2205
2020
Blaine, J.Kalahari meanderings The Falcinbridge diamond exploration story Botswana 1975-1988. https://youtu.be /07lKCVFT7LE , Oct. ppt presentationAfrica, BotswanaFalconbridge history

Abstract: 22 October 2020 Overberg Geoscientists Group talk by John Blaine
DS202002-0166
2019
Blundy, J.Carbon - beautiful, essential, deadly.Elements, Vol. 15, p. 367 1p.Globalcarbon
DS202006-0912
2020
Bodnar, R.J., Frezzotti, M.L.Microscale chemistry: raman analysis of fluid and melt inclusions.Elements, Vol. 16, pp. 93-98.Mantlemelt inclusions

Abstract: Raman spectroscopy is a commonly applied nondestructive analytical technique for characterizing fluid and melt inclusions. The exceptional spatial resolution (~1 µm) and excellent spectral resolution (=1 cm-1) permits the characterization of micrometer-scale phases and allows quantitative analyses based on Raman spectral features. Data provided by Raman analysis of fluid and melt inclusions has significantly advanced our understanding of complex geologic processes, including preeruptive volatile contents of magmas, the nature of fluids in the deep crust and upper mantle, the generation and evolution of methane-bearing fluids in unconventional hydrocarbon reservoirs. Anticipated future advances include the development of Raman mass spectroscopy and the use of Raman to monitor reaction progress in synthetic and natural fluid inclusion microreactors.
DS202002-0167
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. ( not specific to diamonds)Earth's Oldest Rocks, Chapter 28, 20p. Pdf.Canada, Manitobacraton
DS202012-2206
2020
Borisova, A.Y., Bindeman, I.N., Toplis, M.J., Zagrtdenov, N.R., Guignard, J., Safonov, O.G., Bychkov, A.Y., Shcheka, S., Melnik, O.E., Marcelli, M., Fehrenbach, J.Zircon survival in shallow asthenosphere and deep lithosphere.American Mineralogist, Vol. 105, pp. 1662-1671. pdfMantlemelting

Abstract: Zircon is the most frequently used mineral for dating terrestrial and extraterrestrial rocks. However, the system of zircon in mafic/ultramafic melts has been rarely explored experimentally and most existing models based on the felsic, intermediate and/or synthetic systems are probably not applicable for prediction of zircon survival in terrestrial shallow asthenosphere. In order to determine the zircon stability in such natural systems, we have performed high-temperature experiments of zircon dissolution in natural mid-ocean ridge basaltic and synthetic haplobasaltic melts coupled with in situ electron probe microanalyses of the experimental products at high current. Taking into account the secondary fluorescence effect in zircon glass pairs during electron microprobe analysis, we have calculated zirconium diffusion coefficient necessary to predict zircon survival in asthenospheric melts of tholeiitic basalt composition. The data imply that typical 100 micron zircons dissolve rapidly (in 10 hours) and congruently upon the reaction with basaltic melt at mantle pressures. We observed incongruent (to crystal ZrO2 and SiO2 in melt) dissolution of zircon in natural mid-ocean ridge basaltic melt at low pressures and in haplobasaltic melt at elevated pressure. Our experimental data raise questions about the origin of zircons in mafic and ultramafic rocks, in particular, in shallow oceanic asthenosphere and deep lithosphere, as well as the meaning of the zircon-based ages estimated from the composition of these minerals. Large size zircon megacrysts in kimberlites, peridotites, alkali basalts and other magmas suggest the fast transport and short interaction between zircon and melt.The origin of zircon megacrysts is likely related to metasomatic addition of Zr into mantle as any mantle melting episode should obliterate them.
DS202011-2030
2012
Borst, A.M.The formation and modification of the sub-cratonic lithospheric mantle beneath Botswana. A petrological, geochemical and isotopic study of peridotite xenoliths from the Letlhakane kimberlite mine. *** note dateMsc. Thesis VRIJE University Amsterdam, 166p. Academia available pdfAfrica, Botswanadeposit - Letlhakane

Abstract: The Letlhakane kimberlite pipes are emplaced in the Proterozoic Makondi Fold Belt, Botswana. They belong to a cluster of kimberlite diatremes that also includes the Orapa diamond mine, approximately 40 km to the northwest. In a previous geochemical study on Letlhakane xenoliths it was proposed that the Makondi Fold Belt is underlain by Archaean mantle that belongs to the Zimbabwe Craton. This implies the Letlhakane Kimberlites were sourced from the edge of Zimbabwe cratonic mantle and ascended through Proterozoic Makondi crust, explaining their rather anomalous tectonic setting. In this study we aim to verify the Archaean nature of the lithospheric mantle beneath Letlhakane and assess the origin and extent of metasomatic modifications in comparison to the Kaapvaal and Zimbabwe Cratons. We present an extensive petrological, geochemical and isotopic dataset on a selection of 38 peridotite xenoliths from Letlhakane in order to characterize the mantle that underlies northern Botswana. Whole rock and mineral major and trace elements were measured by electron microprobe (EMP), laser ablation ICPMS and XRF. Sm-Nd and Lu-Hf isotope analyses were performed on garnet, cpx and amphibole separates from 12 selected samples. The sample suite includes spinel harzburgites, spinel lherzolites, a spinel dunite, a wehrlite, a garnet websterite, garnet harzburgites, garnet lherzolites and amphibole bearing garnet lherzolites. The samples are categorized into four groups based on garnet chemistry and modal compositions: I) garnet free samples, II) garnet harzburgites, II) garnet lherzolites and IV) amphibole-bearing garnet lherzolites. Whole rock major elements and olivine magnesium numbers suggest that the SCLM experienced 20 to 60% melt depletion between 5 and 3 GPa. Reconstructed whole rock HREE concentrations and Lu-Yb systematics indicate that up to 20% melting occurred in the absence of garnet, leading to strong fractionation of HREE. The data suggest a shallow decompressional melting regime, consistent with Archaean cratonic genesis models. Preliminary Re-Os data suggest melt depletion occurred at ~2.7 Ga. All samples experienced various amounts of metasomatic re-enrichment expressed by high modal abundances of garnet, opx, clinopyroxene and amphibole. Silica enrichment occurred to a lesser extent than observed in the Kaapvaal, but the Letlhakane samples show significantly more opx-rich assemblages than reported for the Zimbabwe Craton. Sm-Nd and Lu-Hf isotope signatures of garnet harzburgites suggest LREE enrichment occurred around ~2.0 Ga, possibly related to major tectono-magmatic activity associated with accretion of the Makondi Fold Belt to the Zimbabwe Craton. Cpx from the garnet lherzolites show major isotopic interaction and re-equilibration with Group I Kimberlites, which probably crystallized from pre-cursor kimberlitic melts prior to the Letlhakane eruption at ~93 Ma. Trace elements and Nd-Hf istope systematics of the amphibole bearing samples suggest amphibole metasomatism occurred from a LREE, Na, Ka, Ca and Al enriched hydrous melt around 500 to 600 Ma, possibly associated with Pan-African magmatic activity in northern Botswana. The overall lack of negative Nb-Ta anomalies suggests that metasomatic melts were generated in a within-plate geodynamical environment, rather than a subduction related setting.
DS202006-0913
2020
Boxer, G.Grant is teaching workshops for geologists on how to use QGIS - free GIS program - great for students to learn GIS."https://qgisforgeos .thinkific.com/"., GIS programGlobalGIS on line
DS202008-1370
2020
Bracco Gartner, A.J.J., Davies, G.R., Koornneef, J.M.Sub-nanogram Pb isotope analysis of individual melt inclusions.Goldschmidt 2020, 1p. AbstractMantlemagmatism

Abstract: Precise analysis of 20xPb/204Pb ratios is challenging when the amount of Pb is limited by sample volume or elemental concentration. The current precision impedes meaningful analyses of analytes with sub-nanogram Pb contents, such as individual melt inclusions with typical diameters (<100 µm). Decreasing this lower limit whilst maintaining precision and accuracy is crucial for studies aiming to understand the composition and heterogeneity of melt source regions, and the effects of magma transport from the Earth’s interior. The preferred method for precise analysis of sub-nanogram Pb samples combines miniaturised ion-exchange separation, a Pb double spike, and thermal ionisation mass spectrometry (TIMS) with 10^13 O amplifier technology. This approach allows for interference-free, instrumental mass fractionation-corrected isotope measurements, and therefore provides precision superior to in situ measurements. As a result, reliable analyses can be conducted on samples which contain only a few hundred picograms of Pb. The principal obstacle at the lower limit is the analytical blank, which usually adds a few pg Pb—and thus up to a few percent—to the sample of interest. This contribution may differ for the 207Pb-204Pb-spiked and unspiked runs of one sample, which in turn convolutes the algebraic inversion of the spike. It is therefore imperative to evaluate the magnitude, isotope composition, and homogeneity of the blanks, and constrain how the uncertainty and potential variability within these parameters affect the inversion. Here, we describe the optimised analytical techniques, and discuss the present feasibility and limitations in obtaining precise Pb isotope compositions of rock reference materials and olivine-hosted melt inclusions with sub-nanogram Pb contents. In addition, we discuss the effect of different blank contributions on double-spike analyses using numerical simulations, and evaluate the potential of accurate blank corrections. We find that the optimised technique allows accurate Pb analyses to be conducted on melt inclusions with >200 pg Pb, which will ultimately help to better constrain mantle heterogeneity beneath mid-ocean ridges, oceanic islands, and volcanic arcs.
DS202012-2207
2020
Bradby, J.Diamond bling made within minutes.Sciencetimes.com, https://www.cnn.com /2020/11/19/world/ diamonds-room- temperature-scli -intl-scn/index.html Australiacarbon
DS202002-0168
2020
Braunger, S., Marks, M.A.W., Wenzel, T., Chmyz, L., Azzone, R.G., Markl, G.Do carbonatites and alkaline rocks reflect variable redox conditions in their upper mantle source? ( metasomatism)Earth and Planetary Science Letters, Vol. 533, 11p. PdfMantlecarbonatite

Abstract: A detailed investigation on seven carbonatites and associated alkaline rock complexes (Kaiserstuhl, Sokli, Kovdor, Palabora, Oka, Magnet Cove, Jacupiranga), together with a world-wide comparison between carbonatites, alkaline silicate rocks and mantle xenoliths, implies peculiar redox conditions for carbonatite-bearing alkaline complexes: Carbonatites and associated alkaline rocks in continental settings crystallize from relatively oxidized magmas, on average 1.4 log units () and 1.3 log units () above the synthetic fayalite-magnetite-quartz (FMQ) buffer. In contrast, alkaline rocks in continental settings that lack associated carbonatites reveal rather reduced conditions (mean ; ). The calculated redox conditions for carbonatites and associated silicate rocks demonstrate that these crystallize from relatively oxidized mantle-derived melts compared to the general range found for alkaline rocks in continental settings.
DS202012-2208
2020
Breeding, C.M., Eaton-Magana, S., Shigley, J.E.Naturallly colored yellow and orange gem diamonds: the nitrogen factor.Gems & Gemology, Vol. 56. 2. summer pp. 194-219. pdfGlobalnitrogen

Abstract: Natural yellow gem diamonds are the most common of the fancy-color diamonds, while orange diamonds are among the rarest when they have unmodified hues. Both categories owe their coloration to atomic-level lattice defects associated with nitrogen impurities in the diamond structure. Four major groups of defects are responsible for the color in nearly all yellow and orange diamonds: cape defects (N3 and associated absorptions), isolated nitrogen defects, the 480 nm visible absorption band, and H3 defects. Nitrogen-bearing diamonds are thought to incorporate isolated nitrogen during growth by substitution for carbon, meaning that natural diamonds start out with yellow to orange color. However, only the very rare type Ib diamonds maintain that original color. With time at high temperatures deep in the earth, the nitrogen atoms in most diamonds aggregate, resulting in either near-colorless stones or yellow diamonds colored by cape defects. Yellow and orange diamonds can be grown in a laboratory or created by color treatments, so a thorough understanding of the defects responsible for color in the natural stones is critical for identification. Yellow diamonds serve as the best ambassador to the colored diamond world due to their abundance and may be the only colored diamond many people will ever see in a jewelry store.
DS202009-1613
2020
Brenker, F.E., Nestola, F., Brenker, L., Peruzzo, L., Harris, J.W.Origin, properties and structure of breyite: the second most abundant mineral inclusion in super-deep diamonds. The American Mineralogist, in press available, 21p. PdfMantlebreyite
DS202008-1371
2018
Brook, M.C.The Botswana pipeline - "prospecting to jewellery"Botswana Journal of Earth Sciences, Vol. 7, pp. 43-57. pdfAfrica, Botswanaprospecting, markets

Abstract: In this paper I describe the different components that make up the Botswana Diamond Pipeline today, which means the supply chain of diamonds, that ranges from diamond prospecting to mining, to diamond processing and recovery, to rough diamond sorting, valuation, sales and marketing, to diamond polishing and cutting, and finally to diamond jewellery manufacturing and retail. In Botswana, we can now truly witness the journey of the diamond from “Rough to Finger” or from “Mine to Store” (Fig. 1). Today, Botswana is the world’s second largest producer of diamonds by value and volume after Russia, and there are currently twelve known kimberlite fields (Fig. 2) and eight operating diamond mines. Botswana’s diamonds are cut and polished into beautiful diamond jewellery locally and across the globe.
DS202003-0331
2020
Brooks, K.Perovskite.Geology Today, Vol. 36, 1, pp. 33-38. pdfMantleperovskite

Abstract: How many people, even those interested in the Earth sciences, have heard of perovskite? Yet minerals with the perovskite structure are the most abundant minerals on the Earth with a corresponding importance for our understanding of the origin, development and functioning of our planet. Furthermore, they play important roles in modern technology, including the storage of nuclear waste, in solar cells and as superconductors.
DS202011-2031
2020
Brooks, K.Lithium mineralsGeology Today, Vol. 6, 5, pp. 192-197.Globallithium

Abstract: Lithium is a critical element in modern technology, and lithium minerals will play a key role in the fight against climate change. However, the demand for lithium-ion batteries is dependent on an expanding supply of primary resources. Lithium occurs in limited amounts on the Earth in a surprising diversity of mineral species, from pyroxenes to amphiboles, phyllosilicates to phosphates. This article examines the principal mineral groups likely to be a target for future exploitation.
DS202003-0332
2020
Broom-Fendley, S., Smith, M.P., Andrade, M.B., Ray, S., Banks, D.A., Loye, E., Antencio, D., Pickles, J.P., Wall, F.Sulfur bearing monzazite (Ce) from the Eureka carbonatite, Namibia: oxidation state, substitution mechanism, and formation conditions.Mineralogical Magazine, pp. 1-14, pdfAfrica, Namibiacarbonatite, REE

Abstract: Sulfur-bearing monazite-(Ce) occurs in silicified carbonatite at Eureka, Namibia, forming rims up to ~0.5 mm thick on earlier-formed monazite-(Ce) megacrysts. We present X-ray photoelectron spectroscopy data demonstrating that sulfur is accommodated predominantly in monazite-(Ce) as sulfate, via a clino-anhydrite-type coupled substitution mechanism. Minor sulfide and sulfite peaks in the X-ray photoelectron spectra, however, also indicate that more complex substitution mechanisms incorporating S2 and S4+ are possible. Incorporation of S6+ through clino-anhydrite-type substitution results in an excess of M2+ cations, which previous workers have suggested is accommodated by auxiliary substitution of OH for O2. However, Raman data show no indication of OH, and instead we suggest charge imbalance is accommodated through F substituting for O2. The accommodation of S in the monazite-(Ce) results in considerable structural distortion that may account for relatively high contents of ions with radii beyond those normally found in monazite-(Ce), such as the heavy rare earth elements, Mo, Zr and V. In contrast to S-bearing monazite-(Ce) in other carbonatites, S-bearing monazite-(Ce) at Eureka formed via a dissolutionprecipitation mechanism during prolonged weathering, with S derived from an aeolian source. While large S-bearing monazite-(Ce) grains are likely to be rare in the geological record, formation of secondary S-bearing monazite-(Ce) in these conditions may be a feasible mineral for dating palaeo-weathering horizons.
DS202009-1614
2020
Brovarone, A.V., Butch, C.J., Ciappa, A., Cleaves, H.J., Elmaleh, A., Faccenda, M., Feineman, M., Hermann, J., Nestola, F., Cordone, A., Giovannelli., D.Let there be water: how hydration/dehydration reactions accompany key Earth and life processes.American Mineralogist, Vol. 105, pp. 1152-1160. pdfMantlecarbon

Abstract: Water plays a key role in shaping our planet and making life possible. Given the abundance of water on Earth's surface and in its interior, chemical reactions involving water, namely hydration and dehydration reactions, feature prominently in nature and are critical to the complex set of geochemical and biochemical reactions that make our planet unique. This paper highlights some fundamental aspects of hydration and dehydration reactions in the solid Earth, biology, and man-made materials, as well as their connections to carbon cycling on our planet.
DS202010-1830
2020
Brown, D.A., Tamblyn, R., Hand, M., Morrissey, L.J.Thermobarometric constraints on burial and exhumation of 2 billion year old eclogites and their metapelitic hosts.Precambrian Research, Vol. 347, 105833, 33p. PdfAfrica, Tanzaniaeclogites

Abstract: One of the first appearances of eclogite-facies mineral assemblages in the geological record occurs in the c. 2000 Ma Palaeoproterozoic Usagaran Belt in central Tanzania, where the extended margin of the Tanzanian Craton is interpreted to have been subducted. Mafic rocks are interpreted to have contained the mineral assemblage garnet + omphacite + rutile + quartz ± amphibole. This high-pressure assemblage has been overprinted by a secondary mineral assemblage containing clinopyroxene + plagioclase + hornblende + ilmenite ± orthopyroxene. Mineral equilibria forward modelling indicates that the eclogite-facies assemblages reached minimum peak pressure-temperature (P-T) conditions of ~17 kbar and ~700 °C. Inclusions in garnet document a prograde P-T history consistent with burial through upper amphibolite-facies conditions and possible partial melting. Petrological and compositional evidence from garnet suggests that following peak metamorphism, the eclogite-facies rocks were heated while stalled at approximate peak pressures. Temperature estimates derived from Zr concentrations in interpreted texturally retrograde rutile support a near-isothermal post-peak P-T evolution for the eclogite-facies rocks - an evolution that terminates at retrograde P-T conditions of approximately 7.6-8.2 kbar and 680-790 °C. The relict eclogite domains form part of a larger assemblage with enclosing migmatitic metapelitic lithologies (the Isimani Suite). The metapelitic gneisses contain garnet + kyanite + biotite + staurolite + hornblende + plagioclase + muscovite + rutile + quartz and preserve minimal evidence of a high-pressure history, conceivably due to post-peak mineralogical recrystallisation. P-T modelling, inclusion assemblages and compositional zonation patterns in porphyroblastic garnet suggests the metapelitic gneisses — similarly to the relict eclogites — experienced burial to minimum peak pressures of approximately 16.5-17 kbar. Compositional zoning patterns in eclogitic garnet suggest the Isimani system was buried, reached peak metamorphic conditions, and was subsequently exhumed within a timeframe of up to 20 Myr. A tectonic regime involving crustal thickening and subduction, followed by extensional exhumation of the entire Isimani Suite is our preferred model for the development of the c. 2000 Ma Usagaran Belt.
DS202005-0723
2020
Brown, M., Johnson, T., Gardiner, N.J.Plate tectonics and the Archean Earth.Annual Review of Earth and Planetary Sciences, Vol. 48, 30p. pdfMantlesubduction, metamorphism

Abstract: If we accept that a critical condition for plate tectonics is the creation and maintenance of a global network of narrow boundaries separating multiple plates, then to argue for plate tectonics during the Archean requires more than a local record of subduction. A case is made for plate tectonics back to the early Paleoproterozoic, when a cycle of breakup and collision led to formation of the supercontinent Columbia, and bimodal metamorphism is registered globally. Before this, less preserved crust and survivorship bias become greater concerns, and the geological record may yield only a lower limit on the emergence of plate tectonics. Higher mantle temperature in the Archean precluded or limited stable subduction, requiring a transition to plate tectonics from another tectonic mode. This transition is recorded by changes in geochemical proxies and interpreted based on numerical modeling. Improved understanding of the secular evolution of temperature and water in the mantle are key targets for future research. 1) Higher mantle temperature in the Archean precluded or limited stable subduction, requiring a transition to plate tectonics from another tectonic mode. 2) Plate tectonics can be demonstrated on Earth since the early Paleoproterozoic (since c. 2.2 Ga), but before the Proterozoic Earth's tectonic mode remains ambiguous. 3) The Mesoarchean to early Paleoproterozoic (3.2-2.3 Ga) represents a period of transition from an early tectonic mode (stagnant or sluggish lid) to plate tectonics. 4) The development of a global network of narrow boundaries separating multiple plates could have been kick-started by plume-induced subduction.
DS202007-1126
2020
Brown, M., Johnson, T., Gardiner, N.J.Plate tectonics and the Archean Earth.Annual Review of Earth and Planetary Sciences, Vol. 48, 1, pp. 291-320.Mantletectonics

Abstract: If we accept that a critical condition for plate tectonics is the creation and maintenance of a global network of narrow boundaries separating multiple plates, then to argue for plate tectonics during the Archean requires more than a local record of subduction. A case is made for plate tectonics back to the early Paleoproterozoic, when a cycle of breakup and collision led to formation of the supercontinent Columbia, and bimodal metamorphism is registered globally. Before this, less preserved crust and survivorship bias become greater concerns, and the geological record may yield only a lower limit on the emergence of plate tectonics. Higher mantle temperature in the Archean precluded or limited stable subduction, requiring a transition to plate tectonics from another tectonic mode. This transition is recorded by changes in geochemical proxies and interpreted based on numerical modeling. Improved understanding of the secular evolution of temperature and water in the mantle is a key target for future research.
DS202005-0724
2020
Brown, M., Kirkland, C.L., Johnson, T.E.Evolution of geodynamics since the Archean: significant change at the dawn of the Phanerozoic.Geology, Vol. 48, 5, pp. 488-492.Globalgeodynamics

Abstract: A time-series analysis of thermobaric ratios (temperature/pressure [T/P]) for Paleoarchean to Cenozoic metamorphic rocks identified significant shifts in mean T/P that may be related to secular change in the geodynamics on Earth. Thermobaric ratios showed significant (>95% confidence) change points at 1910, 902, 540, and 515 Ma, recording drops in mean T/P, and at 1830, 604, and 525 Ma, recording rises in mean T/P. Highest mean T/P occurred during the Mesoproterozoic, and lowest mean T/P occurred from the Cambrian to the Oligocene. Correlated changes were seen between T/P and global data sets of time-constrained hafnium (Hf) and oxygen (O) isotope compositions in zircon. The range of correlated variation in T/P, Hf, and O was larger during the formation of Rodinia than Columbia. Large changes and a wide range for these variables continued through the Phanerozoic, during which a statistically significant 83 m.y. frequency of T/P excursions recorded the high tempo of orogenic activity associated with the separation, migration, and accretion of continental terranes during the formation of Pangea. Since the early Tonian, the decreasing mean T/P of metamorphism, widespread appearance of blueschist and ultrahigh-pressure metamorphism, and wide fluctuations in Hf and O isotope compositions document a change to the modern plate-tectonic regime, characterized by widespread continental subduction and deeper slab breakoff than in the Proterozoic.
DS202002-0169
2019
Buchan, K.L., Ernst, R.E.Giant circumferential dyke swarms: catalogue and characteristics.Dyke Swarms of the World: a modern perspective. Ed. Srivastava Springer, 49p. PdfMantledyke swarms

Abstract: Giant circumferential dyke swarms have a primary geometry that is quasi-circular or quasi-elliptical. Examples and possible examples described previously or identified in this study have outer diameters that range from ~450 to ~2500 km. There has been little study of these features. Here, we present a global catalogue of giant circumferential dyke swarms and discuss their characteristics. All of the identified giant circumferential swarms are of mafic composition. Many, but not all, are associated with a roughly coeval giant radiating dyke swarm whose focus is at or near the centre of the circumferential system. As giant radiating swarms are usually interpreted to focus above mantle plume centres and form a key component of the plumbing system of large igneous provinces (LIPs), it is likely that giant circumferential swarms linked to radiating systems are also plume and LIP related. The largest giant circumferential swarms have diameters comparable to the diameters postulated for the flattened heads of plumes that have risen from the core-mantle boundary, suggesting that they may be associated with the outer edge of a flattening or flattened mantle plume head. Smaller giant circumferential swarms could be linked with small plumes from the mid-mantle or with the edge of a magmatic underplate above a plume head. Giant circumferential dyke swarms on Earth may be analogues of coronae on Venus and similar features on Mars. Coronae are large tectono-magmatic features that typically consist of a quasi-circular or quasi-elliptical graben-fissure system and associated topography (central uplift or depression, and circular rim or moat). In some instances, they are linked to a giant radiating graben-fissure system and LIP-scale volcanism. Both radiating and circumferential graben on Venus and Mars have been interpreted to be underlain by dykes.
DS202012-2209
2020
Buono, G., Fanara, S., Macedonio, G., Palladino, D.M., Petrosino, P., Sottili, G., Pappalardo, L.Dynamics of degassing in evolved alkaline magmas: petrological, experimental and theoretical insights.Earth-Science Reviews, Vol. 211, 103402, 23p. PdfMantlealkaline

Abstract: In the last few decades, advanced monitoring networks have been extended to the main active volcanoes, providing warnings for variations in volcano dynamics. However, one of the main tasks of modern volcanology is the correct interpretation of surface-monitored signals in terms of magma transfer through the Earth's crust. In this frame, it is crucial to investigate decompression-induced magma degassing as it controls magma ascent towards the surface and, in case of eruption, the eruptive style and the atmospheric dispersal of tephra and gases. Understanding the degassing behaviour is particularly intriguing in the case of poorly explored evolved alkaline magmas. In fact, these melts frequently feed hazardous, highly explosive volcanoes (e.g., Campi Flegrei, Somma-Vesuvius, Colli Albani, Tambora, Azores and Canary Islands), despite their low viscosity that usually promotes effusive and/or weakly explosive eruptions. Decompression experiments, together with numerical models, are powerful tools to examine magma degassing behaviour and constrain field observations from natural eruptive products and monitoring signals. These approaches have been recently applied to evolved alkaline melts, yet numerous open questions remain. To cast new light on the degassing dynamics of evolved alkaline magmas, in this study we present new results from decompression experiments, as well as a critical review of previous experimental works. We achieved a comprehensive dataset of key petrological parameters (i.e., 3D textural data for bubbles and microlites using X-ray computed microtomography, glass volatile contents and nanolite occurrence) from experimental samples obtained through high temperature-high pressure isothermal decompression experiments on trachytic alkaline melts at super-liquidus temperature. We explored systematically a range of final pressures (from 200 to 25 MPa), decompression rates (from 0.01 to 1 MPa s-1), and volatile (H2O and CO2) contents. On these grounds, we integrated coherently literature data from decompression experiments on evolved alkaline (trachytic and phonolitic) melts under various conditions, with the aim to fully constrain the degassing mechanisms and timescales in these magmas. Finally, we simulated numerically the experimental conditions to evaluate strengths and weaknesses in decrypting degassing behaviour from field observations. Our results highlight that bubble formation in evolved alkaline melts is primarily controlled by the initial volatile (H2O and CO2) content during magma storage. In these melts, bubble nucleation needs low supersaturation pressures (= 50-112 MPa for homogeneous nucleation, = 13-25 MPa for heterogeneous nucleation), resulting in high bubble number density (~ 1012-1016 m-3), efficient volatile exsolution and thus in severe rheological changes. Moreover, the bubble number density is amplified in CO2-rich melts (mole fraction XCO2 = 0.5), in which continuous bubble nucleation predominates on growth. These conditions typically lead to highly explosive eruptions. However, moving towards slower decompression rates (= 10-1 MPa s-1) and H2O-rich melts, permeable outgassing and inertial fragmentation occur, promoting weakly explosive eruptions. Finally, our findings suggest that the exhaustion of CO2 at deep levels, and the consequent transition to a H2O-dominated degassing, can crucially enhance magma vesiculation and ascent. In a hazard perspective, these constraints allow to postulate that time-depth variations of unrest signals could be significantly weaker/shorter (e.g., minor gas emissions and short-term seismicity) during major eruptions than in small-scale events.
DS202003-0333
2020
Burness, S., Smart, K.A., Tappe, S., Stevens, G., Woodland, A.B., Cano, E.Sulphur rich mantle metasomatism of Kaapvaal craton eclogites and its role in redox controlled platinum group element mobility. Xenoliths from Roberts Victor, Jagersfontein, Kimberley ( Kamfersdam), PremierChemical Geology, in press available 57p.Africa, South Africametasomatism

Abstract: Eclogite mantle xenoliths from various kimberlite occurrences on the Kaapvaal craton show evidence for depth- and redox-dependent metasomatic events that led to variable base metal sulphide and incompatible element enrichments. Eclogite xenoliths from the Roberts Victor, Jagersfontein, Kimberley (Kamfersdam) and Premier kimberlites were investigated for their silicate and base metal sulphide geochemistry, stable oxygen isotope compositions and oxybarometry. The variably metasomatised eclogites had basaltic, picritic and gabbroic protolith compositions and have garnet d18O values that range from +3.3 to +7.9‰, which, when coupled with the trace element characteristics, indicate oceanic lithosphere protoliths that had undergone variable degrees of seawater alteration. The deepest equilibrated eclogites (175220?km depth) from near the base of the Kaapvaal craton lithosphere are the most refractory and feature significant light rare earth element (LREE) depletions. They show the most oxidised redox compositions with ?logƒO2 values of FMQ-3.9 to FMQ-1.5. Subtle metasomatic overprinting of these eclogites resulted in base metal sulphide formation with relatively depleted and highly fractionated HSE compositions. These deepest eclogites and their included base metal sulphides suggest interaction with relatively oxidised melts or fluids, which, based on their HSE characteristics, could be related to precursor kimberlite metasomatism that was widespread within the Kaapvaal craton mantle lithosphere. In contrast, eclogites that reside at shallower, “mid-lithospheric” depths (140180?km) have been enriched in LREE and secondary diopside/phlogopite. Importantly, they host abundant metasomatic base metal sulphides, which have higher HSE contents than those in the deeper eclogites at the lithosphere base. The mid-lithospheric eclogites have more reducing redox compositions (?logfO2?=?FMQ-5.3 - FMQ-3.3) than the eclogites from the lowermost Kaapvaal lithosphere. The compositional overprint of the shallower mantle eclogites resembles basaltic rather than kimberlitic/carbonatitic metasomatism, which is also supported by their relatively reducing redox state. Base metal sulphides from the mid-lithospheric eclogites have HSE abundances and distributions that are similar to Karoo flood basalts from southern Africa, suggesting a link between the identified shallow mantle metasomatism of the Kaapvaal cratonic lithosphere and the Karoo large igneous event during the Mesozoic. The sulphide-hosted platinum group element abundances of the mid-lithospheric eclogites are higher compared with their analogues from the deeper lithospheric eclogites, which in combination with their contrasting oxidation states, may imply redox-controlled HSE mobility during sulphur-rich metasomatism of continental mantle lithosphere.
DS202008-1372
2020
Burness, S., Smart, K.A., Tappe, S., Stevens, G., Woodland, A.B., Cano, E.Sulphur rich mantle metasomatism of Kaapvaal craton eclogites and its role in redox controlled platinum group element mobility.Chemical Geology, Voll. 542, 119476 23p. pdfAfrica, South Africadeposit - Roberts Victor, Jagersfontein, Kimberley, Kamfersdam, Premier

Abstract: Eclogite mantle xenoliths from various kimberlite occurrences on the Kaapvaal craton show evidence for depth- and redox-dependent metasomatic events that led to variable base metal sulphide and incompatible element enrichments. Eclogite xenoliths from the Roberts Victor, Jagersfontein, Kimberley (Kamfersdam) and Premier kimberlites were investigated for their silicate and base metal sulphide geochemistry, stable oxygen isotope compositions and oxybarometry. The variably metasomatised eclogites had basaltic, picritic and gabbroic protolith compositions and have garnet d18O values that range from +3.3 to +7.9‰, which, when coupled with the trace element characteristics, indicate oceanic lithosphere protoliths that had undergone variable degrees of seawater alteration. The deepest equilibrated eclogites (175-220 km depth) from near the base of the Kaapvaal craton lithosphere are the most refractory and feature significant light rare earth element (LREE) depletions. They show the most oxidised redox compositions with ?logƒO2 values of FMQ-3.9 to FMQ-1.5. Subtle metasomatic overprinting of these eclogites resulted in base metal sulphide formation with relatively depleted and highly fractionated HSE compositions. These deepest eclogites and their included base metal sulphides suggest interaction with relatively oxidised melts or fluids, which, based on their HSE characteristics, could be related to precursor kimberlite metasomatism that was widespread within the Kaapvaal craton mantle lithosphere. In contrast, eclogites that reside at shallower, “mid-lithospheric” depths (140-180 km) have been enriched in LREE and secondary diopside/phlogopite. Importantly, they host abundant metasomatic base metal sulphides, which have higher HSE contents than those in the deeper eclogites at the lithosphere base. The mid-lithospheric eclogites have more reducing redox compositions (?logfO2 = FMQ-5.3 - FMQ-3.3) than the eclogites from the lowermost Kaapvaal lithosphere. The compositional overprint of the shallower mantle eclogites resembles basaltic rather than kimberlitic/carbonatitic metasomatism, which is also supported by their relatively reducing redox state. Base metal sulphides from the mid-lithospheric eclogites have HSE abundances and distributions that are similar to Karoo flood basalts from southern Africa, suggesting a link between the identified shallow mantle metasomatism of the Kaapvaal cratonic lithosphere and the Karoo large igneous event during the Mesozoic. The sulphide-hosted platinum group element abundances of the mid-lithospheric eclogites are higher compared with their analogues from the deeper lithospheric eclogites, which in combination with their contrasting oxidation states, may imply redox-controlled HSE mobility during sulphur-rich metasomatism of continental mantle lithosphere.
DS202008-1373
2020
Buyse, F., Dewaele, S., Decree, S., Mees, F.Mineralogical and geochemical study of the rare earth element mineralization at Gakara ( Burundi).Ore Geology Reviews, Vol. 124, 103659 10p. PdfAfrica, BurundiREE

Abstract: The rare earth element (REE) mineralization of Gakara (Burundi) has first been discovered in 1936 and has periodically been the subject of geological studies, at times when the exploitation of bastnäsite-(Ce) and monazite-(Ce) was economically interesting. This study focuses on the establishment of a mineral paragenesis for Gakara, with special attention to the REE-bearing phases, to understand the formation history of the deposit. The paragenesis can be subdivided into 3 stages: primary ore deposition, brecciation stage and supergene alteration. Evidence for fenitization processes (i.e. pinkish-red cathodoluminescence of K-feldpar, brecciation stage) and the strong enrichment of light REEs in bastnäsite and monazite substantiate the hypothesis of a structurally controlled hydrothermal mineralization with a strong carbonatitic affinity. This likely confirms the association of the Gakara REE deposit with the Neoproterozoic alignment of alkaline complexes and carbonatites along the present-day Western Rift. It suggests a direct link with a - currently unidentified - carbonatitic body at depth, possibly derived from a predominantly metasomatized lithospheric mantle.
DS202011-2032
2020
Cai, W-C., Zhang, Z-C., Zhu, J., Santosh, M., Pan, R-H.Genesis of high ni-olivine phenocrysts of the Dali picrites in the central Emeishan large igneous province.Geological Magazine, doi: 10.1017/ S0016756820001053 10p. Chinapicrites

Abstract: The Emeishan large igneous province (ELIP) in SW China is considered to be a typical mantle-plume-derived LIP. The picrites formed at relatively high temperatures in the ELIP, providing one of the important lines of argument for the role of mantle plume. Here we report trace-element data on olivine phenocrysts in the Dali picrites from the ELIP. The olivines are Ni-rich, and characterized by high (>1.4) 100×Mn/Fe value and low (<13) 10 000×Zn/Fe value, indicating a peridotite-dominated source. Since the olivine-melt Ni partition coefficient (KDNiol/melt) will decrease at high temperatures and pressures, the picrites derived from peridotite melting at high pressure, and that crystallized olivines at lower pressure, can generate high concentrations of Ni in olivine phenocrysts, excluding the necessity of a metasomatic pyroxenite contribution. Based on the Al-in-olivine thermometer, olivine crystallization temperature and mantle potential temperature (T P) were calculated at c. 1491°C and c. 1559°C, respectively. Our results are c. 200°C higher than that of the normal asthenospheric mantle, and are consistent with the role of a mantle thermal plume for the ELIP.
DS202008-1374
2020
Campbell, D., Zurevinski, S., Elliott, B.Geochemistry and glacial dispersal patterns of kimberlitic indicator minerals in the South Slave Province, NT.Goldschmidt 2020, 1p. AbstractCanada, Northwest Territoriesgarnets

Abstract: The geochemistry and distribution of garnets in the southern Slave Province could have considerable implications for drift prospecting and diamond potential. Presented here is a study interpretting geochemistry in dispersal trains of the Slave Province. Over one-hundred-thousand garnets have been sampled from the northern Slave Province with quantitative analyses conducted on each sample, and the data has been compiled for public release (NTGS Data Hub, 2018). A smaller subset of samples have been collected in the southern Slave Province by this study and the NTGS within recent years. Data from the NTGS is used in this study to construct regional maps showing dispersal trains of indicator minerals and chemistry of indicator garnets throughout the region. The variation in dispersal train pattern, size, mineralogy, and chemistry are being utilized to assess the southern Slave for it’s kimberlite potential. The geochemistry of garnets is used to make further observations into the diamond potential of the area using the garnet classifications G3D, G4D, G5D, and G10D (Grutter et al., 2004). It has been observed that there is an abundance of Na2O rich (>0.07 wt %) garnets in the northern Slave Province and a deficit of Na2O (<0.07 wt %) in garnets of the south. There is also a visible discrepency in olivine in the north and south, with the north Slave showing olivine in dispersal trains and the south lacking any olivine. These discrepancies in Na2O could be indicative of pressure/temperature conditions that coincide with diamond formation in the north (Grutter et al., 2004). The olivine dispersal may be the product of glacial dispersal in conjunction with the facies/mineralogy of kimberlites in the immediate area.
DS202008-1375
2019
Campbell, J.A.H.Financing diamond projects.The Journal of the Southern African Insitute of Mining and Metallurgy, Vol. 119, Feb. 6p. PdfGlobalfinancing

Abstract: Investment in diamond exploration has been declining over the past decade, in spite of positive long-term industry fundamentals and a growing interest in diamonds as an investment category. The lack of new significant discoveries in recent years has eroded investor confidence, yet no new discoveries are possible without investment in exploration. Junior ‘mine finders’ have been the hardest hit. Their agility, tenacity, and appetite for risk are not sufficient to attract the funding required, even at the greenfield stage. Developing new discoveries into mineral resources can be crippling without solid financial support. Junior incubators could play a crucial role, especially at the project evaluation stage - but where are they? Alternatives to traditional funding mechanisms have become available, many still untested in the junior diamond exploration space. Valuable lessons can be drawn from the past and used to inform emerging new strategies.
DS202008-1376
2018
Campbell, J.A.H., Jooste, V.The AK6 kimberlite - discovery through to production: learning the lessons of history.Botswana Journal of Earth Sciences, Vol. 7, pp. 13-28. pdfAfrica, Botswanadeposit - AK6

Abstract: The AK6 kimberlite in north-eastern Botswana, better known as Karowe, is today one of the world?s top diamond producers by value. Its potential, however, was not recognised when AK6 was first discovered some fifty years ago. This paper traces the history of Karowe from the discovery of AK6 through to evaluation and production, reflecting on the interplay of economic, technical and corporate elements and highlighting some of the lessons learnt along this journey. Karowe Mine has been operating since 2012 and is fully owned by Lucara Diamond Corporation. In 2015, Karowe yielded the second largest diamond ever found, the 1,109ct Lesedi La Rona (Fig. 1).
DS202009-1615
2020
Cannao, E., Scambelluri, M., Bebout, G.E., Agostini, S., Pettke, T., Godard, M., Crispini, L.Ophicarbonate evolution from seafloor to subduction and implications for deep-Earth C cycling.Chemical Geology, Vol. 546, 119626 29p. PdfMantlecarbon, subduction

Abstract: The chemical and physical processes operating during subduction-zone metamorphism can profoundly influence the cycling of elements on Earth. Deep-Earth carbon (C) cycling and mobility in subduction zones has been of particular recent interest to the scientific community. Here, we present textural and geochemical data (CO, Sr isotopes and bulk and in-situ trace element concentrations) for a suite of ophicarbonate rocks (carbonate-bearing serpentinites) metamorphosed over a range of peak pressure-temperature (P-T) conditions together representing a prograde subduction zone P-T path. These rocks, in order of increasing peak P-T conditions, are the Internal Liguride ophicarbonates (from the Bracco unit, N. Apennines), pumpellyite- and blueschist-facies ophicarbonates from the Sestri-Voltaggio zone (W. Ligurian Alps) and the Queyras (W. Alps), respectively, and eclogite-facies ophicarbonates from the Voltri Massif. The Bracco oceanic ophicarbonates retain breccia-like textures associated with their seafloor hydrothermal and sedimentary origins. Their trace element concentrations and d18OVSMOW (+15.6 to +18.2‰), d13CVPDB (+1.1 to +2.5‰) and their 87Sr/86Sr (0.7058 to 0.7068), appear to reflect equilibration during Jurassic seawater-rock interactions. Intense shear deformation characterizes the more deeply subducted ophicarbonates, in which prominent calcite recrystallization and carbonation of serpentinite clasts occurred. The isotopic compositions of the pumpellyite-facies ophicarbonates overlap those of their oceanic equivalents whereas the most deformed blueschist-facies sample shows enrichments in radiogenic Sr (87Sr/86Sr?=?0.7075) and depletion in 13C (with d13C as low as -2.0‰). These differing textural and geochemical features for the two suites reflect interaction with fluids in closed and open systems, respectively. The higher-P-metamorphosed ophicarbonates show strong shear textures, with coexisting antigorite and dolomite, carbonate veins crosscutting prograde antigorite foliation and, in some cases, relics of magnesite-nodules enclosed in the foliation. These rocks are characterized by lower d18O (+10.3 to 13.0‰), enrichment in radiogenic Sr (87Sr/86Sr up to 0.7096) and enrichment in incompatible and fluid-mobile element (FME; e.g., As, Sb, Pb). These data seemingly reflect interaction with externally-derived metamorphic fluids and the infiltrating fluids likely were derived from dehydrating serpentinites with hybrid serpentinite-sediment compositions. The interaction between these two lithologies could have occurred prior to or after dehydration of the serpentinites elsewhere. We suggest that decarbonation and dissolution/precipitation processes operating in ancient subduction zones, and resulting in the mobilization of C, are best traced by a combination of detailed field and petrographic observations, C, O and Sr isotope systematics (i.e., 3D isotopes), and FME inventories. Demonstration of such processes is key to advancing our understanding of the influence of subduction zone metamorphism on the mobilization of C in subducting reservoirs and the efficiency of delivery of this C to depths beneath volcanic arcs and into the deeper mantle.
DS202007-1127
2020
Cannao, E., Tiepolo, M., Bebout, G.E., Scambelluri, M.Into the deep and beyond: carbon and nitrogen subduction recycling in secondary peridotites. Gagnone metaperidotitesEarth and Planetary Science Letters, Vol. 543, 116328 14p. PdfEurope, Switzerland, Alpsboron diamonds

Abstract: Understanding the volatile cycles at convergent margins is fundamental to unravel the Earth's evolution from primordial time to present. The assessment of fluid-mobile and incompatible element uptake in serpentinites via interaction with seawater and subduction-zone fluids is central to evaluate the global cycling of the above elements in the Earth's mantle. Here, we focus on the carbon (C), nitrogen (N) and C isotope compositions of chlorite harzburgites and garnet peridotites deriving from subduction-zone dehydration of former oceanic dehydration of serpentinite - i.e., metaperidotites (Cima di Gagnone, Swiss Central Alps) with the aim of evaluating the contribution of these rocks to the global C-N cycling. These ultramafic rocks, enclosed as lenses in a metasedimentary mélange, represent the destabilization of antigorite and chlorite at high-pressure/temperature (P/T) along a slab-mantle interface. Chlorite- and garnet-bearing rocks have similar ranges in C concentration ([C] = 210 - 2465 ppm and 304 - 659 ppm, respectively), with one magnesite-bearing chlorite harzburgite hosting 11000 ppm C. The average N concentrations ([N]) of the garnet peridotites (54 ± 15 ppm, one standard deviation indicated) are higher than those of the chlorite harzburgites (29 ± 6 ppm). The C of total C (TC) and total organic C (TOC) values of the Gagnone metaperidotites range from -12.2 to -17.8‰ and from -27.8 to -26.8‰, respectively, excluding the magnesite-bearing chlorite harzburgites with higher values of -7.2‰ (TC) and -21.2‰ (TOC). The [C] of these rocks are comparable to those of serpentinites form modern and ancient oceanic environments and with [C] of high-P serpentinites. However, the lack of preserved serpentinite precursors makes it difficult to determine whether release of H2O during high-P breakdown of antigorite and chlorite is coupled with significant C release to fluids. The C values appear to reflect mixing between seawater-derived carbonate and a reduced C source and a contribution from the host metasedimentary rocks ([C] = 301 ppm; [N] = 33 ppm; TC C = -24.4‰; TOC C = -27.0‰) cannot be completely excluded. The C-O isotope composition of the carbonate in magnesite-bearing chlorite harzburgites is compatible with progressive devolatilization at oxidized conditions, whereas the signatures of the majority of the other Gagnone samples appear to reflect different degree of interaction with sedimentary fluids. The [N] of the Gagnone metaperidotites are higher than those of oceanic and subducted serpentinites and show a range similar to that of high-P antigorite-serpentinites from mantle wedges. This enrichment is compatible with fluid-mediated chemical exchange with the surrounding metasedimentary rocks leading to strong modification of the Gagnone metaperidotites' geochemistry during prograde subduction along the slab-mantle interface. Comparing the C data reported in this study with published C values for diamonds, we suggest that the volatile recycling via Gagnone-like metaperidotites in subduction zones could contribute to deep-Earth diamond genesis and in particular to the formation of blue boron (B)-bearing diamonds. Our results highlight that the subduction of secondary peridotites evolved along the slab-mantle interface is a viable mechanism to inject volatiles into the deep mantle, particularly in hotter geothermal regimes such as the ones active during the early Earth's history.
DS202010-1831
2020
Cao, Y., Jung, H., Ma, J.Seismic properties of a unique olivine-rich eclogite in the western Gneiss region, Norway.Minerals ( MDPI), 10.339/min10090774 22p. PdfEurope, Norwayeclogites

Abstract: Investigating the seismic properties of natural eclogite is crucial for identifying the composition, density, and mechanical structure of the Earth’s deep crust and mantle. For this purpose, numerous studies have addressed the seismic properties of various types of eclogite, except for a rare eclogite type that contains abundant olivine and orthopyroxene. In this contribution, we calculated the ambient-condition seismic velocities and seismic anisotropies of this eclogite type using an olivine-rich eclogite from northwestern Flemsøya in the Nordøyane ultrahigh-pressure (UHP) domain of the Western Gneiss Region in Norway. Detailed analyses of the seismic properties data suggest that patterns of seismic anisotropy of the Flem eclogite were largely controlled by the strength of the crystal-preferred orientation (CPO) and characterized by significant destructive effects of the CPO interactions, which together, resulted in very weak bulk rock seismic anisotropies (AVp = 1.0-2.5%, max. AVs = 0.6-2.0%). The magnitudes of the seismic anisotropies of the Flem eclogite were similar to those of dry eclogite but much lower than those of gabbro, peridotite, hydrous-phase-bearing eclogite, and blueschist. Furthermore, we found that amphibole CPOs were the main contributors to the higher seismic anisotropies in some amphibole-rich samples. The average seismic velocities of Flem eclogite were greatly affected by the relative volume proportions of omphacite and amphibole. The Vp (8.00-8.33 km/s) and Vs (4.55-4.72 km/s) were remarkably larger than the hydrous-phase-bearing eclogite, blueschist, and gabbro, but lower than dry eclogite and peridotite. The Vp/Vs ratio was almost constant (avg. ˜ 1.765) among Flem eclogite, slightly larger than olivine-free dry eclogite, but similar to peridotite, indicating that an abundance of olivine is the source of their high Vp/Vs ratios. The Vp/Vs ratios of Flem eclogite were also higher than other (non-)retrograded eclogite and significantly lower than those of gabbro. The seismic features derived from the Flem eclogite can thus be used to distinguish olivine-rich eclogite from other common rock types (especially gabbro) in the deep continental crust or subduction channel when high-resolution seismic wave data are available.
DS202003-0334
2019
Carlson, R.W., Garcon, M., O'Neil, J., Reimink, J.,Rizo, H.The nature of the Earth's crust.Chemical Geology, Vol. 530, 25p. Available pdfMantleArchean geology

Abstract: Recycling of crust into the mantle has left only small remnants at Earth’s surface of crust produced within a billion years of Earth formation. Few, if any, of these ancient crustal rocks represent the first crust that existed on Earth. Understanding the nature of the source materials of these ancient rocks and the mechanism of their formation has been the target of decades of geological and geochemical study. This traditional approach has been expanded recently through the ability to simultaneously obtain U-Pb age and initial Hf isotope data for zircons from many of these ancient, generally polymetamorphic, rocks. The addition of information from the short-lived radiometric systems 146Sm-142Nd and 182Hf-182W allows resolution of some of the ambiguities that have clouded the conclusions derived from the long-lived systems. The most apparent of these is clear documentation that Earth experienced major chemical differentiation events within the first tens to hundreds of millions of years of its formation, and that Earth’s most ancient crustal rocks were derived from these differentiated sources, not from primitive undifferentiated mantle. Eoarchean rocks from the North Atlantic Craton and the Anshan Complex of the North China Craton have sources in an incompatible-element-depleted mantle that dates to 4.44.5 Ga. Hadean/Eoarchean rocks from two localities in Canada show the importance of remelting of Hadean mafic crust to produce Eoarchean felsic crust. The mafic supracrustal rocks of the Nuvvuagittuq Greenstone Belt are a possible example of the Hadean mafic basement that is often called upon to serve as the source for the high-silica rocks that define continental crust. Many, but not all, ancient terranes show a shift in the nature of the sources for crustal rocks, and possibly the physical mechanism of crust production, between 3.03.6 Ga. This transition may reflect the initiation of modern plate tectonics. Eoarchean/Hadean rocks from some terranes, however, also display compositional characteristics expected for convergent margin volcanism suggesting that at least some convergent margin related magmatism began in the Hadean. The persistence of isotopic variability in 142Nd/144Nd into the mid-Archean, and the eventual reduction in that variability by the end of the Archean, provides new information on the efficiency by which mantle convection recombined the products of Hadean silicate-Earth differentiation. The rate of crust production and recycling in the Hadean/Archean, however, is not resolved by these data beyond the observation that extreme isotopic compositions, such as expected for Hadean evolved, continent-like, crust are not observed in the preserved Eoarchean rock record. The lack of correlation between 142Nd/144Nd and 182W/184W variation in Archean rocks suggests that these two systems track different processes; the Sm-Nd system mantle-crust differentiation while Hf-W is dominated by core formation. The major silicate differentiation controlling Sm/Nd fractionation occurred at ~4.4 Ga, possibly as a result of the Moon-forming impact, after the extinction of 182Hf.
DS202011-2033
2020
Casola, V., France, L., Galy, A., Bouden, N., Villeneuve, J.No evidence for carbon enrichment in the mantle source of carbonatites in eastern Africa.Geology, Vol. 48, 10, pp. 971976. pdfAfrica, Tanzaniadeposit - Oldoinyo Lengai

Abstract: Carbonatites are unusual, carbon-rich magmas thought to form either by the melting of a carbon-rich mantle source or by low-degree partial melting of a carbon-poor (<80 ppm C) mantle followed by protracted differentiation and/or immiscibility. Carbonate-bearing mantle xenoliths from Oldoinyo Lengai (East African Rift), the only active volcano erupting carbonatites, have provided key support for a C-rich mantle source. Here, we report unique microscale O and C isotopic analyses of those carbonates, which are present as interstitial grains in the silicate host lava, veins in the xenoliths, and pseudo-inclusions in olivine xenoliths. The d18O values vary little, from 19‰ to 29‰, whereas d13C values are more variable, ranging from -23‰ to +0.5‰. We show that such carbonate d18O values result from the low-temperature precipitation of carbonate in equilibrium with meteoric water, rather than under mantle conditions. In this framework, the observed d13C values can be reproduced by Rayleigh distillation driven by carbonate precipitation and associated degassing. Together with petrological evidence of a physical connection between the three types of carbonates, our isotopic data support the pedogenic formation of carbonates in the studied xenoliths by soil-water percolation and protracted crystallization along xenolith cracks. Our results refute a mechanism of C enrichment in the form of mantle carbonates in the mantle beneath the Natron Lake magmatic province and instead support carbonatite formation by low-degree partial melting of a C-poor mantle and subsequent protracted differentiation of alkaline magmas.
DS202012-2210
2020
Casola, V., France, L., Galy, A., Bouden, N., Villeneuve, J.No evidence for carbon enrichment in the mantle source of carbonatites in eastern Africa.Geology, Vol. 48, 10, 5p. PdfAfrica, Tanzaniacarbonatites

Abstract: Carbonatites are unusual, carbon-rich magmas thought to form either by the melting of a carbon-rich mantle source or by low-degree partial melting of a carbon-poor (<80 ppm C) mantle followed by protracted differentiation and/or immiscibility. Carbonate-bearing mantle xenoliths from Oldoinyo Lengai (East African Rift), the only active volcano erupting carbonatites, have provided key support for a C-rich mantle source. Here, we report unique microscale O and C isotopic analyses of those carbonates, which are present as interstitial grains in the silicate host lava, veins in the xenoliths, and pseudo-inclusions in olivine xenoliths. The d18O values vary little, from 19‰ to 29, whereas d13C values are more variable, ranging from -23‰ to +0.5‰. We show that such carbonate d18O values result from the low-temperature precipitation of carbonate in equilibrium with meteoric water, rather than under mantle conditions. In this framework, the observed d13C values can be reproduced by Rayleigh distillation driven by carbonate precipitation and associated degassing. Together with petrological evidence of a physical connection between the three types of carbonates, our isotopic data support the pedogenic formation of carbonates in the studied xenoliths by soil-water percolation and protracted crystallization along xenolith cracks. Our results refute a mechanism of C enrichment in the form of mantle carbonates in the mantle beneath the Natron Lake magmatic province and instead support carbonatite formation by low-degree partial melting of a C-poor mantle and subsequent protracted differentiation of alkaline magmas.
DS202011-2034
2016
Castillo Clerici, A.M., Gomes, C.B., De Min, A., Comin-Chiaramonti, P.Heavy minerals in the sediments from Paraguay rivers as indicators for diamonds occurrences. *** NOTE DATEBol. Mus. Nac. Hist. Parag. *** ENG, Vol. 20, 2, pp. 188-204. pdfSouth America, Paraguaygeochemistry

Abstract: After some works of Jaime Baez-Presse that quoted the presence of diamonds in Eastern Paraguay, we have perfprmed a whole sampling a study relative to the indicator mineral for diamonds. Indicator minerals are mineral species that, when appearing as transported grains in clastic sediments, indicate the presence in bedrock of a specific type of mineralization, hydrothermal alteration or lithology. Their physical and chemical characteristics, including a relatively high density (heavy minerals), facilitate their preservation and identification. The heavy minerals represent an important exploration method for detecting a variety of ore deposit types including diamond, gold, Ni-Cu, PGE, and so on.. One of the most significant events in the application of indicator mineral methods in the past was the diamond exploration. This paper provides an overview of indicator mineral methods, i.e. presence of Cr-diopside, Pyrope-rich garnet and Picroilmenite, for diamond exploration along the Eastern Paraguay river. Unfortunately the above heavy mineraks, generally associated to the diamonds, do not appear in Eastern Paraguay, excluding this Country as a potential source for the diamond as economic potential source.
DS202005-0725
2020
Castillo-Oliver, M., Giuliani, A., Griffin, W.L., Drsydale, Rn.New constraints on the source, composition, and post-emplacement modification of kimberlites from in situ C-O-Sr-isotope analyses of carbonates from the Benfontein sills ( South Africa).Contributions to Mineralogy and Petrology, in press available, 21p. PdfAfrica, South Africadeposit - Benfontein

Abstract: Primary carbonates in kimberlites are the main CO2 carriers in kimberlites and thus can be used to constrain the original carbon and oxygen-isotope composition of kimberlite melts and their deep mantle sources. However, the contribution of syn- and post-emplacement processes to the modification of the C-O-isotope composition of kimberlites is yet to be fully constrained. This study aims to shed new light on this topic through a detailed textural, compositional (major and trace elements), and in situ C-O-Sr isotopic characterisation of carbonates in the Benfontein kimberlite sills (Kimberley, South Africa). Our multi-technique approach not only reveals the petrographic and geochemical complexity of carbonates in kimberlites in unprecedented detail, but also allows identification of the processes that led to their formation, including: (1) magmatic crystallisation of Sr-rich calcite laths and groundmass; (2) crystallisation of late groundmass calcite from hydrothermal fluids; and (3) variable degrees of crustal contamination in carbonate-rich diapirs and secondary veins. These diapirs most likely resulted from a residual C-O-H fluid or carbonate melt with contributions from methane-rich fluids from the Dwyka shale wall rock, leading to higher 87Sr/86Sr and d18O, but lower d13C values than in pristine magmatic calcite. Before coalescing into the diapiric segregations, these fluids/melts also variably entrained early formed calcite laths and groundmass phases. Comparison between in situ and bulk-carbonate analyses confirms that O isotopic analyses of bulk carbonates from kimberlite rocks are not representative of the original isotopic signature of the kimberlite magma, whereas bulk C-isotope compositions are similar to those of the pristine magmatic carbonates. Calcite laths and most groundmass grains at Benfontein preserve isotopic values (d18O?=?6-8‰ and d13C?=?-?4 to -?6‰), similar to those of unaltered carbonatites worldwide, which, therefore, probably correspond to those of their parental melts. This narrow range suggests kimberlite derivation from a mantle source with little contribution from recycled crustal material unless the recycled material had isotopic composition indistinguishable from typical mantle values.
DS202009-1616
2020
Cawood, P.Earth Matters: a temp to our planet's evolution.Geology, Vol. 48, 5, pp. 525-526.Mantlelithosphere

Abstract: Earth is our home and we, along with all life, are dependent on it for our future. There is no more fundamental issue, from either a philosophical or a practical viewpoint, than to understand Earth history and how it has evolved to form the environment we live in and the resources on which we depend. The origin of Earth, and our role within it, has fascinated humanity from time immemorial, yet we know remarkably little of Earth’s long-term temporal and spatial evolution. Apart from the last few thousand years, most of our 4.55 billion years of history is preserved in the rock archive, but that record is incomplete, and our knowledge of it decreases with increasing age and depth. Furthermore, the long-term record is restricted to relatively buoyant continental lithosphere (crust and upper mantle). Thus, continents provide the only long-term record of development and evolution of our planet’s atmosphere, oceans, crust and underlying mantle from the time of their formation to the present day. Over the past quarter century, our ability to interrogate the continental record has dramatically improved through developments in microanalysis and in computing. This has enabled ever-increasing documentation of spatial and temporal variations in rock units and events, including the composition and pressure-temperature-time conditions to which specific rocks and regions were subjected, and from this data an increased ability to develop high-fidelity numerical models of the processes involved. These expanding data sets and models highlight the dynamic nature of our planet’s feedbacks between its solid and surficial reservoirs, and their response to evolving internal and external forces.
DS202004-0502
2020
Cawood, P.A., Wang, W., Zhao, T., Xu, Y., Mulder, J.A., Pisarevsky, S.A., Zhang, L., Gan, C., He, H., Liu, H., Qi, L., Wang, Y., Yao, J., Zhao, G., Zhou, M-F., Zi, J-W.Deconstructing south China and consequences for reconstructing Nuna and Rodinia.Earth-Science Reviews, in press available, 70p. PdfChinatectonics

Abstract: Contrasting models for internal and external locations of South China within the Nuna and Rodinia supercontinents can be resolved when the current lithotectonic associations of Mesoproterozoic and older rocks units that constitute the craton are redefined into four lithotectonic domains: Kongling, Kunming-Hainan, Wuyi, and Coastal. The Kongling and Kunming-Hainan domains are characterized by isolated Archean to early Paleoproterozoic rock units and events and crop out in northern and southern South China, respectively. The Kunming-Hainan Domain is preserved in three spatially separated regions at Kunming (southwestern South China), along the Ailaoshan shear zone, and within Hainan Island. Both domains were affected by late Paleoproterozoic tectonothermal events, indicating their likely juxtaposition by this time to form the proto-Yangtze Block. Late Paleoproterozoic and Mesoproterozoic sedimentary and igneous rock units developed on the proto-Yangtze Block, especially in its southern portions, and help link the rock units that formed along the shear zone at Ailaoshan and on Hainan Island into a single, spatially unified unit prior to Paleozoic to Cenozoic structural disaggregation and translation. The Wuyi Domain consists of late Paleoproterozoic rock units within a NE-SW trending, fault-bounded block in eastern South China. The Coastal Domain lies east of the Wuyi domain and is inferred to constitute a structurally separate block. Basement to the domain is not exposed, but zircon Hf model ages from Mesozoic granites suggest Mesoproterozoic basement at depth. The Archean to Paleoproterozoic tectonothermal record of the Kongling and Kunming-Hainan domains corresponds closely with that of NW Laurentia, suggesting all were linked, probably in association with assembly and subsequent partial fragmentation of the Nuna supercontinent. Furthermore, the age and character of Mesoproterozoic magmatism and detrital zircon signature of sedimentary rocks in the proto-Yangtze Block matches well with western Laurentia and eastern Australia-Antarctica. In particular, the detrital zircon signature of late Paleoproterozoic to early Mesoproterozoic sedimentary units in the block (e.g. Dongchuan Group) share a similar age spectrum with the Wernecke Supergroup of northwest Laurentia. This, together with similarities in the type and age of Fe-Cu mineralization in the domain with that in eastern Australia-Antarctica, especially northeast Australia, suggests a location adjacent to northwest Laurentia, southern Siberia, and northeast Australia within the Nuna supercontinent. The timing and character of late Paleoproterozoic magmatic activity in the Wuyi domain along with age of detrital zircons in associated sedimentary rocks matches the record of northern India. During rifting between Australia-Antarctica and Laurentia in the late Mesoproterozoic, the proto-Yangtze Block remained linked to northeast Australia. During accretionary orogenesis in the early Neoproterozoic, the proto-Yangtze Block assembled with the Wuyi Domain along the northern margin of India. The Coastal domain likely accreted at this time forming the South China Craton. Displacement of the Hainan and Ailaoshan assemblages from southwest of the Kunming assemblage likely occurred in the Cenozoic with the activation of the Ailaoshan-Red River fault system but could have begun in the early to mid-Paleozoic based on evidence for tectonothermal events in the Hainan assemblage.
DS202001-0004
2019
Cecchi, V.M., Rossi, M., Ghiara, M.R., Franza, A.An unrevealed treasure: a new Italian meteorite from the Royal Mineralogical Museum of Naples.Geology Today, Vol. 35, 6, pp. 212-216.Europe, Italymeteorite

Abstract: Naturalistic and geo-mineralogical museum collections are one of the most relevant sources for research on meteorites the world over. Here, we present the description of a new Italian meteorite that has been recently discovered at the Royal Mineralogical Museum of Naples in Italy.
DS202009-1617
2006
Chalapathi Rao, N.V.Mesoproterozoic diamondiferous ultramafic pipes at Majhgawan and Hinota, Panna area, central India: key to the nature of sub-continental lithospheric mantle beneath the Vindhyan basin.Journal of Earth System Science *** note date 2006 , Vol. 115, 1, Feb. pp. 161-183. pdfIndiadeposit - Panna

Abstract: Amongst all the perceptible igneous manifestations (volcanic tuffs and agglomerates, minor rhyolitic flows and andesites, dolerite dykes and sills near the basin margins, etc.) in the Vindhyan basin, the two Mesoproterozoic diamondiferous ultramafic pipes intruding the Kaimur Group of sediments at Majhgawan and Hinota in the Panna area are not only the most conspicuous but also well-known and have relatively deeper mantle origin. Hence, these pipes constitute the only yet available ‘direct’ mantle samples from this region and their petrology, geochemistry and isotope systematics are of profound significance in understanding the nature of the sub-continental lithospheric mantle beneath the Vindhyan basin. Their emplacement age (~ 1100 Ma) also constitutes the only reliable minimum age constrain on the Lower Vindhyan Group of rocks. The Majhgawan and Hinota pipes share the petrological, geochemical and isotope characteristics of kimberlite, orangeite (Group II kimberlite) and lamproite and hence are recognised as belonging to a ‘transitional kimberlite-orangeite-lamproite’ rock type. The namemajhagwanite has been proposed by this author to distinguish them from other primary diamond source rocks. The parent magma of the Majhgawan and Hinota pipes is envisaged to have been derived by very small (<1%) degrees of partial melting of a phlogopite-garnet lherzolite source (rich in titanium and barium) that has been previously subjected to an episode of initial depletion (extensive melting during continent formation) and subsequent metasomatism (enrichment). There is absence of any subduction-related characteristics, such as large negative anomalies at Ta and Nb, and therefore, the source enrichment (metasomatism) of both these pipes is attributed to the volatile- and K-rich, extremely low-viscosity melts that leak continuously to semi-continuously from the asthenosphere and accumulate in the overlying lithosphere. Lithospheric/crustal extension, rather than decompression melting induced by a mantle plume, is favoured as the cause of melting of the source regions of Majhgawan and Hinota pipes. This paper is a review of the critical evaluation of the published work on these pipes based on contemporary knowledge derived from similar occurrences elsewhere.
DS202008-1377
2020
Chalapathi Rao, N.V., Giri, R.K., Pandey, A.Kimberlites, lamproites and lamprophyres from the Indian shield: highlights of researches during 2016-2019.Proceedings Natural Science Academy, Vol. 86, 1, pp. 301-311.Indiakimberlite, lamproites

Abstract: Highlights of researches on kimberlites, lamproites and lamprophyres (and their entrained xenoliths) during 2016-2019 from the Indian context are presented. A few previously unknown occurrences have been brought to light, and a wealth of petrological, geochemical and isotopic data on these rocks became available. All these studies provided new insights into the nomenclatural as well as geodynamic aspects such as subduction-tectonics, mantle metasomatism, lithospheric thickness, supercontinent amalgamation, and break-up and nature of the sub-continental lithospheric mantle from the Indian shield.
DS202009-1618
2020
Chalapathi Rao, N.V., Giri, R.K., Sharma, A., Pandey, A.Lamprophyres from the Indian shield: a review of their occurrence, petrology, tectonomagmatic significance and relationship with the kimberlites and related rocks.Episodes, Vol. 43, 1, pp. 231-248.Indialamprophyres

Abstract: Lamprophyres are some of the oldest recognized alkaline rocks and have been studied for almost the last 150 years. Known for hosting economic minerals such as gold, diamond and base metals, they are also significant in our understanding of the deep-mantle processes (viz., mantle metasomatism and mantleplume-lithosphere interactions) as well as large-scale geodynamic processes (viz., subduction-tectonics, supercontinent amalgamation and break-up). The Indian shield is a collage of distinct cratonic blocks margined by the mobile belts and manifested by large igneous provinces (LIPs) such as the Deccan. A plethora of lamprophyres, varying in age from the Archaean to the Eocene, with diverse mineralogical and geochemical compositions, are recorded from the Indian shield and played a key role in clarifying the tectonic processes, especially during the Paleo- and Mesoproterozoic and the Late Cretaceous. A comprehensive review of the occurrence, petrology, geochemistry and origin of the Indian lamprophyres is provided here highlighting their tectonomagmatic significance. The relationship of the lamprophyres to the Kimberlite clan rocks (KCRs), focusing on the Indian examples, is also critically examined.
DS202007-1128
2020
Chanturia, V.A., Dvoichenkova, G.P., Morozov, V.V., Kovalchuk, O.E., Pdkamennyi, Yu.A., Yakovlev, V.N.Selective attachment of luminophore bearing emulsion at diamonds - mechanism analysis and mode selection. X-rayJournal of Mining Science, Vol. 56, 1, pp. 96-103. pdfGloballuminescence

Abstract: The authors present an efficient modification method of X-ray fluorescence separation with mineral and organic luminophores used to adjust spectral and kinetic characteristics of anomalously luminescent diamonds. The mechanism of attachment of luminophores at diamonds and hydrophobic minerals is proved, including interaction between the organic component of emulsions and the hydrophobic surface of a treated object and the concentration of insoluble luminophore grains at the organic and water interface. Selective attachment of the luminophore-bearing organic phase of emulsion at the diamond surface is achieved owing to phosphatic dispersing agents. Tri-sodium phosphate and sodium hexametaphosphate added to emulsion reduce attachment of the luminophore-bearing organic phase at the surface of kimberlite minerals. It is shown that phosphate concentration of 1.0-1.5 g/l modifies and stabilizes spectral and kinematic parameters of kimberlite mineral on the level of initial values. This mode maintains the spectral and kinematic characteristics of anomalously luminescent diamonds at the wanted level to ensure extraction of diamonds to concentrate.
DS202004-0503
2020
Chasse, M., Blanchard, M., Cabaret, D., Vantelon, D., Juan, A., Calas, G.First principles modeling of X-ray absorption spectra enlightens the process of scandium sequestration by iron oxides.American Mineralogist, Vol. 105, 7, 10.2138/am-2020-730Globalscandium

Abstract: Scandium is often associated with iron oxides in the environment. Despite the use of scandium as a geochemical tracer and the existence of world-class supergene deposits, uncertainties on speciation obscure the processes governing its sequestration and concentration. Here, we use first-principles approaches to interpret experimental K-edge X-ray absorption near-edge structure spectra of scandium either incorporated in or adsorbed on goethite and hematite, at concentrations relevant for the environment. This modeling helps to interpret the characteristic spectral features, providing key information to determine scandium speciation when associated with iron oxides. We show that scandium is substituted into iron oxides at low concentration without modifying the crystal structure. When scandium is adsorbed onto iron oxide surfaces, the process occurs through outer-sphere complexation with a reduction in the coordination number of the hydration shell. Considering available X-ray absorption spectra from laterites, the present results confirm that scandium adsorption onto iron oxides is the dominant mechanism of sequestration in these geochemical conditions. This speciation explains efficient scandium recovery through mild metallurgical treatments of supergene lateritic ores. The specificities of scandium sorption mechanisms are related to the preservation of adsorbed scandium in million-years old laterites. These results demonstrate the emerging ability to precisely model fine X-ray absorption spectral features of trace metals associated with mineral phases relevant to the environment. It opens new perspectives to accurately determine trace metals speciation from high-resolution spatially-resolved X-ray absorption near-edge structure spectroscopy in order to constrain the molecular mechanisms controlling their dynamics.
DS202005-0726
2020
Chattopadhyay, A., Bhownik, S. K., Roy, A.Tectonothermal evolution of the Central Indian tectonic zone and its implications for Proterozoic supercontinent assembly: the current status.Episodes ( IUGS), Vol. 43, 1, pp. 132-144.Indiacraton

Abstract: The Central Indian Tectonic Zone (CITZ) is a major E-W striking mobile belt dissecting the Indian Craton along which the northern and southern Indian cratonic blocks have joined to make the Greater Indian Landmass (GIL). CITZ has a long evolutionary history spanning over 1000 Myrs (2.1-0.9 Ga), overlapping with the assembly and dispersal of two supercontinents - Columbia and Rodinia. Despite a lot of recent work carried out on the CITZ, several outstanding issues remain, especially on the nature and timing of different orogenic events identified in the southern part of this mobile belt. The present contribution attempts to summarize the major petrological, structural and geochronological studies carried out in the CITZ and reappraise the tectonic models in the context of the current database. It is surmised that, while the northern part of CITZ records Paleoproterozoic (ca. 1.8 Ga) orogenic events, the southern part is dominated by a late Palaeoproterozoic-early Mesoproterozoic (ca.1.6-1.5 Ga) collision, followed by crustal extension, and finally a late Mesoproterozoic to early Neoproterozoic (ca. 1.04-0.93 Ga) collision that led to the final stitching of the North and South Indian cratonic blocks. Tectonic evolution of the CITZ is discussed in the context of the Proterozoic supercontinent cycle.
DS202009-1619
2020
Chaves, A.de O., Porcher, C.C.Petrology, geochemistry and Sm-Nd systematics of the Paleoproterozoic Itaguara retroeclogite from Sao Francisco/Congo craton: one of the oldest records of the modern style plate tectonics.Gondwana Research, in press available 44p. PdfSouth America, Brazileclogite

Abstract: Paleoproterozoic retrogressed eclogite (retroeclogite) occurs in the Itaguara Sequence included in the suture zone formed by collision between the Archean Divinópolis and Campo Belo/Bonfim Complexes in the southern São Francisco Craton, which represents the South American counterpart of the African Congo Craton. The Itaguara retroeclogite contains scarce omphacite and phengite but abundant garnet porphyroblasts embedded in a fine-grained, amphibole, biotite and quartz-bearing matrix. The 2.20 ± 0.05 Ga eclogitization event (garnet and whole rock Sm-Nd isochronic age) of the E-MORB protolith (TDM ~ 2.47 Ga) is recorded by omphacite formation during high-pressure prograde stage in amphibole eclogite facies due to ~70 km depth subduction process. Amphibole eclogite facies metamorphic peak stage of 17-20 kbar and 600-700 °C occurred during ~2.1 Ga continental collision. Tectonic exhumation-related decompression during collision probably triggered partial melting of the eclogitic rock. Finally, decompression late stage estimated between 5 and 8 kbar and 550-650 °C under amphibolite facies overprint during orogenic collapse was responsible for appearance of kelyphitic reaction rims (symplectite) around garnet crystals. As its Paleoproterozoic contemporary analogues from Congo Craton, the Itaguara retroeclogite is one of the oldest records of the modern-style plate tectonics.
DS202008-1378
2020
Chaves, M.L.de Sa.C., Caldas, J.P.de P., Andrade, K.W., Barbosa, M.S.C.Diamonds from the Santo Antonio River ( Delfinopolis Minas Gerais): probable relationship with the Canastra-3 kimberlite.REM, Int. Journal Ouro Preto, Vol. 73, 1, pp. 51-58. pdfSouth America, Brazil, Minas Geraisdeposit - Canastra-3

Abstract: The study identifies the Canastra-3 Kimberlite magnetic anomaly as the likely primary source of the alluvial diamonds recovered by "garimpeiros" in the Santo Antônio River basin (Delfinópolis, southwestern Minas Gerais). This conclusion is based on cumulative geophysical, hydrographic, metallogenical and mineral geochemistry evidences. The study area is located within fertile ground in the border of the São Francisco craton, close to other diamond primary sources and secondary deposits. This kimberlitic target is the only known in the Santo Antônio River basin. In addition, the known mineralized gravels of this river, worked in the past by "garimpeiros", have evidence of a short transport (angular pebbles and blocks), further evidence of a nearby source. The original data collected in the "Minas Gerais Aerogeophysical Survey Program" was processed and analyzed with the Euler Deconvolution method, implemented in software Oasis Montaj. With the exception of the Canastra-3 body anomaly, all others in the study were classified as non-kimberlitic. Recent sampling work on the weathered top of the Canastra-3 Kimberlite recovered indicator minerals, notably a high proportion of pyrope garnets of the G-10 type, which is unusual among the kimberlites of the region.
DS202006-0914
2020
Chayka, I.F., Sobolev, A.V., Izokh, A.E., Batanova, V.G., Krasheninnikov, S.P., Chervyakovskaya, M.V., Kontonikas-Charos, A., Kutyrev, A.V., Lobastov, B.M., Chervyakovskiy, V.S.Fingerprints of kamafugite-like magmas in Mesozoic lamproites of the Aldan Shield: evidence from olivine and olivine-hosted inclusions.Minerals, Vol. 10, 4, 30p.Russia, Siberiadeposit - Ryabinoviy

Abstract: Mesozoic (125-135 Ma) cratonic low-Ti lamproites from the northern part of the Aldan Shield do not conform to typical classification schemes of ultrapotassic anorogenic rocks. Here we investigate their origins by analyzing olivine and olivine-hosted inclusions from the Ryabinoviy pipe, a well preserved lamproite intrusion within the Aldan Shield. Four types of olivine are identified: (1) zoned phenocrysts, (2) high-Mg, high-Ni homogeneous macrocrysts, (3) high-Ca and low-Ni olivine and (4) mantle xenocrysts. Olivine compositions are comparable to those from the Mediterranean Belt lamproites (Olivine-1 and -2), kamafugites (Olivine-3) and leucitites. Homogenized melt inclusions (MIs) within olivine-1 phenocrysts have lamproitic compositions and are similar to the host rocks, whereas kamafugite-like compositions are obtained for melt inclusions within olivine-3. Estimates of redox conditions indicate that “lamproitic” olivine crystallized from anomalously oxidized magma (?NNO +3 to +4 log units.). Crystallization of "kamafugitic" olivine occurred under even more oxidized conditions, supported by low V/Sc ratios. We consider high-Ca olivine (3) to be a fingerprint of kamafugite-like magmatism, which also occurred during the Mesozoic and slightly preceded lamproitic magmatism. Our preliminary genetic model suggests that low-temperature, extension-triggered melting of mica- and carbonate-rich veined subcontitental lithospheric mantle (SCLM) generated the kamafugite-like melts. This process exhausted carbonate and affected the silicate assemblage of the veins. Subsequent and more extensive melting of the modified SCLM produced volumetrically larger lamproitic magmas. This newly recognized kamafugitic "fingerprint" further highlights similarities between the Aldan Shield potassic province and the Mediterranean Belt, and provides evidence of an overlap between "orogenic" and "anorogenic" varieties of low-Ti potassic magmatism. Moreover, our study also demonstrates that recycled subduction components are not an essential factor in the petrogenesis of low-Ti lamproites, kamafugites and leucitites.
DS202010-1832
2020
Chen, H., Leinenweber, K., Prakapenka, V., Kunz, M., Bechtel, H.A., Liu, Z., Shim, S-H.Phase transformation of hydrous ringwoodite to the lower-mantle phases and the formation of hydrous silica.American Mineralogist, Vol. 105, pp. 1342-1348. pdfMantlebridgmanite

Abstract: To understand the effects of H2O on the mineral phases forming under the pressure-temperature conditions of the lower mantle, we have conducted laser-heated diamond-anvil cell experiments on hydrous ringwoodite (Mg2SiO4 with 1.1 wt% H2O) at pressures between 29 and 59 GPa and temperatures between 1200 and 2400 K. Our results show that hydrous ringwoodite (hRw) converts to crystalline dense hydrous silica, stishovite (Stv) or CaCl2-type SiO2 (mStv), containing 1 wt% H2O together with Brd and MgO at the pressure-temperature conditions expected for shallow lower-mantle depths between approximately 660 to 1600 km. Considering the lack of sign for melting in our experiments, our preferred interpretation of the observation is that Brd partially breaks down to dense hydrous silica and periclase (Pc), forming the phase assembly Brd + Pc + Stv. The results may provide an explanation for the enigmatic coexistence of Stv and Fp inclusions in lower-mantle diamonds.
DS202007-1129
2020
Chen, Y., Gu, Y/.J., Heaman, L.M., Wu, L., Saygin, E., Hung, S-H.Reconciling seismic structures and Late Cretaceous kimberlite magmatism in northern Alberta, Canada.Geology, Vol. 48, in press available, 5 p. pdfCanada, Albertadeposit - Birch Mountain, Mountain Lake

Abstract: The Late Cretaceous kimberlites in northern Alberta, Canada, intruded into the Paleoproterozoic crust and represent a nonconventional setting for the discovery of diamonds. Here, we examined the origin of kimberlite magmatism using a multidisciplinary approach. A new teleseismic survey reveals a low-velocity (-1%) corridor that connects two deep-rooted (>200 km) quasi-cylindrical anomalies underneath the Birch Mountains and Mountain Lake kimberlite fields. The radiometric data, including a new U-Pb perovskite age of 90.3 ± 2.6 Ma for the Mountain Lake intrusion, indicate a northeast-trending age progression in kimberlite magmatism, consistent with the (local) plate motion rate of North America constrained by global plate reconstructions. Taken together, these observations favor a deep stationary (relative to the lower mantle) source region for kimberlitic melt generation. Two competing models, mantle plume and slab subduction, can satisfy kinematic constraints and explain the exhumation of ultradeep diamonds. The plume hypothesis is less favorable due to the apparent age discrepancy between the oldest kimberlites (ca. 90 Ma) and the plume event (ca. 110 Ma). Alternatively, magma generation may have been facilitated by decompression of hydrous phases (e.g., wadsleyite and ringwoodite) within the mantle transition zone in response to thermal perturbations by a cold slab. The three-dimensional lithospheric structures largely controlled melt migration and intrusion processes during the Late Cretaceous kimberlite magmatism in northern Alberta.
DS202007-1130
2020
Cheperov, A.I., Sonin, V.M., Zhimulev, E.I., Cheperov, A.A.Preservation conditions of CLIPPIR diamonds in the Earth's mantle in a heterogeneous metal-sulphide-silicate medium ( experimental modeling).Journal of Mineralogical and Petrological Sciences, Vol. 115, pp. 236-246. pdfMantlediamond inclusions

Abstract: The genesis of CLIPPIR diamonds (Cullinan-like, large, inclusion-poor, pure, irregular, and resorbed) have attracted much interest due to their possible crystallization from metal melt in deep horizons of the earth’s mantle. These diamonds usually show a pronounced resorption and irregular morphology. The present paper reports new experimental data on the dissolution of diamond crystals at high P-T parameters in Fe-S melt containing large amounts of silicate components (5-20 wt%). The experiments were performed using a split-sphere multi-anvil apparatus (BARS) at a pressure of 4 GPa and a temperature of 1450 °C. The samples consisted of natural diamond crystals placed in mixtures of Fe, S, and kimberlite. Wide variations in dissolution rates of diamond crystals were obtained. The absence of diamond dissolution in a heterogeneous medium indicates that the amount of solid silicate phases present in metal melt plays a role in the preservation of diamonds. This study demonstrated how diamonds can be stored in natural environments due to the heterogeneity of the medium composition which could insulate diamonds from the metal-sulphide melt. The obtained results improve our understanding of processes that lead to preservation of CLIPPIR diamonds in the deep mantle.
DS202008-1379
2020
Chepurov, A.I., Tomilenko, A.A., Sonin, V.M., Zhimulev, E.I., Bulbak, T.A., Cheperov, A.A., Sobolev, N.V.Interaction of an Fe-Ni melt with anthracene ( C14H10) in the presence of olivine at 3 Gpa: fluid phase composition.Doklady Earth Sciences, Vol. 492, pp. 333-337.MantleUHP, diamond

Abstract: The first results on the interaction between an Fe-Ni melt and anthracene (?14?10) in the presence of olivine at 3 GPa and 1500°? and on the study of the component composition of the fluid generated in this process are presented. The stability of aliphatic hydrocarbons in the implemented conditions is confirmed experimentally. It is established that, under these conditions, crystallization of high-magnesian olivines occurs (Fo = 97-98 mol %). The composition of the fluid is similar to the composition of the fluid from inclusions in synthetic diamonds. The conditions implemented in the experiment might have occurred at the early stages of the Earth’s evolution.
DS202004-0504
2020
Chernykh, S.V., Chernykh, A.V., Tarelkin, S., Didenko, S. ,Kondakov, M.N., Shcherbachev, K.D., Trifonova, E.V., Drozdova, T.E., Troschiev, S.Y., Prikhodko, D.D., Glybin, Y.N., Chubenko, A.P., Britvich, G.I., Kiselev, D.A., Polushin, N.I., Rabinovich, O.IHPHT single crystal diamond type IIa characterization for particle detectors.Physicsa Status Solidi , doi:10.1002/pssa.201900888GlobalHPHT

Abstract: Various samples of multisectoral high-pressure high-temperature (HPHT) single-crystal diamond plate (IIa type) (4?×?4?×?0.53?mm) are tested for particle detection applications. The samples are investigated by X-ray diffractometry, photoluminescence spectroscopy, Raman spectroscopy, Fourier-transform infrared, and visible/ultraviolet (UV) absorption spectroscopy. High crystalline perfection and low impurity concentration (in the {100} growth sector) are observed. To investigate detector parameters, circular 1.0 and 1.5?mm diameter Pt Schottky barrier contacts are created on {111} and {100} growth sectors. On the backside, a Pt contact (3.5?×?3.5?mm) is produced. The {100} growth sector is proved to be a high-quality detector: the full width at half maximum energy resolution is 0.94% for the 5.489?MeV 226Ra a-line at an operational bias of +500?V. Therefore, it is concluded that the HPHT material {100} growth sector is used for radiation detector production, whose quality is not worse than the chemical vapor deposition method or specially selected natural diamond detectors.
DS202007-1131
2020
Chisenga, C., Van der Meijde, M., Yan, J., Fadel. I., Atekwana, E.A., Steffen, R., Ramotoroko, C.Gravity derived crustal thickness model of Botswana: its implication for the Mw 6.5 April 3, 2017, Botswana earthquake. Tectonophysics, Vol. 787, 228479 12p. PdfAfrica, Botswanageophysics - gravity

Abstract: Botswana experienced a Mw 6.5 earthquake on 3rd April 2017, the second largest earthquake event in Botswana's recorded history. This earthquake occurred within the Limpopo-Shashe Belt, ~350 km southeast of the seismically active Okavango Rift Zone. The region has no historical record of large magnitude earthquakes or active faults. The occurrence of this earthquake was unexpected and underscores our limited understanding of the crustal configuration of Botswana and highlight that neotectonic activity is not only confined to the Okavango Rift Zone. To address this knowledge gap, we applied a regularized inversion algorithm to the Bouguer gravity data to construct a high-resolution crustal thickness map of Botswana. The produced crustal thickness map shows a thinner crust (35-40 km) underlying the Okavango Rift Zone and sedimentary basins, whereas thicker crust (41-46 km) underlies the cratonic regions and orogenic belts. Our results also show localized zone of relatively thinner crust (~40 km), one of which is located along the edge of the Kaapvaal Craton within the MW 6.5 Botswana earthquake region. Based on our result, we propose a mechanism of the Botswana Earthquake that integrates crustal thickness information with elevated heat flow as the result of the thermal fluid from East African Rift System, and extensional forces predicted by the local stress regime. The epicentral region is therefore suggested to be a possible area of tectonic reactivation, which is caused by multiple factors that could lead to future intraplate earthquakes in this region.
DS202008-1380
2020
Choi, E., Fiorentini, M.L., Giuliani, A., Foley, S.F., Maas, R., Taylor, W.R.Subduction related petrogenesis of late Archean calc-alkaline lamprophyres in the Yilgarn craton, western Australia.Precambrian Research, Vol. 338, 105550, 18p. PdfAustralialamprophyres

Abstract: We present a comprehensive petrographic, mineralogical and geochemical study of calc-alkaline lamprophyres (CAL) from the Archean Yilgarn Craton, Western Australia. Previous studies have shown that the emplacement age of CAL from the Eastern Goldfields Superterrane of the Yilgarn Craton is ~2684 to ~2640 Ma. A new Rb/Sr mica age for a CAL sample in the Western Yilgarn is ~2070 Ma. Both Archean and Proterozoic CAL analysed in this study display porphyritic textures and contain phenocrysts of amphibole, minor clinopyroxene and biotite in a fine-grained groundmass dominated by feldspar. High MgO, Ni and Cr abundances (up to 11.9 wt%, 373 and 993 ppm. respectively) are consistent with derivation of primitive magmas from a mantle source. Enrichment in H2O, reflected in the abundance of magmatic amphibole and mica, combined with high whole-rock LILE, Th/Yb ratios and negative Nb-Ta anomalies in trace element patterns are consistent with a source that was metasomatised by hydrous fluids analogous to those generated by Phanerozoic subduction-related processes. Chondritic ?Nd and ?Hf signatures and Archean mantle-like Sr isotope signatures of the Late Archean CAL indicate that the fluid metasomatism required to explain their volatile and trace-element enriched composition shortly preceded partial melting (i.e. there was insufficient time to develop enriched radiogenic isotopic signatures). The concurrence of apparently juvenile radiogenic isotopes and fluid-related trace element compositions requires a geodynamic scenario whereby dehydration of a subducted slab triggered metasomatism of the overlying mantle wedge. Our findings therefore support a subduction setting at ~2.6-2.7 Ga along the eastern margin of the Yilgarn Craton. The CAL from the Western Yilgarn have similar compositions but enriched Sr-Nd-Hf isotopes compared to those in the Eastern Goldfields Superterrane. This signature is consistent with melting of lithospheric mantle domains previously enriched by subduction-related metasomatism. Hence, our study suggests the presence of a subduction setting in the Western Yilgarn during the Archean, which is consistent with previous geodynamic reconstructions. However, the geodynamic trigger for the early Proterozoic event that generated CAL magmatism in the Western Yilgarn is currently unclear.
DS202007-1132
2020
Choi, F.M., Fiorentini, M.L., Giuliani, A., Foley, S.F., Maas, R., Taylor, W.R.Subduction related tetrogenesis of late Archean calc-alkaline lamprophyres in the Yilgarn craton ( Western Australia).Precambrian Research, Vol. 338, 105550Australialamprophyres

Abstract: We present a comprehensive petrographic, mineralogical and geochemical study of calc-alkaline lamprophyres (CAL) from the Archean Yilgarn Craton, Western Australia. Previous studies have shown that the emplacement age of CAL from the Eastern Goldfields Superterrane of the Yilgarn Craton is ~2684 to ~2640 Ma. A new Rb/Sr mica age for a CAL sample in the Western Yilgarn is ~2070 Ma. Both Archean and Proterozoic CAL analysed in this study display porphyritic textures and contain phenocrysts of amphibole, minor clinopyroxene and biotite in a fine-grained groundmass dominated by feldspar. High MgO, Ni and Cr abundances (up to 11.9 wt%, 373 and 993 ppm. respectively) are consistent with derivation of primitive magmas from a mantle source. Enrichment in H2O, reflected in the abundance of magmatic amphibole and mica, combined with high whole-rock LILE, Th/Yb ratios and negative Nb-Ta anomalies in trace element patterns are consistent with a source that was metasomatised by hydrous fluids analogous to those generated by Phanerozoic subduction-related processes. Chondritic ?Nd and ?Hf signatures and Archean mantle-like Sr isotope signatures of the Late Archean CAL indicate that the fluid metasomatism required to explain their volatile and trace-element enriched composition shortly preceded partial melting (i.e. there was insufficient time to develop enriched radiogenic isotopic signatures). The concurrence of apparently juvenile radiogenic isotopes and fluid-related trace element compositions requires a geodynamic scenario whereby dehydration of a subducted slab triggered metasomatism of the overlying mantle wedge. Our findings therefore support a subduction setting at ~2.6-2.7 Ga along the eastern margin of the Yilgarn Craton. The CAL from the Western Yilgarn have similar compositions but enriched Sr-Nd-Hf isotopes compared to those in the Eastern Goldfields Superterrane. This signature is consistent with melting of lithospheric mantle domains previously enriched by subduction-related metasomatism. Hence, our study suggests the presence of a subduction setting in the Western Yilgarn during the Archean, which is consistent with previous geodynamic reconstructions. However, the geodynamic trigger for the early Proterozoic event that generated CAL magmatism in the Western Yilgarn is currently unclear.
DS202011-2035
2020
Choudhary, B.R., Santosh, M., Ravi, S., Babu, E.V.S.S.K.Spinel and Ti-rich schorlomite from the Wajrakarur kimberlites, southern India: implications for metasomatism, diamond potential and orangeite lineage.Ore Geology Reviews, Vol. 126, 103727, 19p. PdfIndiadeposit - Wajrakarur

Abstract: Kl-4 and P-5 mesoproterozoic kimberlite pipes along with several other well-known diamondiferous (ca. 1110 Ma) kimberlites in the Wajrakarur kimberlite field (WKF) intruded into the cratonic roots of Eastern Dharwar craton (EDC) in southern India. The groundmass minerals of the kimberlites exhibit inequigranular texture contain spinel, Ti-rich schorlomite garnet, two generations of olivine (macrocrysts and groundmass microphenocrysts), phlogopite, perovskite, clinopyroxene (diopside), ilmenite (low Mn) and rare apatite. We identified three distinct spinel associations in Kl-4 and P-5: (i) fine-grained (<50 µm) microcrysts in the groundmass; (ii) resorbed euhedral atoll spinel, consisting of titanomagnetite (magnesian-ulvospinel-magnetite to titanian-chrome-magnetite) which is isolated from the rim of magnetite by spongy lagoon phase of schorlomite, and (iii) larger chrome spinel macrocrysts/xenocrysts (>500 µm). The schorlomite garnet in both P-5 and Kl-4 represents solid solution of schorlomite-pyrope-almandine-grossular. Additionally, Kl-4 contains another Cr-rich schorlomite-pyrope-almandine-uvarovite solid solution. Macrocrystic spinel exhibits distinct composition of chromium (Cr2O3 up to 59.62 wt%), and poor in TiO2 (<1.19 wt%). The high chromium spinel macrocrysts from Kl-4 are confirmed to be fragments of mantle xenocrysts and their composition falls within the diamond stability field. Atoll-textured epitaxial mantled resorbed spinel associated with schorlomite suggests that they formed through the replacement of spinel possibly through interaction of late residual fluids/melts in the final stages of crystallization of the kimberlite magma. The significant enrichment of Fe and Ti in schorlomite suggests the involvement of metasomatized sub-continental lithospheric mantle. It is also inferred that spinel immiscibility played an important role in the metasomatic replacement. The Ti-rich minerals have orangeitic affinity, similar to those in the Kaapvaal craton of South Africa, and suggest the high Ti-, high Ca- and the low Al-bearing nature of the parent magma (Group II kimberlites). The groundmass tetraferriphlogopite is Al- and Ba-poor and spinel show compositions straddling between magnesian ulvöspinel (Group I kimberlite) and titanomagnetite (Group II kimberlite) comparable with orangeite and lamproites. The results presented in this study suggest that the P-5 and Kl-4 has orengeitic or lamproitic affinity. Our findings can be useful as an indicator mineral in diamond prospecting.
DS202008-1381
2020
Choudhary, B.R., Santosh, M., Ravi, S., Babu, EVSSKIndicator mineral ( spinel) from the Wajrakarur kimberlites, southern India: implications for diamond potential and prospectivity.Goldschmidt 2020, 1p. AbstractIndiadeposit - Wajraarur, Kalandurg

Abstract: P-5 and Kl-4 Mesoproterozoic (ca. 1110 Ma) kimberlites from the Wajrakarur and Kalyandurg clusters, Eastern Dharwar craton (EDC), southern India are intruded into the diamondiferous cratonic roots. The spinel compositions is straddling between magnesian ulvöspinel (Group-1 kimberlite) and titanomagnetite (Group-2 kimberlite), comparable with orangeite and lamproites. These Ti-rich minerals have orangeitic affinity, as in the Kaapvaal craton of South Africa, and reflect the high Ti-, high Ca- and the low Al-bearing nature of the parent magma (Group II kimberlites). Larger chrome spinel macrocrysts/xenocrysts show >500 µm of size with distinctly high chromium (Cr2O3 up to 59.62 wt%), and TiO2-poor (<1.19 wt%). The high chromium spinel macrocrysts represent fragments of mantle xenocrysts and their composition falls within the diamond stability field. The groundmass spinel has been replaced by Ti- schorlomite. The schorlomite garnet represents solid solution of schorlomite -pyrope -almandine-grossular and Crrich schorlomite -pyrope -almandine- uvarovite solid solution. These associations recommend that the schorlomite formed through the replacement of spinel through interaction of late residual fluids/melts in the final stages of crystallization of the kimberlite magma and enrichment in Fe and Ti in schorlomite suggests the involvement of metasomatized sub-continental lithospheric mantle. Present study may have useful application in diamond prospectivity.
DS202009-1620
2020
Choudhary, S., Sen, K., Kumar, S., Rana, S., Ghosh, S.Forsterite repricipitation and carbon dioxide entrapment in the lithospheric mantle during its interaction with carbonatitic melt: a case study from the Sung Valley ultramafic-alkaline-carbonatite complex, Meghalaya, NE India.Geological Magazine, 10.1017/S001675 68200000631 12p.Indiacarbonatites

Abstract: Carbonatite melts derived from the mantle are enriched in CO2- and H2O-bearing fluids. This melt can metasomatize the peridotitic lithosphere and liberate a considerable amount of CO2. Experimental studies have also shown that a CO2-H2O-rich fluid can form Fe- and Mg-rich carbonate by reacting with olivine. The Sung Valley carbonatite of NE India is related to the Kerguelen plume and is characterized by rare occurrences of olivine. Our study shows that this olivine is resorbed forsterite of xenocrystic nature. This olivine bears inclusions of Fe-rich magnesite. Accessory apatite in the host carbonatite contains CO2-H2O fluid inclusions. Carbon and oxygen isotopic analyses indicate that the carbonatites are primary igneous carbonatites and are devoid of any alteration or fractionation. We envisage that the forsterite is a part of the lithospheric mantle that was reprecipitated in a carbonatite reservoir through dissolution-precipitation. Carbonation of this forsterite, during interaction between the lithospheric mantle and carbonatite melt, formed Fe-rich magnesite. CO2-H2O-rich fluid derived from the carbonatite magma and detected within accessory apatite caused this carbonation. Our study suggests that a significant amount of CO2 degassed from the mantle by carbonatitic magma can become entrapped in the lithosphere by forming Fe- and Mg-rich carbonates.
DS202005-0727
2020
Chu, J.Origins of Earth's magnetic field remains a mystery. ( Jack Hills)MIT News, 4p. PdfAustraliaGeophysics - magnetics

Abstract: Microscopic minerals excavated from an ancient outcrop of Jack Hills, in Western Australia, have been the subject of intense geological study, as they seem to bear traces of the Earth’s magnetic field reaching as far back as 4.2 billion years ago. That’s almost 1 billion years earlier than when the magnetic field was previously thought to originate, and nearly back to the time when the planet itself was formed. But as intriguing as this origin story may be, an MIT-led team has now found evidence to the contrary. In a paper published today in Science Advances, the team examined the same type of crystals, called zircons, excavated from the same outcrop, and have concluded that zircons they collected are unreliable as recorders of ancient magnetic fields. In other words, the jury is still out on whether the Earth’s magnetic field existed earlier than 3.5 billion years ago.
DS202011-2036
2020
Chukanov, N.V., Aksenov, S.M., Pekov, I.V., Belakovskiy, D.I., Vozchikova, S.A., Britvin, S.N.Sergevanite, new eudialyte group mineral from the Lovozero alkaline massif, Kola Peninsula.The Canadian Mineralogist, Vol. 58, pp. 421-436.Russia, Kola Peninsuladeposit - Lovozero

Abstract: The new eudialyte-group mineral sergevanite, ideally Na15(Ca3Mn3)(Na2Fe)Zr3Si26O72(OH)3•H2O, was discovered in highly agpaitic foyaite from the Karnasurt Mountain, Lovozero alkaline massif, Kola Peninsula, Russia. The associated minerals are microcline, albite, nepheline, arfvedsonite, aegirine, lamprophyllite, fluorapatite, steenstrupine-(Ce), ilmenite, and sphalerite. Sergevanite forms yellow to orange-yellow anhedral grains up to 1.5 mm across and the outer zones of some grains of associated eudialyte. Its luster is vitreous, and the streak is white. No cleavage is observed. The Mohs' hardness is 5. Density measured by equilibration in heavy liquids is 2.90(1) g/cm3. Calculated density is equal to 2.906 g/cm3. Sergevanite is nonpleochroic, optically uniaxial, positive, with ? = 1.604(2) and e = 1.607(2) (? = 589 nm). The infrared spectrum is given. The chemical composition of sergevanite is (wt.%; electron microprobe, H2O determined by HCN analysis): Na2O 13.69, K2O 1.40, CaO 7.66, La2O3 0.90, Ce2O3 1.41, Pr2O3 0.33, Nd2O3 0.64, Sm2O3 0.14, MnO 4.15, FeO 1.34, TiO2 1.19, ZrO2 10.67, HfO2 0.29, Nb2O5 1.63, SiO2 49.61, SO3 0.77, Cl 0.23, H2O 4.22, -O=Cl -0.05, total 100.22. The empirical formula (based on 25.5 Si atoms pfu, in accordance with structural data) is H14.46Na13.64K0.92Ca4.22Ce0.27La0.17Nd0.12Pr0.06Sm0.02Mn1.81Fe2+0.58Ti0.46Zr2.67Hf0.04Nb0.38Si25.5S0.30Cl0.20O81.35. The crystal structure was determined using single-crystal X-ray diffraction data. The new mineral is trigonal, space group R3, with a = 14.2179(1) Å, c = 30.3492(3) Å, V = 5313.11(7) Å3, and Z = 3. In the structure of sergevanite, Ca and Mn are ordered in the six-membered ring of octahedra (at the sites M11 and M12), and Na dominates over Fe2+ at the M2 site. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 7.12 (70) (110), 5.711 (43) (202), 4.321 (72) (205), 3.806 (39) (033), 3.551 (39) (220, 027), 3.398 (39) (313), 2.978 (95) (?forumla?), 2.855 (100) (404). Sergevanite is named after the Sergevan' River, which is near the discovery locality.
DS202007-1133
2020
Cimen, O., Corcoran, L., Kuebler, C., Simonetti, S.S., Simonetti, A.Geochemical, stable ( O, C, and B) and radiogenic ( Sr, Nd, Pb) isotopic data from the Eskisehir-Kizulxaoren ( NW-Anatolia) and the Malatya-Kuluncak ( E- central Anatolia) F-REE-Th deposits, Turkey: implications for nature of carbonate-hosted mineralizatiTurkish Journal of Earth Sciences, Vol. 29, doe:10.3906/yer-2001-7 18p. PdfEurope, TurkeyREE
DS202010-1833
2020
Clerici, A.M.C., Gomes, C.B.. De Min, A., Comin-Chiaramnti, P.Heavy minerals in the sediments from Paraguay rivers as indicators for diamond occurrences.Bol. Mus. Nac. Hist. Paraguay, , Vol. 20, 2, pp. 188-204. pdfSouth America, Paraguaygeochemistry

Abstract: After some works of Jaime Baez-Presse that quoted the presence of diamonds in Eastern Paraguay, we have perfprmed a whole sampling a study relative to the indicator mineral for diamonds. Indicator minerals are mineral species that, when appearing as transported grains in clastic sediments, indicate the presence in bedrock of a specific type of mineralization, hydrothermal alteration or lithology. Their physical and chemical characteristics, including a relatively high density (heavy minerals), facilitate their preservation and identification. The heavy minerals represent an important exploration method for detecting a variety of ore deposit types including diamond, gold, Ni-Cu, PGE, and so on.. One of the most significant events in the application of indicator mineral methods in the past was the diamond exploration. This paper provides an overview of indicator mineral methods, i.e. presence of Cr-diopside, Pyrope-rich garnet and Picroilmenite, for diamond exploration along the Eastern Paraguay river. Unfortunately the above heavy mineraks, generally associated to the diamonds, do not appear in Eastern Paraguay, excluding this Country as a potential source for the diamond as economic potential source.
DS202009-1621
2020
CNNThe Earth's core is younger than previously believed, according to new research.cnn.com, Aug. 25, 1/2p.MantleNews item - core
DS202002-0170
2019
Coldebella, B.Intensive (P-T-fO2) crystallization paramenters of Alto Paranaiba kimberlites and diamond instability: Tres Ranchos IV and Limeira I intrusions. ***PortThesis, University of Sao Paulo, August 53p. pdfSouth America, Brazildeposit - Tres Rabchos IV and limeira I

Abstract: Temperature (T), Pressure (P) and Oxygen fugacity (fO2) conditions were established for the Três Ranchos IV (diamond-bearing) and Limeira I (sterile) kimberlites of the Coromandel-Três Ranchos kimberlite field (Minas Gerais and Goiás, Brazil), Alto Paranaíba Alkaline Province (APAP), in order to draw a possible correlation between these intensive crystallization parameters and diamond instability. Both Três Ranchos IV and Limeira I are classified as coherent macrocrystic kimberlites, with an inequigranular texture formed by partially-to-fully altered olivine, phlogopite megacrysts up to 1 cm wide, macrocrysts (0.5-10 mm-sized), and crustal xenoliths set in a very fine groundmass composed mainly by perovskite, olivine, phlogopite, spinel, serpentine and carbonates identified in both intrusions. Apatite, ilmenite and monticellite are also present, but only in LM-I. Garnet macrocrysts and centimetric pyroxene xenocrysts phases are also present in Três Ranchos IV and Limeira I, respectively. The samples, strongly enriched in incompatible elements, are all MgO-rich, with high Mg# content. In order to apply different geotherm-and-oxybarometers in the calculation of P-T-fO2 conditions and to characterize the compositional variation of TR-IV and LM-I kimberlites, major, minor and trace-element concentrations of the main mineral phases were obtained by electron microprobe and LA-ICP-MS. Olivine cores of Limeira I present higher NiO, CaO and lower Cr2O3 contents than those from Três Ranchos IV. Mg# [(Mg/Mg+FeT), mol.%) ranges from 87 to 92 mol.% in TR-IV and from 83 to 92 mol.% in LM-I. The trace-element contents of olivine are similar in both kimberlites, the concentrations of Li, Zn and Mn appearing to be higher at olivine rims. In olivines from both intrusions, a pattern of enrichment in Zr, Ga, Nb, Sc, V, P, Al, Ti, Cr, Ca, and Mn in rims regions, is observed in the "melt trend" whereas enrichment in Zn, Co, Ni and possibly Na in cores regions, is found in the "mantle trend." In monticellite specimens from Limeira I, Mg# ranges from 72 to 93.8, while Ca/(Ca+Mg) ratios range from 35 to 58 mol.%. The perovskite composition in both LM-I and TR-IV remains close to the ideal CaTiO3, perovskite, but a variation from core endmembers (average Lop16 and Prv78) towards the rims (average Lop13 and Prv81) can be noticed in TR-IV samples. The highest concentrations of light rare earth elements (LREE), Nb, and Fe3+ are also observed in perovskites from the TR-IV kimberlite. Macrocrystic spinels of TR-IV kimberlite are Al-rich, whereas the groundmass crystals range from magnesiochromite to chromite. Ilmenites from LM-I are characterized by high MgO values at a given TiO2, with a large variation in Cr2O3. Pyrope garnets (62 to 73 mol.%) are present only in TR-IV, with Mg# ranging from 72 to 79 mol.%, being classified as lherzolitic (G9) and pyroxenitic (G4, G5). Diopside occurs as xenocrysts in LM-I and as microphenocrysts in TR-IV, with Mg# ranging from 85 to 91 and from 87 to 92, respectively. Xenocrystic diopsides from LM-I present higher MgO and FeO concentrations with monticellite grains along crystal rims and fractures. Temperature estimates for the LM-I kimberlite, obtained from the composition of diopside xenocrysts and Al-in olivine concentrations, ranging from 718 to 985 °C. Pressure ranges from 34 to 47 Kbar, as calculated using an empirical curve from a 37-mW/m2 geotherm proposed in the literature for Alto Paranaíba magmas. For TR-IV, temperature values ranging from 975 to 1270°C were obtained from Al-in olivine and Ni-in garnet concentrations. Pressures in the range from 18 to 34 Kbar were obtained from major element composition of garnet samples from TR-IV kimberlite. The fO2 of the TR-IV constrained by perovskite (kimberlite cognate phase) oxygen barometry ranges from NNO-7 to NNO+4, while for LM-I values range from NNO+6 to NNO-4. For the LM-I intrusion, monticellite, another cognate phase used as an oxybarometer, yielded a value range of NNO-4 to NNO+2. A change in the oxygen fugacity from cores towards rim recorded in the perovskites and the monticellite crystals is also noticed. The oxygen fugacity estimates of this work are the first ever calculated for magmas of the Alto Paranaíba Alkaline Province. All P-T-fO2 values obtained are consistent with literature data on the APAP. Clinopyroxene xenocrysts from LM-I were classified as garnet-facies clinopyroxene, according to the compositions obtained in this work. Such results, along with pressure, and temperature data from and the presence of Mg-ilmenite in LM-I (known to be sterile), indicate that the kimberlite magma might have at least crossed the diamond stability field. The variation in oxygen fugacity observed in both kimberlites possibly reflects the instability of diamonds in these magmas since LM-I presents slightly higher oxidation conditions.
DS202007-1134
2020
Coldebella, B., Azzone, R.G., Chmyz, L., Ruberti, E., Svisero, D.P.Oxygen fugacity of Alto Paranaiba kimberlites and diamond stability: Tres Ranchos IV and Limeira I intrusions.Brazilian Journal of Geology, Vol. 50, 1, 15p.South America, Brazildeposit - Tres Ranchos IV

Abstract: Oxygen fugacity (ƒO2) conditions were established for Três Ranchos IV (TR-IV, diamond-bearing) and Limeira I (LM-I, barren) kimberlite intrusions, in Alto Paranaíba Alkaline Province, to constrain a possible correlation between fO2 and diamond instability. Temperature and pressure estimates obtained from the xenocryst assemblage composition are compatible up to garnet lherzolite levels. It suggests that both intrusions could cross the diamond-stability field. The ƒO2 of the TR-IV constrained by perovskite oxygen barometry presents an average value of -2.4 for ?NNO, with standard deviation of 1.30 (n = 120), whereas those calculations for LM-I have an average value of -1.31 for ?NNO, with standard deviation of 1.38 (n = 81). Considering these uncertainties, there is an important superposition of fO2 values for both intrusions, in which there is higher tendency of more reduced conditions for TR-IV. For the LM-I, an oxybarometer based on the composition of monticellite yielded a similar ?NNO range: -4.2 and +2.5. Some crystals and samples present trends towards more reduced conditions, while others display more oxidized conditions for each intrusion. Due to the superposition of ranges and absence of a preferential trend, the influence of fO2 for the possible instability of diamonds in the study area remains uncertain.
DS202005-0728
2020
Conceicao, F.T., Vasconcelos, P.M., Godoy, L.H., Navarro, G.R.B.40Ar/40Ar geochronological evidence for multiple magmatic events during the emplacement of Tapira alkaline-carbonatite complex, Minas Gerais, Brazil.Journal of South American Earth Sciences, Vol. 97, 102416, 7p. PdfSouth America, Brazil, Minas Geraiscarbonatite

Abstract: The Alto Parnaíba Igneous Province (APIP) is a voluminous magmatic province composed of various alkaline-carbonatite complexes emplaced in the Brasilia Mobile Belt during the Cretaceous. Relative timing of emplacement of silicate and carbonate magmas in most of these complexes remains mostly unresolved due to conflicting geochronological results. To determine the duration of magmatism and to test the possible existence of multiple magmatic events, we employ 40Ar/39Ar phlogopite single crystal dating to determine the history of magma emplacement at the Tapira alkaline-carbonatite complex, Minas Gerais, Brazil. The new single crystal data indicate at least two magmatic events during the emplacement of this complex, the first at > 96.2 ± 0.8 Ma and the second at 79.15 ± 0.6 Ma. The first igneous event was responsible for emplacement of the silicate plutonic series, while the second event corresponds to the emplacement of primarily carbonatitic magmas, generating metasomatic phlogopite alteration in bebedourites. The ages of intrusion and cooling of the alkaline-carbonatite complexes in the APIP must be investigated in other complexes to determine if intrusion intervals of ~17 Ma or more are common regionally. Protracted intrusive events, if related to magma generation by passage of South America over a stationary Trindade plume, requires complex ponding and lateral magma flow below a slow-moving continent.
DS202008-1382
2020
Conceicao, R.V., Marcon, V.H., Souza, M.R.W., Carniel, L.C., Quinteiro, R.V.S., Rovani, P., Mizusaki, A.M.P., Spitzenberger, M.S.Carbonatite/lamproite liquid imissibility in the Earth's mantle through the nefeline-diopside-kalsilite+-CO2, CH4, H2O diagram.Goldschmidt 2020, 1p. AbstractMantlelamproite

Abstract: The presence and speciation of volatile C-H-O elements in the silicate systems play an important role in the genesis of magmas on the Earth’s mantle, due to the fact that these elements, mainly in the form of H2O, CO2, CH4 and CxHy, decrease the solidi temperatures of source rocks, making magmatism possible in Earth’s present day thermal conditions [1]. Among those elements, carbon is the only element that changes its valence according to the oxygen fugacity (fO2) conditions of the environment, resulting in different speciation, as: CO3 -2, CO2, Cgraphite/diamond, CH4 or heavier hydrocarbons. In the present work, we are determining phase stability of minerals, water, CO2 and CH4 in the system Nefeline-Kalsilite-Diopside. Our experiments are conducted under 4.0 GPa and temperatures up to 1300°C, using a 1000 tonf hydraulic press coupled with toroidal chambers. Preliminary experiments performed at 1300°C and 4.0GPa (initial composition in the Olivine-Quartz- Kalsalite/Nepheline system: 40mol% Ol90, 40mol% Nph50Kls50 and 20mol% Qz, PH2O,CO2=Ptotal) resulted in the formation of forsterite (Fo90) in equilibrium with phlogopite (Phl), melt and volatile phases (CO2 and CH4). Closer to the Diopside vertice, the addition of CO3 to the sample resulted in a imisibility of a carbonatitic and a silicatic melt, in which the carbonititic melt is enriched in sodium, while the silcate melt is enriched in potassium. Appart from that, experiments in different parts of the diagram suggest compositions from nephelinite-kalsilitite to lamproites composition for the silicate melt in equilibrium with diopside (solid solution with omphacite) and phlogopite. This work is a continuation of previous work in the anhydrous diagram and future works will provide the addition of CH4 as the volatile phase
DS202011-2037
2020
Condie, K.C.Revisiting the Mesoproterozoic.Gondwana Research, in press available 9p. pdfMantleNuna

Abstract: Many of the peculiar features of the Mesoproterozoic (1.6-1.0 Ga) are related to the assembly of the first supercontinent Nuna, and some may not be distinctive of this time period. A high frequency of A-type granites at 1.6-1.4 Ga may be due, in part, to sampling biases. The overall increase in frequency in A-type granites beginning at 1.9 Ga may track the propagation of plate tectonics especially in the Great Proterozoic Accretionary Orogen. Increases in alkali and related elements in granitoids at 2.4-2.0 Ga may reflect widespread propagation of subduction as plate tectonics spread around the globe, and increases in HREE, Nb, Ti and Sc in granitoids may be related to decreasing importance of restitic garnet in granitoid sources as Earth transitioned from TTG to calc-alkaline magmatic regimes. Related to possible global mantle events at 1.9, 1.0 and 0.6 Ga are peaks in frequency of LIP and zircon ages related to supercontinent assembly. Mesoproterozoic paleomagnetic data that require at least 12 passive margins during this time. An increase in plate speed with time since 2 Ga may reflect a decreasing viscosity contrast across the lithosphere-asthenosphere boundary in response to a cooling mantle or/and thinning of the lithosphere and corresponding increases in heat flux with time. A relatively constant 87Sr/86Sr of seawater between 1.9 and 1.0 Ga may have resulted from a balance between weathered juvenile and reworked crustal sources as well as enhanced seafloor weathering of oceanic basalts. Mostly positive eHf(t) in detrital zircons and eNd(t) granitoids during the Mesoproterozoic suggest significant juvenile crustal input. However, the sparsity of crust of this age today probably results from recycling of large volumes of continental crust into the mantle in peripheral accretionary orogens during the breakup of Nuna at 1.4-1.2 Ga.
DS202006-0915
2020
Conover, E.Physicists have harnessed the aloofness of quantum particles to create a new type of crystal. Pauli crystal ( not specific to diamonds just for interest)Science News, May 19, 2p.Europe, GermanyCrystallography
DS202010-1834
2020
Cordani, U.G., Colombo, C.G., Tassinari, C.G., Rolim, D.R.The basement of the Rio Apa craton in Mato Grosso do Sul ( Brazil and northern Paraguay): a geochronological correlation with the tectonic provinces of the south western craton.Researchgate, 2p. Abstract in englishSouth America, Brazil, Mato Grosso, Paraguaycraton

Abstract: The Rio Apa cratonic fragment crops out in Mato Grosso do Sul State of Brazil and in northeastern Paraguay. It comprises Paleo-Mesoproterozoic medium grade metamorphic rocks, intruded by granitic rocks, and is covered by the Neoprotero-zoic deposits of the Corumbá and Itapocumi Groups. Eastward it is bound by the southern portion of the Paraguay belt. In this work, more than 100 isotopic determina-tions, including U-Pb SHRIMP zircon ages, Rb-Sr and Sm-Nd whole-rock determina-tions, as well as K-Ar and Ar-Ar mineral ages, were reassessed in order to obtain a complete picture of its regional geological history. The tectonic evolution of the Rio Apa Craton starts with the formation of a series of magmatic arc complexes. The oldest U-Pb SHRIMP zircon age comes from a banded gneiss collected in the northern part of the region, with an age of 1950 23 Ma. The large granitic intrusion of the Alumiador Batholith yielded a U-Pb zircon age of 1839 33 Ma, and from the southeastern part of the area two orthogneisses gave zircon U-Pb ages of 1774 26 Ma and 1721 25 Ma. These may be coeval with the Alto Tererê metamorphic rocks of the northeastern corner, intruded in their turn by the Baía das Garças granitic rocks, one of them yielding a zircon U-Pb age of 1754 49 Ma. The original magmatic protoliths of these rocks involved some crustal component, as indicated by the Sm-Nd T DM model ages, between 1.9 and 2.5 Ga. Regional Sr isotopic homogenization, associated with tectonic deformation and medium-grade metamorphism occurred at approximately 1670 Ma, as suggested by Rb-Sr whole rock reference isochrons. Finally, at 1300 Ma ago, the Ar work indicates that the Rio Apa Craton was affected by widespread regional heating, when the temperature probably exceeded 350°C. Geographic distribution, age and isotopic signature of the lithotectonic units suggest the existence of a major suture separating two different tectonic domains, juxtaposed at about 1670 Ma. From that time on, the unified Rio Apa continental block behaved as one coherent and stable tectonic unit. It correlates well with the SW corner of the Amazonian Craton, where the medium-grade rocks of the Juruena-Rio Negro tectonic province, with ages between 1600 and 1780 Ma, were reworked at about 1300 Ma. Looking at the largest scale, the Rio Apa Craton is probably attached to the larger Amazonian Craton, and the actual configuration of southwestern South America is possibly due to a complex arrangement of allochthonous blocks such as the Arequipa, Antofalla and Pampia, with different sizes, that may have originated as disrupted parts of either Laurentia or Amazonia, and were trapped during later collisions of these continental masses.
DS202007-1135
2020
Corfu, F., Hegde, V.S.U-Pb systematics of the western Dharwar craton - glimpse of a billion year history of crustal evolution and relations to ancient supercratons.Journal of South American Earth Sciences, Vol. 102, 102659, 12p. PdfIndiageochronology

Abstract: The Dharwar Craton developed progressively over a billion years, through two main stages of crustal growth separated by a few-hundred million year long period of relative quiescence. The first stage between 3.4 and 3.0 Ga developed a proto-craton, which was considerably amplified during the second main stage between 2.7 and 2.4 Ga, through extensive magmatism, tectonism, and crustal consolidation. This paper reports U-Pb dating results obtained in four specific areas of the craton, with the data encompassing key moments in this long development. Rocks formed during the proto-craton stage include a 3089 Ma augen gneiss and a 2973 Ma evolved granite, the latter of which marks the final cratonization event of the proto-craton. The beginning of the second main stage is recorded in this study by 2650 Ma tonalite and trondhjemite, a 2623 Ma granite dyke cutting augen gneiss, and 2614, 2602 and 2588 Ma volcanic rocks. Titanite responded differently to the long evolution, as a function of location and type of overprint. It preserved an original 2973 Ma magmatic age in the west, but was reset and/or crystallized during secondary events in central domains of the craton, yielding ages between 2590 and 2360 Ma. A diorite stock intruded at 2207 Ma in the consolidated crust. It is correlated with the Anantapur-Kunigal mafic dyke swarm, one of a series of such events in the Dharwar Craton between 2.35 and 1.79 Ma. In terms of its overall evolution the Dharwar Craton has an affinity with the Slave clan, which includes the Wyoming and Zimbabwe cratons. It also matches many features in the evolution of the São Francisco Craton, a probable other member of Sclavia. This is in contrast to the Amazonian Craton, which has more affinity with the Superior clan.
DS202001-0005
2019
Cui, K., Wardle, B.L.Cited as reference to Ball paper on Black diamonds.ACS Applied Material Interfaces, Vol. 11, pp. 35212-35220Globalnanodiamond
DS202004-0505
2018
Cummings, D.I., Russell, H.A.J.Glacial dispersal trains in North America.Journal of Maps ( Taylor & Francis) on linkedin, Vol. 14, 2, pp. 476-485. pdfUnited States, CanadaGlaciation, geomorphology, map

Abstract: A map depicting glacial dispersal trains in North America has been compiled from published sources. It covers the Canadian Shield, the Arctic Islands, the Cordillera and Appalachian mountains, and Phanerozoic sedimentary basins south of the Shield. In total, 140 trains are portrayed, including those emanating from major mineral-deposit types (e.g. gold, base metal, diamondiferous kimberlite, etc.). The map took 10 years of on-and-off work to generate, and it culls data from over 150 years of work by government, industry, and academia. It provides a new tool to help companies find ore deposits in Canada: the trains are generally a better predictor of dispersal distance and direction than striations and streamlined landforms, the data typically depicted on surficial-geology maps, including the Glacial Map of Canada. It also gives new insight into sedimentation patterns and processes beneath ice sheets, a sedimentary environment that, because of its inaccessibility, remains poorly understood and controversial.
DS202002-0171
2019
Cutts, J.A., Smit, M., Spengler, D., van Roermind, H., Kooijman, E.Punctuated evolution of the Archean SCLM in sync with the supercontinent cycle. Western Gneiss ComplexAmericam Geophysical Union Fall meeting, 1p. AbstractEurope, Norwayeclogites, peridotites

Abstract: The preservation of Archean cratons is typically attributed to the presence of a highly-depleted and buoyant sub-continental lithospheric mantle (SCLM) that is equally old or older than its overlying crust. Time constraints on the formation and petrological evolution of the SCLM are key to investigating its long-term evolution and role in the formation and preservation of the continental crust. Nevertheless, such constraints are difficult to obtain as well-preserved samples of the SCLM are rare and typically lack conventional chronometric minerals. The history of SCLM rocks is typically inferred on the basis of model ages, many of which indicate an Archean origin; however, these dates are difficult to link to specific mineral assemblages or chemical signatures, and the petrological and dynamic processes that these represent. Garnet Lu-Hf geochronology is one of the few chronometers that could overcome this limitation. In this study, a refined method in Lu-Hf garnet chronology was applied to fragments of the Laurentian SCLM that are now exposed as orogenic peridotites in the ultrahigh-pressure domains of the Western Gneiss Complex, Norway. The peridotite bodies comprise a variety of unusually well-preserved rock types-from dunites that record decompression and melting at >350 km depth to fertile lithologies produced by melting and fluid metasomatism. Our internal isochron results from pyrope (after exsolution from majorite) in dunite samples yielded identical Neoarchean ages; these are the first-ever obtained for mantle garnet. The ages coincide with a time interval during which there was voluminous juvenile crust formation, indicating a link between this global process and the deeply sourced mantle upwellings that these samples represent. Internal isochrons from websterite-and clinopyroxenite-hosted pyrope yielded Meso-to Neoproterozoic ages that exactly match two distinct supercontinent break-up events in the overlying continental crust. Together, the new Lu-Hf results indicate that since its extraction during a period of widespread Archean crustal growth, the Laurentian SCLM appears to have largely been at petro-physical and chemical stasis and evolved only during short pulses that ran in sync with the supercontinent cycle.
DS202002-0172
2019
Czas, J., Pearson, G., Stachel, T., Kjarsgaard, B., Read, G.H. J. Pearson, G., Stachel, T., KjaA Paleoproterozoic diamond bearing lithospheric mantle root beneath the Archean Sask craton, Canada.Lithos, DOI:10.1016/ j.lithos.2019.105301Canada, Saskatchewandiamond genesis
DS202010-1835
2020
D'Agrella-Filho, M.S., Paul, Y.J., Antonio, P.Y.J., Bispo-Santos, F.The Precambrian drift history and paleogeography of Amazonia.Chapter 6,, Personen et al. ed. Precambrian Supercontinents, 99p. PdfSouth Americacraton

Abstract: Here, we reassess the paleomagnetic database for Amazonia and its geodynamic implications for supercontinents. According to paleomagnetic and geological data, Amazonia and West Africa joined at ca. 2.00 Ga defining a single long-lived block. This landmass eventually formed a part of the Columbia supercontinent together with Baltica and Laurentia between 1.78 and 1.42 Ga. For the formation of Rodinia paleomagnetic and geological data permit three different models: an oblique collision at ca. 1.2 Ga, a clockwise rotation of Amazonia/West Africa and Baltica from Columbia to Rodinia joining Laurentia at ca. 1.0 Ga, or a scenario where Amazonia/West Africa was a wandering block that did not take part in Columbia and collided with Laurentia to form Rodinia at ca. 1.0-0.95 Ga. The time Amazonia/West Africa joined Gondwana is also debatable, with contrasting geochronological and geological evidence supporting an early collision at 0.65-0.60 Ga or a late collision at 0.53-0.52 Ga.
DS202009-1622
2020
Dai, H-K., Zheng, J.P., Griffin, W.L., O'Reilly, S.Y., Xiong, Q., Ping, X., Chen, F-K., Lu, J.Pyroxenite xenoliths record complex melt impregnation in the deep lithosphere of the northwestern North China Craton.Journal of Petrology, 10.1093/petrology/egaa079 110p. PdfChinaxenoliths

Abstract: Transformation of refractory cratonic mantle into more fertile lithologies is the key to the fate of cratonic lithosphere. This process has been extensively studied in the eastern North China Craton (NCC) while that of its western part is still poorly constrained. A comprehensive study of newly-found pyroxenite xenoliths from the Langshan area, in the northwestern part of this craton is integrated with a regional synthesis of pyroxenite and peridotite xenoliths to constrain the petrogenesis of the pyroxenites and provide an overview of the processes involved in the modification of the deep lithosphere. The Langshan pyroxenites are of two types, high-Mg# [Mg2+/(Mg2++Fe2+)*100 = ~ 90, atomic ratios] olivine-bearing websterites with high equilibration temperatures (880 ~ 970 oC), and low-Mg# (70 ~ 80) plagioclase-bearing websterites with low equilibration temperatures (550 ~ 835 oC). The high-Mg# pyroxenites show trade-off abundances of olivine and orthopyroxene, highly depleted bulk Sr-Nd (?Nd?=?+11.41, 87Sr/86Sr = ~0.7034) and low clinopyroxene Sr isotopic ratios (mean 87Sr/86Sr = ~0.703). They are considered to reflect the reaction of mantle peridotites with silica-rich silicate melts derived from the convective mantle. Their depletion in fusible components (e.g., FeO, TiO2 and Na2O) and progressive exhaustion of incompatible elements suggest melt extraction after their formation. The low-Mg# pyroxenites display layered structures, convex-upward rare earth element patterns, moderately enriched bulk Sr-Nd isotopic ratios (?Nd = -14.20 ~ -16.74, 87Sr/86Sr?=?0.7070 ~ 0.7078) and variable clinopyroxene Sr-isotope ratios (87Sr/86Sr?=?0.706-0.711). They are interpreted to be crustal cumulates from hypersthene-normative melts generated by interaction between the asthenosphere and heterogeneous lithospheric mantle. Combined with studies on regional peridotite xenoliths, it is shown that the thinning and refertilization of the lithospheric mantle was accompanied by crustal rejuvenation and that such processes occurred ubiquitously in the northwestern part of the NCC. A geodynamic model is proposed for the evolution of the deep lithosphere, which includes long-term mass transfer through a mantle wedge into the deep crust from the Paleozoic to the Cenozoic, triggered by subduction of the Paleo-Asian ocean and the Late Mesozoic lithospheric extension of eastern Asia.
DS202008-1383
2020
Dalton, H., Giuiani, A., Phillips, D., Hergt, J., Maas, R., Woodhead, J., Matchan, E., O'Brien, H.Kimberlite magmatism in Finland: distinct sources and links to the breakup of Rodinia.Goldschmidt 2020, 1p. AbstractEurope, Finlanddeposit - Kuusamo

Abstract: The Karelian Craton in Finland is host to (at least) two distinct pulses of kimberlite magmatism. Twenty kimberlite occurrences have so far been discovered on the southwest margin of the craton at Kaavi-Kuopio and seven kimberlites are located in the Kuusamo area within the core of the craton. Comprehensive radiometric age determinations (U-Pb, Ar- Ar and Rb-Sr) reveal that all kimberlite activity was restricted to the Proterozoic. The Kaavi-Kuopio field was emplaced over a protracted period from ~610 to 550 Ma and is predated by the Kuusamo cluster that represents a relatively short pulse of magmatism at ~750 to 730 Ma. The emplacement of kimberlites globally has recently been linked to supercontinent reorganisation and we propose a similar scenario for these Finnish occurrences which, at the time of kimberlite emplacement, were situated on the Baltica paleo-continent. This land mass was contiguous with Laurentia in the Proterozoic and together formed part of Rodinia. The breakup of Rodinia is considered to have commenced at ~750 Ma and initiation of the opening of the Iapetus ocean at ~615 Ma. Contemporaneous with Kaavi-Kuopio magmatism, this latter period of Neoproterozoic crustal extension also includes the emplacement of kimberlites and related rocks in areas that were linked with Baltica as part of Rodinia - West Greenland and eastern North America. Both the initial and final periods of Rodinia’s breakup have been linked to mantle upwellings from the core-mantle boundary. We suggest that kimberlite magmatism in Finland was promoted by the influx of heat from mantle upwellings and lithospheric extension associated with the demise of Rodinia. Although both magmatic episodes are potentially linked to the breakup of Rodinia, whole-rock and perovskite radiogenic isotope compositions for the Kuusamo kimberlites (eNd(i) +2.6 to +3.3, eHf(i) +3.1 to +5.6) are distinct from the Kaavi-Kuopio kimberlites (eNd(i) -0.7 to +1.8, eHf(i) -6.1 to +5.2). The spread in Hf isotope compositions for the Kaavi-Kuopio magmas may be linked to variable assimilation of diverse mantle lithologies.
DS202002-0173
2019
Dalton, H., Giuliani, A., O'Brien, H., Phillips, D., Hergt, J.The role of lithospheric heterogeneity on the composition of kimberlite magmas from a single field: the case of Kaavi-Kuopio, Finland.Lithos, in press available, 61p. PdfEurope, Finlanddeposit - Kaavi-Kuopio

Abstract: Kimberlites are complex, ‘hybrid’ igneous rocks because their parental magmas entrain abundant crust- and mantle-derived components that can be readily assimilated during ascent to surface. Recent studies of olivine zonation patterns have shown compositional relationships between xenocrystic cores and magmatic rims, suggesting that kimberlite melt compositions might be controlled by assimilation of mantle material during emplacement. However, the nature and extent to which this process, as well as assimilation of crustal material, influences melt compositions within single kimberlite fields remains unclear. To address this issue, we have conducted a comprehensive geochemical and petrographic investigation of kimberlites from eight pipes in the Kaavi-Kuopio field in Finland, which were emplaced on the southern margin of the Karelian craton during the Neoproterozoic (~550-600 Ma). While magmatic olivine rims are usually homogeneous in composition 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 are statistically significant differences between the average Mg# of olivine rims in different pipes (89.9 ± 0.2 to 88.5 ± 0.3). Importantly, the Mg# of magmatic olivine rims exhibit a strong correlation with the Mg# of their mantle-derived xenocrystic cores. Furthermore, the compositions of olivine cores and rims exhibit a robust relationship with those of magmatic spinel (e.g., Mg#, TiO2 contents). These geochemical variations also align with the mineralogy of the kimberlites: whereby abundances of phlogopite and oxides (e.g., spinel) are negatively correlated with olivine rim Mg#. The robust relationship between entrained and assimilated lithospheric mantle material (i.e. olivine cores) and magmatic components (i.e. olivine rims, spinel, and groundmass mineral abundance), combined with numerical modelling suggests that up to 10 wt% assimilation of lithospheric mantle material has modified the compositions of the Kaavi-Kuopio kimberlites. These new data are also consistent with significant variations in the lithospheric mantle composition of the Karelian craton beneath the closely spaced (<10 km) kimberlites. Finally, in addition to mantle assimilation, formation of Si-Fe-rich mica in some of the examined kimberlites might be linked to late-stage increases in oxygen fugacity potentially enhanced by crustal contamination. This study shows for the first time that variable assimilation of mantle and crustal material can generate significant variations in kimberlites derived from seemingly similar sources.
DS202002-0174
2019
Dalton, H., Giuliani, A., O'Brien, H., Phillips, D., Maas, R. Petrogenesis of a hybrid cluster of evolved kimberlites and ultramafic lamprophyres in the Kuusamo area, Finland. Kasma 45, Kasma 45 south, Kasma 47, Kalettomanpuro, Kattaisenvaara, Dike 15 and LampiJournal of Petrology, in press available, 79p. PdfEurope, Finlanddeposit - Kuusamo

Abstract: Kimberlites are often closely associated, both in time and space, with a wide variety of alkaline ultramafic rock types; yet the question of a genetic relationship between these rock types remains uncertain. One locality where these relationships can be studied within the same cluster is the Karelian craton in Finland. In this study we present the first petrographic, mineral and whole-rock geochemical results for the most recently discovered kimberlite cluster on this craton, which represents an example of the close spatial overlap of kimberlites with ultramafic lamprophyres. The Kuusamo cluster incorporates seven bodies (Kasma 45, Kasma 45 south, Kasma 47, Kalettomanpuro (KP), Kattaisenvaara (KV), Dike 15 and Lampi) distributed along a 60?km NE-SW corridor. Hypabyssal samples from KV, KP, Kasma 45 and Kasma 47 consist of altered olivine macrocrysts and microcrysts and phlogopite phenocrysts in a groundmass of perovskite, apatite, spinel, ilmenite, serpentine, and calcite. These petrographic features combined with mineral (e.g., Mg-rich ilmenite, Al-Ba-rich, Ti-Fe-poor mica) and whole-rock incompatible trace element compositions (La/Nb = 0.8 ± 0.1; Th/Nb = 0.07 ± 0.01; Nb/U = 66 ± 9) are consistent with these rocks being classified as archetypal kimberlites. These Kuusamo kimberlites are enriched in CaO and poor in MgO, which combined with the absence of chromite and paucity of olivine macrocrysts and mantle-derived xenocrysts (including diamonds), suggest derivation from differentiated magmas after crystal fractionation. Samples from Lampi share similar petrographic features, but contain mica with compositions ranging from kimberlitic (Ba-Al-rich cores) to those more typical of orangeites/lamproites (increasing Si-Fe, decreasing Al-Ti-Ba), and have higher bulk-rock SiO2 contents than the Kuusamo kimberlites. These features, combined with the occurrence of quartz and titanite in the groundmass, indicate derivation from a kimberlite magma that underwent considerable crustal contamination. This study shows that crustal contamination can modify kimberlites by introducing features typical of alkaline ultramafic rock types. Dike 15 represents a distinct carbonate-rich lithology dominated by phlogopite over olivine, with lesser amounts of titaniferous clinopyroxene and manganoan ilmenite. Phlogopite (Fe-Ti-rich) and spinel (high Fe2+/Fe2++Mg) compositions are also distinct from the other Kuusamo intrusions. The petrographic and geochemical features of Dike 15 are typical of ultramafic lamprophyres, specifically, aillikites. Rb-Sr dating of phlogopite in Dike 15 yields an age of 1178.8 ± 4.1?Ma (2s), which is considerably older than the ~750?Ma emplacement age of the Kuusamo kimberlites. This new age indicates significant temporal overlap with the Lentiira-Kuhmo-Kostomuksha olivine lamproites emplaced ~100?km to the southeast. It is suggested that asthenospheric aillikite magmas similar to Dike 15 evolved to compositions akin to the Karelian orangeites and olivine lamproites through interaction with and assimilation of MARID-like, enriched subcontinental lithospheric mantle. We conclude that the spatial coincidence of the Kuusamo kimberlites and Dike 15 is likely the result of exploitation of similar trans-lithospheric corridors.
DS202010-1836
2020
Davaille, A., Romanowicz, B.Deflating the LLSVPs: bundles of mantle thermochemical plumes rather than thick stagnant "piles".Tectonics, e202TC006265 Vol. 39, 4, ? Mantletomography

Abstract: Based on SEMUCB-WM1 tomographic model, validated by other recent models, and fluid mechanics constraints, we show that the large low shear velocity provinces (LLSVPs) present at the base of the Earth's mantle beneath the Pacific and Africa do not extend as compact, uniform structures very high above the core-mantle boundary. In contrast, they contain a number of well-separated, low-velocity conduits that extend vertically throughout most of the lower mantle. The conceptual model of compact piles, continuously covering the areal extent of the LLSVPs, is therefore not correct. Instead, each LLSVP is composed of a bundle of thermochemical upwellings probably enriched in denser than average material. It is only when the tomographic model is filtered to long wavelengths that the two bundles of plumes appear as uniform provinces. Furthermore, the overall shape of the LLSVPs is probably controlled by the distribution of subducted slabs, and due to their thermochemical nature, the position of both LLSVPs and individual upwelling dynamics should be time dependent. There is also evidence for smaller plumes originating near the CMB in the faster than average regions of the voting map of Lekic et al. (2012, https://doi.org/10.1016/j.epsl.2012.09.014) as well as other, barely resolved, weaker plumes within the LLSVPs. These finer-scale features are starting to be resolved tomographically owing to improvements in full waveform modeling of body waves, including diffracted S waves (Sdiff) and waves multiply reflected on the core-mantle boundary (ScS) and their codas.
DS202006-0916
2020
Davey, S.C., Bleeker, W., Kamo, S.L., Vuollo, J., Ernst, R.E., Cousens, B.L.Archean block rotation in western Karelia: resolving dyke swarm patterns in metacraton Karelia-Kola for a refined paleogeographic reconstruction of supercraton Superia.Lithos, in press available 95p. PdfRussia, Kola Peninsulacraton

Abstract: Rifting, breakup, and subsequent collision related to the ca. 1.92-1.79?Ga Svecofennian orogeny fragmented and deformed the western margin of the Archean Karelia-Kola craton into four crustal blocks: Pudasjärvi, Iisalmi, Kuhmo, and Taivalkoski. Detailed quantification of Svecofennian deformation is limited due to poorly exposed basement geology and an as yet incomplete dyke swarm record. New U-Pb ID-TIMS geochronological results on baddeleyite and zircon are presented for three key mafic dykes from the Pudasjärvi block, namely the Uolevinlehto, Myllykangas, and Sipojuntti dykes. The age of the 325°-trending Uolevinlehto dyke is estimated at ca. 2400?±?12?Ma from discordant multigrain baddeleyite fractions, showing it to be younger than ca. 2450?Ma dykes across Karelia. The 350°-trending Myllykangas dyke has a minimum age of 2135.2?+?3.6/-3.7?Ma based on chemically abraded zircon. Results from single baddeleyite grains provide a precise upper intercept age of 2128.9?±?1.2?Ma for the 320°-trending Sipojuntti dyke. Our new U-Pb ages are integrated with those from the literature to define six major dyke swarms in the Pudasjärvi block: the WNW-trending ca. 2.45?Ga Pääjärvi, NW-trending ca. 2.40?Ga Uolevinlehto, NW-trending ca. 2.13-2.10?Ga Tohmajärvi, WNW-trending ca. 2.07?Ga Palomaa, NNW-trending ca. 1.98?Ga Paukkajanvaara and undated"East-West" dykes. Trends of contemporaneous dyke swarms in the Taivalkoski and Kuhmo blocks, however, are systematically offset by 35°. With subvertical dips, offset dyke swarms record 35° clockwise vertical-axis rotation of the Pudasjärvi block relative to the interior of Karelia, consistent with dextral transpression during the Svecofennian orogeny. Structural restoration of the Pudasjärvi blocks improves the constraints on regional dyke swarm patterns, and these are used to revise the position of the Karelia-Kola craton within the context of the paleogeographic reconstruction of supercraton Superia.
DS202002-0175
2019
de Araujo Neto, J.F., de Brito Barreto, S., Carrino, T.A., Muller, A., de Lira Santos, L.C.M.Mineralogical and gemological characterization of emerald crystals from Parana deposit, NE Brazil: a study of mineral chemistry, absorption and reflectance spectroscopy and thermal analysis.Brazil Journal of Geology ( www.scielo.br) ENG, 15p. PdfSouth America, Brazildeposit - Parana

Abstract: The Paraná deposit, located at Southwestern Rio Grande do Norte state, in Brazil, is one of the few emerald deposits found at Borborema Province. The mineralization occurs in phlogopite schists and actinolite-phlogopite schists associated with pegmatites and albitites within the Portalegre Shear Zone. Unlike other well-known Brazilian emerald deposits, the mineralogy of Paraná emeralds has remained poorly investigated for the last 40 years. In this study, we conducted mineralogical characterization of theses emeralds through gemological testing, mineral chemistry, absorption and reflectance spectroscopy, and thermal analysis. The Paraná emeralds are bluish-green colored, characterized by high refractive index, several two-phase fluid inclusions and mica is the main mineral inclusion. Electron probe microanalysis and laser ablation-inductively coupled plasma-mass spectrometry analyses detected the presence of Fe2+ (0.43-1.94 wt.% FeO) and Cr3+ (0.04-0.14 wt.% Cr2O3) as the main chromophores replacing octahedral Al3+ in the crystal structure. In addition, substantial amounts of MgO (0.40-2.72 wt.%), Na2O (0.50-1.81 wt.%), and Cs2O (0.07-0.44 wt.%) were also identified. The main causes for its coloration were attributed to Cr3+ absorption features in visible spectral range, which were corroborated by absorption and reflectance spectra. The presence of types I and II H2O at channel-sites was recorded in Fourier-transform infrared spectra and demonstrated by dehydration processes observed in different thermal and thermogravimetric analyses.
DS202002-0176
2019
De Hoog, J.C.M., Stachel, T., Harris, J.W.Trace element geochemistry of diamond hosted olivine inclusions from the Akwatia mine, West African Craton: implications for diamond paragenesis and geothermobarometry.Contributions to Mineralogy and Petrology, Vol. 174, (12) doi: 10.1007/s00410-019-1634-yAfrica, 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.
DS202002-0177
2019
de Mamam Anzolin H., Dani, N., Remus, M.V.D., da Rocha Ribeiro, R., Nunes, A.R., Ruppel, K.M.V.Apatite multi-generations in the Tres Estradas carbonatite, southern Brazil: physical and chemistry meaning and implications to phosphate ore quality. Brazil Journal of Geology ( www.scielo.br) ENG, 17p. PdfSouth America, Brazildeposit - Tres Estradas

Abstract: Carbonatites were recently discovered in Southern Brazil, which increased the interest to evaluate the economic potential of these uncommon rocks, especially the Três Estradas Carbonatite. Carbonates are the dominant minerals of fresh rock followed by apatite, but the weathering process makes apatite abundant. We focused on apatite from the carbonatite using conventional petrography and electronic microscopy associated with microprobe, micro-Raman and Fourier-transform infrared spectroscopy. Results demonstrate the existence of four types. The primary type is associated with the rock crystallization and the subsequent three others are associated with weathering processes. The alteration mechanism was favorable for initial carbonate leaching and subsequent increase of phosphate with late precipitation of three new apatite generations. The deduced model involves long exposure during polycyclic climate changes, intercalating periods of warm dry with humid climate. The apatite types differ chemically and morphologically and have distinctive characteristics that are suitable to be used to differentiate them. These properties should be considered in future planes of industrial processes to transform apatite into single superphosphate, a basic input for fertilizer production.
DS202012-2211
2020
de Oliveira Chaves, A., Porcher, C.C.Petrology, geochemistry and Sm-Nd systematics of the Paleoproterozoic Itagurra retroeclogite from Sao Francisco/Congo craton: one of the oldest records of the modern-style plate tectonics.Gondwana Research, Vol. 87, pp. 224-237. pdfSouth America, Brazileclogites
DS202011-2038
2020
De Wit, M.Botswana's World Class Diamond Mines.https://www.youtube.com /watch?v=GoqjOMoUw3I, 1hr long Africa, BotswanaHistory
DS202005-0729
2020
Decree, S., Cawthorn, G., Deloule, E., Mercadier, J., Frimmel, H., Baele, J-M.Unravelling the processes controlling apatite formation in the Phalaborwa Complex ( South Africa) based on combined cathodluminescence, LA-ICPMS and in-situ O and Sr isotope analyses.Contributions to Mineralogy and Petrology, Vol. 175, 34 31p. PdfAfrica, South Africacarbonatite

Abstract: The Phalaborwa world-class phosphate deposit (South Africa) is hosted by a Paleoproterozoic alkaline complex mainly composed of phoscorite, carbonatite, pyroxenitic rocks, and subordinate fenite. In addition, syenite and trachyte occur in numerous satellite bodies. New petrological and in-situ geochemical data along with O and Sr isotope data obtained on apatite demonstrate that apatite is in the principal host rocks (pyroxenitic rocks, phoscorite and carbonatite) formed primarily by igneous processes from mantle-derived carbonatitic magmas. Early-formed magmatic apatite is particularly enriched in light rare earth elements (LREE), with a decrease in the REE content ascribed to magma differentiation and early apatite fractionation in isolated interstitial melt pockets. Rayleigh fractionation favored a slight increase in d18O (below 1%) at a constant Sr isotopic composition. Intrusion of fresh carbonatitic magma into earlier-formed carbonatite bodies locally induced re-equilibration of early apatite with REE enrichment but at constant O and Sr isotopic compositions. In fenite, syenite and trachyte, apatite displays alteration textures and LREE depletion, reflecting interaction with fluids. A marked decrease in d18O in apatite from syenite and trachyte indicates a contribution from d18O-depleted meteoric fluids. This is consistent with the epizonal emplacement of the satellite bodies. The general increase of the Sr isotope ratios in apatite in these rocks reflects progressive interaction with the country rocks over time. This study made it possible to decipher, with unmatched precision, the succession of geological processes that led to one of the most important phosphate deposits worldwide.
DS202004-0506
2020
Delord, T., Huillery, P., Nicolas, L., Hetet, G.Spin-cooling of the motion of trapped diamond.Nature, March 23, in press available Globalnitrogen

Abstract: Observing and controlling macroscopic quantum systems has long been a driving force in quantum physics research. In particular, strong coupling between individual quantum systems and mechanical oscillators is being actively studied. Whereas both read-out of mechanical motion using coherent control of spin systems and single-spin read-out using pristine oscillators have been demonstrated, temperature control of the motion of a macroscopic object using long-lived electronic spins has not been reported. Here we observe a spin-dependent torque and spin-cooling of the motion of a trapped microdiamond. Using a combination of microwave and laser excitation enables the spins of nitrogen-vacancy centres to act on the diamond orientation and to cool the diamond libration via a dynamical back-action. Furthermore, by driving the system in the nonlinear regime, we demonstrate bistability and self-sustained coherent oscillations stimulated by spin-mechanical coupling, which offers the prospect of spin-driven generation of non-classical states of motion. Such a levitating diamond-held in position by electric field gradients under vacuum-can operate as a ‘compass’ with controlled dissipation and has potential use in high-precision torque sensing, emulation of the spin-boson problem15 and probing of quantum phase transitions. In the single-spin limit and using ultrapure nanoscale diamonds, it could allow quantum non-demolition read-out of the spin of nitrogen-vacancy centres at ambient conditions, deterministic entanglement between distant individual spins and matter-wave interferometry.
DS202004-0507
2020
Demarco, P.N., Masquelin, H., Prezzi, C., Muzio, R., Loureiro, J., Peel, E., Campal, N., Sanchez Bettucci, L. Aeromagnetic patterns in southern Uruguay: Precambrian- Mesozoic dyke swarms and Mesozoic rifting structural and tectonic evolution.Tectonophysics, in press available 40p. PdfSouth America, Uruguaygeophysics

Abstract: New high-resolution airborne magnetic data of Uruguay allowed constructing new maps concerning the spatial distribution of dyke swarms, main faults and other magnetic bodies, which compose the Uruguayan Shield. We combined geophysical analyses (vertical derivatives, upward continuation, Euler deconvolution), structural analyses of the magnetic maps and previous geological data in order to discriminate the main structural features of the Uruguayan Shield and contribute to a better understanding of its tectonic evolution. The magnetic maps revealed several outstanding features in the Uruguayan Shield. The Paleoproterozoic dyke swarm is larger, denser, more widespread and complex than originally thought, suggesting a possible plume origin. In addition, a new Mesozoic dyke swarm, as complex as the previous one, was identified crosscutting the Paleoproterozoic dyke swarm and the Neoproterozoic orogenic structures. Moreover, this swarm is connected to volcanic calderas in the Merín basin, and shows displacements along Neoproterozoic shear zones, in the magnetic maps, revealing its brittle reactivation during Mesozoic times. The new observations clarify how Proterozoic basement structures controlled the development of the Mesozoic rift. Paleoproterozoic dyke swarms were reactivated as normal faults and Neoproterozoic structures hindered the rift growth, deflecting the deformation in transcurrent movements. Meanwhile, the Mesozoic dyke swarm was developed in a perpendicular direction to the Neoproterozoic structures. Moreover, these findings contradict the current rift model for Uruguay and rise a new model in which the Mesozoic rift developed as two rift basins connected by a central transfer zone, generated by the reactivation of Dom Feliciano Belt structures, between the Sierra Ballena and Sarandí del Yí Shear Zones.
DS202010-1837
2020
den Hond, B.Cratons mark the spot for mineral bonanzas. * not specific to diamonds.EOS, https://doi.org/ 10.1029/2020EO148693Globalcraton

Abstract: The search for deposits of lead, zinc, copper, and nickel might soon become much less of a hit-and-miss activity. Instead of trying their luck over wide areas, mining companies should focus their efforts—and billions of dollars in exploration expenses—on the contours of thick, old pieces of lithosphere strewn across Earth’s continents: cratons. Lithospheric thickness can serve as a treasure map, according to Mark Hoggard, an Earth scientist at Harvard University and Columbia University, and his colleagues from the United Kingdom and Australia. They reported their findings in Nature Geoscience.
DS202010-1838
2020
Deng, L., Geng, X., Liu, Y., Zong, K., Zhu, L., Zhengwei, L., Hu, Z., Guodong, Z., Guangfu, C.Lithospheric modification by carbonatitic to alkaline melts and deep carbon cycle: insights from peridotite xenoliths of eastern China.Lithos, in press available 38p. PdfChinacarbonatite

Abstract: Carbonates in subducting oceanic slabs can survive beyond slab dehydration and be transferred into the deep mantle. Such deep carbon cycling plays a critical role in generating carbonatitic to alkaline melts. However, whether and how this process has influenced the lithospheric mantle still remains enigmatic. To address these issues, here we provide a detailed petrographic, in-situ chemical and Sr isotopic study on two mantle xenoliths (a wehrlite and a melt pocket-bearing peridotite) entrained by the Changle Miocene basalts from the eastern China. The Changle wehrlite contains carbonate melt inclusions and apatites and is merely enriched in clinopyroxene relative to the lherzolites. The clinopyroxenes are characterized by high (La/Yb)N (4.7-41) and low Ti/Eu (873-2292) ratios and equilibrated with carbonated silicate melt-like compositions. These petrographic and chemical features indicate that the wehrlite was formed by reaction between peridotite and carbonated silicate melts. On the other hand, the Changle melt pocket-bearing peridotite is suggested to have been produced by in-situ melting/breakdown of amphiboles of an amphibole-rich dunite. Low olivine Fo (~89), presence of amphiboles with high (La/Yb)N (~50) and low Ti/Eu (~1070) ratios suggest that such amphibole-rich dunite would have been formed by reaction of peridotite with hydrous alkaline basaltic melts from a carbonated mantle. Our data, combined with previously reported data of the Changle lherzolite xenoliths, unravel a series of mantle metasomatisms by carbonatitic to alkaline melts from carbonated mantle sources. The consistently high 87Sr/86Sr ratios (up to 0.7036) of the clinopyroxenes in both the wehrlites and lherzolites indicate the carbonate components in the mantle sources were derived from the stagnant Pacific slab within the Mantle Transition Zone. This study provides a fresh perspective on the role of deep carbon cycling from subducted oceanic slabs in chemical modification of intracontinental lithospheric mantle through reaction with different types of melts.
DS202009-1623
2019
Deng, L-P., Liu, Y-C., Yang, Y., Groppo, C., Rolfo, F., Gu, X-F.Anatexis of high-T eclogites in the Dabie orogen triggered by exhumation and post-orogenic collapse.European Journal of Mineralogy, Vol. 31, pp. 889-803. pdfChinaeclogite

Abstract: A combined study of detailed petrographic observation, mineral chemistry analysis and phase equilibrium modeling indicates that the high-temperature eclogites from the Dabie orogen, central China, experienced two episodes of anatexis: the first is phengite dehydration melting during the exhumation of deeply subducted slices, and the second is heating melting related to the post-orogenic collapse. Petrographic evidence and clues of the anatectic events include biotite + plagioclase + garnet ± amphibole intergrowth in matrix and biotite + plagioclase intergrowth within amphibole porphyroblast. Pressure-temperature (P-T) pseudosection and modal variation diagram indicate that the biotite + plagioclase + garnet ± amphibole in matrix was formed by the reactions phengite + clinopyroxene + quartz = melt + sanidine + garnet + plagioclase and later melt + sanidine + garnet = biotite + plagioclase, while the biotite + plagioclase intergrowths within poikiloblastic amphibole were formed by the reaction amphibole + muscovite + epidote = biotite + plagioclase + melt. In addition, the combination of petrological observations and P-T estimates suggests that the first melting event occurred at the late Triassic, while the second is related to the early Cretaceous mountain-root removal and subsequent asthenospheric upwelling and heat input. As the P-T paths of high-temperature/ultrahigh-pressure rocks have high probabilities to cross-cut phengite-melting curves, phengite melting during decompression may be a common process in these rocks. Moreover, the coexistence of multiple episodes of anatexis in a single tectonic slice suggests caution when identifying and dating partial melting in high-temperature/(ultra)high-pressure rocks.
DS202002-0178
2019
Dewey, J.F.Musings in tectonics.Canadian Journal of Earth Sciences, Vol. 56, pp. 1077-1094.MantleTectonic history

Abstract: I outline and discuss my career in the context of the history of structural geology and tectonics, the progressive developments that led to plate tectonics, the people who have encouraged and influenced me, the events that changed my life, my fifty six doctoral students who have taught me so much, and my principal interests in tectonics. I discuss, in particular, nine topics of special current interest: the evolution of Tibet, the geomorphology of the British Isles, transtension, the Precambrian, the complexities of plate boundary evolution, Appalachian-Caledonian evolution, ophiolites, the structure and strength of the lithosphere, and the subducting slab.
DS202004-0508
2020
Diggle, P.L., Dhaenens-Johannsson, U., Green, B., Welbourn, C.M., Tran Thi, T.N., Wang, W., Newton, M.E. Decoration of growth sector boundaries with single nitrogen vacancy centres in as-grown single crystal HPHT synthetic diamond.Diamond and Related Materials, arxiv.org 21p. Globalsynthetics

Abstract: Large (> 100 mm3), relatively pure (type II) and low birefringence single crystal diamond can be produced by high pressure high temperature (HPHT) synthesis. In this study we examine a HPHT sample of good crystalline perfection, containing less than 1 ppb (part per billion carbon atoms) of boron impurity atoms in the {001} growth sector and only tens of ppb of nitrogen impurity atoms. It is shown that the boundaries between {111} and {113} growth sectors are decorated by negatively charged nitrogen vacancy centres (NV-): no decoration is observed at any other type of growth sector interface. This decoration can be used to calculated the relative {111} and {113} growth rates. The bulk (001) sector contains concentrations of luminescent point defects (excited with 488 and 532 nm wavelengths) below 1011 cm-3 (10-3 ppb). We observe the negatively charged silicon-vacancy (SiV-) defect in the bulk {111} sectors along with a zero phonon line emission associated with a nickel defect at 884 nm (1.40 eV). No preferential orientation is seen for either NV- or SiV- defects, but the nickel related defect is oriented with its trigonal axis along the <111> sector growth direction. Since the NV- defect is expected to readily re-orientate at HPHT diamond growth temperatures, no preferential orientation is expected for this defect but the lack of preferential orientation of SiV- in {111} sectors is not explained.
DS202001-0006
2019
Dirlam, D.M., Rogers, C.L., Weldon, R.Gemstones in the era of the Taj Mahal and the Mughals.Gems & Gemology, Vol. 55, 3, pp. 294-319.Indiahistory

Abstract: The Taj Mahal evokes an image of a monumental building and reflecting pool—its classic view. But the Taj Mahal complex is much more than that. It is actually a series of beautiful buildings and gardens in Agra, India, built in the seventeenth century in loving memory of Mumtaz Mahal. This name, given by the Mughal emperor Shah Jahan to one of his brides, means “Chosen One of the Palace.” Famed for its architectural magnificence, the landmark holds additional significance for the gemologist. Upon closer investigation, one is impressed with the intricacies of the inlay of numerous gems to create thousands of designs throughout the buildings on the grounds. This article sheds light on the gems used in decorating the Taj Mahal and in the extraordinary jewelry collected by Shah Jahan and other Mughals. These gems often took intricate trade routes to Agra, which are also discussed, along with the craft used to create the inlays and the efforts undertaken to preserve this Wonder of the World.
DS202009-1624
2020
Dorfman, S.M., Potapkin, V., Lv, M., Greenberg, E., Kupenko, I., Chumakov, A.I., Bi, W., Alp, E.E., Liu, J., Magrez, A., Dutton, S.E., Cava, R.J., McCammon, C.A., Gillet, P.Effects of composition and pressure on electronic states of iron in bridgmanite.American Mineralogist, Vol. 105, pp. 1030-1039. pdfMantleredox

Abstract: Electronic states of iron in the lower mantle's dominant mineral, (Mg,Fe,Al)(Fe,Al,Si)O3 bridgmanite, control physical properties of the mantle including density, elasticity, and electrical and thermal conductivity. However, the determination of electronic states of iron has been controversial, in part due to different interpretations of Mössbauer spectroscopy results used to identify spin state, valence state, and site occupancy of iron. We applied energy-domain Mössbauer spectroscopy to a set of four bridgmanite samples spanning a wide range of compositions: 10-50% Fe/total cations, 0-25% Al/total cations, 12-100% Fe3+/total Fe. Measurements performed in the diamond-anvil cell at pressures up to 76 GPa below and above the high to low spin transition in Fe3+ provide a Mössbauer reference library for bridgmanite and demonstrate the effects of pressure and composition on electronic states of iron. Results indicate that although the spin transition in Fe3+ in the bridgmanite B-site occurs as predicted, it does not strongly affect the observed quadrupole splitting of 1.4 mm/s, and only decreases center shift for this site to 0 mm/s at ~70 GPa. Thus center shift can easily distinguish Fe3+ from Fe2+ at high pressure, which exhibits two distinct Mössbauer sites with center shift ~1 mm/s and quadrupole splitting 2.4-3.1 and 3.9 mm/s at ~70 GPa. Correct quantification of Fe3+/total Fe in bridgmanite is required to constrain the effects of composition and redox states in experimental measurements of seismic properties of bridgmanite. In Fe-rich, mixed-valence bridgmanite at deep-mantle-relevant pressures, up to ~20% of the Fe may be a Fe2.5+ charge transfer component, which should enhance electrical and thermal conductivity in Fe-rich heterogeneities at the base of Earth's mantle.
DS202003-0335
2020
Doucet, L.S., Li, Z-X., Ernst, R.E., Kirscher, U., Gamel El Dien, H., Mitchell, R.N.Coupled supercontinent-mantle plume events evidence by oceanic plume record.Geology, Vol. 48, pp. 159-163.Mantle, Africageodynamics

Abstract: The most dominant features in the present-day lower mantle are the two antipodal African and Pacific large low-shear-velocity provinces (LLSVPs). How and when these two structures formed, and whether they are fixed and long lived through Earth history or dynamic and linked to the supercontinent cycles, remain first-order geodynamic questions. Hotspots and large igneous provinces (LIPs) are mostly generated above LLSVPs, and it is widely accepted that the African LLSVP existed by at least ca. 200 Ma beneath the supercontinent Pangea. Whereas the continental LIP record has been used to decipher the spatial and temporal variations of plume activity under the continents, plume records of the oceanic realm before ca. 170 Ma are mostly missing due to oceanic subduction. Here, we present the first compilation of an Oceanic Large Igneous Provinces database (O-LIPdb), which represents the preserved oceanic LIP and oceanic island basalt occurrences preserved in ophiolites. Using this database, we are able to reconstruct and compare the record of mantle plume activity in both the continental and oceanic realms for the past 2 b.y., spanning three supercontinent cycles. Time-series analysis reveals hints of similar cyclicity of the plume activity in the continent and oceanic realms, both exhibiting a periodicity of ~500 m.y. that is comparable to the supercontinent cycle, albeit with a slight phase delay. Our results argue for dynamic LLSVPs where the supercontinent cycle and global subduction geometry control the formation and locations of the plumes.
DS202008-1384
2020
Doucet, L.S., Li, Z-X., Gamel El Dien, H., Pourteau, A., Murphy, B., Collins, W.J., Mattielli, N., Olierook, H.K.H., Spencer, C.J., Mitchell, R.N.Distinct formation history for deep mantle domains reflected in geochemical differences.Nature Geoscience, Vol. 13, pp. 511-515. pdfMantlegeochemistry

Abstract: The Earth’s mantle is currently divided into the African and Pacific domains, separated by the circum-Pacific subduction girdle, and each domain features a large low shear-wave velocity province (LLSVP) in the lower mantle. However, it remains controversial as to whether the LLSVPs have been stationary through time or dynamic, changing in response to changes in global subduction geometry. Here we compile radiogenic isotope data on plume-induced basalts from ocean islands and oceanic plateaus above the two LLSVPs that show distinct lead, neodymium and strontium isotopic compositions for the two mantle domains. The African domain shows enrichment by subducted continental material during the assembly and breakup of the supercontinent Pangaea, whereas no such feature is found in the Pacific domain. This deep-mantle geochemical dichotomy reflects the different evolutionary histories of the two domains during the Rodinia and Pangaea supercontinent cycles and thus supports a dynamic relationship between plate tectonics and deep-mantle structures.
DS202009-1625
2020
Doucet, L.S., Li, Z-X., GamelEl Dien, H., Pourteau, A., Murphy, J.B., Collins, W.J., Mattielli, N., Olierook, H.K.H., Spencer, C.J., Mitchell, R.N.Distinct formation history for deep mantle domains reflected in geochemical differences.Nature Geoscience, Vol. 13, July pp. 511-515. pdfMantlegeochemistry

Abstract: The Earth’s mantle is currently divided into the African and Pacific domains, separated by the circum-Pacific subduction girdle, and each domain features a large low shear-wave velocity province (LLSVP) in the lower mantle. However, it remains controversial as to whether the LLSVPs have been stationary through time or dynamic, changing in response to changes in global subduction geometry. Here we compile radiogenic isotope data on plume-induced basalts from ocean islands and oceanic plateaus above the two LLSVPs that show distinct lead, neodymium and strontium isotopic compositions for the two mantle domains. The African domain shows enrichment by subducted continental material during the assembly and breakup of the supercontinent Pangaea, whereas no such feature is found in the Pacific domain. This deep-mantle geochemical dichotomy reflects the different evolutionary histories of the two domains during the Rodinia and Pangaea supercontinent cycles and thus supports a dynamic relationship between plate tectonics and deep-mantle structures.
DS202007-1136
2020
Doucet, L.S., Xu, Y., Klaessens, D., Hui, H., Ionov, D.A., Mattielli, N.Decoupled water and iron enrichments in the cratonic mantle: a study on peridotite xenoliths from Tok, SE Siberian craton.American Mineralogist, Vol. 105, pp. 803-819.Russia, Siberia peridotites

Abstract: Water and iron are believed to be key constituents controlling the strength and density of the lithosphere and, therefore, play a crucial role in the long-term stability of cratons. On the other hand, metasomatism can modify the water and iron abundances in the mantle and possibly triggers thermo-mechanical erosion of cratonic keels. Whether local or large scale processes control water distribution in cratonic mantle remains unclear, calling for further investigation. Spinel peridotite xenoliths in alkali basalts of the Cenozoic Tok volcanic field sampled the lithospheric mantle beneath the southeastern margin of the Siberian Craton. The absence of garnet-bearing peridotite among the xenoliths, together with voluminous eruptions of basaltic magma, suggests that the craton margin, in contrast to the central part, lost its deep keel. The Tok peridotites experienced extensive and complex metasomatic reworking by evolved, Ca-Fe-rich liquids that transformed refractory harzburgite to lherzolite and wehrlite. We used polarized Fourier transform infrared spectroscopy (FTIR) to obtain water content in olivine, orthopyroxene (Opx), and clinopyroxene (Cpx) of 14 Tok xenoliths. Olivine, with a water content of 0-3 ppm H2O, was severely degassed, probably during emplacement and cooling of the host lava flow. Orthopyroxene (49-106 ppm H2O) and clinopyroxene (97-300 ppm H2O) are in equilibrium. The cores of the pyroxene grains, unlike olivine, experienced no water loss due to dehydration or addition attributable to interaction with the host magma. The water contents of Opx and Cpx are similar to those from the Kaapvaal, Tanzania, and North China cratons, but the Tok Opx has less water than previously studied Opx from the central Siberian craton (Udachnaya, 28-301 ppm; average 138 ppm). Melting models suggest that the water contents of Tok peridotites are higher than in melting residues, and argue for a post-melting (metasomatic) origin. Moreover, the water contents in Opx and Cpx of Tok peridotites are decoupled from iron enrichments or other indicators of melt metasomatism (e.g., CaO and P2O5). Such decoupling is not seen in the Udachnaya and Kaapvaal peridotites but is similar to observations on Tanzanian peridotites. Our data suggest that iron enrichments in the southeastern Siberian craton mantle preceded water enrichment. Pervasive and large-scale, iron enrichment in the lithospheric mantle may strongly increase its density and initiate a thermo-magmatic erosion. By contrast, the distribution of water in xenoliths is relatively “recent” and was controlled by local metasomatic processes that operate shortly before the volcanic eruption. Hence, water abundances in minerals of Tok mantle xenoliths appear to represent a snapshot of water in the vicinity of the xenolith source regions.
DS202001-0007
2019
Doucet, L-S., Li, Z-X., Kirscher, U., El Dien, H.G.Coupled supercontinent -mantle plume events evidenced by oceanic plume record.Geology, Vol. 48, 5p. Mantleplumes, hotspots
DS202008-1385
2020
Drenth, B.J., Souders, A.K., Schulz, K.J., Feinberg, J.M., Anderson, R.R., Chandler, V.W., Cannon, W.L., Clark, R.J.Evidence for a concealed Midcontinent Rift related northeast Iowa intrusive complex.Precambrian Research, in press available, 43p. PdfUnited States, Iowageophysics - seismics

Abstract: Large amplitude aeromagnetic and gravity anomalies over a ~9500 km2 area of northeast Iowa and southeast Minnesota have been interpreted to reflect the northeast Iowa intrusive complex (NEIIC), a buried intrusive igneous complex composed of mafic/ultramafic rocks in the Yavapai Province (1.8-1.7 Ga). Hundreds of meters of Paleozoic sedimentary cover and a paucity of basement drilling have prevented detailed studies of the NEIIC. Long considered, but not proven, to be related to the ~1.1 Ga Midcontinent Rift System (MRS), the NEIIC is comparable in areal extent to the richly mineralized Duluth Complex and is similarly located near the margin of the MRS. New geochronological and geophysical data together support an MRS affinity for the NEIIC. A dike swarm imaged in aeromagnetic data is cut by intrusions of the NEIIC, and a new apatite U-Pb date of ~1170 Ma on one of the dikes thus represents a maximum age for the NEIIC. A minimum age constraint is suggested by (1) large-volume magmatism associated with the MRS that was the last such event to affect the region; and (2) the presence of reversely magnetized dikes, similar in character to MRS-related dikes elsewhere, that cut several intrusions of the NEIIC. The NEIIC is largely characterized by the presence of multiple zoned intrusions, many of which contain large volumes of mafic-ultramafic rocks and have strong geophysical similarities to alkaline intrusive complexes elsewhere, including the MRS-related Coldwell Complex of Ontario. The largest of the zoned intrusions are ~40 km in diameter and are interpreted to have thicknesses of many kilometers. Suspected faults, alignments of intrusions, and intrusive margins tend to be aligned along northwest and northeast trends that match the trends of the Belle Plaine fault zone and Fayette structural zone, both previously interpreted as pre-MRS, possibly lithospheric-scale discontinuities that may have controlled NEIIC emplacement. These interpretations collectively imply notable potential for the NEIIC to host several different types of undiscovered base metal and critical mineral deposits.
DS202010-1839
2020
Drenth, N.J., Souders, A.K., Schulz, K.J., Feinberg, J.M., Anderson, R.R., Chandler, V.W., Cannon, W.F., Clark, R.J.Evidence for a concealed Midcontinent Rift related northeast Iowa intrusive complex.Precambrian Research, Vol. 347, 105845, 23p. PdfUnited States, Iowageochronology, geophysics - gravity

Abstract: Large amplitude aeromagnetic and gravity anomalies over a ~9500 km2 area of northeast Iowa and southeast Minnesota have been interpreted to reflect the northeast Iowa intrusive complex (NEIIC), a buried intrusive igneous complex composed of mafic/ultramafic rocks in the Yavapai Province (1.8-1.7 Ga). Hundreds of meters of Paleozoic sedimentary cover and a paucity of basement drilling have prevented detailed studies of the NEIIC. Long considered, but not proven, to be related to the ~1.1 Ga Midcontinent Rift System (MRS), the NEIIC is comparable in areal extent to the richly mineralized Duluth Complex and is similarly located near the margin of the MRS. New geochronological and geophysical data together support an MRS affinity for the NEIIC. A dike swarm imaged in aeromagnetic data is cut by intrusions of the NEIIC, and a new apatite U-Pb date of ~1170 Ma on one of the dikes thus represents a maximum age for the NEIIC. A minimum age constraint is suggested by (1) large-volume magmatism associated with the MRS that was the last such event to affect the region; and (2) the presence of reversely magnetized dikes, similar in character to MRS-related dikes elsewhere, that cut several intrusions of the NEIIC. The NEIIC is largely characterized by the presence of multiple zoned intrusions, many of which contain large volumes of mafic-ultramafic rocks and have strong geophysical similarities to alkaline intrusive complexes elsewhere, including the MRS-related Coldwell Complex of Ontario. The largest of the zoned intrusions are ~40 km in diameter and are interpreted to have thicknesses of many kilometers. Suspected faults, alignments of intrusions, and intrusive margins tend to be aligned along northwest and northeast trends that match the trends of the Belle Plaine fault zone and Fayette structural zone, both previously interpreted as pre-MRS, possibly lithospheric-scale discontinuities that may have controlled NEIIC emplacement. These interpretations collectively imply notable potential for the NEIIC to host several different types of undiscovered base metal and critical mineral deposits.
DS202002-0179
2020
D'Souza, R.J., Canil, D., Coogan, L.A.Geobarometry for spinel peridotites using Ca and Al in olivine.Contributions to Mineralogy and Petrology, Vol. 175, 12 pdfMantleperidotites

Abstract: Experiments were performed from 950 to 1250 °C and 1.5-2.4 GPa to determine the effect of pressure (P) on the temperature (T)-dependent partitioning of Al between olivine and spinel, using mixtures of natural spinel, olivine, clino- and ortho-pyroxene. When compared to 100 kPa experiments, the results show that there is no discernible effect of pressure on the Al-in-olivine thermometer at PT conditions relevant to the spinel peridotite facies. In our experiments with high-Cr spinel, we see no change in Al in olivine from starting values, likely due to the refractory nature of high-Cr spinel. Phase boundary flourescence prevented accurate quantification of Ca in olivine in the run products by electron microprobe analysis but measurements by laser ablation are consistent with the Köhler and Brey (Geochim Cosmochim Acta 54:2375-2388, 1990) Ca-in-olivine thermobarometer. The combination of Al (for T) and Ca (for P) in olivine thus has great potential for thermobarometry in spinel facies peridotites. As a test we apply this approach to published high precision Ca and Al data for olivine from the Ray Pic spinel peridotite xenoliths from the Massif Central (De Hoog et al. Chem Geol 270:196-215, 2010). Reassuringly, the calculated PT conditions (1.0-1.8 GPa; 900-1080 °C) for all samples lie beneath the Moho, within the spinel peridotite facies and fall along a geophysically constrained geotherm.
DS202007-1137
2020
Dube, J-M., Darbyshire, F.A., Liddell, M.V., Stephenson, R.Seismic anisotropy of the Canadian High Arctic: evidence from shear wave splitting.Tectonophysics, Vol. 789, 228524, 13p. PdfCanada, Arcticgeophysics - seismics

Abstract: The Canadian High Arctic preserves a long and complex tectonic history, including craton formation, multiple periods of orogenesis, extension and basin formation, and the development of a passive continental margin. We investigate the possible preservation of deformational structures throughout the High Arctic subcontinental lithosphere using measurements of seismic anisotropy from shear wave splitting at 11 seismograph stations across the region, including a N-S transect along Ellesmere Island. The majority of measurements indicate a fast-polarisation orientation that parallels tectonic trends and boundaries, suggesting that lithospheric deformation is the dominant source of seismic anisotropy in the High Arctic; however, a sub-lithospheric contribution cannot be ruled out. Beneath Resolute in the central Canadian Arctic, distinct back-azimuthal variations in splitting parameters can be explained by two anisotropic layers. The upper layer is oriented E-W and correlates with tectonic trends and the inferred lithospheric deformation history of the region. The lower layer has a ~NNE-SSW orientation and may arise from present-day convective mantle flow beneath locally-thinned continental lithosphere. In addition to inferences of anisotropic structure beneath the Canadian High Arctic, measurements from the far north of our study region suggest the presence of an anisotropic zone in the lowermost mantle beneath northwest Alaska.
DS202008-1386
2020
Duncombe, J.Earth's core is in the hot seat.Eos, 101, doi,org./10.1029 /EO145531 June 24, MantleCore age

Abstract: How old is Earth’s inner core? High-pressure and high-temperature experiments suggest that our planet’s inner furnace may be much younger than expected.
DS202008-1387
2020
Duncombe, J.The ticking time bomb of Arctic permafrost.Eos, 101, doi,org./10.1029/EO1414607 June 24, Russiapermafrost

Abstract: Arctic infrastructure is under threat from thawing permafrost.
DS202012-2212
2019
Dupuy, D.C., Phillips, J.C.Selecting a diamond verification instrument based on the results of the Assure program: an initial analysis.Journal of Gemmology, Vol. 36, pp. 606-619.Globalluminescence

Abstract: Recently, the rapid growth in synthetic diamond production-particularly in melee sizes-and the salting of melee parcels with synthetics have generated a commensurate increase in the need for diamond verification instruments (DVIs). Ongoing independent third-party testing of these instruments is being done through the Assure Program. DVI performance is tested in a UL laboratory using carefully developed testing standards and sample sets (i.e. natural diamonds and as-grown and treated synthetics, as well as simulants as appropriate). The initial phase of testing was performed during latter 2018 and the first part of 2019, and as of July 2019 results for 16 widely available devices from 12 DVI manufacturers were published online in the Assure Directory (https://diamondproducers.com/assure/assure-directory). From these test results, the authors have evaluated several important parameters that will help users select the best instrument for their needs. Performance results from several additional DVIs are expected to be released in the near future, and further testing and publi-cation of the data will occur as new instruments are introduced and existing ones are updated.
DS202001-0008
2019
Dupuy, H., Phillips, J.G.Selecting a diamond verification: instrument based on the results of the Assure program: an initial analysis.Journal of Gemmology, Vol. 36, 7, pp. 606-619.Globaldiamond identification
DS202006-0917
2020
Dushyantha, N., Batapola, N., Ilankoon, I.M.S.K., Rohitha, S., Premasiri, R., Abeysinghe, B., Ratnayake, N., Dissanayake, K.The story of rare earth elements ( REES): occurrences, global distribution, genesis, geology, mineralogy and global production.Ore Geology Reviews, Vol. 122, 17p. PdfGlobalREE

Abstract: Rare earth elements (REEs) including fifteen lanthanides, yttrium and scandium are found in more than 250 minerals, worldwide. REEs are used in various high-tech applications across various industries, such as electrical and electronics, automotive, renewable energy, medical and defence. Therefore, the demand for REEs in the global market is increasing day by day due to the surging demand from various sectors, such as emerging economies, green technology and R&D sectors. Rare earth (RE) deposits are classified on the basis of their genetic associations, mineralogy and form of occurrences. The Bayan Obo, Mountain Pass, Mount Weld and China’s ion adsorption clays are the major RE deposits/mines in the world to date and their genesis, chronology and mineralogy are discussed in this review. In addition, there are other RE deposits, which are currently being mined or in the feasibility or exploration stages. Most of the RE resources, production, processing and supply are concentrated in the Asia-Pacific region. In this regard, China holds the dominancy in the RE industry by producing more than 90% of the current rare earth requirements. Thus, REEs are used as a powerful tool by China in trade wars against other countries, especially against USA in 2019. However, overwhelming challenges in conventional RE explorations and mining make secondary RE resources, such as electric and electronic waste (e-waste) and mine tailings as promising resources in the future. Due to the supply risk of REEs and the monopoly of the REEs market, REEs recycling is currently considered as an effective method to alleviate market fluctuations. However, economical and sustainable processing techniques are yet to be established to exploit REEs via recycling. Moreover, there are growing ecological concerns along with social resistance towards the RE industry. To overcome these issues, the RE industry needs to be assessed to maintain long-term social sustainability by fostering the United Nations sustainable development goals (SDGs).
DS202010-1840
2020
Dymshits, A., Sharygin, I., Malkovets, V., Yakovlev, I.V., Gibsher, A.A., Alifirova, T.A., Vorobei, S.S., Potapov, S.V., Garanin, V.K.Thermal state, thickness and composition of the lithospheric mantle beneath the Upper Muna kimberlite field, Siberian Craton, constrained by clinopyroxene xenocrysts and comparison with Daldyn and Mirny fields.Minerals, 10.1039/DOJA00308E 20p. PdfRussiadeposit - Muna

Abstract: To gain better insight into the thermal state and composition of the lithospheric mantle beneath the Upper Muna kimberlite field (Siberian craton), a suite of 323 clinopyroxene xenocrysts and 10 mantle xenoliths from the Komsomolskaya-Magnitnaya (KM) pipe have been studied. We selected 188 clinopyroxene grains suitable for precise pressure (P)-temperature (T) estimation using single-clinopyroxene thermobarometry. The majority of P-T points lie along a narrow, elongated field in P-T space with a cluster of high-T and high-P points above 1300 °C, which deviates from the main P-T trend. The latter points may record a thermal event associated with kimberlite magmatism (a “stepped” or “kinked” geotherm). In order to eliminate these factors, the steady-state mantle paleogeotherm for the KM pipe at the time of initiation of kimberlite magmatism (Late Devonian-Early Carboniferous) was constrained by numerical fitting of P-T points below T = 1200 °C. The obtained mantle paleogeotherm is similar to the one from the nearby Novinka pipe, corresponding to a ~34-35 mW/m2 surface heat flux, 225-230 km lithospheric thickness, and 110-120 thick "diamond window" for the Upper Muna field. Coarse peridotite xenoliths are consistent in their P-T estimates with the steady-state mantle paleogeotherm derived from clinopyroxene xenocrysts, whereas porphyroclastic ones plot within the cluster of high-T and high-P clinopyroxene xenocrysts. Discrimination using Cr2O3 demonstrates that peridotitic clinopyroxene xenocrysts are prevalent (89%) among all studied 323 xenocrysts, suggesting that the Upper Muna mantle is predominantly composed of peridotites. Clinopyroxene-poor or -free peridotitic rocks such as harzburgites and dunites may be evident at depths of 140-180 km in the Upper Muna mantle. Judging solely from the thermal considerations and the thickness of the lithosphere, the KM and Novinka pipes should have excellent diamond potential. However, all pipes in the Upper Muna field have low diamond grades (<0.9, in carats/ton), although the lithosphere thickness is almost similar to the values obtained for the high-grade Udachnaya and Mir pipes from the Daldyn and Mirny fields, respectively. Therefore, other factors have affected the diamond grade of the Upper Muna kimberlite field.
DS202010-1841
2020
Dymshits, A., Sharygin, I., Liu, Z., Korolev, N., Malkovets, V., Alifirova, T., Yakovlev, I., Xu, Y-G.Oxidation state of the lithospheric mantle beneath Komosomolskaya-Magnitnaya kimberlite pipe, Upper Muna field, Siberian craton.Minerals, Vol. 10, 9, 740 10.3390/ min10090740 24p. PdfRussiadeposit - Muna

Abstract: The oxidation state of the mantle plays an important role in many chemical and physical processes, including magma genesis, the speciation of volatiles, metasomatism and the evolution of the Earth’s atmosphere. We report the first data on the redox state of the subcontinental lithospheric mantle (SCLM) beneath the Komsomolskaya-Magnitnaya kimberlite pipe (KM), Upper Muna field, central Siberian craton. The oxygen fugacity of the KM peridotites ranges from -2.6 to 0.3 logarithmic units relative to the fayalite-magnetite-quartz buffer (?logfO2 (FMQ)) at depths of 120-220 km. The enriched KM peridotites are more oxidized (-1.0-0.3 ?logfO2 (FMQ)) than the depleted ones (from -1.4 to -2.6 ?logfO2 (FMQ)). The oxygen fugacity of some enriched samples may reflect equilibrium with carbonate or carbonate-bearing melts at depths >170 km. A comparison of well-studied coeval Udachnaya and KM peridotites revealed similar redox conditions in the SCLM of the Siberian craton beneath these pipes. Nevertheless, Udachnaya peridotites show wider variations in oxygen fugacity (-4.95-0.23 ?logfO2 (FMQ)). This indicates the presence of more reduced mantle domains in the Udachnaya SCLM. In turn, the established difference in the redox conditions is a good explanation for the lower amounts of resorbed diamonds in the Udachnaya pipe (12%) in comparison with the KM kimberlites (33%). The obtained results advocate a lateral heterogeneity in the oxidation state of the Siberian SCLM.
DS202001-0009
2019
Eaton-Magana, S., Ardon, T., Breeding, C.M., Shigley, J.E.Natural color fancy white and fancy black diamonds: where color and clarity converge.Gems & Gemology, Vol. 55, 3, pp. 320-336.Globalreview

Abstract: Natural Fancy white and Fancy black diamonds are not routinely submitted to GIA for grading (fewer than 2,000 since 2008). These fancy-color diamonds are distinctive since the causes of color generally are not atomic-scale defects, but nanometer- to micrometer-sized inclusions that reduce the diamond’s transparency by scattering or absorbing light (some exceptions exist among Fancy black diamonds). To clarify, Fancy white diamonds are those rare stones colored by inclusions that give a “whitish” appearance, and are distinct from “colorless” diamonds on the D-to-Z scale. These two colors, often thought of as opposites in the color world, are grouped here as outliers within the colored diamond world. Both can be colored by inclusions so numerous the stone would fall below the I3 grade on the clarity scale, demonstrating that inclusions, often perceived as a negative quality factor, can create a distinctive appearance. Among the Fancy white diamonds examined for this study, the vast majority (82%) were type IaB, making them a rare subset of a rare diamond type. Based on prior geological research, these are surmised to be mostly sublithospheric in origin (i.e., forming more than 250 km below the earth’s surface). The Fancy white diamonds generally have a different chemistry from D-to-Z type IaB diamonds, with greater quantities of several hydrogen- and nickel-related defects. Among Fancy black diamonds, the major causes of color are either micrometer-sized dark crystal inclusions, nanometer-sized inclusions clustered into clouds, or a combination of the two. For these two colors of diamond, we summarize their gemological properties along with the absorption and luminescence spectra of a representative subset of diamonds from each color, examining how they deviate from the standard grading methodology. Because of their rarity, there has been very little systematic study of either of these color categories, and never a sample set of this quantity, which includes data for ~500 Fancy white and ~1,200 Fancy black diamonds.
DS202006-0918
2020
Eaton-Magana. S., McElhenny, G., Breeding, C.M., Ardon, T.Comparison of gemological and spectroscopic features in type IIa and Ia natural pink diamonds.Diamonds & Related Materials, Vol. 105, 13p. PdfMantlenitrogen

Abstract: The majority of natural pink diamonds have a color origin due to absorption from a broad 550?nm band that has been associated with plastic deformation. One consistent feature in the photoluminescence spectra of these pink diamonds is a wide emission band extending from ~600 to 750?nm, with a series of smaller oscillations overlaid on the larger emission band. This "pink emission band" is seen in diamonds colored by the 550?nm absorption band; the absorption band often, but not always, shows similar oscillations at ~600?nm (called the 609?nm system by previous researchers). This emission band served as a proxy for the 550?nm absorption band as we performed spatial mapping to chronicle the differences between the uniform coloration in type IIa pink diamonds and the pronounced banding in type Ia pink diamonds. We also used Raman spectroscopy to identify the internal crystal inclusions present in type IIa pink diamonds and determined that the majority have a sub-lithospheric origin.
DS202002-0180
2020
Eguchi, J., Seales, J., Dagupta, R.Great oxidation and Lomagundi events linked by deep cycling and enhanced degassing of carbon.Nature Geoscience, Vol. 13, pp. 71-76. Mantlecarbon

Abstract: For approximately the first 2?billion years of the Earth’s history, atmospheric oxygen levels were extremely low. It was not until at least half a billion years after the evolution of oxygenic photosynthesis, perhaps as early as 3?billion years ago, that oxygen rose to appreciable levels during the Great Oxidation Event. Shortly after, marine carbonates underwent a large positive spike in carbon isotope ratios known as the Lomagundi event. The mechanisms responsible for the Great Oxidation and Lomagundi events remain debated. Using a carbon-oxygen box model that tracks the Earth’s surface and interior carbon fluxes and reservoirs, while also tracking carbon isotopes and atmospheric oxygen levels, we demonstrate that about 2.5?billion years ago a tectonic transition that resulted in increased volcanic CO2 emissions could have led to increased deposition of both carbonates and organic carbon (organic?C)?via enhanced weathering and nutrient delivery to oceans. Increased burial of carbonates and organic?C would have allowed the accumulation of atmospheric oxygen while also increasing the delivery of carbon to subduction zones. Coupled with preferential release of carbonates at arc volcanoes and deep recycling of organic?C to ocean island volcanoes, we find that such a tectonic transition can simultaneously explain the Great Oxidation and Lomagundi events without any change in the fraction of carbon buried as organic?C relative to carbonate, which is often invoked to explain carbon isotope excursions.
DS202001-0010
2019
El Dien, H.G., Doucet, L.S., Li, Z-X.Global geochemical fingerprinting of plume intensity suggests coupling with the supercontinent cycle.Nature Communications, Vol 10, 1, doi.org/10.1038 /s41467-019-13300 8p. PdfMantleplumes, hotspots

Abstract: Plate tectonics and mantle plumes are two of the most fundamental solid-Earth processes that have operated through much of Earth history. For the past 300 million years, mantle plumes are known to derive mostly from two large low shear velocity provinces (LLSVPs) above the core-mantle boundary, referred to as the African and Pacific superplumes, but their possible connection with plate tectonics is debated. Here, we demonstrate that transition elements (Ni, Cr, and Fe/Mn) in basaltic rocks can be used to trace plume-related magmatism through Earth history. Our analysis indicates the presence of a direct relationship between the intensity of plume magmatism and the supercontinent cycle, suggesting a possible dynamic coupling between supercontinent and superplume events. In addition, our analysis shows a consistent sudden drop in MgO, Ni and Cr at ~3.2-3.0 billion years ago, possibly indicating an abrupt change in mantle temperature at the start of global plate tectonics.
DS202007-1138
2020
El Dien, H.G., Doucet, L.S., Murphy, J.B., Li, Z-X.Geochemical evidence for a widespread mantle re-enrichment 3.2 billion years ago: implications for global-scale plate tectonics.Scientific Reports, Vol. 10, 9461 8 pdfMantlemelting

Abstract: Progressive mantle melting during the Earth’s earliest evolution led to the formation of a depleted mantle and a continental crust enriched in highly incompatible elements. Re-enrichment of Earth’s mantle can occur when continental crustal materials begin to founder into the mantle by either subduction or, to a lesser degree, by delamination processes, profoundly affecting the mantle’s trace element and volatile compositions. Deciphering when mantle re-enrichment/refertilization became a global-scale process would reveal the onset of efficient mass transfer of crust to the mantle and potentially when plate tectonic processes became operative on a global-scale. Here we document the onset of mantle re-enrichment/refertilization by comparing the abundances of petrogenetically significant isotopic values and key ratios of highly incompatible elements compared to lithophile elements in Archean to Early-Proterozoic mantle-derived melts (i.e., basalts and komatiites). Basalts and komatiites both record a rapid-change in mantle chemistry around 3.2 billion years ago (Ga) signifying a fundamental change in Earth geodynamics. This rapid-change is recorded in Nd isotopes and in key trace element ratios that reflect a fundamental shift in the balance between fluid-mobile and incompatible elements (i.e., Ba/La, Ba/Nb, U/Nb, Pb/Nd and Pb/Ce) in basaltic and komatiitic rocks. These geochemical proxies display a significant increase in magnitude and variability after ~3.2 Ga. We hypothesize that rapid increases in mantle heterogeneity indicate the recycling of supracrustal materials back into Earth’s mantle via subduction. Our new observations thus point to a?=?3.2 Ga onset of global subduction processes via plate tectonics.
DS202004-0509
2020
Elling, R.P., Stein, S., Stein, C.A., Keller, G.R.Tectonics implications of the gravity signatures of the Midcontinent Rift and Grenville Front.Tectonophysics, Vol. 778, 228369, 6p. PdfUnited States, Canadamidcontinent rift

Abstract: North America's Midcontinent Rift (MCR) and Grenville Front (GF) jointly record aspects of the complex history of the assembly of Rodinia. The ~1100 Ma MCR, remaining from a failed major rifting event, is exposed along Lake Superior and well defined by gravity, magnetic, and seismic data. The GF, which results from collisions with Laurentia, is exposed in and identified by seismic and potential field data in Canada. In the eastern U.S., lineated gravity highs extending southward from Michigan to Alabama, along the trend of the front in Canada, have been interpreted either as a buried Grenville Front or as part of the MCR's east arm. We explore this issue by examining the gravity signatures of the MCR and GF. Both the MCR's arms have pronounced gravity highs, with the west arm's greater than the east arm's. Combining the gravity observations with seismic data suggests that the west arm contains 20-25 km thickness of volcanics, whereas the east arm contains 10-15 km of volcanics. Along the Grenville Front in Canada, thickened crust along the northern portion causes a broad gravity low, whereas the stacked thrusts along the southern portion cause essentially no gravity signature. Hence the lineated gravity highs in the eastern U.S. appear similar to those along the remainder of the MCR, and unlike those on either portion of the GF. These data favor the gravity anomalies traditionally interpreted as the Grenville Front in the eastern U.S. as instead being part of the MCR's east arm. A thrust sheet structure like that of the southern Canadian Grenville Front - which would have essentially no gravity effect - could also be present along the MCR's east arm, as implied by recent EarthScope seismic data.
DS202002-0181
2020
Elliott, B.A summary of the Slave geological province exploration development initiative - revitalizing mineral exploration and facilitating sustainable development in a a key economic region.Vancouver Kimberlite Cluster meeting, Jan. 23, 1/4p. AbstractCanada, Northwest Territoriesdata sets
DS202008-1388
2020
Eppelbaum, L., Ben-Avraham, Z., Katz, Y., Cloetingh, S., Kaban, M.Combined multifactor evidence of a giant lower mantle ring structure below the eastern mediterranean.Positioning, Vol. 11, pp. 11-32. pdf Africa, Arabiageophysics - gravity

Abstract: In the Arabian-Northern African region, interaction of the Nubian, Arabian and Eurasian plates and many small tectonic units is conspicuous. In order to better understand this interaction, we use satellite derived gravity data (retracked to the Earth’s surface) recognized now as a powerful tool for tectono-geodynamic zonation. We applied the polynomial approximation to the gravity data which indicated the presence of a large, deep ring structure in the eastern Mediterranean centered below the Island of Cyprus. Quantitative analysis of residual gravity anomaly provides an estimate of the deep anomalous body’s upper edge at a depth of about 1700 km. Computations of the residual gravity anomalies for the lower mantle also indicate presence of anomalous sources. The GPS vector pattern coinciding with the gravity trend implies counter clockwise rotation of this structure. Independent analyses of the geoid isolines map and seismic tomography data support the existence of a deep anomaly. Paleomagnetic data analysis from the surrounding regions confirms a counter clockwise rotation. Numerous petrological, mineralogical, geodynamical and tectonic data suggest a relation between this deep structure and near-surface processes. This anomaly sheds light on a number of phenomena including the Cyprus gravity anomaly, counter clockwise rotation of the Mesozoic terrane belt and asymmetry of basins along continental transform faults.
DS202012-2213
2021
Eppelbaum, L.V., Ben-Avraham, Z., Youri, K., Kaban, M.K.Giant quasi-ring structure if the African-Arabian junction: results derived from the geological-geophsyical data integration.Geotectonics, Mantletectonics

Abstract: The tectonic-geodynamic characteristics of the North African-Arabian region are complicated by interaction of numerous factors. To study this interaction, we primarily used the satellite gravity data (retracked to the Earth's surface), recognized as a powerful tool for tectonic-geodynamic zonation. The applied polynomial averaging of gravity data indicated the presence of a giant, deep quasi-ring structure in the Eastern Mediterranean, the center of which is located under the Island of Cyprus. Simultaneously, the geometrical center of the revealed structure coincides with the Earth's critical latitude of 35?. A quantitative analysis of the obtained gravitational anomaly made it possible to estimate the depth of the upper edge of the anomalous body as 1650?1700 km. The GPS vector map coinciding with the gravitational trend indicates counterclockwise rotation of this structure. Review of paleomagnetic data on the projection of the discovered structure into the earth's surface also confirms its counterclockwise rotation. The analysis of the geoid anomalies map and seismic tomography data commonly approve presence of this deep anomaly. The structural and geodynamic characteristics of the region and paleobiogeographic data are consistent with the proposed physical-geological model. Comprehensive analysis of petrological, mineralogical, and tectonic data suggests a relationship between the discovered deep structure and near-surface processes. The revealed geological deep structure sheds light on specific anomalous effects in the upper crustal layer, including the high-intensity Cyprus gravity anomaly, counterclockwise rotation of the Mesozoic terrane belt, configuration of the Sinai plate, and the asymmetry of sedimentary basins along the continental faults.
DS202002-0182
2019
Eppelbaum, L.V., Kutasov, I.M.Well drilling in permafrost regions: dynamics of the thawed zone. ( not specific to diamonds)Polar Research, Vol. 38, 3351 9p. PdfRussiapermafrost

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.
DS202007-1139
2020
Eppelbaum, L.V., Youri, K.Significant tectono-geophysical features of the African-Arabian tectonic region: an overview.Geotectonics, Vol. 54, 2, pp. 266-283.AfricaArabian craton

Abstract: Satellite gravimetry is recognized now as powerful and reliable tool for regional tectono-geodynamic zonation. The studied region contains intricate geodynamical features (high seismological indicators, active rift systems and collision processes), richest structural arrangement (existence of mosaic blocks of oceanic and continental Earth’s crust of various age), and a number of high-amplitude gravity anomalies and complex geomagnetic pattern. The most hydrocarbon reserves and diamonds, gold, platinum and deposits occur in this region. Comprehensive analysis of satellite derived gravity data by different methodologies were used to develop a sequence of maps specifying crucial properties of the region deep structure. Combined analysis of the compiled gravity map and its transformations with obtained geological data allowed to detecting significant geotectonic features of lithosphere of the region. For instance, Zagros-Makran terrane was classified as a separately developing structural segment (element) of the Arabian craton. Detailed examination of numerous geological sources and their combined examination with the GPS pattern, paleomagnetic, tectonic, geoid isoline map, seismic and other data revealed some sophisticated tectono-geophysical feature apparently located in middle-lower mantle below the Arabian-African region.
DS202009-1626
2011
Eriksson, P.G., Lenhardt, N., Wright, D.T., Mazumder, R., Bumby, A.J.Late Neoarchean-paleoproterozoic supracrustal basin-fills of the Kaapvaal craton: relevance of the supercontinent cycle, the "Great Oxidation Event" and "Snowball Earth?". Note Date*** glaciationMarine and Petroleum Geology, Vol. 28, pp. 1385-1401.Africa, South Africageomorphology

Abstract: The application of the onset of supercontinentality, the “Great Oxidation Event” (GOE) and the first global scale glaciation in the Neoarchaean-Palaeoproterozoic as panacea-like events providing a framework or even chronological piercing points in Earth’s history at this time, is questioned. There is no solid evidence that the Kaapvaal craton was part of a larger amalgamation at this time, and its glacigenic record is dominated by deposits supporting the operation of an active hydrological cycle in parallel with glaciation, thereby arguing against the “Snowball Earth Hypothesis”. While the Palaeoproterozoic geological record of Kaapvaal does broadly support the GOE, this postulate itself is being questioned on the basis of isotopic data used as oxygen-proxies, and sedimentological data from extant river systems on the craton argue for a prolongation of the greenhouse palaeo-atmosphere (possibly in parallel with a relative elevation of oxygen levels) which presumably preceded the GOE. The possibility that these widespread events may have been diachronous at the global scale is debated.
DS202010-1842
2020
Ernst, W.G.How American Mineralogist and the Mineralogical Society of America influenced a career in mineralogy, petrology, and plate pushing, and thoughts on mineralogy's future role.American Mineralogist, Vol. 105, pp. 1285-1296.Globalhistory

Abstract: My geologic research began at Carleton College. I studied heavy minerals in some midcontinent orthoquartzites, publishing my very first paper in American Mineralogist in 1954. As a master's candidate at the University of Minnesota, I investigated igneous differentiation in a diabase-granophyre sill of the Duluth Gabbro Complex. Later, in a Ph.D. program at Johns Hopkins University, I became Joe Boyd's apprentice at the Geophysical Laboratory (GL), and for a time was phase-equilibrium god of the Na-amphiboles. Doctoral research earned me an offer of a UCLA assistant professorship as a mineralogist in 1960. There, I continued pursuing amphibole P-T stability relations in lab and field. My glaucophane phase equilibrium research would later be found to have instead crystallized Na-magnesiorichterite. However, amphibole research led me to map field occurrences of HP-LT (high P-low T) blueschists of the Franciscan Complex. Thus, when plate tectonics emerged in the late 1960s, I was deep in the subduction zone. My recent studies focused on the petrology and geochemistry of oceanic crustal rocks, Californian calc-alkaline arcs, and coesite ± microdiamond-bearing crustal margin rocks in various parts of Eurasia. Other works treated global mineral resources and population, mineralogy and human health, and early Earth petrotectonic evolution. I tried to work on important problems, but mainly studied topics that fired my interest. For the future, I see the existential challenge facing humanity and the biosphere as the imperative to stop our overdrafting of mineral resources. This will require reaching a dynamic equilibrium between the use and replenishment of near-surface resources (i.e., nutrients) essential for life. Earth scientists are planetary stewards, so we must lead the way forward in life-supporting mineral usage, recycling, substitution, and dematerialization. In any event, sustainable development will soon return to the Earth's Critical Zone of life because Mother Nature—the ruling terrestrial economist—abhors long-term overdrafting of resources.
DS202010-1843
2020
Erofeeva, K.G., Samsonov, A.V., Stepanova, A.V., Larionova, Yu.O., Dubinina, E.O., Egorova, S.V., Arzamastesev, A.A., Kovalchuk, E.V., Abramova, V.D.Olivine and clinopyroxene phenocrysts as a proxy for the origin and crustal evolution of primary mantle melts: a case study of 2.40 Ga mafic sills in the Kola-Norwegian Terrane, northern Fennoscandia.Petrology, Vol. 28, 4, pp. 338-356. pdfEurope, Norway, Kola Peninsulamelting

Abstract: New petrographic, geochemical, and isotopic (Sr, Nd, and d18?) data on olivine and pyroxene phenocrysts provide constraints on the composition and crustal evolution of primary melts of Paleoproterozoic (2.40 Ga) picrodoleritic sills in the northwest Kola province, Fennoscandian Shield. The picrodolerites form differentiated sills with S-shaped compositional profiles. Their chilled margins comprise porphyritic picrodolerite (upper margin) and olivine gabbronorite (bottom) with olivine and clinopyroxene phenocrysts. Analysis of the available data allows us to recognize three main stages in the crystallization of mineral assemblages. The central parts of large (up to 2 mm) olivine phenocrysts (Ol-1-C) crystallized at the early stage. This olivine (Mg# 85-92) is enriched in Ni (from 2845 to 3419 ppm), has stable Ni/Mg ratio, low Ti, Mn and Co concentrations, and contains tiny (up to 10 µm) diopside-spinel dendritic lamella that probably originated due to the exsolution from high Ca- and Cr- primary magmatic olivine. All these features of Ol-1-C are typical of olivine from primitive picritic and komatiitic magmas (De Hoog et al., 2010; Asafov et al., 2018). Ol-1-C contains large (up to 0.25 mm) crystalline inclusions of high-Al enstatite (Mg# 80-88) and clinopyroxene (Mg# 82-90), occasionally in association with Ti-pargasite and chromian spinel (60.4 wt.% Al2O3). These inclusions are regarded as microxenoliths of wall rock that were captured by primary melt at depths more than 30 km and preserved due to the conservation in magmatic olivine. The second stage was responsible for the crystallization of Ol-1 rim (Ol-1-R), small (up to 0.3 mm) olivine (Ol-2, Mg# 76-85) grains, and central parts of large (up to 1.5 mm) clinopyroxene (Cpx-C) phenocrysts in the mid-crustal transitional magma chamber (at a depth of 15-20 km) at 1160-1350°C. At the third stage, Cpx-C phenocrysts were overgrown by low-Mg rims (Mg# 70-72) similar in composition to the groundmass clinopyroxene from chilled picrodolerite and gabbro-dolerite in the central parts of the sills. This stage likely completed the evolution of picrodoleritic magma and occurred in the upper crust at a depth of about 5 km. All stages of picrodoleritic magma crystallization were accompanied by contamination. Primary melts were contaminated by upper mantle and/or lower crust as recognized from xenocrystic inclusions in Ol-1-C. The second contamination stage is supported by the negative values of eNd(2.40) = -1.1 in clinopyroxene phenocrysts. At the third stage, contamination likely occurred in the upper crust when ascending melts filled gentle fractures. This caused vertical whole-rock Nd heterogeneity in the sills (Erofeeva et al., 2019), and difference in Nd isotopic composition of clinopyroxene phenocrysts and doleritic groundmass. It was also recognized that residual evolved melts are enriched in radiogenic strontium but have neodymium isotopic composition similar to other samples. It could be explained by the interaction of the melts with fluid formed via decomposition of biotite from surrounding gneisses under the effect of high-temperature melts.
DS202003-0336
2020
Ethier, B.Analyzing entangled territorialities and indigenous use of maps: Atikamekw Nehirowisiwok ( Quebec, Canada) dynamics of territorial negotiations, frictions, and creativity.The Canadian Geographer, https://doi.org/ 10.1111/cag.12603Canada, Quebeclegal

Abstract: This paper highlights the relevance of analyzing entangled territorialities and Indigenous use of maps in order to better understand what Lévy describes in terms of “spatial capital”—the socio-economic dynamics and power relationships maintained and negotiated between the stakeholders interacting within the Indigenous forestland. More specifically, it discusses the entanglement dynamics of land tenures coexisting today within Nitaskinan, the ancestral territory claimed by the Atikamekw Nehirowisiwok. Within Nitaskinan, members of the First Nation negotiate the continuity of their practices, occupation, and use of ancestral hunting territories with state institutions, logging companies, and non-Indigenous members of civil society who have interests in the land resources. All these stakeholders implement different territorial regimes that interact and sometimes conflict. Based on concrete ethnographic examples, the analysis presented here focuses on the compromises, frictions, resistance, and creativity that are part of territorial coexistence between Indigenous and non-Indigenous people. This paper is about the entanglement of Indigenous and state's land tenures in a Canadian context. The study highlights the relevance of analyzing entangled territorialities to better understand the power relationships within Indigenous forestland. The study demonstrates the complex articulations between domination and resistance dynamics in Indigenous mapping in a territorial negotiation process. This paper is about the entanglement of Indigenous and state's land tenures in a Canadian context. The study highlights the relevance of analyzing entangled territorialities to better understand the power relationships within Indigenous forestland. The study demonstrates the complex articulations between domination and resistance dynamics in Indigenous mapping in a territorial negotiation process.
DS202009-1627
2020
Fareeduddin, Pant, N.C., Gupta, S., Chakraborty, P., Sensarma, S., Jain, A.K., Prasad, G.V.R., Srivastava, P., Rajan, S., Tiwari, V.M.The geodynamic evolution of the Indian subcontinent - an introduction.Episodes, Vol. 43, 1, pp. 8p.Indiacarbonatites
DS202005-0730
2020
Fareeduddin., Pant, N.C., Gupta, S., Chakraborty, P., Sensarma, S., Jain, A.K., Prasad, G.V.R., Srivastava, P., Rjan, S., Tiwari, V.M.The geodynamic evolution of the Indian subcontinent - an introduction.Episodes ( IUGS), Vol. 43, 1, pp. 1-18.Indiacarbonatite
DS202004-0510
2020
Faryad, S.W., Cuthbert, S.J.High temperature overprint in (U)HPM rocks exhumed from subduction zones: a product of isothermal decompression or a consequence of slab break-off ( slab rollback?) Dabie Sulu, KokechtavEarth-Science Reviews, Vol. 202, 103108 14p. PdfChina, Russiasubduction

Abstract: This paper presents and discusses petrological observations from high- to ultrahigh-pressure (U)HP metamorphic terrains in relation to existing geophysical and numerical models for subduction and exhumation processes in orogenic belts. The interpretations are mostly based on observations from gneiss terrains bearing abundant bodies mafic (meta-)eclogite and ultramafic garnet peridotite and pyroxenite, exposed in collisional orogens. The inclusions and compositional zoning of minerals are considered to be first order information that is needed to constrain PT paths of HP-UHP rocks and reconstruct the related geodynamic models for subduction and exhumation of crustal and mantle rocks. The Bohemian Massif of the European Variscides is used as the basis for a model example to explain these processes, but (U)HP rocks from various other terrains are taken into consideration to discuss available PT paths in relation to proposed subduction and exhumation rates of (U)HP rocks based on geophysical and geochronological data. Primarily information used in this respect include textural relations and preserved prograde zoning in minerals from many (U)HP rocks, which reveal that a relatively cool geothermal gradient typical of subduction zones tended to prevail during the prograde and peak pressure segments of PT paths prior to initiation of exhumation and may have continued, even with cooling, if exhumation rates were rapid. The commonly applied interpretation of isothermal decompression during exhumation is critically appraised, considering whether a simple thermal relaxation (and radiogenic heating) during exhumation is responsible for formation of post-peak pressure, retrograde mineral assemblages and textures observed in (U)HP rocks. We go on to consider whether this can satisfactorily explain the often pervasive medium-pressure, high-temperature metamorphic re-equilibration of (U)HP rocks or whether an additional, external source of heat is a better explanation. We conclude that the commonly observed high-temperature metamorphic overprint exhibited by (U)HP rocks occurs mostly after rocks have been exhumed from the subduction channel and have reached normal crustal positions, when mantle upwelling resulting from slab breakoff (delamination) or slab rollback takes place at the onset of continent-continent collision. We also explore contrasting PT trajectories for mantle rocks that have been entrained into crustal material during their subduction or exhumation; PT paths of mantle and subducted crustal rocks tend to converge as mantle rocks impinge upon the cooler subduction zone and, once entrained, share a common evolution that depends on the exhumation mechanism and rate. Considering all of the data presented in this work we conclude that the diverse, polyphase metamorphic evolution exhibited by (U)HP terrains, embodied in the PT paths of HP and UHP rocks, has important consequences for reconstructing their changing thermal regimes and provides important constraints for geodynamic models involving subduction and the transition to collision.
DS202008-1389
2020
Fedortchouk, Y., Chinn, I.L.Crystallization conditions of kimberlite magma.Goldschmidt 2020, 1p. AbstractAfrica, Botswana, Canada, Northwest Territoriesdeposit - Orapa, Lac de Gras

Abstract: Experiments on diamond crystallization in kimberlite melt were performed for 40 h at 6.3 GPa in the temperature range of 1300-1570 °C and at 7.5 GPa in the temperature range of 1450-1570 °C, using a multianvil high-pressure apparatus of split-sphere type. Group I kimberlite from the Udachnaya-East pipe and a synthetic multicomponent mixture modeling the average composition of group II kimberlites were used as starting materials. The experiments have shown that diamond growth on seed crystals in the kimberlite melt in equilibrium with olivine, pyroxene, and garnet starts from 1400 °C at 7.5 GPa and from 1520 °C at 6.3 GPa. Diamond nucleation requires higher temperature and pressure, 1570 °C and 7.5 GPa. The alkali-enriched and silicate-depleted derivates of kimberlite melts ensure the growth and nucleation of diamond at lower P and T values: 1400 °C at 7.5 GPa and 1520 °C at 6.3 GPa. The results obtained evidence that temperature, pressure, and the composition of crystallization medium are the main factors controlling diamond formation processes in the kimberlite melts and their derivates.
DS202003-0337
2020
Feng, M., Song, W., Kynicky, J., Smith, M., Cox, C., Kotlanova, M., Brtnicky, M., Fu, W., Wei, C.Primary rare earth element enrichment in carbonatites: evidence from melt inclusions in Ulgii Khild carbonatite, Mongolia.Ore Geology Reviews, Vol. 117, 14p. PdfAsia, Mongoliadeposit - Ulgii Khild
DS202002-0183
2019
First, E.C., Leonhardi, T.C., Hammer, J.E.Effects of superheating magnitude on olivine growth.Contributions to Mineralogy and Petrology, Vol. 175, 13p. pdfMantlemagmatism

Abstract: Magmatic superheating is a condition with relevance to natural systems as well as experimental studies of crystallization kinetics. Magmas on Earth and other planetary bodies may become superheated during adiabatic ascent from the mantle or as a consequence of meteorite impact-generated crustal melting. Experimental studies of igneous processes commonly employ superheating in the homogenization of synthetic starting materials. We performed 1-atmosphere dynamic crystallization experiments to study the effects of superliquidus thermal history on the morphologies and compositions of subsequently grown olivine crystals. An ultramafic volcanic rock with abundant olivine was fused above the experimentally determined liquidus temperature (1395 °C), held for 0, 3, or 12 h, cooled at 25 °C h-1, and quenched from 200 °C below the liquidus, all at constant fO2, corresponding to FMQ-2?±?0.2 log units. An increase in olivine morphologic instability is correlated with superheating magnitude, parameterized as the integrated time the sample is held above the liquidus (“TtL”; °C h). We infer that a delay in nucleation, which intensifies monotonically with increasing TtL, causes crystal growth to be increasingly rapid. This result indicates that the structural relaxation time scale controlling the formation of crystal nuclei is (a) far longer than the time scale associated with viscous flow and (b) exceeds the liquidus dwell times typically imposed in crystallization experiments. The influence of magmatic superheating on crystal morphology is similar in sense and magnitude to that of subliquidus cooling rate and thus, both factors should be considered when interpreting the thermal history of a volcanic rock containing anhedral olivine.
DS202007-1140
2020
Fitzpayne, A., Giuliani, A., Hergt, J., Woodhead, J.D., Maas, R.Isotopic analyses of clinopyroxene demonstrate the effects of mantle metasomatism upon the lithospheric mantle.Lithos, in press available, 77p. PdfAfrica, South Africadeposit - Kimberley

Abstract: The trace element and radiogenic isotope systematics of clinopyroxene have frequently been used to characterise mantle metasomatic processes, because it is the main host of most lithophile elements in the lithospheric mantle. To further our understanding of mantle metasomatism, both solution-mode Sr-Nd-Hf-Pb and in situ trace element and Sr isotopic data have been acquired for clinopyroxene grains from a suite of peridotite (lherzolites and wehrlites), MARID (Mica-Amphibole-Rutile-Ilmenite-Diopside), and PIC (Phlogopite-Ilmenite-Clinopyroxene) rocks from the Kimberley kimberlites (South Africa). The studied mantle samples can be divided into two groups on the basis of their clinopyroxene trace element compositions, and this subdivision is reinforced by their isotopic ratios. Type 1 clinopyroxene, which comprises PIC, wehrlite, and some sheared lherzolite samples, is characterised by low Sr (~100-200 ppm) and LREE concentrations, moderate HFSE contents (e.g., ~40-75 ppm Zr; La/Zr < 0.04), and restricted isotopic compositions (e.g., 87Sr/86Sri = 0.70369-0.70383; eNdi = +3.1 to +3.6) resembling those of their host kimberlite magmas. Available trace element partition coefficients can be used to show that Type 1 clinopyroxenes are close to being in equilibrium with kimberlite melt compositions, supporting a genetic link between kimberlites and these metasomatised lithologies. Thermobarometric estimates for Type 1 samples in this study indicate equilibration depths of 135-160 km within the lithosphere, thus showing that kimberlite melt metasomatism is prevalent in the deeper part of the lithosphere beneath Kimberley. In contrast, Type 2 clinopyroxenes occur in MARID rocks and coarse granular lherzolites in this study, which derive from shallower depths (<135 km), and have higher Sr (~350-1000 ppm) and LREE contents, corresponding to higher La/Zr of > ~ 0.05. The isotopic compositions of Type 2 clinopyroxenes are more variable and extend from compositions resembling the “enriched mantle” towards those of Type 1 rocks (e.g., eNdi = -12.7 to -4.4). To constrain the source of these variations, in situ Sr isotope analyses of clinopyroxene were undertaken, including zoned grains in Type 2 samples. MARID and lherzolite clinopyroxene cores display generally radiogenic but variable 87Sr/86Sri values (0.70526-0.71177), which are correlated with Sr contents and La/Zr ratios, and which might be explained by the interaction between peridotite and melts from different enriched sources within the lithospheric mantle. Most notably, the rims of these Type 2 clinopyroxenes trend towards compositions similar to those of the host kimberlite and Type 1 clinopyroxene from PIC and wehrlites. These results are interpreted to represent clinopyroxene overgrowth during late-stage (shortly before/during entrainment) metasomatism by kimberlite magmas. Our study shows that a pervasive, alkaline metasomatic event caused MARID to be generated and harzburgites to be converted to lherzolite in the lithospheric mantle beneath the Kimberley area, which was followed by kimberlite metasomatism during Cretaceous magmatism. This latter event is the time at which discrete PIC, wehrlite, and sheared lherzolite lithologies were formed, and MARID and granular lherzolites were partly modified.
DS202007-1141
2020
Fitzpayne, A., Prytulak, J., Giuliani, A., Hergt, J.Thallium content and isotopic composition of phlogopite in mantle derived MARID and PIC rocks.Chemical Geology, Vol. 531, 119347Mantlegeochronology
DS202008-1390
2020
Fitzpaynek, A., Giuliani, A., Magalhaes, N., Soltys, A., Fiorentini, M., Farquhar, J.The petrology and sulphur istopic composition of sulphide and sulphate in the Kimberley kimberlites.Goldschmidt 2020, 1p. AbstractAfrica, South Africadeposit - Kimberley

Abstract: The petrology and bulk-rock sulphur isotopic compositions of kimberlite samples from four localities (Bultfontein, De Beers, Kimberley, Wesselton) of the archetypal Kimberley cluster, South Africa, were used to investigate the origin(s) of S in kimberlites and gain insights into the occurrence of recycled crustal material in the source of Mesozoic kimberlites. The samples, which show variable degrees of alteration, are all hypabyssal and were derived from coherent root-zones as well as dykes and sills. Typical sulphide minerals are Cu-Fe-Ni-sulphides with less common pyrite, galena, sphalerite, and djerfisherite. They occur in a variety of textural associations, for example as groundmass phases, secondary inclusions in olivine, inclusions in matrix phases (e.g., phlogopite), or in carbonate-serpentine segregations. Barite is the most commonly observed sulphate phase. Bulk-sample d34SVCDT values of sulphides in fresh kimberlites, which mostly do not contain barite, vary from - 2.0 to -5.7 ‰. Slightly altered kimberlite samples, in which sulphides were generally associated with serpentine, returned somewhat higher bulk-sulphide d34SVCDT (-3.8 to +1.1 ‰). One sample from the Wesselton Water Tunnel Sills complex contains abundant barite and pyrite in its groundmass, with the latter having d34SVCDT (+0.2 to +1.9 ‰) similar to altered kimberlites. Two further altered samples returned d34SVCDT values (-10.1 to -13.0 ‰) that suggest a contribution from the local country rocks (Dwyka shale: d34SVCDT from -10.2 to -10.5 ‰). All samples have near-zero ?33S values, suggesting that material displaying mass-independent fractionation has not played an important role. The negative d34SVCDT values of fresh kimberlites from Kimberley suggest the involvement of recycled crustal material in their source, which is consistent with radiogenic isotope compositions. Overall, it appears that most kimberlitic sulphide S isotopic compositions can be explained by the action of a few typical magmatic/hydrothermal processes.
DS202012-2214
2009
Flament, N.Secular cooling of the solid Earth, emergence of the continents , and evolution of Earth's external envelopes.Thesis, Phd Univ. Sydney *** NOTE DATE, 210p. PdfMantlecratons

Abstract: The secular cooling of the mantle and of the continental lithosphere trigger an increase in the area of emerged land. The corollary increase in weathering and erosion processes has major consequences for the evolution of Earth's external envelopes. We developed a physical model to evaluate the area of emerged land as a function of mantle temperature, continental area, and of the distribution of continental elevations. Our numerical results show that less than 15% of Earth's surface consisted of emerged land by the end of the Archaean. This is consistent with many geological and geochemical observations. To estimate the secular cooling of the continental lithosphere, we combined thermo-mechanical models with fi eld observations. Our results, constrained by geological data, suggest that the Moho temperature has decreased by ~ 200ºC over 2.7 Ga in the Pilbara Craton. To evaluate the eff ect of continental growth on the evolution of the area of emerged land, we developed a model based on published thermal evolution models. Our results suggest that the area of emerged land was less than 5% of Earth's surface in the Archaean, and that it does not depend on crustal growth. This allows to reconcile the evolution of oceanic 87Sr/86Sr with early crustal growth models. Continents are enriched in phosphorus, which is essential to the biosphere. The emergence of the continents would thus have triggered an increase in the production of oxygen by photosynthetic micro-organisms, possibly contributing to the oxidation of the atmosphere 2.4 Ga ago.
DS202006-0919
2020
Flowers, R.M., Macdonald, F.A., Siddoway, C.S., Havranek, R.Diachronous development of Great Unconformities before Neoproterozoic Snowlball Earth. Proceedinds of the National Academy of Sciences, Vol. 117, 19, 9p. PdfUnited States, Coloradogeothermometry

Abstract: The Great Unconformity marks a major gap in the continental geological record, separating Precambrian basement from Phanerozoic sedimentary rocks. However, the timing, magnitude, spatial heterogeneity, and causes of the erosional event(s) and/or depositional hiatus that lead to its development are unknown. We present field relationships from the 1.07-Ga Pikes Peak batholith in Colorado that constrain the position of Cryogenian and Cambrian paleosurfaces below the Great Unconformity. Tavakaiv sandstone injectites with an age of =676 ± 26 Ma cut Pikes Peak granite. Injection of quartzose sediment in bulbous bodies indicates near-surface conditions during emplacement. Fractured, weathered wall rock around Tavakaiv bodies and intensely altered basement fragments within unweathered injectites imply still earlier regolith development. These observations provide evidence that the granite was exhumed and resided at the surface prior to sand injection, likely before the 717-Ma Sturtian glaciation for the climate appropriate for regolith formation over an extensive region of the paleolandscape. The 510-Ma Sawatch sandstone directly overlies Tavakaiv-injected Pikes granite and drapes over core stones in Pikes regolith, consistent with limited erosion between 717 and 510 Ma. Zircon (U-Th)/He dates for basement below the Great Unconformity are 975 to 46 Ma and are consistent with exhumation by 717 Ma. Our results provide evidence that most erosion below the Great Unconformity in Colorado occurred before the first Neoproterozoic Snowball Earth and therefore cannot be a product of glacial erosion. We propose that multiple Great Unconformities developed diachronously and represent regional tectonic features rather than a synchronous global phenomenon.
DS202008-1391
2019
Fofana, M., Steyn, T.Monitoring the performance of DMS circuits using RhoVol technology. ( DMC)The Journal of the Southern African Insitute of Mining and Metallurgy, Vol. 119, Feb. 6p. PdfAfrica, South AfricaDMC

Abstract: The petrology and bulk-rock sulphur isotopic compositions of kimberlite samples from four localities (Bultfontein, De Beers, Kimberley, Wesselton) of the archetypal Kimberley cluster, South Africa, were used to investigate the origin(s) of S in kimberlites and gain insights into the occurrence of recycled crustal material in the source of Mesozoic kimberlites. The samples, which show variable degrees of alteration, are all hypabyssal and were derived from coherent root-zones as well as dykes and sills. Typical sulphide minerals are Cu-Fe-Ni-sulphides with less common pyrite, galena, sphalerite, and djerfisherite. They occur in a variety of textural associations, for example as groundmass phases, secondary inclusions in olivine, inclusions in matrix phases (e.g., phlogopite), or in carbonate-serpentine segregations. Barite is the most commonly observed sulphate phase. Bulk-sample d34SVCDT values of sulphides in fresh kimberlites, which mostly do not contain barite, vary from - 2.0 to -5.7 ‰. Slightly altered kimberlite samples, in which sulphides were generally associated with serpentine, returned somewhat higher bulk-sulphide d34SVCDT (-3.8 to +1.1 ‰). One sample from the Wesselton Water Tunnel Sills complex contains abundant barite and pyrite in its groundmass, with the latter having d34SVCDT (+0.2 to +1.9 ‰) similar to altered kimberlites. Two further altered samples returned d34SVCDT values (-10.1 to -13.0 ‰) that suggest a contribution from the local country rocks (Dwyka shale: d34SVCDT from -10.2 to -10.5 ‰). All samples have near-zero ?33S values, suggesting that material displaying mass-independent fractionation has not played an important role. The negative d34SVCDT values of fresh kimberlites from Kimberley suggest the involvement of recycled crustal material in their source, which is consistent with radiogenic isotope compositions. Overall, it appears that most kimberlitic sulphide S isotopic compositions can be explained by the action of a few typical magmatic/hydrothermal processes. One of the most important performance indicators of a dense medium cyclone (DMC) circuit is the Tromp curve, and by extension the separation density and Ecart Probable (Ep) values. The densimetric profiles of DMC product streams have been traditionally acquired using heavy liquid sinkfloat analysis, which has certain disadvantages, such as the associated safety and health risks. More recently, non-toxic media such as lithium hetero-polytungstates (LST) have been used, with the desired densities being achieved by maintaining the solutions at specific temperatures. However, the high costs of these liquids can be prohibitive. The long turnaround time of the sink-float analysis is a further disadvantage for timeous interventions to the operating set-points of the DMC process. The RhoVol technology can generate the density distribution of a batch of particles in a rapid, accurate, repeatable, and safe manner. Additional data of interest, such as particle size and shape, are also measured and reported on a per-particle basis. Furthermore, samples can be sorted into discrete sorting bins based on any of the measured parameters of the particle, making further analyses of the material possible. This technology has applications across all commodities that use the DMC, particularly in the size fractions 25 +8 mm and 8 +3 mm. To date, laboratory results have proved very encouraging separation densities are within 5% of traditional sink-float results, and the technology is being introduced to diamond DMC plants.
DS202002-0184
2019
Forster, M.W.Subduction zone metasomatism and its consequences for potassium rich magmatism and deep nitrogen recycling.Thesis Phd .Macquarie University, 250p. PdfMantlemetasomatism

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 %.
DS202002-0185
2020
Forster, M.W., Buhre, S., Xu, B., Prelevic, D., Mertz-Kraus, R., Foley, S.F.Two stage origin of K-enrichment in ultrapotassic magmatism simulated by melting of experimentally metasomatized mantle.MDPI Minerals, Vol. 10, 41;doe.10.3390/min10010041 21p. PdfMantlemetasomatism

Abstract: The generation of strongly potassic melts in the mantle requires the presence of phlogopite in the melting assemblage, while isotopic and trace element analyses of ultrapotassic rocks frequently indicate the involvement of subducted crustal lithologies in the source. However, phlogopite-free experiments that focus on melting of sedimentary rocks and subsequent hybridization with mantle rocks at pressures of 1-3 GPa have not successfully produced melts with K2O >5 wt%-6 wt%, while ultrapotassic igneous rocks reach up to 12 wt% K2O. Accordingly, a two-stage process that enriches K2O and increases K/Na in intermediary assemblages in the source prior to ultrapotassic magmatism seems likely. Here, we simulate this two-stage formation of ultrapotassic magmas using an experimental approach that involves re-melting of parts of an experimental product in a second experiment. In the first stage, reaction experiments containing layered sediment and dunite produced a modally metasomatized reaction zone at the border of a depleted peridotite. For the second-stage experiment, the metasomatized dunite was separated from the residue of the sedimentary rock and transferred to a smaller capsule, and melts were produced with 8 wt%-8.5 wt% K2O and K/Na of 6-7. This is the first time that extremely K-enriched ultrapotassic melts have been generated experimentally from sediments at low pressure applicable to a post-collisional setting.
DS202006-0920
2020
Foster, A., Darbyshire, F., Schaeffer, A.Anisotropic structure of the central North American craton surrounding the Mid-continent rift: evidence form Rayleigh waves.Precambrian Research, Vol. 342, 18p. PdfUnited States, Canadageophysics - seismics
DS202004-0511
2020
Fosu, B.R., Ghosh, P., Viladkar, S.G.Clumped isotope geochemistry of carbonatites in the north-western Deccan igneous province: aspects of evolution, post-depositional alteration and mineralization.Geochimica et Cosmochimica Acta, Vol. 274, pp. 118-135.Indiacarbonatite

Abstract: Carbonatites crystallise along a wide range of solidus temperatures and are commonly affected by post-magmatic textural re-equilibration and diagenesis. Further insights into the formation and modification of carbonatites are provided using carbon, oxygen and clumped isotope (?47) data of rocks from spatially associated Amba Dongar and Siriwasan alkaline complexes in the north-western Deccan igneous province, India. We derive apparent equilibrium blocking temperatures to help constrain the thermal evolution of the different rock types found within the alkaline complexes in a petrographic context. The apparent temperatures for the carbonatites are significantly low but are consistent with reports on other global carbonatites and model predictions. Rapidly cooled Oldoinyo Lengai natrocarbonatite yielded similar low temperatures, even in the absence of bulk isotopic alteration. The isotopic proxies and petrographic observations favour both isotopic exchange reactions and diagenesis in altering ?47 values in calciocarbonatites. Diagenetic reactions are however strongly favoured, as secondary calcites in nephelinites and ferrocarbonatites record much lower temperatures than in the calciocarbonatites, highlighting the effect of fluids and diagenetic reactions in 13C18O bond ordering in carbonatites. Variations in the CO isotope data reveal the coupling of fractional crystallisation and post-magmatic fluid-rock interactions on bulk rock composition. After emplacement, the resetting of clumped isotope signatures in carbonatites is facilitated by post-magmatic processes in both open and closed systems.
DS202003-0338
2020
Franz, G., Vyshnevsky, O., Taran, M., Khomenko, V., Wiedenbeck, M., Schiperski, F., Nissen, J.A new emerald occurrence from Kruta Balka, western Peri-Azovian, Ukraine: implications for understanding the crystal chemistry of emerald.American Mineralogist, Vol. 105, pp. 162-181. pdfEurope, Ukraineemerald

Abstract: We investigated emerald, the bright-green gem variety of beryl, from a new locality at Kruta Balka, Ukraine, and compare its chemical characteristics with those of emeralds from selected occurrences worldwide (Austria, Australia, Colombia, South Africa, Russia) to clarify the types and amounts of substitutions as well as the factors controlling such substitutions. For selected crystals, Be and Li were determined by secondary ion mass spectrometry, which showed that the generally assumed value of 3 Be atoms per formula unit (apfu) is valid; only some samples such as the emerald from Kruta Balka deviate from this value (2.944 Be apfu). An important substitution in emerald (expressed as an exchange vector with the additive component Al2Be3Si6O18) is (Mg,Fe2+)NaAl1?1, leading to a hypothetical end-member NaAl(Mg,Fe2+)[Be3Si6O18] called femag-beryl with Na occupying a vacancy position (?) in the structural channels of beryl. Based on both our results and data from the literature, emeralds worldwide can be characterized based on the amount of femag-substitution. Other minor substitutions in Li-bearing emerald include the exchange vectors LiNa2Al1?2 and LiNaBe1?1, where the former is unique to the Kruta Balka emeralds. Rarely, some Li can also be situated at a channel site, based on stoichiometric considerations. Both Cr- and V-distribution can be very heterogeneous in individual crystals, as shown in the samples from Kruta Balka, Madagascar, and Zimbabwe. Nevertheless, taking average values available for emerald occurrences, the Cr/(Cr+V) ratio (Cr#) in combination with the Mg/(Mg+Fe) ratio (Mg#) and the amount of femag-substitution allows emerald occurrences to be characterized. The "ultramafic" schist-type emeralds with high Cr# and Mg# come from occur-rences where the Fe-Mg-Cr-V component is controlled by the presence of ultramafic meta-igneous rocks. Emeralds with highly variable Mg# come from "sedimentary" localities, where the Fe-Mg-Cr-V component is controlled by metamorphosed sediments such as black shales and carbonates. A "transitional" group has both metasediments and ultramafic rocks as country rocks. Most "ultramafic" schist type occurrences are characterized by a high amount of femag-component, whereas those from the "sedimentary" and "transitional" groups have low femag contents. Growth conditions derived from the zoning pattern combined replacement, sector, and oscillatory zoning in the Kruta Balka emeralds indicate disequilibrium growth from a fluid along with late-stage Na-infiltration. Inclusions in Kruta Balka emeralds (zircon with up to 11 wt% Hf, tourmaline, albite, Sc-bearing apatite) point to a pegmatitic origin.
DS202001-0011
2019
Frezzotti, M.L.Diamond growth from organic compounds in hydrous fluids deep within the Earth.Nature Communications, doi.org/10.1038/ s41467-019-12984-y 8p. 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.
DS202008-1392
2020
Frezzotti, M.L.Diamond growth from organic compounds in hydrous fluids deep within the Earth.Goldschmidt 2020, 1p. AbstractMantlesubduction

Abstract: Subduction diamonds represent the sequestration of carbon from fluids released from lithospheric plates at mantle depths. In deep fluids, besides reactive molecular species (e.g., CO2), inorganic, and organic aqueous ionic species have been proposed as a source of carbon in diamonds (Sverjensky et al., 2014). Unequivocal signatures of organic species, however, have not been found, neither a unified model for diamond nucleation and growth has been proposed. Here, I use Raman microspectroscopy to determine the structure and composition of carbon-based phases precipitated inside diamond-bearing fluid inclusions in metamorphic rocks from the Alps to reveal the spontaneous products on carbon saturation in deep Earth’s aqueous fluids. I find that microand nano-sized diamonds are coated by sp2-, and sp3-bonded amorphous carbon that shows Raman modes of attached organic functional group structures (e.g., carboxyl, carboxylate, methyl, and methylene). Present data suggest that decomposition of complex carboxylic acids can induce diamond nucleation on the reduction of the carboxyl groups, whereas sp3-bonded radicals can create structural intermediates allowing diamond growth (Frezzotti, 2019). This formation mechanism is consistent with nucleation models via metastable molecular precursors (Gebbie et al., 2018). The present study provides direct evidence that, deep within the Earth, dissolved inorganic carbon can spontaneously evolve to organic species in the absence of biologically catalyzed processes. Results suggest that the Earth’s interior should be considered as a favorable environment for the origin of prebiotic organic compounds.
DS202004-0512
2020
Gales, E., Black, B., Elkins-Tanton, E.Carbonatites as a record of the carbon isotope composition of large igneous province outgassing.Earth and Planetary Science Letters, Vol. 535, 116076 11p. PdfRussia, Siberiacarbonatite

Abstract: Large igneous province (LIP) eruptions have been linked in some cases to major perturbations of Earth's carbon cycle. However, few observations directly constrain the isotopic composition of carbon released by LIP magmas because carbon isotopes fractionate during degassing, which hampers understanding of the relative roles of mantle versus crustal carbon reservoirs. Carbonatite magmatism associated with LIPs provides a unique window into the isotopic systematics of LIP carbon because the majority of carbon in carbonatites crystalizes rather than degassing. Although the volume of such carbonatites is small, they offer one of the few available constraints on the mantle carbon originally hosted in other more voluminous magma types. Here, we present new data for the Guli carbonatites in the Siberian Traps. In addition, we compile ~260 published measurements of from carbonatites related to the Deccan Traps and the Paraná-Etendeka. We find no evidence for magmas with carbon isotope ratios lighter than depleted mantle values of ‰ from any of these LIPs, though some carbonatites range to heavier . We attribute relatively heavy in some carbonatites to either slightly 13C-enriched domains in the mantle lithosphere or carbon isotope fractionation in deep, carbon-saturated LIP magma reservoirs. The absence of a light component in LIP magmas supports the view that lithospheric carbon reservoirs must be tapped during cases of LIP magmatism linked with sharp negative carbon isotope excursions and mass extinctions.
DS202005-0731
2020
Galimov, E.M., Kaminsky, F.V., Shilobreeva, S.N., Sevastyanov, V.S., Voropaev, S.A., Khachatryan, G.K., Wirth, R., Schreiber, A., Saraykin, V.V., Karpov, G.A., Anikin, L.P.Enigmatic diamonds from the Tolbachik volcano, Kamchatka.American Mineralogist, Vol. 105, pp. 498-509. pdfRussiadeposit - Tolbachik

Abstract: Approximately 700 diamond crystals were identified in volcanic (mainly pyroclastic) rocks of the Tolbachik volcano, Kamchatka, Russia. They were studied with the use of SIMS, scanning and transmission electron microscopy, and utilization of electron energy loss spectroscopy and electron diffraction. Diamonds have cube-octahedral shape and extremely homogeneous internal structure. Two groups of impurity elements are distinguished by their distribution within the diamond. First group, N and H, the most common structural impurities in diamond, are distributed homogeneously. All other elements observed (Cl, F, O, S, Si, Al, Ca, and K) form local concentrations, implying the existence of inclusions, causing high concentrations of these elements. Most elements have concentrations 3-4 orders of magnitude less than chondritic values. Besides N and H, Si, F, Cl, and Na are relatively enriched because they are concentrated in micro- and nanoinclusions in diamond. Mineral inclusions in the studied diamonds are 70-450 nm in size, round- or oval-shaped. They are represented by two mineral groups: Mn-Ni alloys and silicides, with a wide range of concentrations for each group. Alloys vary in stoichiometry from MnNi to Mn2Ni, with a minor admixture of Si from 0 to 5.20-5.60 at%. Silicides, usually coexisting with alloys, vary in composition from (Mn,Ni)4Si to (Mn,Ni)5Si2 and Mn5Si2, and further to MnSi, forming pure Mn-silicides. Mineral inclusions have nanometer-sized bubbles that contain a fluid or a gas phase (F and O). Carbon isotopic compositions in diamonds vary from -21 to -29‰ d13CVPDB (avg. = -25.4). Nitrogen isotopic compositions in diamond from Tolbachik volcano are from -2.32 to -2.58‰ d15NAir. Geological, geochemical, and mineralogical data confirm the natural origin of studied Tolbachik diamonds from volcanic gases during the explosive stage of the eruption.
DS202009-1628
2018
Garber, J.M., Maurya, S., Hernandez, J.A., Duncan, M.S., Zeng, L., Zhang, H.L.Multidisciplenary constraints on the abundance of diamond and eclogite in the cratonic lithosphere.Geochemistry, Geophysics, Geosystems, Vol. 19: https://doi.org/10.1029/2018GC007534Mantleeclogite

Abstract: Some seismic models derived from tomographic studies indicate elevated shear-wave velocities (=4.7 km/s) around 120-150 km depth in cratonic lithospheric mantle. These velocities are higher than those of cratonic peridotites, even assuming a cold cratonic geotherm (i.e., 35 mW/m2 surface heat flux) and accounting for compositional heterogeneity in cratonic peridotite xenoliths and the effects of anelasticity. We reviewed various geophysical and petrologic constraints on the nature of cratonic roots (seismic velocities, lithology/mineralogy, electrical conductivity, and gravity) and explored a range of permissible rock and mineral assemblages that can explain the high seismic velocities. These constraints suggest that diamond and eclogite are the most likely high-Vs candidates to explain the observed velocities, but matching the high shear-wave velocities requires either a large proportion of eclogite (>50 vol.%) or the presence of up to 3 vol.% diamond, with the exact values depending on peridotite and eclogite compositions and the geotherm. Both of these estimates are higher than predicted by observations made on natural samples from kimberlites. However, a combination of =20 vol.% eclogite and ~2 vol.% diamond may account for high shear-wave velocities, in proportions consistent with multiple geophysical observables, data from natural samples, and within mass balance constraints for global carbon. Our results further show that cratonic thermal structure need not be significantly cooler than determined from xenolith thermobarometry.
DS202002-0186
2020
Garcia, L.F., Abel, M., Perrin, M., dos Santis Alvarenga, R.The GeoCore ontology: a core ontology for general use in geology.Computers and Geosciences, Vol. 135, 104387 9p. PdfGlobalGeoCore

Abstract: Domain ontologies assume the role of representing, in a formal way, a consensual knowledge of a community over a domain. This task is especially difficult in a wide domain like Geology, which is composed of diversified science resting on a large variety of conceptual models that were developed over time. The meaning of the concepts used by the various professionals often depends on the particular vision that they have of a domain according to their background and working habits. Ontology development in Geology thus necessitates a drastic elucidation of the concepts and vocabulary used by geologists. This article intends to contribute to solving these difficulties by proposing a core ontology named GeoCore Ontology resting on the BFO top ontology, specially designed for describing scientific fields. GeoCore Ontology contains well-founded definitions of a limited set of general concepts within the Geology field that are currently considered by all geologists whatever their skill. It allows modelers to separately consider a geological object, the substance that constitutes it, the boundaries that limit it and the internal arrangement of the matter inside it. The core ontology also allows the description of the existentially dependent qualities attached to a geological object and the geological process that generated it in a particular geological age. This small set of formally defined and described concepts combined with concepts from BFO provides a backbone for deriving by subsumption more specialized geological concepts and also constitutes a baseline for integrating different existent domain ontologies within the Geology domain. The GeoCore ontology and the methodology that we used for building it, provide solutions for unveiling major misunderstanding regarding the concepts that are commonly used for formulating geological interpretations. This will facilitate the communication of this information to external Geology users and its integration in domain applications.
DS202002-0187
2020
Gardiner, N.J., Kirkland, C.L., Hollis, J.A., Cawood, P.A., Nebel, O., Szilas, K., Yakymchuk, C.North Atlantic craton architecture revealed by kimberlite-hosted crustal zircons.Earth and Planetary Science Letters, Vol. 534, 8p. PdfEurope, Greenlandkimberlite genesis

Abstract: Archean cratons are composites of terranes formed at different times, juxtaposed during craton assembly. Cratons are underpinned by a deep lithospheric root, and models for the development of this cratonic lithosphere include both vertical and horizontal accretion. How different Archean terranes at the surface are reflected vertically within the lithosphere, which might inform on modes of formation, is poorly constrained. Kimberlites, which originate from significant depths within the upper mantle, sample cratonic interiors. The North Atlantic Craton, West Greenland, comprises Eoarchean and Mesoarchean gneiss terranes - the latter including the Akia Terrane - assembled during the late Archean. We report U-Pb and Hf isotopic, and trace element, data measured in zircon xenocrysts from a Neoproterozoic (557 Ma) kimberlite which intruded the Mesoarchean Akia Terrane. The zircon trace element profiles suggest they crystallized from evolved magmas, and their Eo-to Neoarchean U-Pb ages match the surrounding gneiss terranes, and highlight that magmatism was episodic. Zircon Hf isotope values lie within two crustal evolution trends: a Mesoarchean trend and an Eoarchean trend. The Eoarchean trend is anchored on 3.8 Ga orthogneiss, and includes 3.6-3.5 Ga, 2.7 and 2.5-2.4 Ga aged zircons. The Mesoarchean Akia Terrane may have been built upon mafic crust, in which case all zircons whose Hf isotopes lie within the Eoarchean trend were derived from the surrounding Eoarchean gneiss terranes, emplaced under the Akia Terrane after ca. 2.97 or 2.7 Ga, perhaps during late Archean terrane assembly. Kimberlite-hosted peridotite rhenium depletion model ages suggest a late Archean stabilization for the lithospheric mantle. The zircon data support a model of lithospheric growth via tectonic stacking for the North Atlantic Craton.
DS202004-0513
2020
Gaucher, E.C.New perspectives in the industrial exploration for native hydrogen.Elements, Vol. pp. 8-9.Globalhydrogen

Abstract: Hydrogen gas (H2), when combusted, produces heat and water. There is no pollution, just water vapor. When hydrogen combines with oxygen, there is no generation of carbon dioxide, no production of cyclic hydro-carbons, no sulfur oxides (SOx), no nitrogen oxides (NOx), no ozone cogeneration. It seems that hydrogen, along with efficient energy production, solves many of our pollution problems, from urban air pollution to global warming. In the so-called Hydrogen Age of the future (Holland and Provenzano 2007), H2 will be mainly produced by the electrolysis of water using electricity that itself is derived from renewable energy sources or nuclear power plants. Steam methane reforming (a catalyzed reaction at high temperature where CH4 is combined with water to produce CO2 and H2) will only be acceptable as a source of H2 if it is associated with low-cost CO2 storage. But, in this future energy landscape, what is the role of naturally occurring hydrogen, sometimes referred to as native hydrogen?
DS202005-0732
2020
Gaucher, E.C.New perspectives in the industrial exploration for native hydrogen. ( brief review) whole issue on hydrogenElements, Vol. 18, 1, pp. 8-9.Globalhydrogen

Abstract: This article is a broad summary of the current state of knowledge concerning the potential exploration for native hydrogen across the globe. Native hydrogen has been identified in numerous source rocks in zones beyond sedimentary basins where petroleum companies typically operate. At the beginning of 2019 we may be at a tipping point with the first exploitable H2 field, potentially discovered in Mali. Of course, a number of issues and questions must still be resolved if these initial discoveries are to be transformed into a sustainable and abundant source of energy for society. However, the competencies that exist in the petroleum industry can readily be adapted by and to this new sector. New expertise will be needed to account for the reactivity of the hydrogen molecule in order to maximize exploration efforts and minimize the potential for chemical or biological consumption.
DS202012-2215
2020
Gautheron, C., Zeitler, P.K.Noble gases deliver cool dates from hot rocks. Elements, Vol. 16, pp. 303-309.MantleThermochronology

Abstract: Heat transfer in the solid Earth drives processes that modify temperatures, leaving behind a clear signature that we can measure using noble gas thermochronology. This allows us to record the thermal histories of rocks and obtain the timing, rate, and magnitude of phenomena such as erosion, deformation, and fluid flow. This is done by measuring the net balance between the accumulation of noble gas atoms from radioactive decay and their loss by temperature-activated diffusion in mineral grains. Together with knowledge about noble gas diffusion in common minerals, we can then use inverse models of this accumulation-diffusion balance to recover thermal histories. This approach is now a mainstream method by which to study geodynamics and Earth evolution.
DS202001-0012
2019
Gauthier, M.S., Hodder, T., Ross, M., Kelley, S.E. Rochester, A., McCausland< P. The subglacial mosaic of the Laurentide ice sheet; a study of the interior region of southwestern Hudson Bay.Quaternary Science Reviews, Vol. 214, pp. 1-27.Canada, Manitobageomorphology

Abstract: Reconstructions of past ice-flow provide useful insights into the long-term behaviour of past ice sheets and help to understand how glaciated landscapes are shaped. Here, we present reconstruction of a 10-phase ice-flow history from southwestern Hudson Bay in northeastern Manitoba (Canada), a dynamic region situated between two major ice dispersal centres of the Laurentide Ice Sheet. We utilize a diverse geologic dataset including 1900 field-based erosional indicators, 12 streamlined-landform flowsets, esker and meltwater corridor orientations, 103 till-fabrics analyses, and 1344 till-clast lithology counts. Our reconstruction suggests that both pre-MIS 2 and MIS 2 glaciations followed similar growth patterns, where ice advanced into study area from ice centered to the east (probably in northern Quebec), followed by a switch in ice-flow direction indicating flow from the Keewatin ice centre to the northwest and north. The cause for this switch in ice-flow orientation is uncertain, but the youngest switch may relate to retreat of ice during MIS 3 that then left space for Keewatin-sourced ice to advance over the study area. While modelling experiments indicate widespread cold-based conditions in the study area during the last glacial cycle, uniformly relict landscapes are not common. Instead, the glaciated landscape is palimpsest and commonly fragmented, forming a subglacial bed mosaic of erosional and depositional assemblages that record both shifting ice-flow direction through time and shifting subglacial conditions. Each assemblage formed, or modified, during times of dynamic (warm-based) ice, and later preserved under conditions below or close to the pressure melting point (slow and sluggish, or cold-based).
DS202005-0733
2020
Geballe, Z.M., Sime, N., Badro, J., van Keken, P.E., Goncharov, A.F.Thermal conductivity near the bottom of the Earth's lower mantle: measurements of pyrolite up to 120 Gpa and 2500 K.Earth and Planetary Science Letters, Vol. 536, 116161, 11p. PdfMantlegeothermometry

Abstract: Knowledge of thermal conductivity of mantle minerals is crucial for understanding heat transport from the Earth's core to mantle. At the pressure-temperature conditions of the Earth's core-mantle boundary, calculations of lattice thermal conductivity based on atomistic models have determined values ranging from 1 to 14 W/m/K for bridgmanite and bridgmanite-rich mineral assemblages. Previous studies have been performed at room temperature up to the pressures of the core-mantle boundary, but correcting these to geotherm temperatures may introduce large errors. Here we present the first measurements of lattice thermal conductivity of mantle minerals up to pressures and temperatures near the base of the mantle, 120 GPa and 2500 K. We use a combination of continuous and pulsed laser heating in a diamond anvil cell to measure the lattice thermal conductivity of pyrolite, the assemblage of minerals expected to make up the lower mantle. We find a value of W/m/K at 80 GPa and 2000 to 2500 K and 5.9 W/m/K at 124 GPa and 2000 to 3000 K. These values rule out the highest calculations of thermal conductivity of the Earth's mid-lower mantle (i.e. W/m/K at 80 GPa), and are consistent with both the high and low calculations of thermal conductivity near the base of the lower mantle.
DS202004-0514
2020
Gebralle, Z.M., Sime, N., Badro, J., van Kekn, P.E.Thermal conductivity near the bottom of the Earth's lower mantle: mesurements of pyrolite up to 120 GPa and 2500 K. Earth and Planetary Science Letters, Vol. 536, 116161 7p. PdfMantlegeothermometry

Abstract: Knowledge of thermal conductivity of mantle minerals is crucial for understanding heat transport from the Earth's core to mantle. At the pressure-temperature conditions of the Earth's core-mantle boundary, calculations of lattice thermal conductivity based on atomistic models have determined values ranging from 1 to 14 W/m/K for bridgmanite and bridgmanite-rich mineral assemblages. Previous studies have been performed at room temperature up to the pressures of the core-mantle boundary, but correcting these to geotherm temperatures may introduce large errors. Here we present the first measurements of lattice thermal conductivity of mantle minerals up to pressures and temperatures near the base of the mantle, 120 GPa and 2500 K. We use a combination of continuous and pulsed laser heating in a diamond anvil cell to measure the lattice thermal conductivity of pyrolite, the assemblage of minerals expected to make up the lower mantle. We find a value of W/m/K at 80 GPa and 2000 to 2500 K and 5.9 W/m/K at 124 GPa and 2000 to 3000 K. These values rule out the highest calculations of thermal conductivity of the Earth's mid-lower mantle (i.e. W/m/K at 80 GPa), and are consistent with both the high and low calculations of thermal conductivity near the base of the lower mantle.
DS202010-1844
2020
Genish, H., Ganesan, K., Stacey, A., Prawer, S., Rosenbluh, M.Effect of radiation damage on the quantum optical properties of nitrogen vacancies in diamond.Diamond & Related Materials, Vol. 109, 108049, 6p. PdfMantlenitrogen

Abstract: Single crystal diamond (<5?ppm nitrogen) containing native NV centers with coherence time of 150?µs was irradiated with 2?MeV alpha particles, with doses ranging from 1012 ion/cm2 to 1015 ion/cm2. The effect of ion damage on the coherence time of NV centers was studied using optically detected magnetic resonance and supplemented by fluorescence and Raman microscopy. A cross-sectional geometry was employed so that the NV coherence time could be measured as a function of increasing defect concentration along the ion track. Surprisingly, although the ODMR contrast was found to decrease with increasing ion induced vacancy concentration, the measured decoherence time remained undiminished at 150us despite the estimated vacancy concentration reaching a value of 40?ppm at the end of range. These results suggest that ion induced damage in the form of an increase in vacancy concentration does not necessarily result in a significant increase in the density of the background spin bath.
DS202003-0339
2020
Geological Survey of IndiaMineral resources of India. ( first 19p. Kimberlites )Geological Survey of India, 75p. PdfIndiadiamond

Abstract: India has a rich tradition of mineral exploration. Innumerable old workings, mine dumps slag heaps, etc. are the tell tale signs of this glorious tradition. The flourishing diamond trade in the Deccan peninsula, mainly in the Golconda kingdom, had attracted world’s attention during historical time. Copper and gold were also used locally since the days of Indus Valley civilizations. East India Company started exploration for coal in the Eighteenth century with setting up of , the premier Earth science organisation and the second oldest survey of the country, in 1851 for the systematic geological survey and prospecting for coal. India was a notable producer of gold in the early part of twentieth century and major exporter of mica, sillimanite, kyanite, magnetite and chromite. Metallurgical industry started with the setting up of steel plants at Burnpur, Jamshedpur and copper smelter at Ghatsila. Second World War created great demand for various minerals and metals including those of strategic importance e.g., tungsten. Industrial policy, formulated after Independence, brought about a radical change in the mining and metallurgical industry. During the post-Independence period, GSI has embarked upon the exploration for minerals, particularly in favourable geological milieu spread over Dharwar, Bastar, Singhbhum and Aravalli cratons. The investigations carried out since 1960s provide us firsthand information of different mineral occurrences as well as their potential. Keeping in tune with the modern trends of mineral exploration, the GSI oriented its programmes through multidisciplinary surveys. From time to time it equipped itself with state-of-the-art laboratories to back up its various exploration programmes. The efforts have led to discovery of several mineral deposits in virgin areas in different parts of the country. A few other central and state government organisations were also involved in mineral exploration now and then, mostly in collaboration with foreign organisations. The liberalisation of India’s National Mineral Policy in 1993 paved the way for the entry of private entrepreneurs, including those from overseas for carrying out mineral exploration. The database developed by GSI has been found very useful for taking investment decisions by the Multi-National Companies.
DS202012-2216
2020
GeologypageNatural nanodiamonds in oceanic rocks.Geologypage.com, http://www.geologypage .com/2020/10/natural- nanodiamonds-in- oceanic-rocks.html Globalnanodiamonds

Abstract: Natural diamonds can form through low pressure and temperature geological processes on Earth, as stated in an article published in the journal Geochemical Perspectives Letters. The newfound mechanism, far from the classic view on the formation of diamonds under ultra-high pressure, is confirmed in the study, which draws on the participation of experts from the Mineral Resources Research Group of the Faculty of Earth Sciences of the University of Barcelona (UB).
DS202002-0188
2019
Ghent, E.D., Edwards, B.R., Russell, J.K.Pargasite bearing vein in spinel lherzolite from the mantle lithosphere of the North American Cordillera. Canadian Journal of Earth Sciences, Vol. 56, pp. 870-885.Canada, British Columbialherzolite

Abstract: Basanite lavas near Craven Lake, British Columbia, host a spinel lherzolite xenolith containing cross-cutting veins with pargasitic amphibole (plus minor apatite). The occurrence of vein amphibole in spinel lherzolite is singular for the Canadian Cordillera. The vein crosscuts foliated peridotite and is itself cut by the basanite host. The amphibole is pargasite, which is the most common amphibole composition in mantle peridotite. Rare earth element concentrations in the pargasite are similar to those for mafic alkaline rocks across the northern Cordilleran volcanic province (light rare earth elements ~50× chondrite and heavy rare earth elements ~5× chondrite). Two-pyroxene geothermometry suggests that the vein and host peridotite were thermally equilibrated prior to sampling by the basanite magma. Calculated temperature conditions for the sample, assuming equilibration along a model steady-state geotherm, are between 990 and 1050 °C and correspond to a pressure of 0.15 GPa (~52 ± 2 km depth). These conditions are consistent with the stability limits of mantle pargasite in the presence of a fluid having XH2O < ~0.1. The pargasite vein and associated apatite provide direct evidence for postaccretion fracture infiltration of CO2-F-H2O-bearing silicate fluids into the Cordilleran mantle lithosphere. Pargasite with low aH2O is in equilibrium with parts per million concentrations of H2O in mantle olivine, potentially lowering the mechanical strength of the lithospheric mantle underlying the Cordillera and making it more susceptible to processes such as lithospheric delamination. Remelting of Cordilleran mantle lithosphere containing amphibole veins may be involved in the formation of sporadic nephelinite found in the Canadian Cordillera.
DS202004-0515
2020
Gibson, S.A., Rooks, E.E., Day, J.A., Petrone, C.M., Leat, P.T.The role of sub-continental mantle as both "sink" and "source" in deep Earth volatile cycles.Geochimica et Cosmochimica Acta, Vol. 275, pp. 140-162.Mantlecraton

Abstract: The extent to which Earth’s sub-continental lithospheric mantle modulates the flux of volatile elements from our planet’s deep interior to its atmosphere (via volcanism) is poorly constrained. Here, we focus on "off-craton" sub-continental lithospheric mantle because this long-lived reservoir potentially acts as both a volatile “sink” and “source” during major heating and rifting events. The sub-continental lithospheric mantle is primarily formed of peridotites with subordinate amounts of pyroxenites. While both lithologies are dominated by nominally-volatile-free mantle minerals, some of these phases have been shown to contain non-negligible amounts of H2O (e.g. 100’s of ppmw in clinopyroxene). Data for volatile elements other than Li are, however, limited. We present new, high-precision, in-situ Secondary Ion Mass Spectrometry analyses of H, F, Cl, Li and B in olivine and pyroxenes from well-characterised garnet- and spinel-bearing peridotites and pyroxenites (from southern Patagonia and the Antarctic Peninsula). Our study confirms that clinopyroxene is the main host of H2O and F. The maximum F contents we report (up to 154 ppmw) are higher than those in previous studies and occur in Ti-Cr diopsides in highly-metasomatised peridotites and Ti-Al augites from clinopyroxenite veins. Water contents of clinopyroxenes (up to 615 ppmw) are within the range previously published for continental mantle. Lithium concentrations are low (<5 ppmw) in all analysed phases and both Cl and B are below detection levels (14 ppmw and 0.03 ppmw, respectively). Unique to our study is the large variation in major- and trace-element concentrations of the clinopyroxenes, which allows us to place quantitative constraints on how volatiles are stored in the mantle. We demonstrate that: (i) F contents of clinopyroxenes closely correlate with Ti and (ii) and is systematic and inversely correlated with temperature. Despite the redistribution of volatiles during sub-solidus re-equilibration, we show that the first order control on the concentration of volatiles in clinopyroxene is the style of metasomatism, i.e. channellised flow versus reactive percolation. The mean bulk volatile contents of peridotites from Pali Aike and the Antarctic Peninsula (H2O?=?89?±?31 ppmw, F?=?16?±?11.2 ppmw and Li?=?2?±?0.7 ppmw) are within the range previously published for continental "off-craton" mantle. The pyroxenites have significantly higher mean bulk concentrations of H2O (260?±?59 ppmw), F (86?±?43 ppmw) and Li (1.0?±?0.35 ppmw). While the greater capacity of mantle pyroxenites to host H2O relative to the associated peridotites has previously been observed in global "off-craton" mantle xenolith suites (e.g. Oahu, Hawaii; eastern China and the Rio Grande Rift, SW USA), here we show for the first time that pyroxenites are also major hosts of F (but not Cl, Li or B). Because of their relatively low solidus temperatures, pyroxenites in "off-craton" settings will be readily re-mobilised during lithospheric extension (and heating). We suggest these pyroxene-rich mantle lithologies may be responsible for the elevated concentrations of H2O and F observed in basalts and volcanic gasses from major continental rift zones and flood basalt provinces, and hence an important consideration in models of global volatile cycles.
DS202004-0516
2020
Giovannini, A.L., Mitchell, R.H., Bastos Neto, A.C., Moura, C.A.V., Pereira, V.P., Porto, C.G.Mineralogy and geochemistry of the Morro dos Seis Lagos siderite carbonatite, Amazonas, Brazil.Lithos, vol. 360-361, 105433 20p. PdfSouth America, Brazil, Amazonascarbonatite

Abstract: The Morro dos Seis Lagos niobium rare earth element, Ti-bearing lateritic deposit (Amazonas, Brazil) is derived from a primary siderite carbonatite. The complex is the only example of a Nb deposit in which Nb-rich rutile is the main Nb ore mineral. Apart from the laterites, at the current level of exposure the complex consists only of siderite carbonatite; silicate rocks are absent. Three types of siderite carbonatite are recognized: (1) a brecciated and oxidized core siderite carbonatite consisting of up to 95 vol% siderite together with: hematite; pyrochlore; Nb-brookite; Ti-maghemite; and thorobastnäsite; (2) a REE- and P-rich variety of the core siderite carbonatite consisting of siderite (up to 95 vol%), hematite, minor pyrochlore, monazite and bastnäsite; (3) a border hydrothermal siderite carbonatite with ~70 vol% siderite, barite (~15 vol%), gorceixite (~7 vol%) and minor rhabdophane and pyrochlore. The country rock gneiss in which the carbonatite was emplaced was affected by potassic fenitization, with the formation of phlogopite and orthoclase together with monazite, fluorapatite and bastnäsite. The siderite carbonatites exhibit a wide variation of d13C (-5.39‰ to -1.40‰), accompanied by a significant variation in d18O (17.13‰ to 31.33‰), especially in the REE-rich core siderite carbonatite, and are explained as due to the presence of both H2O and CO2 in the magma. The core siderite carbonatite is the richest in Fe (48.64-70.85 wt% Fe2O3) and the poorest in Ca (up 0.82 wt% CaO) example of a siderite carbonatite yet recognized The ferrocarbonatite has significant contents of Mn, Ba, Th, Pb and LREE, and a very high Nb (up to 7667 ppm) content due to the presence of Nb-brookite. The substitution 3Ti4+ = Fe2+ + 2Nb5+ recognized in Nb-rich brookite explains enrichment of Nb in the core siderite carbonatite and indicates formation in a reducing environment. The high Nb/Ta ratio (1408-11,459) of the carbonatite is compatible with residual liquids derived by fractional crystallization. The 87Sr/86Sr (0.70411-0.70573) and 144Nd/143Nd (0.512663-0.512715) isotopic data suggest the carbonatite is mantle-derived with essentially no crustal contamination and is younger than the maximum age of 1328 ± 58 Ma (UPb in zircon). We suggest that the Morro dos Seis Lagos carbonatite complex represents the upper-most parts of a differentiated carbonatite magmatic system, and that the siderite carbonatite is related to late-magmatic-to-carbo-hydrothermal processes.
DS202008-1393
2020
Giuliani, A., Jackson, M.G., Fitzpayne, A.The role of FOZO-PREMA in kimberlite genesis. Goldschmidt 2020, 1p. AbstractMantlekimberlite

Abstract: FOZO-PREMA is an ubiquitous component of oceanic basalts and was originally defined by the convergence of Sr- Nd-Pb isotope trends of ocean island basalts (OIBs) from individual island-seamount chains [1]. FOZO-PREMA is also widespread in juvenile continental magmas, which argue for a global relevance of this component irrespective of the tectonic settings. Early studies proposed that FOZO-PREMA could be a physically discrete reservoir derived from depletion of primitive mantle based on the combination of geochemically depleted 143Nd/144Nd combined with elevated 3He/4He ratios [2]. Conversely, later models showed that isotopic compositions spanning the FOZO-PREMA field can be obtained by mixing recycled oceanic crust and mantle material previously depleted by crust extraction [3]. Kimberlites can provide a new perspective on this debate because a recent study of the Nd and Hf isotope compositions of kimberlite through time shows that these magmas sample a deep, long-lived, homogeneous reservoir, which might contain remnants of early Earth differentiation processes [4]. We critically review the Sr, Nd and Hf isotope compositions of kimberlites that were emplaced from ~2.1 Ga. After screening kimberlite isotopic data for the effects of lithospheric contamination and secondary alteration, we show that kimberlites through time have been derived from a mantle source with FOZO-PREMA composition. This observation makes it unlikely that FOZO-PREMA derives from continuous mixing of depleted and recycled components because the composition of subducted lithologies, pressure and temperature conditions in subduction zones, and temperature and oxygen fugacity conditions of the convective mantle have changed throughout Earth history. We therefore conclude that FOZO-PREMA is a long-lived component of Earth’s mantle, which must have existed for at least the last 2.1 Ga, the wider implications of which will be discussed.
DS202007-1142
2020
Giuliani, A., Pearson, D.G., Soltys, A., Dalton, H., Phillips, D., Foley, S.F., Lim, E.Kimberlite genesis from a common primary melt modified by lithospheric mantle assimilation.Science Advances, Vol. 6, eeaz0424Mantlemelting

Abstract: Quantifying the compositional evolution of mantle-derived melts from source to surface is fundamental for constraining the nature of primary melts and deep Earth composition. Despite abundant evidence for interaction between carbonate-rich melts, including diamondiferous kimberlites, and mantle wall rocks en route to surface, the effects of this interaction on melt compositions are poorly constrained. Here, we demonstrate a robust linear correlation between the Mg/Si ratios of kimberlites and their entrained mantle components and between Mg/Fe ratios of mantle-derived olivine cores and magmatic olivine rims in kimberlites worldwide. Combined with numerical modeling, these findings indicate that kimberlite melts with highly variable composition were broadly similar before lithosphere assimilation. This implies that kimberlites worldwide originated by partial melting of compositionally similar convective mantle sources under comparable physical conditions. We conclude that mantle assimilation markedly alters the major element composition of carbonate-rich melts and is a major process in the evolution of mantle-derived magmas.
DS202003-0340
2019
Giuliani, G., Groat, L.A.Geology of corundum and emerald gem deposits: a review.Gems & Gemology, Vol. 55, 4, pp. 464-511.Africa, Madagascar, Zambia, Asia, Sri Lanka, South America, Colombiaemerald

Abstract: The great challenge of geographic origin determination is to connect the properties and features of individual gems to the geology of their deposits. Similar geologic environments can produce gems with similar gemological properties, making it difficult to find unique identifiers. Over the last two decades, our knowledge of corundum and emerald deposit formation has improved significantly. The mineral deposits are classically separated into primary and secondary deposits. Primary corundum deposits are subdivided into two types based on their geological environment of formation: (1) magmatic and (2) metamorphic. Magmatic deposits include gem corundum in alkali basalts as in eastern Australia, and sapphire in lamprophyre and syenite as in Montana (United States) and Garba Tula (Kenya), respectively. Metamorphic deposits are divided into two subtypes (1) metamorphic deposits sensu stricto (in marble; mafic and ultramafic rocks, or M-UMR), and (2) metamorphic-metasomatic deposits characterized by high fluid-rock interaction and metasomatism (i.e., plumasite or desilicated pegmatites in M-UMR and marble, skarn deposits, and shear zonerelated deposits in different substrata, mainly corundum-bearing Mg-Cr-biotite schist). Examples of the first subtype include the ruby deposits in marble from the Mogok Stone Tract or those in M-UMR from Montepuez (Mozambique) and Aappaluttoq (Greenland). The second subtype concerns the sapphire from Kashmir hosted by plumasites in M-UMR. Secondary corundum deposits (i.e., present-day placers) result from the erosion of primary corundum deposits. Here, corundum is found in the following types of deposits: eluvial (derived by in situ weathering or weathering plus gravitational movement), diluvial (scree or talus), colluvial (deposited at the base of slopes by rainwash, sheetwash, slow continuous downslope creep, or a combination of these processes), and alluvial (deposited by rivers). Today, most sapphires are produced from gem placers related to alkali basalts, as in eastern Australia or southern Vietnam, while placers in metamorphic environments, such as in Sri Lanka (Ratnapura, Elahera) and Madagascar (Ilakaka), produce the highest-quality sapphires. The colluvial Montepuez deposit in Mozambique provides a huge and stable supply of clean and very high-quality rubies. Primary emerald deposits are subdivided into two types based on their geological environment of formation: (1) tectonic-magmatic-related (Type I) and (2) tectonic-metamorphic-related (Type II). Several subtypes are defined and especially Type IA, hosted in M-UMR, which accounts for about 70% of worldwide production (Brazil, Zambia, Russia, and others). It is characterized by the intrusion of pegmatites or quartz veins in M-UMR accompanied by huge hydrothermal fluid circulation and metasomatism with the formation of emerald-bearing desilicated pegmatite (plumasite) and biotite schist. Type IB in sedimentary rocks (China, Canada, Norway, Kazakhstan, and Australia) and Type IC in granitic rocks (Nigeria) are of minor importance. The subtype Type IIA of metamorphic deposits is related to hydrothermal fluid circulation at high temperature, in thrust fault and/or shear zones within M-UMR of volcano-sedimentary series, such as at the Santa Terezinha de Goiás deposit in Brazil. The subtype Type IIB is showcased by the Colombian emerald deposits located in the Lower Cretaceous black shales of the Eastern Cordillera Basin. These are related to the circulation of hydrothermal basinal fluids in black shales, at 300330°C, that dissolved evaporites in (1) thrust and tear faults for the deposits of the western emerald zone (Yacopi, Coscuez, Muzo, Peñas Blancas, Cunas, and La Pita mines) and (2) a regional evaporite level intercalated in the black shales or the deposits of the eastern emerald zone (Gachalá, Chivor, and Macanal mining districts). Secondary emerald deposits are unknown because emerald is too fragile to survive erosion and transport in rivers.
DS202007-1143
2020
Gladkochub, D.P., Donskaya, T.V.Geochemical composition of dolerites as an indicator of the distance of a dike swarm from the mantle plume center ( case study of Proterozoic dike swarms, Siberian craton).Doklady Earth Sciences, Vol. 491, pp. 243-246.Russia, Siberiadyke

Abstract: Based on investigation of Proterozoic mafic dike swarms of the Siberian Craton, we inferred how the geochemical and isotopic characteristics of dike swarms of dolerites of Large Igneous Provinces depend on their distance from the mantle plume head. It has been found that the dolerite parent melts near the mantle plume head correspond to OIB compositions. At significant distances from the plume, the initial melts of dolerites are generated in the subcontinental lithospheric mantle, which provides a wide range of their compositions differing from typical OIB and do not indicate directly the genetic relationship of these mafic rocks with the mantle plume.
DS202008-1394
2020
Goes, S., Hasterok, D., Schutt, D.L., Klocking, M.Continental lithospheric temperatures: a review.Physics of the Earth and Planetary Interiors, Vol. 306, 106509, 18p. PdfMantlegeothermometry

Abstract: Thermal structure of the lithosphere exerts a primary control on its strength and density and thereby its dynamic evolution as the outer thermal and mechanic boundary layer of the convecting mantle. This contribution focuses on continental lithosphere. We review constraints on thermal conductivity and heat production, geophysical and geochemical/petrological constraints on thermal structure of the continental lithosphere, as well as steady-state and non-steady state 1D thermal models and their applicability. Commonly used geotherm families that assume that crustal heat production contributes an approximately constant fraction of 25-40% to surface heat flow reproduce the global spread of temperatures and thermal thicknesses of the lithosphere below continents. However, we find that global variations in seismic thickness of continental lithosphere and seismically estimated variations in Moho temperature below the US are more compatible with models where upper crustal heat production is 2-3 times higher than lower crustal heat production (consistent with rock estimates) and the contribution of effective crustal heat production to thermal structure (i.e. estimated by describing thermal structure with steady-state geotherms) varies systematically from 40 to 60% in tectonically stable low surface heat flow regions to 20% or lower in higher heat flow tectonically active regions. The low effective heat production in tectonically active regions is likely partly the expression of a non-steady thermal state and advective heat transport.
DS202001-0013
2019
Goldie, R.Approximation of Tiffany & Co. seasonally - adjusted, quarterly sales per store ( sales x $ 000). Raymondgoldie @outlook.com, Dec. 6, 1p. GraphGlobalTiffany
DS202008-1395
2019
Golovin, A.V., Sharygin, I., Korsakov, A.V., Abersteiner, A.Can primitive kimberlitic melts be alkali-carbonate liquids: composition of the melt snapshots preserved in deepest mantle xenoliths.Journal of Raman Spectroscopy, doi.org/10.1002/jrs.5701 19p pdfRussiadeposit - Udachnaya-East

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.
DS202008-1396
2020
Gonzales-Jiminez, J.M., Tassara, S., Schettino, E., Roque-Rosell, J., Farre-de-Pablo, J., Saunders, J.E., Deditius, A.P., Colas, V., Rovira-Medina, J.J., Guadalupe Davalos, M., Schilling, M., Jiminez-Franco, A., Marchesi, C., Nieto, F., Proenza, J.A., GerMineralogy of the HSE in the subcontinental lithospheric mantle - an interpretive review.Lithos, in press available, 44p. PdfMantleHSE

Abstract: The highly siderophile elements (HSE: Os, Ir, Ru, Rh, Pt, Pd, Re, Au) exist in solid solution in accessory base-metal sulfides (BMS) as well as nano-to-micron scale minerals in rocks of the subcontinental lithospheric mantle (SCLM). The latter include platinum-group minerals (PGM) and gold minerals, which may vary widely in morphology, composition and distribution. The PGM form isolated grains often associated with larger BMS hosted in residual olivine, located at interstices in between peridotite-forming minerals or more commonly in association with metasomatic minerals (pyroxenes, carbonates, phosphates) and silicate glasses in some peridotite xenoliths. The PGM found inside residual olivine are mainly Os-, Ir- and Ru-rich sulfides and alloys. In contrast, those associated with metasomatic minerals or silicate glasses of peridotite xenoliths consist of Pt, Pd, and Rh bonded with semimetals like As, Te, Bi, and Sn. Nanoscale observations on natural samples along with the results of recent experiments indicate that nucleation of PGM is mainly related with the uptake of HSE by nanoparticles, nanominerals or nanomelts at high temperature (> 900?°C) in both silicate and/or sulfide melts, regardless of the residual or metasomatic origin of their host minerals. A similar interpretation can be assumed for gold minerals. Our observations highlight that nanoscale processes play an important role on the ore-forming potential of primitive mantle-derived magmas parental to magmatic-hydrothermal deposits enriched in noble metals. The metal inventory in these magmas could be related with the physical incorporation of HSE-bearing nanoparticles or nanomelts during processes of partial melting of mantle peridotite and melt migration from the mantle to overlying continental crust.
DS202010-1845
2020
Gordeychik, B., Churikova, T., Shea, T., Kronz, A,m Simakin, A., Worner, G.Fo and Ni relations in olivine differentiate between crystallization and diffusion trends.Journal of Petrology, 10.1093/petrology/egaa083Mantleolivine

Abstract: Nickel is a strongly compatible element in olivine, and thus fractional crystallization of olivine typically results in a concave-up trend on a Fo-Ni diagram. "Ni-enriched" olivine compositions are considered those that fall above such a crystallization trend. To explain Ni-enriched olivine crystals, we develop a set of theoretical and computational models to describe how primitive olivine phenocrysts from a parent (high-Mg, high-Ni) basalt re-equilibrate with an evolved (low-Mg, low-Ni) melt through diffusion. These models describe the progressive loss of Fo and Ni in olivine cores during protracted diffusion for various crystal shapes and different relative diffusivities for Ni and Fe-Mg. In the case when the diffusivity of Ni is lower than that for Fe-Mg interdiffusion, then olivine phenocrysts affected by protracted diffusion form a concave-down trend that contrasts with the concave-up crystallization trend. Models for different simple geometries show that the concavity of the diffusion trend does not depend on the size of the crystals and only weakly depends on their shape. We also find that the effect of diffusion anisotropy on trend concavity is in the same magnitude as the effect of crystal shape. Thus, both diffusion anisotropy and crystal shape do not significantly change the concave-down diffusion trend. Three-dimensional numerical diffusion models using a range of more complex, realistic olivine morphologies with anisotropy corroborate this conclusion. Thus, the curvature of the concave-down diffusion trend is mainly determined by the ratio of Ni and Fe-Mg diffusion coefficients. The initial and final points of the diffusion trend are in turn determined by the compositional contrast between mafic and more evolved melts that have mixed to cause disequilibrium between olivine cores and surrounding melt. We present several examples of measurements on olivine from arc basalts from Kamchatka, and several published olivine datasets from mafic magmas from non-subduction settings (lamproites and kimberlites) that are consistent with diffusion-controlled Fo-Ni behaviour. In each case the ratio of Ni and Fe-Mg diffusion coefficients is indicated to be?
DS202010-1846
2020
Gorojovsky, L., Alard, O.Optimization of laser and mass spectrometer parameters for the in situ analysis of Rb/Sr ratios by LA-ICP-MS/MS. ( mentions Monastery phlogopite megacrystJournal of Analytical Atomic Spectrometry, 10.1039/DOJA00308E 15p. PdfGlobalgeochronology

Abstract: The Rb-Sr isotopic system is widely used in geochronology. Conventionally burdened by the isobaric overlap of 87Rb and 87Sr, Rb/Sr dating in situ has only recently become achievable with the newly developed LA-ICP-MS/MS system. Simultaneous use of reactive gas (e.g. O2, N2O, or CH3F) during LA-ICP-MS/MS analysis has been shown to resolve the Rb and Sr overlap, thus now making available key spatial and temporal information that can only be accessed via in situ analytical techniques. The accuracy and precision of Rb/Sr ratios and ages are largely dependent on the laser and ICP-MS/MS parameters used. Rb/Sr isotopic analysis by LA-ICP-MS/MS is a recently developed technique and these parameters are yet to be fully explored. We investigate the effects of laser wavelength (213 nm and 193 nm), laser frequency (5 Hz and 10 Hz), laser carrier gas (He, H2, and N2), dwell time, and external standard calibration on the accuracy and precision of 87Rb/86Sr and 87Sr/86Sr ratios and ages. These analytical conditions have been tested on the commercially available reference materials: NIST SRM 610, USGS BHVO-2G, and pressed nano-particulate powder tablet CRPG Mica-mg, as well as a Monastery phlogopite megacryst. Our results show that accuracy and precision for 87Rb/86Sr and 87Sr/86Sr ratios are significantly affected by laser wavelength and frequency. Variation in these parameters can strongly magnify any matrix effects which directly influences the ability to apply effective external corrections. We obtain the best accuracy and precision when using a 193 nm laser wavelength, ablating at a frequency of 5 Hz (0.30 2s% and 0.15 2s% for 87Rb/86Sr and 87Sr/86Sr ratios, respectively). Meanwhile we find that age accuracy is highly dependant on external reference materials. When these analytical settings are put to test on the Monastery phlogopite, we obtain an age of 90.0 ± 3.6 (0.24% accuracy) when using mica-mg (87Rb/86Sr) and NIST 610 (87Sr/86Sr) as external standards.
DS202002-0189
2019
Goss, H.The shape of the world.EOS, 100, Dec. 31, http://doi.org/ 10.1029/2019EO138179Mantlegeodynamics
DS202008-1397
2020
Goss, H.A dive into the deep Earth.Eos, 101, doi.org/10.1029 /2020EO145467 1p. Mantlemineralogy

Abstract: In July, Eos looks at the incredible capabilities scientists have developed to recreate the enormous pressures and temperatures that exist far below the planet’s surface.
DS202005-0734
2020
Gramling, C.Plate tectonics may have started 400 million years earlier than we thought. sciencemag.org, April 22, 3p.AustraliaTectonics

Abstract: Modern plate tectonics may have gotten under way as early as 3.2 billion years ago, about 400 million years earlier than scientists thought. That, in turn, suggests that the movement of large pieces of Earth’s crust could have played a role in making the planet more hospitable to life. Geologist Alec Brenner of Harvard University and his colleagues measured the magnetic orientations of iron-bearing minerals in the Honeyeater Basalt, a layer of rock that formed between 3.19 billion and 3.18 billion years ago. The basalt is part of the East Pilbara Craton, an ancient bit of continent in Western Australia that includes rocks as old as 3.5 billion years. This craton, the researchers found, was on the move between 3.35 billion and 3.18 billion years ago, drifting around the planet at a rate of at least 2.5 centimeters per year. That’s a speed comparable to modern plate motions, the team reports April 22 in Science Advances.
DS202008-1398
2020
Greene, S., Jacob, D.E., O'Reilly, S.Y., Henry, H., Pinter, Z., Heaman, L.Extensive prekimberlitic lithosphere modification recorded in Jericho mantle xenoliths in kimberlites, Slave Craton.Goldschmidt 2020, 1p. AbstractCanada, Northwest Territoriesdeposit - Jericho

Abstract: Wehrlite and pyroxenite xenoliths and megacrysts from the Jericho kimberlite were analyzed by µXRF and EBSD, and for major elements, trace elements, and isotopes (Pb-Sr- O) in major phases. Thermobarometry places these samples at 60 - 180 km and 600 - 1200 ??C. While modes and textures vary, many samples have olivine-olivine grain boundaries with straight edges and 120° angle junctions, indicating granoblastic recrystallisation, while clinopyroxene and orthopyroxene are complexly intergrown. Clinopyroxene twins and subgrains recording orientations distinct from the encapsulating grain were detected using EBSD and are inferred to represent recent modification processes. Several distinct garnet compositions were measured, with multiple thin garnet rims in some samples suggesting possible successive stages of garnet crystallisation. Complex chromium zoning in garnet is detected by µXRF in several samples (fig.1). Pb-Pb ages for most samples are similar to the age of kimberlite entrainment (173 Ma), but the shallowest pyroxenite sample preserves the most radiogenic Pb composition, intercecting concordia at 0.7 - 1.1 Ga, and is the only sample with d18O above the mantle range (6.2±0.1 ‰). The deepest sample has the lowest d18O (5.5±0.1 ‰) and radiogenic 87Sr/86Sr similar to MARID rocks (0.709±1 ‰). These results suggest the Jericho lithosphere experienced several melt/fluid injection events that modified substantial portions of the sampled section soon before kimberlite entrainment.
DS202011-2039
2020
Gress, M.U., Koorneef, J.M., Thomassot, E., Chinn, I.L., van Zuilen, K., Davies, G.R.Sm-Nd isochron ages coupled with C-N isotope data of eclogitic diamonds from Jwaneng, Botswana.Geochimica et Cosmochimica Acta, 10.1016/j.gca.2020.10.010 35p. PdfAfrica, Botswanadeposit - Jwaneng

Abstract: Constraining the formation age of individual diamonds from incorporated mineral inclusions and assessing the host diamonds’ geochemical characteristics allows determination of the complex history of diamond growth in the sub-continental lithospheric mantle (SCLM). It also provides the rare opportunity to study the evolution of the deep cycling of volatiles over time. To achieve these aims, Sm-Nd isotope systematics are presented for 36 eclogitic garnet and clinopyroxene inclusions from 16 diamonds from the Jwaneng mine, Botswana. The inclusions and host diamonds comprise at least two compositional suites that record different ‘mechanisms’ of diamond formation and define two isochrons, one Paleoproterozoic (1.8 Ga) and one Neoproterozoic (0.85 Ga). There are indications of at least three additional diamond-forming events whose ages currently cannot be well constrained. The Paleoproterozoic diamond suite formed by large-scale (> 100’s km), volatile-rich metasomatism related to formation and re-working of the Proto-Kalahari Craton. In contrast, the heterogeneous composition of the Neoproterozoic diamond suite indicates diamond formation on a small-scale, through local (< 10 km) equilibration of compositionally variable diamond-forming fluids in different eclogitic substrates during the progressive breakup of the Rodinia supercontinent. The results demonstrate that regional events appear to reflect the input of volatiles (i.e., carbon-bearing) derived from the asthenospheric mantle, whereas local diamond-forming events mainly promote the redistribution of volatiles within the SCLM. The occurrence of isotopically light carbon analysed in distinct growth zones from samples of this study (d13C < -21.1‰) provides further indication of a recycled origin for surface-derived carbon in some diamonds from Jwaneng. Determining Earth’s long-term deep carbon cycle using diamonds, however, requires an understanding of the nature and scale of specific diamond-forming events.
DS202012-2217
2020
Griffin, W.L., Gain, S.E.M., Saunders, M., Bindi, L., Alard, O., Toledo, V., O'Reilly, S.Y.Parageneses of TiB2 in corundum xenoliths from Mt. Carmel, Israel: siderophile behavior of boron under reducing conditions.American Mineralogist, Vol. 105, pp. 1609-1621. pdfEurope, Israeldeposit - Mt. Carmel

Abstract: Titanium diboride (TiB2) is a minor but common phase in melt pockets trapped in the corundum aggregates that occur as xenoliths in Cretaceous basaltic volcanoes on Mt. Carmel, north Israel. These melt pockets show extensive textural evidence of immiscibility between metallic (Fe-Ti-C-Si) melts, Ca-Al-Mg-Si-O melts, and Ti-(oxy)nitride melts. The metallic melts commonly form spherules in the coexisting oxide glass. Most of the observed TiB2 crystallized from the Fe-Ti-C silicide melts and a smaller proportion from the oxide melts. The parageneses in the melt pockets of the xenoliths require fO2 = ?IW-6, probably generated through interaction between evolved silicate melts and mantle-derived CH4+H2 fluids near the crust-mantle boundary. Under these highly reducing conditions boron, like carbon and nitrogen, behaved mainly as a siderophile element during the separation of immiscible metallic and oxide melts. These parageneses have implications for the residence of boron in the peridotitic mantle and for the occurrence of TiB2 in other less well-constrained environments such as ophiolitic chromitites.
DS202001-0014
2019
Groat, L.A.Adding logic to luck: recent advances in coloured stone exploration in Canada.Journal of Gemmology, Vol. 36, pp. 620-633.Canadagemstones
DS202003-0341
2019
Groat, L.A., Giuilani, G.,, Stone-Sundberg, J., Sun, Z., Renfro, N.D., Palke, A.C.A review of analytical methods used in geographic origin determination of gemstones.Gems & Gemology, Vol. 55, 4, pp. 512-535.Globalemerald, sapphire

Abstract: Origin determination is of increasing importance in the gem trade. It is possible because there is a close relationship between the geological environment of formation and the physical and chemical properties of gemstones, such as trace element and isotopic compositions, that can be measured in the laboratory using combinations of increasingly sophisticated instrumentation. Origin conclusions for ruby, sapphire, and emerald make up the bulk of demand for these services, with growing demand for alexandrite, tourmaline, and spinel. However, establishing origin with a high degree of confidence using the capabilities available today is met with varying degrees of success. Geographic origin can be determined with a high level of confidence for materials such as emerald, Paraíba-type tourmaline, alexandrite, and many rubies. For some materials, especially blue sapphire and some rubies, the situation is more difficult. The main problem is that if the geology of two deposits is similar, then the properties of the gemstones they produce will also be similar, to the point where concluding an origin becomes seemingly impossible in some cases. Origin determination currently relies on a combination of traditional gemological observations and advanced analytical instrumentation.
DS202002-0190
2020
Grocholski, B.Synthesizing single-layer diamond: Carbon allotropes of diamond and graphene.Science, Vol. 367, 6476, p. 402.Globalcarbon

Abstract: The carbon allotropes of diamond and graphene have different types of bonding that lead to their exceptional properties. Bakharev et al. pull off the impressive trick of making a monolayer carbon film that is diamond-like in its bonding. The authors accomplish this by attaching fluorine atoms to the carbon film, creating “F-diamane.” Diamane is a long-sought-after, but challenging to make, material that should have useful properties. F-diamane may find use in a variety of applications, from microelectronics as a semiconductor to a seed material for growing single-crystal diamond films.
DS202009-1629
2020
Groves, D.I., Santosh, M.Craton and thick lithosphere margins: the sites of giant mineral deposits and mineral provinces. Not specific to diamonds.Gondwana Research, in press available 28p. PdfGlobalgeodynamics
DS202004-0517
2019
Gruber, B.H.Temperatures and heat production in the Slave Craton lower crust: evidence from exnoliths in the Diavik A-154 kimberlite.Thesis MSc University of Alberta , 123p. Pdf Canada, Northwest Territoriesdeposit - Diavik A-154

Abstract: Lower crustal heat production is poorly constrained due to the relative inaccessibility of lower crustal samples and their inherent complexity. To obtain the requisite information, the current project conducts spatially resolved geochemical analyses on minerals in 15 lower crustal xenoliths erupted via the Diavik A-154 kimberlite of the Northwest Territories, Canada. The aims are to: 1) conduct geothermometric measurements on lower crustal minerals, 2) construct a heatproducing element budget of the lower crust of the Slave craton, and 3) test the validity of these measurements in a parameter space relevant to geodynamic modeling and diamond exploration. The Diavik lower crustal xenolith suite comprises two main lithologies, mafic granulite (garnet-plagioclase-clinopyroxene ± orthopyroxene) and metasedimentary granulite (garnetplagioclase- orthopyroxene ± quartz ± K-feldspar ± kyanite), which are present in proportions of approximately 80:20, respectively. Application of mineral-pair, iron-magnesium exchange geothermometers (garnet-biotite, garnet-amphibole, and garnet-clinopyroxene) to these xenoliths indicates that the lower crust was at a maximum temperature of roughly 500 °C at the time of kimberlite eruption (~ 55 Ma). The actual temperature of the lower crust is likely lower than 500 °C as the geothermometers probably record the closure temperature of diffusional Fe2+-Mg exchange between touching mineral pairs rather than the ambient temperature of the rocks prior to their entrainment in the kimberlite magma. Heat-producing element (HPE) concentration measurements show that the lower crustal heat production of the Slave craton is likely 0.14 ± 0.02 µW/m3, which is lower than most values in the literature but broadly comparable to some geophysical estimates. This estimate is the result of (20:80) bimodal mixing of idealized lower crustal endmembers: a metasedimentary lower crust (0.37 ± 0.06 µW/m3) and a mafic lower crust (0.08 ± 0.01 µW/m3). These endmembers were iii calculated via a reconstructed bulk rock calculation utilizing trace element concentrations of constituent lower crustal minerals and idealized lithologies from the lower crustal xenoliths. Using these heat production estimates and other crustal parameters such as continental heat flux, mantle heat flux, crustal thickness, and crustal thermal conductivity, I modeled a Moho temperature for the Slave craton of 425 °C, which is consistent with maximum lower crustal temperature estimate given by geothermometry. Adjusting the lower crustal heat production in the geotherm modeling program FITPLOT changes the temperature of the Moho in a similar fashion to the calculated models; however, the diamond propensity of the mantle lithosphere (partially a function of Moho temperature and heat production) does not appear to be strongly affected by a changing Moho temperature and is more strongly controlled by the conditions of the mantle P-T array.
DS202005-0735
2020
Gryaznov, I.A., Zhimulev, E.I., Sonin, V.M., Lindenblot, E.S., Chepurov, A.A.Morphological features of diamond crystals resulting from dissolution in a Fe-Ni-S melt under high pressure.Doklady Earth Sciences, Vol. 489, 2, pp. 1449-1452 .pdfRussiadiamond morphology, CLIPPIR

Abstract: The primary results are presented on the dissolution of plane-faced diamond crystals of octahedral habit in a Fe-Ni-S melt under 3.5 GPa and 1400°C. It was found that the dissolution resulted in the transformation of plane-faced into curve-faced individuals of morphological features characteristic for kimberlite diamonds. It was concluded that the diamond forms as such might have formed in reduced domains of the Earth’s mantle before becoming involved in the kimberlite magma.
DS202002-0191
2019
Guice, G.L.Origin and geodynamic significance of ultramafic- mafic complexes in the North Atlantic and Kaapvaal cratons.Thesis, Phd Cardiff University, 315p. PdfEurope, Africa, South Africacraton
DS202008-1399
2020
Gukurume, S., Nhodo, L.Forced displacements in mining communities: politics in Chiadzwa diamond area, Zimbabwe.Journal of Contemporary African Studies, Vol. 38, 1, pp. 39-54.Africa, Zimbabwedeposit - Chiadzwa

Abstract: The Chiadzwa diamonds attracted widespread attention due to human rights violations and illegal smuggling. When diamonds were discovered in 2006, thousands of artisanal miners descended on the diamond fields. In response, the government unleashed the army and police in brutal crackdowns to drive artisanal miners off the diamond fields. This militarisation of diamond fields and extraction was followed by forced displacement of the Chiadzwa people. This article examines the lived, everyday experiences of the displaced Chiadzwa people. Findings reveal that displacements dislocated the livelihoods and socialities of the people. Displacements also exacerbated people's vulnerability to livelihood shocks, insecurity, and poverty. In relocating people the government adopted a ‘top-down’ approach which triggered contestations and conflicts with the people who felt alienated from their ancestral land and excluded from diamond wealth. Consequently, sabotage, resistance and subversion were commonplace in the relocation process. These socio-political ‘tactics’ should be viewed as ‘weapons of the weak’.
DS202006-0921
2020
Gusev, N.I., Sergeeva, L. Yu., Larionov, A.N., Skublov, S.G.Relics of the Eoarchean continental crust of the Anabar shield, Siberian Craton.Petrology, Vol. 28, 2, pp. 118-140.Russiadeposit - Daldyn

Abstract: In the northern part of the Anabar Shield, orthopyroxene plagiogneisses of the granulite Daldyn Group host lenses of mafic rocks surrounded by melanocratic rims. According to their chemical composition, the mafic rocks correspond to subalkaline gabbro, the plagiogneisses correspond to granodiorites contaminated with mafic material, and the rims are diorites. The orthopyroxene plagiogneisses of granodiorite composition have 147Sm/144Nd = 0.1097, eNd(?) = 1.6, TNd(DM) = 3.47 Ga and are metamorphosed anatectic granitoids with an age of 3.34 Ga. The mafic rocks have high Zr, Th, and Pb contents, are enriched in REE (SREE = 636 ppm), with a high degree of fractionation [(La/Yb)N = 17.73] and a well-defined Eu minimum (Eu/Eu* = 0.51), and have 147Sm/144Nd = 0.099, eNd(?) = 1.4 and TNd(DM) = 3.65 Ga. It is assumed that these rocks crystallized from melt derived from an enriched mantle (plume) source. Based on U-Pb (SHRIMP-II) dating of 50 zircon grains from the mafic rocks, a group of grains with concordant ages from 3567 to 1939 Ma was distinguished, along with a large number of discordant values. Multiple measurements in zircon grains with discordant age values make it possible to identify seven grains of Eoarchean age, with upper intercepts of the discordia corresponding to 3987 ± 71 to 3599 ± 33 Ma. The Lu-Hf systematics of 14 zircon grains is characterized by eHf(T) = +3.7 and by close values of THf(DM) = 3.95 and TCHf = 3.93 Ga (3.99 Ga for the oldest zircon). The Paleoarchean (3.57 Ga) zircons are characterized by negative values of eHf(T) = -5.3 and -6.8, THf(DM) = 3.92-3.98 Ga, and TCHf = 4.14-4.24 Ga, which indicate recycling of the preexisting Eoarchean and Hadean continental crust. The younger zircon (3287-2410 Ma) was also formed when the preexisting crust was recycled.
DS202007-1144
2020
Haddock, D., Manya, S., Brown, R.J., Jones, T.J., Wadsworth, F.B., Dobson, K.J., Gernon, T.M.Syn-eruptive agglutination of kimberlite volcanic ash. PyroclastsVolcanica, Vol. 3, 1, pp. 169-182. PdfAfrica, Tanzaniadeposit - Igwisi Hills

Abstract: Pyroclastic deposits of the Holocene Igwisi Hills kimberlite volcanoes, Tanzania, preserve unequivocal evidence for rapid, syn-eruptive agglutination. The unusual pyroclasts are composed of ash-sized particles agglutinated to each other by thin necks. The textures suggest the magma was disrupted into droplets during ascent. Collisions between particles occurred within a volcanic plume and on deposition within the conduit to form a weakly agglutinated, porous pyroclastic deposit. Theoretical considerations indicate that agglutination occurred over short timescales. Agglutinated clasts were entrained into weak volcanic plumes and deposited around the craters. Our results support the notion that agglutination can occur during kimberlite eruptions, and that some coherent, dense rocks in ancient kimberlite pipes interpreted as intrusive rocks could instead represent agglutinated pyroclastic rocks. Differentiating between agglutinated pyroclastic rocks and effusive or intrusive rocks in kimberlite pipes is important because of the potential effects that pyroclastic processes might have on diamond concentrations in deposits.
DS202011-2040
2020
Haddock, D., Manya, S., Brown, R.J., Jones, T.J., Wadsworth, F.B., Dobson, K.J., Gernon, T.M.Syn-eruptive agglutination of kimberlite volcanic ash.Volcanica, 15p. PdfAfrica, Tanzaniadeposit - Igwisi Hills kimberlite

Abstract: Pyroclastic deposits of the Holocene Igwisi Hills kimberlite volcanoes, Tanzania, preserve unequivocal evidence for rapid, syn-eruptive agglutination. The unusual pyroclasts are composed of ash-sized particles agglutinated to each other by thin necks. The textures suggest the magma was disrupted into droplets during ascent. Collisions between particles occurred within a volcanic plume and on deposition within the conduit to form a weakly agglutinated, porous pyroclastic deposit. Theoretical considerations indicate that agglutination occurred over short timescales. Agglutinated clasts were entrained into weak volcanic plumes and deposited around the craters. Our results support the notion that agglutination can occur during kimberlite eruptions, and that some coherent, dense rocks in ancient kimberlite pipes interpreted as intrusive rocks could instead represent agglutinated pyroclastic rocks. Differentiating between agglutinated pyroclastic rocks and effusive or intrusive rocks in kimberlite pipes is important because of the potential effects that pyroclastic processes might have on diamond concentrations in deposits.
DS202012-2218
2020
Hainschwang, T., Notari, F., Pamies, G.The origin of 1330 nm center diamonds. ( hydrogen)Diamond and Related Materials, in press available, 19p. PdfGlobalspectroscopy

Abstract: This study covers hydrogen-rich fancy color diamonds that exhibit complex spectra from the UV all the way to the mid-IR. The diamonds with such spectra that are included here show a large range of colors from brownish yellow to brown, yellow-green to olive and gray to violet. The color origin of such diamonds has always been stated as “hydrogen-related”, without much evidence pointing towards hydrogen actually causing absorptions in the visible spectral range, but only based on their unusually high IR active hydrogen content determined via their FTIR spectra. The diamonds analyzed during this work always showed a series of absorptions in the near-infrared at 7495, 7850, 8255, and 8615 cm-1. For the first time, this here presented study shows the results of low temperature near-infrared spectroscopy performed for a series of differently colored diamonds that all showed these NIR absorptions. When measured at 77 K, it became clear that these NIR bands are actually part of an electronic optical center with ZPLs at 1329.8 to 1330.2 nm (7520-7518 cm-1)/1331.8 to 1332.2 nm (7508-7506 cm-1) and 1341 to 1341.2 nm (7457-7456 cm-1). In this paper we will refer to this defect as the "1330 nm center" (which corresponds to 7519 cm-1) for the sake of brevity. The detailed analysis of the spectra has demonstrated that the colors of diamonds that exhibit the 1330 nm center spectra are caused partially by this same center, and by complex absorption bands associated to two series of ZPLs represented by a number of sharp bands between 965 and 1001 nm, referred to as the 990 nm series in this study. Of these, the 990 nm series was found only in diamonds with significant IR active hydrogen concentrations, while the 1330 nm center was determined to be independent from the concentration of IR active hydrogen. The 1330 nm center was found in spectra lacking the 990 nm series of ZPLs, but the 990 nm series has never been found in spectra without the 1330 nm center. We are suggesting that the defects involved in these absorptions are all nickel-nitrogen-related, with the 1330 nm center lacking hydrogen while it seems reasonable to assume that the 990 nm series includes hydrogen in its structure.
DS202002-0192
2019
Hazarika, B., Malpe, D.B., Dongre, A.Petrology and geochemistry of a boninite dyke from the western Bastar craton of central India.Journal of Earth System Science, Vol. 128, 17p. PdfIndiaboninite

Abstract: The Dongargarh Supergroup along with the basal Amgaon Gneissic Complex constitutes the northwestern part of the central Indian Bastar craton. In the present study, we report a new finding of a boninite dyke intruded in the Amgaon gneisses of this area. The dyke composed of mainly pyroxenes, amphiboles and subordinate amount of plagioclase. The higher contents of SiO2 (51-54 wt.%), MgO (12-14 wt.%), Ni (375-473 ppm), Cr (1416-1580 ppm) and very low TiO2 (0.2-0.4 wt.%) are consistent with the boninite nature of the dyke as well as the unevolved primary nature of the source magma. The extraordinarily high CaO content (15.97-17.7 wt.%) with higher CaO/Al2O3 (3.13-3.96) ratios classifies it as high-Ca boninite. The trace element ratios including Zr/Ti, Ti/V, Ti/Sc and Ti/Yb further show its geochemical similarity with the Archaean boninite. The dyke also shows negative high-field strength element (Nb, Ta and Ti) anomalies which are the characteristics of the boninite rocks reported elsewhere and along with the enriched light rare earth element pattern, it shows more affinity particularly with the northern Bastar boninite dyke. The mineralogical and geochemical similarities of the boninite dykes from the Bastar craton indicate a widespread boninitic event during the Palaeoproterozoic having a similar origin. These boninite dykes indicate the preservation of subduction-related signatures in the lithospheric mantle beneath the Bastar craton at the time of its evolution or may be during the convergence of the Bastar and Bundelkhand cratons.
DS202003-0342
2020
Hazarika, B., Malpe, D.B., Dongre, A.Petrogenesis of mafic dykes from the western Bastar craton of central India and their relation to ourgrowth of Columbia supercontinent.Mineralogy and Petrology, in press available, 20p. PdfIndiacraton

Abstract: We report mineral compositions and bulk rock geochemistry of mafic dykes intruded in the western part of Bastar craton, comprising of Archaean Amgaon Group and Proterozoic Dongargarh Supergroup of rocks. Field relations show two distinct trends of these dykes which are almost perpendicular to each other but having similar mineralogical and geochemical characteristics. Dykes are mostly composed of pyroxenes, plagioclase and subordinate amount of amphiboles and Fe-Ti oxides (magnetite and ilmenite). These hypersthene normative basaltic dykes show tholeiitic trend and are characterised by narrow compositional variations of MgO (6.067.08 wt%), FeOt (15.0617.78 wt%), TiO2 (1.182.24 wt%), Al2O3 (11.9615.54 wt%) and low Mg# [atomic Mg/(Mg?+?Fe2+)?×?100] values in the range of 3748. Low loss on ignition (LOI) values <2 wt% and significant trends of trace elements (Nb, La, Th, Sr) with Zr indicate insignificant effects of post magmatic processes in these dykes. Smooth correlations between major oxides and MgO, among trace element ratios (Ce/La, Th/Yb, Nb/Yb) and negative Nb-Ta anomalies without positive Zr and Hf anomalies negate the crustal contamination effects. The correlations of compatible (e.g. Cr, Ni) and incompatible (e.g. Ba, Rb) elements show involvement of both fractional crystallisation and partial melting processes in their formation. Flat heavy rare earth element (HREE) pattern with low (Tb/Yb)n values reveal their genesis from a mantle source without involvement of garnet and geochemical models suggested in the present study indicate melting from spinel lherzolite mantle source. Strong geochemical similarities of present dykes with those of earlier reported Lakhna (1.46 Ga) and Bandimal (1.42 Ga) dykes of northern Bastar craton suggest a widespread mafic magmatic event across the Bastar craton during 1.421.46 Ga. Present dykes therefore represent a subduction related outgrowth of Columbia supercontinent due to the accretion of continental margins.
DS202007-1145
2020
Hecker, J.G., Marks, M.A.W., Wenzel, T., Markl, G.Halogens in amphibole and mica from mantle xenoliths: implications for the halogen distribution and halogen budget of the metasomatized continental lithosphere.American Mineralogist, Vol. 105, pp. 781-794.Mantlemetasomatism

Abstract: This study reports halogen contents (F and Cl) of amphibole and phlogopite derived from mantle xenoliths and one peridotite massif, for amphibole and phlogopite megacrysts and ultramafic magmatic cumulates (hornblendites) found in alkaline volcanic rocks from 12 localities in Europe and Africa. Amphibole and phlogopite contain more F than Cl with F/Cl ratios reaching about 160 in phlogopites and 50 in amphiboles. Phlogopites are higher in F (median of 3400 µg/g) than amphibole (median of 1000 µg/g), while median Cl contents are higher in amphibole (290 µg/g) compared to phlogopite (180 µg/g). The Cl contents and the F/Cl ratios in amphibole and phlogopite from mantle xenoliths exhibit large differences between samples of the same region, recording very large variations of halogen contents in the continental lithosphere. We suggest that the halogen content in such samples largely depends on the initial composition of percolating melts and fluids in the continental lithosphere. During reaction of these agents with peridotitic wall-rocks, Cl is preferentially retained in the fluid as it is much more incompatible compared to water and F. This desiccation effect continuously increases salinity (Cl content) and decreases the F/Cl ratio in the agent with time, causing variable Cl contents and F/Cl ratios in amphibole and phlogopite at a specific locality. Subsequent partial melting processes may then sequester and re-distribute, especially Cl among amphibole, phlogopite and melts/fluids as a result of its strong incompatibility, whereas F is much less affected as it behaves slightly compatible. The impact of even small amounts of amphibole and mica on the total halogen budget in the continental lithosphere is significant and both minerals can effectively contribute to the high halogen contents typical of alkaline melts.
DS202009-1630
2020
Hegner, E., Rajesh, S., Willbold, M., Muller, D., Joachimiski, M., Hofmann, M., Linnemann, U., Zieger, J., Pradeepkumar, A.P.Sediment derived origin of the putatative Munnar carbonatite, South India.Journal of Asian Earth Science, Vol. 200, 104432, 18p. PdfIndiadeposit - Munnar

Abstract: Metacarbonate assemblages in high-grade metamorphic terranes often pose challenges when trying to distinguish between mantle-derived carbonatite and sedimentary carbonate protoliths. We present a study of granulite-facies metacarbonate samples of the putative Munnar carbonatite described as decimeter-thick dikes and veins, and layers of a meter-thick metacarbonate and calc-silicate assemblage, respectively. Thin sections of the metacarbonate dike samples show absence of pyrochlore and ubiquitous scapolite, titanite, wollastonite, and detrital zircons are compatible with impure limestone protoliths. Nd and Sr isotope compositions indicate protoliths with Paleoproterozoic crustal residence times which contrast the mantle sources of Indian and global carbonatites. Trace-element patterns display the characteristics of upper crust, and Ce- and Y-anomalies in a number of samples suggest protolith formation under marine conditions. Carbon and oxygen isotope compositions of the metacarbonate samples interlayered with calc-silicate rocks are similar to those in marine limestone. The metacarbonate dikes, however, show mantle-like compositions which are interpreted as reflecting equilibration with mantle-derived CO2 during granulite-facies metamorphism. The dikes yielded a U-Pb zircon crystallization age of 1020 ± 70 Ma and a cross-cutting quartz syenite, thought to be cogenetic, a magmatic age of 620 ± 35 Ma; the hosting gneiss provided a magmatic age of 2452 ± 14 Ma. We conclude that the layered metacarbonate and calc-silicate rocks represent a former marine limestone and marl sequence and the metacarbonate dikes and veins small-volume melts of crust-derived carbonate-rich sediment.
DS202011-2041
2013
Henderson, B., Collins, A.S., Payne, J., Forbes, C., Saha, D.Geological and geochemistry constraining India in Columbia: the age, isotopic provenance and geochemistry of the protoliths of the Ongole Domain, southern eastern Ghats, India. *** NOTE DATEGondwana Research, in press available. 19p. PdfIndiaNuna

Abstract: The Ongole Domain in the southern Eastern Ghats Belt of India formed during the final stages of Columbia amalgamation at ca. 1600 Ma. Yet very little is known about the protolith ages, tectonic evolution or geographic affinity of the region. We present new detrital and igneous U-Pb-Hf zircon data and in-situ monazite data to further understand the tectonic evolution of this Columbia-forming orogen. Detrital zircon patterns from the metasedimentary rocks are dominated by major populations of Palaeoproterozoic grains (ca. 2460, 2320, 2260, 2200-2100, 2080-2010, 1980-1920, 1850 and 1750 Ma), and minor Archaean grains (ca. 2850, 2740, 2600 and 2550 Ma). Combined U-Pb ages and Lu-Hf zircon isotopic data suggest that the sedimentary protoliths were not sourced from the adjacent Dharwar Craton. Instead they were likely derived from East Antarctica, possibly the same source as parts of Proterozoic Australia. Magmatism occurred episodically between 1.64 and 1.57 Ga in the Ongole Domain, forming felsic orthopyroxene-bearing granitoids. Isotopically, the granitoids are evolved, producing eHf values between - 2 and - 12. The magmatism is interpreted to have been derived from the reworking of Archaean crust with only a minor juvenile input. Metamorphism between 1.68 and 1.60 Ga resulted in the partial to complete resetting of detrital zircon grains, as well as the growth of new metamorphic zircon at 1.67 and 1.63 Ga. In-situ monazite geochronology indicates metamorphism occurred between 1.68 and 1.59 Ga. The Ongole Domain is interpreted to represent part of an exotic terrane, which was transferred to proto-India in the late Palaeoproterozoic as part of a linear accretionary orogenic belt that may also have included south-west Baltica and south-eastern Laurentia. Given the isotopic, geological and geochemical similarities, the proposed exotic terrane is interpreted to be an extension of the Napier Complex, Antarctica, and may also have been connected to Proterozoic Australia (North Australian Craton and Gawler Craton).
DS202007-1146
2020
Heyn. B.H., Conrad, C.P., Tronnes, R.G.Core-mantle boundary topography and its relation to the viscosity structure of the lowermost mantle.Earth and Planetary Science Letters, Vol. 543, 116358 14p. PdfMantlemantle plumes

Abstract: Two large areas of anomalously low seismic velocities are visible in all tomographic models of the lowermost mantle. Depending on the density structure of these Large Low Shear Velocity Provinces (LLSVPs), the core-mantle boundary (CMB) will deform upwards or downwards due to isostatic and dynamic topography, the latter being sensitive to the viscosity structure of the lowermost mantle. Heterogeneities in the viscosity structure, although difficult to constrain, might be especially important if the LLSVPs are thermochemical piles with elevated intrinsic viscosity as suggested by mineral physics. Based on numerical models, we identify a short-wavelength (about 80-120 km wide, up to a few km deep) topographic depression that forms around the pile edges if the pile is more viscous than the surrounding mantle. The depression forms when a wedge of thermal boundary layer material becomes compressed against the viscous pile, and is enhanced by relative uplift of the CMB beneath the pile by plumes rising above it. The depth and asymmetry of the depression constrain the magnitude of the viscosity contrast between pile and the surrounding mantle. Furthermore, (periodic) plume initiation and pile collapse at the pile margin systematically modify the characteristic depression, with a maximum in asymmetry and depth at the time of plume initiation. Core-reflected waves or scattered energy may be used to detect this topographic signature of stiff thermochemical piles at the base of the mantle.
DS202011-2042
2020
Hilson, G.The African mining vision: a manifesto for more inclusive extractive industry-led developments.Canadian Journal of Development Studies, Vol. 41, 3, pp. 417-431. pdfAfricalegal

Abstract: This paper introduces a special section of the Canadian Journal of Development Studies, "The Africa Mining Vision: A Manifesto for More Inclusive Extractive Industry-Led Development?" Conceived by African ministers "in charge of mineral resources" with inputs and guidance from African Union Heads of State, the Africa Mining Vision (AMV) was officially launched in February 2009. The papers presented in this special section reflect critically on progress that has since been made with operationalising the AMV at the country level across Africa; the general shortcomings of the manifesto; and the challenges that must be overcome if the continent is to derive greater economic benefit from its abundant mineral wealth.
DS202005-0736
2020
Hinze, W. J,, Chandler, V.W.Reviewing the configuration and extent of the Midcontinent rift system.Precambrian Research, Vol. 342, 18p. PdfUnited States, Michigan, Ohio, Oklahomageophsyics - magnetics

Abstract: Uncertainty exists in the configuration and extent of the Midcontinent Rift System (MRS) because of deficiencies in geophysical data and limited information from outcrops and basement drill holes. Additional ambiguity is caused by misunderstanding the definition of continental rifts. Six principal problematic regions in mapping the MRS are described. Gravity and magnetic data, supported by drill hole and seismic reflection data, show that the Eastern Lake Superior rift segment of the MRS continues south from Lake Superior and connects to a much narrower rift in northern Lake Michigan. The eastern margin of this transition is ill defined because of the lack of definitive anomalies and supporting seismic and drill hole data, but is interpreted to occur near the U.S. - Canada border. The rift segment in southeastern Michigan intersects the Grenville Front and likely continues eastwards in modified form to near the boundary with Canada. Cross-cutting gravity and magnetic signatures may reflect Grenvillian overthrusts near the terminus of the MRS in Michigan. The proposed southerly extensions of both branches of the rift system into Oklahoma and Ohio are based primarily on positive gravity anomalies, but neither postulated extension appears to be associated with rifted troughs. Rather the gravity anomalies of the western branch are related to intrusive mafic rocks and those of the eastern branch are most likely related to deep crustal metamorphic rocks thrust into juxtaposition with less dense crust by Grenville orogenesis. Recent paleomagnetic investigations, in conjunction with high-resolution radiometric dating, imply that the MRS developed during the rapid southward movement of Laurentia during a quiescent period along its eastern continental margin. Massive magmatic activity accompanying the rifting was likely due to rising mantle material that was displaced by subducted lithosphere along the southern margin. The heated crust was made more ductile, fostering rifting due to extensional stresses. The Nipigon Embayment remains as a possible candidate for an early "third branch" of the MRS, but current evidence is insufficient to include the Fort Wayne "rift" as part of the MRS. Future studies of the MRS would be well-served by new age-dating and high-resolution seismic studies of the lithosphere.
DS202001-0015
2018
Hodder, T. Kelley, S.E.Kimberlite indicator minerals and clast lithology composition of till, Kaskattama region northeastern Manitoba (parts of NTS 53N, O, 54 B,C.)Manitoba Report, GS2018-13 pdf 17p. Canada, Manitobageochemistry

Abstract: Canada exhibits many of the challenges involved with exploring for coloured stones in countries with very low population densities, temperate-to-arctic climates and a lack of infrastructure hindering access to most prospective areas. Despite this, a number of discoveries have occurred, mainly during the past two decades. These include emeralds from Northwest Territories (1997) and Yukon (1998); sapphire (2002) and spinel (from 1982)—including cobalt-blue stones—from Baffin Island in Nunavut; and ruby and pink sapphire (2002) from British Columbia. Such discoveries can be assisted by undertaking scientific research into gem formation, as well as by applying exploration criteria developed elsewhere to uncharted territory. Future exploration in Canada and other countries facing similar challenges will likely benefit from additional geological studies to identify prospective areas and features; innovative means of transportation, such as boats instead of aircraft; drones for exploring rugged terrain; hyperspectral imaging for mineral sensing; surveying with UV lamps to identify minerals associated with gem mineralisation; and careful prospecting (including field mapping and collecting heavy mineral concentrates) by experienced individuals. Quaternary geology fieldwork was conducted at a reconnaissance-scale in the Kaskattama highland area to document the Quaternary stratigraphy and till composition. The diamond potential of this region was investigated using kimberlite-indicator-mineral (KIM) counts from till samples. Indicator mineral results are the focus of this report and are combined with ice-flow and till-clast-lithology data to provide a context to interpret provenance. Kimberlite-indicator minerals were recovered from glacial sediments (till) in the Kaskattama highland area and KIM counts are elevated relative to data from the surrounding area. The lowest KIM counts were from till with a high Hudson Bay Basin (carbonatedominated) and low undifferentiated greenstone and greywacke (UGG) provenance signature. The highest KIM counts are associated with till samples that have a relatively elevated UGG or elevated granitoid provenance signature. Till samples with relatively elevated UGG concentration have an interpreted east or southeast provenance, which is supported by ice-flow data and the recovery of distinct east-sourced erratics. Till samples with a relatively elevated granitoid clast concentration have a correlation with the southwest- trending Hayes streamlined-landform flowset. Considering the likely provenance for granitoid clasts is to the northwest, the presence of relatively high concentrations of granitoid clasts in the Hayes flowset could be indicative of a higher inheritance from previous ice-flow events or a palimpsest dispersal pattern. Interpretation of till-composition and ice-flow data has indicated there are likely multiple sources for the KIMs recovered during this study. Detailed work is recommended to clarify local-scale dispersal patterns.
DS202005-0737
2019
Hoffman, P.F.Big Time: Proterozoic Eon.Annual Review of Earth and Planetary Sciences, Vol. 47, pp. 1-17. pdfMantleplate tectonics

Abstract: The Proterozoic Eon was once regarded as the neglected middle half of Earth history. The name refers to early animals, but they did not appear until the eon (2.5-0.54 Ga) was nearly over. Eukaryotic cells and sexual reproduction evolved much earlier in the eon, as did chloroplasts. Molecular dioxygen, the presence of which altered the geochemical behavior of nearly every element essential to life, rose from negligible to near-modern levels, and then plummeted before rising fitfully again. Plate tectonics took on a modern form, and two supercontinents, Nuna and Rodinia, successively congregated and later dispersed. Climate regulatory failures, i.e., Snowball Earth, appear to be a uniquely Proterozoic phenomenon, having occurred twice in rapid succession near the end of the eon (from 717 to 660 Ma and from 650 to 635 Ma) and arguably once near its beginning (ca. 2.43 Ga). Dynamic sea glaciers covered Snowball Earth oceans from pole to pole, and equatorial sublimation drove slow-moving ice sheets on land. Ultimately, the gradual accumulation of CO2 triggered rapid deglaciation and transient greenhouse aftermaths. Physically based and geologically tested, Neoproterozoic Snowball Earth appears to have molecular legacies in ancient bitumens and modern organisms. This is the story of my love affair with an eon that is now a little less neglected.
DS202008-1400
2020
Hoggard, M.J., Czarnota, K., Richards, F.D., Huston, D.L., Jaques, A.L., Ghelichkhan, S.Global distribution of sediment hosted metals controlled by craton edge stability. ( not specific to diamonds but of interest)Nature Geoscience, Vol. 13, pp. 504-510.Mantlelithospheric thickness

Abstract: Sustainable development and the transition to a clean-energy economy drives ever-increasing demand for base metals, substantially outstripping the discovery rate of new deposits and necessitating dramatic improvements in exploration success. Rifting of the continents has formed widespread sedimentary basins, some of which contain large quantities of copper, lead and zinc. Despite over a century of research, the geological structure responsible for the spatial distribution of such fertile regions remains enigmatic. Here, we use statistical tests to compare deposit locations with new maps of lithospheric thickness, which outline the base of tectonic plates. We find that 85% of sediment-hosted base metals, including all giant deposits (>10?megatonnes of metal), occur within 200?kilometres of the transition between thick and thin lithosphere. Rifting in this setting produces greater subsidence and lower basal heat flow, enlarging the depth extent of hydrothermal circulation available for forming giant deposits. Given that mineralization ages span the past two?billion?years, this observation implies long-term lithospheric edge stability and a genetic link between deep Earth processes and near-surface hydrothermal mineral systems. This discovery provides an unprecedented global framework for identifying fertile regions for targeted mineral exploration, reducing the search space for new deposits by two-thirds on this lithospheric thickness criterion alone.
DS202007-1147
2020
Hoggard, M.J., Parnell-Turner, R., White, N. Hotspots and mantle plumes revisited: towards reconciling the mantle heat transfer discrepancy.Earth and Planetary Science Letters, Vol. 542, 116317 16p. PdfMantleplumes, geothermometry

Abstract: Mantle convection is the principal mechanism by which heat is transferred from the deep Earth to the surface. Cold subducting slabs sink into the mantle and steadily warm, whilst upwelling plumes carry heat to the base of lithospheric plates where it can subsequently escape by conduction. Accurate estimation of the total heat carried by these plumes is important for understanding geodynamic processes and Earth's thermal budget. Existing estimates, based upon swell geometries and velocities of overriding plates, yield a global heat flux of ~2 TW and indicate that plumes play only a minor role in heat transfer. Here, we revisit the Icelandic and Hawaiian plumes to show that their individual flux estimates are likely to be incorrect due to the assumption that buoyancy is mainly produced within the lithosphere and therefore translates at plate velocities. We develop an alternative methodology that depends upon swell volume, is independent of plate velocities, and allows both for decay of buoyancy through time and for differential motion between asthenospheric buoyancy and the overlying plate. Reanalysis of the Icelandic and Hawaiian swells yields buoyancy fluxes of Mg s-1 and Mg s-1, respectively. Both swells are used to calibrate a buoyancy decay timescale of ~45 Myr for the new volumetric approach, which enables buoyancy fluxes to be estimated for a global inventory of 53 swells. Estimates from magmatic hotspots yield a cumulative lower bound on global plume flux of 2 TW, which increases to 6 TW if amagmatic swells are also included and if all buoyancy is assumed to be thermal in origin. Our results suggest that upwelling plumes play a significant role in the transfer of heat into the uppermost mantle.
DS202001-0016
2019
Holwell, D.A., Fiorentini, M., McDonald, I., Lu, Y., Giuliani, A., Smith, D.J., Keith, M., Locmelis, M.A metasomatized lithospheric mantle control on the metallogenic signature of post-subduction magmatism. ( Not specific to diamonds)Nature Communications, doi.org/10.1038/s41467-019-11065-4 pdf 10p.Mantlesubduction

Abstract: Ore deposits are loci on Earth where energy and mass flux are greatly enhanced and focussed, acting as magnifying lenses into metal transport, fractionation and concentration mechanisms through the lithosphere. Here we show that the metallogenic architecture of the lithosphere is illuminated by the geochemical signatures of metasomatised mantle rocks and post-subduction magmatic-hydrothermal mineral systems. Our data reveal that anomalously gold and tellurium rich magmatic sulfides in mantle-derived magmas emplaced in the lower crust share a common metallogenic signature with upper crustal porphyry-epithermal ore systems. We propose that a trans-lithospheric continuum exists whereby post-subduction magmas transporting metal-rich sulfide cargoes play a fundamental role in fluxing metals into the crust from metasomatised lithospheric mantle. Therefore, ore deposits are not merely associated with isolated zones where serendipitous happenstance has produced mineralisation. Rather, they are depositional points along the mantle-to-upper crust pathway of magmas and hydrothermal fluids, synthesising the concentrated metallogenic budget available.
DS202006-0922
2020
Hong, L., Znag,, M.Object oriented multiscale deep features for hyperspectral image classification. (Not specific to diamonds)International Journal of Remote Sensing, Vol. 41, 14, pp. 5549-5572.Globalhyperspectral

Abstract: The classification of hyperspectral images (HSIs) is one of the most popular topics in the remote sensing community. Numerous feature extraction methods have been proposed to improve the classification accuracy of HSIs. Recently, deep features extracted by convolution neural network (CNN) have been introduced into the classification process of HSIs. Due to the nonlinear and invariant advantages of the features, CNN methods provide a powerful tool for representing geographic objects and classifying HSIs. However, traditional deep features only extracted at pixel-level and often neglect multiscale characteristics of geographic objects. In this study, a new deep feature extraction method is proposed, which takes advantage of multi-scale object analysis and the CNN model. Firstly, multiscale image objects are obtained by the multiscale segmentation algorithm and multiscale low-level features of objects are extracted. Secondly, the CNN is devoted to obtain deep features from low-level object features at each scale, respectively. Thirdly, the obtained deep features at all scales are stacked and fed to one fully connected layer to extract the multiscale deep learning features for classification. Finally, the logistic regression classifier is applied to hyperspectral image (HSI) classification based on object-oriented multiscale deep features. The proposed method was carried out on three widely used hyperspectral data sets: University of Pavia, Salinas, and Washington DC. The results reveal that the proposed method provides better results than other state-of-the-art methods.
DS202012-2219
2020
Hoover, W.F., Page, F.Z., Schulze, D.J., Kitajima, K., Valley, J.W.Massive fluid influx beneath the Colorado Plateau ( USA) related to slab removal and diatreme emplacement: evidence from oxygen isotope zoning in eclogite xenoliths.Journal of Petrology, in press available, 52p. PdfUnited States, Colorado Plateaueclogite

Abstract: The Colorado Plateau has undergone as much as 1.8?km of uplift over the past 80?Ma, but never underwent the pervasive deformation common in the neighboring tectonic provinces of the western USA. To understand the source, timing and distribution of mantle hydration, and its role in plateau uplift, garnets from four eclogite xenoliths of the Moses Rock diatreme (Navajo Volcanic Field, Utah, USA) were analyzed in situ for d18O by secondary ion mass spectrometry. These garnets have the largest reported intra-crystalline oxygen isotope zoning to date in mantle-derived xenoliths with core-to-rim variations of as much as 3‰. All samples have core d18O values greater than that of the pristine mantle (~5.3‰, mantle garnet as derived from mantle zircon; Valley et al., 1998; Page et al., 2007) consistent with an altered upper oceanic crust protolith. Oxygen isotope ratios decrease from core to rim recording interaction with a low-d18O fluid at high temperature, likely derived from serpentinite in the foundering Farallon slab. All zoned samples converge at a d18O value of ~6‰, regardless of core composition, suggesting that fluid infiltration was widely distributed. Constraints on the timing of this fluid influx, relative to diatreme emplacement, can be gained from diffusion modeling of major element zoning in garnet. Modeling using best-estimates of peak metamorphic conditions (620ºC, 3.7?GPa) yield durations of?
DS202011-2043
2019
Horvath, L., Gault, R.A., Pfenninger-Horvath, Poirier, G.Mont Saint-Hilaire: history, geology, mineralogy.The Canadian Mineralogist, Special Publication 14, 634p. Canada, QuebecBook

Abstract: This paper introduces a special section of the Canadian Journal of Development Studies, "The Africa Mining Vision: A Manifesto for More Inclusive Extractive Industry-Led Development?" Conceived by African ministers "in charge of mineral resources" with inputs and guidance from African Union Heads of State, the Africa Mining Vision (AMV) was officially launched in February 2009. The papers presented in this special section reflect critically on progress that has since been made with operationalising the AMV at the country level across Africa; the general shortcomings of the manifesto; and the challenges that must be overcome if the continent is to derive g Taking over 20 years of meticulous preparation, László and Elsa Horváth, a duo of dedicated and dynamic amateur mineralogists, along with two researchers, Robert Gault, a mineralogist, and Glenn Poirier, a geologist, have produced the ultimate book "Mont Saint-Hilaire: History, Geology, Mineralogy". The photography captures the colors of Vásárely, the symmetry of Escher, the form of Bartók and the intricate patterns of Mandelbrot, all found here, in this miracle of nature. One cannot but marvel at how this single, small quarry contains such mineral diversity. At last count, over 434 mineral species have been found at Mont Saint-Hilaire, representing 9% of all known mineral species. The 66 type minerals first described from this locality represent 1.3 % of all mineral species, placing the Poudrette quarry in an extremely rarified class for worldwide mineral localities. Almost half, 47, of all known chemical elements are included in this mineral mix. Beginning some 124 million years ago, several million years and a variety of geological processes were needed to accomplish this assemblage. Be captivated, learn and, most of all, enjoy!reater economic benefit from its abundant mineral wealth.
DS202011-2044
2020
Hou, X-Z., Yang, Z-F., Wang, Z-J.The occurrence characteristics and recovery potential of middle-heavy rare earth elements in the Bayan Obo deposit, northern China.Ore Geology Reviews, Vol. 126, 103737, 13p. PdfChinaREE

Abstract: The Bayan Obo deposit is a world-class Fe-REE-Nb deposit, and its reserves of rare earth element (REE) resources rank the first over the world. In the face of the current situation of insufficient utilization rate of rare earth resources and scarcity of middle-heavy rare earth elements (M-HREE) resources, the Bayan Obo deposit with such a huge amount of M-HREE cannot be underestimated. In this paper, the occurrence characteristics of M-HREE in different types of iron ore in the Bayan Obo main ore body are studied by using field emission scanning electron microscope (FESEM), energy dispersive spectrometer (EDS) and advanced mineral identification and characterisation system (AMICS), and the enrichment mechanism is also discussed. The results show that both Sm and Y are the most abundant M-HREE in each type of iron ore in the main ore body, and the content of M-HREE accounts for 1.41%-5.57% of total REE, among which the content of M-HREE in aegirine type Nb-REE-Fe ore (824.47 ppm) and fluorite type Nb-REE-Fe ore (794.82 ppm) are higher, and the content of M-HREE in massive type Nb-REE-Fe ore is lower (318.49 ppm). The main minerals containing M-HREE are bastnasite, parisite, Huanghoite, monazite, aeschynite and fergusonite, among which the content of M-HREE in fergusonite and aeschynite are the highest. According to the characteristics of mineral paragenetic association of REE in this ore district, it is believed that the REE migrates mainly in many different forms of complexes. Heavy rare earth elements (HREE) mainly experienced carbonatite magmatism stage, sodium-fluorine metasomatism stage and late vein mineralization stage, and finally got enrichment.
DS202012-2220
2020
Howarth, G.What meteorites can tell us about Mars.Univ. Cape Town, https://www.news.uct.ac.za /news/research-office/ -article/2020-11-24-what -meteorites-can-tell- us-about-marsMarsmeteorites

Abstract: Hundreds of millions of years ago something crashed into the planet Mars with enough force to eject pieces of Martian rock into space. Some of these pieces of rock made their way to Earth where they entered our atmosphere as meteors. A precious few landed on the surface of our planet as meteorites. Thanks to scientists like Geoffrey Howarth, a geologist based at the University of Cape Town (UCT), these Martian meteorites are now being studied to better understand the structure and geological history of the red planet. Here’s what we know so far.
DS202004-0518
2020
Howarth, G.H., Giuliani, A.Contrasting types of miceaceous kimberlite-lamproite magmatism from the Man craton ( West Africa): new insights from petrography and mineral chemistry.Lithos, in press available 63p. PdfAfrica, Sierra Leone, Liberiadeposit - Tongo, Weasua

Abstract: Diamondiferous rock types worldwide are broadly divided into kimberlite and lamproite, the latter of which have unique characteristics in different regions and include carbonate-rich varieties (formerly orangeites/Group II kimberlites). Diamondiferous rocks in West Africa are typically micaceous and share petrographic, mineralogical, and geochemical characteristics with both kimberlites and lamproites. To further constrain the classification and petrogenesis of diamondiferous rocks worldwide and their variability between different cratonic regions, in this study we combine detailed petrographic observations with olivine, phlogopite, and spinel chemistry for hypabyssal samples from the Jurassic Tongo dike (Sierra Leone) and the Neoproterozoic Weasua cluster (Liberia). The Tongo dike contains macrocrysts of olivine and phlogopite in a groundmass of olivine, abundant phlogopite, spinel, perovskite, and apatite with a base of calcite, dolomite, and lesser serpentine. The phlogopite is characterised by concurrent FeO and Al2O3 enrichment, which is typical of kimberlites and unlike lamproites. These features and the kimberlite-like spinel compositions allow us to classify the Tongo samples as micaceous kimberlites. The Weasua rocks comprise macrocrysts of olivine in a groundmass of olivine, phlogopite, diopside (zoned towards aegirine-rich rims), spinel, perovskite, and apatite with a base of serpentine and less common calcite. The composition of Weasua phlogopite trends to significant FeO enrichment and Al2O3 depletion, i.e. towards tetraferriphlogopite. The enrichment in mica, phlogopite chemistry and presence of magmatic diopside indicates that these rocks are olivine lamproites. The populations of olivine macrocrysts and microcrysts at Tongo and Weasua are similar and characterised by distinct core and rim zones. Two distinct olivine core populations are observed. 1) forsterite-rich (Fo?>?90) olivine interpreted to reflect xenocrysts from typical mantle peridotites. Al-in-olivine thermometry suggests that these cores have P-T equilibration within diamond stability at Weasua and Tongo. 2) Al-, Ca- and Na- rich cores with P-T formation conditions extending beyond the mantle adiabat. These cores are interpreted to reflect metasomatic and thermal perturbation linked with the infiltration of kimberlite/lamproite melts in the deep lithosphere shortly before entrainment in the ascending magma. The olivine rims at Tongo and Weasua show limited variations in Fo contents at similar values of 88.9?±?0.8 for Tongo and 89.6?±?1.2 for Weasua, as well as similar minor and trace element concentrations. Thus, whereas the Tongo and Weasua rock types are classified as kimberlite and olivine lamproite, respectively, the olivine chemistry suggests a similar petrogenetic evolution.
DS202006-0923
2020
Howell, D., Collins, A.T., Loudin, L.C., Diggle, P.L., D'Haenens-Johansson, U.F.S., Smit, K.V., Katrusha, A.N., Butler, J.E., Nestola, F.Automated FTIR mapping of boron distribution in diamond. DiaMap_IIb ( synthetics)Diamonds & Related Materials, In press available, 30p. PdfGlobalsynthetics

Abstract: Type IIb diamonds are those that contain more boron than nitrogen. The presence of this uncompensated boron gives rise to absorption in the infrared part of the electromagnetic spectrum, extending into the visible region and often resulting in blue colouration. Here we report on the expansion of the DiaMap freeware (for the automated spectral deconvolution of Type I [nitrogen containing] diamonds) to work on Type IIb diamonds, returning concentrations from three boron-related absorption bands, and determining which band provides the most reliable value. The program uses the calibration coefficients of Collins (2010), which show good relative agreement between the three bands, but might require some further study to confirm their absolute accuracy to the uncompensated boron concentration. The methodology of DiaMap_IIb is applicable to all Type IIb diamonds, both natural and synthetic. Analysis of high-resolution Fourier-transform infrared (FTIR) maps of two high-pressure high-temperature (HPHT) synthetic diamonds using DiaMap_IIb, confirm the growth sector dependence of the boron incorporation. Partitioning of boron strongly favours the octahedral {111} sectors.
DS202004-0519
2020
Howell, D., Stachel, T., Stern, R.A., Pearson, D.G., Nestola, F., Hardman, M.F., Harris, J.W., Jaques, A.L., Shirery, S.B., Cartigny, P., Smit, K.V., Aulbach, S., Brenker, F.E., Jacob, D.E., Thomassot, E., Walter, M.J., Navon, O.Deep carbon through time: Earth's diamond record and its implications for carbon cycling and fluid speciation in the mantle.(peridotite and eclogite used)Geochimica et Cosmochimica Acta, Vol. 275, pp. 99-122.Mantlecarbon

Abstract: Diamonds are unrivalled in their ability to record the mantle carbon cycle and mantle fO2 over a vast portion of Earth’s history. Diamonds’ inertness and antiquity means their carbon isotopic characteristics directly reflect their growth environment within the mantle as far back as ~3.5 Ga. This paper reports the results of a thorough secondary ion mass spectrometry (SIMS) carbon isotope and nitrogen concentration study, carried out on fragments of 144 diamond samples from various locations, from ~3.5 to 1.4 Ga for P [peridotitic]-type diamonds and 3.0 to 1.0 Ga for E [eclogitic]-type diamonds. The majority of the studied samples were from diamonds used to establish formation ages and thus provide a direct connection between the carbon isotope values, nitrogen contents and the formation ages. In total, 908 carbon isotope and nitrogen concentration measurements were obtained. The total d¹³C data range from -17.1 to -1.9 ‰ (P = -8.4 to -1.9 ‰; E = -17.1 to -2.1‰) and N contents range from 0 to 3073 at. ppm (P = 0 to 3073 at. ppm; E = 1 to 2661 at. ppm). In general, there is no systematic variation with time in the mantle carbon isotope record since > 3 Ga. The mode in d¹³C of peridotitic diamonds has been at -5 (±2) ‰ since the earliest diamond growth ~3.5 Ga, and this mode is also observed in the eclogitic diamond record since ~3 Ga. The skewness of eclogitic diamonds’ d¹³C distributions to more negative values, which the data establishes began around 3 Ga, is also consistent through time, with no global trends apparent. No isotopic and concentration trends were recorded within individual samples, indicating that, firstly, closed system fractionation trends are rare. This implies that diamonds typically grow in systems with high excess of carbon in the fluid (i.e. relative to the mass of the growing diamond). Any minerals included into diamond during the growth process are more likely to be isotopically reset at the time of diamond formation, meaning inclusion ages would be representative of the diamond growth event irrespective of whether they are syngenetic or protogenetic. Secondly, the lack of significant variation seen in the peridotitic diamonds studied is in keeping with modeling of Rayleigh isotopic fractionation in multicomponent systems (RIFMS) during isochemical diamond precipitation in harzburgitic mantle. The RIFMS model not only showed that in water-maximum fluids at constant depths along a geotherm, fractionation can only account for variations of <1‰, but also that the principal d¹³C mode of -5 ± 1‰ in the global harzburgitic diamond record occurs if the variation in fO2 is only 0.4 log units. Due to the wide age distribution of P-type diamonds, this leads to the conclusion that the speciation and oxygen fugacity of diamond forming fluids has been relatively consistent. The deep mantle has therefore generated fluids with near constant carbon speciation for 3.5 Ga.
DS202001-0017
2019
Huang, C., Zhang, N, Li, Z.X., Dang, Z.Modeling the inception of supercontinent breakup: stress state and the importance of orogens.Geochemistry, Geophysics, Geosystems, in press available pdf 20p.Globalgeodynamics

Abstract: The relative significance of various geodynamic mechanisms that drive supercontinent breakup is unclear. A previous analysis of extensional stress during supercontinent breakup demonstrated the importance of the plume-push force relative to the dragging force of subduction retreat. Here, we extend the analysis to basal traction (shear stress) and cross-lithosphere integrations of both extensional and shear stresses, aiming to understand more clearly the relevant importance of these mechanisms in supercontinent breakup. More importantly, we evaluate the effect of preexisting orogens (mobile belts) in the lithosphere on supercontinent breakup process. Our analysis suggests that a homogeneous supercontinent has extensional stress of 20-50 MPa in its interior (<40° from the central point). When orogens are introduced, the extensional stress in the continents focuses on the top 80-km of the lithosphere with an average magnitude of ~160 MPa, whereas at the margin of the supercontinent the extensional stress is 5-50 MPa. In both homogeneous and orogeny-embedded cases, the subsupercontinent mantle upwellings act as the controlling factor on the normal stress field in the supercontinent interior. Compared with the extensional stress, shear stress at the bottom of the supercontinent is 1-2 order of magnitude smaller (0-5 MPa). In our two end-member models, the breakup of a supercontinent with orogens can be achieved after the first extensional stress surge, whereas for a hypothetical supercontinent without orogens it starts with more diffused local thinning of the continental lithospheric before the breakup, suggesting that weak orogens play a critical role in the dispersal of supercontinents.
DS202007-1148
2020
Huang, F., Sverjensky, D.A.Mixing of carbonatitic into saline fluid fluid during Panda diamond formation.Geochimica et Cosmochimica Acta, in press available 59p. PdfCanada, Northwest Territoriesdeposit - Panda

Abstract: Diamonds containing fluid inclusions provide invaluable samples of upper mantle fluids, the study of which illuminates not only diamond formation but also the long-term evolution of the subcratonic, lithospheric mantle. The very large range of inclusion compositions worldwide has been interpreted to represent four end-member fluids: saline (rich in Na+K+Cl); silicic (rich in Si+Al); and carbonatitic (rich in Ca+Mg+Fe, with low-Mg and high-Mg end members). However, the sources and evolution of these fluids and the processes involved in diamond formation are still unclear. We used an unusual study of diamonds from the Panda kimberlite (Ekati Mine, Northwest Territories, Canada) in which both mineral and fluid inclusions in the diamonds were analyzed (Tomlinson et al., 2006) to develop models of the saline, silicic, and low-Mg carbonatitic fluids present in the Panda fluid inclusions. The models used aqueous speciation and solubility calculations to link the solid and fluid inclusion chemistry with