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Sheahan Diamond Literature Technical Reference Compilation 2021


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.
Link to external location of article: If the title has a link, it means we have found a location online where you can either retrieve the full article free, or purchase access to it. The Sheahan Diamond Literature Service is not a technical article procurement service; if you want a restricted article, you must deal directly with the vendor who controls the copyright to the article.
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Monthly Sheahan Diamond Newsletters for 2021
January 2021 May 2021 September 2021
February 2021 June 2021 October 2021
March 2021 July 2021 November 2021
April 2021 August 2021 December 2021
2021 Technical Reference Compilation
Posted/
Published
AuthorTitleSourceRegionKeywords
DS202108-1266
2021
Abersteiner, A., Kamenetsky, V.S., Golovin, A., Goemann, K., Ehrig, K.Dissolution of mantle orthopyroxene in kimberlitic melts: petrographic, geochemical and melt inclusion constraints from an orthopyroxenite xenolith from the Udachnaya-East kimberlite ( Siberian Craton, Russia).Lithos, Vol. 398-399, 17p. PdfRussia, Siberiadeposit - Udachnaya-East

Abstract: Reconstructing the original composition of kimberlite melts in the mantle and delineating the processes that modify them during magmatic ascent and emplacement in the crust remains a significant challenge in kimberlite petrology. One of the most significant processes commonly cited to drive initial kimberlite melts towards more Si-Mg-rich compositions and decrease the solubility of CO2 is the assimilation of mantle orthopyroxene. However, there is limited direct evidence to show the types of reactions that may occur between mantle orthopyroxene and the host kimberlite melt. To provide new constraints on the interaction between orthopyroxene and parental kimberlite melts, we examined a fresh (i.e. unmodified by secondary/post-magmatic alteration) orthopyroxenite xenolith, which was recovered from the serpentine-free units of the Udachnaya-East kimberlite (Siberian Craton, Russia). This xenolith is composed largely of orthopyroxene (~ 90%), along with lesser olivine and clinopyroxene and rare aluminous magnesian chromite. We can show that this xenolith was invaded by the host kimberlite melt along grain interstices and fractures, where it partially reacted with orthopyroxene along the grain boundaries and replaced it with aggregates of compositionally distinct clinopyroxene, olivine and phlogopite, along with subordinate Fe-Cr-Mg spinel, Fesingle bondNi sulphides and djerfisherite (K6(Fe,Ni,Cu)25S26Cl). Primary melt inclusions in clinopyroxene replacing xenolith-forming orthopyroxene, as well as secondary melt inclusion trails in xenolith orthopyroxene, clinopyroxene and olivine are composed of similar daughter mineral assemblages that consist largely of: Nasingle bondK chlorides, along with varying proportions of phlogopite, Fe-Cu-Ni sulphides, djerfisherite, rasvumite (KFe2S3), Cr-Fe-Mg spinel, nepheline and apatite, and rare rutile, sodalite, barite, olivine, Ca-K-Na carbonates and Nasingle bondK sulphates. The melt entrapped by these inclusions likely represent the hybrid products produced by the invading kimberlite melt reacting with orthopyroxene in the xenolith. The mechanism that could explain the partial replacement of orthopyroxene in this xenolith by clinopyroxene, olivine and phlogopite could be attributed to the following reaction: Orthopyroxene + Carbonatitic (melt) ? Olivine + Clinopyroxene + Phlogopite + CO2. This reaction is supported by theoretical and experimental studies that advocate the dissolution of mantle orthopyroxene within an initially silica-poor and carbonate-rich kimberlite melt. The mineral assemblages replacing orthopyroxene in the xenolith, together with hosted melt inclusions, suggests that the kimberlitic melt prior to reaction with orthopyroxene was likely carbonate-rich and Na-K-Cl-S bearing. The paucity of carbonate in the reaction zones around orthopyroxene and in melt inclusions in clinopyroxene replacing xenolith-forming orthopyroxene and xenolith minerals (orthopyroxene, clinopyroxene and olivine) is attributed to the consumption of carbonates and subsequent exsolution of CO2 by the proposed decarbonation reaction. Concluding, we propose that this orthopyroxenite xenolith provides a rare example of the types of reactions that can occur between mantle orthopyroxene and the host kimberlite melt. The preservation of this xenolith and zones around orthopyroxene present new insights into the composition and evolution of parental kimberlite melts and CO2 exsolution.
DS202104-0563
2020
Afanasiev, V.P., Pohilenko, N.P., Kuligin, S.S., Samdanov, D.A.On the prospects of diamond content of the southern side of the Vilyui syneclise. ( Lena River)Geology of Ore Deposits, Vol. 62, 6, pp. 535-541.RussiaIndicator minerals

Abstract: The paper describes indicator minerals of kimberlites found on the southern side of the Vilyui syneclise in the Markha River basin, a tributary of the Lena River. It is shown that indicator minerals-pyrope and picroilmenite-derive from Middle Paleozoic kimberlites, very likely diamondiferous. Methods are proposed for further studies on determining the prospects for the diamond content of the southern side of the Vilyui syneclise and the northern slope of the Aldan anteclise.
DS202106-0920
2021
Agasheva, E.Magmatic material in sandstone shows prospects for new diamond deposits within the northern east European platform.Minerals, Vol. 11, 339. doi.org/10.3390/min11040339 27p. PdfRussia, Arkhangelskdeposit - KL-01

Abstract: A detailed study of sandstones recovered from the upper part of the recently discovered KL-01 magmatic pipe in the southern part of the Arkhangelsk diamondiferous province (ADP), containing magmatic material and rare kimberlite indicator minerals, is presented in this paper. Results are compared to the composition of crater samples of the highly diamondiferous Vladimir Grib kimberlite pipe and several poorly to non-diamondiferous ADP pipes. To identify the type of magmatic material admixture, a model of binary mixing between country Vendian sandstones and typical ADP magmatic rocks based on correlations of La/Yb and Zr/Nb ratios and Ni contents is proposed. The modeling results show that the type of magmatic component in the KL-01 samples can be identified as kimberlite, with a maximum admixture of 20 vol.%. Kimberlite indicator mineral geochemistry did not exclude the interpretation that the composition, structure, thermal state and metasomatic enrichment of the lithospheric mantle sampled by the KL-01 pipe were suitable for the formation and preservation of diamonds. The lower boundary of the sampled lithospheric mantle could be in the depth range of 175-190 km, with a diamond window width of 55-70 km. Thus, the sandstones could represent the upper level of the crater of a new kimberlite pipe.
DS202108-1267
2021
Agasheva, E.V., Kolesnichenko, M.V., Malygina, E.V., Agashev, A.M., Zedgenizov, D.A.Origin of water in mantle eclogites from the V. Grib kimberlite pipe, NW Russia.Lithosphere, Vol. 2021, 7866657, 18p. PdfRussia, Arkangelskdeposit - Grib

Abstract: The water content in the garnet and clinopyroxene in the mantle eclogites from the V. Grib kimberlite pipe (Arkhangelsk Diamondiferous Province, NW Russia) was analysed using Fourier transform infrared spectrometry. The results show that all clinopyroxene grains contained structural water at concentrations of 39 to 247?ppm, whereas two garnet samples contained detectable water at concentrations of 211 and 337?ppm. The low-MgO eclogites with oceanic gabbro precursors contained significantly higher water concentrations in the omphacites (70-247?ppm) and whole rock (35-224?ppm) compared to those with oceanic basalt protoliths (49-73?ppm and 20-36?ppm, respectively). The incorporation of water into the clinopyroxene may be associated with vacancies at the M2 site, Al in the tetrahedral position, and the elements that filled the M2 site (mostly Na and Ca). The highest water content in the omphacite was detected in a nonmetasomatised sample and was assumed to represent residual water that survived during subduction. Other eclogite samples showed signs of modal and/or cryptic metasomatism and contained less water in the omphacites compared to the nonmetasomatised sample. The water content was heterogeneous within the eclogite section of the sampled lithospheric mantle. The lack of distinct and uniform correlations between the indices of eclogite modification and their water content indicated that the saturation with water was disturbed during their residence within the lithospheric mantle.
DS202108-1268
2021
Aguila, M.Diamonds are a physicist's best friend. Imperfections in jewels used as sensors for new quantum materials. See full ref. McLaughlinucsdnews.ucsd.edu, June 17, 1p. Overview Globaldiamond inclusions

Abstract: Defects found in diamonds are typically received as unwelcome news to the discerning jewelry shopper. But for some physicists, diamond imperfections offer a new opportunity to push the boundaries of futuristic devices that could become the backbone of tomorrow’s computers. UC San Diego Department of Physics Assistant Professor Chunhui Rita Du is a condensed matter experimentalist whose research takes advantage of impurities in diamonds. Du’s research group leverages the red, yellow and blue colors that result from diamond defects to develop sensors that can evaluate the properties of specialized materials down to the nanometer level.
DS202104-0564
2021
Ahline, N., Ardon, T., Overlin, S.D-Z Diamonds ( from the print copy of article in Gems & Gemology)GIAcommunications @gia.edu, gia.org and knowledge sessionsGlobaldiamond genesis

Abstract: G&G’s most recent issue captured the past, present and future of the gem industry - with an overview of European royal jewelry sales (including the sale of Marie Antoinette’s jewelry), in-depth coverage of D-Z diamond knowledge (such as causes of color and formation) and a journey into Vietnamese pearl farming. Tune in as G&G contributors Troy Ardon and Nicole Ahline touch upon these and other highlights from the most recent publication of GIA’s prestigious scientific journal.
DS202110-1598
2021
Aifa, T.Mineralization and sustainable development in the west African craton: from field observations to modelling. ** not specific to diamondsGeological Society of London Special Publication, SP502, 353p. ISBN 9781786204899 July publ. approx lbs 81.00 cost Africacraton

Abstract: This volume combines the results obtained by interdisciplinary groups working on Paleoproterozoic Formations to decipher the origins of the main natural resources through mineralizations and their impacts on the African Economic development. Structural, geophysical, sedimentological, stratigraphical, geochemical, petrophysical and mineralogical analyses are used to highlight the complex mineralizations emplacement and their origin and evolution within the West African Craton.
DS202110-1599
2021
AlrosaAlrosa has completed the first phase of a study into kimberlites' ability to absorb CO2 from the atmosphereMining Magazine.com, Sept. 16, 1p.Russiacarbon
DS202109-1448
2021
Ansari, E., Bidgoli, T.S.Precambrian crystalline basement properties from pressure history matching and implications for induced seismicity in the US Midcontinent.Geochemistry, Geophysics, Geosystems, 10.1029/2021GC009660 11p. PdfUnited States, Kansasgeophysics- seismic

Abstract: Wastewater injection tied to oil and gas development has induced earthquakes across a broad swath of the central US. These earthquakes have almost exclusively occurred in the crystalline rocks, many kilometers below the main disposal zone in this portion of the country, the Arbuckle Group aquifer. However, the hydrologic properties of these deep crystalline rocks are not well known and are needed to accurately model pressure transmission from injection wells to faults in the deep basement and related earthquake hazards. Newly compiled pressure data, from wastewater disposal wells in Kansas, provide an opportunity to constrain these properties. In this study, we construct a detailed, three-dimensional geological model for the Arbuckle and basement, based on data from >400 wells covering south-central Kansas. We use the model to simulate injection and pressures from more than 300 wells. The model indicates that Arbuckle pressures increased by 1.1 MPa in high injection rate areas and overpressures of <0.1 MPa may be the cause of seismicity in the basement. The simulation results also yield the likely range in hydrologic properties for the crystalline basement and suggests large-scale properties of the basement are enhanced by hidden networks of faults and fractures.
DS202106-0921
2021
Antonini, A., Ganuza, M.L. , Ferracutti, G., Gagiulo, M.F., Matkovic, K., Groller, E., Bjerg, E.A., Castro, S.M.Spinel web: an interactive web application for visualizing the chemical composition of spinel group minerals. ** not specific to diamondsEarth Science Informatics, Vol. 14, pp. 521-528. pdfMantletectonics

Abstract: The spinel group minerals provide useful information regarding the geological environment in which the host rocks were formed, constituting excellent petrogenetic indicators, and guides in the search for mineral deposits of economic interest. In this article, we present the Spinel Web, a web application to visualize the chemical composition of spinel group minerals. Spinel Web integrates most of the diagrams commonly used for analyzing the chemical characteristics of the spinel group minerals. It incorporates parallel coordinates and a 3D representation of the spinel prisms. It also provides coordinated views and appropriate interactions for users to interact with their datasets. Spinel Web also supports semi-automatic categorization of the geological environment of formation through a standard Web browser.
DS202103-0367
2021
Armistad, S.E., Collins, A.S., Schmitt, R.S., Costa, R.L., De Waele, B., Razakamanana, T., Payne, J.L., Foden, J.D.Proterozoic basin evolution and tectonic geography of Madagascar: implications for an East Africa connection during the Paleoproterozoic. ( zircon analyses link Tanzania craton and India)Tectonics, doi/epdf/10. 10292020Tc006498 Africa, Madagascarcraton

Abstract: Madagascar hosts several Paleoproterozoic sedimentary sequences that are key to unravelling the geodynamic evolution of past supercontinents on Earth. New detrital zircon U-Pb and Hf data, and a substantial new database of ?15,000 analyses are used here to compare and contrast sedimentary sequences in Madagascar, Africa and India. The Itremo Group in central Madagascar, the Sahantaha Group in northern Madagascar, the Maha Group in eastern Madagascar, and the Ambatolampy Group in central Madagascar have indistinguishable age and isotopic characteristics. These samples have maximum depositional ages > 1700 Ma, with major zircon age peaks at c. 2500 Ma, c. 2000 Ma and c. 1850 Ma. We name this the Greater Itremo Basin, which covered a vast area of Madagascar in the late Paleoproterozoic. These samples are also compared with those from the Tanzania and the Congo cratons of Africa, and the Dharwar Craton and Southern Granulite Terrane of India. We show that the Greater Itremo Basin and sedimentary sequences in the Tanzania Craton of Africa are correlatives. These also tentatively correlate with sedimentary protoliths in the Southern Granulite Terrane of India, which together formed a major intra?Nuna/Columbia sedimentary basin that we name the Itremo?Muva?Pandyan Basin. A new Paleoproterozoic plate tectonic configuration is proposed where central Madagascar is contiguous with the Tanzania Craton to the west and the Southern Granulite Terrane to the east. This model strongly supports an ancient Proterozoic origin for central Madagascar and a position adjacent to the Tanzania Craton of East Africa.
DS202104-0565
2021
Arnaiz-Rodriguez, M., Zhao, Y., Sanchez-Gamboa, A.K., Audemard, F.Crustal and upper-mantle structure of the eastern Caribbean and northern Venezuela from passive Rayleigh wave tomography.Tectonophysics, Vol. 804, 228711 18p. pdf South America, Venezuelageophysics - seismic

Abstract: We explore the shear-wave lithospheric velocity structure of the Eastern Caribbean and Northern Venezuela using ambient noise tomography with stations deployed around the study area. We construct cross-correlation functions from continuous seismic records, and measure phase velocities of fundamental-mode Rayleigh waves. These velocities are further projected onto 0.6°x0.6° phase velocity grids for each period between 5 s and 50 s. The pseudo-dispersion curve at each grid point is inverted for 1D shear velocity profiles by using a Markov Chain Monte Carlo scheme. The interpolated 3D velocity model shows that the mean shear velocity of the Eastern Caribbean lithospheric mantle is lower than the global average, which is in agreement with values reported in other large igneous provinces. We interpret that low velocities in the lithospheric keel are associated with an anomalous composition and/or an elevated thermal state; this gives the Caribbean plate a high buoyancy that determines the subduction polarities in the region. The results also indicate that: (a) the mantle beneath Northern Venezuela retains compositional anomalies related to extension processes of different ages; (b) the overriding of the Caribbean plate by the Great Antilles arc seems to be much slower than previously suggested; and (c) the localized volcanism in the center of the Lesser Antilles arc is related to asthenospheric flow through the tear induced on the subducted slab by major strike-slip faults.
DS202108-1269
2021
Ashchepkov, I.Diamondiferous kimberlites from recently explored Upper Muna field ( Siberian craton): petrology, mineralogy and geochemistry insights.Geological Society of London Special Publications, 513, 34p. PdfRussiadeposit - Upper Muna

Abstract: Petrographic, geochemical and mineralogical characteristics of diamond deposits from the Upper Muna field have been investigated. Geochemically, diamondiferous kimberlites from Upper Muna belong to the most widespread Fe-Mg-rich rocks in the Yakutian kimberlite province (average FeOtotal = 8.4 wt%, MgO = 32.36 wt%, TiO2 = 1.6 wt.%). Striking mineralogical features of Upper Muna kimberlites are: 1) abundance of monticellite and perovskite in the groundmass; 2) rare occurrence of Mg-ilmenite; 3) abundance of phlogopite megacrysts (up to 8 cm across); 4) coexistence of low-Cr (0.1-4wt. % Cr2O3, with 0.8-1.2 wt.% TiO2), and high-Cr (3-8 wt.% Cr2O3, with 0.1-0.6 wt.% TiO2) garnet megacrysts with contrasting REE patterns. The compositional features of groundmass minerals, the relatively low CaO and CO2 contents in kimberlites, and few deuteric alteration in Upper Muna kimberlites suggest high-temperature melt crystallization during pipe emplacement. Based on the compositional data of garnet and Cr-diopside from megacrysts and peridotites, we suggest a poor Cr dunite-harzburgitic and lherzolitic mantle source beneath the Upper Muna field where Cr-diopside crystallized within a wide P-T range (40-65 kbar and 900-1350 °C). Mineral geochemistry, trace element distribution and Sr-Nd isotope variations of Upper Muna kimberlites are typical for group I kimberlites and reflect a deep-seated asthenospheric (convective mantle) source for the kimberlites.
DS202106-0922
2021
Ashchepkov, I.,Medvedev, N.,Ivanov, A., Vladykin, N., Ntafos,T.,Downes, H.,Saprykin, A.,Tolstov, A.Vavilov, M., Shmarov, G.Deep mantle roots of the Zarnitsa kimberlite pipe, Siberian craton, Russia: evidence for multistage polybaric interaction with mantle melts.Journal of Asian Earth Sciences, Vol. 213, 104756, 22p.pdfRussia, Siberiadeposit - Zarnitsa

Abstract: Zarnitsa kimberlite pipe in Central Yakutia contains pyrope garnets with Cr2O3 ranging from 9 to 19.3 wt% derived from the asthenospheric mantle. They show mostly S-shaped, inflected rare earth element (REE) patterns for dunitic and harzburgitic, lherzolitic and harzburgitic varieties and all are rich in high field strength elements (HFSE) due to reaction with protokimberlite melts. Lithospheric garnets (<9 wt% Cr2O3) show a similar division into four groups but have more symmetric trace element patterns. Cr-diopsides suggest reactions with hydrous alkaline, protokimberlitic and primary (hydrous) partial melts. Cr-diopsides of metasomatic origin have inclined REE patterns and high LILE, U, Th and Zr concentrations. Four groups in REE of Ti-rich Cr-diopsides, and augites have asymmetric bell-like REE patterns and are HFSE-rich. Mg-ilmenites low in REE were formed within dunite conduits. Ilmenite derived from differentiated melts have inclined REE patterns with LREE ~ 100 × chondrite levels. Thermobarometry for dunites shows a 34 mWm?2 geotherm with a HT branch (>50 mWm?2) at 6-9 GPa, and a stepped HT geotherm with heated pyroxenite lenses at four levels from 6.5 to 3.5 GPa. Parental melts calculated with KDs suggest that augites and high-Cr garnets in the lithosphere base reacted with essentially carbonatitic melts while garnets from lower pressure show subduction peaks in U, Ba and Pb. The roots of the Zarnitsa pipe served to transfer large portions of deep (>9 GPa) protokimberlite melts to the lithosphere. Smaller diamonds were dissolved due to the elevated oxidation state but in peripheral zones large diamonds could grow.
DS202112-1919
2021
Ashchepkov, I.V., Alymova, N.V., Loginova, A.M., Vladykin, N.V.. Kuligin, S.S., Mityukhin, S.I., Stegnitsky, Y.B., Prokopiev, S.A.Picroilmenites in Yakutian kimberlites: variations and genetic models.Lithos, Vol. 406-407. doi: 10.1016/j.lithos.2021.106499 77p. PdfRussiakimberlite genesis

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.
DS202107-1088
2021
Ashchepkov, 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 Proazovie, Ukrainian shield: volatile enriched focused melt flow and connection to mature crust?International Geology Review, Vol. 63, 10, pp. 1288-1309.Europe, 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.
DS202109-1449
2021
Ashwal, L.D.Sub-lithospheric mantle sources for overlapping southern African Large Igneous Provinces.South African Journal of Geology, Vol. 124, pp. 421-442.Africa, South Africamagmatism

Abstract: At least four spatially overlapping Large Igneous Provinces, each of which generated ~1 x 106 km3 or more of basaltic magmas over short time intervals (<5 m.y.), were emplaced onto and into the Kaapvaal Craton between 2.7 and 0.18 Ga: Ventersdorp (2 720 Ma, ~0.7 x 106 km3), Bushveld (2 056 Ma, ~1.5 x 106 km3), Umkondo (1 105 Ma, ~2 x 106 km3) and Karoo (182 Ma, ~3 x 106 km3). Each of these has been suggested to have been derived from melting of sub-continental lithospheric mantle (SCLM) sources, but this is precluded because: (1) each widespread heating event sufficient to generate 1 to 2 x 106 km3 of basalt from the Kaapvaal SCLM (volume = 122 to 152 x 106 km3) would increase residual Mg# by 0.5 to 2 units, depending on degree of melting, and source and melt composition, causing significant depletion in already-depleted mantle, (2) repeated refertilization of the Kaapvaal SCLM would necessarily increase its bulk density, compromising its long-term buoyancy and stability, and (3) raising SCLM temperatures to the peridotite solidus would also have repeatedly destroyed lithospheric diamonds by heating and oxidation, which clearly did not happen. It is far more likely, therefore, that the Kaapvaal LIPs were generated from sub-lithospheric sources, and that their diverse geochemical and isotopic signatures represent variable assimilation of continental crustal components. Combined Sr and Nd isotopic data (n = 641) for the vast volumetric majority of Karoo low-Ti tholeiitic magmatic products can be successfully modelled as an AFC mixing array between a plume-derived parental basalt, with <10% of a granitic component derived from 1.1 Ga Namaqua-Natal crust. Archaean crustal materials are far too evolved (?Nd ~ -35) to represent viable contaminants. However, a very minor volume of geographically-restricted (and over-analysed) Karoo magmas, including picrites, nephelinites, meimechites and other unusual rocks may represent low-degree melting products of small, ancient, enriched domains in the Kaapvaal SCLM, generated locally during the ascent of large-volume, plume-derived melts. The SCLM-derived rocks comprise the well-known high-Ti (>2 to 3 wt.% TiO2) magma group, have ?Nd, 182 values between +10.5 and -20.9, and are characteristically enriched in Sr (up to 1 500 ppm), suggesting a possible connection to kimberlite, lamproite and carbonatite magmatism. These arguments may apply to continental LIPs in general, although at present, there are insufficient combined Sr + Nd isotopic data with which to robustly assess the genesis of other southern African LIPs, including Ventersdorp (n = 0), Bushveld (n = 55) and Umkondo (n = 18).
DS202111-1756
2021
Assouline PublisherDiamonds: Diamond Stories ( about fans and celebrities jewels)Assouline.com $95.00, https://lnkd.in/dXWdRYzGlobalBook

Abstract: Formed billions of years ago deep below the surface of the earth, natural diamonds have always had an ethereal mysticism about them. Once reserved only for royals, red carpets, and life’s most celebratory moments, diamonds were seen as symbols of wealth and prosperity that only few could access. But with a new century comes a new expression of luxury, as a new crop of young designers and heritage jewelry houses alike including Sabyasachi, Messika, Anita Ko, Boucheron, and Fernando Jorge are celebrating natural diamonds as an everyday indulgence. Today’s tastemakers are incorporating diamonds into their designs in unexpected ways, unafraid to play around with interesting cuts and colorful hues. In telling the story of today’s expression of natural diamonds and their continous impact on the world, this new volume dives into tales of the world’s most captivating stones, from the Hope Diamond to the legend of the Beau Sancy Diamond. Featuring stunning images; tall tales; and interviews with top designers, tastemakers, and enthusiasts alike; Diamonds is the definitive book on the world’s most sought-after jewel.
DS202102-0173
2020
Aulbach, S., Giuliani, A., Fiorentini, M.L., Baumgartner, R.J., Davard, D., Kamenetsky, V.S., Caruso, S., Danyushevsky, L.V., Powell, W., Griffin, W.L.Siderophile and chalcophile elements in spinels, sulphides and native Ni in strongly metasomatised xenoliths from the Bultfontein kimberlite (South Africa).Lithos, doi.org/10.1016/ jlithos.2020.105880, 26p. PdfAfrica, South Africadeposit - Bultfontein

Abstract: The metasomatised continental mantle may play a key role in the generation of some ore deposits, in particular mineral systems enriched in platinum-group elements (PGE) and Au. The cratonic lithosphere is the longest-lived potential source for these elements, but the processes that facilitate their pre-concentration in the mantle and their later remobilisation to the crust are not yet well-established. Here, we report new results on the petrography, major-element, and siderophile- and chalcophile-element composition of native Ni, base metal sulphides (BMS), and spinels in a suite of well-characterised, highly metasomatised and weakly serpentinised peridotite xenoliths from the Bultfontein kimberlite in the Kaapvaal Craton, and integrate these data with published analyses. Pentlandite in polymict breccias (failed kimberlite intrusions at mantle depth) has lower trace-element contents (e.g., median total PGE 0.72 ppm) than pentlandite in phlogopite peridotites and Mica-Amphibole-Rutile-Ilmenite-Diopside (MARID) rocks (median 1.6 ppm). Spinel is an insignificant host for all elements except Zn, and BMS and native Ni account for typically <25% of the bulk-rock PGE and Au. High bulk-rock Te/S suggest a role for PGE-bearing tellurides, which, along with other compounds of metasomatic origin, may host the missing As, Ag, Cd, Sb, Te and, in part, Bi that are unaccounted for by the main assemblage. The close spatial relationship between BMS and metasomatic minerals (e.g., phlogopite, ilmenite) indicates that the lithospheric mantle beneath Bultfontein was resulphidised by metasomatism after initial melt depletion during stabilisation of the cratonic lithosphere. Newly-formed BMS are markedly PGE-poor, as total PGE contents are <4.2 ppm in pentlandite from seven samples, compared to >26 ppm in BMS in other peridotite xenoliths from the Kaapvaal craton. This represents a strong dilution of the original PGE abundances at the mineral scale, perhaps starting from precursor PGE alloy and small volumes of residual BMS. The latter may have been the precursor to native Ni, which occurs in an unusual Ni-enriched zone in a harzburgite and displays strongly variable, but overall high PGE abundances (up to 81 ppm). In strongly metasomatised peridotites, Au is enriched relative to Pd, and was probably added along with S. A combination of net introduction of S, Au +/? PGE from the asthenosphere and intra-lithospheric redistribution, in part sourced from subducted materials, during metasomatic events may have led to sulphide precipitation at ~80-120 km beneath Bultfontein. This process locally enhanced the metallogenic fertility of this lithospheric reservoir. Further mobilisation of the metal budget stored in these S-rich domains and upwards transport into the crust may require interaction with sulphide-undersaturated melts that can dissolve sulphides along with the metals they store.
DS202108-1270
2021
Baes, M., Sobolev, S., Gerya, T., Stern, R., Brune, S.Plate motion and plume-induced subduction inititation.Gondwana Research, Vol. 98, pp. 277-288. pdfSouth Americasubduction

Abstract: Impingement of a hot buoyant mantle plume head on the lithosphere is one of the few scenarios that can initiate a new subduction zone without requiring any pre-existing weak zones. This mechanism can start subduction and plate tectonics on a stagnant lid and can also operate during active plate tectonics where plume-lithosphere interactions is likely to be affected by plate motion. In this study, we explore the influence of plate motion on lithospheric response to plume head-lithosphere interaction including the effect of magmatic weakening of lithosphere. Using 3d thermo-mechanical models we show that the arrival of a new plume beneath the lithosphere can either (1) break the lithosphere and initiate subduction, (2) penetrate the lithosphere without subduction initiation, or (3) spread asymmetrically below the lithosphere. Outcomes indicate that lithospheric strength and plume buoyancy control plume penetration through the lithosphere whereas the plate speed has a subordinate influence on this process. However, plate motion may affect the geometry and dynamics of plume-lithosphere interaction by promoting asymmetry in the subduction zone shape. When a sufficiently buoyant plume hits a young but subductable moving lithosphere, a single-slab modern-style subduction zone can form instead of multiple subduction zones predicted by stagnant lid models. In the case of subduction initiation of older moving oceanic lithosphere, asymmetrical cylindrical subduction is promoted instead of more symmetrical stagnant lid subduction. We propose that the eastward motion of the Farallon plate in Late Cretaceous time could have played a key role in forming one-sided subduction along the southern and western margin of the Caribbean and NW South America.
DS202106-0923
2021
Baioumy, H.Geochemistry and origin of high Sr carbonatite from the Nuba Mountains, Arabian-Nubian Shield, Sudan.Journal of Asian Earth Sciences, Vol. 214, 104773, 9p. PdfAfrica, Sudancarbonatites

Abstract: Carbonatite from the Arabian-Nubian Shield of Sudan occurs as dykes in the Nuba Mountains. It is composed of calcite with some feldspars, quartz and fluorite. CaO is the major constituent in this carbonatite and accordingly, it is classified as calico-carbonatite. The studied carbonatite shows exceptionally high concentrations of SrO (4.4 to 5.9 wt%). Ba, Pb and Y occur in relatively higher concentrations compared to other trace elements. Concentration of rare earth elements (?REEs) is relatively low (average 1550 ppm) compared to many primary igneous carbonatites. The chondrite-normalized REE patterns display higher light rare earth elements (LREEs) compared to heavy rare earth elements (HREEs) with slight negative Ce/Ce* and Eu/Eu* anomalies. The ?18OV-SMOW values range between 7.48 and 10.05‰, while ?13CV-PDB values vary from ?6.24 to ?7.38‰, which is close to the primary carbonatites values. Occurrence of carbonatite as dykes with cumulate and triple junction textures, plot of the carbonatite in the true carbonatite fields of the Ba-Sr and Ba + Sr-REE + Y diagrams, igneous-derived ?13CV-PDB and ?18OV-SMOW values and high (La/Yb)N ratios indicate its primary igneous origin. The strong positive correlation between REEs and Sr suggests the occurrence of these elements as secondary strontianite, which was confirmed by SEM and EDX analyses. This might indicate that the enrichment of REEs and Sr in the studied carbonatite is not from the primary magma and most probably took place during a sub-solidus metasomatic process after the carbonatite emplacement.
DS202109-1450
2021
Baioumy, H.Geochemistry and origin of high -Sr carbonatite from the Nuba Mountains, Arabian-Nubian shield, Sudan.Journal of Asian Earth Sciences, Vol. 214, 104773, 10p. PdfAfrica, Sudancarbonatite
DS202109-1451
2021
Bajgain, S.K. Earth's core could be the largest terrestrial carbon reservoir.Communications Earth & Environment, doi.org/10.1038/s43247-021-00222-7Mantlecarbon

Abstract: Evaluating carbon’s candidacy as a light element in the Earth’s core is critical to constrain the budget and planet-scale distribution of this life-essential element. Here we use first principles molecular dynamics simulations to estimate the density and compressional wave velocity of liquid iron-carbon alloys with ~4-9 wt.% carbon at 0-360 gigapascals and 4000-7000 kelvin. We find that for an iron-carbon binary system, ~1-4 wt.% carbon can explain seismological compressional wave velocities. However, this is incompatible with the ~5-7 wt.% carbon that we find is required to explain the core’s density deficit. When we consider a ternary system including iron, carbon and another light element combined with additional constraints from iron meteorites and the density discontinuity at the inner-core boundary, we find that a carbon content of the outer core of 0.3-2.0 wt.%, is able to satisfy both properties. This could make the outer core the largest reservoir of terrestrial carbon.
DS202108-1271
2021
Banerjee, A., Satish-Kumar, M., Chakrabarti, R.Sulfur, carbon and oxygen isotopic compositions of Newania carbonatites of India: implications for the mantle source characteristics.Journaof Mineralogical and Petrological Sciences, Vol. 116, pp. 121-128 pdfIndiadeposit - Newania

Abstract: This study presents first report of the sulfur isotopic compositions of carbonatites from the Mesoproterozoic Newania complex of India along with their stable C and O isotope ratios. The ?34SV-CDT (?1.4 to 2‰) and ?33S (?0.001 to ?0.13‰) values of these carbonatite samples (n = 7) overlap with the S isotope compositions of Earth’s mantle. Additionally, the ?13CV-PDB and ?18OV-SMOW values of these carbonatites also show overlapping compositions to that of Earth’s mantle. Based on these mantle-like stable isotopic compositions of carbonatites along with their higher crystallization temperature (~ 600 °C) compared to a hydrothermal fluid (<250 °C), we suggest that the sulfide minerals in these carbonatites were formed under a magmatic condition. The mantle like signatures in the ?34S, ?13C- ?18O, and 87Sr/86Sr values of these carbonatites rule out possible crustal contamination. Coexistence of the sulfide phase (pyrrhotite) with magnesite in these carbonatites suggests that the sulfide phase has formed early during the crystallization of carbonatite magmas under reducing conditions. Overall restricted variability in the ?34S values of these samples further rules out any isotopic fractionation due to the change in the redox condition of the magma and reflect the isotopic composition of the parental melts of the Newania carbonatite complex. A compilation of ?34S of carbonatites from Newania and other complexes worldwide indicates limited variability in the isotopic composition for carbonatites older than 400 Ma, which broadly overlaps with Earth’s asthenospheric mantle composition. This contrasts with the larger variability in ?34S observed in carbonatites younger than 400 Ma. Such observation could suggest an overall lower oxidation state of carbonatite magmas emplaced prior to 400 Ma.
DS202108-1272
2021
Barbaro, B.A., Domeneghetti, M.C., Litasov, K.D., Ferriere, L., Pittarello, L., Christ, O., Lorenzon, S., Alvaro, M., Nestola, F.Origin of micrometer-sized impact diamonds in urelilites by catalytic growth involving Fe-Ni-silicide: the example of Kenna meteorite.Geochimica et Cosmochimica Acta, doi.org/10.1016/j.gca.2021.06.022 31p. PdfGlobalmeteorite

Abstract: The occurrence of shock-induced diamonds in ureilite meteorites is common and is used to constrain the history of the ureilite parent bodies. We have investigated a fragment of the Kenna ureilite by micro-X-ray diffraction, micro-Raman spectroscopy and scanning electron microscopy to characterize its carbon phases. In addition to olivine and pigeonite, within the carbon-bearing areas, we identified microdiamonds (up to about 10 ?m in size), nanographite and magnetite. The shock features observed in the silicate minerals and the presence of microdiamonds and nanographite indicate that Kenna underwent a shock event with a peak pressure of at least 15 GPa. Temperatures estimated using a graphite geothermometer are close to 1180 °C. Thus, Kenna is a medium-shocked ureilite, yet it contains microdiamonds, which are typically found in highly shocked carbon-bearing meteorites, instead of the more common nanodiamonds. This can be explained by a relatively long shock event duration (in the order of 4-5 s) and/or by the catalytic effect of Fe-Ni alloys known to favour the crystallization of diamonds. For the first time in a ureilite, carletonmooreite with formula Ni3Si and grain size near 4-7 nm, was found. The presence of nanocrystalline carletonmooreite provides further evidence to support the hypothesis of the catalytic involvement of Fe-Ni bearing phases into the growth process of diamond from graphite during shock events in the ureilite parent body, enabling the formation of micrometer-sized diamond crystals.
DS202108-1273
2021
Barnes, S.J., Williams, M., Smithies, R.H., Hanski, E., Lowrey, J.R.Trace element contents of mantle derived magmas through time.Mineralium Deposita, Vol. 56, pp. 1133-1150.Mantlemagmatism

Abstract: A large compilation of quality-curated major and trace element data has been assembled to investigate how trace element patterns of mafic and ultramafic magmas have varied with time through particular settings from the Archean to the Phanerozoic, the primary objective being to recognise at what times particular patterns of variation emerge, and how similar these are to baseline data sets representing tectonic settings in the modern Earth. The most informative element combinations involve Nb, Th and the REE, where REE are represented by ‘lambda’ parameters describing slope and shape of patterns. Combinations of the ratios of Th, Nb, La and lambda values from Archean and early Proterozoic basalts and komatiites reveal a distinctive pattern that is common in most well-sampled terranes, defining a roughly linear trend in multi-dimensional space from compositions intermediate between modern n-MORB and primitive mantle at one end, towards compositions approximating middle-to-upper continental crust at the other. We ascribe this ‘Variable Th/Nb’ trend in most instances to varying degrees of crustal contamination of magmas with similar compositions to modern oceanic plateau basalts. Komatiites had slightly more depleted sources than basalts, consistent with the hypothesis of derivation from plume tails and heads, respectively. The most significant difference between Precambrian and Phanerozoic plume-derived basalts is that the distinctive OIB-like enriched source component appears to be largely missing from the Archean and Proterozoic geologic record, although isolated examples of OIB-like trace element characteristics are evident in datasets from even the oldest preserved greenstones. Phanerozoic intra-cratonic LIPs, such as the 260?Ma Emeishan LIP in China, have fundamentally different geochemical characteristics to Archean and Paleoproterozoic assemblages; the oldest Proterozoic LIP we have identified that has this type of ‘modern’ signal is the Midcontinent Rift at 1100?Ma. The data are consistent with plume tail sources having changed from being dominantly depleted in the Archean Earth to dominantly enriched in the Phanerozoic Earth, while plume head sources have hardly changed at all. Trace element patterns considered to be diagnostic of subduction are locally present but rare in Archean terranes and become more prevalent through the Proterozoic, although this conclusion is tempered by the large degree of overlap in compositional space between continental arc magmas and continental flood basalts. This overlap reflects the difficulty of distinguishing the effects of supra-subduction metasomatizm and flux melting from those of crustal contamination. Additional factors must also be borne in mind, particularly that trace element partitioning systematics may have been different in all environments in a hotter planet, and large-scale asthenospheric overturns might have been predominant over modern-style plumes in the Archean Earth. Some basaltic suites in particular Archean terranes, notably the western parts of both the Yilgarn and Pilbara cratons in Western Australia and parts of the Superior Craton, have restricted, but locally predominant, suites of basalts with characteristics akin to modern oceanic arcs, suggesting that some process similar to modern subduction was preserved in these particular belts. Ferropicrite magmas with distinctive characteristics typical of modern OIBs and some continental LIPs (notably Emeishan) are rare but locally predominant in some Archean and early Proterozoic terranes, implying that plume sources were beginning to be fertilised by enriched, probably subducted, components as far back as the Mesoarchean. We see no evidence for discontinuous secular changes in mantle-derived magmatism with time that could be ascribed to major mantle reorganisation events. The Archean-Proterozoic transition appears to be entirely gradational from this standpoint. The transition from Archean-style to Phanerozoic-style plume magmatism took place somewhere between 1900?Ma (age of the Circum-Superior komatiitic basalt suites) and 1100?Ma (the age of the Midcontinent Rift LIP).
DS202110-1600
2021
Barrie, E., Eaton-Magana, S.CVD Laboratory-grown diamond with counterfeit GIA inscription.Gems & Gemology, Vol. 57, 2, summer pp. 150-152. gia.edu/gems-gemologyUnited States, Californiasynthetic

Abstract: In recent months, GIA has seen a number of laboratory-grown diamonds submitted for update or verification services with counterfeit inscriptions referencing GIA natural diamond reports ("GIA laboratory prevents attempted fraud"). One recent example is a 3.07 ct round brilliant submitted to the Antwerp lab for update service (figure 1). It bore an inscription matching a GIA report for a natural diamond that had been submitted in 2018. Microscopic examination quickly revealed, however, that the inscription was in fact fraudulent. Further analysis indicated a laboratory-grown origin.
DS202102-0174
2021
Barry, P.H., Broadley, M.W.Nitrogen and noble gases reveal a complex history of metasomatism in the Siberian lithospheric mantle.Earth and Planetary Science Letters, Vol. 556, doi.org/10.1016 /j.epsl.2020. 116707 12p. PdfRussianitrogen

Abstract: The Siberian flood basalts (SFB) erupted at the end of the Permian period (?250 Ma) in response to a deep-rooted mantle plume beneath the Siberian Sub-Continental Lithospheric Mantle (SCLM). Plume-lithosphere interaction can lead to significant changes in the structure and chemistry of the SCLM and trigger the release of metasomatic material that was previously stored within the stable craton. Here, we investigate the nature of the Siberian-SCLM (S-SCLM) by measuring nitrogen abundances and isotopes (N) in 11 samples of two petrologically-distinct suites of peridotitic xenoliths recovered from kimberlites which bracket the eruption of the SFB: the 360 Myr old Udachnaya and 160 Myr old Obnazhennaya pipes. Nitrogen isotope (N) values range from -5.85 ± 1.29‰ to +3.94 ± 0.63‰, which encompasses the entire range between depleted Mid-Ocean Ridge Basalt (MORB) mantle (DMM; -5 ± 2‰) and plume-derived (+3 ± 2‰) endmembers. In addition, we present neon (n=7) and argon (n=8) abundance and isotope results for the same two suites of samples. The 20Ne/22Ne and 21Ne/22Ne range from atmospheric-like values of 9.88 up to 11.35 and from 0.0303 to 0.0385, respectively, suggesting an admixture of DMM and plume-derived components. Argon isotopes (40Ar/36Ar) range from 336.7 to 1122 and correlate positively with 40Ar contents. We show that volatile systematics of Siberian xenoliths: (1) exhibit evidence of ancient metasomatic and/or recycled signatures, and (2) show evidence of subsequent plume-like re-fertilization, which we attribute to the emplacement of the SFB. Metasomatic fluids are highly enriched in radiogenic gases and have elevated Br/Cl and I/Cl values, consistent with an ancient subducted crustal component. The metasomatic component is marked by light N isotope signatures, suggesting it may be derived from an anoxic Archean subducted source. Taken together, these N2-Ne-Ar isotope results suggest that mantle plume impingement has profoundly modified the S-SCLM, and that N, Ne and Ar isotopes are sensitive tracers of metasomatism in the S-SCLM. Metasomatic fluids that permeate the S-SCLM act to archive a “subduction-fingerprint” that can be used to probe relative volatile-element recycling efficiencies and thus provide insight into volatile transport between the surface and mantle reservoirs over Earth history.
DS202107-1089
2021
Bassoo, R., Befus, K.S.Composition of the sub-cratonic mantle of the Guiana shield inferred from diamond-hosted inclusions.Geochemistry, Geophysics, Geosytems, 24p. PdfSouth America, Venezueladiamond inclusions

Abstract: Diamonds entrap mantle inclusions and shield them from alteration by magmatic and tectonic processes. Diamonds from Guyana are an understudied diamond suite, and the inclusions they contain provide us a window into the sub-cratonic mantle beneath northern South America. We used crystalline inclusions inside of Guyanese diamonds to infer the composition of the underlying mantle, and make estimates for its structural properties. The inclusions empirically demonstrate the long-lived, dry, and reduced nature of cratonic roots, lending evidence to the mechanism behind their preservation through time.
DS202109-1452
2021
Bates, R.So what happens to Afghanistan's gems now?JCKmagazine.com, Aug. 20, 4p. PdfAsia, Afghanistanemerald
DS202106-0924
2021
Becker, T., Boschi, L.Multi-scale, radially anisotropic shear wave imaging of the mantle underneath the contiguous United States through joint inversion of USArray and global datasets.Geophysical Journal International, 34p. PdfUnited Statestomography

Abstract: EarthScope's USArray seismic component provided unprecedented coverage of the contiguous United States and has therefore spurred significant advances in tomographic imaging and geodynamic modelling. Here, we present a new global, radially anisotropic shear wave velocity tomography model to investigate upper mantle structure and North American Plate dynamics, with a focus on the contiguous United States. The model uses a data-adaptive mesh and traveltimes of both surface waves and body waves to constrain structure in the crust and mantle in order to arrive at a more consistent representation of the subsurface compared to what is provided by existing models. The resulting model is broadly consistent with previous global models at the largest scales, but there are substantial differences under the contiguous United States where we can achieve higher resolution. On these regional scales, the new model contains short wavelength anomalies consistent with regional models derived from USArray data alone. We use the model to explore the geometry of the subducting Farallon Slab, the presence of upper mantle high velocity anomalies, low velocity zones in the central and eastern United States and evaluate models of dynamic topography in the Cordillera. Our models indicate a single, shallowly dipping, discontinuous slab associated with the Farallon Plate, but there are remaining imaging challenges. Inferring dynamic topography from the new model captures both the long-wavelength anomalies common in global models and the short-wavelength anomalies apparent in regional models. Our model thus bridges the gap between high-resolution regional models within the proper uppermost mantle context provided by global models, which is crucial for understanding many of the fundamental questions in continental dynamics.
DS202111-1757
2021
Bedard, J.H., Troll, V,R., Deegan, F.M., Tegner, C., Saumur, B.M., Evenchick, C.A., Grasby, S.E., Dewing, K.High Arctic large igneous province alkaline rocks in Canada: evidence for multiple mantle components.Journal of Petrology, Vol. 62, 9, pp. 1-31. pdfCanada, Ellesmere Islandalkaline rocks

Abstract: The Cretaceous High Arctic Large Igneous Province (HALIP) in Canada, although dominated by tholeiites (135-90?Ma), contains two main groups of alkaline igneous rocks. The older alkaline rocks (?96?Ma) scatter around major fault and basement structures. They are represented by the newly defined Fulmar Suite alkaline basalt dykes and sills, and include Hassel Formation volcanic rocks. The younger alkaline group is represented by the Wootton Intrusive Complex (92•2-92•7?Ma), and the Audhild Bay Suite (83-73?Ma), both emplaced near the northern coast of Ellesmere Island. Fulmar Suite rocks resemble EM-type ocean island basalts (OIB) and most show limited crustal contamination. The Fulmar Suite shows increases of P2O5 at near-constant Ba-K-Zr-Ti that are nearly orthogonal to predicted fractionation- or melting-related variations, which we interpret as the result of melting composite mantle sources containing a regionally widespread apatite-bearing enriched component (P1). Low-P2O5 Fulmar Suite variants overlap compositionally with enriched HALIP tholeiites, and fall on common garnet lherzolite trace element melting trajectories, suggesting variable degrees of melting of a geochemically similar source. High-P2O5 Hassel Formation basalts are unusual among Fulmar rocks, because they are strongly contaminated with depleted lower crust; and because they involve a high-P2O5-Ba-Eu mantle component (P2), similar to that seen in alkali basalt dykes from Greenland. The P2 component may have contained Ba-Eu-rich hawthorneite and/or carbonate minerals as well as apatite, and may typify parts of the Greenlandic sub-continental lithospheric mantle (SCLM). Mafic alkaline Audhild Bay Suite (ABS) rocks are volcanic and hypabyssal basanites, alkaline basalts and trachy-andesites, and resemble HIMU ocean island basalts in having high Nb, low Zr/Nb and low 87Sr/86Sri. These mafic alkaline rocks are associated with felsic alkaline lavas and syenitic intrusions, but crustally derived rhyodacites and rhyolites also exist. The Wootton Intrusive Complex (WIC) contains geochemically similar plutonic rocks (alkali gabbros, diorites and anatectic granites), and may represent a more deeply eroded, slightly older equivalent of the ABS. Low-P2O5 ABS and WIC alkaline mafic rocks have flat heavy rare earth element (HREE) profiles suggesting shallow mantle melting; whereas High-P2O5 variants have steep HREE profiles indicating deeper separation from garnet-bearing residues. Some High-P2O5 mafic ABS rocks seem to contain the P1 and P2 components identified in Fulmar-Hassel rocks, whereas other samples trend towards possible High-P2O5 + Zr (PZr) and High-P2O5 + K2O (PK) components. We argue that the strongly alkaline northern Ellesmere Island magmas sampled mineralogically heterogeneous veins or metasomes in Greenlandic-type SCLM, which contained trace phases such as apatite, carbonates, hawthorneite, zircon, mica or richterite. The geographically more widespread apatite-bearing component (P1) could have formed part of a heterogeneous plume or upwelling mantle current that also generated HALIP tholeiites when melted more extensively, but may also have resided in the SCLM as relics of older events. Rare HALIP alkaline rocks with high K-Rb-U-Th fall on mixing paths implying strong local contamination from either Sverdrup Basin sedimentary rocks or granitic upper crust. However, the scarcity of potassic alkaline HALIP facies, together with the other trace element and isotopic signatures, provides little support for a ubiquitous fossil sedimentary subduction-zone component in the HALIP mantle source.
DS202107-1090
2021
Bedard, J.H., Troll, V.R., Deegan F.M., Tegner, C., Sauumur, B. M., Evenchick, C.A., Grasby, S.E., Dewing, K.High Arctic large igneous province alkaline rocks in Canada: evidence for multiple mantle components.Journal of Petrology, 113p. In press availableCanada, Ellesmerealkaline rocks

Abstract: The Cretaceous High Arctic Large Igneous Province (HALIP) in Canada, although dominated by tholeiites (135-90?Ma), contains two main groups of alkaline igneous rocks. The older alkaline rocks (?96?Ma) scatter around major fault and basement structures. They are represented by the newly-defined Fulmar Suite alkaline basalt dykes and sills, and include Hassel Formation volcanics. The younger alkaline group is represented by the Wootton Intrusive Complex (92.2-92.7?Ma), and the Audhild Bay Suite (83-73?Ma); both emplaced near the northern coast of Ellesmere Island. Fulmar Suite rocks resemble EM-type ocean island basalts (OIB) and most show limited crustal contamination. The Fulmar Suite shows increases of P2O5 at near-constant Ba-K-Zr-Ti that are nearly orthogonal to predicted fractionation- or melting-related variations; which we interpret as the result of melting composite mantle sources containing a regionally widespread apatite-bearing enriched component (P1). Low-P2O5 Fulmar Suite variants overlap compositionally with enriched HALIP tholeiites, and fall on common garnet lherzolite trace element melting trajectories, suggesting variable degrees of melting of a geochemically similar source. High-P2O5 Hassel Formation basalts are unusual among Fulmar rocks, because they are strongly contaminated with depleted lower crust; and because they involve a high-P2O5-Ba-Eu mantle component (P2), similar to that seen in alkali basalt dykes from Greenland. The P2 component may have contained Ba-Eu-rich hawthorneite and/or carbonate minerals as well as apatite, and may typify parts of the Greenlandic sub-continental lithospheric mantle (SCLM). Mafic alkaline Audhild Bay Suite (ABS) rocks are volcanic and hypabyssal basanites, alkaline basalts and trachy-andesites, and resemble HIMU ocean island basalts in having high Nb, low Zr/Nb and low 87Sr/86Sri. These mafic alkaline rocks are associated with felsic alkaline lavas and syenitic intrusions, but crustally-derived rhyodacites and rhyolites also exist. The Wootton Intrusive Complex (WIC) contains geochemically similar plutonic rocks (alkali gabbros, diorites and anatectic granites), and may represent a more deeply eroded, slightly older equivalent of the ABS. Low-P2O5 ABS and WIC alkaline mafic rocks have flat heavy rare-earth (HREE) profiles suggesting shallow mantle melting; whereas High-P2O5 variants have steep HREE profiles indicating deeper separation from garnet-bearing residues. Some High-P2O5 mafic ABS rocks seem to contain the P1 and P2 components identified in Fulmar-Hassel rocks, whereas other samples trend towards possible High-P2O5+Zr (PZr) and High-P2O5+K2O (PK) components. We argue that the strongly alkaline northern Ellesmere Island magmas sampled mineralogically heterogeneous veins or metasomes in Greenlandic-type SCLM, which contained trace phases like apatite, carbonates, hawthorneite, zircon, mica or richterite. The geographically more widespread apatite-bearing component (P1), could have formed part of a heterogeneous plume or upwelling mantle current that also generated HALIP tholeiites when melted more extensively, but may also have resided in the SCLM as relics of older events. Rare HALIP alkaline rocks with high K-Rb-U-Th fall on mixing paths implying strong local contamination from either Sverdrup Basin sedimentary rocks or granitic upper crust. However, the scarcity of potassic alkaline HALIP facies, together with the other trace element and isotopic signatures, provide little support for an ubiquitous fossil sedimentary subduction zone component in the HALIP mantle source.
DS202108-1274
2021
Bedard, J.H., Troll, V.R., Deegan, F.M., Tegner, C., Saumor, B.M., Evenchick, C.A., Grasby, S.E., Dewing, K.High arctic large igneous province alkaline rocks in Canada: evidence for multiple mantle components.Journal of Petrology, 113p. PdfCanada, Ellesmere Islandalkaline rocks

Abstract: The Cretaceous High Arctic Large Igneous Province (HALIP) in Canada, although dominated by tholeiites (135-90?Ma), contains two main groups of alkaline igneous rocks. The older alkaline rocks (?96?Ma) scatter around major fault and basement structures. They are represented by the newly-defined Fulmar Suite alkaline basalt dykes and sills, and include Hassel Formation volcanics. The younger alkaline group is represented by the Wootton Intrusive Complex (92.2-92.7?Ma), and the Audhild Bay Suite (83-73?Ma); both emplaced near the northern coast of Ellesmere Island. Fulmar Suite rocks resemble EM-type ocean island basalts (OIB) and most show limited crustal contamination. The Fulmar Suite shows increases of P2O5 at near-constant Ba-K-Zr-Ti that are nearly orthogonal to predicted fractionation- or melting-related variations; which we interpret as the result of melting composite mantle sources containing a regionally widespread apatite-bearing enriched component (P1). Low-P2O5 Fulmar Suite variants overlap compositionally with enriched HALIP tholeiites, and fall on common garnet lherzolite trace element melting trajectories, suggesting variable degrees of melting of a geochemically similar source. High-P2O5 Hassel Formation basalts are unusual among Fulmar rocks, because they are strongly contaminated with depleted lower crust; and because they involve a high-P2O5-Ba-Eu mantle component (P2), similar to that seen in alkali basalt dykes from Greenland. The P2 component may have contained Ba-Eu-rich hawthorneite and/or carbonate minerals as well as apatite, and may typify parts of the Greenlandic sub-continental lithospheric mantle (SCLM). Mafic alkaline Audhild Bay Suite (ABS) rocks are volcanic and hypabyssal basanites, alkaline basalts and trachy-andesites, and resemble HIMU ocean island basalts in having high Nb, low Zr/Nb and low 87Sr/86Sri. These mafic alkaline rocks are associated with felsic alkaline lavas and syenitic intrusions, but crustally-derived rhyodacites and rhyolites also exist. The Wootton Intrusive Complex (WIC) contains geochemically similar plutonic rocks (alkali gabbros, diorites and anatectic granites), and may represent a more deeply eroded, slightly older equivalent of the ABS. Low-P2O5 ABS and WIC alkaline mafic rocks have flat heavy rare-earth (HREE) profiles suggesting shallow mantle melting; whereas High-P2O5 variants have steep HREE profiles indicating deeper separation from garnet-bearing residues. Some High-P2O5 mafic ABS rocks seem to contain the P1 and P2 components identified in Fulmar-Hassel rocks, whereas other samples trend towards possible High-P2O5+Zr (PZr) and High-P2O5+K2O (PK) components. We argue that the strongly alkaline northern Ellesmere Island magmas sampled mineralogically heterogeneous veins or metasomes in Greenlandic-type SCLM, which contained trace phases like apatite, carbonates, hawthorneite, zircon, mica or richterite. The geographically more widespread apatite-bearing component (P1), could have formed part of a heterogeneous plume or upwelling mantle current that also generated HALIP tholeiites when melted more extensively, but may also have resided in the SCLM as relics of older events. Rare HALIP alkaline rocks with high K-Rb-U-Th fall on mixing paths implying strong local contamination from either Sverdrup Basin sedimentary rocks or granitic upper crust. However, the scarcity of potassic alkaline HALIP facies, together with the other trace element and isotopic signatures, provide little support for an ubiquitous fossil sedimentary subduction zone component in the HALIP mantle source.
DS202109-1453
2021
Beddie, H., Coper, C.M., Frost, C.D.Nature versus Nurture: preservation and destruction of Archean cratons.Tectonics, e2021TC006714 67p. PdfMantlecratons

Abstract: Because of Earth’s dynamic tectonic processes, much of its continental crust has been eroded and recycled and only a fraction of crust older than 2.5 billion years has survived to the present-day. These areas of old crust, known as Archean cratons, have not experienced deformation or magmatism for a billion years or more. This paper investigates whether craton survival is related to their nature, that is, the conditions of their formation, or to nurture, the subsequent events they experienced. Eight case studies are used to evaluate the properties and processes that promote craton stability. Nature is important: surviving Archean cratons tend to be buoyant, viscous, cold, and thick. Some survive because they have not experienced destabilizing geologic processes that introduce heat, magma, and fluids. Others have been modified to various extents by these processes. Some have been weakened and thinned and other, only marginally stable cratons are susceptible to future deformation and destruction. We conclude that both nature and nurture are essential to the survival of Earth’s oldest crust.
DS202107-1091
2021
Bekaert, D.V., Turner, S.J., Broadley, M.W., Barnes, J.D., Halldorsson, S.A., Labidi, J., Wade, J., Walowski, K.J., Barry, P.H.Subduction-driven volatile recycling: a global mass balance.Annual Review of Earth and Planetary Sciences, Vol. 49, pp. 37-70.Mantlesubduction

Abstract: Volatile elements (water, carbon, nitrogen, sulfur, halogens, and noble gases) played an essential role in the secular evolution of the solid Earth and emergence of life. Here we provide an overview of Earth's volatile inventories and describe the mechanisms by which volatiles are conveyed between Earth's surface and mantle reservoirs, via subduction and volcanism. Using literature data, we compute volatile concentration and flux estimates for Earth's major volatile reservoirs and provide an internally balanced assessment of modern global volatile recycling. Using a nitrogen isotope box model, we show that recycling of N (and possibly C and S) likely began before 2 Ga and that ingassing fluxes have remained roughly constant since this time. In contrast, our model indicates recycling of H2O(and most likely noble gases) was less efficient in the past. This suggests a decoupling of major volatile species during subduction through time, which we attribute to the evolving thermal regime of subduction zones and the different stabilities of the carrier phases hosting each volatile. This review provides an overview of Earth's volatile inventory and the mechanisms by which volatiles are transferred between Earth reservoirs via subduction. The review frames the current thinking regarding how Earth acquired its original volatile inventory and subsequently evolved through subduction processes and volcanism.
DS202110-1601
2021
Benmore, C.J., Wilding, M.C.Probing the structure of melts, glasses, and amorphous materials.Elements, Vol. 17, pp. 175-180.Mantlemelting

Abstract: Liquids, glasses, and amorphous materials are ubiquitous in the Earth sciences and are intrinsic to a plethora of geological processes, ranging from volcanic activity, deep Earth melting events, metasomatic processes, frictional melting (pseudotachylites), lighting strikes (fulgurites), impact melting (tektites), hydrothermal activity, aqueous solution geochemistry, and the formation of dense high-pressure structures. However, liquids and glassy materials lack the long-range order that characterizes crystalline materials, and studies of their structure require a different approach to that of conventional crystallography. The pair distribution function is the neutron diffraction technique used to characterize liquid and amorphous states. When combined with atomistic models, neutron diffraction techniques can determine the properties and behavior of disordered structures.
DS202103-0368
2021
Bergman, S.C., Eldrett, J.S., Minisini, D.Phanerozoic Large Igneous Province, Petroleum system, and source rock links.American Geophysical Union and Wiley editors Ernst, R.E., Dickson, A.J., Bekker, A. Monograph 255, Chapter 9, 38p. Pdf doi:10.1002/ 9781119507444 open accessMantleplumes

Abstract: This chapter summarizes geochronologic and other data for major Phanerozoic Large Igneous Provinces (LIPs), Oceanic Anoxic Events (OAEs) and organic?rich petroleum source rocks. It also evaluates the models that support or refute genetic links between the three groups. The evidence appears to favor genetic links between the three groups, however, additional high precision age and geochemical data are needed to validate several events. Furthermore, the chapter provides insights into the importance of LIPs in hydrocarbon exploration.
DS202103-0369
2021
Bettucci, L.S., Loureiro, J., Demarco, P.N.Airborne geophysical characterization of Uruguayan basement.Journal of South American Earth Sciences, Vol. 108, 103206, 17p. PdfSouth America, Uruguaygeophysics

Abstract: The integrated observation of geology, gammaspectrometry and magnetometry of southern Uruguay was made possible by the high-resolution aerogeophysical survey carried out during 2014 and 2015. This survey covers nearly the outcropping area of the Uruguayan basement. Previous studies focused on the Proterozoic and Mesozoic dike swarms present in the Uruguayan basement. In this work we address features previously undescribed and unstudied in the Uruguayan basement. Structures previously grouped with the dike swarm are separated (subcircular structures and a lava river) and the basement general patterns were studied. Distinctive magnetic and radiometric features characterize each structural block in the Uruguayan basement, supporting the main tectonic units previously described, but improving the location of their limits.
DS202101-0001
2020
Bindi, L., Camara, F., Gain, S.E.M., Griffin, W.L., Huang, J-X., Saunders, M., Toledo, V.Kishonite, VH2 and oreillyite, Cr2N, two new minerals from the conundrum xenocrysts of Mt. Carmel, northern Israel.Minerals MDPI, Vol. 10, 1118, doi:10.3390/ min10121118 10p. PdfEurope, Israeldeposit - Mt. Carmel

Abstract: Here, we describe two new minerals, kishonite (VH2) and oreillyite (Cr2N), found in xenoliths occurring in pyroclastic ejecta of small Cretaceous basaltic volcanoes exposed on Mount Carmel, Northern Israel. Kishonite was studied by single-crystal X-ray diffraction and was found to be cubic, space group Fm3¯m, with a = 4.2680(10) Å, V = 77.75(3) Å3, and Z = 4. Oreillyite was studied by both single-crystal X-ray diffraction and transmission electron microscopy and was found to be trigonal, space group P3¯1m, with a = 4.7853(5) Å, c = 4.4630(6) Å, V = 88.51 Å3, and Z = 3. The presence of such a mineralization in these xenoliths supports the idea of the presence of reduced fluids in the sublithospheric mantle influencing the transport of volatile species (e.g., C, H) from the deep Earth to the surface. The minerals and their names have been approved by the Commission of New Minerals, Nomenclature and Classification of the International Mineralogical Association (No. 2020-023 and 2020-030a).
DS202109-1454
2021
Bindi, L., Sinmyo, R., Bykova, E., Ovsyannikov, S.V., McCammon, C., Kupenko, I., Ismailova, L., Dubrovinsky, L., Xie, X.Discovery of Elgoresyite ( Mg,FE)5Si2O9: implications for novel iron magnesium silicates in rocky planetery interiors. Mentions Earth's magmatismACS Earth Space Chemistry, Vol. 5, pp. 2124-2130.Mantlebridgmanite

Abstract: As the most abundant material of rocky planets, high-pressure polymorphs of iron- and aluminum-bearing magnesium silicates have long been sought by both observations and experiments. Meanwhile, it was recently revealed that iron oxides form (FeO)m(Fe2O3)n homologous series above ?10 GPa according to laboratory high-pressure experiments. Here, we report a new high-pressure iron-magnesium silicate, recently approved by the International Mineralogical Association as a new mineral (No. 2020-086) and named elgoresyite, in a shock-induced melt vein of the Suizhou L6 chondrite with a chemistry of (Mg,Fe)5Si2O9. The crystal structure of this new silicate is the same as the iron oxide Fe7O9, strongly suggesting that silicates also form ((Mg,Fe)O)m + n(SiO2)n series that are isostructural to iron oxides via (Mg2+,Fe2+) + Si4+ = 2Fe3+ substitution. To test this hypothesis, the phase relationships of the silicates and iron oxides should be further investigated at higher temperature conditions. Newly found iron-magnesium silicate is a potential constituent mineral in rocky planets with relatively high MgO + FeO content.
DS202112-1920
2021
Blanchard. I., Abeykon, S., Frost, D.J., Rubie, D.C.Sulfur content at sulfide saturation of peridotitic melt at upper mantle conditions.American Mineralogist, Vol. 106, pp. 1835-1843. pdfMantlesulfides

Abstract: The concentration of sulfur that can be dissolved in a silicate liquid is of fundamental importance because it is closely associated with several major Earth-related processes. Considerable effort has been made to understand the interplay between the efects of silicate melt composition and its capacity to retain sulfur, but the dependence on pressure and temperature is mostly based on experiments performed at pressures and temperatures below 6 GPa and 2073 K. Here we present a study of the effects of pressure and temperature on sulfur content at sulfide saturation of a peridotitic liquid. We performed 14 multi-anvil experiments using a peridotitic starting composition, and we produced 25 new measurements at conditions ranging from 7 to 23 GPa and 2173 to 2623 K. We analyzed the recovered samples using both electron microprobe and laser ablation ICP-MS. We compiled our data together with previously published data that were obtained at lower P-T conditions and with various silicate melt compositions. We present a new model based on this combined data set that encompasses the entire range of upper mantle pressure-temperature conditions, along with the efect of a wide range of silicate melt compositions. Our findings are consistent with earlier work based on extrapolation from lower-pressure and lower-temperature experiments and show a decrease of sulfur content at sulfide saturation (SCSS) with increasing pressure and an increase of SCSS with increasing temperature. We have extrapolated our results to pressure-temperature conditions of the Earth’s primitive magma ocean, and show that FeS will exsolve from the molten silicate and can efectively be extracted to the core by a process that has been termed the "Hadean Matte." We also discuss briefly the implications of our results for the lunar magma ocean.
DS202102-0175
2020
Blanks, D.E., Holwell, D.A., Fiorentini, M.L., Moroni, M., Giuliani, A., Tassara, S., Gonzales-Jiminez, J.M., Boyce, A.J., Ferrari, E.Fluxing of mantle carbon as a physical agent for metallogenic fertilization of the crust.Nature Communications, doi.org/10.1038/ s41467-020-18157-6 11p. Pdf Mantlecarbon

Abstract: Magmatic systems play a crucial role in enriching the crust with volatiles and elements that reside primarily within the Earth’s mantle, including economically important metals like nickel, copper and platinum-group elements. However, transport of these metals within silicate magmas primarily occurs within dense sulfide liquids, which tend to coalesce, settle and not be efficiently transported in ascending magmas. Here we show textural observations, backed up with carbon and oxygen isotope data, which indicate an intimate association between mantle-derived carbonates and sulfides in some mafic-ultramafic magmatic systems emplaced at the base of the continental crust. We propose that carbon, as a buoyant supercritical CO2 fluid, might be a covert agent aiding and promoting the physical transport of sulfides across the mantle-crust transition. This may be a common but cryptic mechanism that facilitates cycling of volatiles and metals from the mantle to the lower-to-mid continental crust, which leaves little footprint behind by the time magmas reach the Earth’s surface.
DS202110-1602
2021
Boneh, Y., Chin, E.J., Hirth, G.Microstructural analysis of a mylonitic mantle xenolith sheared laboratory-like strain rates from the edge of the Wyoming craton.Minerals MDPI, Vol. 11, 995, 18p. PdfUnited States, Montana, Wyoming, Utah, Canada, Alberta, Saskatchewancraton

Abstract: Combined observations from natural and experimental deformation microstructures are often used to constrain the rheological properties of the upper mantle. However, relating natural and experimental deformation processes typically requires orders of magnitude extrapolation in strain rate due to vastly different time scales between nature and the lab. We examined a sheared peridotite xenolith that was deformed under strain rates comparable to laboratory shearing time scales. Microstructure analysis using an optical microscope and electron backscatter diffraction (EBSD) was done to characterize the bulk crystallographic preferred orientation (CPO), intragrain misorientations, subgrain boundaries, and spatial distribution of grains. We found that the microstructure varied between monophase (olivine) and multiphase (i.e., olivine, pyroxene, and garnet) bands. Olivine grains in the monophase bands had stronger CPO, larger grain size, and higher internal misorientations compared with olivine grains in the multiphase bands. The bulk olivine CPO suggests a dominant (010)[100] and secondary activated (001)[100] that are consistent with the experimentally observed transition of the A to E-types. The bulk CPO and intragrain misorientations of olivine and orthopyroxene suggest that a coarser-grained initial fabric was deformed by dislocation creep coeval with the reduction of grain size due to dynamic recrystallization. Comparing the deformation mechanisms inferred from the microstructure with experimental flow laws indicates that the reduction of grain size in orthopyroxene promotes activation of diffusion creep and suggests a high activation volume for wet orthopyroxene dislocation creep.
DS202110-1603
2021
Borenstein, G., Oneal, S.Rare mixed type IaB-IIb diamond with a long-lasting phosphorescence. Stuller's Gem Lab.Gems & Gemology, Vol. 57, 2, summer pp. 178-179. gia.edu/gems-gemologyUnited States, Louisiannaluminescence
DS202111-1758
2020
Boutyon, A., Klausen, M., Mata, J., Tappe, S., Farquhar, J., Cartigny, P.Multiple sulfur isotopes of carbonatites, a window into their formation conditions.Goldschmidt2020, 1p. Abstract pdfMantlecarbonatite

Abstract: Carbonatites are rare volcanic rocks whose carbon/oxygen isotope signatures point towards a mantle origin. However there is still debate on the role of processes such as partial melting or the recycling of sediments for their generation. Carbonatite quadruple sulfur isotope measurements should be useful for deciphering the imprints of Earth’s earliest atmosphere and microbial cycling, two processes isotopically characterized by different slopes in a ?33S-?36S diagram, and thus help to better understand the origin of carbonatites, and the possiblity of sedimentary precursors, in greater detail. We report here multiple sulfur data for a wide range of carbonatite samples: 4 continents, from today to 3Ga, oceanic and continental settings. 80 measurements from 18 localities yielded sulfur in sulfides between 0 to 1wt%, with ?34S ranging from -20‰ to +10‰. The record through time seems to correlate with the sedimentary record albeit with some delay. ?33S varies between -0.1 to 0.4‰. Most of the samples display unequivocal mass-dependent fractionation, characteristic of the sedimentary record. A few samples show mass-independent fractionation. ?33S shows a temporal variation from near zero at 3Ga to positive values until 500Ma and then a broadening with both positive and negative values. This is interpreted to reflect the assimilation of surface derived sulfur in the source of carbonatites. The mixing with mantle sulfur narrows the amplitude of the variation and a crustal imprint could blur the signal as well. However coupled ?34S-?33S point toward two different stages in the sulfur isotopic signature: a long recycling before 900Ma and a much shorter residence time, on the order of 300 Myrs, after. This could be linked with a preferential recycling of sulfides in the early time and a recycling of both sulfides and sulfates later on.
DS202104-0566
2021
Branchetti, M., Zepper, J.C.O., Peters, S.T.J., Koornneef, J.M., Davies, G.Multi-stage formation and destruction in Kimberley harzburgitic xenoliths, South Africa.Lithos, in press available, 57p. PdfAfrica, South Africadeposit - Kimberley

Abstract: Thirty-nine garnet harzburgites from Kimberley in the Kaapvaal Craton (South Africa) were studied to constrain the origin, age and evolution of sub-cratonic lithospheric mantle (SCLM). In order to avoid chemical overprinting by recent metasomatism, only garnet harzburgites that appeared clinopyroxene-free to the naked eye were sampled. The majority of garnets were, however, in equilibrium with clinopyroxene (24 of 39). Whole rock and mineral major-trace element geochemistry and garnet Sr-Nd-Hf isotope data are presented. Equilibration pressures range from 3.8-6.1?GPa, indicating the harzburgites were derived from a large portion of the SCLM (~115-185?km). High olivine Mg# (~93.4, n?=?39) and low whole rock heavy rare earth elements (HREE) contents are consistent with large degrees of partial melting (>45%) and garnet exhaustion leaving a dunitic residue with olivine ?90%, orthopyroxene ?10% and HREE <0.01 times chondrite. Mineral modes, whole rock Al2O3 (0.5-3.2?wt%) and SiO2 (43.1-49.1?wt%), however, indicate heterogeneous re-introduction of garnet (?13%) and orthopyroxene (?50%). Harzburgites with high garnet and relatively low orthopyroxene modes (mostly ~7-13% and?~?9-30%; n?=?6) are characterised by mildly sinusoidal garnet REE patterns (Tbsingle bondDy minimum and high HREE) and Archaean depleted Hf TDM ages (2.7-3.3?Ga; ?Hfe: +190 to +709). In contrast, harzburgites with high orthopyroxene and relatively low garnet and modes (~1.5-7.5% and?~?25-50%; n?=?19) are characterised by highly sinuous REE patterns (Hosingle bondYb minimum and low HREE) and Proterozoic enriched Hf TDM ages (0.7-1.6?Ga; ?Hfe: ?16 to +6). It is inferred that Archaean G10 garnet re-introduction caused a significant increase in HREE, making melt depletion models based on HREE inaccurate. Orthopyroxene addition, a few hundred million years later, most likely at ~2.7?Ga and associated with Ventersdorp magmatic activity, caused partial consumption of garnet and olivine, and changed garnet compositions leading to: 1) Cr/Al ratio increase; 2) HREE decrease; 3) more sinusoidal REE patterns; and 4) un-radiogenic 176Hf/177Hf. Garnets define a Lusingle bondHf isochron age of 2702?±?64?Ma (?Hfi?=?+44, n?=?31), which is interpreted as a consequence of partial isotopic equilibrium within the SCLM and mixing of the garnet- and orthopyroxene-rich metasomatic components. The low LILE contents and absence of Nbsingle bondTa anomalies are consistent with modal metasomatism caused by intra-plate magmatism. In addition, the REE signatures of metasomatic agents in equilibrium with the garnets suggest that carbonatitic melts and SiO2-rich hydrous melts were responsible for re-introduction of garnet and orthopyroxene, respectively. Srsingle bondNd isotope systematics were disrupted associated with kimberlite magmatism (Nd isochron: 217?±?58?Ma, ?Ndi?=?+4; n?=?34), consistent with recent G10 garnet transformation into G9 garnets (Ca?+?Fe-enriched). This event may have caused garnet addition (up to 1%), suggesting that garnet was formed or destroyed in at least 4 different events: i) initial extensive polybaric melting, ii) asthenospheric melts re-introducing the bulk of the garnet, iii) orthopyroxene addition and garnet loss, all in the Archaean, and iv) minor garnet addition possibly related to recent kimberlite magmatism prior to eruption.
DS202102-0176
2021
Brenker, F.E., Nestola, F., Brenker, L., Peruzo, L., Harris, J.WOrigin, properties, and structure of breyite: the second most abundant mineral inclusion in super-deep diamonds.The American Mineralogist, Vol. 106, pp. 38-43. pdfMantleperovskites, mineral inclusions

Abstract: Earth's lower mantle most likely mainly consists of ferropericlase, bridgmanite, and a CaSiO3- phase in the perovskite structure. If separately trapped in diamonds, these phases can be transported to Earth's surface without reacting with the surrounding mantle. Although all inclusions will remain chemically pristine, only ferropericlase will stay in its original crystal structure, whereas in almost all cases bridgmanite and CaSiO3-perovskite will transform to their lower-pressure polymorphs. In the case of perovskite structured CaSiO3, the new structure that is formed is closely related to that of walstromite. This mineral is now approved by the IMA commission on new minerals and named breyite. The crystal structure is triclinic (space group: P1) with lattice parameters a0 = 6.6970(4) Å, b0 = 9.2986(7) Å, c0 = 6.6501(4) Å, ? = 83.458(6)°, ? = 76.226(6)°, ? = 69.581(7)°, and V = 376.72(4) Å. The major element composition found for the studied breyite is Ca3.01(2)Si2.98(2)O9. Breyite is the second most abundant mineral inclusion after ferropericlase in diamonds of super-deep origin. The occurrence of breyite has been widely presumed to be a strong indication of lower mantle (=670 km depth) or at least lower transition zone (=520 km depth) origin of both the host diamond and the inclusion suite. In this work, we demonstrate through different formation scenarios that the finding of breyite alone in a diamond is not a reliable indicator of the formation depth in the transition zone or in the lower mantle and that accompanying paragenetic phases such as ferropericlase together with MgSiO3 are needed.
DS202107-1092
2021
Brennan, D.T., Li, Z-X., Rankenburg, K., Evans, N., Link, P.K.Recalibrating Rodinian rifting in the northwestern United States.Geology Today, Vol. 49, pp. 617-622.United States, Washingtongeochronology

Abstract: A lack of precise age constraints for Neoproterozoic strata in the northwestern United States (Washington State), including the Buffalo Hump Formation (BHF), has resulted in conflicting interpretations of Rodinia amalgamation and breakup processes. Previous detrital zircon (DZ) studies identified a youngest ca. 1.1 Ga DZ age population in the BHF, interpreted to reflect mostly first-cycle sourcing of unidentified but proximal magmatic rocks intruded during the amalgamation of Rodinia at ca. 1.0 Ga. Alternatively, the ca. 1.1 Ga DZ population has been suggested to represent a distal source with deposition occurring during the early phases of Rodinia rifting, more than 250 m.y. after zircon crystallization. We combined conventional laser-ablation split-stream analyses of U-Pb/Lu-Hf isotopes in zircon with a method of rapid (8 s per spot) U-Pb analysis to evaluate these opposing models. Our study of ?2000 DZ grains from the BHF identified for the first time a minor (?1%) yet significant ca. 760 Ma population, which constrains the maximum depositional age. This new geochronology implies that the BHF records early rift deposition during the breakup of Rodinia and correlates with sedimentary rocks found in other late Tonian basins of southwestern Laurentia.
DS202103-0370
2021
Brennan, M.C., Fischer, R.A,m Couper, S., Miyagi, L., Antonangeli, D., Morard, G.High-pressure deformation of iron-nickel-silicon alloys and implications for Earth's inner core.Journal of Geophysical Research, Solid Earth, https://eartharxiv.org /repository/ view/1694/ 21p. PdfMantleGeophysics - seismics

Abstract: The inner core is a Moon?sized ball of solid metal at the very center of the Earth. Vibrations from earthquakes move faster through the inner core if they travel parallel to Earth's axis (the line between the North and South Poles) than if they travel parallel to the Equator. This probably means that the grains of metal in the inner core are themselves aligned with Earth's axis. Previous studies determined that this alignment likely happened after the inner core had formed, but those experiments were done on pure iron, whereas the inner core is mostly iron but also contains other elements. We did experiments at high pressures and temperatures on a more realistic core metal containing iron, nickel, and silicon. We found that this metal would be much stronger than pure iron at inner core pressures and temperatures; it is still possible for it to produce a north-south alignment, but it is much more difficult for it to do so. This could mean that the alignment occurred while the inner core was forming (rather than afterward), which might change how we think about the forces present in the deep Earth today.
DS202111-1759
2021
Britvin, S., Vlasenko, N.S., Aslandukov, A., Aslandova, A., Dubovinsky, L., Gorelova, L.A., Krzhizhanvskaya, M.G., Vereshchagin, O.S., Bocharov, V.N., Shelukina, Y.S., Lozhkin, M.S., Zaitsev, A.N., Nestola, F.Natural cubic perovskite, Ca(Ti,Si,Cr) O 3-delta, a versatile potential host rock-forming and less common elements up to Earth's mantle pressure.American Mineralogist, doi:10.2138/am-2022-8186 in pressMantleperovskite

Abstract: Perovskite, CaTiO3, originally described as a cubic mineral, is known to have a distorted (orthorhombic) crystal structure. We herein report on the discovery of natural cubic perovskite. This was identified in gehlenite rocks occurring in a pyrometamorphic complex of the Hatrurim Formation (the Mottled Zone), in the vicinity of the Dead Sea, Negev Desert, Israel. The mineral is associated with native ?-(Fe,Ni) metal, schreibersite (Fe3P) and Si-rich fluorapatite. The crystals of this perovskite reach 50 ?m in size and contain many micron sized inclusions of melilite glass. The mineral contains significant amounts of Si substituting for Ti (up to 9.6 wt.% SiO2) corresponding to 21 mol.% of the davemaoite component (cubic perovskite-type CaSiO3), in addition to up to 6.6 wt.% Cr2O3. Incorporation of trivalent elements results in the occurrence of oxygen vacancies in the crystal structure; this being the first example of natural oxygen-vacant ABO3 perovskite with the chemical formula Ca(Ti,Si,Cr)O3-? (? ~ 0.1). Stabilization of cubic symmetry (space group Pm?3m) is achieved via the mechanism not reported so far for CaTiO3, namely displacement of an oxygen atom from its ideal structural position (site splitting). The mineral is stable at atmospheric pressure to 1250±50 °C; above this temperature its crystals fuse with the embedded melilite glass, yielding a mixture of titanite and anorthite upon melt solidification. The mineral is stable upon compression to at least 50 GPa. The a lattice parameter exhibits continuous contraction from 3.808(1) Å at atmospheric pressure to 3.551(6) Å at 50 GPa. The second-order truncation of the Birch-Murnaghan equation of state gives the initial volume V0 equal to 55.5(2) Å3 and room temperature isothermal bulk modulus K0 of 153(11) GPa. The discovery of oxygen-deficient single perovskite suggests previously unaccounted ways for incorporation of almost any element into the perovskite framework up to pressures corresponding to those of the Earth’s mantle.
DS202108-1275
2021
Broom-Fendley, S., Elliott, H.A.L., Beard, C.D., Wall, F., Armitage, P.E.B., Brady, A.E., Deady, A.E., Dawes, W.Enrichment of heavy REE and Th in carbonatite-derived fenite breccia.Geological Magazine, in press available Africa, Malawideposit - Songwe Hill

Abstract: Enrichment of the heavy rare earth elements (HREE) in carbonatites is rare as carbonatite petrogenesis favours the light (L)REE. We describe HREE enrichment in fenitized phonolite breccia, focusing on small satellite occurrences 1-2 km from the Songwe Hill carbonatite, Malawi. Within the breccia groundmass, a HREE-bearing mineral assemblage comprises xenotime, zircon, anatase/rutile and minor huttonite/thorite, as well as fluorite and apatite. A genetic link between HREE mineralization and carbonatite emplacement is indicated by the presence of Sr-bearing carbonate veins, carbonatite xenoliths and extensive fenitization. We propose that the HREE are retained in hydrothermal fluids which are residually derived from a carbonatite after precipitation of LREE minerals. Brecciation provides a focusing conduit for such fluids, enabling HREE transport and xenotime precipitation in the fenite. Continued fluid-rock interaction leads to dissolution of HREE-bearing minerals and further precipitation of xenotime and huttonite/thorite. At a maximum Y content of 3100 µg g?1, HREE concentrations in the presented example are not sufficient to constitute ore, but the similar composition and texture of these rocks to other cases of carbonatite-related HREE enrichment suggests that all form via a common mechanism linked to fenitization. Precipitation of HREE minerals only occurs where a pre-existing structure provides a focusing conduit for fenitizing fluids, reducing fluid - country-rock interaction. Enrichment of HREE and Th in fenite breccia serves as an indicator of fluid expulsion from a carbonatite, and may indicate the presence of LREE mineralization within the source carbonatite body at depth.
DS202106-0925
2021
Broom-Findley, S., Siegfried, P.R., Wall, F., O'Neill, M., Brooker, R.A., Fallon, E.K., Pickles, J.R., Banks, D.A.The origin and composition of carbonatite-derived carbonate bearing fluorapatite deposits.Mineralium Deposita, Vol. 56, pp. 863-884.Globaldeposit - Kovdor, Sokli, Bukusu, Catalao 1, Glenover

Abstract: Carbonate-bearing fluorapatite rocks occur at over 30 globally distributed carbonatite complexes and represent a substantial potential supply of phosphorus for the fertiliser industry. However, the process(es) involved in forming carbonate-bearing fluorapatite at some carbonatites remain equivocal, with both hydrothermal and weathering mechanisms inferred. In this contribution, we compare the paragenesis and trace element contents of carbonate-bearing fluorapatite rocks from the Kovdor, Sokli, Bukusu, Catalão I and Glenover carbonatites in order to further understand their origin, as well as to comment upon the concentration of elements that may be deleterious to fertiliser production. The paragenesis of apatite from each deposit is broadly equivalent, comprising residual magmatic grains overgrown by several different stages of carbonate-bearing fluorapatite. The first forms epitactic overgrowths on residual magmatic grains, followed by the formation of massive apatite which, in turn, is cross-cut by late euhedral and colloform apatite generations. Compositionally, the paragenetic sequence corresponds to a substantial decrease in the concentration of rare earth elements (REE), Sr, Na and Th, with an increase in U and Cd. The carbonate-bearing fluorapatite exhibits a negative Ce anomaly, attributed to oxic conditions in a surficial environment and, in combination with the textural and compositional commonality, supports a weathering origin for these rocks. Carbonate-bearing fluorapatite has Th contents which are several orders of magnitude lower than magmatic apatite grains, potentially making such apatite a more environmentally attractive feedstock for the fertiliser industry. Uranium and cadmium contents are higher in carbonate-bearing fluorapatite than magmatic carbonatite apatite, but are much lower than most marine phosphorites.
DS202111-1760
2021
Bruno, H., Helibron, M., Strachen, R., Fowler, M., de MorrisonValeriano , C., Bersan, S., Moreira, H., Cutts, K., Dunlop, J., Almeida, R., Almeida, J., Storey, C.Earth's new tectonic regime at the dawn of the Paleozoic: Hf isotope evidence for efficient crustal growth and reworking in the Sao Francisco craton, Brazil.Geology, Vol. 49, 10, pp. 1214-1219. pdfSouth America, Brazilcraton

Abstract: A zircon Hf isotope data set from Archean and Paleoproterozoic magmatic and metasedimentary rocks of the southern São Francisco craton (Brazil) is interpreted as evidence of accretionary and collisional plate tectonics since at least the Archean-Proterozoic boundary. During the Phanerozoic, accretionary and collisional orogenies are considered the end members of different plate tectonic settings, both involving preexisting stable continental lithosphere and consumption of oceanic crust. However, mechanisms for the formation of continental crust during the Archean and Paleoproterozoic are still debated, with the addition of magmatic rocks to the crust being explained by different geodynamic models. Hf isotopes can be used to quantify the proportion of magmatic addition into the crust: positive ?Hf values are usually interpreted as indications of magmatic input from the mantle, whereas crust-derived rocks show more negative ?Hf. We show that the crust of the amalgamated Paleoproterozoic tectonostratigraphic terranes that make up the southern São Francisco craton were generated from different proportions of mantle and crustal isotopic reservoirs. Plate tectonic processes are implied by a consistent sequence of events involving (1) the generation of juvenile subduction-related magmatic arc rocks, followed by (2) collisional orogenesis and remelting of older crust, and (3) post-collisional bimodal magmatism.
DS202104-0567
2021
Brzozowski, M., Samson, I.M., Gagnon, J.E., Linnen, R.L., Good, D.J.Effects of fluid-induced oxidation on the composition of Fe-Ti oxides in the eastern gabbro, Coldwell Complex, Canada: implications for the application of Fe-Ti oxides to petrogenesis and mineral exploration.Mineralium Deposita, Vol. 56, pp. 601-618. pdfCanada, Ontariodeposit - Coldwell

Abstract: Magnetite (mag)-ilmenite (ilm) intergrowths are more common than mag-ulvöspinel (usp) intergrowths in mafic-ultramafic Ni-Cu-PGE systems, yet the former has no known solid solution. The most accepted model for the formation of mag-ilm intergrowths in terrestrial environments is fluid-induced oxidation of mag-usp assemblages by oxygen in water. In this study, we re-examine this model in light of the fact that crustal fluids have very low pO2 and that mag-ilm intergrowths commonly occur in rocks that show little or no evidence of hydrothermal alteration. We also characterize the chemical changes that occurred during the formation of mag-ilm intergrowths and how they affect the use of Fe-Ti oxide chemistry for petrogenesis and mineral exploration. In the Eastern Gabbro, Coldwell Complex, a continuum of Fe-Ti oxide intergrowths occur ranging from cloth (mag-usp) to trellis (mag-ilm) types. Trellis-textured intergrowths have higher bulk Fe3+:Fe2+ ratios and are predominantly enriched not only in some multivalent (Ge, Mo, W, Sn) elements, but also in Cu and Ga, consistent with their formation via oxidation by a metal-rich fluid. These compositional changes are significant relative to typical elemental abundances in Fe-Ti oxides and could potentially lead to erroneous interpretations regarding primary magmatic processes if they are not taken into consideration. The irregular distribution of the intergrowths throughout the Eastern Gabbro suggests that different rock series and mineralized zones experienced variable degrees of fluid-induced oxidation. It is proposed that C in CO2 rather than O2 in water could potentially be an important oxidizing agent in mafic systems: 9Fe2+2TiO4+0.75CO2+1.5H2O?9Fe2+TiO3+3Fe3+2Fe2+O4+0.75CH4. The applicability of this model is supported by the common occurrence of CO2 and CH4 in fluid inclusions in mafic rocks.
DS202104-0568
2021
Brzozowski, M.J., Samson, I.M., Gagnon, J.E., Good, D.J., Linnen, R.L.Oxide mineralogy and trace element chemistry as an index to magma evolution and Marathon-type mineralization in the eastern gabbro of the alkaline Coldwell Complex, Canada.Mineralium Deposita, Vol. 56, pp. 621-642. pdfCanada, Ontariodeposit - Coldwell

Abstract: The Eastern Gabbro of the alkaline Coldwell Complex, Canada, represents a Ni-poor conduit-type system that comprises two rock series, the Layered Series and Marathon Series, which intruded into a metabasalt package. Based on distinct variations in magnetite compatible (e.g., Ni, Cr) and incompatible (e.g., Sn, Nb) elements in Fe-Ti oxide intergrowths, the metabasalts, Layered Series, and Marathon Series must have crystallized from magmas that originated from compositionally distinct sources. Of these rock units, the metabasalts crystallized from a more primitive melt than the Layered Series as Fe-Ti oxides in the former have higher concentrations of magnetite-compatible elements. Unlike the metabasalts and Layered Series, the Marathon Series crystallized from multiple, compositionally distinct magmas as Fe-Ti oxides in this series exhibit large variations in both magnetite compatible and incompatible elements. Accordingly, the various rock types of the Marathon Series cannot be related by fractional crystallization of a single batch of magma. Rather, the magmas from which the rock types crystallized had to have interacted to variable degrees with a late input of more primitive melt. The degree of this magma interaction was likely controlled by the geometry of the conduit and the location of emplacement given that Fe-Ti oxides in the oxide-rich rocks occur in pod-like bodies and exhibit no compositional evidence for magma mixing. Mirrored variations in magnetite compatible and incompatible elements in Fe-Ti oxides in the Footwall Zone, Main Zone, and W Horizon of the Marathon Cu-PGE deposit indicate that these zones could not have formed from a single, evolving magma, but rather multiple batches of compositionally distinct magmas. Fe-Ti oxides exhibit no compositional difference between those hosted by barren and mineralized rock. This is likely because sulfide liquated at depth in all of the magmas from which the Marathon Series crystallized. The composition of Fe-Ti oxides in the Eastern Gabbro fall outside of the compositional fields for Ni-Cu mineralization defined by Dupuis and Beaudoin (Mineral Deposita 46:319-335, 2011) and Ward et al. (J Geochem Explor 188:172-184, 2018) demonstrating that their discrimination diagrams can distinguish between Ni-rich and Ni-poor systems that contain disseminated and massive sulfides.
DS202104-0569
2021
Buccione, R., Kechiched, R., Mongelli, G., Sinisi, R.REEs in the North Africa P-bearing deposits, paleoenvironments, and economic perspectives: a review.MDPI Minerals, Vol. 11, 27p. PdfAfrica, Algeria, Tunisia, MoroccoREE

Abstract: A review of the compositional features of Tunisia, Algeria, and Morocco phosphorites is proposed in order to assess and compare the paleoenvironmental conditions that promoted the deposit formation as well as provide information about their economic perspective in light of growing worldwide demand. Since these deposits share a very similar chemical and mineralogical composition, the attention was focused on the geochemistry of rare earth elements (REEs) and mostly on ?REEs, Ce and Eu anomalies, and (La/Yb) and (La/Gd) normalized ratios. The REEs distributions reveal several differences between deposits from different locations, suggesting mostly that the Tunisian and Algerian phosphorites probably were part of the same depositional system. There, sub-reducing to sub-oxic conditions and a major REEs adsorption by early diagenesis were recorded. Conversely, in the Moroccan basins, sub-oxic to oxic environments and a minor diagenetic alteration occurred, which was likely due to a different seawater supply. Moreover, the drastic environmental changes associated to the Paleocene-Eocene Thermal Maximum event probably influenced the composition of Northern African phosphorites that accumulated the highest REEs amounts during that span of time. Based on the REEs concentrations, and considering the outlook coefficient of REE composition (Koutl) and the percentage of critical elements in ?REEs (REEdef), the studied deposits can be considered as promising to highly promising REE ores and could represent a profitable alternative source for critical REEs.
DS202112-1921
2021
Buikin, A.J., Hopp, J., Verchovsky, A., Trieloff, M.The sources and evolution of fluid phases of Guli Massif carbonatites ( West Siberia): summarizing of noble gases, N2, CO2, H2O stepwise crushing data.Petrology, Vol. 29, 6, pp. 657-675. pdfRussia, Siberiadeposit - Guli Massif

Abstract: Here we present summarizing of isotopic compositions and element ratios of noble gases, nitrogen, carbon and hydrogen in carbonatites of different generations of the Guli massif (West Siberia, Russia) obtained by stepwise crushing. The data point to the subcontinental lithospheric mantle (SCLM) as a primary source of the fluid phase in Guli carbonatites. However, the estimated 40Ar/36Ar ratio in the Guli mantle source of about 5400 is similar to the Kola plume value of 5000 ± 1000 (Marty et al., 1998). One explanation of such a low estimated 40Ar/36Ar ratio in the mantle end-member with SCLM type helium (4??/3?? ~ 120000) and neon (21N?/22N?mantle ~ 0.7) is an admixture of atmospheric argon to the local mantle source. This assumption is supported by the Ar-Ne systematics as well as by the data for hydrogen isotopic composition. Early carbonatite differs significantly from the later ones by the concentration of highly volatile components, as well as by the isotopic compositions of carbon (CO2), argon, and hydrogen (H2O). The mantle component dominated in fluids at the early formation stages of the Guli massif rocks, whereas the late stages of carbonatite formation were characterized by an additional fluid source, which introduced atmospheric argon and neon, and most likely a high portion of CO2 with isotopically heavy carbon. The argon-neon-hydrogen isotope systematics suggest that the most plausible source of these late stage fluids are high temperature paleometeoric waters. The absence of a plume signature could be explained in terms that Guli carbonatites have been formed at the waning stage of plume magmatic activity with an essential input of SCLM components.
DS202109-1455
2021
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. PdfMantlegeodynamics

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.
DS202110-1604
2021
Burness, S., Thomassot, E., Smart, K., Tappe, S.Sulphur isotopes in sulphides from cratonic mantle eclogites: a glimpse of volatile recycling in ancient subduction zones.Earth and Planetary Science Letters, Vol. 572, 1, 117118Africa, South Africadeposit - Premier, Roberts Victor, Jagersfontein

Abstract: Multiple sulphur isotopic compositions of sulphides from Kaapvaal craton mantle eclogites allow to elucidate the recycling of sulphur into the deep Earth and to differentiate between recycled crust and mantle origins of eclogite-hosted sulphides, including the precious metals that they capture. We present multiple sulphur isotope ratio measurements by secondary ion mass spectrometry for sulphides from a collection of mantle-derived eclogite xenoliths from Proterozoic and Mesozoic kimberlite occurrences in South Africa (Premier, Roberts Victor, Jagersfontein). Previous work established that the host eclogites have elemental and oxygen isotopic compositions in support of seawater-altered oceanic lithosphere protoliths, and for many of these xenolith suites Archean ages have been suggested. The eclogite-hosted sulphides have values from ?5.7 to ‰, with the upper end of this wide range representing the highest-ever recorded composition of material derived from the Earth's mantle. The values range from ?0.29 to ‰ and do not record significant mass-independent sulphur isotope fractionation, i.e., there is no compelling S-MIF signature. Most of the sulphide grains have values that fall within a range between ?6 and ‰, and they probably retain an isotopic record of sulphides that formed originally within altered oceanic crust. In contrast, the highly positive values from +13 to ‰ detected in sulphide grains from a single eclogite xenolith are similar to those of marine sulphates, which were probably a minor sulphur component of the oceanic crustal protolith. The lack of a significant S-MIF signature in the eclogitic sulphides that show evidence for a recycled crust origin implies that this sulphur component stems from a post-Archean surficial reservoir. This finding suggests that the cratonic mantle eclogites may have formed from post-Archean oceanic crust (e.g., Paleoproterozoic eclogite protoliths), or - as is preferred here - the ‘surficial’ sulphur was introduced into the cratonic root during relatively young metasomatic events and is thus unrelated to eclogite petrogenesis and Archean continent formation.
DS202101-0002
2020
Carniel, L.C., Conceicao, R.V., Klemme, S., Berndt,J., Jalowitzki, T.Origin and redox conditions of the Rosario-6 alnoite of southern Brazil: implications for the state of the mantle during Gondwana breakup.Lithos, Vol. 376-377, 105751, 13p. PdfSouth America, Brazildeposit - Rosario do Sul

Abstract: The Rosário-6 alnöite is an alkaline occurrence that belongs to the Rosário do Sul kimberlitic field, situated in the south-eastern edge of the Paraná Basin, in the South of Brazil, and erupted concomitant or just after the volcanism of the Paraná-Etendeka Large Igneous Province (LIP). Following recent published nomenclature, Rosário-6 was classified as a kimberlite from a deep mantle source with a distinctive inequigranular texture resulting from the presence of olivine macrocrysts set in a finer-grained matrix. Trace element compositions of olivine, monticellite, spinel, phlogopite, perovskite and apatite show an enrichment of Nb, Ce, Ta and U, which implies that the Rosário-6 mantle source was enriched by recycled oceanic crust. The positive anomalies of Rb, Ba and Sr, the enrichment in LREE, and the negative anomalies of HREE in the Rosário-6 minerals, are indicative of a metasomatic process in the mantle source that could be caused by fluids from recycled oceanic crust. Temperature, pressure and redox conditions (fO2) of Rosário-6 crystallization are estimated from olivine, spinel, perovskite and monticellite compositions: Rosário-6 crystallization temperatures using olivine-spinel geothermobarometry were around 1390(±56)°C at a pressure of 2 GPa, and 1405(±56)°C at 3 GPa with ?NNO = 2.8, at pressures constrained by the silica activity limited by the crystallization of monticellite. Using a perovskite oxybarometer, we obtained a larger range of ?NNO (from -2.8 to 3.4), whereas the monticellite oxybarometer results in fO2 of -2.6 to -0.8 ?NNO units. The fO2 indicate that the mantle source of Rosário-6 at the time of crystallization was possibly oxidized by materials from ancient subduction, which may be the cause for Rosário-6's low potential to carry and preserve diamonds. Horizontal tomographic images derived from P-wave velocity data constrain the thickness of the lithosphere in this region and the overall information indicates that mantle cooling at depths below 200 km may have resulted of an accumulation of oceanic plate slabs from old subduction. The geochemical data in conjunction with the geophysical characterizes the conditions of Rosário-6 mineral crystallization and also the mantle of this part of South America during Gondwana breakup.
DS202106-0926
2021
Casalini, M., Avanzinelli, R., Tommasini, S., Natali, C., Bianchini, G., Prelevic, D., Mattei, M., Conticelli, S.Petrogenesis of Mediterranean lamproites and associated metasomatic events in the postcollisional lithospheric upper mantle.Geological Society, London Special Publication, doi.org/10.1144/SP513-2021-36 49p. PdfEurope, Italy, France, Spain, Serbia, Macedonia, Turkeylamproites

Abstract: High-MgO lamproite and lamproite-like (i.e., lamprophyric) ultrapotassic rocks are recurrent in the Mediterranean and surrounding regions. They are associated in space and time with ultrapotassic shoshonites and high-K calc-alkaline rocks. This magmatism is linked with the geodynamic evolution of the westernmost sector of the Alpine-Himalaya collisional margin, which followed the closure of the Tethys ocean. Subduction-related lamproites, lamprophyres, shoshonites and high-K calc-alkaline suites were emplaced in the Mediterranean region in the form of shallow level intrusions (e.g., plugs, dykes, and laccoliths), and small volume lava flows, with very subordinate pyroclastic rocks, starting from the Oligocene, in the Western Alps (Northern Italy), through the Late Miocene in Corsica (Southern France) and in Murcia-Almeria (South-Eastern Spain), to the Plio-Pleistocene in Southern Tuscany and Northern Latium (Central Italy), in the Balkan peninsula (Serbia and Macedonia), and in the Western Anatolia (Turkey). The ultrapotassic rocks are mostly lamprophyric, but olivine latitic lavas with a clear lamproitic affinity are also found, as well as dacitic to trachytic differentiated products. Lamproite-like rocks range from slightly silica under-saturated to silica over-saturated composition, have relatively low Al2O3, CaO, and Na2O contents, resulting in plagioclase-free parageneses, and consist of abundant K-feldspar, phlogopite, diopsidic clinopyroxene and highly forsteritic olivine. Leucite is generally absent and it is rarely found only in the groudmasses of Spanish lamproites. Mediterranean lamproites and associated rocks share an extreme enrichment in many incompatible trace elements and depletion in High Field Strength Elements and high, and positively correlated Th/La and Sm/La ratios. They have radiogenic Sr and unradiogenic Nd isotope compositions, high 207Pb over 206Pb and high time integrated 232Th/238U. Their composition requires an originally depleted lithospheric mantle source metasomatised by at least two different agents: i) a high Th/La and Sm/La (i.e., SALATHO) component deriving from lawsonite-bearing, ancient crustal domains likely hosted in mélanges formed during the diachronous collision of the northward drifting continental slivers from Gondwana; ii) a K-rich component derived from a recent subduction and recycling of siliciclastic sediments. These metasomatic melts produced a lithospheric mantle source characterised by network of felsic and phlogopite-rich veins, respectively. Geothermal readjustment during post-collisional events induced progressive melting of the different types of veins and the surrounding peridotite generating the entire compositional spectrum of the observed magmas. In this complex scenario, orogenic Mediterranean lamproites represent rocks that characterise areas that were affected by multiple Wilson cycles, as observed in the the Alpine-Himalayan realm.
DS202107-1093
2021
Casalini, M., Avanzinellli, R., Tommasini, S., Natali, C., Bianchini, G., Prelevic, D., Mattei, M., Conticelli, S.Petrogenesis of Mediterranean lamproites and associated rocks: the role of overprinted metasomatic events in the postcollisional lithospheric upper mantle.Geological Society London Special Publication, doi.org/10.1144/SP513-2021-36. pdfMantlelamproite

Abstract: High-MgO lamproite and lamproite-like (i.e., lamprophyric) ultrapotassic rocks are recurrent in the Mediterranean and surrounding regions. They are associated in space and time with ultrapotassic shoshonites and high-K calc-alkaline rocks. This magmatism is linked with the geodynamic evolution of the westernmost sector of the Alpine-Himalaya collisional margin, which followed the closure of the Tethys ocean. Subduction-related lamproites, lamprophyres, shoshonites and high-K calc-alkaline suites were emplaced in the Mediterranean region in the form of shallow level intrusions (e.g., plugs, dykes, and laccoliths), and small volume lava flows, with very subordinate pyroclastic rocks, starting from the Oligocene, in the Western Alps (Northern Italy), through the Late Miocene in Corsica (Southern France) and in Murcia-Almeria (South-Eastern Spain), to the Plio-Pleistocene in Southern Tuscany and Northern Latium (Central Italy), in the Balkan peninsula (Serbia and Macedonia), and in the Western Anatolia (Turkey). The ultrapotassic rocks are mostly lamprophyric, but olivine latitic lavas with a clear lamproitic affinity are also found, as well as dacitic to trachytic differentiated products. Lamproite-like rocks range from slightly silica under-saturated to silica over-saturated composition, have relatively low Al2O3, CaO, and Na2O contents, resulting in plagioclase-free parageneses, and consist of abundant K-feldspar, phlogopite, diopsidic clinopyroxene and highly forsteritic olivine. Leucite is generally absent and it is rarely found only in the groudmasses of Spanish lamproites. Mediterranean lamproites and associated rocks share an extreme enrichment in many incompatible trace elements and depletion in High Field Strength Elements and high, and positively correlated Th/La and Sm/La ratios. They have radiogenic Sr and unradiogenic Nd isotope compositions, high 207Pb over 206Pb and high time integrated 232Th/238U. Their composition requires an originally depleted lithospheric mantle source metasomatised by at least two different agents: i) a high Th/La and Sm/La (i.e., SALATHO) component deriving from lawsonite-bearing, ancient crustal domains likely hosted in mélanges formed during the diachronous collision of the northward drifting continental slivers from Gondwana; ii) a K-rich component derived from a recent subduction and recycling of siliciclastic sediments. These metasomatic melts produced a lithospheric mantle source characterised by network of felsic and phlogopite-rich veins, respectively. Geothermal readjustment during post-collisional events induced progressive melting of the different types of veins and the surrounding peridotite generating the entire compositional spectrum of the observed magmas. In this complex scenario, orogenic Mediterranean lamproites represent rocks that characterise areas that were affected by multiple Wilson cycles, as observed in the the Alpine-Himalayan realm.
DS202110-1605
2021
Chakaoumakos, B.C., Parise, J.B.Probing phase transitions and magnetism in minerals with neutrons.Elements, Vol. 17, pp. 181-188.Mantlegeophysics - magnetics, HP

Abstract: The development of sophisticated sample environments to control temperature, pressure, and magnetic field has grown in parallel with neutron source and instrumentation development. High-pressure apparatus, with high- and low-temperature capability, novel designs for diamond cells, and large volume presses are matched with next-generation neutron sources and moderator designs to provide unprecedented neutron beam brightness. Recent developments in sample environments are expanding the pressure-temperature space accessible to neutron scattering experiments. Researchers are using new capabilities and an increased understanding of the fundamentals of structural and magnetic transitions to explore new territories, including hydrogenous minerals (e.g., ices and hydrates) and magnetic structural phase diagrams.
DS202103-0371
2021
Chakhmouradian, A.R., Dahlgren, S.Primary inclusions of burbankite in carbonatites from the Fen complex, southern Norway.Mineralogy and Petrology, doi.org/10.1007/ s00710-021-00736-0 11p. PdfEurope, Norwaycarbonatite

Abstract: Carbonatites in the Fen intrusive complex (southern Norway) contain abundant burbankite (confirmed by Raman microspectroscopy) as inclusions in calcite, dolomite and, less commonly, fluorapatite and pyrochlore. Typically the inclusions occur in the core of calcite or dolomite grains relatively unaffected by subsolidus processes, and are associated with Fe-poor dolomite or Sr-rich calcite, respectively. Burbankite does not exceed 30?×?50 ?m in size and is characteristically absent from the peripheral areas of carbonate grains affected by recrystallization or interaction with fluids. Compositionally, the mineral falls within the following range: (Na1.51-2.16Ca0.58-1.21)(Sr1.50-2.42Ca0.28-0.57LREE0.05-0.64Ba0.06-0.41)(CO3)5 and contains low Th, but no detectable Mg, Fe or F (LREE?=?light rare-earth elements: Ce?>?La?>?Nd?>?Pr?>?Sm). Burbankite inclusions at Fen are interpreted as primary and indicative of Na enrichment in their parental carbonatitic magma. Dissociation of burbankite during subsolidus re-equilibration of its host phases with fluids undoubtedly served as one of the sources of LREE for the development of late-stage mineralization in the Fen complex.
DS202111-1761
2020
Chanturia, V.A., Dvoichenkova, G.P., Morozov, V.V., Kovalchuk, O.E., Podkamennyi, Yu.A., Yakolev, V.N.Selective attachment of luminophore-bearing emulsion at diamonds - mechanism analysis and mode selection.Journal of Mining Science, Vol. 56, 1, pp. 96-103, 8p. PdfRussialuminescence

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.
DS202104-0570
2021
Charles, N., Tuduri, J., Lefebvre, G., Pourret, O., Gaillard, F., Goodenough, K.Ressources en terres rares de l'Europe et du Groenland: un potential minier remarquable mais tabou?In: Boulvais, P., Decree, S. Eds. Ressources metalliques: cadre geodynamique et exemples remarquables. ISTE Science Pub. Researchgate, 97p. pdfEurope, GreenlandREE
DS202105-0758
2021
Chatterjee, N.Origin of the primitive, strongly SiO2-undersaturated alkalic rocks from the Deccan Traps by low degree mantle melting and high pressure fractional crystallization.Contributions to Mineralogy and Petrology, 176, 21p. PdfIndiaalkaline rocks

Abstract: Strongly SiO2-undersaturated alkalic rocks (Mg#?>?50, SiO2???45 wt%, Na2O?+?K2O???3 wt%) occur in three early-stage (Sarnu-Dandali, Mundwara, Bhuj) and one late-stage (Murud-Janjira) rift-associated volcanic complexes in the Cretaceous-Paleogene Deccan Traps flood basalt province of India. Thermobarometry based on clinopyroxene-liquid equilibrium suggests that they mostly crystallized beneath the Moho at?~?15 kbar/1270 °C to?~?11-12 kbar/1115-1156 °C pressures and temperatures. Primary magma compositions in equilibrium with lherzolite were estimated through reverse fractionation calculations by incrementally adding equilibrium phases to the rocks in olivine:clinopyroxene:spinel:phlogopite?=?12:68:20:15 proportions at low temperatures followed by olivine:clinopyroxene:spinel?=?12:68:20 proportions at higher temperatures. A comparison of the primary magmas with experimentally generated melts shows that their compositions are consistent with an origin from garnet lherzolite sources with?
DS202111-1762
2021
Chaurasiya, S.K., Markamdeya, R.Utilization of kimberlite as binder for iron ore pellet making.Transactions Indian Institute of Metallurgy, Vol. 74, 8, pp. 1969-1977. 9p. PdfIndiadeposit - Panna

Abstract: During diamond mining at Panna Mines [India], a huge amount of tailing (Kimberlite) is generated. About 6 Million Tonnes is accumulated and stored near mine site and about 0.9 Million Tonnes of tailings are further being generated each year. Till now, no established method is available for utilization of this material, effective utilization is essential for sustainable diamond mining. The Kimberlite contains about 32% [MgO?+?CaO] and 2% Al2O3, and rest are primarily silica, iron oxide [Fe2O3] and LOI. Initially, attempts were made to utilize Kimberlite as flux in iron ore pellet making; however, during green pellet making, it was observed that strength of pellets improved with higher dosages of Kimberlite. Accordingly, further studies were taken to replace conventional binder bentonite with binder prepared from Kimberlite. The iron ore pellet produced with Kimberlite-based binder have exhibited better physical and metallurgical characteristics than pellets produced with conventional binders (Bentonite).
DS202102-0177
2019
Chayka, I., Izokh, A.E., Vasyukova, E.A.Can low-titanium lamproite magmas produce ore deposits? Evidence from Mesozoic Aldan Shield lamproites. *** note dateResearchgate Conference paper, 335395794 5p. PdfRussialamproites

Abstract: Lamproites and lamprophyres from Ryabinovoye gold deposit (Aldan Shield, Siberia) were studied. We demonstrate that these rocks, varying from Ol-Di-Phl-lamproites to syenite-porphyries, form a continuous series of lamproite magma differentiation. At the stage of phlogopite and clinopyroxene crystallization, silicate-carbonate and then carbonate-salt immiscibilities occur. A suggestion is that during these processes LREE, Y, U, Sr and Ba distribute to a phosphate-fluoride fraction and probably accumulate in apatite-fluorite gangues. Based on our results and considering existing data onore-bearing massifs within Central Aldan (lnagli, Ryabinoviy) and also of the Nam-Xe ore-bearing province (Vietnam), we concluded that Au, PGE and Th-U-Ba-REE deposits can be genetically connected with low-titanium lamproite magmas.
DS202102-0178
2020
Chayka, I., Kamenetsky, V.S., Vasilyev, Y., Prokopyev, I.R.Spinel-group minerals in peridotites of the Guli and Bor-Uryakh intrusions ( Meimecha-Kotuy Province, northern Siberia).SGEM Conference 20th., doi:10.5593/ sgem2020/1.1. /s01.038Russia, Siberiaperidotites

Abstract: The Guli and Bor-Uryakh massifs, a part of the Siberian Large igneous province (LIP) are mafic-ultramafic intrusive complexes, withstrongalkaline affinity. They contain deposits of apatite and arealsoknown to be source rocks ofOs-Ir-Ruplacers.These massifs are of great interest for petrologists worldwide, as they are composed of an unusual variety of rocks (dunites/olivinites, shonkinites, melilitites, alkali syenites and carbonatites) and being coeval with Siberian trap volcanic rocks, includingdiamondiferous kimberlites. Since mineralogical approaches based on spinel-group minerals have been proved to be efficient in constraining origin of the ultramafics, we present the first descriptive study of chromite and magnetite mineralization, observed in olivine-dominated rocks of the Guli and Bor-Uryakh intrusions. In dunites of Guli massif spinel-group minerals are dominated by Mg-poor chromite (FeMg)Cr2O4and Cr-Ti-rich magnetiteFeFe2O4, while in Bor-Uryakh massif spinel-group minerals are predominantly magnetite with only minor Mg-poor chromite.These minerals form either small euhedral inclusions in olivine or largesubhedral to anhedral grains in serpentinized fractures and interstitial space. The lattertype of grainscan have intricated irregular shapeand contain inclusions. We also observed abundant Cr-magnetite lamellae in olivine and chromite/magnetite micro-grains within olivine-hosted multiphase inclusions.Spinel (MgAl2O4) is occasionally found in intergrowths with chromite and magnetite.The obtained data show that spinel-group minerals in the massifsdo not correspond to primary-magmatic varieties and suggestextensive alteration during post-magmatic processes. Textural and chemical evidenceof substantial modification of initially-cumulative lithologies of Guli and Bor-Uryakh massifsfavorsmeta-magmatic origin for these massifs.
DS202106-0927
2021
Chen, Q., Liu, S-g., Qiu L., Liao, R-q., Xie, G-Z., Sun, W-d.Enhanced deep carbon cycle marked by the upsurge of silica-undersaturated nephelinitic magmatism at the Proterozoic-Phanerozoic boundary.Journal of Asian Earth Sciences, Vol. 214, 104772, 8p. PdfMantlecarbon

Abstract: The temperature of the upper mantle was a principal factor controlling the style of plate tectonics and influencing magmatism and metamorphism on Earth over geological history. Recent studies emphasized that Earth’s tectonic style has transited into the modern plate tectonics since the late Neoproterozoic, which is characterized by a global network of plate boundaries with deep and cold oceanic plate subduction. However, the consequence of the establishment of modern plate tectonics to Earth’s mantle temperature and deep carbon cycle has not been fully understood. Here we apply statistical analysis on the geochemical data of continental igneous rocks and identify an increased magnitude of nephelinitic volcanism at the end of the Ediacaran. Nephelinitic rocks, a silica-undersaturated high-alkaline rock group, are mostly formed by low-degree melting of carbonated mantle sources. We link their widespread emergence with an enhanced mantle cooling event and a dramatically increased flux of crustal carbonates transporting to the mantle. The rapid cooling of the mantle was ascribed to the onset of modern-style plate tectonics with global-scale cold oceanic and continental subduction since the late Neoproterozoic. The declined upper-mantle temperature could not only favor the low-degree melting but also allow the subduction of carbonates into the deep mantle without decarbonation at shallow depth. Considering the high oxygen fugacity feature of the nephelinitic rocks and some other high-alkaline volcanism, the establishment of modern plate tectonics and thereafter enhanced mantle cooling and deep carbon cycle might contribute to the high-level atmospheric oxygen content during the Phanerozoic.
DS202108-1276
2021
Chen, W., Lu, X.B., Cao, X.F., Yuan, Q., Wang, D.Genetic and ore forming ages of Fe-P-(Ti) oxide deposits associated with mafic-ultramafic-carbonatite complexes in the Kuluketage block, NW China.Australian Journal of Earth Sciences, Vol. 66, 7, pp. 1041-1062.Chinacarbonatite

Abstract: During the past 50 years, many geological and ore-deposit investigations have led to the discovery of the Fe-P-(Ti)-oxide deposits associated with mafic-ultramafic-carbonatite complexes in the Kuluketage block, northeastern Tarim Craton. In this paper, we discuss the genetic and ore-forming ages, tectonic setting, and the genesis of these deposits (Kawuliuke, Qieganbulake and Duosike). LA-ICP-MS zircon U-Pb dating yielded a weighted mean 206Pb/238U ages of 811?±?5?Ma, 811?±?4?Ma, and 840?±?5?Ma for Kawuliuke ore-bearing pyroxenite, Qieganbulake gabbro and Duosike ore-bearing pyroxenite, respectively. The CL images of the Kawuliuke apatite grains show core-rim structure, suggesting multi-phase crystallisation, whereas the apatite grains from Qieganbulake and Dusike deposits do not show any core-rim texture, suggesting a single-stage crystallisation. LA-ICP-MS apatite 207Pb-corrected U-Pb dating provided weighted mean 206Pb/238U ages of 814?±?21?Ma and 771?±?8?Ma for the Kawuliuke ores, and 810?±?7?Ma and 841?±?7?Ma for Qieganbulake and Duosike ores, respectively. The core-rim texture in apatite by CL imaging as well as two different ore-forming ages in the core and rim of the apatite indicate two metallogenic events for the Kawuliuke deposit. The first metallogenic period was magmatic in origin, and the second period was hydrothermal in origin. The initial ore-forming age of the Kawuliuke Fe-P-Ti mineralisation was ca 814?Ma and the second one was ca 771?Ma. On the other hand, the ore-forming ages of the Qieganbulake and Duosike deposits were ca 810?Ma and ca 841?Ma, respectively. Qieganbulake and Duosike deposits were of magmatic origin. Combined with previous geochronological data and the research on the tectonic background, we infer that the Kawuliuke, Qieganbulake and Duosike Fe-P-(Ti)-oxide deposits were formed in a subduction-related tectonic setting and were the product of subduction-related magmatism.
DS202112-1922
2021
Chepurov, A., Sonin, V., Shcheglov, D., Zhimulev, E., Sitnikov, S., Yelisseyev, A., Chepurov, A.Surface porosity of natural crystals after the catalytic hydrogenation.Crystals, Vol. 11, 1341 9p pdfRussiadeposit - Popigai

Abstract: The study of diamond surfaces is traditionally undertaken in geology and materials science. As a sample material, two natural diamond crystals of type Ia were selected, and their luminescence and nitrogen state was characterized. In order to etch the surface catalytic hydrogenation was performed using Fe particles as an etchant. Micromorphology of the surface was investigated by scanning electron and laser confocal microscopy. It was demonstrated that etching occurred perpendicular to the crystal surface, with no signs of tangential etching. The average depth of caverns did not exceed 20-25 ?m with a maximal depth of 40 ?m. It is concluded that catalytic hydrogenation of natural type Ia diamonds is effective to produce a porous surface that can be used in composites or as a substrate material. Additionally, the comparison of results with porous microsculptures observed on natural impact diamond crystals from the Popigai astrobleme revealed a strong resemblance.
DS202110-1606
2021
Chepurov, A., Zhimulev, E., Chepurov, A., Sonin, V.Where did the largest diamonds grow? The experiments on percolation of Fe-Ni melt through olivine matrix in the presence of hydrocarbons.Lithos, Vol. 404-405, 106437, 10p. PdfMantlediamond genesis

Abstract: Recently it was found that large natural diamonds can grow from a metal liquid. One of the principal issues of the proposed hypothesis is the formation of so-called “pockets” filled with Fe-Ni melt and hydrocarbons in the Earth's mantle. The existing models of Fe migration imply percolation of liquid melt through interconnected interstices between silicate minerals, although these models face several fundamental problems in explaining the process of penetration of Fe melt between solid crystalline phases like silicate and oxide minerals. The aim of the present study is to contribute to the mechanism of Fe-Ni melt migration, and to elucidate the evolution of the "pockets" in the presence of hydrocarbons. The experiments were performed using a high-pressure apparatus "BARS" at pressures 3 and 5?GPa, and temperature 1600?°C. A silicate matrix consisting of natural olivine grains was used. The interstices in olivine were filled with anthracene that decomposes under high P-T into a complex hydrocarbon fluid. Percolation of Fe-Ni (64/36?wt%) melt through the interstices was demonstrated which occurred at relatively high rates. The basis of the proposed mechanism is "solubility-enhanced infiltration": Fe-Ni occupies the space filled with light elements or substances that are soluble in the melt. It is suggested that the following simple, but efficient mechanism supports the growth of large diamonds as well as their resorption and storage within silicate mantle of the Earth for a long time.
DS202106-0928
2021
Cherry, J.The future of pink diamonds.Gems&Jewellery, Vol. 30, 1, pp. 32-35.Globalmarkets
DS202111-1763
2021
Chin, E.J., Chilson-Parks, B., Boneh, Y., Hirth, G., Saal, A.E., Hearn, B.C., Hauri, E.H.The peridotite deformation cycle in cratons and the deep impact of subduction.Tectonophysics, Vol. 817, 229029, 22p. PdfUnited States, Wyomingdeposit - Homestead, Williams

Abstract: Xenoliths play a crucial role in interpretation of mantle deformation and geochemistry. The classic work of Mercier and Nicolas (1975) introduced the concept of the peridotite deformation cycle, which connected observed microstructures to a physical sequence of deformation. We revisit Mercier and Nicolas' original concept, bringing in new constraints using large area EBSD maps and associated microstructural datasets, analysis of water contents in nominally anhydrous minerals, and trace element chemistry of pyroxenes and garnets. We apply these techniques to a well-characterized suite of peridotite xenoliths from the Eocene-age Homestead and Williams kimberlites in the northwestern Wyoming Craton. Pyroxene water content and trace element mineral chemistries reveal ubiquitous hydrous metasomatism beneath the craton, most likely linked to the Cenozoic Laramide Orogeny. Homestead xenoliths primarily exhibit coarse protogranular and equigranular textures, B-type olivine fabrics, and generally elevated mineral water contents compared to Williams. Xenoliths from Williams are strongly deformed, with porphyroclastic and transitional textures containing annealed olivine tablets, mostly A-type olivine fabrics, and generally lower mineral water contents. As a whole, mantle from Homestead to Williams reflects a cratonic scale deformation cycle that likely initiated in Laramide times and lasted until the end of orogeny in the Eocene. At Williams, evidence for a rapid deformation “sub-cycle” within the main deformation cycle is preserved in the tablet-bearing xenoliths, corresponding to the enigmatic “transitional” texture of Mercier and Nicolas (1975). Our results suggest that this texture reflects interruption of the main deformation cycle by processes possibly related to a rapidly forming lithospheric instability and generation of the kimberlite magma - offering a new interpretation of this ambiguous peridotite texture. Collectively, our results incorporate typically disparate geochemical and textural datasets on xenoliths to shed new insights into how metasomatism, volatiles, and deformation are connected in the deep cratonic lithosphere.
DS202109-1456
2021
Cho, A.Tiny mirrors could smooth out already revolutionary x-ray lasers.Science Magazine Physics, doi:10.1126/science.abm1196 3p. PdfGlobalXFELS
DS202106-0929
2021
Choi, E., Fiorentini, M.L., Giuliani, A., Foley, S.F., Maas, R., Graham, S.Petrogenesis of Proterozoic alkaline ultramafic rocks in the Yilgarn Craton, western Australia.Gondwana Research, Vol. 93, pp. 197-217. pdfAustraliacarbonatites

Abstract: The Yilgarn Craton and its northern margin contain a variety of petrogenetically poorly defined small-volume alkaline ultramafic rocks of Proterozoic age. This study documents the petrography, mineral and bulk-rock geochemistry and Nd-Hf-Sr-Pb isotope compositions of a selected suite of these rocks. They comprise ~2.03-2.06 Ga ultramafic lamprophyres (UML) and carbonatites from the Eastern Goldfields Superterrane (EGS), ~0.86 Ga UML from Norseman, and orangeites from the Earaheedy Basin, including samples from Jewill (~1.3 Ga), Bulljah (~1.4 Ga) and Nabberu (~1.8-1.9 Ga). The Proterozoic UML and carbonatites from the EGS and Norseman display very consistent chondritic to superchondritic Nd-Hf isotope compositions and trace-element ratios similar to modern OIBs, which are indicative of a common mantle source across this wide alkaline province. These Nd-Hf isotope compositions overlap with the evolution trends of global kimberlites through time, thus suggesting that this mantle source could be deep and ancient as that proposed for kimberlites. Conversely, the orangeites located in the Earaheedy Basin along the northern margin of the Yilgarn Craton display trace element signatures similar to subduction-related calc-alkaline magmas. Taken together with their highly enriched Sr-Nd-Hf isotope compositions, these characteristics indicate an ancient lithospheric mantle source, which was probably metasomatised by subduction-related fluids. As the ages of the Bulljah and Jewill orangeites overlap with the breakup of the Columbia supercontinent, it is proposed that orangeite magmatism was triggered by changes in plate stress conditions associated with this event. This study provides a comprehensive picture of the genesis of Proterozoic alkaline magmatism in the Yilgarn Craton, highlighting the complex tectono-magmatic evolution of this lithospheric block after its assembly in the Archean.
DS202101-0003
2020
Choudhary, S., Sen, K., Kumar, S., Rana, S., Ghosh, S.Forsterite reprecipitation 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, doi:1017/S001 6756820000631, 12p.Indiadeposit - Sung Valley

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.
DS202103-0372
2021
Choudhary, S., Sen, K., Kumar, S., Rana, S., Ghosh, S.Forsterite reprecipitation 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, Vol. 158, 3, pp. 475-486.Indiadeposit - Sung Valley

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.
DS202109-1457
2021
Choudhury, A.R., Lahiri-Dutt, K.Extractive capital and multi-scalar environmental politics: interpreting the exit of Rio Tinto from the diamond fields of Central India.Third World Quarterly, Vol. 42, 8, pp. 1770-1787. Indiaeconomics

Abstract: Rio Tinto had been developing a diamond mining project in Madhya Pradesh for a decade when in 2017 it hastily abandoned the project. We analyse this counterintuitive exit through an ethnographic approach nested within a qualitative case study framework. We argue that the exit was caused by multi-scalar politics. Local protests over livelihood and labour issues -pre-emptively rearticulated by regional civil society groups through an ecological ‘framing’ - led to litigation. The national forest bureaucracy posed regulatory hurdles, and a change in the national political regime in 2014 brought to power a party that leveraged national capital of a certain variety, which weakened Rio Tinto’s political position. Lastly, a slump in the global diamond market created economic uncertainties, finally leading to its exit. It has not, however, deterred the government from facilitating investment by Indian mega-corporate houses in mining diamonds, once again ignoring local dissent. Under the current regime in India, the space for activism is increasingly restricted, and that restriction, we contend, can lead to the disarray in strategising alliances and goals between ecological and social justice concerns.
DS202112-1923
2021
Choudhury, P., Nukder, J.A., Cawood, P.A., Bhattacharjee, S., Roy, S., Wainwright, A.N., Nebel, O., Mukherjee, S.Magmatic thickening of crust in non-plate tectonic settings initiated the subaerial rise of Earth's first continents 3.3 to 3.2 billion years ago.PNAS, Vol. 118 (46) e2105746118 doi.org/10.73/pnas.210746118 pdfMantletectonics

Abstract: When and how Earth's earliest continents—the cratons—first emerged above the oceans (i.e., emersion) remain uncertain. Here, we analyze a craton-wide record of Paleo-to-Mesoarchean granitoid magmatism and terrestrial to shallow-marine sedimentation preserved in the Singhbhum Craton (India) and combine the results with isostatic modeling to examine the timing and mechanism of one of the earliest episodes of large-scale continental emersion on Earth. Detrital zircon U-Pb(-Hf) data constrain the timing of terrestrial to shallow-marine sedimentation on the Singhbhum Craton, which resolves the timing of craton-wide emersion. Time-integrated petrogenetic modeling of the granitoids quantifies the progressive changes in the cratonic crustal thickness and composition and the pressure-temperature conditions of granitoid magmatism, which elucidates the underlying mechanism and tectonic setting of emersion. The results show that the entire Singhbhum Craton became subaerial ?3.3 to 3.2 billion years ago (Ga) due to progressive crustal maturation and thickening driven by voluminous granitoid magmatism within a plateau-like setting. A similar sedimentary-magmatic evolution also accompanied the early (>3 Ga) emersion of other cratons (e.g., Kaapvaal Craton). Therefore, we propose that the emersion of Earth’s earliest continents began during the late Paleoarchean to early Mesoarchean and was driven by the isostatic rise of their magmatically thickened (?50 km thick), buoyant, silica-rich crust. The inferred plateau-like tectonic settings suggest that subduction collision-driven compressional orogenesis was not essential in driving continental emersion, at least before the Neoarchean. We further surmise that this early emersion of cratons could be responsible for the transient and localized episodes of atmospheric-oceanic oxygenation (O2-whiffs) and glaciation on Archean Earth.
DS202112-1924
2021
Chowdhury, A.R., Lahiri-Dutt, K.Extractive capital and multi-scalar environmental politics: interpreting the exit of Rio Tinto from the diamond fields of central India.Third World Quarterly, Vol. 42, 8, pp. 1770-1787. pdfIndiaeconomics

Abstract: Rio Tinto had been developing a diamond mining project in Madhya Pradesh for a decade when in 2017 it hastily abandoned the project. We analyse this counterintuitive exit through an ethnographic approach nested within a qualitative case study framework. We argue that the exit was caused by multi-scalar politics. Local protests over livelihood and labour issues -pre-emptively rearticulated by regional civil society groups through an ecological ‘framing’ - led to litigation. The national forest bureaucracy posed regulatory hurdles, and a change in the national political regime in 2014 brought to power a party that leveraged national capital of a certain variety, which weakened Rio Tinto’s political position. Lastly, a slump in the global diamond market created economic uncertainties, finally leading to its exit. It has not, however, deterred the government from facilitating investment by Indian mega-corporate houses in mining diamonds, once again ignoring local dissent. Under the current regime in India, the space for activism is increasingly restricted, and that restriction, we contend, can lead to the disarray in strategising alliances and goals between ecological and social justice concerns.
DS202103-0373
2020
Cimen, O., Corcoran, L., Kuebler, C., Simonetti, S., Simonetti, A.Geochemical stable (O, C, and B) and radiogenic ( Sr, Nd, Pb) isotopic data from the of carbonate hosted mineralization.Eskisehir- Kizilcaoren ( NW Anatolia) and the Malatya-Kuluncak( E-central Anatolia) F-REE-Th deposits, Turkey: implications for natureTurkish Journal of Earth Sciences, Vol. 29, pp. 798-814. pdfEurope, TurkeyREE

Abstract: In Turkey, the largest fluorine (F)-rare earth element (REE)-thorium (Th) deposits are located within the Eski?ehir-K?z?lcaören (north-western Anatolia) and the Malatya-Kuluncak (east-central Anatolia) regions, and these are associated with Oligocene extensional alkaline volcanic and Late Cretecaous-Early Paleocene postcollisional intrusive rocks, respectively. In the K?z?lcaören region, the basement units include the Triassic Karakaya Complex and the Late Cretaceous oceanic units (Neotethyan suture) that are cut and overlain by phonolite and carbonatite intrusions and lava flows. In the Kuluncak region, the plutonic rocks are mainly composed of syenite, quartz syenite, and rare monzonite, and these cut the late-Cretaceous Karap?nar limestone, which hosts the F-REE-Th mineralization in contact zones. A carbonatite sample from the K?z?lcaören region displays both a total rare earth element (TREE) concentration (4795 ppm) and ?11B (-6.83‰) isotope composition consistent with mantle-derived carbonatite; whereas it is characterized by heavier ?13C (+1.43‰) and ?18O (+20.23‰) isotope signatures compared to those for carbonatites worldwide. In contrast, the carbonates which host the F-REE-Th mineralization in the Kuluncak region are characterized by lower TREE concentrations (5.13 to 55.88 ppm), and heavier ?13C (-0.14 to -0.75‰), ?18O (+27.36 to +30.61‰), and ?11B (+5.38 to +6.89‰) isotope ratios compared to mantle-derived carbonatites. Moreover, the combined initial 87Sr/86Sr (0.70584 to 0.70759) and 143Nd/144Nd (0.512238 to 0.512571) isotope ratios for samples investigated here are distinct and much more radiogenic compared to those for carbonatites worldwide, and therefore indicate significant crustal input and/or hydrothermal metasomatic-related alteration. Overall, stable and radiogenic isotope data suggest that the host carbonate rocks for the F-REE-Th mineralization in both the K?z?lcaören and the Kuluncak regions consist of hydrothermally metasomatized carbonatite and limestone, respectively. The mineralization in the K?z?lcaören region may potentially be related to carbonatite magmatism, whereas the mineralization in the Kuluncak region, which most likely formed through interactions between the plutonic rocks and surrounding limestone at contact metamorphism zone, involved hydrothermal/magmatic fluids associated with extensive postcollisional magmatism.
DS202101-0004
2021
Cleland, C.E., Hazen, R.M., Morrison, S.M.Historical natural kinds and mineralogy: systematizing contingency in the context of necessity.Proceedings of the National Academy of Sciences PNAS, Vol. 118, 1 doi.org/10.1073 /pnas.2015370118 9p. PdfGlobalmineral classification

Abstract: The advancement of science depends upon developing classification protocols that systematize natural objects and phenomena into “natural kinds”—categorizations that are conjectured to represent genuine divisions in nature by virtue of playing central roles in the articulation of successful scientific theories. In the physical sciences, theoretically powerful classification systems, such as the periodic table, are typically time independent. Similarly, the standard classification of mineral species by the International Mineralogical Association’s Commission on New Minerals, Nomenclature, and Classification relies on idealized chemical composition and crystal structure, which are time-independent attributes selected on the basis of theoretical considerations from chemical theory and solid-state physics. However, when considering mineral kinds in the historical context of planetary evolution, a different, time-dependent classification scheme is warranted. We propose an "evolutionary" system of mineral classification based on recognition of the role played by minerals in the origin and development of planetary systems. Lacking a comprehensive theory of chemical evolution capable of explaining the time-dependent pattern of chemical complexification exhibited by our universe, we recommend a bootstrapping approach to mineral classification based on observations of geological field studies, astronomical observations, laboratory experiments, and analyses of natural samples and their environments. This approach holds the potential to elucidate underlying universal principles of cosmic chemical complexification.
DS202101-0005
2020
Clements, B.Diamond Exploration in Covid times . 1hr 28 mins.Vancouver Kimberlite Cluster talk Dec. 4, https://www.youtube.com /channel/UCcZvay DnqDDazIHAh1OtregCanadaHistory of diamond discoveries in Canada
DS202102-0179
2020
Cohen, T.Crowning glory ( Almod Diamonds) patented diamond cut.Gems & Jewellery, Vol. 29, 4, pp. 42-44. pdfUnited States, New Yorkdiamond cutting
DS202102-0180
2021
Cone, D., Kopylova, M.Origin of megacrysts by carbonate-bearing metasomatism - case study for the Muskox kimberlite, Slave craton, Canada.Journal of the Geological Society, doi.org/10.1144 /jgs2020-184 53p. Pdf Canada, Northwest Territoriesdeposit - Muskox

Abstract: Low-Cr and high-Cr clinopyroxene, garnet, olivine, and ilmenite megacrysts from the Muskox kimberlite (Canada) have been analyzed for major and trace elements, as well as Sr, Nd, and Pb isotopes. Samples display compositional overlap with respective phases in websterite, while clinopyroxene isotope systematics reveal similarities with both websteritic and metasomatic clinopyroxene in peridotites from the same kimberlite, in addition to Muskox and Jericho kimberlite. All lithologies may represent the products of mixing between EM1 mantle, relic Proterozoic enriched mantle and HIMU carbonatitic fluid. Equilibrium melts calculated from clinopyroxene trace element data using experimental distribution coefficients for feasible proto-kimberlitic melts yield a range of possible metasomatic agents. Conclusion on the carbonate-bearing nature of the metasomatism was based on the presence of a HIMU isotopic signature and results obtained from thermodynamic modeling using the Deep Earth Water model. The latter shows that mineral compositions analogous to megacrysts cannot be produced by metasomatism of mantle peridotite by H2O-rich kimberlitic fluids, or fluids in equilibrium with either asthenospheric or eclogitic mantle. Isotope systematics argue against a strictly cognate relationship between megacrysts and their host kimberlite, instead suggesting megacrysts and websterites may represent products of regional metasomatism by carbonatitic HIMU fluids shortly predating kimberlite magmatism.
DS202107-1094
2021
Consuma, G., Aulbach, S., Braga, R., Martin, L.A.J., Tropper, P., Gerdes, A., Fiorentini, M.L.Multi-stage sulfur and carbon mobility in fossil continental subduction zones: new insights from carbonate-bearing orogenic peridotites. *** Not specific to diamondsGeochimica et Cosmochimica Acta, Vol. 306, pp. 143-170. pdfEurope, Italysubduction

Abstract: The volatile transfer in subduction zones and the role of sulfate as a vector for the mobilization of oxidized components from down-going slabs remain hotly debated issues. Orogenic spinel and garnet peridotite lenses from the Ulten Zone (Eastern Alps, Italy), exhumed as part of felsic metamorphic terranes in continental collision zones, bear witness to mass transfer processes in these pivotal environments. In this study, we carried out a multi-method investigation of mantle sulfides coexisting with four generations of carbonates, indicating coupled sulfur and carbon mobility throughout the peridotites’ metamorphic evolution as part of the Variscan subduction architecture. Detailed petrography, bulk rock measurements, in situ chemical and geochemical analyses of sulfides as well as Sr isotope analyses of associated clinopyroxene and amphibole are combined with the aim to constrain the origin, nature and effect of multiple C-O-H-S-bearing fluids and melts the peridotites interacted with. The first, pre-peak, metasomatic pulse (Stage 1) is represented by an H2S-CO2-bearing melt from the subduction-modified hot mantle wedge, which formed a pyroxenite layer hosting matrix pentlandite with ?34S of +2.77‰. Matrix carbonates occasionally occur in the coarse-grained peridotite under eclogite-facies conditions (Stage 2), with heavier ?34S (up to +3.43‰), radiogenic Sr (87Sr/86Srclinopyroxene > 0.7052) and elevated Pb abundances. These are ascribed to interaction with isotopically heavy melts carrying recycled crustal component, permissive of, but not requiring, involvement of oxidized S species. Conversely, isotopically lighter matrix pentlandite (?34S = ?1.62 to +0.67‰), and radiogenic Sr in amphibole (87Sr/86Sr = 0.7056) and associated dolomite (published data) from fine-grained garnet-amphibole peridotites may point to involvement of H2S-CO2-bearing crustal fluids, which variably equilibrated with the mantle before interacting with the peridotites. The post-peak Stage 3 marks the entrapment of peridotites into a tectonic mélange. Here, kelyphitization of garnet is catalyzed by further ingress of a S-bearing fluid (?34S = ?0.38‰), while carbonate veining with occasional sulfides bear witness to channelized fluid flow. Sulfide and amphibole grains in retrogressed spinel peridotites reveal the highest contents of fluid-mobile elements (As, Sb) and 87Sr/86Sramphibole up to 0.7074, suggesting late interactions with isotopically heavy crustal fluids at high fluid-rock ratios. Textural observations indicate that, during Stage 4, serpentinization of peridotites at low ƒS2 played an active role not only in CO2 release by conversion of dolomite to calcite + brucite intergrowths, but also in local removal of 32S during the final exhumation stage. Late channelized sulfur remobilization is evidenced by the serpentine + magnetite (±millerite ± calcite) vein carrying > 300 ppm S. Overall, the relatively narrow range of sulfur isotope composition (?34S = ?1.62 to +3.76‰) is indicative of limited interaction with isotopically heavy crustal liquids, and points to a subordinate role of subduction-derived sulfate throughout the extended fluid(melt)/rock evolution of the Ulten Zone peridotites, first in the mantle wedge and then as part of a tectonic mélange.
DS202103-0374
2021
Cooper, C.M., Farrington, R.J., Miller, M.S.On the destructive tendencies of cratons.Geology, Vol. 49, pp. 195-200. pdfMantlesubduction

Abstract: We propose that subducting slabs may cause lithospheric removal by directing mantle flow along the craton margin. This process could carve and shape the cratons, leading to conditions that impact the overall (in)stability of the lithosphere. We use three-dimensional geodynamic models to investigate how subduction-driven directed flow interacts with cratonic lithosphere of differing shape, concluding that the margin shape controls both channelization of flow around the craton as well as the potential for destruction. While the simulations show that all craton shapes aid in channelization, the cratons with straight vertical margins are the most resistant to deformation, and the cratons with gradually thickening margins are less resistant to deformation. The dependence on shape could contribute to the progressive removal of cratonic lithosphere along its margin in a runaway process until a more stable vertical margin shape evolves.
DS202103-0375
2021
Corrigan, D., van Roogen, D., Wodicka, N.Indenter tectonics in the Canadian shield: a case study for Paleoproterozoic lower crust exhumation, orocline development, and lateral extrusion.Precambrian Research, Vol. 355, 106083, 23p. PdfCanada, Quebec, Ungava tectonics

Abstract: There are lingering questions about how far back in geologic time plate tectonic processes began. In the Paleoproterozoic of eastern Laurentia, accretion of intra-oceanic juvenile terranes along the leading edge of the Superior craton apex (Ungava indenter) during the interval 1.87-1.83 Ga was followed by collision with the Churchill plate at ca. 1.83-1.79 Ga. Orthogonal shortening along the indenter led to early obduction of the juvenile terranes including the ca. 2.0 Ga Watts Group ophiolite, followed by out-of-sequence thrusting at ca. 1.83 Ga of granulite-facies crystalline basement of the Sugluk block (Churchill plate) along the Sugluk suture. Exhumation and erosion of the Sugluk block led to deposition of a foreland/delta fan sequence in the Hudson Bay re-entrant (Omarolluk and Loaf formations of the Belcher Group), with detritus sourced exclusively from the Sugluk block. Continued collision led to critical wedge development and orocline formation in the Hudson Bay re-entrant, forming a strongly arcuate fold-thrust belt. On the other (eastern) side of the indenter, material flow during crustal shortening was accommodated by lateral extrusion of microplates towards a then open ocean basin, in a manner similar to present-day extrusion of Indochina as a response to India - South China craton convergence. In the Churchill plate hinterland W-NW of the indenter, propagating strike-slip faults resulted in the far-field extrusion and oblique exhumation of Archean crustal slices of the Rae crustal block. The 1.83-1.79 Ga Superior-Churchill collision accommodated a minimum of 500 km of continent-continent convergence, with resulting style and mechanisms of orogenic growth and material flow similar to those observed in the Alpine-Himalayan orogenic system.
DS202107-1095
2021
Coward, S., Campbell, JAHAnalytics for effective investment in early stage diamond exploration. SAIMM Conference, 36 ppts. PdfGlobaleconomics
DS202110-1607
2021
Cowing, M.D.Diamond's spectral constellation. Reverse ray tracingGemmology Today, Vol. 1, 1, June pp. 24-31. Globalreflectance
DS202101-0006
2020
Cui, D., Liao, Z., Qi, L., Zhong, Q., Zhou, Z.A study of emeralds from Davdar, north-western China.Journal of Gemology, Vol. 37, 4, pp. 374-392Chinaemerald

Abstract: At the Davdar mine in Xinjiang, north-western China, emeralds are hosted mainly by carbonate, quartz-carbonate and quartz veins cutting metasedimentary rocks, and are associated with minerals such as hematite, dolomite, quartz, orthoclase and albite. Sixteen rough emeralds obtained during the authors’ visit to the mining area in 2019 were studied by standard gemmolog-ical techniques and various spectroscopic methods (FTIR, Raman, UV-Vis-NIR and EPR), as well as LA-ICP-MS chemical analysis. The analysed samples were mostly coloured by Cr, and showed a wide range of Fe, V, Mg and alkali contents, along with relatively low Cs, Rb and Sc. UV-Vis-NIR spectra showed features at 370 nm (Fe3+), 430 nm (Cr3+ with contributions from V3+ and possibly Fe3+), 580-630 nm (Cr3+ and V3+), 638 and 683 nm (Cr3+), and 850 nm (Fe2+ and possibly Fe2+-Fe3+interactions). In addition, the more V-rich emeralds displayed a distinct V3+ absorption band at about 385-395 nm. Notably, the chemical composition of Davdar emeralds shows significant overlap with those from Panjshir, Afghanistan.
DS202110-1608
2021
da Silva, G.F., Ferreira, M., Costa, I., Borges Bernardes, R.Qmin: A machine learning-based application for mineral chemistry data processing and analysis. * note not specific to diamonds.Researchgate Preprint, 23p. PdfGlobalmineralogy

Abstract: Mineral chemistry analysis is a valuable tool in several phases of mineralogy and mineral prospecting studies. This type of analysis can point out relevant information, such as concentration of the chemical element of interest in the analyzed phase and, thus, the predisposition of an area for a given commodity. Due to this, considerable amount of data has been generated, especially with the use of electron probe micro-analyzers (EPMA), either in research for academic purposes or in a typical prospecting campaign in the mineral industry. We have identified an efficiency gap when manually processing and analyzing mineral chemistry data, and thus, we envisage this research niche could benefit from the versatility brought by machine learning algorithms. In this paper, we present Qmin, an application that assists in increasing the efficiency of mineral chemistry data processing and analysis stages through automated routines. Our code benefits from a hierarchical structure of classifiers and regressors trained by a Random Forest algorithm developed on a filtered training database extracted from the GEOROC (Geochemistry of Rocks of the Oceans and Continents) repository, maintained by the Max Planck Institute for Chemistry. To test the robustness of our application, we applied a blind test with more than 11,000 mineral chemistry analyses compiled for diamond prospecting within the scope of the Diamante Brasil Project of the Geological Survey of Brazil. The blind test yielded a balanced classifier accuracy of ca. 99% for the minerals known by Qmin. Therefore, we highlight the potential of machine learning techniques in assisting the processing and analysis of mineral chemistry data.
DS202111-1764
2021
D'Agrella-Filho, M.S., Antonio, P.Y.J., Trindade, R.I.F., Texeira, W., Bispo-Santos, F.The Precambrian drift history and paleogeography of Amazonia. Chapter 6.Ancient supercontinents and the paleogeography of Earth eds Pesonen, Salminen, Elming, Evans, Veikkolainen, 41p. pdfMantlesupercontinents, craton, Colombis, Rodinia, Gondwana

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 c.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 c.1.2 Ga, a clockwise rotation of Amazonia/West Africa and Baltica from Columbia to Rodinia joining Laurentia at c.1.0 Ga, or a scenario where Amazonia/West Africa were a wandering block that did not take part in Columbia and collided with Laurentia to form Rodinia at c.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.
DS202105-0759
2021
Dai, H-K., Zheng, J-P., Griffin, W.L., O'Reilly, S.Y., Xiong, Q., Ping, X-Q., Chen, F-K., Lu, J-G.Pyroxenite xenoliths record complex melt impregnation in the deep lithosphere of the northwestern North China craton.Journal of Petrology, Vol. 62, 2, pp. 1-32. pdf.ChinaCraton

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.
DS202105-0760
2021
Dalton, H.Temporal evolution of kimberlite magmatism in Finland: an evaluation of geochronological methods commonly applied to kimberlites.Vancouver Kimberlite Cluster , May 25, 6pm PSTEurope, Finlandmagmatism
DS202112-1925
2021
Danilov, K., Yakovlev, E., Afonin, N.Study of deep structure of the kimberlite pipe named after M. Lomonosov of the Arkhangelsk diamondiferous province obtained by joint using of passive seismic and radiometric methods.Pure and Applied Geophysics, Vol. 178, 10, pp, 3933-3952.Russia, Arkangelskdeposit - Lomonsov

Abstract: Kimberlite pipes are difficult to investigate due to their vertical orientation, conic shape and diverse physical characteristics and petrological compositions, all of which obstruct the use of magnetic methods, reflection and refraction seismic surveys to examine kimberlite pipes. Wherein the emplacement model for kimberlite pipes has important significance in resource geology and in mine design process. As a result, the development of new methods of investigating kimberlite pipes remains necessary. To that end, because the most stable characteristic of kimberlite pipes is their downward-tapering structure, the pipes can be more effectively examined by using methods offering high resolution and new indicators for prospecting. Herein, we present the results of jointly using passive seismic and radiometric methods to study the structure of a kimberlite pipe and its enclosing environment. In particular, we employed a microseismic sounding method, passive seismic interferometry, the H/V method, gamma spectrometry and emanation mapping to model the kimberlite pipe named after M. Lomonosov of the Arkhangelsk diamondiferous province. The combined use of those methods revealed an ore-controlled fault and probably a supply channel (i.e. dyke). The obtained model is correspondent to drill whole data and includes additional information about the structure and elastic properties of the studied pipe. Amongst its principal benefits, the proposed technique affords the possibility of discerning the primary elements of the kimberlite pipes and enclosing environments at depths from 30 m to 2 km, which can significantly increase the effectiveness of investigations into kimberlite pipes.
DS202110-1609
2021
Dasari, V., Sharma, A., Marvillet, E., Singh, P., Rudashevsky, V., Alikin, O., Zaveri, V.Liberation of emeralds from micaeous host rocks using electric-pulse dissaggregation vs conventional processing.Journal of Gemmology, Vol. 37, 7, pp. 716-724.Globalemeralds

Abstract: In ore processing, electric-pulse disaggregation (EPD) is used for the liberation of mineral crystals from host rocks. Since 2019, EPD technology has been used exclusively to recover emeralds produced from the Kagem mine in Zambia. This article compares the differences in the recovery of emeralds from micaceous schist host rock at the Kagem mine by EPD technology versus the conventional hand-cobbing method. The amount of emeralds obtained using both methods was similar, but EPD had numerous advantages in terms of liberation speed, ease of performing the process and the characteristics of the liberated emeralds.
DS202110-1610
2021
de Barros Gomes, C., Azzone, R.G., Rojas, G.E.E., Guarino, V., Ruberti, E.Agpaitic alkaline rocks in southern Brazilian platform: a review.Minerals MDPI, Vol. 11, 934, 30p. PdfSouth America, Brazil, Paraguayalkaline magmatism

Abstract: General information is presented on ten agpaitic occurrences located in southern Brazil and at the border between Brazil and Paraguay. All the Brazilian agpaitic rocks are Late Cretaceous in age, whereas the Paraguayan ones are older than Early Triassic. The most significant occurrence is Poços de Caldas, the largest alkaline massif in South America. In general, these agpaitic rocks contain mineral assemblages that indicate presence of typical halogen-bearing Na-Ca-HFSE phases, eudialyte-, rinkite- and wöhlerite-group minerals being the most frequent ones. However, these associations are indeed more complex in terms of composition, with accessory phases in some cases consisting of various minerals, including U-Th oxides/silicates, Nb oxides, REE-Sr-Ba bearing carbonates-fluorocarbonates-phosphates-silicates and Zr-Na rich silicates. They usually form late magmatic stage to hydrothermal/deuteric assemblages linked with coarse and fine-grained, mainly silica-undersaturated evolved rocks. Data also indicate significant differences in type, amount and composition of agpaitic minerals in all investigated occurrences.
DS202109-1458
2021
de Caravlho, L.D.V., Jalowitzki, T., Scholz, R., de Oliveira Gonzales, G., Rocha, M.P., Peeira, R.S., Lana, C., de Castro, P., Queiroga, G., Fuck, R.A.An exotic Cretaceous kimberlite linked to metasomatized lithospheric mantle beneath the southwestern margin of the Sao Francisco Craton, Brazil.Geoscience Frontiers, doi,org/101016/j.gsf.2021.101.28South America, Brazildeposit - Osvaldo Franca 1

Abstract: We present major and trace element compositions of mineral concentrates comprising garnet xenocrysts, ilmenite, phlogopite, spinel, zircon, and uncommon minerals (titanite, calzirtite, anatase, baddeleyite and pyrochlore) of a newly discovered Late Cretaceous kimberlite (U-Pb zircon age 90.0 ± 1.3 Ma; 2?) named Osvaldo França 1, located in the Alto Paranaíba Igneous Province (APIP), southeastern Brazil. Pyrope grains are lherzolitic (Lherz-1, Lherz-2 and Lherz-3), harzburgitic (Harz-3) and wehrlitic (Wehr-2). The pyrope xenocrysts cover a wide mantle column in the subcratonic lithosphere (66-143 km; 20-43 kbar) at relatively low temperatures (811-875 °C). The shallowest part of this mantle is represented by Lherz-1 pyropes (20-32 kbar), which have low-Cr (Cr2O3 = 1.74-6.89 wt.%) and fractionated middle to heavy rare earth elements (MREE-HREE) pattern. The deepest samples are represented by Lherz-2, Lherz-3, Harz-3, and Wehr-2 pyropes (36-43 kbar). They contain high-Cr contents (Cr2O3 = 7.36-11.19 wt.%) and are characterized by sinusoidal (Lherz-2 and Wehr-2) and spoon-like (Lherz-3 and Harz-3) REE patterns. According to their REE and trace elements, pyrope xenocrysts have enriched nature (e.g., Ce and Yb vs. Cr2O3), indicating that the cratonic lithosphere has been affected by a silicate melt with subalkaline/tholeiite composition due to their low Zr, Ti and Y concentrations. Besides minerals with typical kimberlitic signatures, such as ilmenite and zircon, the exotic compositions of phlogopite and ulvöspinel suggest an enriched component in the magma source. The formation of rare mineral phases with strong enrichment of light-REE (LREE) and high field strength elements (HFSE) is attributed to the late-stage kimberlitic melt. We propose a tectonic model where a thermal anomaly, represented by the low-velocity seismic anomaly observed in P-wave seismic tomography images, supplied heat to activate the alkaline magmatism from a metasomatized cratonic mantle source during the late-stages of Gondwana fragmentation and consequent South Atlantic Ocean opening. The metasomatism recorded by mineral phases is a product of long-lived recycling of subducted oceanic plates since the Neoproterozoic (Brasiliano Orogeny) or even older collisional events, contributing to the exotic character of the Osvaldo França 1 kimberlite, as well as to the cratonic lithospheric mantle.
DS202105-0761
2021
De Wit, M.Paleozoic diamond deposits of the NW Province, South Africa.Wits Geotalk recorded, https://youtu.be/ BajbGtkTqpEAfrica, South Africaalluvials
DS202107-1096
2021
de Wit, M., Bamford, M.Fossil wood from the Upper Cretaceous crater sediments of the Salpeterkop volcano, North West Province, South Africa. Carbonatite, melilititesSouth African Journal of Geology, doi:10.25131/sajg.124.0028 10p. PdfAfrica, South Africadeposit - Salpeterkop

Abstract: The Salpeterkop volcano forms part of what has been referred to as the Upper Cretaceous Sutherland Suite of alkaline rocks, an igneous province composed of olivine melilitites, carbonatites, trachytes and ultramafic lamprophyres. Salpeterkop is a remnant of the summit tuff ring structure that surrounds a crater which is almost 1 km in diameter and is filled with epiclastic strata. Five pieces of silicified wood were collected from the crater filled sediments, sectioned and identified as a new species of Cupressinoxylon, C. widdringtonioides. This is the first example of the fossil genus in South Africa. Only one member of the Cupressaceae s.l. occurs in southern Africa today. From the wide and indistinct growth rings in the fossil wood it can be deduced that the local climate was warm and humid with little or no seasonality, in support of global records of a warm Late Cretaceous. The preservation of the crater further signifies the low level of erosion the region has experienced since its emplacement.
DS202112-1926
2021
de Wit, M.C.J.The geology of the late-Cretaceous Saltpeterkop volcano near Sutherland: a geomorphic benchmark.Journal of African Earth Sciences, Vol. 185, 104414, 19p. PdfAfrica, South Africacarbonatite

Abstract: The Salpeterkop volcano is spatially part of the Sutherland Suite of alkaline rocks in the Northern Cape. It is one of the best preserved volcanoes in South Africa with part of the tuff ring still intact, remnants of the ejecta mantle outside the crater still preserved, and is host to epiclastic rocks, including ash and lapillistone and water lain sediments, inside the crater. New dates from apatites and phlogopites from Salpeterkop suggest an age close to 70 Ma. This Upper Cretaceous age is supported by the silicified wood found within the epiclastic sediments. Its relationship to the alkaline rocks in this cluster is not entirely clear but field evidence suggests that initial olivine melilitites and ultramafic bodies were followed by the main eruption that produced Salpeterkop. Clear igneous components in the associated breccias and pyroclastics are rare but indicate that this volcano was linked to an alkaline (trachytic) intrusion driven by phreatic magmatism. This is further highlighted by the presence of (nepheline?) syenite xenoliths in some carbonatite breccias and dykes that are part of the later carbonatites with its associated hydrothermal alteration products. Although the carbonatites are largely late-stage, there is evidence of earlier carbonatite activity from a precursor carbonatite dyke that has off-set an olivine melilitite dyke. Relatively unaltered pyroclastics, associated with two vents, northeast and northwest of the crater respectively, represent the final phase of this volcanic centre. Finally, the preservation of the Salpeterkop crater and its associated volcaniclastics highlights the change of intense landscape denudation, that ensued from Gondwana break-up to the end of the Cretaceous, to a period of drastically reduced erosion rates during the Cenozoic Era.
DS202101-0007
2020
Decree, S., Savolainen, M., Mercadier, J., Debaille, V., Hohn, S., Frimmel, H., Baele, J-M.Geochemical and spectroscopic investigation of apatite in the Siilinjarvi carbonatite complex: keys to understanding apatite forming processes and assessing potential for rare earth elements.Applied Geochemistry, Vol. 123, 104778 17p. PdfEurope, Finlanddeposit - Siilinjarvi

Abstract: The Siilinjärvi phosphate deposit (Finland) is hosted by an Archean carbonatite complex. The main body is composed of glimmerite, carbonatite and combinations thereof. It is surrounded by a well-developed fenitization zone. Almost all the rocks pertaining to the glimmerite-carbonatite series are considered for exploitation of phosphate. New petrological and in-situ geochemical as well as spectroscopic data obtained by cathodoluminescence, Raman and laser-induced breakdown spectroscopy make it possible to constrain the genesis and evolution of apatite through time. Apatite in the glimmerite-carbonatite series formed by igneous processes. An increase in rare earth elements (REE) content during apatite deposition can be explained by re-equilibration of early apatite (via sub-solidus diffusion at the magmatic stage) with a fresh carbonatitic magma enriched in these elements. This late carbonatite emplacement has been known as a major contributor to the overall P and REE endowment of the system and is likely connected to fenitization and alkali-rich fluids. These fluids - enriched in REE - would have interacted with apatite in the fenite, resulting in an increase in REE content through coupled dissolution-reprecipitation processes. Finally, a marked decrease in LREE is observed in apatite hosted by fenite. It highlights the alteration of apatite by a REE-poor fluid during a late-magmatic/hydrothermal stage. Regarding the potential for REE exploitation, geochemical data combined with an estimation of the reserves indicate a sub-economic potential of REE to be exploited as by-products of phosphate mining. Spectroscopic analyses further provide helpful data for exploration, by determining the P and REE distribution and the enrichment in carbonatite and within apatite.
DS202106-0930
2020
Dellas, G.Diamond plant statistics, process efficiencies, liberation modelling, and simulation: the art of the possible.saimm.co.za, 8p. pdfAfrica, South Africamining

Abstract: The paper brings together the language of diamond numbers and the underlying principles for calculation of diamond liberation, followed by estimation of process efficiency at circuit and complete plant levels. In this way it provides a reference point, albeit a mixture of the theoretical and empirical, to assess the effectiveness of diamond plant accounting systems in the field. Having established today's baseline, the wider aim is ongoing education, peer technical debate, and progression to a more exact science.
DS202108-1277
2021
Derycke, A., Gautheron, C., Barbarand, J., Bourbon, P., Aertgeerts, G., Simon-Labric, T., Sarda, P., Pinna-Jamme, R., Boukari, C., Gaurine, F.French Guiana margin evolution: from Gondwana break-up to Atlantic Ocean.Terra Nova, Vol. 33, 4, pp. 415-422. pdfSouth America, French GuianaGuiana Shield

Abstract: Knowledge of the Guiana Shield evolution during the Gondwana break-up is key to a better understanding of craton dynamics and margin response to transtensional opening. To improve this knowledge, we investigated the dynamics and thermal evolution of French Guiana, using several low-temperature thermochronology methods applied to basement rocks, including apatite and zircon (U-Th)/He and apatite fission tracks. Inverse modelling of results allows us to reconstruct the Phanerozoic thermal history of French Guiana margin and to give a preview of the Guiana Shield evolution. Three main events are inferred: firstly, a long-term period of relative stability since ~1.2 Ga, with no strong evidence for any erosional or burial event (>5-7 km); secondly, a heating phase between ~210 and ~140 Ma consistent with the Central Atlantic Magmatic Province-related event. Finally, an exhumation phase between ~140 and ~90 Ma, triggered by the Equatorial Atlantic opening, brought samples close to the surface (<40°C).
DS202109-1459
2021
Dessai, A.G., Griffin, W.L. Decratonization and reactivation of the southern Indian shield: an integrated perspective. Earth Science Reviews , Vol. 220, 103702 16p. PdfIndiacraton - Dharwar

Abstract: A 150-200 km thick, cold (35-45 mWm?2), melt-depleted lithospheric keel characterised the eastern cratons of the Indian shield at the end of the Precambrian. Differing chemical- and isotopic-characteristics, and ages of the crust and mantle rocks reveal the decoupling of the crust and mantle beneath the cratons, beginning at 2.45 Ga, in the Bastar craton. The Pan-African event was more pervasive and brought about widespread reworking in most of the cratons of the shield. Major-, trace- and rare-earth elements combined with Sr, Nd and Hf isotope data suggest a heterogenous SCLM beneath southern India. The trace element signatures of xenoliths and the presence of majoritic garnet inclusions in diamond suggest that some kimberlites were derived from the mantle transition zone. Mesoproterozoic (1.2-1.4 Ga) modal and cryptic refertilisation by asthenosphere-derived, low-degree carbonated melts led to the generation of the fluids responsible for the metasomatic transformation of the source rocks. The western craton of the shield has witnessed more severe reactivation than the eastern due to the frequent interaction of the Indian plate with mantle plumes. One plume caused major igneous activity during the late Cretaceous, synchronous with crustal attenuation, rifting and the ridge-jump at 66 Ma, in the Indian Ocean. By the end of the Palaeocene the geotherm of the western craton had risen from 50 to 55 mWm?2 in the Proterozoic to a peak 80-90 mWm?2. This increase in heat flow not only modulated the mantle thermal regime, but led to a net loss of more than 100 km of lithosphere and to destabilisation of the craton. After this thermal event, the lithosphere preserves a thickness of barely 60-80 km, and a thin crust (10-21 km) beneath the continental margin in the west. These changes decratonized the western part of the shield and the transitional region further west in the Indian Ocean where the continental ridges are almost devoid of crustal sections and the lithosphere is ~60 km thick. The waning of the Deccan Traps (65 Ma) magmatism was marked by alkaline intrusive activity along the western margin of the shield, probably derived from the SCLM in response to the rise of the mantle plume. Low degree (2-3%) partial melting of a modally and cryptically metasomatized source may have been involved in the generation of alkaline magmas from a depleted mantle source variously contaminated by an enriched endmember.
DS202101-0008
2020
Dessai, A.G., Viegas, A., Griffin, W.L.Thermal architecture of cratonic India and implications for decratonization of the western Dharwar craton: evidence from mantle xenoliths in the Deccan traps.Lithos, in press available, 56p. PdfIndiageothermometry

Abstract: The mantle beneath the Western Dharwar Craton of the Indian shield comprises a suite of refractory and fertile peridotites and mafic granulites. Detailed petrographic studies coupled with new mineral analysis and geothermobarometric estimations permit to decipher the thermal architecture and get an insight into the evolution of this ancient craton. The refractory rocks are coarse grained harzburgites/dunites, whereas the more fertile ones are at times, porphyroclastic lherzolites. Both show a similar range of equilibration temperatures and pressures indicating intermixing between the two at various levels. The peridotites contain undeformed interstitial REE-enriched clinopyroxene, phlogopite, apatite and carbonates recording post-kinematic modal and cryptic metasomatic events in the Precambrian cratonic lithosphere. Xenoliths of mafic granulite contain layers of clinopyroxenite which also vein the granulite. The P-T range of the granulites overlaps that of the ultramafic rocks. This study in combination with previous investigations reveals a distinct change in the thermal architecture of the craton from a warm/hot geotherm in the Proterozoic to a highly perturbed, still hotter geotherm of the Palaeocene. The Cenozoic thermotectonic rifting episodes heated, refertilized and thinned the bulk of the cratonic lithosphere beneath the Western Dharwar Craton, which has witnessed the most re-activation among cratons of the Indian shield. The waning of the Deccan Traps volcanism in Palaeocene time saw the reworking of ancient cratonic lithosphere and its replacement by non-cratonic, juvenile mantle and magmatic accretions, indicated by compound xenoliths. Differing petrological and geochemical characteristics of refractory xenoliths and fertile lherzolites serve to constrain the relative timing and composition of non-cratonic lithosphere. By the end of the Palaeocene the Western Dharwar Craton was characterised by a thermal high, an attenuated continental lithosphere (60-80 km), and a thin crust (<10- ~ 21 km), reflecting the decratonization of at least the western part of the Western Dharwar Craton.
DS202106-0931
2021
Dewey, J.F., Kiseeva, E.S., Pearce, J.A., Robb, L.J.Precambrian tectonic evolution of Earth: an outline.South African Journal of Geology, Vol. 124, 1, pp. 141-162. pdfMantletectonics

Abstract: Space probes in our solar system have examined all bodies larger than about 400 km in diameter and shown that Earth is the only silicate planet with extant plate tectonics sensu stricto. Venus and Earth are about the same size at 12 000 km diameter, and close in density at 5 200 and 5 500 kg.m-3 respectively. Venus and Mars are stagnant lid planets; Mars may have had plate tectonics and Venus may have had alternating ca. 0.5 Ga periods of stagnant lid punctuated by short periods of plate turnover. In this paper, we contend that Earth has seen five, distinct, tectonic periods characterized by mainly different rock associations and patterns with rapid transitions between them; the Hadean to ca. 4.0 Ga, the Eo- and Palaeoarchaean to ca. 3.1 Ga, the Neoarchaean to ca. 2.5 Ga, the Proterozoic to ca. 0.8 Ga, and the Neoproterozoic and Phanerozoic. Plate tectonics sensu stricto, as we know it for present-day Earth, was operating during the Neoproterozoic and Phanerozoic, as witnessed by features such as obducted supra-subduction zone ophiolites, blueschists, jadeite, ruby, continental thin sediment sheets, continental shelf, edge, and rise assemblages, collisional sutures, and long strike-slip faults with large displacements. From rock associations and structures, nothing resembling plate tectonics operated prior to ca. 2.5 Ga. Archaean geology is almost wholly dissimilar from Proterozoic-Phanerozoic geology. Most of the Proterozoic operated in a plate tectonic milieu but, during the Archaean, Earth behaved in a non-plate tectonic way and was probably characterised by a stagnant lid with heat-loss by pluming and volcanism, together with diapiric inversion of tonalite-trondjemite-granodiorite (TTG) basement diapirs through sinking keels of greenstone supracrustals, and very minor mobilism. The Palaeoarchaean differed from the Neoarchaean in having a more blobby appearance whereas a crude linearity is typical of the Neoarchaean. The Hadean was probably a dry stagnant lid Earth with the bulk of its water delivered during the late heavy bombardment, when that thin mafic lithosphere was fragmented to sink into the asthenosphere and generate the copious TTG Ancient Grey Gneisses (AGG). During the Archaean, a stagnant unsegmented, lithospheric lid characterised Earth, although a case can be made for some form of mobilism with “block jostling”, rifting, compression and strike-slip faulting on a small scale. We conclude, following Burke and Dewey (1973), that there is no evidence for subduction on a global scale before about 2.5 Ga, although there is geochemical evidence for some form of local recycling of crustal material into the mantle during that period. After 2.5 Ga, linear/curvilinear deformation belts were developed, which “weld” cratons together and palaeomagnetism indicates that large, lateral, relative motions among continents had begun by at least 1.88 Ga. The “boring billion”, from about 1.8 to 0.8 Ga, was a period of two super-continents (Nuna, also known as Columbia, and Rodinia) characterised by substantial magmatism of intraplate type leading to the hypothesis that Earth had reverted to a single plate planet over this period; however, orogens with marginal accretionary tectonics and related magmatism and ore genesis indicate that plate tectonics was still taking place at and beyond the bounds of these supercontinents. The break-up of Rodinia heralded modern plate tectonics from about 0.8 Ga. Our conclusions are based, almost wholly, upon geological data sets, including petrology, ore geology and geochemistry, with minor input from modelling and theory.
DS202109-1460
2021
Dey, M., Bhattacharjee, S., Chakrabarty, A., Mitchell, R.H., Pal, S., Pal, S, Sen, A.K. Compositional variation and genesis of pyrochlore, belkovite and baotite from the Sevattur carbonatite complex, India.Mineralogical Magazine, Vol. 85, 4, pp. 588-606.Indiadeposit - Sevattur

Abstract: Pyrochlore-group minerals are common in the Neoproterozoic Sevattur carbonatite complex. This complex is composed of dolomite-, calcite-, banded- and blue carbonatite together with pyroxenite, albitite and diverse syenites. This work reports the paragenetic-textural types and compositional variation of pyrochlore hosted by dolomite carbonatite, banded carbonatite and albitite together with that of alteration assemblages containing belkovite and baotite. On the basis of composition, five different types of pyrochlore are recognised and termed Pcl-I through to Pcl-V. The Pb-rich Pcl-I are present exclusively as inclusions in U-rich Pcl-IIa in dolomite carbonatite. The alteration assemblages of Pb-poor Pcl-IIb + Ba-rich or Ba-Si- rich Pcl-IV + belkovite (dolomite carbonatite) and Si-rich Pcl-V + baotite (banded carbonatite) formed after Pcl-IIa differ in these carbonatites. The albitite hosts extremely U-Ti-rich Pcl-III, mantled by Ba-rich potassium feldspar. In common with the banded carbonatite, Pcl-V is formed by alteration of Pcl-III where this mantle is partially, or completely broken. The Ba-Si-enrichment of Pcl-IV and Pcl-V together with the ubiquitous presence of baryte in all Sevattur lithologies suggests late-stage interaction with a Ba-Si-rich acidic hydrothermal fluid. This fluid was responsible for leaching silica from the associated silicates and produced Pcl-V in the silicate-rich lithologies of the banded carbonatite and albitite. The absence of Pcl-V in dolomite carbonatite is a consequence of the low modal abundance of silicates. The complex compositional diversity and lithology specific pyrochlore alteration assemblages suggest that all pyrochlore (Pcl-I to Pcl-IV) were formed initially in an unknown source and transported subsequently in their respective hosts as altered antecrysts.
DS202109-1461
2021
Dey, M., Mitchell, R.H., Bhattacharjee, S., Chakrabarty, A., Pal, S., Pal, S, Sen, A.K. Compositiion and genesis of albitite-hosted antecrystic pyrochlore from the Sevattur carbonatite complex, Inida.Mineralogical Magazine, Vol. 85, 4, pp. 568-587.Indiadeposit - Sevattur

Abstract: The Neoproterozoic Sevattur complex is composed essentially of calcite and dolomite carbonatites together with pyroxenites and diverse syenites. This work reports the compositions and paragenesis of different pyrochlore generations hosted by albitite veins in this complex. The pyrochlore are distinctive, being exceptionally rich in uranium (26 to 36 wt.% UO2). Five types of pyrochlore (Pcl-I to Pcl-V) are recognised on the basis of composition and texture. With the exception of Pcl-V, the majority of the pyrochlore (Pcl-II to Pcl-IV) are surrounded by a thick orbicular mantle of Ba-rich potassium feldspar. This mantle around Pcl-V is partially-broken. Pcl-I is restricted to the cores of crystals, and associated with Pcl-II and -III and is relatively rich in Nb (0.53-0.62 apfu) together with more A-site vacancies (0.37-0.71 apfu) compared to Pcl-II to Pcl-IV. Other pyrochlore (Pcl-II to Pcl-IV) are characterised by elevated Ca and Ti compared to Pcl-I, which are related to the (3Nb5+ + Na+ ? 3Ti4+ + U4+) and (2Nb5+ ? 2Ti4+ + Ca2+) substitutions, respectively. These substitutions represent replacement of Pcl-II to Pcl-IV. Alteration and Ba-enrichment in all the pyrochlore are marked by interaction with an externally-derived Ba-rich hydrothermal fluid following the (2Nb5+ ? 2Ti4+ + Ba2+) substitution. This substitution, coupled with extensive metamictisation leads to the formation of Ba-rich (15.9-16.3 wt.% BaO) patchy-zoned Pcl-V. The orbicular mantles around Pcl-I to Pcl-IV have prevented extensive metamictisation and extensive secondary alteration compared to Pcl-V, where mantling is partially disrupted. The compositional and textural variation suggests that Pcl-II to Pcl-IV form by nucleation on Pcl-I, and are transported subsequently as antecrysts in the host albitite.
DS202103-0376
2021
Dey, M., Mitchell, R.H., Bhattacharjee, S., Chakrabarty, A., Pal, S., Pal, S., Sen, A.K.Composition and genesis of albitite-hosted antecrystic pyrochlore from the Sevattur carbonatite complex, India.Mineralogical Magazine, 20p. Doi:10.1180/mgm.2021.6 24p. PdfIndiadeposit - Sevattur
DS202109-1462
2021
Dhansay, T.Shattered crust: how brittle deformation enables critical zone processes beneath southern Africa.South African Journal of Geology, Vol. 124, pp. 519-536.Africa, South Africageodynamics

Abstract: The delicate interplay of various Earth’s systems processes in the Critical Zone is vital in ensuring an equilibrium across the different spheres of life. The upper crust forms a thin veneer on the Earth’s surface that is defined by an interconnected network of brittle structures. These brittle structures enable various Earth System processes. Increased anthropogenic interactions within the very upper crust have seemingly resulted in a growing number of negative natural effects, including induced seismicity, mine water drainage and land degradation. Brittle structures across South Africa are investigated. These structures include various fractures and dykes of different ages and geodynamic evolutions. The orientation of these structures is compared to the underlying tectonic domains and their bounding suture zones. The orientations corroborate an apparent link between the formation of the brittle structures and the tectonic evolution of the southern African crust. Reactivation and the creation of new structures are also apparent. These are linked to the variability of the surrounding stress field and are shown to have promoted magmatism, e.g., Large Igneous Provinces, and the movement of hydrothermal fluids. These fluids were commonly responsible for the formation of important mineral deposits. The preferred structural orientations and their relationship to underlying tectonic zones are also linked to fractured groundwater aquifers. Subsurface groundwater displays a link to structural orientations. This comparison is extended to surficial water movement. Surface water movement also highlights an apparent link to brittle structures. The apparent correlation between these Earth’s systems processes and the interconnectivity developed by brittle structures are clear. This highlights the importance of high-resolution geological and structural mapping and linking this to further development of the Earth’s Critical Zone.
DS202106-0932
2021
Dhote, P., Bhan, U., Verma, D.Genetic model of carbonatite hosted rare earth elements mineralization from Ambadongar carbonatite complex, Deccan Volcanic Province, India.Ore Geology Reviews, Vol. 135, 104215, 22p. PdfIndiadeposit - Ambadongar

Abstract: Carbonatites and associated alkaline rocks are the primary sources for REE mineralization. The Ambadongar Carbonatite Complex (ADCC) from NW Deccan Volcanic Province (DVP) constitutes the largest Carbonatite Associated REE Deposits (CARD) in India. ADCC belongs to the final stages of the Late Cretaceous alkaline-carbonatite magmatism associated with main Deccan basalt volcanic activity. The ADCC is an envisioned diatreme structure in which four carbonatitic phases are recognized, mainly calcio-carbonatites and ferro-carbonatites. Each successive carbonatite phase shows higher REE enrichment. The primary REE mineralization with bastnäsite as the dominant REE phase is hosted by pervasive hydrothermally altered ferro-carbonatite plugs. The secondary mineralogy formed with barites in the main orebody during late- to post-magmatic hydrothermal fluid alteration is fluorite, quartz, ankerite, and other REE-bearing minerals like bastnäsite, parisite, synchysite, strontianite, florencite, monazite and columbite. Carbonatite samples contain 18.61% to 52.42% of CaO, and the LOI varies from 5.28% to 38.79%. Most can be classified as calcio-carbonatites. Since all the samples also contain an appreciable amount of Fe2O3 (4.13% to 20.20%) and MnO (0.07% to 5.46%), some may be classified as ferro-carbonatites. Total REE content varies from 0.6 to 4%, with a high Ce concentration and LREE/HREE ratio. The highest values for La, Ce, Pr, and Nd are 1.95%, 1.56%, 0.16%, and 0.45%, respectively. Metasomatism of SCLM from asthenospheric melts followed by the low degree partial melting of the SCLM region is responsible for fertile carbonatite generation in ADCC. The multiphase liquid immiscibility of carbonatite melts from carbonate-silicate magma followed by immiscibility of REE rich carbonatite melt and REE deficient fluoride-rich aqueous fluids explain the higher level of REE enrichment in each successive phases of carbonatites in ADCC. The mineralizing fluids were probably the result of residual magmatic volatiles that brought mainly REE and later SiO2 into the overprinted rocks. Ambadongar carbonatites' stable isotopic compositions agree with a magmatic origin (?13C = ?4.1 ± 1.9‰ [PDB] and ?l8O = 10.3 ± 1.7‰ [SMOW]). The C-O stable isotopic modeling indicates re-equilibration under hydrothermal conditions between 180 °C and 70 °C. Significant amounts of REE fluorocarbonate minerals, relatively Sr- and Th-rich, were deposited during re-equilibration. The REE fluorocarbonate bastnäsite-(Ce) occurs as late individual crystals, overgrown on the synchysite and parisite polycrystals. Textural and chemical reactions between the REE fluorocarbonates provide insights into rare-earth elements' mobility during fluid-rock interaction. Early crystallization of synchysite/parisite indicates the high activity of Ca2+, OH?, (SO4)2?, Al and Si in the fluid. Later, the fluid was characterized by increased activity of F?, (SO4)2?, REE and Si, and decreased activity of Ca2+ as reflected in the association of barite, fluorite, quartz, and bastnäsite typical of strongly overprinted ferro-carbonatites. Re-equilibration and recrystallization of the primary minerals in the presence of OH?, (SO4)2?, F?, REE, Al, and Si carried in solution by the hydrothermal fluid is the leading cause behind the refixing of REE in the form of REE fluorocarbonate in REE rich ferro-carbonatites.
DS202102-0181
2020
Dilissen, N., Hidas, K., Garrido, C.J., Kahl, W-A., Sanchez-Vizcaino, V.L.Graphical abstract: Morphological transition during prograde olivine growth formed by high-pressure dehydration of antigorite-serpentinite to chlorite-harzburgite in a subduction setting.Lithos, doi. 10.1016/j. lithos.2020.105949 1p. PdfMantlesubduction

Abstract: Crystal morphologies are essential for deciphering the reaction history of igneous and metamorphic rocks because they often record the interplay between nucleation and growth rates controlled by the departure from equilibrium. Here, we report an exceptional record of the morphological transition of olivine formed during subduction metamorphism and high-pressure dehydration of antigorite-serpentinite to prograde chlorite-harzburgite in the Almirez ultramafic massif (Nevado-Filábride Complex, Betic Cordillera, SE Spain). In this massif, rare varied-textured chlorite-harzburgite (olivine+enstantite+chlorite+oxides) —formed after high-P dehydration of antigorite-serpentinite— exhibits large olivine porphyroblasts made up of rounded cores mantled by coronas of tabular olivine grains, similar to single tabular olivines occurring in the matrix. The correlative X-ray ?-CT and EBSD study of two varied-textured chlorite-harzburgite samples show that tabular olivine in coronas is tabular on (100)Ol with c > b >> a, and grew in nearly the same crystallographic orientation as the rounded olivine cores of the porphyroblast. Quantitative textural analysis and mass balance indicate that varied-textured chlorite-harzburgite is the result of a two-stage nucleation and growth of olivine during the progress of the high-P dehydration of antigorite-serpentinite to chlorite-harzburgite reaction. The first stage occurred under a low affinity (?Gr) and affinity rate (?Gr/dt) of the antigorite dehydration reaction that resulted in a low time-integrated nucleation rate and isotropic growth of olivine, forming rounded olivine porphyroblasts. With further progress of the dehydration reaction, a second stage of relatively higher affinity and affinity rate resulted in a higher time-integrated nucleation rate of olivine coeval with a shift from isotropic to anisotropic olivine growth, leading to tabular olivines. The two-stage evolution resulted in olivine porphyroblasts made up of rounded cores mantled by coronas of tabular olivine grains characteristic of varied-texture chlorite-harzburgite. Although a switch to anisotropic tabular olivine in the second stage is consistent with the relative increase in the affinity and affinity rate, these changes cannot solely account for the growth of Almirez olivine tabular on (100). Tabular olivines in komatiites and other igneous rocks are tabular on (010)Ol with either a > c >> b, or a ? c > > b, in agreement with experimentally determined growth rates of olivine phenocrysts under moderate to high undercooling and cooling rates. On the other hand, olivine tabular on (100) is expected in the presence of highly polymerized fluids where inhibited growth of the olivine (100) and (010) interfaces occurs, respectively, due to dissociative and molecular adsorption of water monolayers. Rounded and tabular olivines in Almirez varied-textured chlorite-harzburgite show differing trace element compositions that we interpret as due to the infiltration of external fluids during antigorite dehydration. Isothermal infiltration of highly polymerized fluids would explain the shift in the affinity and affinity rate of the antigorite dehydration reaction, as well as the olivine morphology tabular on (100) due to the inhibited growth on the (100) and, to a lesser extent, (010). Our study shows that surface-active molecules may play an essential role in shaping the morphology of growing crystals during fluid-present metamorphic crystallization.
DS202108-1278
2021
Ding, J., Zhang, S., Evans, D.A.D., Yang, T., Li, H.North China craton: the conjugate margin for northwestern Laurentia in Rodinia.Geology, Vol. 49, March pp. 773-778.ChinaRodinia

Abstract: In the Rodinia supercontinent, Laurentia is placed at the center because it was flanked by late Neoproterozoic rifted margins; however, the conjugate margin for western Laurentia is still enigmatic. In this study, new paleomagnetic results have been obtained from 15 ca. 775 Ma mafic dikes in eastern Hebei Province, North China craton (NCC). Stepwise thermal demagnetization revealed a high-temperature component, directed northeast or southwest with shallow inclinations, with unblocking temperatures of as high as 580 °C. Rock magnetism suggests the component is carried by single-domain and pseudo-single-domain magnetite grains. Its primary origin is supported by a positive reversal test and regional remanence direction correlation test, and the paleomagnetic pole (29.0°S, 64.7°E, A95 = 5.4°) is not similar to any published younger poles of the NCC. Matching the late Mesoproterozoic to early Neoproterozoic (ca. 1110-775 Ma) apparent polar wander paths of the NCC and Laurentia suggests that the NCC could have been the conjugate margin for northwestern Laurentia in Rodinia, rather than sitting off the northeast coast of the main Rodinian landmass. Geological data indicate that breakup of the NCC and Laurentia occurred between ca. 775 and 720 Ma.
DS202109-1463
2021
Dlakavu, S.AEON Report - Status of the small and junior diamond mining sector.AEON Report, see Cover second page for pdf 88p.Africa, South Africadiamond mining

Abstract: The Small and Junior diamond mining industry, which is dominated by alluvial diamond miners, and a few remaining small kimberlite operations, produced a high proportion of diamonds in South Africa in the late 1950s and early 1960s, prior to the discovery and development of major kimberlite mines such as Finsch and Venetia, in the 1970’s and 80’s. Subsequent to these discoveries the Small and Junior sector remained an active and important participant in the local diamond industry, particularly in respect of the highly sought after top-quality gemstone diamonds produced from the extensive alluvial deposits of South Africa. Since 2004 the sector has shown a strong decline. This report highlights the challenges faced by the Small and Junior diamond miners and makes recommendations for the revival of this sector.
DS202104-0571
2021
Dobretsov, N.L., Zhmodik, S.M., Lazareva, E.V., Bryanskaya, A.V., Ponomarchuk, V.A., Saryg-ool, B. Yu., Kirichenko, I.S., Tolstov, A.V., Karmanov, N.S.Structural and morphological features of the participation of microorganisms in the formation of Nb-REE-rich ores of the Tomtor field, Russia.Doklady Earth Sciences, Vol. 496, pp. 135-138. Russiadeposit - Tomtor

Abstract: Data indicating the important role of microorganisms in the redistribution of REEs in the weathering crust and the decisive role in the concentration of REEs during the formation of ores in the upper ore horizon of the Tomtor field are obtained. The uptake of REEs was carried out by the community of microorganisms, such as phototrophs, methanogens, methanotrophs, and proteobacteria, which form the basis of the microbiocenosis for this paleoecosystem. The isotopic composition of C carbonates in all samples studied with fossilized microorganisms corresponds to the biogenic one, and the isotopic composition ?18?SMOW (from 7 to 20‰) indicates the endogenous (hydrothermal) and, to a lesser extent, exogenous nature of the solutions. The low (87Sr/86Sr)I values of carbonates (~0.7036-0.7042) exclude the participation of seawater.
DS202105-0762
2021
Dong, B., Shi, C., Xu, Z., Wang, K., Luo, H., Sun, F., Wang, P., Wu, E., Zhang, K., Liu, J., Song, Y., Fan, Y.Temperature dependence of optical centers in 1b diamond characteristics by photoluminescence spectra. CVDDiamond & Related Materials, Vol. 116, 108389, 10p. PdfGlobalsynthetics
DS202104-0572
2021
Dong, J., Fischer, R., Stixrude, L., Lithgow-Bertelloni, C.Constraining the volume of Earth's early oceans with a temperature-dependent 2 mantle water storage capacity model.AGU Advances, 1,e2020AV000323Mantlewater

Abstract: At the Earth's surface, the majority of water resides in the oceans, while in the interior, major rock?forming minerals can incorporate significant amounts of water as hydroxyl groups (OH), likely forming another reservoir of water inside the planet. The amount of water that can be dissolved in Earth's mantle minerals, called its water storage capacity, generally decreases at higher temperatures. Over billion?year timescales, the exchange of water between Earth's interior and surface may control the surface oceans' volume change. Here, we calculated the water storage capacity in Earth's solid mantle as a function of mantle temperature. We find that water storage capacity in a hot, early mantle may have been smaller than the amount of water Earth's mantle currently holds, so the additional water in the mantle today would have resided on the surface of the early Earth and formed bigger oceans. Our results suggest that the long?held assumption that the surface oceans' volume remained nearly constant through geologic time may need to be reassessed.
DS202106-0933
2021
Dongre, A., Lavhale, P.,Li, Q-L.Perovskite U-Pb age and petrogenesis of the P-12 kimberlite from the Eastern Dharwar craton, southern India: impilcations for a possible linkage at the 1110 Ma large igneous province.Journal of Asian Earth Sciences, Vol.213, 104750, 12p.pdfIndiadeposit -P12

Abstract: Petrology, bulk-rock geochemistry, and perovskite U-Pb age for the P-12 kimberlite pipe from the Wajrakarur kimberlite field, Eastern Dharwar craton (EDC) of southern India is reported. Perovskites yielded a high-precision U-Pb age of 1122 ± 7.7 Ma, taken to be an emplacement age of the host P-12 kimberlite pipe. The groundmass of coherent facies P-12 kimberlite contains monticellite, clinopyroxene, andradite, atoll spinel with titanomagnetite trend, and perovskite with an elevated REE contents. Phlogopite shows restricted Al2O3 and TiO2 contents. Furthermore, olivines with a wider and higher range of core compositions (i.e. Mg# = 84-94) and multi-granular nodules are the hallmark features of the P-12 pipe. This assorted primary mineral content and its composition indicates the transitional nature of the P-12 towards the Kaapvaal lamproites. However, concentrations of bulk-rock major and trace elements in the P-12 and other Wajrakarur kimberlites are similar to the global hypabyssal magmatic kimberlites. Large ion lithophile and high field strength elements (e.g. Ba and Nb) and their ratios (e.g. La/Nb and Th/Nb) suggest the presence of a heterogeneous and lithosphere influenced mantle source region which have been severely overprinted by metasomatizing fluids/melts emanating from the deep sourced upwelling mantle. The presence of such mixed and metasomatized mantle source regions likely to be an important factor for the transitional nature of the P-12 and other Mesoproterozoic kimberlites. Based on the availability of the newest emplacement ages, we propose a geodynamic model for the origin of kimberlites in the Indian subcontinent. The U-Pb age of 1122 ± 7.7 Ma for the P-12 pipe shows its close temporal association to the emplacement of the recently proposed 1110 Ma Large Igneous Province (LIP), with plume center beneath the NW part of the Kalahari craton. Emplacement of the P-12 and other contemporaneous Indian kimberlites, therefore, marks the impingement of mantle plume which contributed heat and triggered partial melting of metasomatized lithospheric mantle without melt input. The eruption phase of ~ 100 million years (i.e. 1050-1153 Ma), for the kimberlites and related rocks in the Indian shield, does not appear to be continuous and can be separated into several short-durational magmatic events. For this reason, small-volume, volatile-rich magmatism during the Mesoproterozoic time in India is linked to the presence of a number of LIPs and associated mantle plumes during Columbia to Rodinia supercontinent transition and assembly of cratonic blocks of the latter.
DS202109-1464
2021
Doucet, L.S., Li, Z-X., El Dien, H.GOceanic and super-deep continental diamond share a transition zone origin and mantle plume transportation.Nature Scientific Reports, Vol. 11, 16958, 11p. Open access https://www.nature .com/articles/s41598- 021-96286-8.pdf Mantlediamond genesis

Abstract: Rare oceanic diamonds are believed to have a mantle transition zone origin like super-deep continental diamonds. However, oceanic diamonds have a homogeneous and organic-like light carbon isotope signature (?13C ? 28 to ? 20‰) instead of the extremely variable organic to lithospheric mantle signature of super-deep continental diamonds (?13C ? 25‰ to?+?3.5‰). Here, we show that with rare exceptions, oceanic diamonds and the isotopically lighter cores of super-deep continental diamonds share a common organic ?13C composition reflecting carbon brought down to the transition zone by subduction, whereas the rims of such super-deep continental diamonds have the same ?13C as peridotitic diamonds from the lithospheric mantle. Like lithospheric continental diamonds, almost all the known occurrences of oceanic diamonds are linked to plume-induced large igneous provinces or ocean islands, suggesting a common connection to mantle plumes. We argue that mantle plumes bring the transition zone diamonds to shallower levels, where only those emplaced at the base of the continental lithosphere might grow rims with lithospheric mantle carbon isotope signatures.
DS202110-1611
2021
Doucet, L.S., Li, Z-X., El Dien, G.H.Oceanic and super-deep continental diamonds share a transition zone origin and mantle plume transportation.Nature Scientfic Reports, Vol. 11, 16958 11p. PdfMantlediamond genesis

Abstract: Rare oceanic diamonds are believed to have a mantle transition zone origin like super-deep continental diamonds. However, oceanic diamonds have a homogeneous and organic-like light carbon isotope signature (?13C ? 28 to ? 20‰) instead of the extremely variable organic to lithospheric mantle signature of super-deep continental diamonds (?13C ? 25‰ to?+?3.5‰). Here, we show that with rare exceptions, oceanic diamonds and the isotopically lighter cores of super-deep continental diamonds share a common organic ?13C composition reflecting carbon brought down to the transition zone by subduction, whereas the rims of such super-deep continental diamonds have the same ?13C as peridotitic diamonds from the lithospheric mantle. Like lithospheric continental diamonds, almost all the known occurrences of oceanic diamonds are linked to plume-induced large igneous provinces or ocean islands, suggesting a common connection to mantle plumes. We argue that mantle plumes bring the transition zone diamonds to shallower levels, where only those emplaced at the base of the continental lithosphere might grow rims with lithospheric mantle carbon isotope signatures.
DS202108-1279
2021
Dragone, G.N., Bologna, M.S., Ussami, N., Gimenez, M.E., Alvarez, O., Klinger, F.G.L., Correa-Otto, S.Lithosphere of South American intracratonic basins: electromagnetic and potential field data reveal cratons, terranes, and sutures.Tectonophysics, Vol. 811, 13p. PdfSouth America, Argentinacratons

Abstract: A magnetotelluric survey comprising 18 broadband stations disposed along a 450 km-long profile was carried out at the transition between the Chaco-Paraná (CPB) and the Paraná (PB) intracratonic basins in northeastern Argentina. Three-dimensional inversions of the responses show that the CPB and southern PB lithospheres are resistive (~103 ? m) down to 120 km, but with distinct crustal and upper mantle electrical properties. Also, Bouguer gravity and density anomalies are positive at CPB, whereas they are negative at PB. We associate the CPB lithosphere with the Paleoproterozoic Rio Tebicuary craton and the southern PB lithosphere with an ancient and buried piece of craton, the Southern Paraná craton. Geochemical data of mantle xenoliths from the Cenozoic alkaline/carbonatitic province within the Rio Tebicuary craton suggest a subcontinental lithospheric mantle affected by metasomatic processes, which explains its lower resistivity (reaching values as low as 300 ? m) and higher density (#Mg = 0.87). In contrast, the Southern Paraná craton is more resistive (>103 ? m) and less dense, suggesting a de-hydrated, depleted, and thicker craton. These cratons are separated by a crustal conductor (15 to 20 km depth; 1-10 ? m) that we interpret as a southward continuation of a linear anomaly (Paraná Axial Anomaly) defined in former induction studies within the PB in Brazil. Hence, we redefined the trace of this conductive lineament: instead of bending towards the Torres Syncline, it continues inside the CPB. We propose the lineament to be an Early Neoproterozoic suture zone that controlled the location of maximum subsidence in the intracratonic basins during the Paleozoic. In the Early Cretaceous, the Paraná Axial Anomaly was the site of maximum extrusion and deposition of Serra Geral basalts. This anomaly separates compositionally distinct cratonic lithospheres along its path. Melting of this heterogeneous and enriched mantle created the Paraná igneous province.
DS202106-0934
2021
Drollner, M., Barham, M., Kirkland, C.L., Ware, B.Every zircon deserves a date: selection bias in detrital geochronology.** not specific to diamondsGeological Magazine, Vol. 158, 6, pp. 1135-1142. pdfGlobalgeochronology

Abstract: Detrital zircon geochronology can help address stratigraphic- to lithospheric-scale geological questions. The approach is reliant on statistically robust, representative age distributions that fingerprint source areas. However, there is a range of biases that may influence any detrital age signature. Despite being a fundamental and controllable source of bias, handpicking of zircon grains has received surprisingly little attention. Here, we show statistically significant differences in age distributions between bulk-mounted and handpicked fractions from an unconsolidated heavy mineral sand deposit. Although there is no significant size difference between bulk-mounted and handpicked grains, there are significant differences in their aspect ratio, circularity and colour, which indicate inadvertent preferential visual selection of euhedral and coloured zircon grains. Grain colour comparisons between dated and bulk zircon fractions help quantify bias. Bulk-mounting is the preferred method to avoid human-induced selection bias in detrital zircon geochronology.
DS202106-0935
2021
Du Toit, E., Delport, P.W.J.Supplementary mineral resources and mineral reserves reports: readibility and textural choice.saimm.co.za, 10P. PDFAfrica, South Africaeconomics

Abstract: Investing in a mining venture can be risky and stakeholders need transparent, unbiased reports to understand the Mineral Resources and Mineral Reserves a mining company holds. Readability and textual choice can be used consciously to manipulate perceptions, or it can be done unconsciously. This exploratory study investigates the readability and textual choice of supplementary Mineral Resources and Mineral Reserves Reports of companies listed on the Johannesburg Stock Exchange. The results indicate that narrative manipulation occurs in these reports through word choices that make the reports difficult to read, as well as specific narrative selections. This reduces the informational value of the reports. The results of the study will be useful to various stakeholders, such as mining company management, investors, investment specialists, financial analysts, and even employees and the general community, who all use these reports to make important decisions. It is also useful for the preparers of the Mineral Resources and Mineral Reserves Reports, Competent Persons, and other technical specialists to be aware of readability and that certain textual choices can affect the interpretation of these reports. It is recommended that bodies such as the JSE and the SAMREC and SAMVAL Code committees consider adding a plain language requirement to regulations, guidelines, and codes to ensure transparent, unbiased, and objective reports.
DS202102-0182
2020
Dunkl, I. Comparability of heavy mineral data - the first interlaboratory round robin. *** authors cited are too many + 50 more Not specific to diamondsEarth-Science Reviews, Vol. 211, doi.org/ 10.1016/ j.earscirev.2020 .103210 27p. Pdf Globalmineralogy - data

Abstract: Heavy minerals are typically rare but important components of siliciclastic sediments and rocks. Their abundance, proportions, and variability carry valuable information on source rocks, climatic, environmental and transport conditions between source to sink, and diagenetic processes. They are important for practical purposes such as prospecting for mineral resources or the correlation and interpretation of geologic reservoirs. Despite the extensive use of heavy mineral analysis in sedimentary petrography and quite diverse methods for quantifying heavy mineral assemblages, there has never been a systematic comparison of results obtained by different methods and/or operators. This study provides the first interlaboratory test of heavy mineral analysis. Two synthetic heavy mineral samples were prepared with considerably contrasting compositions intended to resemble natural samples. The contributors were requested to provide (i) metadata describing methods, measurement conditions and experience of the operators and (ii) results tables with mineral species and grain counts. One hundred thirty analyses of the two samples were performed by 67 contributors, encompassing both classical microscopic analyses and data obtained by emerging automated techniques based on electron-beam chemical analysis or Raman spectroscopy. Because relatively low numbers of mineral counts (N) are typical for optical analyses while automated techniques allow for high N, the results vary considerably with respect to the Poisson uncertainty of the counting statistics. Therefore, standard methods used in evaluation of round robin tests are not feasible. In our case the ‘true’ compositions of the test samples are not known. Three methods have been applied to determine possible reference values: (i) the initially measured weight percentages, (ii) calculation of grain percentages using estimates of grain volumes and densities, and (iii) the best-match average calculated from the most reliable analyses following multiple, pragmatic and robust criteria. The range of these three values is taken as best approximation of the ‘true’ composition. The reported grain percentages were evaluated according to (i) their overall scatter relative to the most likely composition, (ii) the number of identified components that were part of the test samples, (iii) the total amount of mistakenly identified mineral grains that were actually not added to the samples, and (iv) the number of major components, which match the reference values with 95% confidence. Results indicate that the overall comparability of the analyses is reasonable. However, there are several issues with respect to methods and/or operators. Optical methods yield the poorest results with respect to the scatter of the data. This, however, is not considered inherent to the method as demonstrated by a significant number of optical analyses fulfilling the criteria for the best-match average. Training of the operators is thus considered paramount for optical analyses. Electron-beam methods yield satisfactory results, but problems in the identification of polymorphs and the discrimination of chain silicates are evident. Labs refining their electron-beam results by optical analysis practically tackle this issue. Raman methods yield the best results as indicated by the highest number of major components correctly quantified with 95% confidence and the fact that all laboratories and operators fulfil the criteria for the best-match average. However, a number of problems must be solved before the full potential of the automated high-throughput techniques in heavy mineral analysis can be achieved.
DS202111-1765
2021
Eakin, C.M.Quasi-Love wave scattering reveals tectonic history of Australia and its margins reflected by mantle anisotropy.Communications Earth & Environment, Vol. 2, 10p. Pdf doi:10.1038/s43247-021-00276-7.Australiageophysics - seismics

Abstract: The Australian continental crust preserves a rich geological history, but it is unclear to what extent this history is expressed deeper within the mantle. Here an investigation of Quasi-Love waves is performed to detect scattering of seismic surface waves at mantle depths (between 100-200?km) by lateral gradients in seismic anisotropy. Across Australasia 275 new observations of Quasi-Love waves are presented. The inferred scattering source and lateral anisotropic gradients are preferentially located either near the passive continental margins, or near the boundaries of major geological provinces within Australia. Pervasive fossilized lithospheric anisotropy within the continental interior is implied, on a scale that mirrors the crustal geology at the surface, and a strong lithosphere that has preserved this signal over billions of years. Along the continental margins, lateral anisotropic gradients may indicate either the edge of the thick continental lithosphere, or small-scale dynamic processes in the asthenosphere below.
DS202104-0573
2021
Eaton-Magana, S., Ardon, T., Breeding, C., Shigley, J.D-Z Diamonds ( Ardon presents the information from the article in Gems & Gemology **** see ref under Ahline same one…….gia.org and knowledge session utube, March GlobalDiamond colour

Abstract: Did you know that certain diamonds can temporarily change color when exposed to heat, ultraviolet light, or even when kept in the dark? Some natural greenish diamonds are known as “chameleon” diamonds due to this property. Other natural pink diamonds and some color-treated and laboratory-grown diamonds can also change color in unexpected ways. Before this phenomenon was known, there were stories of customers returning diamonds they purchased because the diamonds turned out to be the “wrong” color! What exactly causes these interesting diamonds to shift their hues? Find out as GIA senior manager of diamond research Dr. Ulrika D'Haenens-Johansson and senior research scientist Dr. Mike Breeding dive into the mystery of these ultra-cool gems.
DS202103-0377
2020
Eaton-Magana, S., Ardon, T., Breeding, C.M., Shigley, J.E.Natural color D-to-Z diamonds: a crystal clear perspective.Gems & Gemology, Vol. 56, 3, pp. 318-335. pdfGlobaldiamond - colour

Abstract: Colorless to light yellow or brown diamonds with a “D-to-Z” color grade make up the overwhelming majority of the world’s gem diamond trade. Besides clarity features (such as inclusions) and fluorescence observations, however, comparatively little has been explored and published regarding the distinguishing characteristics of these diamonds. The vast majority are type Ia, with infrared spectra showing very high concentrations of nitrogen aggregates. This population of diamonds could not have been subjected to HPHT decolorizing treatment or been laboratory grown, and thus they have been spectroscopically scrutinized in much less detail than the far more rare natural diamonds of types IIa, IIb, and IaB, which need to be investigated as potentially color-treated or synthetic. This study examines a large sample set comprising the full complement of D-to-Z diamonds submitted to GIA laboratories during a significant portion of 2017. The data were evaluated on the basis of diamond type properties, as well as distribution among various grading quality factors, to provide an unprecedented glimpse into the role of these diamond types and differences in their geologic conditions of formation.
DS202108-1280
2021
Eaton-Magana, S., Johnson, P., Barrie, E., Harinova, M.Bicolor rough diamond crystals. ( pink)Gems & Gemology , Vol. 57, 1, pp. 53-55.Australiadiamond colour
DS202102-0183
2020
Eaton-Magana, S., McElhenny, G.Diamond with cavities showing radiation evidence. Gems & Gemology , Vol. 56, 1, pp. 126-127Technologydiamond inclusions

Abstract: The Carlsbad laboratory recently examined a 0.70 ct, E-color round brilliant. Infrared spectroscopy showed this to be a type IIa diamond, so we performed a variety of additional spectroscopy and imaging to verify its natural origin. This diamond also had I1 clarity due to a large inclusion under the table (figure 1). Raman analysis of the inclusions verified that this crystal was a metastable composite of the minerals wollastonite (CaSiO3) and CaSiO3-breyite (E.M. Smith et al., “The very deep origin of the world’s biggest diamonds,” Winter 2017 G&G, pp. 388-403), which indicates a sublithospheric origin. These minerals are believed to be the lower-pressure phases of CaSiO3-perovskite. Around these minerals were large disk-like graphitic fractures indicating inclusion expansion as pressures on the diamond reduced during exhumation from the mantle. The other inclusion present was unidentifiable due to its graphitic casing. Recent research of inclusions in other type II diamonds shows that many, if not most, have a superdeep origin (again, see Smith et al., 2017). This stone is one more example of diamonds forming at incredible depths of 360-750 km before being transported to near the surface.
DS202108-1281
2021
Eaton-Magana, S., Renfro, N., Vavadiya, A.Diamond shaped cloud in diamond.Gems & Gemology , Vol. 57, 1, pp. 65-66.Globaldiamond morphology
DS202103-0378
2021
Eppelbaum, L., Katz, Y.Integrated geological-geophysical study of the junction zone of Eurasia and Gondwana.EGU , 3p. Abstract pdfAfricageophysics

Abstract: Tectonically the considered area of junction of four lithospheric plates (Nubian, Arabian, Aegean- Anatolian and Sinai) belongs to the Eastern Mediterranean, with its Cyprus-Levantine marine and Anatolian-Nubian-Arabian continental framing. The anomalousness of the region is manifested in the tectono-structural features of the mantle, lithosphere, hydrosphere and specifics of atmospheric, biospheric processes, and Hominid evolution.
DS202104-0574
2021
Eppelbaum, L.V., Ben-Avraham, Z., Youri, K., Cloetough, S., Kaban, M.K.Giant quasi-ring mantle structure in the African-Arabian junction: results derived from the geological-geophysical data integration.Geotectonics, 10.1134/S0016 85212010052Africageophysics - seismic

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.
DS202110-1612
2021
Eppelbaum, L.V., Katz, Y.I.Tectono-paleomagnetic mapping as unique combined interpretation tool: implication in geologically complex regions of Israel ( eastern Mediterranean).Proceedings of the VIII International Scientific Conference "Geophysics and Geodynamics" held Lviv, Ukraine., 5p. PdfEurope, Israelgeophysics - magnetics

Abstract: The eastern Mediterranean is a tectonically complex region evolving in the long term located in the midst of the progressive Afro-Eurasian collision. Despite years of investigation, its geological-geophysical structure is not completely known. At the same time, the recent discovery of large gas deposits has attracted the attention of many researchers to this region. For instance, the latest U. S. Geological Survey estimates using conventional assessment methodology suggest that there are on the order of 1.7 billion barrels of recoverable oil and more than 4 trillion m3 of recoverable gas in the Levant Basin [1]. This highlights the need for analysis of the paleogeographical conditions that can yield deep paleotectonic criteria for oil and gas discovery in this region. For this purpose, isopach maps of the Middle-Upper Jurassic and Lower Cretaceous were generated from detailed examinations of numerous well sections and the most sig- nificant outcroppings in the eastern Mediterranean. The maps confirm an earlier model of continental accretion [2]. In particular, abrupt changes in the trend and thickness of the Early Mesozoic formations coincide with the terrane boundaries. These compiled isopach maps also pinpoint significant distinctions between the Arabian and Sinai plates on the one hand and the Syrian arc on the other. A new tectonic map of the eastern Mediterranean is presented that first of all integrates geophysical satellite-derived gravity and airborne magnetic fields, as well as tectonic-structural, paleo-geographical and facial analyses. The results have clear implications for hydrocarbon prospecting in this region.
DS202102-0184
2020
Evans, R.Grading fancy shaped diamonds. Gems & Gemology , Vol. 29, 4, p. 31. pdfGlobalgemmology
DS202110-1613
2021
Faccincani, L., Faccini, B., Casetta, F., Mazzurchelli, M., Nastola, F., Coltorti, M.EoS of mantle minerals coupled with composition and thermal state of the lithosphere: inferring the density structure of peridotitic systems.Lithos, Vol. 401-404, 12p. PdfMantle peridotites

Abstract: Unravelling the physical state and properties of mantle rocks is crucial for understanding both plate tectonics, seismic activity, and volcanism. In this context, the knowledge of accurate elastic parameters of constituent mineral phases, and their variations with pressure (P) and temperature (T), is an essential requirement, that coupled with the thermal state of the lithosphere can provide a better understanding of its petrophysics and thermochemical structure. In this paper, we present an assessment of the thermoelastic parameters [in the form of P-V-T-K Equations of State (EoS)] of orthopyroxene, clinopyroxene, spinel and garnet based on X-Ray diffraction data and direct elastic measurements available in literature. The newly developed EoS are appropriate to describe the elastic behaviour of these phases under the most relevant P-T conditions and bulk compositions of the Earth's mantle. In combination with the published EoS for mantle olivine and magnesiochromite, these EoS are suitable to calculate the physical properties of mantle peridotites and their variation with P and T. Thanks to these EoS, we can evaluate how the variations in bulk composition and thermal regimes affect the density structure of the lithospheric mantle. Accordingly, the density structure of fertile and depleted peridotitic systems was calculated along the 35, 45 and 60 mWm?2 geothermal gradients at P comprised between 1 and 8 GPa. Under very cold geothermal gradients, the density of both fertile and depleted peridotitic systems progressively increases with depth, whereas under relatively hot conditions a first downwards decrease from 1 to ca 3 GPa is observed, followed by an increase downward. In mantle sections characterized by intermediate geotherms (45 mWm?2), the behaviour of the two systems differs up to ca 4 GPa, as the density of the depleted system remains nearly constant down to this depth whereas it moderately increases in the fertile system. The results of our simplified parameterisation, in agreement with classical thermodynamic modelling, indicate that the density structure of the lithospheric mantle is predominantly controlled by the P - T gradient variations, with some compositional control mostly arising at cold-intermediate thermal conditions. Integrated by geophysical and thermodynamic modelling, the newly developed and selected EoS could provide an alternative strategy to infer the elastic properties of mineral phases and peridotite rocks, under the most relevant P-T conditions and compositions of the Earth's mantle, without requiring sets of end-member properties and solution models.
DS202109-1465
2012
Farrell, J.M.The impact of the mineral and petroleum resources development act, ACT 28 of 2002 ( MPRDA) on th sustainability of the alluvial diamond mining sector in the northern Cape Province.Msc thesis, see Cover second page for pdf 213p.Africa, South Africalegal
DS202108-1282
2019
Fedoraeva, A.S., Shatskiy, A., Litasov, K.D.The join CaCO3 -CaSiO3 at 6 Gpa with implication to Ca-rich lithologies trapped by kimberlitic diamonds. ** dateInternational Journal of High Pressure Research, Vol. 39, 4, pp. 547-560.RussiaUHP
DS202102-0185
2020
Fegley, B., Lodders, K., Jacobson, N.S.Volatile element chemistry during accretion of the Earth.Geochemistry, Vol. 80, doi.org/10.1016/ j.chemer. 2019.125594 40p. PdfMantlegeochemistry

Abstract: We review some issues relevant to volatile element chemistry during accretion of the Earth with an emphasis on historical development of ideas during the past century and on issues we think are important. These ideas and issues include the following: (1) whether or not the Earth accreted hot and the geochemical evidence for high temperatures during its formation, (2) some chemical consequences of the Earth’s formation before dissipation of solar nebular gas, (3) the building blocks of the Earth, (4) the composition of the Earth and its lithophile volatility trend, (5) chemistry of silicate vapor and steam atmospheres during Earth’s formation, (6) vapor - melt partitioning and possible loss of volatile elements, (7) insights from hot rocky extrasolar planets. We include tabulated chemical kinetic data for high-temperature elementary reactions in silicate vapor and steam atmospheres. We finish with a summary of the known and unknown issues along with suggestions for future work.
DS202102-0186
2021
Feng, P., Wang, L., Brown, M., Johnson, T.E., Kylander-Clark, A., Piccoli, P.M.Partial melting of ultrahigh pressure eclogite by omphacite-breakdown facilitates exhumation of deeply-subducted crust.Earth and Planetary Science Letters, Vol. 554, doi.org/10.1016/ j.epsl.2020. 116664 13p. PdfMantleeclogite

Abstract: Results from numerical modelling and experimental petrology have led to the hypothesis that partial melting was important in facilitating exhumation of ultrahigh-pressure (UHP) metamorphic rocks from mantle depths. However, the melting reactions responsible are rarely well-documented from natural examples. Here we report microstructural features and compositional data that indicate in situ partial melting dominated by breakdown of omphacite in UHP eclogite from the Sulu belt, China. Diagnostic microstructures include: (i) the presence of in situ leucosome pockets composed of plagioclase, euhedral amphibole, minor K-feldspar and epidote within host zoisite- and phengite-bearing eclogite; (ii) skeletal omphacite within the leucosome pockets that has a lower jadeite content (25-45 mol.%) than rock-forming omphacite (39-54 mol.%); and, (iii) seams of Na-rich plagioclase that extend along grain boundaries separating phengite, quartz and zoisite, and which commonly exhibit low dihedral angles where they terminate at triple grain-boundary junctions. Major oxide proportions of 57 leucosome pockets, calculated using mineral modes and compositions, yield leucodiorite bulk compositions characterized by intermediate SiO2, high Al2O3 and Na2O, and low K2O contents. In primitive mantle-normalised trace element diagrams, the leucosome pockets show enrichment in large ion lithophile elements, U, Pb, Zr, Hf and Ti, but depletion in Th and Ta, patterns that are similar to those of rock-forming omphacite. Rather than forming predominantly by breakdown of phengite and/or zoisite, as widely proposed in the literature, the leucosome pockets have petrographic characteristics and major oxide and trace element compositions that are consistent with partial melting dominated by omphacite breakdown. Based on conventional thermobarometry, the eclogite was exhumed from pressure-temperature (P-T) conditions of 3.6-3.1 GPa and 900-840 °C. Partial melting led to the formation of the leucosome pockets, which equilibrated with the rims of surrounding rock-forming garnet and pyroxene during crystallisation. Conventional thermobarometry using rim compositions yields P-T conditions of 1.6-1.2 GPa and 780-690 °C, broadly consistent with calculated phase equilibria and Ti-in-zircon temperatures from zircon overgrowths. Weighted mean ages of ca 217-214 Ma from thin overgrowths on zircon are interpreted to record melt crystallisation. This study provides insight into an overlooked mechanism by which eclogites partially melt during exhumation from UHP conditions, and permits a better understanding of the processes that assist deeply-subducted continental crust to return to shallower depths.
DS202101-0009
2020
Ferrand, T.P.Conductive channels in the deep oceanic lithosphere could consist of garnet pyroxenites at the fossilized lithosphere-asthenosphere boundary.Minerals MDPI, Vol. 10, 1107, doi.10.3390/ min10121107 28p. PdfMantlegeophysics - magnetotellurics

Abstract: Magnetotelluric (MT) surveys have identified anisotropic conductive anomalies in the mantle of the Cocos and Nazca oceanic plates, respectively, offshore Nicaragua and in the eastern neighborhood of the East Pacific Rise (EPR). Both the origin and nature of these anomalies are controversial as well as their role in plate tectonics. The high electrical conductivity has been hypothesized to originate from partial melting and melt pooling at the lithosphere-asthenosphere boundary (LAB). The anisotropic nature of the anomaly likely highlights high-conductivity channels in the spreading direction, which could be further interpreted as the persistence of a stable liquid silicate throughout the whole oceanic cycle, on which the lithospheric plates would slide by shearing. However, considering minor hydration, some mantle minerals can be as conductive as silicate melts. Here I show that the observed electrical anomaly offshore Nicaragua does not correlate with the LAB but instead with the top of the garnet stability field and that garnet networks suffice to explain the reported conductivity values. I further propose that this anomaly actually corresponds to the fossilized trace of the early-stage LAB that formed near the EPR about 23 million years ago. Melt-bearing channels and/or pyroxenite underplating at the bottom of the young Cocos plate would transform into garnet-rich pyroxenites with decreasing temperature, forming solid-state high-conductivity channels between 40 and 65 km depth (1.25-1.9 GPa, 1000-1100 °C), consistently with experimental petrology.
DS202104-0575
2020
Ferreira, A.C.D., Dantas, E.L., Fuck, R.A.The previously missing c. 2.9 Ga high-K continental crust in West Gondwana revealed in northwest Brazil. Terra Nova, 10.1111/ter.12504 11p. PdfSouth America, Brazil, Borboremaalkaline rocks

Abstract: 2.9 Ga is an uncommon magmatic age in Archean evolution worldwide, especially in West Gondwana. We identified so far unknown 2.97-2.92 Ga high?K calc?alkaline magmatism in the Borborema Province, northeast Brazil. It appears to indicate that the transition to high?K magmas occurred before c. 2.7 Ga in Earth's history. The 2.9 Ga protoliths were reworked and progressively changed composition to 2.65 Ga and 2.25 Ga higher?K granites in early magmatic arcs. Therefore, despite several reworking events from the Archean to Proterozoic times, these rare relicts of K?rich magmatism indicate that reworking of felsic components was significant for the growth and differentiation of continental crust from c. 2.9 Ga onwards in West Gondwana.
DS202102-0187
2021
Fichtner, C.E., Schmidt, M.W., Liebske, C., Bouvier, A-S., Baumgartner, L.P.Carbon partitioning between metal and silicate melts during Earth accretion.Earth and Planetary Science Letters, Vol. 554, doi.org/10.1016/ j.epsl.2020. 116659 12p . PdfMantlecarbon

Abstract: In the accreting Earth and planetesimals, carbon was distributed between a core forming metallic melt, a silicate melt, and a hot, potentially dense atmosphere. Metal melt droplets segregating gravitationally from the magma ocean equilibrated near its base. To understand the distribution of carbon, its partitioning between the two melts is experimentally investigated at 1.5-6.0 GPa, 1300-2000 °C at oxygen fugacities of ?0.9 to ?1.9 log units below the iron-wuestite reference buffer (IW). One set of experiments was performed in San Carlos olivine capsules to investigate the effect of melt depolymerization (NBO/T), a second set in graphite capsules to expand the data set to higher pressures and temperatures. Carbon concentrations were analyzed by secondary ionization mass spectrometry (SIMS) and Raman spectra were collected to identify C-species in the silicate melt. Partition coefficients are governed by the solubility of C in the silicate melt, which varies from 0.01 to 0.6 wt%, while metal melts contain ?7 wt% C in most samples. C solubility in the silicate melt correlates strongly with NBO/T, which, in olivine capsules, is mostly a function of temperature. Carbon partition coefficients DCmetal/silicate at 1.5 GPa, 1300-1750 °C decrease from 640(49) to 14(3) with NBO/T increasing from 1.04 to 3.11. For the NBO/T of the silicate Earth of 2.6, DCmetal/silicate is 34(9). Pressure and oxygen fugacity show no clear effect on carbon partitioning. The present results differ from those of most previous studies in that carbon concentrations in the silicate melt are comparatively higher, rendering C to be about an order of magnitude less siderophile, and the discrepancies may be attributed to differences in the experimental protocols. Applying the new data to a magma ocean scenario, and assuming present day mantle carbon mantle concentrations from 120 to 795 ppm, implies that the core may contain 0.4-2.6 wt% carbon, resulting in 0.14-0.9 wt% of this element for the bulk Earth. These values are upper limits, considering that some of the carbon in the modern silicate Earth has very likely been delivered by the late veneer.
DS202101-0010
2020
Figueiredo, J.Diamond desire: probing the epistemological entanglements of geology and ethnography at Diamang ( Angola).South African Historical Journal, Vol. 72, 3, pp. 431-460.Africa, Angolahistory

Abstract: In the wake of the Anthropocene there is a growing body of literature questioning the colonial and imperialistic underpinnings of geology, mineralogy and mining sciences. When focused on the African continent, these critiques echo and complement previous analyses of the role that anthropology has played as the ‘handmaiden of colonialism’. This article proposes to liken the two debates by focusing on the ethnographic practices promoted by the Angolan diamond mining company Diamang (1917-1988) during the interwar period. It argues that mineral desire, the greed for mineral resources such as diamonds, copper or gold, was the drive behind the introduction of ethnographic collecting and field-working to the Portuguese colony. The implications of this shift in perspective will be explored regarding the ongoing restitution debate. First, the article demonstrates that the history of the objects collected by Diamang disrupts ‘classic’ readings of the history of Portuguese anthropology focused on ‘disciplinary big men’ and their agendas. Second, it shows how the gathering and interpretation of ethnographic and archaeological data were totally integrated into the extractive apparatus of Diamang. The article then concludes by suggesting that the decolonisation of ethnographic collections must consider their entanglements with mining, geology and mineralogy.
DS202107-1097
2021
Finger, N-P., Kaban, M.K., Tesauro, M., Haeger, C., Mooney, W.D., Thomas, M.A thermo-compositional model of the cratonic lithosphere of South America. Geochemistry, Geophysics, Geosytems, 26p. PdfSouth Americageothermometry

Abstract: The lithosphere and upper mantle of South America is investigated using multiple data sets, including the topography, crustal structure, regional seismic tomography, gravity, and mineral physics. These data are jointly inverted to estimate variations in temperature, density and composition in the lithospheric and sub-lithospheric upper mantle to a depth of 325 km. Our results show significant variations in lithospheric properties, including thick, depleted roots beneath large parts of the Amazon, São Francisco, and Paranapanema Cratons. However, portions of some cratons, such as the western Guyana Shield, lack a depleted root. We hypothesize that these regions either never developed a depleted root, or that the root was rejuvenated by lithospheric processes.
DS202102-0188
2020
Fiorentini, M.L., O'Neill, C., Giuliani, A., Choi, E., Maas, R., Pirajno, F., Foley, S.Bushveld superplume drove Proterozoic magmatism and metallogenesis in Australia. Nature Scientific Reports, doi.org/10.1038/ s41598-020-76800-0 10p. PdfAustralia, Africa, South Africaalkaline magmatism

Abstract: Large-scale mantle convective processes are commonly reflected in the emplacement of Large Igneous Provinces (LIPs). These are high-volume, short-duration magmatic events consisting mainly of extensive flood basalts and their associated plumbing systems. One of the most voluminous LIPs in the geological record is the ~?2.06 billion-year-old Bushveld Igneous Complex of South Africa (BIC), one of the most mineralised magmatic complexes on Earth. Surprisingly, the known geographic envelope of magmatism related to the BIC is limited to a series of satellite intrusions in southern Africa and has not been traced further afield. This appears inconsistent with the inferred large size of the BIC event. Here, we present new radiometric ages for alkaline magmatism in the Archean Yilgarn Craton (Western Australia), which overlap the emplacement age of the BIC and indicate a much more extensive geographic footprint of the BIC magmatic event. To assess plume involvement at this distance, we present numerical simulations of mantle plume impingement at the base of the lithosphere, and constrain a relationship between the radial extent of volcanism versus time, excess temperature and plume size. These simulations suggest that the thermal influence of large plume events could extend for thousands of km within a few million years, and produce widespread alkaline magmatism, crustal extension potentially leading to continental break-up, and large ore deposits in distal sectors. Our results imply that superplumes may produce very extensive and diverse magmatic and metallogenic provinces, which may now be preserved in widely-dispersed continental blocks.
DS202101-0011
2020
Fischer, K.M., Rychert, C.A., Dalton, C.A., Miller, M.S., Begheim, C., Schutt, D.L.A comparison of oceanic and continental mantle lithsophere.Physics of the Earth and Planetary Interiors, Vol. 309, 106600, 20p. PdfMantlemelting

Abstract: Over the last decade, seismological studies have shed new light on the properties of the mantle lithosphere and their physical and chemical origins. This paper synthesizes recent work to draw comparisons between oceanic and continental lithosphere, with a particular focus on isotropic velocity structure and its implications for mantle temperature and partial melt. In the oceans, many observations of scattered and reflected body waves indicate velocity contrasts whose depths follow an age-dependent trend. New modeling of fundamental mode Rayleigh waves from the Pacific ocean indicates that cooling plate models with asymptotic plate thicknesses of 85-95 km provide the best overall fits to phase velocities at periods of 25 s to 250 s. These thermal models are broadly consistent with the depths of scattered and reflected body wave observations, and with oceanic heat flow data. However, the lithosphere-asthenosphere velocity gradients for 85-95 km asymptotic plate thicknesses are too gradual to generate observable Sp phases, both at ages less than 30 Ma and at ages of 80 Ma or more. To jointly explain Rayleigh wave, scattered and reflected body waves and heat flow data, we propose that oceanic lithosphere can be characterized as a thermal boundary layer with an asymptotic thickness of 85-95 km, but that this layer contains other features, such as zones of partial melt from hydrated or carbonated asthenosphere, that enhance the lithosphere-asthenosphere velocity gradient. Beneath young continental lithosphere, surface wave constraints on lithospheric thickness are also compatible with the depths of lithosphere-asthenosphere velocity gradients implied by converted and scattered body waves. However, typical steady-state conductive models consistent with continental heat flow produce thermal and velocity gradients that are too gradual in depth to produce observed converted and scattered body waves. Unless lithospheric isotherms are concentrated in depth by mantle upwelling or convective removal, the presence of an additional factor, such as partial melt at the base of the thermal lithosphere, is needed to sharpen lithosphere-asthenosphere velocity gradients in many young continental regions. Beneath cratons, numerous body wave conversions and reflections are observed within the thick mantle lithosphere, but the velocity layering they imply appears to be laterally discontinuous. The nature of cratonic lithosphere-asthenosphere velocity gradients remains uncertain, with some studies indicating gradual transitions that are consistent with steady-state thermal models, and other studies inferring more vertically localized velocity gradients.
DS202102-0189
2021
Fischer, K.M., Rychert, C.A., Dalton, C.A., Miller, M.S., Beghein, C., Schutt, D.L.A comparison of oceanic and continental mantle lithosphere.Physics of the Earth and Planetary Interiors, Vol. 309, di.org/10.1016/ jpepi.2020.106600 20p. PdfMantlegeophysics - seismics

Abstract: Over the last decade, seismological studies have shed new light on the properties of the mantle lithosphere and their physical and chemical origins. This paper synthesizes recent work to draw comparisons between oceanic and continental lithosphere, with a particular focus on isotropic velocity structure and its implications for mantle temperature and partial melt. In the oceans, many observations of scattered and reflected body waves indicate velocity contrasts whose depths follow an age-dependent trend. New modeling of fundamental mode Rayleigh waves from the Pacific ocean indicates that cooling plate models with asymptotic plate thicknesses of 85-95 km provide the best overall fits to phase velocities at periods of 25 s to 250 s. These thermal models are broadly consistent with the depths of scattered and reflected body wave observations, and with oceanic heat flow data. However, the lithosphere-asthenosphere velocity gradients for 85-95 km asymptotic plate thicknesses are too gradual to generate observable Sp phases, both at ages less than 30 Ma and at ages of 80 Ma or more. To jointly explain Rayleigh wave, scattered and reflected body waves and heat flow data, we propose that oceanic lithosphere can be characterized as a thermal boundary layer with an asymptotic thickness of 85-95 km, but that this layer contains other features, such as zones of partial melt from hydrated or carbonated asthenosphere, that enhance the lithosphere-asthenosphere velocity gradient. Beneath young continental lithosphere, surface wave constraints on lithospheric thickness are also compatible with the depths of lithosphere-asthenosphere velocity gradients implied by converted and scattered body waves. However, typical steady-state conductive models consistent with continental heat flow produce thermal and velocity gradients that are too gradual in depth to produce observed converted and scattered body waves. Unless lithospheric isotherms are concentrated in depth by mantle upwelling or convective removal, the presence of an additional factor, such as partial melt at the base of the thermal lithosphere, is needed to sharpen lithosphere-asthenosphere velocity gradients in many young continental regions. Beneath cratons, numerous body wave conversions and reflections are observed within the thick mantle lithosphere, but the velocity layering they imply appears to be laterally discontinuous. The nature of cratonic lithosphere-asthenosphere velocity gradients remains uncertain, with some studies indicating gradual transitions that are consistent with steady-state thermal models, and other studies inferring more vertically localized velocity gradients.
DS202104-0576
2021
Foerster, M.W., Selway, K.Melting of subducted sediments reconciles geophysical images of subduction zones.Nature Communications, Vol. 12, 1, doi:10.10.1038/ s41467-021-21657-8 8p. PdfMantlegeophysics - seismic

Abstract: ediments play a key role in subduction. They help control the chemistry of arc volcanoes and the location of seismic hazards. Here, we present a new model describing the fate of subducted sediments that explains magnetotelluric models of subduction zones, which commonly show an enigmatic conductive anomaly at the trenchward side of volcanic arcs. In many subduction zones, sediments will melt trenchward of the source region for arc melts. High-pressure experiments show that these sediment melts will react with the overlying mantle wedge to produce electrically conductive phlogopite pyroxenites. Modelling of the Cascadia and Kyushu subduction zones shows that the products of sediment melting closely reproduce the magnetotelluric observations. Melting of subducted sediments can also explain K-rich volcanic rocks that are produced when the phlogopite pyroxenites melt during slab roll-back events. This process may also help constrain models for subduction zone seismicity. Since melts and phlogopite both have low frictional strength, damaging thrust earthquakes are unlikely to occur in the vicinity of the melting sediments, while increased fluid pressures may promote the occurrence of small magnitude earthquakes and episodic tremor and slip.
DS202108-1283
2021
Fomina, E.N., Kozlov, E.N.Stable ( C, O) radiogenic ( Sr, Nd) isotopic evidence for REE- carbonatite formation processes in Petyayan-Vara ( Vuoriyarvi Massif, NW Russia).Lithos, Vol. 398-399, 17p. PdfRussiaREE

Abstract: A study of radiogenic (Sr, Nd) and stable (C, O) isotopic data for rare earth carbonatites from the Petyayan-Vara field of the Devonian Vuoriyarvi alkaline-ultrabasic massif is presented. The cumulative evidence indicates that the primary igneous rocks of the Petyayan-Vara area are burbankite-bearing magnesiocarbonatites having isotopic signatures of the depleted mantle (?Nd365Ma = 5.0, 87Sr/86Sr(i) = 0.7031, ?13C ca. -4‰, and ?18O ca. 11‰). Interaction of the primary carbonatite melt with the host silicate rocks produced high-Ti carbonatites with a mantle ?13C (ca. -4‰) and isotopically heavy ?18O (ca. 20‰). These rocks trapped K, Na, Mg, CO2, and rare earth elements (REEs) (mainly heavy REEs) from the melt and Si, Al, Fe, Ti, and P from the host rocks. Early post-magmatic exposure of burbankite-bearing carbonatites to a mixture of fluids of crustal and orthomagmatic carbonatite origin caused redistribution of REEs, Ba, and Sr and formation of REE-rich carbonatites with abundant ancylite mineralization. This effect did not disturb the Smsingle bondNd system but induced radiogenic Sr accumulation and a change in C and O isotopic composition towards heavier values. Later, but most likely before denudation, the Petyayan-Vara rocks underwent another metasomatic event involving crustal fluids infiltrating through fracture systems. This event triggered formation of bastnäsite-rich carbonatites with fewer REEs at the expense of ancylite-rich carbonatites, and changed all the isotopic systems in the affected rocks. This model successfully accounts for the evolution of all the carbonatite varieties discovered to date in the Petyayan-Vara field.
DS202110-1614
2021
Forster, M.W., Bussweiler, Y., Prelevic, D., Daczko, N.R., Buhre, S., Mertz-Kraus, R., Foley, S.F.Sediment-peridotite reaction controls fore-arc metasomatism and arc magma geochemical signatures.Geosciences MDPI, Vol. 11, 372, 24p. PdfMantlesubduction

Abstract: Subduction of oceanic crust buries an average thickness of 300-500 m of sediment that eventually dehydrates or partially melts. Progressive release of fluid/melt metasomatizes the fore-arc mantle, forming serpentinite at low temperatures and phlogopite-bearing pyroxenite where slab surface reaches 700-900 °C. This is sufficiently high to partially melt subducted sediments before they approach the depths where arc magmas are formed. Here, we present experiments on reactions between melts of subducted sediments and peridotite at 2-6 GPa/750-1100 °C, which correspond to the surface of a subducting slab. The reaction of volatile-bearing partial melts derived from sediments with depleted peridotite leads to separation of elements and a layered arrangement of metasomatic phases, with layers consisting of orthopyroxene, mica-pyroxenite, and clinopyroxenite. The selective incorporation of elements in these metasomatic layers closely resembles chemical patterns found in K-rich magmas. Trace elements were imaged using LA-ICP-TOFMS, which is applied here to investigate the distribution of trace elements within the metasomatic layers. Experiments of different duration enabled estimates of the growth of the metasomatic front, which ranges from 1-5 m/ky. These experiments explain the low contents of high-field strength elements in arc magmas as being due to their loss during melting of sedimentary materials in the fore-arc.
DS202105-0763
2021
Fosu, B.R., Ghosh, P., Weisenberger, T.B., Spurgin, S., Viladar, S.G.A triple oxygen isotope perspective on the origin, evolution, and diagenetic alteration of carbonatites.Geochimica et Cosmochimica Acta, Vol. 299, pp. 52-68. pdfMantlecarbonatites

Abstract: Carbonatites are unique magmatic rocks that are essentially composed of carbonates, and they usually host a diverse suite of minor and accessory minerals. To provide additional insights on their petrogenesis, triple oxygen isotope analyses were carried out on carbonatites from sixteen localities worldwide in order to assess the behaviour of oxygen isotopes (mass-dependent fractionation) during their formation. The study evaluates the mineralogical differences, i.e., calcite, dolomite, ankerite, and Na-carbonates, and the mode of emplacement (intrusive or extrusive) in the mantle-derived carbonatites to further constrain the triple oxygen isotopic composition (??17O) of the upper mantle. ??17O values in the intrusive calcite carbonatites vary between ?0.003 to ?0.088‰ (n?=?20) and ?0.024 to ?0.085‰ (n?=?5) in the dolomite varieties. We surmise that the magnitude of isotopic fractionation in the different carbonate phases during their formation is similar and thus, the observed variations are independent of mineralogy and may be related to alteration in the rocks. Taking the samples that classify as primary igneous carbonatites altogether, the average ??17O value of the mantle is estimated as ?0.047?±?0.027‰ (1SD, n?=?18) which overlaps those of other mantle rocks, minerals and xenoliths, indicating that the mantle has a relatively homogenous oxygen isotope composition. Two ankerite carbonatites have identical ??17O values as calcite but a few samples, together with pyroclastic tuffs have significantly lower ??17O values (?0.108 to ?0.161‰). This deviation from mantle ??17O signature suggests diagenetic alteration (dissolution and recrystallisation) and mixing of carbonate sources (juvenile and secondary carbonates) which is consistent with the high ?18O and clumped isotope (?47) values recorded in the pyroclastic and ankeritic rocks. In summary, diagenetic alteration driven by fluid-rock interaction at low temperatures, sub-solidus re-equilibration with magmatic waters, and the incorporation of secondary carbonates altogether facilitate the alteration of original isotopic compositions of carbonatites, obliterating their primary mantle signatures.
DS202109-1466
2021
Frank, M.G.Flight of the diamond smugglers: a tale of pigeons, obsession, and greed along the coastal South Africa.Icon books available through Jonathan Ball Publishers, Amazon approx 15.00 224p. Africa, South Africabook
DS202104-0577
2021
Fritsch, E.Revealing the formation secrets of the Matryosha diamond.Journal of Gemmology, Vol. 37, 5, pp. 528-533.Russiadiamond genesis
DS202105-0764
2021
Fuston, S., Wu, J.Raising the Resurrection plate from an unfolded-slab plate tectonic reconstruction of northwestern North America since early Cenozoic time.Geological Society of America Bulletin, Vol. 133, pp. 1128-1140.United Statestectonics

Abstract: The configuration of mid-ocean ridges subducted below North America prior to Oligocene time is unconstrained by seafloor isochrons and has been primarily inferred from upper-plate geology, including near-trench magmatism. However, many tectonic models are permitted from these constraints. We present a fully kinematic, plate tectonic reconstruction of the NW Cordillera since 60 Ma built by structurally unfolding subducted slabs, imaged by mantle tomography, back to Earth’s surface. We map in three-dimensions the attached Alaska and Cascadia slabs, and a detached slab below western Yukon (Canada) at 400-600 km depth that we call the “Yukon Slab.” Our restoration of these lower plates within a global plate model indicates the Alaska slab accounts for Pacific-Kula subduction since ca. 60 Ma below the Aleutian Islands whereas the Cascadia slab accounts for Farallon subduction since at least ca. 75 Ma below southern California, USA. However, intermediate areas show two reconstruction gaps that persist until 40 Ma. We show that these reconstruction gaps correlate spatiotemporally to published NW Cordillera near-trench magmatism, even considering possible terrane translation. We attribute these gaps to thermal erosion related to ridge subduction and model mid-ocean ridges within these reconstruction gap mid-points. Our reconstructions show two coeval ridge-trench intersections that bound an additional “Resurrection”-like plate along the NW Cordillera prior to 40 Ma. In this model, the Yukon slab represents a thermally eroded remnant of the Resurrection plate. Our reconstructions support a “northern option” Farallon ridge geometry and allow up to ?1200 km Chugach terrane translation since Paleocene time, providing a new “tomographic piercing point” for the Baja-British Columbia debate.
DS202102-0190
2019
Gaillard, F., Sator, N., Guillot, B., Massuyeau, M.The link between the physical and chemical properties of carbon-bearing melts and their application for geophysical imaging of Earth's mantleResearchgate , DOI: 10.1017/ 9781108677950.007 26p. Pdfmantlecarbon

Abstract: Significant investment in new capacities for experimental research at high temperatures and pressures have provided new levels of understanding about the physical properties of carbon in fluids and melts, including its viscosity, electrical conductivity, and density. This chapter reviews the physical properties of carbon-bearing melts and fluids at high temperatures and pressures and highlights remaining unknowns left to be explored. The chapter also reviews how the remote sensing of the inaccessible parts of the Earth via various geophysical techniques - seismic shear wave velocity, attenuation, and electromagnetic signals of mantle depths - can be reconciled with the potential presence of carbon-bearing melts or fluids.
DS202102-0191
2021
Galimov, E.M., Kaminsky, F.V.Diamond in oceanic lithosphere. Volcanic diamonds and diamonds in ophiolites.Geochemistry International, Vol. 59, 1, pp. 1-11. pdfRussiadeposit - Tolbachik, Kamchatka
DS202103-0379
2021
Ganbat, A., Tsujimori, T., Boniface, N., Pastor-Galan, D., Aoki, S., Aoki, K.Crustal evolution of Paleoproterozoic Ubendian Belt ( SW Tanzania) western margin: a central African shield amalgamation take.Gondwana Research, Vol. 91, pp. 286-306. pdfAfrica, Tanzaniamagmatism

Abstract: The Ubendian Belt between the Archean Tanzania Craton and the Bangweulu Block, represents a Paleoproterozoic orogeny of these two constituents of the Congo Craton assembled at ~1.8?Ga, forming the Central African Shield, during the Columbia Supercontinent cycle and consolidated during the Gondwana assembly. Metagranitoids from the Southern and Northern Ufipa Terranes (Western Ubendian Corridor) and those of the Bangweulu Block are compositionally similar and are contemporaneous. The protolith of the Ufipa Terrane is originated from the collided crustal rocks of the Bangweulu Block. New LA-ICPMS zircon U-Pb age of metagranitoids and granoporphyries confirmed magmatic events from 1.89 to 1.85?Ga. The metagranitoids of the Western Ubendian Corridor and that of the Bangweulu Block cannot be distinguished by their trace element characteristics and ages. Geochemically, they belong to high-K calc-alkaline to tholeiite series. The 1.89-1.85?Ga metagranitoids and granoporphyries are characterized by evolved nature, which are common for slab-failure derived magmas. Such geochemical features and the presence of ~2.0?Ga eclogites suggest an Orosirian oceanic subduction and subsequent slab break-off. Melt derived from the mafic upper portion of torn slab led to the partial melting of crust which formed high-K and calc-alkaline, I- and S-type magmatism in the Bangweulu Block and the Ufipa Terrane. Zircons from two metagranites from the Northern Ufipa Terrane show Neoproterozoic (Ediacaran) overprints at ~570?Ma, suggesting the Bangweulu Block collided with the continental margin of the Tanzania Craton. However, we found non-annealed Orosirian apatites in metagranitoids from the Southern Ufipa Terrane and the Kate-Ufipa Complex, implying that areal heterogeneity of the Pan-African tectonothermal overprint in the Ufipa Terrane. All evidences suggest that the Bangweulu Block and the Ubendian Belt participated in the amalgamation of the Central African Shield as separated continents surrounded by oceanic crusts during the Paleoproterozoic Eburnean and the Neoproterozoic Pan-African orogenies.
DS202107-1098
2021
Gao, L-G., Chen, Y-W., Bi, X-W., Gao, J.F., Chen, W.T., Dong, S-H., Luo, J-C., Hu, R-Z.Genesis of carbonatite and associated U-Nb-REE mineralization at Huayang-chuan, central China: insights from mineral paragenesis, chemical and Sr-Nd-C-O isotopic compositions of calcite.Ore Geology Reviews, doi.org/10.1016/j.oregeorev.2021.104310, 50p. PdfChinacarbonatite, REE

Abstract: The Huayangchuan deposit in the North Qinling alkaline province of Central China is a unique carbonatite-hosted giant U-Nb-REE polymetallic deposit. The mineralization is characterized by the presence of betafite, monazite, and allanite as the main ore minerals, but also exhibit relatively high budgets of heavy rare earth elements (HREE = Gd-Lu and Y). The origin of carbonatites has long been controversial, thus hindering our understanding of the genesis of the deposit. Here, we conducted an in-situ trace elemental, Sr-Nd isotopic, and bulk C-O isotopic analyses of multi-type calcites in the deposit. Two principal types (Cal-I and Cal-II), including three sub-types (Cal-I-1, Cal-I-2 and Cal-I-3) of calcites were identified based on crosscutting relationships and calcite textures. Texturally, Cal-I calcites in carbonatites display cumulates with the grain size decreasing from early coarse- (Cal-I-1) to medium- (Cal-I-2) and late fine-grained (Cal-I-3), whereas Cal-II calcites coexist with zeolite displaying zeolite-calcite veinlets. Geochemically, Cal-I calcites contain relatively high REE(Y) (151-2296 ppm), Sr (4947-9566 ppm) and Na (28.6-390 ppm) contents, characterized by right- to left-inclined flat distribution patterns [(La/Yb)N=0.2-4.2] with enrichment of HREE(Y) (136-774 ppm), whereas Cal-II calcites display low REE, Sr and undetectable Na contents, characterized by a right-inclined distribution pattern [(La/Yb)N=13.5, n=16]. The U-Nb-REE mineralization, accompanied with intense and extensive fenitization and biotitization, is mainly associated with the Cal-I-3 calcites which show flat to relatively left-inclined flat REE distribution patterns [(La/Yb)N=0.2-1.0]. Isotopic results show that Cal-I calcites with mantle signatures are primarily igneous in origin, whereas Cal-II are hydrothermal, postdating the U-Nb-REE mineralization. Cal-I calcites (Cal-I-1, Cal-I-2 and Cal-I-3) from mineralized and unmineralized carbonatites, displayed regular changes in REE, Na and Sr contents, but similar trace element distribution patterns and Sr-Nd-C-O isotopic signatures, indicating that these carbonatites originated from the same enriched mantle (EM1) source by low-degree partial melting of HREE-rich carbonated eclogites related to recycled marine sediments. The combination of trace elements and Sr-Nd isotopic composition of calcites further revealed that these carbonatites have undergone highly differentiated evolution. Such differentiation is conducive to the enrichment of ore-forming elements (U-Nb-REE) in the late magmatic-hydrothermal stages owing to extensive ore-forming fluids exsolved from carbonatitic melts. The massive precipitation of the U-Nb-REE minerals from ore-forming hydrothermal fluids may have been triggered by intense fluid-rock reactions indicated by extensive and intense fenitization and biotitization. Therefore, the Huayangchuan carbonatite-related U-Nb-REE deposit may have formed by a combination of processes involving recycled U-Nb-REE-rich marine sediments in the source, differentiation of the produced carbonatitic magmas, and subsequent exsolution of U-Nb-REE-rich fluids that precipitated ore minerals through reactions with wall rocks under the transitional tectonic regime from compression to extension at the end of Late Triassic.
DS202111-1766
2021
Garanin, V., Garanin, K., Kriulina, G., Samosorov, G.Diamonds from the Arkangelsk Province, NW Russia. ENGLISHSpringer Mineralogy http://www.springer.com/series/13488, Reference to the book only! Russia, Arkangelskdiamond - morphology

Abstract: Provides researchers the latest data on the Arkhangelsk and Yakutian Diamondiferous Provinces in Russia. Enriches readers’ understanding of diamond geology and its evolution. Illustrates the complete process of diamond formation in the Archangelsk Diamondiferous Provinces.
DS202108-1284
2021
Garanin, V., Garanin, K., Kriulina, G., Samosorov, G.Geological summary of kimberlites and related rocks in the Archangelsk diamondiferous region ( ADR).Book: Diamonds from the Arkangelk Province, NW Russia., July doi.10.1007/978-3-030-35717-7_1 30p.Russia, Archangelkimberlites

Abstract: The chapter headlines the historical perspective of discovering the Arkhangelsk Diamondiferous Region, previously was also called the Arkhangelsk Diamondiferous Province (hereinafter named ADR), offers the contemporary concept of the ADR geology, and location of kimberlite fields and magmatic rock bodies in its area. It describes the layout, structure, mineralogical characteristics and lithology of pipes from the Grib and Lomonosov deposits. It gives a snapshot of the alkaline ultrabasic rocks’ representatives from the Zimny Bereg area of the ADR that is not covered by the deposits.
DS202112-1927
2021
Gardes, E., Gilbouin, D., Radiquet, B., David, A., Prellier, W., Marquardt, K.Magnesium transport in olivine mantle: new insights from miniturized study of volume and grain boundary diffusion in Mg2Si04 bi-crystals.Contribution to Mineralogy and Petrology, Vol. 176, 99 16p. PdfMantleolivine

Abstract: We report experimental measurements of volume and grain boundary diffusion of 26Mg in Mg2SiO4 bi-crystals at asthenosphere temperatures as a ground reference for olivine. By analysis of literature and combination with previous data, we provide Arrhenius laws D = D0 exp(- E/RT) at ambient pressure for volume diffusion of Mg in Mg2SiO4 in the intrinsic regime along the three crystallographic axes as well as grain boundary diffusion.
DS202106-0936
2021
Garel, F., Thoraval, C.Lithosphere as a constant-velocity plate: chasing a dynamical LAB in a homogenous mantle material.Physics of the Earth and Planetary Interiors, Vol. 316, 106710 13p. PdfMantlegeophysics - seismic

Abstract: While the lateral limits of tectonic plates are well mapped by seismicity, the bottom boundary of the lithosphere, the uppermost rigid layer of the Earth comprising both crust and shallow mantle, remains elusive. The lithosphere is usually viewed as consisting of cold, rigid, internally undeformed blocks that translate coherently. The base of the lithosphere, designated as the lithosphere-asthenosphere boundary (LAB), may thus be characterised by different physical fields: temperature, viscosity, strain rate and velocity. The LABs as defined by these different fields are investigated here using thermo-mechanical models of plate and upper mantle dynamics, either in a transient subduction or in a steady-state plate-driven set-up. Mantle material is modelled as homogeneous in composition with a viscosity that depends on temperature, pressure and strain rate. In such a system, the thermo-mechanical transition between lithosphere and asthenosphere occurs over a finite depth interval in temperature, strain rate and velocity. We propose that the most useful dynamical LAB is defined as the base of a “constant-velocity” plate (i.e. the material translating at constant horizontal velocity). The bottom part of this plate deforms at strain rates comparable to those in the underlying asthenosphere mantle: the translating block is not fully rigid. Thermal structure exerts a major control on this dynamical LAB, which deepens with increasing plate age. However, the surface plate velocity, the asthenospheric flow geometry and magnitude also influence the depth of the dynamical LAB, as well as the thickness of the deformed region at the base of the constant-velocity plate. The mechanical transitions from lithosphere to asthenosphere adjust when mantle dynamics evolves. The dynamical and thermo-mechanical LABs occur within a thermal lithosphere-asthenophere gradual transition, similar to the one imaged by geophysical proxies. The concept of a constant-velocity plate can be extended to a constant-velocity subducting slab, which also deforms at its borders and drags the surrounding mantle. This framework is relevant to quantify mass transport within the Earth's mantle.
DS202110-1615
2021
Gatta, G.D., Hradil, K., Meven, M.Where is the hydrogen? ( neutron diffraction technology) Elements, Vol. 17, pp. 163-168.Mantlehydrogen

Abstract: How is hydrogen distributed among minerals and how is it bonded in their crystal structures? These are important questions, because the amount of hydrogen and the bonding configuration of hydrogen in crystalline materials governs many of that material’s properties: its thermal and compressional behavior, P-T phase stability, rheology, and electrical conductivity. A reliable reconstruction of the Earth’s interior, or the prediction of mineral transformations in complex industrial processes, must account for these parameters. Neutron diffraction can locate hydrogen sites in mineral structures, reveal any static or dynamic hydrogen disorder, help define the libration regime of hydrogen, and elucidate hydrogen-bonding configurations. Thus, that most elusive element for X-ray probes is perfectly detectable using neutrons.
DS202109-1467
2021
Gems & JeweleryPerseverance on the banks of the Itoco River.Gems & Jewelery, Vol. 30, 2, p. 8.South America, Colombiaemerald
DS202109-1468
2021
Gems & JeweleryWhat will happen to fancy pink diamonds? Argyle closure.Gems & Jewelery, Vol. 30, 2, pp. 14-15.Australia, globaldeposit - Argyle
DS202102-0192
2021
Geng, Y., Du, L., Kuang, H., Liu, Y.Ca. 1.7 Ga magmatism on southwestern margin of the Yangtze block: response to the breakup of Columbia.Acta Geologica Sinica, Vol. 94, 6, pp. 2031-2052.Chinamagmatism

Abstract: This paper presents some data of the Jiaopingdu gabbro and Caiyuanzi granite at the southwestern margin of the Yangtze Block, on the geochemical compositions, zircon LA-ICP-MS U-Pb ages and Hf isotopic data. The Jiaopingdu gabbro gives the age of 1721 ± 5 Ma, the Caiyuanzi granite 1732 ± 6 Ma and 1735 ± 4 Ma, and the Wenjiacun porphyry granite 1713 ± 4 Ma, suggesting nearly contemporaneous formation time of the gabbro and granite. The bimodal feature is demonstrated by the gabbro SiO2 content of 44.64-46.87 wt% and granite 73.81-77.03 wt%. In addition, the granite has high content of SiO2 and Na2O + K2O, low content of Al2O3 and CaO, enriched in REEs (except Eu) and Zr, Nb, Ga and Y, depleted in Sr, implying it belongs to A?type granite geochemistry and origin of within?plate environment. The zircon ?Hf(t) of the granite and gabbro is at the range of 2-6, which is near the 2.0 Ga evolution line of the crust, implying the parent magma of the gabbro being derived from the depleted mantle and a small amount of crustal material, and the parent magma of the granite from partial melting of the juvenile crust and some ancient crustal material at the same time. Compared with 1.8-1.7 Ga magmatism during breakup of other cratons in the world, we can deduce that the Columbia has initially broken since ca. 1.8 Ga, and some continental marginal or intra?continental rifts occurred at ca. 1.73 Ga.
DS202103-0380
2021
Geophysics ContractorsCompiled List of geophysical contractors sent out to members of SEGMIN. *** not specific to diamonds Geophysical contractors, SEGMIN website 13p. PdfGlobalgeophysics
DS202107-1099
2021
Giovannini, A.L., Bastos Neto, A.C., Porto, C.G., Takehara, L., Pereira, V.P., Bidone, M.H.REE mineralization (primary, supergene and sedimentary) associated to the Morro dos Seis Lagos Nb( REE, Ti) deposit (Amazonas, Brazil).Ore Geology Reviews, doi.org/10.1016/ j.oregeorev. 2021.104308 59p. PdfSouth America, BrazilREE

Abstract: In the Morro dos Seis Lagos Nb (Ti, REE) deposit (MSLD), Amazonas state, Brazil, there are four types of REE mineralization: primary, associated to siderite carbonatite; supergene, associated to laterite profile; and sedimentary (detrital and authigenic). The mineralogical and geochemical evolutions of the REE in these domains are integrated into a comprehensible metallogenic model. The main primary ore in the core siderite carbonatite is 52 m thick with 1.47 wt% REE2O3 mainly in monazite-(Ce) and bastnäsite. However, considering the entire section intersected in the core siderite carbonatite, the average grade drops to 0.7 wt% REE2O3 mainly contained in thorbastnasite. In the border siderite carbonatite, the REE mineralization is hydrothermal [rhabdophane-(Ce) and REE-rich gorceixite]. The LREE and phosphates are concentrated at the reworked laterites from where the HREE were leached. With the advance of lateritization, pyrochlore was completely decomposed. The final secondary Ce-pyrochlore was progressively enriched in Ce4+ with loss in REE3+, resulting in the breakdown of the structure and release Ce under strongly oxidizing conditions (high Ce4+/Ce3+) thus forming extremely pure cerianite-(Ce). This mineral occurs intercalated with goethite bands in the lower part of the weathering profile, represented by the brown laterite, and forms intergrowth with hollandite in the manganiferous laterite, formed in a more alkaline environment closer to the water table. The brown laterite has 1.30 wt% REE2O3, the manganese laterite has 1.54 wt% REE2O3, of which 1.42 wt% is Ce2O3. Tectonic and karstic processes over the carbonatite formed several sedimentary basins. In the Esperança Basin, the sedimentary record (233 m thick) shows the whole evolution of the MSLD. The base of the basin (layer 5) is formed by abundant carbonatite fragments, have florencite-(Ce) mineralization with 1.07 wt% REE2O3; layer 4 is formed by carbonatite fragments interbedded with clayey bed; layer 3 is a rhythmite deposited in a lacustrine environment, with clasts of ferruginous materials related to early stages of carbonatite alteration; layer 2 is made up by clays, is rich in organic matter, has authigenic florencite-(Ce), florencite-(La) and base metals. This layer marks the inversion of the relief and the input into the basin of REE leached from the upper laterites, carried by the groundwater flow; layer 1 was formed by the oxidation of the upper part of layer 2. Layers 1 + 2 have 73 m thick and average of 1.72 wt% REE2O3.
DS202103-0381
2021
Giro, J.P., Almeida, J., Guedes, E., Bruno, H.Tectonic inheritances in rifts: the meaning of NNE lineaments in the continental rift of SE Brazil.Journal of South American Earth Sciences, Vol. 108, 103255. 17p. PdfSouth America, Brazillineaments, tectonics

Abstract: The effect of previous structures inheritance is known to be important in the development of tectonic rifts. A series of overlapping structures generally can be represented by lineaments marking the successive tectonic events. We studied the NNE structural lineaments corridor in the central region of the Ribeira Belt. We used a digital elevation model (DEM) and new and previous fieldwork data to investigate the structural control of such lineaments and their relevance for the Brazilian continental margin. Our results suggest that the NNE direction is a crustal weakness zone characterising corridors of intense ductile and brittle deformation which was recurrently reactivated. Aligned NNE Neoproterozoic-Ordovician ductile and brittle structures as foliations, shear zones, lithological boundaries, and fractures filled by pegmatitic veins coincide with the lineaments. During the Cretaceous rift, a transtensional sinistral regime generated NNE T-fractures filled by mafic dykes. In the Cenozoic, the NNE direction is represented by transfer and domino faults developed within a mega accommodation zone in an intracontinental rift system. Our results suggest that the NNE direction was active in this region throughout the Phanerozoic and has high relevance for the structural development of the continental margin of southeastern Brazil.
DS202102-0193
2020
Giuliani, A., Jackson, M.G., Fitzpayne, A., Dalton, H.Remnants of early Earth differentiation in the deepest mantle-derived lavas. ( kimberlite source)PNAS, Vol. 118, 1 e201521118, 9p. PdfMantlekimberlite

Abstract: The noble gas isotope systematics of ocean island basalts suggest the existence of primordial mantle signatures in the deep mantle. Yet, the isotopic compositions of lithophile elements (Sr, Nd, Hf) in these lavas require derivation from a mantle source that is geochemically depleted by melt extraction rather than primitive. Here, this apparent contradiction is resolved by employing a compilation of the Sr, Nd, and Hf isotope composition of kimberlites—volcanic rocks that originate at great depth beneath continents. This compilation includes kimberlites as old as 2.06 billion years and shows that kimberlites do not derive from a primitive mantle source but sample the same geochemically depleted component (where geochemical depletion refers to ancient melt extraction) common to most oceanic island basalts, previously called PREMA (prevalent mantle) or FOZO (focal zone). Extrapolation of the Nd and Hf isotopic compositions of the kimberlite source to the age of Earth formation yields a 143Nd/144Nd-176Hf/177Hf composition within error of chondrite meteorites, which include the likely parent bodies of Earth. This supports a hypothesis where the source of kimberlites and ocean island basalts contains a long-lived component that formed by melt extraction from a domain with chondritic 143Nd/144Nd and 176Hf/177Hf shortly after Earth accretion. The geographic distribution of kimberlites containing the PREMA component suggests that these remnants of early Earth differentiation are located in large seismically anomalous regions corresponding to thermochemical piles above the core-mantle boundary. PREMA could have been stored in these structures for most of Earth’s history, partially shielded from convective homogenization.
DS202104-0578
2020
Giuliani, A., Jackson, M.G., Fitzpayne, A., Dalton, H.Remnants of early Earth differentiation in the deepest mantle-derived lavas.Proceedings of the National Academy of Sciences PNAS, Vol. 118, 1 e201521118 9p. PdfMantlekimberlite

Abstract: The noble gas isotope systematics of ocean island basalts suggest the existence of primordial mantle signatures in the deep mantle. Yet, the isotopic compositions of lithophile elements (Sr, Nd, Hf) in these lavas require derivation from a mantle source that is geochemically depleted by melt extraction rather than primitive. Here, this apparent contradiction is resolved by employing a compilation of the Sr, Nd, and Hf isotope composition of kimberlites—volcanic rocks that originate at great depth beneath continents. This compilation includes kimberlites as old as 2.06 billion years and shows that kimberlites do not derive from a primitive mantle source but sample the same geochemically depleted component (where geochemical depletion refers to ancient melt extraction) common to most oceanic island basalts, previously called PREMA (prevalent mantle) or FOZO (focal zone). Extrapolation of the Nd and Hf isotopic compositions of the kimberlite source to the age of Earth formation yields a 143Nd/144Nd-176Hf/177Hf composition within error of chondrite meteorites, which include the likely parent bodies of Earth. This supports a hypothesis where the source of kimberlites and ocean island basalts contains a long-lived component that formed by melt extraction from a domain with chondritic 143Nd/144Nd and 176Hf/177Hf shortly after Earth accretion. The geographic distribution of kimberlites containing the PREMA component suggests that these remnants of early Earth differentiation are located in large seismically anomalous regions corresponding to thermochemical piles above the core-mantle boundary. PREMA could have been stored in these structures for most of Earth’s history, partially shielded from convective homogenization.
DS202102-0194
2021
Gladkochub, D.P., Donskaya, T.V., Pisarevesky, S.A., Salnikova E.B., Mazukabzov, A.M., Kotov, A.B., Motova, Z.I., Stepanova, A.V., Kovach, V.P.Evidence of the latest Paleoproterozoic ( ~1615 Ma) mafic magmatism the southern Siberia: extensional environments in Nuna subcontinent.Precambrian Research, Vol. 354, doi.org/10.1016 /j.precamres. 2020.10049 14p. PdfRussiaCraton - Siberian
DS202111-1767
2021
Godet, A., Guilmette, C., Labrousse, L., Smit, M.A., Cutts, J.A., Davis, D.W., Vanier, M-A.Lu-Hf garnet dating and the timing of collisions: Paleoproterozoic accretionary tectonics revealed in the southeastern Churchill Province, Trans-Hudson orogen, Canada.Journal of Metamorphic Geology, Vol. 39, 8, 31p. PdfCanadageochronology

Abstract: Dating the onset of continental collision is fundamental in defining orogenic cycles and their effects on regional tectonics and geodynamic processes through time. Part of the Palaeoproterozoic Trans-Hudson Orogen, the Southeastern Churchill Province (SECP) is interpreted to result from the amalgamation of Archean to Palaeoproterozoic crustal blocks (amalgamated as the central Core Zone) that diachronically collided with the margins of the North Atlantic and Superior cratons, resulting in two bounding transpressive orogens: the Torngat and New Quebec Orogens. The SECP exposes mainly gneissic middle to lower orogenic crust in which deformation and amphibolite to granulite facies metamorphism and anatexis overprinted the early geological features classically used to constrain the timing of collisional events. To enable improved tectonic models for the development of the SECP, and the Trans-Hudson as a whole, we investigated granulite facies supracrustal sequences from the Tasiuyak Complex (TC) accretionary prism and the western margin of the North Atlantic Craton—that is, Saglek Block (upper plate)—using a multi-chronometer approach coupled with trace element geochemistry. In particular, the use of garnet Lu-Hf geochronology provides an important minimal time constraint for crustal thickening and collision. Garnet growth in the TC is constrained at 1885 ± 12 Ma (Lu-Hf), indistinguishable from U-Pb age of prograde monazite at 1873 ± 5 Ma. Zircon growth during melt crystallization occurred at 1848 ± 12 Ma. Garnet from the overriding Saglek Block is dated at 2567 ± 4.4 Ma (Lu-Hf) and indicates that gneissic rocks from the upper plate did not record the metamorphic imprint of the Torngat Orogeny. The diachronicity of the integrated metamorphic record across the strike of the SECP is explained by the location of terrane boundaries, consistent with the westward growth of the Churchill plate margin through sequential amalgamation of narrow crustal blocks during accretionary tectonics from c. 1.9 to 1.8 Ga.
DS202104-0579
2021
Godet, A., Guilmette, C.,Labrousse, L., Smit, M.A., Cutts, J.A., Davis, D.W., Vanier, M-A.Lu-Hf garnet dating and the timing of collisions: Paleoproterozoic accretionary tectonics revealed in the southeastern Churchill Province Trans-Hudson Orogen, Canada. Torngat, New QuebecJournal of Metamorphic Geology, doi:10.1111/jmg.12599Canada, Quebeccratons

Abstract: Dating the onset of continental collision is fundamental in defining orogenic cycles and their effects on regional tectonics and geodynamic processes through time. Part of the Palaeoproterozoic Trans?Hudson Orogen, the Southeastern Churchill Province (SECP) is interpreted to result from the amalgamation of Archean to Palaeoproterozoic crustal blocks (amalgamated as the central Core Zone) that diachronically collided with the margins of the North Atlantic and Superior cratons, resulting in two bounding transpressive orogens: the Torngat and New Quebec Orogens. The SECP exposes mainly gneissic middle to lower orogenic crust in which deformation and amphibolite to granulite facies metamorphism and anatexis overprinted the early geological features classically used to constrain the timing of collisional events. To enable improved tectonic models for the development of the SECP, and the Trans?Hudson as a whole, we investigated granulite facies supracrustal sequences from the Tasiuyak Complex (TC) accretionary prism and the western margin of the North Atlantic Craton-that is, Saglek Block (upper plate)-using a multi?chronometer approach coupled with trace element geochemistry. In particular, the use of garnet Lu-Hf geochronology provides an important minimal time constraint for crustal thickening and collision. Garnet growth in the TC is constrained at 1885 ± 12 Ma (Lu-Hf), indistinguishable from U-Pb age of prograde monazite at 1873 ± 5 Ma. Zircon growth during melt crystallization occurred at 1848 ± 12 Ma. Garnet from the overriding Saglek Block is dated at 2567 ± 4.4 Ma (Lu-Hf) and indicates that gneissic rocks from the upper plate did not record the metamorphic imprint of the Torngat Orogeny. The diachronicity of the integrated metamorphic record across the strike of the SECP is explained by the location of terrane boundaries, consistent with the westward growth of the Churchill plate margin through sequential amalgamation of narrow crustal blocks during accretionary tectonics from c. 1.9 to 1.8 Ga.
DS202106-0937
2021
Gomez-Arias, A., Yesares, L., Carabello, M.A., Maleke, M., Vermeulen, D., Nieto, J.M., van Heerden, E., Castillo, J.Environmental and geochemical characterization of alkaline mine wastes from Phalaborwa ( Palabora) complex, South Africa.Journal of Geochemical Exploration, Vol. 224, 106757, 13p. PdfAfrica, South Africadeposit - Palabora

Abstract: A detailed characterization of alkaline tailing ponds and waste rock dumps from Phalaborwa Igneous Complex (PIC) South Africa, has been accomplished. The study goes beyond the environmental characterization of mining wastes, offering the first insight towards the recycling of the wastes as alkaline reagent to neutralize acid industrial wastewater. To achieve these aims, tailings and waste rocks were characterized using a combination of conventional, novel and modified Acid Rock Drainage (ARD) prediction methodologies, as well as South African leachate tests, sequential extractions and pseudo-total digestions. The scarcity of Fe-sulphide minerals and the abundance of alkaline minerals indicated that PIC wastes are not ARD producers. The highest neutralization potential was found in the carbonatite rocks and East tailing samples (range between 289 and 801 kg CaCO3 eq/t). According to the National Environmental Management Waste Act (59/2008) of South Africa, tailing ponds and waste rock dumps from PIC classify as non-hazardous (Type 3 waste). The sequential extractions showed that the different fractions from most of the samples would mostly release sulphate and non-toxic elements, such as Ca, Mg, Na and K, which might be a concern if leached in high concentration. In addition, relatively high concentrations of radionuclides, such as U and Th (average of 6.7 and 36.3 mg/kg, respectively) are present in the non-labile fraction of PIC wastes, while the leachable concentrations were always below 0.006 mg/L. Among PIC wastes, East tailing would be the best option as alkaline reagent to neutralize acid wastewater because of its high neutralization potential and non-harmful leachate composition. In general, this study exposes the shortcomings in mine waste characterization, particularly for alkaline mine wastes, and introduces the assessment of potential revalorization as a novel practice in mine waste characterization that, if extended as a regular practice, would facilitate a circular economy approach to the mining industry with its consequent economic and environmental benefits.
DS202111-1768
2021
Gong, Z., Evans, D.A.D., Youbi, N., Lahna, A.A., Sodelund, U., Malek, M.A., Wen, B., Jing, X., Ding, J., Boumedhdi, M.A., Ernst, R.E.Reorienting the West African craton in Paleoproterozoic-Msoproterozoic supercontinent Nuna.Geology, Vol. 49, 10, pp. 1171-1176. pdfAfrica, west AfricaNuna

Abstract: The location of the West African craton (WAC) has been poorly constrained in the Paleoproterozoic-Mesoproterozoic supercontinent Nuna (also known as Columbia). Previous Nuna reconstruction models suggested that the WAC was connected to Amazonia in a way similar to their relative position in Gondwana. By an integrated paleomagnetic and geochronological study of the Proterozoic mafic dikes in the Anti-Atlas Belt, Morocco, we provide two reliable paleomagnetic poles to test this connection. Incorporating our new poles with quality-filtered poles from the neighboring cratons of the WAC, we propose an inverted WAC-Amazonia connection, with the northern WAC attached to northeastern Amazonia, as well as a refined configuration of Nuna. Global large igneous province records also conform to our new reconstruction. The inverted WAC-Amazonia connection suggests a substantial change in their relative orientation from Nuna to Gondwana, providing an additional example of large-magnitude cumulative azimuthal rotations between adjacent continental blocks over supercontinental cycles.
DS202106-0938
2021
Gonzales, A.New rating system for coloured gemstones.Gems&Jewellery, Vol. 30, 1, p. 31.Globalgemstones
DS202105-0765
2021
Gonzalez-Alvarez, I., Stoppa, F., Yang, X.Y., Porwal, A.Introduction to the special issue, insights on carbonatites and their mineral exploration approach: a challenge towards resourcing critical metals.Ore Geology Reviews, Vol. 133, 104073, 7p. PdfGlobalcarbonatites

Abstract: Population growth and technological progress in the last 50 years have resulted in the global demand for mineral resources increasing by 400% since 1970, and it is further expected to almost double by 2050. This context forecasts a never-seen-before market for some specific mineral commodities, termed critical metals. The resource and supply flow of critical metals would be decisive for the economic well-being of economies in near future. Carbonatites are the most prospective host rocks for Rare Earth Elements (REEs), which constitute some of the most important critical elements. This special issue aims to contribute to the debate on understanding the genesis of carbonatites and their prospectivity for REEs (including exploration strategies), by presenting a wide variety of studies on carbonatites from around the globe.
DS202109-1469
2021
Good, D.J., Hollings, P., Dunning, G., Epstein, R., McBride, J., Jedemann, A., Magnus, S., Bohav, T., Shore, G.A new model for the Coldwell Complex and associated dykes of the Midcontinent Rift, Canada.Journal of Petrology, Vol. 62, 7, 10.1093/petrology/ega036Canadadeposit - Coldwell

Abstract: Mafic intrusions on the NE shoulder of the Midcontinent Rift (Keweenawan LIP), including Cu-PGE mineralized gabbros within the Coldwell Complex (CC), and rift parallel or radial dykes outside the CC are correlated based on characteristic trace element patterns. In the Coldwell Complex, mafic rocks are subdivided into four groups: (1) early metabasalt; (2) Marathon Series; (3) Layered Series; (4) Geordie-Wolfcamp Series. The Marathon Series are correlated with the rift radial Abitibi dykes (1140?Ma), and the Geordie-Wolfcamp Series with the rift parallel Pukaskwa and Copper Island dykes. U-Pb ages determined for five gabbros from the Layered and Marathon Series are between 1107•7 and 1106•0?Ma. Radiogenic isotope ratios show near chondritic (CHUR) ?Nd(1106?Ma) and 87Sr/86Sri values that range from -0•38 to +1•13 and 0•702537 to 0•703944, respectively. Distinctive geochemical properties of the Marathon Series and Abitibi dykes, such as Ba/La (14-37), Th/Nb (0•06-0•12), La/Sm (3•8-7•7), Sr/Nd (21-96) and Zr/Sm (9-19), are very different from those of the Geordie-Wolfcamp Series and a subset of Copper Island and Pukaskwa dykes with Ba/La (8•7-11), Th/Nb (0•12-0•13), La/Sm (6•7-7•9), Sr/Nd (5-7•8) and Zr/Sm (18-24). Each unit exhibits covariation between incompatible element ratios such as Zr/Sm and Nb/La or Gd/Yb, Sr/Nd and Ba/La, and Nb/Y and Zr/Y, which are consistent with mixing relationship between two or more mantle domains. These characteristics are unlike those of intrusions on the NW shoulder of the MCR, but resemble those of mafic rocks occurring in the East Kenya Rift. The results imply that an unusual and long-lived mantle source was present in the NE MCR for at least 34?Myr (spanning the 1140?Ma Abitibi dykes and the 1106?Ma Marathon series) and indicate potential for Cu-PGE mineralization in an area much larger than was previously recognized.
DS202102-0195
2020
Goodden, R.Ocean diamonds - alluvialsGems & Jewellery, Vol. 29, 4, pp. 14-16. pdfAfrica, Namibiaalluvials
DS202111-1769
2019
Gouvea, Y., Stehmann, J.Solanum adamantium, a new narrowly endemic species from a diamondiferous region of the Espinhaco Range in Minas Gerais, Brazil.Systematic Botany, Vol. 44, 4, pp. 923-929. pdfSouth America, Brazilbotany

Abstract: Solanum adamantium is described from Serra de Grão Mogol, located in the Espinhaço range, in northern Minas Gerais State, Brazil. The new species is ecologically and morphologically similar to the prickly species S. buddleiifolium and S. thomasiifolium, from which it differs in a series of vegetative and reproductive characters. We discuss the morphological similarities and differences among these species, as well as certain aspects of the new taxon's ecology and geographic distribution. Images of diagnostic characters, a map of geographical distribution, a preliminary conservation assessment, and full specimen citations are provided.
DS202107-1100
2019
Graf, C., Woodland, A., Hofer, H., Seitz, H-M., Pearson, G., Kjarsgaard, B.Metasomatism and oxidation state of lithospheric mantle beneath the Rae Craton, Canada as revealed by xenoliths from Somerset Island and Pelly Bay. ** Note dateGeophysical Research Abstracts , 1p. PdfCanada, Somerset Island , Nunavutcratons

Abstract: We present the first oxidation state measurements for the subcontinental lithospheric mantle (SCLM) beneath the Rae craton, northern Canada, one of the largest components of the Canadian shield. In combination with major and trace element compositions for garnet and clinopyroxene, we assess the relationship between oxidation state and metasomatic overprinting. The sample suite comprises peridotite xenoliths from the central part (Pelly Bay) and the craton margin (Somerset Island) providing insights into lateral and vertical variations in lithospheric character. Our suite contains spinel, garnet-spinel and garnet peridotites, with most samples originating from 100 to 140 km depth. Within this narrow depth range we observe strong chemical gradients, including variations in oxygen fugacity (ƒO2) of over 4 log units. Both Pelly Bay and Somerset Island peridotites reveal a change in metasomatic type with depth. Observed geochemical systematics and textural evidence support the notion that Rae SCLM developed through amalgamation of different local domains, establishing chemical gradients from the start. These gradients were subsequently modified by migrating melts that drove further development of different types of metasomatic overprinting and variable oxidation at a range of length scales. This oxidation already apparent at ~?100 km depth could have locally destabilised any pre-existing diamond or graphite.
DS202104-0580
2019
Grass, C., Woodland, A., Hoferm H,m Seitz, H-M., Pearson, G., Kjarsgaard, B.Metasomatism and oxidation state of the lithospheric mantle beneath the Rae Craton, Canada as revealed by xenoliths from Somerset Island and Pelly Bay. ***note dateGeophysical Research abstracts, EGU, EGU2019-9348, 1p. PdfCanadageodynamics

Abstract: We present the first oxidation state measurements for the subcontinental lithospheric mantle (SCLM) beneath the Rae craton, northern Canada, one of the largest components of the Canadian shield. In combination with major and trace element compositions for garnet and clinopyroxene, we assess the relationship between oxidation state and metasomatic overprinting. The sample suite comprises peridotite xenoliths from the central part (Pelly Bay) and the craton margin (Somerset Island) providing insights into lateral and vertical variations in lithospheric character. Our suite contains spinel, garnet-spinel and garnet peridotites, with most samples originating from 100 to 140 km depth. Within this narrow depth range we observe strong chemical gradients, including variations in oxygen fugacity (ƒO2) of over 4 log units. Both Pelly Bay and Somerset Island peridotites reveal a change in metasomatic type with depth. Observed geochemical systematics and textural evidence support the notion that Rae SCLM developed through amalgamation of different local domains, establishing chemical gradients from the start. These gradients were subsequently modified by migrating melts that drove further development of different types of metasomatic overprinting and variable oxidation at a range of length scales. This oxidation already apparent at ~?100 km depth could have locally destabilised any pre-existing diamond or graphite.
DS202108-1285
2021
Greenman, J.W., Rooney, A.D., Patzke, M., Ielpi, A., Halverson, G.P.Re-Os geochronology highlights widespread latest Mesoproterozoic ( ca 1090-1050 Ma) cratonic basin development on northern Laurentia.Geology, Vol. 49, March pp. 779-783.Canada, Greenlandgeochronology

Abstract: The terminal Mesoproterozoic was a period of widespread tectonic convergence globally, culminating in the amalgamation of the Rodinia supercontinent. However, in Laurentia, long-lived orogenesis on its eastern margin was punctuated by short-lived extension that generated the Midcontinent Rift ca. 1110-1090 Ma. Whereas this cratonic rift basin is typically considered an isolated occurrence, a series of new depositional ages demonstrate that multiple cratonic basins in northern Laurentia originated around this time. We present a Re-Os isochron date of 1087.1 ± 5.9 Ma from organic-rich shales of the Agu Bay Formation of the Fury and Hecla Basin, which is one of four closely spaced cratonic basins spanning from northeastern Canada to northwestern Greenland known as the Bylot basins. This age is identical, within uncertainty, to ages from the Midcontinent Rift and the Amundsen Basin in northwestern Canada. These ages imply that the late Mesoproterozoic extensional episode in Laurentia was widespread and likely linked to a common origin. We propose that significant thermal anomalies and mantle upwelling related to supercontinent assembly centered around the Midcontinent Rift influenced the reactivation of crustal weaknesses in Arctic Laurentia beginning ca. 1090 Ma, triggering the formation of a series of cratonic basins.
DS202103-0382
2021
Gress, M.U., Koornneef, J.M., Thomassot, E., Chinn, I.L., van Zuilen, K., Davies, G.R.Sm-Nd isochron age coupled with C-N isotope data of eclogitic diamonds from Jwaneng, Botswana.Geochimica et Cosmochimica Acta, Vol. 293, pp. 1-17. 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 (?13C?
DS202103-0383
2021
Gress, M.U., Pearson, D.G., Chinn, I.L., Thomassot, E., Davies, G.R.Mesozoic to Paleoproterozoic diamond growth beneath Botswana recorded by Re-Os ages from individual eclogitic and websteritic inclusions.Lithos, 38p. PdfAfrica, Botswanadeposit - Orapa, Jwaneng

Abstract: Re-Os isotope systematics are reported from a suite of eclogitic and websteritic sulphide inclusions extracted from well-characterised diamond growth zones from the Orapa and Jwaneng kimberlite clusters. Re-Os ages (786 ± 250 Ma) are within uncertainty of previously determined Sm-Nd ages (853 ± 55 Ma), demonstrating isotopic equilibrium, at varying levels of completeness, across multiple isotopic systems in different minerals at the time of diamond formation and inclusion encapsulation. These data confirm the concept that inclusion isochron ages, when used with detailed textural/ growth zone control, reflect the timing of diamond crystallisation. Our data substantiate previous Re-Os and Sm-Nd inclusion ages of diamonds from Orapa and Jwaneng, indicating that major tectono-magmatic events formed discrete diamond populations of Paleo- (~ 2.0 to 1.7 Ga), Meso- (~ 1.2 to 1.1 Ga) and Neoproterozoic (~ 0.9 to 0.75 Ga) age. Some of these processes occurred simultaneously across the Kalahari Craton and can be traced over 100's of km illustrating the significance of diamond inclusions for monitoring continental tectonics. Inclusion ages indicating diamond formation that are younger than 300 Ma appear to be more common than previously recognised, consistent with evidence of relatively abundant, young, fluid-rich "fibrous" and polycrystalline diamonds at Jwaneng and Orapa. The increasingly widespread evidence for Mesozoic diamond-forming events in southern Africa and elsewhere appears closely linked with the kimberlite-related magmatism that affected these regions and subsequently transported diamonds to the surface. The inclusion isochron ages emphasise that diamond formation is a multi-stage and episodic process that can occur contemporaneously in disparate substrates and produce multiple diamond populations in the sub-continental lithospheric mantle.
DS202104-0581
2021
Gress, M.U., Pearson, D.G., Chinn, I.L., Thomassot, E., Davies, G.R.Mesozoic to Paleozoic diamond growth beneath Botswana recorded by Re-Os ages from individual eclogitic and websteritic inclusions.Appendix to previous Lithos article in March 2021, 11p. PdfAfrica, Botswanadeposit - Damtshaa, Orapa

Abstract: Re-Os isotope systematics are reported from a suite of eclogitic and websteritic sulphide inclusions extracted from well-characterised diamond growth zones from the Orapa and Jwaneng kimberlite clusters. Re-Os ages (786 ± 250 Ma) are within uncertainty of previously determined Sm-Nd ages (853 ± 55 Ma), demonstrating isotopic equilibrium, at varying levels of completeness, across multiple isotopic systems in different minerals at the time of diamond formation and inclusion encapsulation. These data confirm the concept that inclusion isochron ages, when used with detailed textural/ growth zone control, reflect the timing of diamond crystallisation. Our data substantiate previous Re-Os and Sm-Nd inclusion ages of diamonds from Orapa and Jwaneng, indicating that major tectono-magmatic events formed discrete diamond populations of Paleo- (~ 2.0 to 1.7 Ga), Meso- (~ 1.2 to 1.1 Ga) and Neoproterozoic (~ 0.9 to 0.75 Ga) age. Some of these processes occurred simultaneously across the Kalahari Craton and can be traced over 100's of km illustrating the significance of diamond inclusions for monitoring continental tectonics. Inclusion ages indicating diamond formation that are younger than 300 Ma appear to be more common than previously recognised, consistent with evidence of relatively abundant, young, fluid-rich “fibrous” and polycrystalline diamonds at Jwaneng and Orapa. The increasingly widespread evidence for Mesozoic diamond-forming events in southern Africa and elsewhere appears closely linked with the kimberlite-related magmatism that affected these regions and subsequently transported diamonds to the surface. The inclusion isochron ages emphasise that diamond formation is a multi-stage and episodic process that can occur contemporaneously in disparate substrates and produce multiple diamond populations in the sub-continental lithospheric mantle.
DS202101-0012
2020
Gribkoff, E.Geologists shed light on the mantle with 3D model.EOS, 101, doi.org/10.1029/2020EOE152364 Dec. 4, 2p.Mantlegeophysics - seismics

Abstract: The model, which will incorporate 227 million surface wave measurements, could help with everything from earthquake characterization to neutrino geosciences.
DS202108-1286
2021
Griffin, W.L., Gain, S.E.M., Saunders, M., Alard, O., Shaw, J., Toledo, V.Nitrogen under super-reducing conditions: Ti Oxynitride melts in xenolithic corundum aggregates from Mt. Carmel.Minerals, Vol. 11, 780, 16p. PdfEurope, Israeldeposit - Mt. Carmel

Abstract: Titanium oxynitrides (Ti(N,O,C)) are abundant in xenolithic corundum aggregates in pyroclastic ejecta of Cretaceous volcanoes on Mount Carmel, northern Israel. Petrographic observations indicate that most of these nitrides existed as melts, immiscible with coexisting silicate and Fe-Ti-C silicide melts; some nitrides may also have crystallized directly from the silicide melts. The TiN phase shows a wide range of solid solution, taking up 0-10 wt% carbon and 1.7-17 wt% oxygen; these have crystallized in the halite (fcc) structure common to synthetic and natural TiN. Nitrides coexisting with silicide melts have higher C/O than those coexisting with silicate melts. Analyses with no carbon fall along the TiN-TiO join in the Ti-N-O phase space, implying that their Ti is a mixture of Ti3+ and Ti2+, while those with 1-3 at.% C appear to be solid solutions between TiN and Ti0.75O. Analyses with >10 at% C have higher Ti2+/Ti3+, reflecting a decrease in fO2. Oxygen fugacity was 6 to 8 log units below the iron-wüstite buffer, at or below the Ti2O3-TiO buffer. These relationships and coexisting silicide phases indicate temperatures of 1400-1100 °C. Ti oxynitrides are probably locally abundant in the upper mantle, especially in the presence of CH4-H2 fluids derived from the deeper metal-saturated mantle.
DS202101-0013
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 behaviour of boron under reducing conditions.American Mineralogist , in press available 33p. 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.
DS202110-1616
2021
Griffin, W.L., Gain, S.E.M., Saunders, M., Camara, F., Bindi, L., Sparta, D., Toledo, V., O'Reilly, S.Y.Cr203 in corundum: ultrahigh contents under reducing conditions. American Mineralogist, Vol. 106, pp. 1420-1437. pdfEurope, Israeldeposit - Mount Carmel

Abstract: Xenocrysts and xenoliths in Upper Cretaceous pyroclastics on Mount Carmel (northern Israel) represent a series of similar magma-fluid systems at different stages of their evolution, recording a continuous decrease in oxygen fugacity (fO2) as crystallization proceeded. Corundum coexisting with Fe-Mg-Cr-Al spinels, other Fe-Mg-Al-Na oxides, and Fe-Ni alloys in apparent cumulates crystallized at fO2 values near the iron-wüstite (IW) buffer (fO2 = IW±1) and is zoned from high-Cr cores to lower-Cr rims, consistent with fractional crystallization trends. The reconstructed parental melts of the cumulates are Al-Cr-Fe-Mg oxides with ca. 2 wt% SiO2. Corundum in other possible cumulates that contain Cr-Fe (Fe 45 wt%) alloys has low-Cr cores and still lower-Cr rims. Corundum coexisting with Cr0 (fO2 = IW-5) in some possible cumulates has low-Cr cores, but high-Cr rims (to >30% Cr2O3). These changes in zoning patterns reflect the strong decrease in the melting point of Cr2O3, relative to Al2O3, with decreasing fO2. The electron energy loss spectroscopy (EELS) analyses show that all Cr in corundum that coexists with Cr0 is present as Cr3+. This suggests that late in the evolution of these reduced melts, Cr2+ has disproportionated via the reaction 3Cr2+(melt) ? 2Cr3+(Crn) + Cr0. The most Cr-rich corundum crystallized together with ?-alumina phases including NaAl11O17 (diaoyudaoite) and KAl11O17 (kahlenbergite) and ??-alumina phases; residual melts crystallized a range of (K,Mg)2(Al,Cr)10O17 phases with the kahlenbergite structure. The parental melts of these assemblages appear to have been Al-Cr-K-Na-Mg oxides, which may be related to the Al-Cr-Fe-Mg oxide melts mentioned above, through fractional crystallization or liquid immiscibility. These samples are less reduced (fO2 from IW to IW-5) than the assemblages of the trapped silicate melts in the more abundant xenoliths of corundum aggregates (fO2 = IW-6 to IW-10). They could be considered to represent an earlier stage in the fO2 evolution of an “ideal” Mt. Carmel magmatic system, in which mafic or syenitic magmas were fluxed by mantle-derived CH4+H2 fluids. This is a newly recognized step in the evolution of the Mt. Carmel assemblages and helps to understand element partitioning under highly reducing conditions.
DS202111-1770
2021
Grishina, S., Goryainov, S., Oreshonkov, A., Karmanov, N.Micro-Raman study of cesanite ( Ca2Na3(OH)(SO4)3) in chloride segregations from Udachnaya-East kimberlites.Journal of Raman Spectroscopy, 11p. PdfRussiadeposit - Udachnay-East

Abstract: Cesanite (Ca2Na3(OH)(SO4)3), a rare mineral, has been found in a few places restricted to a geothermal field and caves. We report the new occurrence of cesanite in quite different geological site—within sulfate-rich melt inclusions in chloride segregations from kimberlites of Udachnaya-East pipe (Siberia). Two halite generations: ?esanite free and ?esanite-bearing, were distinguished in concentrically zonal segregations according to the results of the mineral and sulfate melt inclusion study by micro-Raman spectroscopy and SEM-EDS. We have applied the Raman spectroscopy and first principles calculations to understand structural and vibrational properties of cesanite daughter mineral in polyphase sulfate inclusions. Polarized spectra provided additional information on the overlapped components of the spectral profile. The Raman spectra of cesanite in the range of OH stretching vibrations are reported for the first time. The study aims to clarify the source of the Na-S-Cl-enrichment in the Udachnaya-East pipe, which is highly discussed.
DS202101-0014
2020
Gruber, B., Chacko, T., Pearson, D.G., Currie, C., Menzies, A.Heat production and moho temperatures in cratonic crust: evidence from lower crustal xenoliths from the Slave craton.Lithos, doi.org/10.1016/ j.lithos.2020.105889 13p. PdfCanada, Northwest Territoriesdeposit - Diavik A-154

Abstract: Ambient Moho temperatures and lower crustal heat production are surprisingly poorly constrained in cratons. Here we address these problems using 15 lower crustal xenoliths from the Diavik A-154 kimberlite, Slave craton, Canada. Iron?magnesium exchange geothermometry on small biotite and amphibole inclusions in garnet indicates that the Slave craton lower crust was at a temperature of ?500 °C at the time of kimberlite eruption (~55 Ma). The ambient lower crustal temperature was likely lower than 500 °C because the thermometers record the closure temperature of diffusional Fe2+-Mg exchange between touching mineral pairs. New measurements of K, U and Th concentrations in the constituent minerals, together with xenolith modes, allow reconstruction of the heat-producing element (HPE) K, U, and Th budget of the Slave craton lower crust. Metasedimentary granulites have an average heat production of 0.29 ± 0.01 ?W/m3 (n = 3) whereas mafic granulites have an average heat production of 0.13 ± 0.03 ?W/m3 (n = 12). Our new data clearly show that plagioclase abundance in both lithologies has a major influence on overall lower crustal heat production, being an important reservoir of all three HPE. Combining the heat production of mafic and metasedimentary granulites in their observed 80:20 proportions results in an average heat production value for the Slave craton lower crust of 0.16 ± 0.03 ?W/m3. Using these heat production estimates, modeled Moho temperatures beneath Diavik of ~450-470 °C are broadly consistent with maximum lower crustal temperatures indicated by geothermometry. The low HPE contents predicted for cratonic lower crust must result in lower temperatures in the deep crust and mantle lithosphere, and in turn higher estimates for the thickness of mantle lithosphere. This effect becomes larger as the thickness of the low-HPE lower crustal layer increases. In the specific case of the central Slave craton, we find that model estimates of the diamond potential of the mantle lithosphere, as judged by the proportion of lithospheric mantle in the diamond stability field, are not strongly affected by small variations in lower crustal heat production and Moho temperature.
DS202112-1928
2021
Grutter, H.Observations on "Lows" and "Highs" in contemporary  microdiamond data.VCK Talk Nov. 2, https://youtu.be/Be3BNqDZTw0Globalmicrodiamond

Abstract: The evaluation of advanced stage diamond projects is materially constrained by the time and cost involved in bulk sampling (or trial mining) campaigns that serve to demonstrate the grade and value of (macro)diamonds in a deposit. However, comparatively inexpensive assay data for (micro)diamonds may also be used to estimate (macro)diamond grade, by way of geostatistical extrapolation or modelling of total diamond content curves and diamond size frequency distributions. Geoscientists at SRK (Canada) Inc. compiled publicly available technical disclosure related to micro/macrodiamond sampling campaigns completed since early-2004 and developed a model-independent benchmarking approach to estimate in-situ (macro)diamond grades based on microdiamond assay results - a one-page summary of that work is available here: here Our ongoing investigation of microdiamond data has developed a focus on the occurrence of "low-count" and "high-count" microdiamond assay results. In this VKC talk we contrast "normal"-count with "low"-count results (Snap Lake vs FALC and others) and appeal to diamond-bearing mantle xenoliths to explain occasional "high"-count results. Real-world examples are used to cover topics like microdiamond sample sizes and (attained) resolution thresholds in the range 1 part in 1010 to 1012. The talk closes out with an examination of the microdiamond dataset for the Tuwawi pipe (northern Baffin Island).
DS202106-0939
2021
Guan, H., Geoffroy, L., Xu, M.Magma-assisted fragmentation of Pangea: continental breakup initiation and propagation.Gondwana Research, Vol. 96, pp. 56-75. pdfMantlemagmatism

Abstract: Pre-magmatic continental extension often precedes the major magmatic expulsion of large igneous provinces (LIPs). However, the cause-and-effect relationship between pre-magmatic rifting and the extrusion of large amount of magma is controversial. It remains unclear whether magmatism arises as a consequence of passive rifting or whether it is related to active upwelling of the mantle. In addition, the relationship between the pre-magmatic stages and the final breakup, with the onset of conjugate passive margins, is ambiguous. In this study, we compiled available data from six LIPs (Central Atlantic, Karoo, Parana-Etendeka, Deccan, North Atlantic, and Afar igneous provinces) that successively occurred during the fragmentation of Pangea and found that pre-magmatic rift trends may show a high obliquity or even be orthogonal with respect to the future passive margins. We conclude that syn-magmatic rifts should not be directly correlated, both structurally and dynamically, to the ancient pre-magmatic rift phase. Furthermore, following the breakup of a supercontinent, seafloor spreading usually initiates within volcanic passive margins (VPMs) and then propagates away to create non-volcanic passive margins (NVPMs) as a consequence of the consumption and cooling of a sub-lithospheric positive thermal anomaly. Major transform faults often exist between VPMs and NVPMs, acting as a mechanical barrier to mantle melting and magmatism transportation.
DS202107-1101
2018
Guha, A., Rani, K., Varma, C.B., Sarwate, N.K., Sharma, N., Mukherjee, A., Kumar, K.V., Pal, S.K., Saw, A.K., Jha, S.K.Identification of potential zones for kimberlite exploration - an Earth observation approach. ChhatarpurThe International Achives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol. XLII-5 12p. PdfIndia, Madhya PradeshASTER, lineament

Abstract: In the present study, we have prepared the thematic evidence layers for identifying the potential zones of kimberlite emplacement in parts of Chhatarpur district, Madhya Pradesh. These thematic layers or evidence layers are geological structure, alteration zones, lineament density, surface alteration and geomorphic anomaly and these layers are prepared from the remote sensing data. As orientation of the geological structures (i.e fault system) and their density have the major role in the emplacement of kimberlite; both of these evidence layers are integrated using "AND" Boolean Logical Operator. On the other hand, two evidential layers regarded as the proxy to indicate the "surface expressions on kimberlite (i.e. alteration zones and geomorphic anomaly) are combined using "OR" operator as either of these two surface expression is indicative of kimberlite. Consequently, conjugate evidence layers on the surface expressions of kimberlite are integrated with the causative evidence layers of kimberlite emplacement using "AND" operator to identify the potential zones of diamond occurrences. Potential zones of kimberlite are overlaid on the residual gravity anomaly map derived from space-based gravity model of European Improved Gravity of Earth by New Technique (EIGEN6C4) to relate potential zones of kimberlite with the similar structural alignment (delineated in the residual gravity map) of known occurrence of kimberlite. We also have carried out indicator mineral survey around these potential zones and some of the kimberlite specific indicator minerals are identified in the stream sediments within these potential zones.
DS202103-0384
2021
Gunduz, M., Asan, K.PetroGram: an excel-based petrology program for modeling of magmatic processes.Geoscience Frontiers, Vol. 12, pp. 81-92. pdfGlobalpetrology

Abstract: PetroGram is an Excel© based magmatic petrology program that generates numerical and graphical models. PetroGram can model the magmatic processes such as melting, crystallization, assimilation and magma mixing based on the trace element and isotopic data. The program can produce both inverse and forward geochemical models for melting processes (e.g. forward model for batch, fractional and dynamic melting, and inverse model for batch and dynamic melting). However, the program uses a forward modeling approach for magma differentiation processes such as crystallization (EC: Equilibruim Crystallization, FC: Fractional Crystallization, IFC: Imperfect Fractional Crystallization and In-situ Crystallization), assimilation (AFC: Assimilation Fractional Crystallization, Decoupled FC-A: Decoupled Fractional Crystallization and Assimillation, A-IFC: Assimilation and Imperfect Fractional Crystallization) and magma mixing. One of the most important advantages of the program is that the melt composition obtained from any partial melting model can be used as a starting composition of the crystallization, assimilation and magma mixing. In addition, PetroGram is able to carry out the classification, tectonic setting, multi-element (spider) and isotope correlation diagrams, and basic calculations including Mg#, Eu/Eu?, ?Sr and ?Nd widely used in magmatic petrology.
DS202103-0385
2020
Guo, H., Yu, X., Zheng, Y., Sun, Z., Ng, M.F-Y.Inclusion and trace element characteristics of emeralds from Swat Valley, Pakistan.Gems & Gemology, Vol. 56, 3, pp. 336-355. pdfAsia, Pakistandeposit - Swat Valley. Emerald

Abstract: Swat Valley has become an important source of emeralds, including recently discovered trapiche-type crystals. In this study, emerald samples from Swat were examined by standard gemological testing, UV-Vis-NIR, FTIR, Raman analysis, EDXRF, and LA-ICP-MS. The study found three-phase hexagonal inclusions consisting of water, gaseous carbon dioxide and nitrogen, and a magnesite crystal. The gaseous mixture in two-phase inclusions is characteristic in both trapiche-type (CO2 + N2) and non-trapiche samples (CO2 + N2 + CH4). Mineral inclusions of hematite, magnetite, rutile, graphite, and siderite are reported for the first time. Regular non-trapiche-type Swat emeralds contain high chromium (avg. 7471 ppmw), alkali metal (avg. 21040 ppmw), magnesium (avg. 34263 ppmw), and iron (avg. 9265 ppmw), as well as scandium (avg. 633 ppmw). Infrared spectra show that the absorption of type II H2O is stronger than that of type I H2O. Logarithm plots of trace elements appear to be diagnostic. Based on Raman spectroscopy, the trapiche-type emeralds’ colorless core, light green hexagonal growth zone area, and green rim are emerald, while the six black arms are a mixture of hematite and graphite.
DS202102-0196
2020
Hainschwang, T.Wrestling with radiation ( diamonds)Gems & Jewellery, Vol. 29, 4, pp. 28-41.Globaldiamond colour
DS202106-0940
2021
Halim, A.Y., Kelloway, S.J., Marjo, C., Regenauer-Lieb. K.A Hylogger-Itrax core-scanner comparison for multi-scale high resolution petrophysical characterization workflow. * not specific to diamondsApplied Chemistry, in press available, 18p. PdfGlobalHylogger

Abstract: Recent advances in core scanning technologies allow for fast and non-destructive chemical and mineral profiling of rock samples for mineral services and oil and gas exploration. The aim of these automatic core scan methods is to obtain valuable information for profiling drill core cuttings with minimum sample preparation at relatively high speed. In the last decade, a core logging system using an automated infrared-based hyperspectral line-profiling system, Hylogger, has progressed to become an effective standard for the Australian mineral exploration industry. Its results are used to rapidly obtain mineralogical information allowing the characterisation of different geological formations in near real-time. The interpretation of Hylogger data can be challenging for certain complex mineral mixtures. Here we solve this issue by augmenting the Hylogger interpretation with elemental analysis using the Itrax core scanner equipped with an X-ray fluorescence (XRF) spectrometer. The Itrax core scanner produces high-resolution elemental data of major, minor and trace elements in one dimension. We analyse and compare the Hylogger and Itrax data, with each dataset independently cross-checked using X-ray diffraction (XRD) and thin-section petrology and propose a workflow harvesting the mutual strengths of each method. The recommended workflow consists of rapid screening using Hylogger and XRF analysis, providing new insights into the mineralogy based on comparative multiscale element-mineral analysis. The workflow is tested on four different types of volcanic rock samples, where infrared spectra of individual minerals overlap. We tested tuffaceous ash, basaltic, dolerite, and basaltic-andesitic rocks. Our study shows that embedding Itrax core scanner data into the workflow provides a solution to the challenges of interpreting Hylogger data in complex mineral samples. The proposed workflow provides a total system for multiscale, high-resolution petrophysical analyses and rock property modelling.
DS202103-0386
2021
Hall, A.M., Putkinen, N., Hietala,, S., Lindsberg, E., Holma, M.Ultra-slow cratonic denudation in Finland since 1.5 Ga indicated by tiered unconformities and impact structures.Precambrian Research, Vol. 352, 106000, 18p. PdfEurope, Finlandgeothermometry

Abstract: The Earth’s cratons are traditionally regarded as tectonically stable cores that were episodically buried by thin sedimentary covers. Cratonic crust in southern Finland holds seven post-1.7 Ga tiered unconformities, with remnants of former sedimentary covers. We use the geometries of the tiered unconformities, along with previously dated impact structures and kimberlite and carbonatite pipes, to reconstruct the erosion and burial history of the craton and to derive estimates of depths of erosion in basement and former sedimentary rocks. The close vertical spacing (<200 m) of the unconformities and the survival of small (D ? 5 km) Neoproterozoic and Early Palaeozoic impact structures indicate minor later erosion. Average erosion rates (<2.5 m/Ma) in basement and cover are amongst the lowest reported on Earth. Ultra-slow erosion has allowed the persistence in basement fractures of Phanerozoic fracture coatings and Palaeogene groundwater and microbiomes. Maximum thicknesses of foreland basin sediments in Finland during the Sveconorwegian and Caledonide orogenies are estimated as ~1.0 km and <0.68-1.0 km, respectively. Estimated losses of sedimentary cover derived from apatite fission track thermochronology are higher by factors of at least 2 to 4. A dynamic epeirogenic history of the craton in Finland, with kilometre-scale burial and exhumation, proposed in recent thermochronological models is not supported by other geological proxies. Ultra-slow erosion rates in southern Finland reflect long term tectonic stability and burial of the craton surface for a total of ~1.0 Ga beneath generally thin sedimentary cover.
DS202112-1929
2021
Hardman, M.F., Stachel, T., Pearson, D.G., Cano, E.J., Stern, R.A., Sharp, Z.D.Characterising the distinct crustal protoliths of Roberts Victor Type I and II eclogites.Journal of Petrology, doi.org/petrology/egab090 65p. PdfAfrica, South Africadeposit - Roberts Victor

Abstract: The origin of the eclogites that reside in cratonic mantle roots has long been debated. In the classic Roberts Victor kimberlite locality in South Africa, the strongly contrasting textural and geochemical features of two types of eclogites have led to different genetic models. We studied a new suite of 63 eclogite xenoliths from the former Roberts Victor Mine. In addition to major- and trace-element compositions for all new samples, we determined 18O/16O for garnet from 34 eclogites. Based on geochemical and textural characteristics we identify a large suite of Type I eclogites (n = 53) consistent with previous interpretations that these rocks originate from metamorphosed basaltic-picritic lavas or gabbroic cumulates from oceanic crust, crystallised from melts of depleted MORB mantle. We identify a smaller set of Type II eclogites (n = 10) based on geochemical and textural similarity to eclogites in published literature. We infer their range to very low ?18O values combined with their varied, often very low Zr/Hf ratios and LREE-depleted nature to indicate a protolith origin via low-pressure clinopyroxene-bearing oceanic cumulates formed from melts that were more depleted in incompatible elements than N-MORB. These compositions are indicative of derivation from a residual mantle source that experienced preferential extraction of incompatible elements and fractionation of Zr-Hf during previous melting.
DS202110-1617
2021
Hardy, J.Sapphire: a celebration of colour. ( sponsored by Gemfields)jeweleryconnisseur.net, Thames & Hudson series Book no info.Globalsapphires
DS202106-0941
2021
Harlow, G.The American Museum of Natural History Gem exhibit.Gems&Jewellery, Vol. 30, 1, pp. 18-20.United States, New YorkGem exhibit
DS202106-0942
2021
Harmon, R.S., Senesi, G.S.Laser-induced breakdown spectroscopy - a geochemical tool for the 21st century. * not specific to diamondsApplied Chemistry, Vol. 128, 104929 55p. PdfGlobalgeochemistry

Abstract: Laser-induced breakdown spectroscopy (LIBS) is a simple, straightforward, and versatile form of atomic emission spectroscopy that focuses a rapidly-pulsed laser beam onto a sample to form a plasma containing its constituent elements and then uses spectral analysis of the emitted light to detect the elements present. In theory, LIBS is capable of qualitative, semi-quantitative, and quantitative analysis of all elements in the periodic table. LIBS can be performed in the laboratory or outside in the ambient environment for on-site analysis in situ; LIBS can also be used for rapid microscale compositional imaging. This review first presents a description of the LIBS technique and then discusses and illustrates through a historic literature review how LIBS has been used to analyze gases, natural waters, minerals, rocks, sediments, and soils. Given the persistent need of analytical instrumentation for the rapid chemical analysis of geologic materials in the field, and the capability of LIBS to analyze any type of sample in real time with little to no preparation, there is a vast potential for the routine application of LIBS across a broad spectrum of the geosciences that is as yet only minimally realized.
DS202108-1287
2021
Harte, B., Helmstaedt, H., Kopylova, M., Moore, A.E.John Gurney - a career of discovery and promotion of scientific knowledge.Lithos, Vol. 398-399, 1p. Africa, South Africa, GlobalTribute, obituary
DS202110-1618
2021
Haugaard, R., Waterton, P., ootes, L., Pearson, D.G., Luo,Y., Konhauser, K.Detrital chromites reveal Slave craton's missing komatite.Geology, Vol. 49, 9, pp. 1079-1083. pdfCanada, Northwest Territorieschromites

Abstract: Komatiitic magmatism is a characteristic feature of Archean cratons, diagnostic of the addition of juvenile crust, and a clue to the thermal evolution of early Earth lithosphere. The Slave craton in northwest Canada contains >20 greenstone belts but no identified komatiite. The reason for this dearth of komatiite, when compared to other Archean cratons, remains enigmatic. The Central Slave Cover Group (ca. 2.85 Ga) includes fuchsitic quartzite with relict detrital chromite grains in heavy-mineral laminations. Major and platinum group element systematics indicate that the chromites were derived from Al-undepleted komatiitic dunites. The chromites have low 187Os/188Os ratios relative to chondrite with a narrow range of rhenium depletion ages at 3.19 ± 0.12 Ga. While these ages overlap a documented crust formation event, they identify an unrecognized addition of juvenile crust that is not preserved in the bedrock exposures or the zircon isotopic data. The documentation of komatiitic magmatism via detrital chromites indicates a region of thin lithospheric mantle at ca. 3.2 Ga, either within or at the edge of the protocratonic nucleus. This study demonstrates the applicability of detrital chromites in provenance studies, augmenting the record supplied by detrital zircons.
DS202109-1470
2021
Helmstaedt, H., Pehrsson, S.J., Stubley, M.P.The Slave Province, Canada - geological evolution of an archean diamondiferous craton.Geological Association of Canada Bookstore, https://gac.ca/publications/bookstore Special Paper 51, 216p. Prices 42.50 member, $75.00 non-member isbn:978-1-897095-89-8Canada, Northwest TerritoriesCraton

Abstract: With its well-exposed geologic record from the Hadean Acasta gneiss complex through to Phanerozoic kimberlites, the Slave craton of northwestern Canada has long been a focus for research into early Earth evolution of both the crust and lithosphere. As a result, it has become one of the most extensively studied Archean cratons in the world. This multidisciplinary volume provides an authoritative overview of the Slave craton literally from the bottom up, integrating the nature of its lithosphere based on kimberlitic mantle samples with its upper crustal geology to provide a new model for its Archean assembly and cratonization. All aspects of Slave craton geology are covered, from the stratigraphy of its famous gold camps to the history of exploration and nature of its world-class diamondiferous kimberlite fields. Detailed and well-illustrated chapters cover its terranes and greenstone belts, magmatism, geophysical character, tectono-metamorphic evolution, and Paleoproterozoic marginal sequences. The book’s wealth of data and up-to-date bibliography provide a unique resource for understanding, researching and teaching Archean geology and subcrustal and cratonic evolution. It elegantly integrates diverse fields to provide one of the most comprehensive models for the craton and the protracted, multiphase formation of its diamond-bearing lithospheric root. (JK Note: the link above takes you to the GAC web site where Special Paper 51 can be purchased. Because the GAC only provides the abstract and a photo of the front page, I am providing a Table of Contents pdf.)
DS202108-1288
2021
Hermann, J., Lakey, S.Water transfer to the deep mantle through hydrous, Al-rich silicates in subduction zones.Geology, Vol. 49, pp. 911-915.Mantlewater

Abstract: Constraining deep-water recycling along subduction zones is a first-order problem to understand how Earth has maintained a hydrosphere over billions of years that created conditions for a habitable planet. The pressure-temperature stability of hydrous phases in conjunction with slab geotherms determines how much H2O leaves the slab or is transported to the deep mantle. Chlorite-rich, metasomatic rocks that form at the slab-mantle interface at 50-100 km depth represent an unaccounted, H2O-rich reservoir in subduction processes. Through a series of high-pressure experiments, we investigated the fate of such chlorite-rich rocks at the most critical conditions for subduction water recycling (5-6.2 GPa, 620-800 °C) using two different natural ultramafic compositions. Up to 5.7 GPa, 740 °C, chlorite breaks down to an anhydrous peridotite assemblage, and H2O is released. However, at higher pressures and lower temperatures, a hydrous Al-rich silicate (11.5 Å phase) is an important carrier to enable water transfer to the deep mantle for cold subduction zones. Based on the new phase diagrams, it is suggested that the deep-water cycle might not be in secular equilibrium.
DS202102-0197
2021
Hill, E.J., Pearce, M.A., Stromberg, J.M.Improving automated geological logging of drill holes by incorporating multiscale spatial methods. ( not specific to diamonds)Mathematical Geosciences, Vol. 53, pp. 21-53. pdfGlobaldrill hole data

Abstract: Manually interpreting multivariate drill hole data is very time-consuming, and different geologists will produce different results due to the subjective nature of geological interpretation. Automated or semi-automated interpretation of numerical drill hole data is required to reduce time and subjectivity of this process. However, results from machine learning algorithms applied to drill holes, without reference to spatial information, typically result in numerous small-scale units. These small-scale units result not only from the presence of very small rock units, which may be below the scale of interest, but also from misclassification. A novel method is proposed that uses the continuous wavelet transform to identify geological boundaries and uses wavelet coefficients to indicate boundary strength. The wavelet coefficient is a useful measure of boundary strength because it reflects both wavelength and amplitude of features in the signal. This means that boundary strength is an indicator of the apparent thickness of geological units and the amount of change occurring at each geological boundary. For multivariate data, boundaries from multiple variables are combined and multiscale domains are calculated using the combined boundary strengths. The method is demonstrated using multi-element geochemical data from mineral exploration drill holes. The method is fast, reduces misclassification, provides a choice of scales of interpretation and results in hierarchical classification for large scales where domains may contain more than one rock type.
DS202105-0766
2021
Hills, S.Fluorescence microscopy: the revolution revolving.Carnegiescience.edu, June 8, 2pm. ESTGlobalfluorescence
DS202102-0198
2021
Hoare, B.C., Tomlinson, E.L., Barnes, J.D., Tappe, S., Marks, M.A.W., Epp, T., Caulfield, J., Riegler, T.Tracking halogen recycling and volatile loss in kimberlite magmatism from Greenland: evidence from combined F-Cl-Br and Delta 37Cl systematics.Lithos, doi;101016/j. lithos.2021.105976 78p. PdfEurope, Greenlandhalogen
DS202109-1471
2019
Hoekstra, Q.Conflict diamonds and the Angolan Civil War (1992-2002).Third World Quarterly, Vol. 40, 7, pp. 1322-1339.Africa, Angolalegal

Abstract: In the early 1990s several rebel groups turned to natural resource extraction to pay for war. A key form of this is rebel diamond production, commonly referred to as conflict diamonds, which is widely perceived as being highly beneficial to insurgent organisations. Yet in the Angolan Civil War (1992-2002), the use of conflict diamonds by the National Union for the Total Independence of Angola (UNITA) resulted in a decisive insurgent defeat. How can this outcome be explained? Offering a nuanced understanding of how conflict diamonds affect civil war, this article shows that although diamonds generated considerable revenue for UNITA, they were not an effective method for them to take on the Angolan government. This was for two reasons: internally, the rebels greatly struggled to convert their diamond proceeds into sufficient goods and services; and externally, it left the group highly vulnerable to international countermeasures in the form of United Nations Security Council sanctions. Natural resource extraction may therefore not be as useful to rebel groups as is frequently believed.
DS202109-1472
2021
Hoffman, P.F., Halverson, G.P., Schrag, D.P., Higgins, J.A., Domack, E.W., Macdonald, F.A., Pruss, S.B., Blattler, C.L., Crockford, P.W., Hodgin, E.B., Bellefroid, E.J., Johnson, B.W., Hodgskiss, M.S.W., Lamothe, K.G., LoBianco, S.J.C., Busch, J.F., HowesSnowballs in Africa: sectioning a long-lived Neoproterozoic carbonate platform and its bathyal foreslope ( NW Namibia). (Octavi Group)Earth Science Reviews , Vol. 219, 103616 231p. PdfAfrica, NamibiaCraton - Congo

Abstract: Otavi Group is a 1.5-3.5-km-thick epicontinental marine carbonate succession of Neoproterozoic age, exposed in an 800-km-long Ediacaran?Cambrian fold belt that rims the SW cape of Congo craton in northern Namibia. Along its southern margin, a contiguous distally tapered foreslope carbonate wedge of the same age is called Swakop Group. Swakop Group also occurs on the western cratonic margin, where a crustal-scale thrust cuts out the facies transition to the platformal Otavi Group. Subsidence accommodating Otavi Group resulted from S?N crustal stretching (770-655?Ma), followed by post-rift thermal subsidence (655-600?Ma). Rifting under southern Swakop Group continued until 650-635?Ma, culminating with breakup and a S-facing continental margin. No hint of a western margin is evident in Otavi Group, suggesting a transform margin to the west, kinematically consistent with S?N plate divergence. Rift-related peralkaline igneous activity in southern Swakop Group occurred around 760 and 746?Ma, with several rift-related igneous centres undated. By comparison, western Swakop Group is impoverished in rift-related igneous rocks. Despite low paleoelevation and paleolatitude, Otavi and Swakop groups are everywhere imprinted by early and late Cryogenian glaciations, enabling unequivocal stratigraphic division into five epochs (period divisions): (1) non-glacial late Tonian, 770-717?Ma; (2) glacial early Cryogenian/Sturtian, 717-661?Ma; (3) non-glacial middle Cryogenian, 661-646?±?5?Ma; (4) glacial late Cryogenian/Marinoan, 646?±?5-635?Ma; and (5) non-glacial early Ediacaran, 635-600?±?5?Ma. Odd numbered epochs lack evident glacioeustatic fluctuation; even numbered ones were the Sturtian and Marinoan snowball Earths. This study aimed to deconstruct the carbonate succession for insights on the nature of Cryogenian glaciations. It focuses on the well-exposed southwestern apex of the arcuate fold belt, incorporating 585?measured sections (totaling >190?km of strata) and?>?8764 pairs of ?13C/?18Ocarb analyses (tabulated in Supplementary On-line Information). Each glaciation began and ended abruptly, and each was followed by anomalously thick ‘catch-up’ depositional sequences that filled accommodation space created by synglacial tectonic subsidence accompanied by very low average rates of sediment accumulation. Net subsidence was 38% larger on average for the younger glaciation, despite its 3.5-9.3-times shorter duration. Average accumulation rates were subequal, 4.0 vs 3.3-8.8?m Myr?1, despite syn-rift tectonics and topography during Sturtian glaciation, versus passive-margin subsidence during Marinoan. Sturtian deposits everywhere overlie an erosional disconformity or unconformity, with depocenters ?1.6?km thick localized in subglacial rift basins, glacially carved bedrock troughs and moraine-like buildups. Sturtian deposits are dominated by massive diamictite, and the associated fine-grained laminated sediments appear to be local subglacial meltwater deposits, including a deep subglacial rift basin. No marine ice-grounding line is required in the 110 Sturtian measured sections in our survey. In contrast, the newly-opened southern foreslope was occupied by a Marinoan marine ice grounding zone, which became the dominant repository for glacial debris eroded from the upper foreslope and broad shallow troughs on the Otavi Group platform, which was glaciated but left nearly devoid of glacial deposits. On the distal foreslope, a distinct glacioeustatic falling-stand carbonate wedge is truncated upslope by a glacial disconformity that underlies the main lowstand grounding-zone wedge, which includes a proximal 0.60-km-high grounding-line moraine. Marinoan deposits are recessional overall, since all but the most distal overlie a glacial disconformity. The Marinoan glacial record is that of an early ice maximum and subsequent slow recession and aggradation, due to tectonic subsidence. Terminal deglaciation is recorded by a ferruginous drape of stratified diamictite, choked with ice-rafted debris, abruptly followed by a syndeglacial-postglacial cap-carbonate depositional sequence. Unlike its Sturtian counterpart, the post-Marinoan sequence has a well-developed basal transgressive (i.e., deepening-upward) cap dolomite (16.9?m regional average thickness, n?=?140) with idiosyncratic sedimentary features including sheet-crack marine cements, tubestone stromatolites and giant wave ripples. The overlying deeper-water calci-rhythmite includes crystal-fans of former aragonite benthic cement ?90?m thick, localized in areas of steep sea-floor topography. Marinoan sequence stratigraphy is laid out over ?0.6?km of paleobathymetric relief. Late Tonian shallow-neritic ?13Ccarb records were obtained from the 0.4-km-thick Devede Fm (~770-760?Ma) in Otavi Group and the 0.7-km-thick Ugab Subgroup (~737-717?Ma) in Swakop Group. Devede Fm is isotopically heavy, +4-8‰ VPDB, and could be correlative with Backlundtoppen Fm (NE Svalbard). Ugab Subgroup post-dates 746?Ma volcanics and shows two negative excursions bridged by heavy ?13C values. The negative excursions could be correlative with Russøya and Garvellach CIEs (carbon isotope excursions) in NE Laurentia. Middle Cryogenian neritic ?13C records from Otavi Group inner platform feature two heavy plateaus bracketed by three negative excursions, correlated with Twitya (NW Canada), Taishir (Mongolia) and Trezona (South Australia) CIEs. The same pattern is observed in carbonate turbidites in distal Swakop Group, with the sub-Marinoan falling-stand wedge hosting the Trezona CIE recovery. Proximal Swakop Group strata equivalent to Taishir CIE and its subsequent heavy plateau are shifted bidirectionally to uniform values of +3.0-3.5‰. Early Ediacaran neritic ?13C records from Otavi Group inner platform display a deep negative excursion associated with the post-Marinoan depositional sequence and heavy values (??+?11‰) with extreme point-to-point variability (?10‰) in the youngest Otavi Group formation. Distal Swakop Group mimics older parts of the early Ediacaran inner platform ?13C records, but after the post-Marinoan negative excursion, proximal Swakop Group values are shifted bidirectionally to +0.9?±?1.5‰. Destruction of positive and negative CIEs in proximal Swakop Group is tentatively attributed to early seawater-buffered diagenesis (dolomitization), driven by geothermal porewater convection that sucks seawater into the proximal foreslope of the platform. This hypothesis provocatively implies that CIEs originating in epi-platform waters and shed far downslope as turbidites are decoupled from open-ocean DIC (dissolved inorganic carbon), which is recorded by the altered proximal Swakop Group values closer to DIC of modern seawater. Carbonate sedimentation ended when the cratonic margins collided with and were overridden by the Atlantic coast-normal Northern Damara and coast-parallel Kaoko orogens at 0.60-0.58?Ga. A forebulge disconformity separates Otavi/Swakop Group from overlying foredeep clastics. In the cratonic cusp, where the orogens meet at a right angle, the forebulge disconformity has an astounding ?1.85?km of megakarstic relief, and km-thick mass slides were displaced gravitationally toward both trenches, prior to orogenic shortening responsible for the craton-rimming fold belt.
DS202109-1473
2021
Hollis, J.C., Kirk;amd, C.., Hartnady, M., Barham, M., Steenfelt, A.Earth's continents share an ancient crustal ancestor.Eos, https://doi.org/10.1029/2021EO162087.Europe, Greenlandgeochronology - zircon

Abstract: The jigsaw fit of Earth’s continents, which long intrigued map readers and inspired many theories, was explained about 60 years ago when the foundational processes of plate tectonics came to light. Topographic and magnetic maps of the ocean floor revealed that the crust—the thin, rigid top layer of the solid Earth—is split into plates. These plates were found to shift gradually around the surface atop a ductile upper mantle layer called the asthenosphere. Where dense oceanic crust abuts thicker, buoyant continents, the denser crust plunges back into the mantle beneath. Above these subduction zones, upwelling mantle melt generates volcanoes, spewing lava and creating new continental crust.
DS202107-1102
2021
Holt, A.F., Condit, C.B.Slab temperature evolution over the lifetime of a subduction zone.Geochemistry, Geophysics, Geosytems, 22p. PdfMantlesubduction

Abstract: The thermal evolution of subducting slabs controls a range of subduction processes, yet we lack a robust understanding of how thermal structure develops over a subduction zone's lifetime. We investigate the time-dependence of slab thermal structure using dynamically consistent, time evolving models. Pressure-temperature (P-T) conditions along the slab Moho and slab top exhibit substantial variability throughout the various phases of subduction: initiation, free sinking, and mature subduction. This variability occurs in response to time-dependent subduction properties (e.g., fast vs. slow convergence) and thermal structure inherited from previous phases (e.g., due to upper plate aging). At a given depth, the slab cools rapidly during initiation, after which slower cooling occurs. In the case of the Moho, additional cooling occurs during the free sinking phase. We explore the implications of time-dependent thermal structure on exhumed rocks and slab dehydration. Modeled slab top P-T paths span much of the P-T space associated with exhumed rocks, suggesting a significant component of recorded variability may have dynamic origins. Coupling our P-T profiles with thermodynamic models of oceanic lithosphere, we show that dehydrating ultramafic rocks at the slab Moho provide the bulk of hydrous fluid at subarc depths during the earliest phases. Over subsequent phases, these rocks carry fluids into the deeper mantle, and it is mafic crust along the slab top that releases water at subarc depths. We conclude that varying subduction conditions, and non-steady-state thermal structure, challenge the utility of kinematically driven models with constant subduction parameters, particularly for investigating thermal structure in the geological past.
DS202101-0015
2020
Houser, C., Hernlund, J.W., Valencia-Cardona, J., Wentzcovitch, R.M.Discriminating lower mantle composition.Physics of the Earth and Planetary Interiors, Vol. 308, 106552, 14p. PdfMantlegeophysics - seismics

Abstract: Constraining Earth's bulk composition is fundamental to understanding our planet's formation and evolution. While the lower mantle accounts for a majority of the bulk silicate Earth, it is also the least accessible. As experimental and theoretical mineral physics constraints on mineral elasticity at lower mantle temperatures and pressures have improved, comparisons between predicted seismic velocity and density profiles for hypothesized bulk compositions and 1D seismic models have become commonplace. However, the degree to which a given composition is a better or worse fit than another composition is not always reported, nor are the influences of the assumed temperature profile and other uncertainties discussed. Here we compare seismic velocities and densities for perovskitite, pyrolite, and harzburgite bulk compositions calculated using advanced ab initio techniques to explore the extent to which the associated uncertainties affect our ability to distinguish between candidate compositions. We find that predicted differences between model compositions are often smaller than the influence of temperature uncertainties and therefore these comparisons lack discriminatory power. The inability to distinguish between compositions is largely due to the high sensitivity of seismic properties to temperature accompanied by uncertainties in the mantle geotherm, coupled with diminished sensitivity of seismic velocity to composition toward the base of the mantle. An important exception is the spin transition in (Mg,Fe)O-ferropericlase, which is predicted to give a distinct variation in compressional wave velocity that should distinguish between relatively ferro-magnesian and silica-rich compositions. However, the absence of an apparent spin transition signature in global 1D seismic profiles is a significant unresolved issue in geophysics, and it has important geochemical implications. The approach we present here for establishing discriminatory power for such comparisons can be applied to any estimate of seismic velocities and associated uncertainties, and offers a straightforward tool to evaluate the robustness of model comparisons.
DS202102-0199
2021
Houser, C., Hernlund, J.W., Valencia-Cardona, J., Wentzcovitch, R.M.Discriminating lower mantle composition.Physics of the Earth and Planetary Interiors, Vol. 308, di.org/10.1016 /jpepi.2020. 106552 14p. PdfMantlegeophysics - seismics

Abstract: Constraining Earth's bulk composition is fundamental to understanding our planet's formation and evolution. While the lower mantle accounts for a majority of the bulk silicate Earth, it is also the least accessible. As experimental and theoretical mineral physics constraints on mineral elasticity at lower mantle temperatures and pressures have improved, comparisons between predicted seismic velocity and density profiles for hypothesized bulk compositions and 1D seismic models have become commonplace. However, the degree to which a given composition is a better or worse fit than another composition is not always reported, nor are the influences of the assumed temperature profile and other uncertainties discussed. Here we compare seismic velocities and densities for perovskitite, pyrolite, and harzburgite bulk compositions calculated using advanced ab initio techniques to explore the extent to which the associated uncertainties affect our ability to distinguish between candidate compositions. We find that predicted differences between model compositions are often smaller than the influence of temperature uncertainties and therefore these comparisons lack discriminatory power. The inability to distinguish between compositions is largely due to the high sensitivity of seismic properties to temperature accompanied by uncertainties in the mantle geotherm, coupled with diminished sensitivity of seismic velocity to composition toward the base of the mantle. An important exception is the spin transition in (Mg,Fe)O-ferropericlase, which is predicted to give a distinct variation in compressional wave velocity that should distinguish between relatively ferro-magnesian and silica-rich compositions. However, the absence of an apparent spin transition signature in global 1D seismic profiles is a significant unresolved issue in geophysics, and it has important geochemical implications. The approach we present here for establishing discriminatory power for such comparisons can be applied to any estimate of seismic velocities and associated uncertainties, and offers a straightforward tool to evaluate the robustness of model comparisons.
DS202112-1930
2021
Howarth, G.H., Nembambula, T.Petrogenesis of Kaapvaal lamproites ( aka orangeites) constrained by the composition of olivine and similarities with kimberlites and other diamondiferous lamproites.Lithos, Vol. 406-407, 106499 13p. PdfAfrica, South Africaorengeites

Abstract: Kaapvaal lamproites, also known as orangeites, are H2O-rich, diamondiferous, highly micaceous, ultrapotassic rocks. Olivines in kimberlites have been shown to be extremely useful in tracking melt evolution, highlighting the importance of the chemical effects of SCLM assimilation on asthenosphere-derived melts. Kaapvaal lamproites are derived from melting metasomatised SCLM and may be expected to form an endmember to the asthenosphere melt-SCLM trend defined by kimberlites. In this contribution, we use olivine composition in Kaapvaal lamproites to further understand melt evolution in the SCLM and assess the similarity between Kaapvaal lamproite, other diamondiferous lamproites, and kimberlite petrogenesis in cratonic regions. We present olivine composition for representative on- and off-craton Kaapvaal lamproites from Finsch and Melton Wold, respectively. Olivines from these Kaapvaal lamproites are characterized by distinct core and rim zones, regardless of the size of individual grains. Polycrystalline grains are abundant at Finsch but relatively rare at Melton Wold. The olivine cores from both occurrences are predominantly Mg-rich (Fo>89) whereas Fe-rich cores (Fo<89) are rare. Mg-rich cores are interpreted to be derived from the disaggregation of mantle peridotites, including sheared peridotites, whereas Fe-rich cores are derived from olivines of the Cr-poor megacryst suite. The average Fo and NiO concentrations of the Melton Wold cores are lower than Finsch cores, likely related to less refractory off-craton mantle. The olivine rims at Finsch and Melton Wold are characterized by reverse zoning with ranges of Fo89-92 and Fo90-91, respectively. The rims are interpreted to represent crystallisation related to a complex interplay between increasing oxidation, assimilation of orthopyroxene, and increasing alkali content of the melt during evolution. The average core and rim compositions of Finsch and Melton Wold, in conjunction with data from diamondiferous lamproites of other cratonic regions, define a broad positive correlation. Kaapvaal lamproites have Mg-rich core and rim compositions, similar to that of Lac de Gras kimberlites, and interpreted to reflect sampling and equilibration of low volume Kaapvaal lamproite melt with refractory mantle. In contrast to Lac de Gras kimberlites, Kaapvaal lamproites have high abundances of groundmass phlogopite that reflect metasomatic material in the SCLM source, likely present as veins within refractory peridotite. This suggests that increasing proportions of melt-metasomatised SCLM interactions are not always linked with increasing Fe content of melts. We show that the petrogenesis of Kaapvaal lamproites is similar to that of kimberlites and lamproites from other cratonic regions, however, the high abundance of phlogopite and Fo-rich olivine rims suggest a distinct metasomatic lithology in the source and that olivine composition; i.e., a proxy for melt composition, may be strongly controlled by melt volume during melt-SCLM interactions.
DS202101-0016
2020
Hu, L., Li, Y., Chuan, M., Li, R., Ke, C., Wu, Z.Post-magmatic fluids dominate the mineralization of dolomite carbonatitic dykes next to the giant Bayan Obo REE deposit, northern China.Minerals MDPI, Vol. 10, 1117, doi:10.3390/ min10121117 20p. PdfChinadeposit - Bayan Obo

Abstract: The Bayan Obo rare earth element (REE) deposit in Inner Mongolia, northern China, is the largest REE deposit in the world, whose mineralization process remains controversial. There are dozens of carbonatite dykes that are tightly related to the deposit. Here we report the petrological and mineralogical characteristics of a typical dolomite carbonatite dyke near the deposit. The dolomite within the dyke experienced intense post-emplacement fluids metasomatism as evidenced by the widespread hydrothermal REE-bearing minerals occurring along the carbonate mineral grains. REE contents of bulk rocks and constituent dolomite minerals (>90 vol.%) are 1407-4184 ppm and 63-152 ppm, respectively, indicating that dolomite is not the dominant mineral controlling the REE budgets of the dyke. There are three types of apatite in the dyke: Type 1 apatite is the primary apatite and contains REE2O3 at 2.35-4.20 wt.% and SrO at 1.75-2.19 wt.%; Type 2 and Type 3 apatites are the products of replacement of primary apatite. The REE2O3 (6.10-8.21 wt.%) and SrO (2.83-3.63 wt.%) contents of Type 2 apatite are significantly elevated for overprinting of REE and Sr-rich fluids derived from the carbonatite. Conversely, Type 3 apatite has decreased REE2O3 (1.17-2.35 wt.%) and SrO (1.51-1.99 wt.%) contents, resulting from infiltration of fluids with low REE and Na concentrations. Our results on the dyke suggest that post-magmatic fluids expelled from the carbonatitic melts dominated the REE mineralization of the Bayan Obo deposit, and a significant fluid disturbance occurred but probably provided no extra REEs to the deposit.
DS202108-1289
2021
Hu, Z., Zeng, L., Foerster, M.W., Li, S., Zhao, L., Gao, L., Li, H., Yang, Y.Recycling of subducted continental crust: geochemical evidence from syn-exhumation Triassic alkaline mafic rocks of the southern Liaodong Peninsula, China.Lithos, 10.1016/j.lithos.2021.106353 13p. Chinaalkaline rocks

Abstract: Syn-exhumation mafic magmatism during continental collision provides insights into the crust-mantle reaction during deep subduction and the nature of orogenic lithospheric mantle in collisional orogens. In this study, we present a comprehensive data set of zircon U-Pb ages and whole-rock major-trace elements as well as Sr-Nd-Pb isotopes of alkaline mafic rocks from the southern Liaodong Peninsula, eastern China. Zircon U-Pb analyses yield Late Triassic age of 213 ± 3 to 217 ± 3 Ma, younger than the Middle Triassic ultrahigh-pressure metamorphic rocks of the Dabie-Sulu orogen. Thus, the alkaline mafic rocks are products of syn-exhumation magmatism during continental collision of the South and North China blocks. The rocks show shoshonitic affinities with high K2O (3.78-5.23 wt%) and K2O/Na2O (0.71-1.22). They are characterized by arc-like trace-element patterns with enriched LILE, Pb, and LREE, and depleted HFSE. They exhibit enriched Sr-Nd isotopic compositions with high initial 87Sr/86Sr isotopic ratios of 0.7058-0.7061 and negative ?Nd(t) values of ?13.0 to ?15.1. These results suggest involvement of recycled continental crust in their mantle source. The mantle source likely formed by the metasomatic reaction of subducted continental crust-derived melts with the overlying subcontinental lithospheric mantle during the Triassic continental collision. Decompressional melting of this metasomatized mantle formed syn-exhumation mafic magmas during the transition from convergent to extensional tectonics in the Late Triassic. Accordingly, mafic rocks from the southern Liaodong Peninsula provide a geochemical record of the subduction and recycling of continental crust into the mantle and melt-mantle reaction induced metasomatism within the orogen.
DS202105-0767
2021
Huang, R., Boffa Ballaran, T., McCammon, C.A., Miyajima, N., Frost, D.J.The composition and redox state of bridgmanite in the lower mantle as a function of oxygen fugacity.Geochimica et Cosmochimica Acta, Vol. 30, pp. 110-136.Mantleredox

Abstract: The chemistry of bridgmanite (Brg), especially the oxidation state of iron, is important for understanding the physical and chemical properties, as well as putting constraints on the redox state, of the Earth’s lower mantle. To investigate the controls on the chemistry of Brg, the Fe3+ content of Brg was investigated experimentally as a function of composition and oxygen fugacity (fo2) at 25 GPa. The Fe3+/?Fe ratio of Brg increases with Brg Al content and fo2 and decreases with increasing total Fe content and with temperature. The dependence of the Fe3+/?Fe ratio on fo2 becomes less steep with increasing Al content. Thermodynamic models were calibrated to describe Brg and ferropericlase (Fp) compositions as well as the inter-site partitioning of trivalent cations in Brg in the Al-Mg-Si-O, Fe-Mg-Si-O and Fe-Al-Mg-Si-O systems. These models are based on equilibria involving Brg components where the equilibrium thermodynamic properties are the main adjustable parameters that are fit to the experimental data. The models reproduce the experimental data over wide ranges of fo2 with a relatively small number of adjustable terms. Mineral compositions for plausible mantle bulk compositions can be calculated from the models as a function of fo2 and can be extrapolated to higher pressures using data on the partial molar volumes of the Brg components. The results show that the exchange of Mg and total Fe (i.e., ferric and ferrous) between Brg and Fp is strongly fo2 dependent, which allows the results of previous studies to be reinterpreted. For a pyrolite bulk composition with an upper mantle bulk oxygen content, the fo2 at the top of the lower mantle is ?0.86 log units below the iron-wüstite buffer (IW) with a Brg Fe3+/?Fe ratio of 0.50 and a bulk rock ratio of 0.28. This requires the formation of 0.7?wt.% Fe-Ni alloy to balance the raised Brg ferric iron content. With increasing pressure, the model predicts a gradual increase in the Fe3+/?Fe ratio in Brg in contrast to several previous studies, which levels off by 50 GPa. Oxygen vacancies in Brg decrease to practically zero by 40 GPa, potentially influencing elasticity, diffusivity and rheology in the top portion of the lower mantle. The models are also used to explore the fo2 recorded by inclusions in diamonds, which likely crystallized as Brg in the lower mantle, revealing oxygen fugacities which likely preclude the formation of some diamonds directly from carbonates, at least at the top of the lower mantle.
DS202101-0017
2020
Hughes, H.S.R., Compton-Jones, C., MvDonald, I., Kiseeva, E.S., Kamenetsky, V.S., Rollinson, G., Coggon, J.A., Kinnaird, J.A., Bybee, G.M.Base metal sulphide geochemistry of southern African mantle eclogites ( Roberts Victor): implications for cratonic mafic magmatism and metallogenesis.Lithos, doi.org/10.1016/ j.lithos.2020.105918 67p. PdfAfrica, South Africadeposit - Roberts Victor

Abstract: Platinum-group elements (PGE) display a chalcophile behaviour and are largely hosted by base metal sulphide (BMS) minerals in the mantle. During partial melting of the mantle, BMS release their metal budget into the magma generated. The fertility of magma sources is a key component of the mineralisation potential of large igneous provinces (LIP) and the origin of orthomagmatic sulphide deposits hosted in cratonic mafic magmatic systems. Fertility of mantle-derived magma is therefore predicated on our understanding of the abundance of metals, such as the PGE, in the asthenospheric and lithospheric mantle. Estimations of the abundance of chalcophile elements in the upper mantle are based on observations from mantle xenoliths and BMS inclusions in diamonds. Whilst previous assessments exist for the BMS composition and chalcophile element budget of peridotitic mantle, relatively few analyses have been published for eclogitic mantle. Here, we present sulphide petrography and an extensive in situ dataset of BMS trace element compositions from Roberts Victor eclogite xenoliths (Kaapvaal Craton, South Africa). The BMS are dominated by pyrite-chalcopyrite-pentlandite (± pyrrhotite) assemblages with S/Se ratios ranging 1200 to 36,840 (with 87% of analyses having S/Se this editing is incorrect. This should read "(with 87% of analyses having S/Se < 10,000)" Please note the 100 ppm) and are characteristically enriched in Os, Ir, Ru and Rh. Nano- and micron-scale Pd-Pt antimonide, telluride and arsenide platinum-group minerals (PGM) are observed spatially associated with BMS. We suggest that the predominance of pyrite in the xenoliths reflects the process of eclogitisation and that the trace element composition of the eclogite BMS was inherited from oceanic crustal protoliths of the eclogites, introduced into the SCLM via ancient subduction during formation of the Colesberg Magnetic Lineament c. 2.9 Ga and the cratonisation of the Kaapvaal Craton. Crucially, we demonstrate that the PGE budget of eclogitic SCLM may be substantially higher than previously reported, akin to peridotitic compositions, with significant implications for the PGE fertility of cratonic mafic magmatism and metallogenesis. We quantitatively assess these implications by modelling the chalcophile geochemistry of an eclogitic melt component in parental magmas of the mafic Rustenburg Layered Suite of the Bushveld Complex.
DS202101-0018
2020
Humbert, F., Elburg, M.A., Agangi, A., Belyanin, G., Akoh, J., Smith, A.J.B., Chou, Y-M., Beukes, N.J.A ~ 1.4 Ga alkaline mafic sill from the Carletonville area: connection to the Pilanesbeg alkaline province?South African Journal of Geology, Vol. 123, 4, pp. 597-614. pdfAfrica, South Africaalkaline rocks

Abstract: Numerous Mesoproterozoic alkaline intrusions belonging to the Pilanesberg Alkaline Province are present within the Transvaal sub-basin of the Kaapvaal Craton. The Pilanesberg Complex is the best-known example; it represents one of the world’s largest alkaline complexes, and is associated with a northwest-southeast trending dyke swarm that extends from Botswana to the southwest of Johannesburg. This paper documents the results of a petrological and geochemical study of a thin mafic sill (here referred to as an alkaline igneous body, AIB), which intrudes the ca. 2 200 Ma Silverton Formation close to the southernmost part of the Pilanesberg dyke swarm. The AIB has only been observed in cores from a borehole drilled close to Carletonville. It is hypocrystalline, containing randomly oriented elongated skeletal kaersutite crystals and 6 to 8 mm varioles mainly composed of radially oriented acicular plagioclase. These two textures are related to undercooling, probably linked to the limited thickness (70 cm) of the AIB coupled with a probable shallow emplacement depth. Ar-Ar dating of the kaersutite gives an age of ca. 1 400 Ma, similar to the age of Pilanesberg Complex. However, the AIB is an alkaline basaltic andesite and is thus notably less differentiated than the Pilanesberg Complex and some of its associated dykes, such as the Maanhaarrand dyke, for which we provide whole-rock geochemical data. Literature data indicate that the Pilanesberg dyke swarm also contains mafic hypabyssal rocks suggesting a link between the dyke swarm and the AIB. The AIB is characterized by strongly negative ?Nd and ?Hf, that cannot be related to crustal contamination, as shown by positive Ti and P anomalies, and the absence of negative Nb-Ta anomalies in mantle-normalised trace element diagrams. The AIB magma is interpreted to have been derived from a long-lived enriched, probably lithospheric mantle reservoir. The AIB thus provides important information on the magma source of the Pilanesberg Alkaline Province.
DS202106-0943
2021
Illa, B., Reshma, K.S., Kumar, P., Srinagesh, D., Haldar, C., Kumar, S., Mandal, P.Pn tomography and anisotropic study of the Indian Shield and the adjacent regions.Tectonophysics, Vo. 813, 228932 23p. PdfIndiatomography

Abstract: High-resolution P-wave velocity and anisotropy structure of the hitherto elusive uppermost mantle beneath the Indian shield and its surrounding regions are presented to unravel the tectonic imprints in the lithosphere. We inverted high quality 19,500 regional Pn phases from 172 seismological stations for 4780 earthquakes at a distance range of 2° to 15° with a mean apparent Pn velocity of 8.22 km/s. The results suggest that the Pn velocity anomalies with fast anisotropic directions are consistent with the collision environments in the Himalaya, Tibetan Plateau, Tarim Basin, and Burmese arc regions. The higher Pn anomalies along the Himalayan arc explicate the subducting cold Indian lithosphere. The cratonic upper mantle of the Indian shield is characterized by Pn velocity of 8.12-8.42 km/s, while the large part of the central Indian shield has higher mantle-lid velocity of ~8.42 km/s with dominant anisotropic value of 0.2-0.3 km/s (~7.5%) suggesting the presence of mafic ‘lava pillow’ related to the Deccan volcanism. The impressions of the rifts and the mobile belts are conspicuous in the velocity anomaly image indicating their deep seated origin. The Pn anisotropy in the Indian shield exhibits a complex pattern and deviates from the absolute plate motion directions derived from the SKS study, demonstrating the presence of frozen anisotropy in the Indian lithospheric uppermost mantle, due to the large scale tectonic deformation after its breakup from the Gondwanaland. Whereas, Pn and SKS anisotropic observations are well consistent in Tarim basin, Tibetan regions, eastern Himalayan syntaxis and the Burmese arc. The modeled anisotropic Pn clearly manifests a lower velocity anomaly bounded by 85°E and 90°E ridges in the southern Bay of Bengal. Further, 85°E ridge spatially separates the BoB lithosphere into faster and slower regions consistent with the body wave tomography and free-air gravity observation.
DS202108-1290
2021
Ionov, D.A., Wang, K.Potassium distribution and isotope composition in the lithospheric mantle in relation to global Earth's reservoirs.Geochimica et Cosmochimica Acta, doi.org/10.1016/j.gca.2021.06.033 49p. PdfMantlepotassium
DS202107-1103
2021
Ivanov, A.V., Corfu, F., Kamenetsky, V.S., Marfin, A.E., Vladykin, N.V.207Pb-excess in carbonatitic baddeleyite as the result of Pa scavenging from the melt. ( Guli Siberian traps)Geochemical Perspectives Letters, Vol. 18, pp. 11-15. pdfRussia, Siberiacarbonatite

Abstract: For the last two decades, the end of the voluminous phase of eruptions of the Siberian Traps large igneous province has been constrained by a U-Pb date of discordant baddeleyite collected from the Guli carbonatite intrusion with the assumption that the discordance resulted from unsupported 207Pb. In this study we have re-analysed baddeleyite from the same intrusion and found two types of discordance: (1) due to 207Pb-excess, and (2) radiogenic lead loss from high U mineral inclusions. The former implies that baddeleyite is an efficient scavenger of protactinium during crystallisation, leaving the magma depleted in this element. Together with a published high precision U-Pb date of 252.24?±?0.08 Ma for the Arydzhansky Formation, our new date of 250.33?±?0.38 Ma for the Guli carbonatite constrains the total duration of the voluminous eruptions of the Siberian Traps LIP at 1.91?±?0.38 million years. The lower intercept of the (231Pa)/(235U) corrected discordance line yields a date of 129.2?±?65.0 Ma, which points to the widespread Early Cretaceous rifting in East and Central Asia.
DS202109-1474
2020
Ivanov, A.V., Corfu, F., Kamenetsky, V.S., Marfin, A.E., Vladykin, N.V.207 Pb-excess in carbonatitic baddeleyite as the result of Pa scavenging from the melt.Geochemical Perspectives Letters, Vol. 18, pp. 11-15. pdfRussia, Siberiadeposit - Guli

Abstract: For the last two decades, the end of the voluminous phase of eruptions of the Siberian Traps large igneous province has been constrained by a U-Pb date of discordant baddeleyite collected from the Guli carbonatite intrusion with the assumption that the discordance resulted from unsupported 207Pb. In this study we have re-analysed baddeleyite from the same intrusion and found two types of discordance: (1) due to 207Pb-excess, and (2) radiogenic lead loss from high U mineral inclusions. The former implies that baddeleyite is an efficient scavenger of protactinium during crystallisation, leaving the magma depleted in this element. Together with a published high precision U-Pb date of 252.24?±?0.08 Ma for the Arydzhansky Formation, our new date of 250.33?±?0.38 Ma for the Guli carbonatite constrains the total duration of the voluminous eruptions of the Siberian Traps LIP at 1.91?±?0.38 million years. The lower intercept of the (231Pa)/(235U) corrected discordance line yields a date of 129.2?±?65.0 Ma, which points to the widespread Early Cretaceous rifting in East and Central Asia.
DS202106-0944
2021
Jelsma, H.A., Nesbitt, R.W., Fanning, C.M.Exploring our current understanding of the geological evolution and mineral endowment of the Zimbabwe craton.South African Journal of Geology, Vol. 124, 1, pp. 279-301. pdfAfrica, Zimbabwecraton

Abstract: A.M. Macgregor (1888-1961) is remembered for his enormous contribution to geology. His maps changed the course of geological thinking in southern Africa. Following in his footsteps we examine aspects of our current understanding of the geological evolution of the Zimbabwe Craton and, using new SHRIMP U-Pb ages of zircons from felsic volcanic and plutonic rocks from northern Zimbabwe and unpublished data related to the seminal paper by Wilson et al. (1995), a synthesis is proposed for the formation of the Neoarchaean greenstones. The data suggest marked differences (lithostratigraphy, geochemistry and isotope data, mineral endowment and deformational history), between Eastern and Western Successions, which indicate fundamentally different geodynamic environments of formation. The Eastern Succession within the southcentral part of the craton, largely unchanged in terms of stratigraphy, is reminiscent of a rift-type setting with the Manjeri Formation sediments and overlying ca. 2 745 Ma Reliance Formation komatiite magmatism being important time markers. In contrast, the Western Succession is reminiscent of a convergent margin subduction-accretion system with bimodal mafic-felsic volcanism and accompanying sedimentation constrained to between 2 715 and 2 683 Ma. At ca. 2 670 Ma, a tectonic switch likely marks the onset of deposition of Shamvaian felsic volcanism and sedimentation. The Shamvaian resembles pull-apart basin successions and is dominated by deposition of a coarse clastic sedimentary succession, with deposition likely constrained to between 2 672 and 2 647 Ma. The late tectonic emplacement of small, juvenile multiphase stocks, ranging in composition from gabbroic to granodioritic was associated with gold ± molybdenum mineralisation. Their emplacement at 2 647 Ma provides an upper age limit to the timespan of Shamvaian deposition. Amongst the youngest granites are the extensive, largely tabular late- to post-tectonic ca. 2 620 to 2 600 Ma Chilimanzi Suite granites. These granites are characterised by evolved isotopic systems and have been related to crustal relaxation and anatexis following deformation events. After their emplacement, the Zimbabwe Craton cooled and stabilised, with further deformation partitioned into lower-grade, strike-slip shear zones, and at ca. 2 575 Ma the craton was cut by the Great Dyke, its satellite dykes and related fractures.
DS202108-1291
2021
Jennings, S.J.A., Hambrey, M.J.Structures and deformation in glaciers and ice sheetsReviews of Geophysics, e2021RG000743 1Globalgeomorphology

Abstract: The major structures in the long, narrow tongue of a sub-polar valley glacier are described: namely, longitudinal foliation, crevasses, clear-ice layers related to crevasses, debris-rich layers (frequently referred to as thrust or shear planes in the past), and folds. The foliation is vertical, is as well-developed in the centre of the glacier as at the margins, and does not, apparently, form perpendicular to the principal compressive strain-rate axis, nor exactly parallel to a line of maximum shearing strain-rate, although it sometimes approximately coincides with the latter. The intensity of foliation development is not related to the magnitude of the strain-rates, but the structure consistently lies parallel to flow lines through the glacier. There is no critical extending strain-rate, as such, associated with the development of new crevasses. Some crevasses have formed where the principal extending strain-rate is as low as 0.004 a-1 while, in other areas, extending strain-rates of 0.163 a-1 have not always resulted in fracturing. Prominent clear-ice layers, referred to as crevasse traces as displayed at the glacier surface, have formed in crevasse belts parallel to the main fracture directions. These are interpreted either as tensional veins or as the result of the freezing of water in crevasses. Extension parallel to the layering occurs during flow and, near the snout, the surface dip decreases rapidly. The fact that the crevasse traces can be followed to the snout implies that fracture occurs almost to the bottom of the glacier in the source area of the traces. Near the snout, debris-rich layers have developed parallel to the crevasse traces; frequently these are marked by prominent ridge-like ice-cored moraines. It is suggested that these structures are formed by a combination of basal freezing and thrusting. Isoclinal and tight similar folds on all scales are present. Some may be formed by the passive deformation of clear-ice layers as a result of differential flow; others may arise from the lateral compression of the original stratification in areas where ice flow becomes constricted by the narrowing of the valley. An axial plane foliation sometimes is associated with these folds.
DS202109-1475
2021
Jiang, J., Muir, J.M.R., Zhang, F.Vibrational and thermodynamic properties of hydrous iron-bearing lowermost mantle minerals.MDPI Minerals, Vol. 11, 11080885 14p. PdfMantlebridgmanite

Abstract: The vibrational and thermodynamic properties of minerals are key to understanding the phase stability and the thermal structure of the Earth’s mantle. In this study, we modeled hydrous iron-bearing bridgmanite (Brg) and post-perovskite (PPv) with different [Fe3+-H] defect configurations using first-principles calculations combined with quasi-harmonic approximations (QHA). Fe3+-H configurations can be vibrationally stable in Brg and PPv; the site occupancy of this defect will strongly affect its thermodynamic properties and particularly its response to pressure. The presence of Fe3+-H introduces distinctive high-frequency vibrations to the crystal. The frequency of these peaks is configuration dependence. Of the two defect configurations, [Fe?Si+OH?] makes large effects on the thermodynamic properties of Brg and PPv, whereas [V??Mg+Fe?Mg+OH?] has negligible effects. With an expected lower mantle water concentrations of <1000 wt. ppm the effect of Fe3+-H clusters on properties such as heat capacity and thermal expansion is negligible, but the effect on the Grüneisen parameter ? can be significant (~1.2%). This may imply that even a small amount of water may affect the anharmonicity of Fe3+-bearing MgSiO3 in lower mantle conditions and that when calculating the adiabaticity of the mantle, water concentrations need to be considered.
DS202105-0768
2020
Jiang, S. Su, H., Xiong, Y., Liu, T., Zhu, K., Zhang, L.Spatial temporal distribution, geological characteristics and ore formation controlling factors of major types of rare metal mineral deposits in China.Acta Geologica Sinica, Vol. 94, 6, pp. 1757-1773.ChinaREE

Abstract: Rare metals including Lithium (Li), Beryllium (Be), Rubidium (Rb), Cesium (Cs), Zirconium (Zr), Hafnium (Hf), Niobium (Nb), Tantalum (Ta), Tungsten (W) and Tin (Sn) are important critical mineral resources. In China, rare metal mineral deposits are spatially distributed mainly in the Altay and Southern Great Xingán Range regions in the Central Asian orogenic belt; in the Middle Qilian, South Qinling and East Qinling mountains regions in the Qilian-Qinling-Dabie orogenic belt; in the Western Sichuan and Bailongshan-Dahongliutan regions in the Kunlun-Songpan-Garze orogenic belt, and in the Northeastern Jiangxi, Northwestern Jiangxi, and Southern Hunan regions in South China. Major ore?forming epochs include Indosinian (mostly 200-240 Ma, in particular in western China) and the Yanshanian (mostly 120-160 Ma, in particular in South China). In addition, Bayan Obo, Inner Mongolia, northeastern China, with a complex formation history, hosts the largest REE and Nb deposits in China. There are six major rare metal mineral deposit types in China: Highly fractionated granite; Pegmatite; Alkaline granite; Carbonatite and alkaline rock; Volcanic; and Hydrothermal types. Two further types, namely the Leptynite type and Breccia pipe type, have recently been discovered in China, and are represented by the Yushishan Nb-Ta- (Zr-Hf-REE) and the Weilasituo Li-Rb-Sn-W-Zn-Pb deposits. Several most important controlling factors for rare metal mineral deposits are discussed, including geochemical behaviors and sources of the rare metals, highly evolved magmatic fractionation, and structural controls such as the metamorphic core complex setting, with a revised conceptual model for the latter.
DS202105-0769
2021
Johnson, K., Donatti-Filho, J.P.Brauna 3 mine - South America's first diamond mine developed on a kimberlite deposit.Vancouver Kimberlite Cluster recorded, https://diamonds.eoas. ubc.ca/vancouver kimberliteclusterSouth America, Brazildeposit - Brauna

Abstract: Brazil hosts 1365 kimberlite or kimberlite-like bodies, as well as alluvial diamond deposits that have historically produced the bulk of Brazil's diamond production. Only five kimberlites have been subjected to bulk sampling evaluation using current exploration techniques and diamond recovery technology. The first of these kimberlite deposits to reach commercial production was the Brauna 3 kimberlite, with U-Pb age of 642±6 Ma elocated in the State of Bahia and owned and operated by Lipari Mineracao Ltds. The brauna mine commenced commercial production in 2016 at a capital cost of US $ 65 million, and to date has produced approximately 830,000 cts at an average recovered diamond grade of 21 cpht. The Brauna cluster features two pipe-like bodies, Brauna 3 and Brauna 7, and 22 kimberlite dyke occurrences located on the NE part of the Sao Francisco craton. A robust geological model delineates the Brauna 3 kimberlite pipe to depths of 550 and 410 m below surface for the South and Central-North Lobes, respectively. The geological model reveals a issregularly shapes kimberlite pipe which is structurally controlled by the NW trending strutural lineaments. petrographuic study of the Brauna 3 kimberlite has identified volcaniclastic and coherent kimberlites coexisting in a complex root to diatreme transition zone. The kimberlite is mineralogically close to Group 2 kimberlite containing olivine, spinel, ilmenite, phlogopite, perovskite, apatite, melilite, serpentine, carbonate and sulfates. Geochemically, the Brauna 3 kimberlite is transitional between Group 1 and Group 2 rocks.
DS202106-0945
2021
Joshi, K.B., Goswami, V., Bannerji, U.S., Shankar, R.Recent developments in instrumentation and its application in absolute dating: historical perspective and overview.** not specific to diamondsJournal of Asian Earth Sciences, Vol. 211, 104690, 23p. PdfGlobalradiometric dating

Abstract: The discovery of radioactivity in the early 20th century led to the development of several radiometric dating methods (e.g., Rb-Sr, Sm-Nd, Re-Os, U-Pb, etc.). These radiometric dating methods are frequently used in earth science studies to constrain the deposition/formation timing of various natural archives (e.g., bulk rocks, minerals, carbonaceous materials, detrital clastic sedimentary materials, ore deposits, hydrocarbon deposits). The last few decades have witnessed significant improvements in overall accuracy and precision of these absolute radiometric dating methods due to continuous developments and refinements in sample processing and analytical techniques. In this contribution, we discuss some of the frequently used radiometric dating techniques for obtaining absolute ages in various natural archives and associated advancements in the instrumentation. The present attempt emphasizes on a multi-mineral and multi-isotopic approach with continuous developments in obtaining better precision and accuracy in the ages through improved analytical and measurement protocols that are the pre-requisite in absolute dating.
DS202102-0200
2020
Joshi, K.B., Sorcar, N., Pant, N.C., Nandakumar, V., Ahmad, T., Tomson, J.K.Characterization of multiple episodes of melt generation from lower crust during Archean using amphibole composition.Episodes, doi.org/10.18814/ epiiugs/2020 /020092 24p. PdfIndiaCraton - Bundelkhand

Abstract: Spatial association of tonalite trondhjemite granodiorites (TTGs) and high-K granitoids (anatectic and hybrid granites) from the Bundelkhand Craton (BC), Central India, is well known. Geochronological data indicates multiple episodes of formation of these high silica rocks showing a spread of ~1 Ga during Paleo to Neoarchaean. In the present study, we try to understand the evolution of TTGs and high-K granitoids (hybrid granites) from the BC using amphibole composition. The amphibole in both TTGs and high-K granitoids (hybrid granites) from the BC are characterised as magmatic, zoned, and calcic in nature. We find that the amphibole composition of the studied rocks is dominated by magnesiohornblende along with less common occurrence of tschermakite, magnesiohastingsite and edenite. Overall variation in amphibole compositions in terms of exchange vectors show a well defined linear trend (except for a late stage low-grade metamorphic readjustment), which suggests melt control over crystallization and evolution of amphibole chemistry. Moreover, the geothermobarometric analysis points towards higher pressure formation of TTGs in comparison to that of high-K granitoids (hybrid granites), with nearly the same temperature conditions in both the cases. Combining all our findings, we propose the evolution of the two considered rock types through lower crustal melting under varying PH2O conditions at different depths of emplacement.
DS202105-0770
2021
Jowitt, S.M., McNulty, B.A.Geology and mining: mineral resources and reserves: their estimation, use, and abuse. *** not specific to diamonds .. Of interest for studentsSEG Discovery, No. 125, April pp. 27-36. pdfGlobaloverview

Abstract: Resource and reserve estimation is a critical step in mine development and the progression from mineral exploration to commodity production. The data inputs typically change over time and reflect variations in geoscientific knowledge as well as the modifying factors required by regulation for estimating a reserve. These factors include mineral (ore) processing, metallurgical treatment of the ore, infrastructure requirements for mine and workforce, and the transportation of processed products to buyers; others that will affect the production of metals and/or minerals from a deposit include economic, marketing, legal, environmental, social, and governmental factors. All are needed by the mining industry to quantify the contained mineralization within mineral deposits that likely warrant the significant capital investment required to build a mine. However, these resource and reserve data are estimates that change over time due to unpredicted variations in the initial inputs. Paramount to the two estimates are the quality and accuracy of the geologic inputs and the communication of these to the professionals tasked with making each estimate. Geostatistical processing of the grade of the resource has become a dominant element of the estimation process, but this requires transparent and informed communication between geologists and mining engineers with the geostatistician responsible for mathematically processing the grade data. Regulatory constraints also mean that estimated resources and reserves seldom capture the full extent of a mineral deposit. Similarly, co- and by-product metals and minerals that are commonly produced by mines may not be captured by resource and reserve estimates because of their limited economic contribution. This suggests that reporting standards for co- and by-products—particularly for the critical metals that may have a sharp increase in demand—need improvement. Finally, the importance of these data to the mining industry is such that informing investors and the broader public about the nature of resource and reserve estimates, and the meaning of associated terminology, is also essential when considering the global metal and mineral supply, and the role of mining in modern society.
DS202112-1931
2021
Kaempfer, K.M., Guentthner, W.R., Pearson, D.R.Proterozoic to Phanerozoic tectonism in southwestern Montana basement and ranges constrained by low temperature thermochronometric data.Tectonics, Vol. 40, 11 22021TC006744United States, Montanageothermometry

Abstract: Crystalline basement rocks of southwestern Montana have been subjected to multiple tectonothermal events since ?3.3 Ga: the Paleoproterozoic Big Sky/Great Falls orogeny, Mesoproterozoic extension associated with Belt-Purcell basin formation, Neoproterozoic extension related to Rodinia rifting, and the late Phanerozoic Sevier-Laramide orogeny. We investigated the long-term (>1 Ga), low-temperature (erosion/burial within 10 km of the surface) thermal histories of these tectonic events with zircon and apatite (U-Th)/He thermochronology. Data were collected across nine sample localities (n = 55 zircon and n = 26 apatite aliquots) in the northern and southern Madison ranges, the Blacktail-Snowcrest arch, and the Tobacco Root uplift. Our zircon (U-Th)/He data show negative trends between single aliquot date and effective uranium (a radiation damage proxy), which we interpreted with a thermal history model that considers the damage-He diffusivity relationship in zircon. Our model results for these basement ranges show substantial cooling from temperatures above 400°C to near surface conditions between 800 and 510 Ma. Subsequent Phanerozoic exhumation culminated by ?75 Ma. Late Phanerozoic cooling is coincident with along-strike Sevier belt thin-skinned thrusting in southeastern Idaho, and older than exhumation in basement-involved uplifts of the Wyoming Laramide province. Our long-term, low-temperature thermal record for these southwestern Montana basement ranges shows that: (a) these basement blocks have experienced multiple episodes of upper crustal exhumation and burial since Archean time, possibly influencing Phanerozoic thrust architecture and (b) the late Phanerozoic thick-skinned thrusting recorded by these rocks is among the earliest thermochronologic records of Laramide basement-involved shortening and was concomitant with Sevier belt thin-skinned thrusting.
DS202101-0019
2020
Kalugina, A.D., Zedgenizov, D.A.Micro-Raman spectroscopy assessment of chemical compounds of mantle clinopyroxenes. ( diamond)Minerals MDPI, Vol. 10, 1084, doi:10.3390/ min10121084 10p. PdfMantlespectroscopy

Abstract: The composition of clinopyroxenes is indicative for chemical and physical properties of mantle substrates. In this study, we present the results of Raman spectroscopy examination of clinopyroxene inclusions in natural diamonds (n = 51) and clinopyroxenes from mantle xenoliths of peridotites and eclogites from kimberlites (n = 28). The chemical composition of studied clinopyroxenes shows wide variations indicating their origin in different mantle lithologies. All clinopyroxenes have intense Raman modes corresponding to metal-oxygen translation (~300-500 cm?1), stretching vibrations of bridging O-Si-Obr (?11~670 cm?1), and nonbridging atoms O-Si-Onbr (?16~1000 cm?1). The peak position of the stretching vibration mode (?11) for the studied clinopyroxenes varies in a wide range (23 cm?1) and generally correlates with their chemical composition and reflects the diopside-jadeite heterovalent isomorphism. These correlations may be used for rough estimation of these compounds using the non-destructive Raman spectroscopy technique.
DS202112-1932
2021
Kaminsky, F.V., Voropaev, S.A.Modern concepts on diamond genesis.Geochemistry International, Vol. 59, 11, pp. 1038-1051. pdfGlobaldiamond genesis
DS202108-1292
2021
Kaminsky, F.V., Zedgenizov, D.A.Composition, structure and dynamics of the Earth's lower mantle. Introduction for special issueLithos, https://doi.org/ 10.1016/j.lithos. 2021.106335, 4p. PdfMantlegeodynamics

Abstract: The issue is devoted to new data on composition, structure and dynamics of the Earth’s lower mantle. The Earth’s lower mantle is the largest portion of our planet, comprising more than 50 % of its volume, but major questions remain as to chemical composition, thermal regime and global heterogeneity, as well as to its role in controlling mantle dynamic processes. The composition of the lower mantle is now understood to be more complex than had been suggested in theoretic and experimental works based solely on ‘pyrolitic’ compositions. Little is known about lower-mantle mineralogy and phase chemistry, especially at greater depth. Recent studies of inclusions in so-called superdeep diamonds have revealed a range of mineral associations having their specific geochemical features. Aside from a few inclusions found in diamonds, the mineralogy of the lower mantle is, for the most part, inferred from the results of theoretic and experimental data resembling natural environments. This volume presents new results on all aspects of composition of lower mantle including high pressure measurements, petrology and geochemistry, as well as numerical modelling of both the propagation of seismic waves and the geochemical composition and physical state of the deepest mantle rocks.
DS202110-1619
2020
Kane, R.E.America's Royal Gem: Montana and Yogo sapphires.www.gemstone.org/ incolormagazine.com, Vol. 45, p. 30-39. pdfUnited States, Montanasapphires
DS202101-0020
2020
Karato, S-i., Karki, B., Park, J.Deep mantle melting, global water circulation and its implications for the stability of the ocean mass.Progress in Earth and Planetary Science, Vol. 7, 76 25p. Doi.org/10.1186 /s40645-020-00379-3 pdfMantlewater

Abstract: Oceans on Earth are present as a result of dynamic equilibrium between degassing and regassing through the interaction with Earth’s interior. We review mineral physics, geophysical, and geochemical studies related to the global water circulation and conclude that the water content has a peak in the mantle transition zone (MTZ) with a value of 0.1-1 wt% (with large regional variations). When water-rich MTZ materials are transported out of the MTZ, partial melting occurs. Vertical direction of melt migration is determined by the density contrast between the melts and coexisting minerals. Because a density change associated with a phase transformation occurs sharply for a solid but more gradually for a melt, melts formed above the phase transformation depth are generally heavier than solids, whereas melts formed below the transformation depth are lighter than solids. Consequently, hydrous melts formed either above or below the MTZ return to the MTZ, maintaining its high water content. However, the MTZ water content cannot increase without limit. The melt-solid density contrast above the 410 km depends on the temperature. In cooler regions, melting will occur only in the presence of very water-rich materials. Melts produced in these regions have high water content and hence can be buoyant above the 410 km, removing water from the MTZ. Consequently, cooler regions of melting act as a water valve to maintain the water content of the MTZ near its threshold level (~?0.1-1.0 wt%). Mass-balance considerations explain the observed near-constant sea-level despite large fluctuations over Earth history. Observations suggesting deep-mantle melting are reviewed including the presence of low-velocity anomalies just above and below the MTZ and geochemical evidence for hydrous melts formed in the MTZ. However, the interpretation of long-term sea-level change and the role of deep mantle melting in the global water circulation are non-unique and alternative models are reviewed. Possible future directions of studies on the global water circulation are proposed including geodynamic modeling, mineral physics and observational studies, and studies integrating results from different disciplines.
DS202106-0946
2021
Kargin, A.V.Multistage mantle metasomatism during the generation of kimberlite melts: evidence from mantle xenoliths and megacrysts of the Grib kimberlite, Arkangelsk, Russia.Petrology, Vol. 29, 3, pp. 221-245. pdfRussia, Arkhangelskdeposit - Grib

Abstract: Major and trace element compositions of garnet, clinopyroxene, orthopyroxene, phlogopite, and ilmenite from garnet peridotite, ilmenite-bearing peridotite (dunites), and clinopyroxene-phlogopite xenoliths, as well as megacrysts of these minerals from the Grib kimberlite, Arkhangelsk diamond province, Russia, have been analyzed. These data are used to propose a model for mantle metasomatism of lithospheric mantle by kimberlite melts, including their generation and evolution, geochemical enrichment of depleted lithosphere mantle, and formation of megacrystic assemblage. The lithospheric mantle beneath the Arkhangelsk diamond province, from its base (depth ~180-210 km) to a depth of ~100-120 km (corresponding to a pressure of 3.5 GPa) experienced extensive metasomatism along the main kimberlite melt channel. Petrography of the peridotite xenoliths indicates a progressive refertilization of depleted harzburgite into garnet lherzolite, phlogopite-garnet wehrlite, and clinopyroxene-phlogopite rocks. Metasomatic refertilization occurred shortly before the capture of these xenoliths by the kimberlite melt. The model melt compositions calculated from garnet-clinopyroxene equilibria in different types of xenoliths and megacrysts show that alkaline-carbonate-ultramafic kimberlite melt acted as a metasomatic agent in the sheared peridotite at the base of the lithospheric mantle. High-Ti garnet and high-Cr clinopyroxene megacrysts in the middle part of the lithospheric mantle, as well as the main volume of garnet lherzolite xenoliths were formed in geochemical equilibrium with the kimberlite melts, which demonstrate an increase of silicate components and fractionation of Fe-Ti phases. The modification could be related to the interaction of ascending carbonate-rich protokimberlite melts with surrounding lithospheric mantle. The similarities in the compositions of garnet, clinopyroxene, phlogopite, and ilmenite megacrysts with minerals of peridotite xenoliths in the Grib kimberlite suggest that these megacrysts are disintegrated fragments of coarsest grained metasomatized garnet lherzolite, ilmenite-bearing peridotite, and clinopyroxene-phlogopite mantle rocks or formed under the same conditions as xenoliths or directly crystallized from metasomatic melts.
DS202107-1104
2021
Kargin, A.V., Nosova, A.A., Sazonova, L.V., Tretyachenko, V.V., Larinova, Y.O., Kovalchuk, E.V.Ultramafic alkaline rocks of Kepino cluster, Arkhangelsk, Russia: different evolution of kimberlite melts in sills and pipes.Minerals MDPI, Vol. 11, 540, 33p. PdfRussia, Arkhangelskdeposit - Kepino

Abstract: To provide new insights into the evolution of kimberlitic magmas, we have undertaken a detailed petrographic and mineralogical investigation of highly evolved carbonate-phlogopite-bearing kimberlites of the Kepino cluster, Arkhangelsk kimberlite province, Russia. The Kepino kimberlites are represented by volcanoclastic breccias and massive macrocrystic units within pipes as well as coherent porphyritic kimberlites within sills. The volcanoclastic units from pipes are similar in petrography and mineral composition to archetypal (Group 1) kimberlite, whereas the sills represent evolved kimberlites that exhibit a wide variation in amounts of carbonate and phlogopite. The late-stage evolution of kimberlitic melts involves increasing oxygen fugacity and fluid-phase evolution (forming carbonate segregations by exsolution, etc.). These processes are accompanied by the transformation of primary Al- and Ti-bearing phlogopite toward tetraferriphlogopite and the transition of spinel compositions from magmatic chromite to magnesian ulvöspinel and titanomagnetite. Similar primary kimberlitic melts emplaced as sills and pipes may be transitional to carbonatite melts in the shallow crust. The kimberlitic pipes are characterised by low carbonate amounts that may reflect the fluid degassing process during an explosive emplacement of the pipes. The Kepino kimberlite age, determined as 397.3 ± 1.2 Ma, indicates two episodes of ultramafic alkaline magmatism in the Arkhangelsk province, the first producing non-economic evolved kimberlites of the Kepino cluster and the second producing economic-grade diamondiferous kimberlites.
DS202111-1771
2021
Kasuma, K.N., Prasath, H.L.R.Application of feature based principal component analysis (FPCA) technique on Landsat8 OLI multispectral data to map kimberlite pipes.Indian Journal of Science and Technology, 12p. PdfIndiaCraton - Dharwar

Abstract: Objectives: To map the kimberlite pipes emplaced in parts of Anantpur District, India using Landsat-8 OLI multispectral data. Kimberlite are considered as the primary host of natural diamond. Kimberlite pipes have very limited exposure and are altered, therefore the indirect surface indicators associated with kimberlite such as ferric iron bearing minerals (hematite, goethite), hydroxyl (clay) and carbonate (calcrete) minerals, were mapped to trace kimberlite pipe. Methods: Feature based Principal Component Analysis (FPCA) was applied over the OLI bands 2, 4, 5 and 6, and 2, 5, 6 and 7 to generate ferric iron (F image) and hydroxyl/carbonate image (H/C images). The color composite was generated by assigning RGB colours to F, H/C and F+H/C images. Findings: When matched with the pre-explored kimberlite pipe locations, it was observed that the kimberlitic pipes display different colours in the above colour composite. Hence, the Isodata clustering was carried out to segregate the classes, which resulted in 12 unique classes. Of these, the kimberlite pipes fall in 4 classes. However, due to the moderate resolution of OLI, false positive areas were also noted. Further the target area was found to be reduced by incorporating the structural control (lineament) over the emplacement of Kimberlite pipes. Novelty: The present work highlights the usefulness of the moderate resolution multispectral image in mapping the Kimberlite pipes in semiarid region, in absence of a hyperspectral sensor.
DS202107-1105
2021
Kempe, Y., Weiss, Y., Chinn, L. L., Navon, O.Multiple metasomatic diamond-forming events in a cooling lithosphere beneath Voorspoed, South Africa.Lithos, Vol. 398-399, 106285 pdfAfrica, South Africadeposit - Voorspoed

Abstract: Thermal events and metasomatic processes have influenced the Kaapvaal craton in South Africa. High-density fluids (HDFs) trapped as microinclusions in diamond are main metasomatic agents which provide an insight to these processes in the Earth's mantle. Here we present data for 15 fibrous, HDF-bearing diamonds from the Voorspoed mine, South Africa, reflecting multiple diamond-forming events in a cooling lithosphere. Analyzed by FTIR and EPMA, the Voorspoed fibrous diamonds reveal three populations that differ in their nitrogen aggregation and HDF composition. A silicic?carbonatitic group containing 11-30% B-centers, a saline group containing 5-16% B-centers, and a single high-Mg carbonatitic diamond with 0% B-centers. The distinct nitrogen aggregation of the fibrous diamond groups in Voorspoed and the lack of clear major element evolutionary trends for each HDF type or intermediate compositions between the different types suggest different time-temperature formation histories. Thermobarometry of mineral inclusions in non-fibrous monocrystalline Voorspoed diamonds (Viljoen et al., 2018) indicates that the Voorspoed lithosphere cooled by 100-200 °C since their host diamonds crystallized at high initial temperatures. High temperatures in Voorspoed lithosphere can be correlated with the eruption of the Ventersdorp flood basalts at the central Kaapvaal (ca. 2.7 Ga) or the Bushveld complex (ca. 2.06 Ga), and cooling rates of the lithosphere provide a time frame for a cooling process that originated ~2-3 Ga. Combining these data with the nitrogen aggregation systematics of fibrous and monocrystalline Voorspoed diamonds, we suggest that most Voorspoed diamonds formed during 4 metasomatic events: the oldest one recorded took place between 2 and 3 Gyr as a result of a major thermal perturbation, whereas the following three occurred between 200 and 600 Myr, 30-90 and < 30 Myr before kimberlite eruption in a cooling lithosphere. An even older (or deeper) event is hinted by a few diamonds where all nitrogen is in B-centers. The sequence of events implied by Voorspoed HDF compositional and nitrogen aggregation differences show affinities with other occurrences in South Africa (e.g. Kimberley, Finsch and Koffiefontein) and may reflect thermal and lithological variation between the central and southwest Kaapvaal lithosphere.
DS202105-0771
2021
Khokhryakov, A., Kruk, A.N., Sokol, A.G.The effect of oxygen fugacity on diamond resorption in ascending kimberlite melt.Lithos, 10.1016/j.lithos.2021.106166, 12p.Russiadeposit - Udachnaya

Abstract: When transported by magmas to the Earth's surface, diamond crystals underwent resorption, the intensity of which significantly differed in various kimberlite pipes. We experimentally simulated diamond resorption at different oxygen fugacities (fO2) in ascending kimberlite magma enriched in CO2 and H2O. The experiments were carried out using specially prepared unaltered Group I kimberlite from the Udachnaya East pipe (Yakutia) and model carbonatite at 3.0 GPa, 1200-1400 °C, and fO2 in a range of NNO-2 to NNO + 3.2 log units (where NNO is Ni-NiO buffer). Over the investigated range of conditions, resorption of octahedral diamond crystals is found to occur according to a single scenario. Negative trigons and shield-shaped laminae develop on the {111} faces and crystal edges are truncated by the surfaces of tetrahexahedroids. The rate of diamond resorption increases in all studied systems as fO2 and temperature are raised. In this case, water-enriched melts are the most aggressive media in the investigated T-fO2 interval. Among the most oxidized high-temperature melts, it is carbonatite melts depleted in SiO2 that provide the maximum rate of diamond resorption. Furthermore, the rates of diamond resorption we obtained are an order of magnitude higher than those previously measured in silicate melts containing CO2 and H2O, at fO2 values from the NNO buffer to NNO-2. Therefore, high oxygen fugacity, a temperature of ~1400 °C, and essentially carbonate composition of water-containing magma could provide a high intensity of diamond resorption at the mantle stage of magma ascent to the surface. Apparently, this process primarily influenced the formation of the appearance and preservation of natural diamond crystals in kimberlite pipes.
DS202112-1933
2020
Khokhryakov, A., Nechaev, D.V., Sokol, A.G.Microrelief of rounded diamond crystals as an indicator of the redox conditions of their resorption in a kimberlite melt.Crystals, Vol. 10, 12p. Pdf Russiadiamond morphology

Abstract: We conducted a detailed study of the morphology of diamond crystals partially dissolved in a water-bearing kimberlite melt at pressure of 6.3 GPa, temperature of 1400 °C, and two oxygen fugacities (fO2) corresponding to the Re-ReO2 buffer and near the magnetite-hematite (MH) buffer. The triangular etch pits on the {111} faces, which formed during experimental diamond dissolution, were found to completely correspond to negative trigons on natural diamond crystals in the shape and sidewalls inclination angle. Furthermore, two experimental fO2 values were associated with two relief types of the rounded tetrahexahedroid surfaces typical of natural rounded diamonds. Therefore, the surface microrelief on rounded natural diamond crystals was concluded to be an indicator of the redox conditions of natural diamond resorption.
DS202108-1293
2021
Kimberley ProcessProduction statistics for 2020.Kimberley Process *** 1p. , https://kimberley processstatistics.org /static/pdfs/ public_statistics/ 2020/20 20GlobalSummary.pdfGlobalchart
DS202104-0582
2020
Klepikov, I.V., Vasilev, E.A., Antonov, A.V.The defect impurity composition of diamond crystals with ( 100) growth pyramids from placers of the Krasnovishersk district, the Urals.Geology of Ore Deposits, Vol. 62, 8, pp. 743-753. pdfRussia, Uralscuboid diamonds

Abstract: The internal structure and spectroscopic features of cuboid diamonds from recent alluvial placers of the Krasnovishersk District (the Urals) have been investigated. Crystals were divided into four groups by their anatomy and spectroscopy: cuboids of the II group (according to the Yu.L. Orlov classification): cuboids with a transparent core and peripheral zone saturated with inclusions; crystals with mixed habit growth of ?100? and ?111? pyramids, and crystals with the sequential growth of ?100? and ?111? pyramids. In all studied crystals, the regenerative formation of the {111} face steps together with the formation of tetragonal pits on the cuboid surface was the last stage of growth. Local photoluminescence investigations have been carried out for all cubic diamond crystals of the Urals for the first time. It was established that luminescence bands at 926 and 933 nm are related to growth pyramids of ?100? and ?111?, respectively. Bands with peaks at 800, 820.5, 840, 860, and 869 nm were revealed in the luminescence systems of the cuboids of II group. We note that the cuboid diamonds from different regions of the world have similar internal structures and spectroscopic features.
DS202107-1106
2021
Kogarko, L.N., Nielsen, T.F.D.Compositional variation of eudialyte-group minerals from the Lovozero and Ilmaussaq complexes on the origin of peralkaline systems.Minerals MDPI, Vol. 11, 548, 15p. PdfRussia, Kola Peninsula, Europe, Greenlanddeposit - Lovozero, Ilimaussaq

Abstract: The Lovozero complex, Kola peninsula, Russia and the Ilímaussaq complex in Southwest Greenland are the largest known layered peralkaline intrusive complexes. Both host world-class deposits rich in REE and other high-tech elements. Both complexes expose spectacular layering with horizons rich in eudialyte group minerals (EGM). We present a detailed study of the composition and cryptic variations in cumulus EGM from Lovozero and a comparison with EGM from Ilímaussaq to further our understanding of peralkaline magma chambers processes. The geochemical signatures of Lovozero and Ilímaussaq EGM are distinct. In Lovozero EGMs are clearly enriched in Na + K, Mn, Ti, Sr and poorer Fe compared to EGM from Ilímaussaq, whereas the contents of ?REE + Y and Cl are comparable. Ilímaussaq EGMs are depleted in Sr and Eu, which points to plagioclase fractionation and an olivine basaltic parent. The absence of negative Sr and Eu anomalies suggest a melanephelinitic parent for Lovozero. In Lovozero the cumulus EGMs shows decrease in Fe/Mn, Ti, Nb, Sr, Ba and all HREE up the magmatic layering, while REE + Y and Cl contents increase. In Lovozero EGM spectra show only a weak enrichment in LREE relative to HREE. The data demonstrates a systematic stratigraphic variation in major and trace elements compositions of liquidus EGM in the Eudialyte Complex, the latest and uppermost part of Lovozero. The distribution of elements follows a broadly linear trend. Despite intersample variations, the absence of abrupt changes in the trends suggests continuous crystallization and accumulation in the magma chamber. The crystallization was controlled by elemental distribution between EGM and coexisting melt during gravitational accumulation of crystals and/or mushes in a closed system. A different pattern is noted in the Ilimaussaq Complex. The elemental trends have variable steepness up the magmatic succession especially in the uppermost zones of the Complex. The differences between the two complexes are suggested to be related dynamics of the crystallization and accumulation processes in the magma chambers, such as arrival of new liquidus phases and redistributions by mush melts
DS202103-0387
2021
Kopylova, M.G.Constraining carbonation freezing and petrography of the carbonated cratonic mantle with natural samples.Lithos, in press available 49p. PdfCanada, Nunavut, Baffin Islanddeposit - Chidliak

Abstract: Peridotite xenoliths from the Cretaceous Chidliak kimberlite province (SE Baffin Island, Canada) were recently studied by Kopylova et al. (2019). Here, we focus on rare textures, with orthopyroxene grains invariably rimmed by 3-20??m coronas of clinopyroxene, while all clinopyroxenes are rimmed by equally thin monticellite coronas. Thicker, 0.1-0.5?mm texturally equilibrated clinopyroxene also mantles garnet, and there is a gradual transition from micron- to millimeter-thick clinopyroxene mantles. We investigated the origin of these rarely preserved textures using major and trace element zoning in minerals, and measured and reconstructed bulk compositions of xenoliths. Fluxes of major elements were identified based on the conserved element ratios while accounting for the closure effect due to normalization of bulk compositions to 100%. Ca dominates the absolute elemental gain, expressed in moles per 1000?mol of Fe. The observed mineralogical and compositional changes are associated with the significant metasomatic removal of Na (70% of its budget) Al, and Cr (35% loss), minor removal of Si, Mn, Mg and Ni and the gain of Ca (~ 20%), Ti, K and incompatible trace elements. The metasomatic fluid addition beneath Chidliak was likely below 10%. The fluid was very enriched and fractionated resembling volatile-rich low-degree melts like carbonatites or kimberlites. The Chidliak peridotites were affected by "“carbonation freezing", i.e. immobilization of a carbonate-rich metasomatic agent via reactions with pyroxenes. Clinopyroxene and monticellite coronas formed in decarbonation reactions, whereby ephemeral carbonatitic fluid readily gave away Ca to silicate minerals and exsolved CO2. Chidliak peridotites highlight that it would be deceptive to imagine "carbonated peridotites" storing carbon in a normal assemblage of peridotite plus carbonate. "Carbonated peridotites" are coarse peridotites with elevated modes of clinopyroxene, garnet and olivine, and with thin rims of calcic silicate minerals storing incompatible elements. The CO2-rich magmatism on cratons and the match between the temporal Ca addition to the cratonic mantle and the observed fluxes from the carbonate-rich metasomatism underscores the importance of the latter process in shaping up the lithospheric mantle and its melts.
DS202112-1934
2021
Korolev, N., Nikitina, L.P., Goncharov, A., Dubinina, V.N., Melnik, A., Muller, D., Chen, Y-X., Zinchenko, V.N.Three types of mantle eclogite from two layers of oceanic crust: a key case of metasomatically-aided transformation of low-to-high-magnesian eclogite.Journal of Petrology, Vol. 62, 11, pp. 1-38. pdfAfrica, Angoladeposit - Catoca

Abstract: Reconstructed whole-rock (RWR) and mineral major- and trace-element compositions, as well as new oxygen isotope data, for 22 mantle eclogite xenoliths from the Catoca pipe (Kasai Craton) were used to constrain their genesis and evolution. On the basis of mineralogical and major-element compositions, the Catoca eclogites can be divided into three groups: high-alumina (high-Al) (kyanite-bearing), low-magnesian (low-Mg#), and high-magnesian (high-Mg#) eclogites. The high-Al Catoca eclogites contain kyanite and corundum; high Al2O3 contents in rock-forming minerals; rare earth element (REE) patterns in garnets showing depleted LREEs, positive Eu anomalies (1.03-1.66), and near-flat HREEs; and high Sr contents in garnets and whole-rock REE compositions. All of these features point to a plagioclase-rich protolith (probably gabbro). RWR compositions (major elements, MREEs, HREEs, Li, V, Hf, Y, Zr, and Pb) and ?18O of 5.5-7.4‰ of the low-Mg# Catoca eclogites are in good agreement with the compositions of picrite basalts and average mid-ocean ridge basalt (MORB). The depleted LREEs and NMORB-normalised Nd/Yb values of 0.07-0.41 indicate that the degree of partial melting for the majority of the low-Mg# eclogites protolith was ?30%. The narrow ?18O range of 5.5-7.4‰ near the ‘gabbro-basalt’ boundary (6‰) obtained for the high-Al and low-Mg# Catoca eclogites reflects the influence of subduction-related processes. This case shows that mantle eclogites represented by two different lithologies and originating from different protoliths—plagioclase-rich precursor, presumably gabbro (for high-Al eclogites), and basalt (low-Mg# eclogites)—can provide similar and overlapping ?18O signatures on account of the influence of subduction-related processes. Chemical compositions of the high-Mg# eclogites indicate a complicated petrogenesis, and textural signatures reveal recrystallisation. The presence of Nb-rich rutile (8-12 wt% of Nb2O5) enriched with high field strength elements (HFSE) (Zr/Hf of 72.6-75.6) and multiple trace-element signatures (including RWR, NMORB-normalised Ce/Yb of 3.9-10.6 and Sr/Y of 5.8-9.6, MgO contents of 15.7-17.9 wt%, and high Ba and Sr) provide strong evidence for deep metasomatic alteration. High Cr contents in clinopyroxene (800-3740 ppm), garnet (430-1400 ppm), and accessory rutile (700-2530 ppm), together with extremely low Li contents of 1.0-2.4 ppm in clinopyroxene, may indicate hybridisation of the eclogites with peridotite. Comparison of the chemical compositions (major and trace elements) of (1) unaltered fresh cores of coarse-grained garnets from the low-Mg# eclogites, (2) secondary garnet rims (ubiquitous in the low-Mg# eclogites), (3) proto-cores in the coarse-grained garnet (high-Mg# eclogites), and (4) homogeneous recrystallised fine-grained garnets (high-Mg# eclogites) suggests that the high-Mg# eclogites formed through recrystallisation of low-Mg# eclogite in the presence of an external fluid in the mantle. Four of the five high-Mg# samples show that mantle metasomatism inside the Kasai craton mantle beneath the Catoca pipe occurred at a depth range of 145-160 km (4.5-4.8 GPa).
DS202110-1620
2021
Korolev, N., Nikitina, L.P., Goncharov, A.,Dubinina, E., Melnik, A.E., Muller, D., Chen, Y-X., Zinchenko, V.Three types of mantle eclogite from two layers of oceanic crust: a key case of metasomatically- aided transformation of low-to-high-magnesian eclogite.Journal of Petrology, 10.1093/petrology /egab070 98p. PdfAfrica, Angoladeposit - Catoca

Abstract: Reconstructed whole-rock and mineral major- and trace-element compositions, as well as new oxygen isotope data, for 22 mantle eclogite xenoliths from the Catoca pipe (Kasai Craton) were used to constrain their genesis and evolution. On the basis of mineralogical and major-element compositions, the Catoca eclogites can be divided into three groups: high-alumina (high-Al) (kyanite-bearing), low-magnesian (low-Mg#), and high-magnesian (high-Mg#) eclogites. The high-Al Catoca eclogites contain kyanite and corundum; high Al2O3 contents in rock-forming minerals; rare earth element (REE) patterns in garnets showing depleted LREEs, positive Eu anomalies (1.03-1.66), and near-flat HREEs; and high Sr contents in garnets and whole-rock REE compositions. All of these features point to a plagioclase-rich protolith (probably gabbro). Reconstructed whole-rock compositions (major elements, MREEs, HREEs, Li, V, Hf, Y, Zr, and Pb) and ?18O of 5.5-7.4‰ of the low-Mg# Catoca eclogites are in good agreement with the compositions of picrite basalts and average mid-ocean ridge basalt (MORB). The depleted LREEs and NMORB-normalised Nd/Yb values of 0.07-0.41 indicate that the degree of partial melting for the majority of the low-Mg# eclogites protolith was ?30%. The narrow ?18O range of 5.5-7.4‰ near the ‘gabbro-basalt’ boundary (6‰) obtained for the high-Al and low-Mg# Catoca eclogites reflects the influence of subduction-related processes. This case shows that mantle eclogites represented by two different lithologies and originating from different protoliths — plagioclase-rich precursor, presumably gabbro (for high-Al eclogites), and basalt (low-Mg# eclogites) — can provide similar and overlapping ?18O signatures on account of the influence of subduction-related processes. Chemical compositions of the high-Mg# eclogites indicate a complicated petrogenesis, and textural signatures reveal recrystallisation. The presence of Nb-rich rutile (8-12 wt% of Nb2O5) enriched with HFSE (Zr/Hf of 72.6-75.6) and multiple trace-element signatures (including reconstructed whole-rock NMORB-normalised Ce/Yb of 3.9-10.6 and Sr/Y of 5.8-9.6, MgO contents of 15.7-17.9 wt%, and high Ba and Sr) provide strong evidence for deep metasomatic alteration. High Cr contents in clinopyroxene (800-3740 ppm), garnet (430-1400 ppm), and accessory rutile (700-2530 ppm), together with extremely low Li contents of 1.0-2.4 ppm in clinopyroxene, may indicate hybridisation of the eclogites with peridotite. Comparison of the chemical compositions (major and trace elements) of (1) unaltered fresh cores of coarse-grained garnets from the low-Mg# eclogites, (2) secondary garnet rims (ubiquitous in the low-Mg# eclogites), (3) proto-cores in the coarse-grained garnet (high-Mg# eclogites), and (4) homogeneous recrystallised fine-grained garnets (high-Mg# eclogites) suggests that the high-Mg# eclogites formed through recrystallisation of low-Mg# eclogite in the presence of an external fluid in the mantle. Four of the five high-Mg# samples show that mantle metasomatism inside the Kasai craton mantle beneath the Catoca pipe occurred at a depth range of 145-160 km (4.5-4.8 GPa).
DS202107-1107
2021
Kostrovitsky, S.I., Yakolev, D.A., Suvorova, L.F., Demonterova, E.I.Carbonatite-like rock in a dike of the Aikhal kimberlite pipe: comparison with carbonatites of the Nomokhtookh site ( Anabar area).Russian Geology and Geophysics, Vol. 62, pp. 605-618.Russiadeposit - Aikhal

Abstract: A dike of rock similar in composition to carbonatites has been found in the Aikhal diamondiferous pipe of the Alakit-Markha field of the Yakutian kimberlite province (YaKP). The fine-grained rock of essentially carbonate composition (dolomite and calcite) rich in thin-platy phlogopite contains minerals typical of carbonatites: monazite, baddeleyite, and pyrochlore. In the high contents and distribution of incompatible elements the rock differs significantly from kimberlites and is transitional from kimberlites to carbonatites. The content of incompatible elements in this rock is 3-5 times lower than that in carbonatite breccias of the pipes in the Staraya Rechka kimberlite field of the YaKP (Nomokhtookh site). The compositions of accessory trace element minerals from the Aikhal dike rock and the Nomokhtookh carbonatite breccias are compared. An assumption is made that the high contents of incompatible elements in the carbonatite-like rock, which caused the crystallization of accessory minerals, are due to the differentiation of kimberlite melt/fluid. The high Sr isotope ratios indicate that the rock altered during hydrothermal and metasomatic processes. The obtained data on the composition of the carbonatite-like rock cannot serve as an argument for the genetic relationship between the Aikhal kimberlites and typical carbonatites. The genetic relationship between kimberlites and carbonatites in the northern fields of the YaKP remains an open issue.
DS202109-1476
2021
Kostyuk, A.V., Gorbachev, N.S., Nekrasov, A.N.Petrogenesis of garnet-bearing carbonatite in the Tromso Nappe, Norway.Geochemistry International, Vol. 59, 8, pp. 801-812. pdfEurope, Norwaydeposit - Tromso Nappe

Abstract: The paper presents data on phase relations in garnet-bearing carbonatite from the Tromsø Nappe, Norway. The carbonatite matrix consists of calcite-dolomite carbonate with three generations of garnet inclusions (up to 15-20%). The relics of the primary garnets (Grt1) are depleted (<10-2 wt %) in the rare earth elements (REE). The garnet of the second and third generations (Grt2-3) is anomalously enriched (up to 10-15 wt %) in the light REE (LREE), and the carbonates are depleted in these elements. The distribution of REE between the garnet and carbonate indicates the absence of equilibrium. The melting of the carbonatite at T = 950-1400°C, P = 4.0 GPa showed that the “dry” solidus temperature is 1150°C, and the liquidus temperature is >1300°C. In the experiment with H2O + CO2 fluid, the solidus and liquidus temperatures are ?950 and 1250°C, respectively. The subsolidus association is calcite, garnet, clinopyroxene, biotite, and accessory minerals: apatite, ilmenite, rutile, and titanite. The garnet and carbonatite melt occur in reaction relationships, as is evident from the garnet zoning with a decrease in the FeO and increase in the MgO, CaO, TiO2, and LREE concentrations. The geological setting, phase relationships, and experimental data indicate that the garnet-bearing carbonatites in the Tromsø area were formed in relation to the carbonatization and melting of upper mantle material at high pressures during the collision of the Baltica and Laurentia plates in the course of the Caledonian orogenesis, with subsequent intrusion and crystallization of silicate-carbonate magmas.
DS202103-0388
2018
Kozlov, E., Fomina, E., Sidorov, M., Shilovskikh, V.Ti-Nb mineralization of late carbonatites and role of fluid in its formation: Petyayan-Vara rare-earth carbonatites ( Vuoriyarvi Massif, Russia). ***dateMDPI Applied Sciences, 19p. PdfRussiacarbonatite

Abstract: This article is devoted to the geology of titanium-rich varieties of the Petyayan-Vara rare-earth dolomitic carbonatites in Vuoriyarvi, Northwest Russia. Analogues of these varieties are present in many carbonatite complexes. The aim of this study was to investigate the behavior of high field strength elements during the late stages of carbonatite formation. We conducted a multilateral study of titanium- and niobium-bearing minerals, including a petrographic study, Raman spectroscopy, microprobe determination of chemical composition, and electron backscatter diffraction. Three TiO2-polymorphs (anatase, brookite and rutile) and three pyrochlore group members (hydroxycalcio-, fluorcalcio-, and kenoplumbopyrochlore) were found to coexist in the studied rocks. The formation of these minerals occurred in several stages. First, Nb-poor Ti-oxides were formed in the fluid-permeable zones. The overprinting of this assemblage by residual fluids led to the generation of Nb-rich brookite (the main niobium concentrator in the Petyayan-Vara) and minerals of the pyrochlore group. This process also caused niobium enrichment with of early generations of Ti oxides. Our results indicate abrupt changes in the physicochemical parameters at the late hydro (carbo) thermal stage of the carbonatite formation and high migration capacity of Ti and Nb under these conditions. The metasomatism was accompanied by the separation of these elements.
DS202104-0583
2020
Krivovichev, V.G., Charykova, M.V., Krivovichev, S.V.Mineral systems based on the number of species-defining chemical elements in minerals: their diversity, complexity, distribution, and the mineral evolution of the Earth's crust: a review.Geology of Ore Deposits, Vol. 62,8, pp. 704-718. pdfRussia, Canadaalkaline rocks

Abstract: The chemical diversity of minerals can be analyzed in terms of the concept of mineral systems based on the set of chemical elements that are essential for defining a mineral species. Only species-defining elements are considered to be essential. According to this approach, all minerals are classified into ten types of mineral systems with the number of essential components ranging from 1 to 10. For all known minerals, only 70 chemical elements act as essential species-defining constituents. Using this concept of mineral systems, various geological objects may be compared from the viewpoint of their mineral diversity: for example, alkali massifs (Khibiny and Lovozero in Russia; Mont Saint Hilaire in Canada), evaporite deposits (Inder in Kazakhstan and Searles Lake in the United States), fumaroles of active volcanoes (Tolbachik in Kamchatka and Vulcano in Sicily, Italy), and hydrothermal deposits (Otto Mountain in the United States and El Dragon in Bolivia). Correlations between chemical and structural complexities of the minerals were analyzed using a total of 5240 datasets on their chemical compositions and 3989 datasets on their crystal structures. The statistical analysis yields strong and positive correlations (R2 > 0.95) between chemical and structural complexities and the number of different chemical elements in a mineral. The analysis of relationships between chemical and structural complexities provides strong evidence for the overall trend of a greater structural complexity at a higher chemical complexity. Following R. Hazen, four groups of minerals representing four mineral evolution stages have been considered: (I) “Ur-minerals,” (II) minerals from chondrite meteorites, (III) Hadean minerals, and (IV) contemporary minerals. According to the obtained data, the number of species-defining elements in minerals and their average contents increase regularly and significantly from stage I to stage IV. The analyzed average chemical and structural complexities in these four groups demonstrate that both are gradually increasing in the course of mineral evolution. The increasing complexity follows an overall trend: the more complex minerals were formed in the course of geological time, without replacing the simpler ones. The observed correlations between chemical and structural complexities understood in terms of the Shannon information suggest that chemical differentiation is the major force that drives the increase of mineral complexity over the course of geological time.
DS202105-0772
2021
Krivovichev, V.G., Charykova, M.V., Krivovichev, S.V.Mineral systems based on the number of species-defining chemical elements in minerals: their diversity, complexity, distribution, and the mineral evolution of the Earth's crust: a review. Mentions Khibiny, Lovozero, Mount St. HilaireGeology of Ore Deposits, Vol. 62, 8, pp. 704-718. pdfRussia, Canada, QuebecMineralogy

Abstract: The chemical diversity of minerals can be analyzed in terms of the concept of mineral systems based on the set of chemical elements that are essential for defining a mineral species. Only species-defining elements are considered to be essential. According to this approach, all minerals are classified into ten types of mineral systems with the number of essential components ranging from 1 to 10. For all known minerals, only 70 chemical elements act as essential species-defining constituents. Using this concept of mineral systems, various geological objects may be compared from the viewpoint of their mineral diversity: for example, alkali massifs (Khibiny and Lovozero in Russia; Mont Saint Hilaire in Canada), evaporite deposits (Inder in Kazakhstan and Searles Lake in the United States), fumaroles of active volcanoes (Tolbachik in Kamchatka and Vulcano in Sicily, Italy), and hydrothermal deposits (Otto Mountain in the United States and El Dragon in Bolivia). Correlations between chemical and structural complexities of the minerals were analyzed using a total of 5240 datasets on their chemical compositions and 3989 datasets on their crystal structures. The statistical analysis yields strong and positive correlations (R2 > 0.95) between chemical and structural complexities and the number of different chemical elements in a mineral. The analysis of relationships between chemical and structural complexities provides strong evidence for the overall trend of a greater structural complexity at a higher chemical complexity. Following R. Hazen, four groups of minerals representing four mineral evolution stages have been considered: (I) “Ur-minerals,” (II) minerals from chondrite meteorites, (III) Hadean minerals, and (IV) contemporary minerals. According to the obtained data, the number of species-defining elements in minerals and their average contents increase regularly and significantly from stage I to stage IV. The analyzed average chemical and structural complexities in these four groups demonstrate that both are gradually increasing in the course of mineral evolution. The increasing complexity follows an overall trend: the more complex minerals were formed in the course of geological time, without replacing the simpler ones. The observed correlations between chemical and structural complexities understood in terms of the Shannon information suggest that chemical differentiation is the major force that drives the increase of mineral complexity over the course of geological time.
DS202108-1294
2021
Krmicek, L., Magna, T., Chalapathi Rao, Pandey, A.Lithium isotopes in kimberlites, lamproites and lamprophyres as tracers of source components and processes related to supercontinent cycles.Geological Society of London Special Publications, doi:10.1144/SP513-2021-60geodynamics

Abstract: Our pilot study reveals potential fingerprints of Li isotopes recorded in the Mesoproterozoic (?1.4-1.1 Ga) kimberlites, lamproites and lamprophyres from the Eastern Dharwar Craton and Paleocene (62 Ma) orangeite from the Bastar Craton in India. The new data are interpreted in the context of available Li isotope composition of lamproitic to lamprophyric rocks occurring in Variscan (Bohemian Massif) and Alpine-Himalayan (SW Tibet) orogenic belts formed in response to Gondwana-Pangea amalgamation and break-up. As a result of supercontinents development, kimberlites from the Eastern Dharwar Craton and ‘orangeite’ from the Bastar Craton show clear presence of a component with a heavy Li isotope signature (?7Li up to 9.7‰) similar to an ancient altered oceanic crust, whereas the Eastern Dharwar Craton lamproites (2.3-6.3‰) and lamprophyres (3.3-6.7‰) show Li isotope signatures indicative of a dominant contribution from heterogeneous lithospheric mantle. Variscan lamprophyric to lamproitic rocks and post-collisional mantle-derived (ultra)potassic volcanic rocks from SW Tibet, i.e., rocks from the orogenic belts outside the cratonic areas, are characterized by a clear Li isotope shift towards isotopically lighter component (?7Li as low as -9.5‰) comparable with the involvement of an evolved continental crust and high-pressure metamorphic rocks in their orogenic mantle source. Such components with isotopically light Li are strikingly missing in the source of cratonic kimberlites, lamproites and lamprophyres.
DS202101-0021
2020
Krmicek, L., Romer, R.L., Timmerman, M.J., Ultych, J., Glodny, J.Long lasting ( 65Ma) regionally contrasting Late-to Post-orogenic variscan mantle-derived potassic magmatism in the Bohemian Massif.Journal of Petrology, Vol. 61, 7, doi.org/10.1093 /petrology/egaa072Europemagmatism

Abstract: The orogenic development after the continental collision between Laurussia and Gondwana, led to two contrasting associations of mantle-derived magmatic rocks on the territory of the Bohemian Massif: (i) a 340-310?Ma lamprophyre-lamproite orogenic association; and (ii) a 300-275?Ma lamprophyre association of anorogenic affinity. Major types of potassic mantle-derived magmatic rocks recognized in the orogenic and anorogenic associations include: (i) calc-alkaline to alkaline lamprophyres; (ii) alkaline ‘orthopyroxene minettes’ and geochemically related rocks grouped here under the new term lampyrite; and (iii) peralkaline lamproites. These three types significantly differ with respect to mineral, whole-rock and Sr-Nd-Pb-Li isotope composition and spatial distribution. The calc-alkaline lamprophyres occur throughout the entire Saxo-Thuringian and Moldanubian zones, whereas the different types of malte-derived potassic rocks are spatially restricted to particular zones. Rocks of the Carboniferous lamprophyre-lamproite orogenic association are characterized by variable negative ?Nd(i) and variably radiogenic Sr(i), whereas the rocks of the Permian lamprophyre association of anorogenic affinity are characterized by positive ?Nd(i) and relatively young depleted-mantle Nd-model ages reflecting increasing input from upwelling asthenospheric mantle. The small variation in the Pb isotopic composition of post-collisional potassic mantle-derived magmatic rocks (of both the orogenic and anorogenic series) implies that the Pb budget of the mantle beneath the Bohemian Massif is dominated by the same crust-derived material, which itself may include material derived from several sources. The source rocks of ‘orthopyroxene minettes’ are characterized by isotopically light (‘eclogitic’) Li and strongly radiogenic (crustal) Sr and may have been metasomatized by high-pressure fluids along the edge of a subduction zone. In contrast, the strongly Al2O3 and CaO depleted mantle source of the lamproites is characterized by isotopically heavy Li and high SiO2 and extreme K2O contents. This mantle source may have been metasomatized predominantly by melts. The mantle source of the lamprophyres may have undergone metasomatism by both fluids and melts.
DS202101-0022
2020
Kropac, K., Dolnicek, Z., Uher, P., Burianek, D., Safai, A., Urubek, T.Zirconian-niobian titanite and associated Zr-, Nb-, REE-rich accessory minerals: products of hydrothermal overprint of leucocratic teschenites ( Sileasian Unit, outer western Carpathians, Czech Republic).Geologica Carpathica ** Eng, Vol. 71, 4, pp. 343-360. pdfEurope, Czech Republicalkaline rocks

Abstract: Sills of hydrothermally altered alkaline magmatic rock (teschenite) of Lower Cretaceous age at the ?er?ák and ?epišt? sites in the Silesian Unit (Flysch Belt of the Outer Western Carpathians, Czech Republic) host leucocratic dykes and nests which contain accessory minerals enriched in Zr, Nb and REE: Zr-, Nb-rich titanite, zircon, gittinsite, pyrochlore, monazite, REE-rich apatite, epidote, and vesuvianite. Titanite forms wedge-shaped crystals or irregular aggregates enclosed in the analcime groundmass or overgrowths on Zr-rich ferropargasite and taramite or Zr-rich aegirine-augite to aegirine. Titanite crystals show oscillatory or irregular patchy to sector zoning and contain up to 17.7 wt. % ZrO2 and 19.6 wt. % Nb2O5, and ?1.1 wt. % REE2O3. High-field-strength elements (HFSE) are incorporated into the structure of the studied titanite predominantly by substitutions: (i) [6]Ti4+???[6]Zr4+; (ii) [6]Ti4+?+?[6]Al3+???[6]Zr4+?+?[6]Fe3+; and (iii) [6]2Ti4+???[6]Nb5+?+?[6](Al, Fe)3+. Magmatic fractional crystallization, high-temperature hydrothermal autometasomatic overprint and low-temperature hydrothermal alterations resulted in the formation of the HFSE-rich mineral assemblages within the leucocratic teschenites. Autometamorphic processes caused by high-temperature hypersaline aqueous solutions (salinity ~50 wt. %, ~390-510 °C), which were released from the HFSE-enriched residual melt, played a major role in the crystallization of Zr-, Nb-, and REE-rich minerals. The mobilization of HFSE could have occurred either by their sequestration into a fluid phase exsolved from the crystallizing melt or by superimposed alteration processes. The distinctive positive Eu anomaly (EuCN/Eu*?=?1.85) of leucocratic dykes infers possible mixing of Eu2+-bearing magmatic fluids with more oxidized fluids.
DS202107-1108
2021
Krueger, H.E., Gama, I., Fischer, K.M.Global patterns in cratonic mid-lithospheric discontinuities from Sp receiver functions. ( shield)Geochemistry, Geophysics, Geosytems, 19p. PdfCanada, Ontariogeophysics - seismics

Abstract: We investigate the structure of the continental lithosphere (tectonic plate) in regions that have had negligible tectonic activity, such as mountain building, for the past 500 million years. The internal structure of the lithosphere in these regions can be indicative of the ancient processes that first formed continents. Due to challenges in methodology, layering within the upper 150 km of the continental lithosphere is poorly understood. We carefully process earthquake data to avoid problems that previous studies encountered. We observe layering in 50% of the ancient continental regions. Most of this layering can be explained by the presence of minerals that have lower seismic velocities than the surrounding rock because they have been altered by fluids during the formation of the continent. In regions closer to more recent tectonic activity, some layering has stronger seismic velocity decreases, indicating the effects of more recent alteration. We also find that layering is more prevalent in the continental regions that last experienced tectonic activity no later than 1.6 billion years ago. This corresponds with a global transition in the depth to which the subducting lithosphere carries fluids into the mantle, indicating that subduction has a key role in generating layering in the ancient continental lithosphere.
DS202107-1109
2021
Kruk, M.N., Doroshkevich, A.G., Prokopyev, I.R., Izbrodin, I.A.Mineralogy of phoscorites of the Arbarastakh complex, Republic of Sakha, Yakutia, Russia).Minerals MDPI, Vol. 11, 556 24p. PdfRussia, Yakutiacarbonatite

Abstract: The Arbarastakh ultramafic carbonatite complex is located in the southwestern part of the Siberian Craton and contains ore-bearing carbonatites and phoscorites with Zr-Nb-REE mineralization. Based on the modal composition, textural features, and chemical compositions of minerals, the phoscorites from Arbarastakh can be subdivided into two groups: FOS 1 and FOS 2. FOS 1 contains the primary minerals olivine, magnetite with isomorphic Ti impurities, phlogopite replaced by tetraferriphlogopite along the rims, and apatite poorly enriched in REE. Baddeleyite predominates among the accessory minerals in FOS 1. Zirconolite enriched with REE and Nb and pyrochlore are found in smaller quantities. FOS 2 has a similar mineral composition but contains much less olivine, magnetite is enriched in Mg, and the phlogopite is enriched in Ba and Al. Of the accessory minerals, pyrochlore predominates and is enriched in Ta, Th, and U; baddeleyite is subordinate and enriched in Nb. Chemical and textural differences suggest that the phoscorites were formed by the sequential introduction of different portions of the melt. The melt that formed the FOS 1 was enriched in Zr and REE relative to the FOS 2 melt; the melt that formed the FOS 2 was enriched in Al, Ba, Nb, Ta, Th, U, and, to a lesser extent, Sr.
DS202104-0584
2021
Krzemnicki, M.S., Wang, H.O., Buche, S.A new type of emerald from Afghanistan's Panjshir Valley.Journal of Gemmology, Vol. 37, 5, pp. 474-495.Asia, Afghanistanemerald

Abstract: Since 2017, a new type of emerald from the Panjshir Valley, Afghanistan, has entered the gem trade. This material is commonly of excellent quality and compares with the finest emeralds from Colombia, not only visually, but also with respect to inclusions, spectral features and chemical composition. As a result, some of these stones have entered the market as Colombian emeralds. This study presents detailed microscopic, spectral and trace-element data for these recently produced Afghan emeralds and compares them to ‘classic’ emeralds from the Panjshir Valley and from Laghman Province in Afghanistan. The samples from each of the three Afghan occurrences showed differences in their UV-Vis-NIR spectra and water-related features in their Raman spectra, and they could also be distinguished from one another-as well as those from other important emerald deposits worldwide- by their trace-element composition. A distinctly higher Fe concentration is the main criterion that separates the recent Panjshir production from Colombian emeralds. This study further shows that it is possible to clearly differentiate emeralds from different localities based on trace-element data using t-SNE statistical processing, which is an unsupervised machine-learning method.
DS202104-0585
2021
Kubik, E., Siebert, J., Blanchard, I., Agranier, A., Mahan, B., Moynier, F.Earth's volatile accretion as told by Cd, Bi, Sb and Ti core-mantle distribution.Geochimica et Cosmochimica Acta, in press available, 35p. PdfMantlegeodynamics
DS202103-0389
2020
Kumar, A., Talukdar, D., Chalapathi Rao, N.V., Burgess, R., Lehmann, B.Mesoproterozoic 40Ar-39Ar ages of some lamproites from the Cuddapah Basin and eastern Dharwar craton, southern India: implications for diamond provenance of the Banganapalle conglomerates, age of the Kurnool Group and Columbia tectonics.Geological Society, London, Special Publication , 10.1144/SP513- 2020-247 53p. PdfIndialamproites

Abstract: We report Mesoproterozoic 40Ar-39Ar (whole-rock) ages of lamproites from (i) the Ramadugu field (R4 dyke : 1434 ± 19 Ma and R5 dyke: 1334 ± 12 Ma) and the Krishna field (Pochampalle dyke: 1439 ± 3 Ma and Tirumalgiri dyke: 1256 ± 12 Ma) from the Eastern Dharwar Craton (EDC) and (ii) the Garledinne (1433 ± 8 Ma) and the Chelima (1373 ± 6 Ma) dykes from within the Paleo-Mesoproterozoic Cuddapah Basin, southern India. The ages reported for the Ramadugu and Tirumalgiri lamproites constitute their first radiometric dates. Ages of the Pochampalle and the Chelima lamproites from this study are broadly comparable to their previously reported 40Ar-39Ar (phlogopite) ages of c. 1500 Ma and 1418 ± 8 Ma, respectively. The ages of all these lamproites are much older than those of the (i) c. 1.1 Ga kimberlites from the Wajrakarur and Narayanpet fields of the EDC and (ii) c. 1.09 Ga lamproitic dykes at Zangamarajupalle which intrude the Cumbum Formation of the Cuddapah Basin. However, the age of the Tirumalgiri lamproite (c. 1256 Ma) is similar to that of the Ramannapeta lamproite (c. 1224 Ma) within the Krishna field. Our study provides evidence for protracted ultrapotassic (lamproitic) magmatism from c. 1.43 to 1.1 Ga over a widespread area (c. 2500 km2) in and around the Cuddapah Basin and the EDC. Implications of the obtained new ages for the diamond provenance of the Banganapalle Conglomerates, the age of the Kurnool Group and for the timing of break-up of the Paleo-Mesoproterozoic supercontinent of Columbia/Nuna are explored.
DS202112-1935
2021
Kumar, P., Mandal, B., Kumar, M.P.Seismic structure of the crust and lithospheric mantle of the Indian Shield: a review.Journal of the Geological Society of India, Vol. 97, 10, pp. 1169-1189.Indiageophysics - seismics

Abstract: The article reviews the history and accomplishments of CSIR-NGRI over the past 60 years, related to elucidating the seismic structure of the crust and lithospheric mantle of the Indian shield. Extensive investigations have been carried out in diverse geological and tectonic provinces of India, employing seismic reflection, refraction/wide-angle reflection and passive seismology to decipher (a) the evolution of the Indian plate through geological time, (b) hazard and its mitigation and (c) accumulation and disposition of natural resources. These endeavours entailed the application and development of state-of-the-art methodologies. Synthesis of the results from active and passive seismology reveals that the thickness of the crust varies between 28 and 65 km in the Kachchh and Aravalli regions respectively, consistent with their evolutionary histories. The thickest crust is observed in the western Dharwar craton (WDC) and the shallowest lies in the west coast. The crust in the shield region is mostly thicker, while it is thin beneath the rift zones. Results from coincident reflection and wide-angle seismic reflection studies broadly suggest a three-layered crust with magmatic underplating. Interestingly, the seismic sections traversing the Aravalli fold belt, central Indian suture zone, Dharwar craton and Southern Granulite Terrain (SGT) depict paleo-collision and subduction environments. The diverse character of the Moho, crustal fabrics and structure in different geological provinces indicate that contrasting tectonic environments might have influenced their evolution and support the hypothesis that plate tectonic processes were operative since Neoarchean. The thickness of the lithosphere estimated from receiver functions varies from 80 to 140 km. An undulation in the Lithosphere Asthenosphere Boundary reveals evidence for a flexure on a regional scale, owing to the continental collision of the Indian and Asian plates. However, the lithospheric thickness derived from surface wave dispersion studies is somewhat larger, ranging from 100 to 250 km, with some body wave tomographic studies suggesting it to be ?400 km, in consonance with the concept of Tectosphere. The thickness values derived from both the methods agree at a few locales such as the Eastern Dharwar Craton, SGT, Cambay, Singhbhum and western DVP. However, a broad disagreement prevails in WDC and northern part of the Indian shield where surface wave tomography reveals the thickness of lithosphere to be 140 to 200 km.
DS202106-0947
2021
Kumar, S., Kumar, D., Sengupta, K., Giri, T.K.Impact of community based business model and competitive advantage on exports: evidence from diamond industry.Competitive Review, Vol. 31, 2, pp. 276-296. pdfGlobalmarkets

Abstract: his study aims to examine the altering paradigms for two specific characteristics of the international diamond industry: community-based business model and competitive advantage and their impact and interaction effect.
DS202103-0390
2021
Kumar, S.P., Shaikh, A.M., Patel, S.C., Sheikh, J.M., Behera, D., Pruseth, K.L., Ravi, S., Tappe, S.Multi-stage magmatic history of olivine-leucite lamproite dykes from Banganapalle, Dharwar craton, India: evidence from compositional zoning of spinel.Mineralogy and Petrology, Vol. 115, pp. 87-112. pdfIndialamproite

Abstract: Mesoproterozoic lamproite dykes occurring in the Banganapalle Lamproite Field of southern India show extensive hydrothermal alteration, but preserve fresh spinel, apatite and rutile in the groundmass. Spinels belong to three genetic populations. Spinels of the first population, which form crystal cores with overgrowth rims of later spinels, are Al-rich chromites derived from disaggregated mantle peridotite. Spinels of the second population include spongy-textured grains and alteration rims of titanian magnesian aluminous chromites that formed by metasomatic interactions between mantle wall-rocks and precursor lamproite melts before their entrainment into the erupting lamproite magma. Spinels that crystallised directly from the lamproite magma constitute the third population and show five distinct compositional subtypes (spinel-IIIa to IIIe), which represent discrete stages of crystal growth. First stage magmatic spinel (spinel-IIIa) includes continuously zoned macrocrysts of magnesian aluminous chromite, which formed together with Al-Cr-rich phlogopite macrocrysts from an earlier pulse of lamproite magma at mantle depth. Crystallisation of spinel during the other four identified stages occurred during magma emplacement at crustal levels. Titanian magnesian chromites (spinel-IIIb) form either discrete crystals or overgrowth rims on spinel-IIIa cores. Further generations of overgrowth rims comprise titanian magnesian aluminous chromite (spinel-IIIc), magnetite with ulvöspinel component (spinel-IIId) and lastly pure magnetite (spinel-IIIe). Abrupt changes of the compositions between successive zones of magmatic spinel indicate either a hiatus in the crystallisation history or co-crystallisation of other groundmass phases, or possibly magma mixing. This study highlights how different textural and compositional populations of spinel provide important insights into the complex evolution of lamproite magmas including clues to elusive precursor metasomatic events that affect cratonic mantle lithosphere.
DS202106-0948
2021
Kusham, B., Naick, P., Pratap, A. Naganjaneyulu, K.Magnetotelluric 3-D full tensor inversion in the Dharwar craton, India: mapping of subduction polarity and kimberlitic melt.Physics of the Earth and Planetary Interiors, Vol. 315, 106708, 13p. PdfIndiakimberlites

Abstract: Complex geological structures and processes that took place in the Dharwar craton formation make it difficult to understand the evolution history. 3-D magnetotelluric inversion is a challenging task for the imaging of sub-surface structures. Data at 40 stations in a gridded fashion are used in this study for inversion. A controversy exists regarding the subduction polarity between the eastern and western Dharwar craton. Based on the conductivity anomalies mapped in the sub-surface, the lithosphere can be divided into the shallower and deeper lithosphere. The study delineated several crustal and lithospheric upper mantle conductors. In the crustal region, several conductive features (~10 ?-m) are imaged in the western part, central, and eastern part of the profile. A new finding of this 3-D study is a conductor in the eastern Dharwar craton in the depth range of 65-140 km. The base of this conductor shows the graphite diamond stability field and is correlated with the kimberlites/lamproites present in the region. An uppermost mantle conductor is present at the depth range of 80-200 km in the central part of the study area. Sulphides and carbon-rich fluids could be one cause of the conductors mapped in the crust. The low electrical resistivity imaged in the deeper lithosphere could be due to the refertilization of the mantle scar in the Cretaceous age by the passage of several hotspots. The lithospheric thickness estimated beneath the Dharwar craton in this study is more than 200 km. This study reveals geophysical evidence for the eastward subduction polarity in the Dharwar craton.
DS202103-0391
2021
Kvasnytsya, V.M., Kaminsky, F.VUnusual green type lb-lab Dniester-type diamond from Ukrainian placers.Mineralogy and Petrology, doi.org/10.1007/ s00710-020-00732-w 12p. PdfEurope, Ukrainediamond morphology

Abstract: Among placer diamond occurrences in Ukraine, a group of microdiamonds have been distinguished that have specific morphological, color and spectral characteristics, not observed in other natural diamonds. These diamonds, termed "Dniester-type diamonds", have tetrahexahedroidal and rhombododecahedroidal morphologies, green coloration, and high concentrations of single-atom, unaggregated nitrogen in the form of C-centers (66-74% of all N atoms), along with low ratios of nitrogen aggregation (0-13% agrregation ratio) and high total nitrogen content (892-1493 atomic ppm). With these characteristics, Dniester-type diamonds are approximate the Type Ib-Iab classification. The predominance of single-atom, unaggregated nitrogen indicates a short residence time under high-temperature conditions. These Dniester-type diamonds have a narrow range of carbon isotopic compositions, from ?¹³? = -10.52‰ VPDB t? -12.82‰ VPDB (average ?¹³? = -11.85‰ VPDB). They are distributed in Quaternary and Neogene sediments of the southwestern part of the Ukrainian Shield. This distribution forms a local halo within the Dniester and Southern Bug rivers interfluve and Black Sea beach sediments, approximately 650 km in length. This implies their endemic character and the likely nearby presence of primary source(s) of unknown, possibly non-kimberlitic type.
DS202112-1936
2021
Lanese, N.Earth's 1st continents arose hundreds of millions of years earlier than thought.livescience.com, Nov. 8, 5p.Globalcratons

Abstract: Earth's first continents, known as the cratons, emerged from the ocean between 3.3 billion and 3.2 billion years ago, a new study hints. This pushes back previous estimates of when the cratons first rose from the water, as various studies suggested that large-scale craton emergence took place roughly 2.5 billion years ago. "There was no uncertainty that continents were partly sticking out of water as early as 3.4 billion years ago," said Ilya Bindeman, a professor of geology at the University of Oregon, who was not involved in the new study. That's because scientists have found sedimentary rocks - which form from the broken-up bits of other rocks that have undergone erosion and weathering — that date back to that era. Such sedimentary rocks could only form once land broke through the surface of early Earth's oceans.
DS202108-1295
2021
Lapin, A.V., Kulikova, I.M., Nabelkin, O.A.Surface formations in the weathering crusts of carbonatites: implication for the genesis of unique rare metal ores in the Tomtor deposit, Russia.Lithology and Mineral Resources, Vol. 56, pp. 356-374.Russiadeposit - Tomtor

Abstract: A comparative analysis of the composition and structure of the surface facies of carbonatite weathering crusts (profiles) in the Chuktukon (Russia) and Seis Lagos (Brazil) deposits and ultra-rich rare metal ores in the Tomtor deposit (Russia) is presented. It is shown that the main geochemical trends in the formation of the Tomtor-type ultra-rich rare metal ores and the surface facies of weathering profiles are opposite. The obtained results do not confirm the genetic link between the unique Tomtor ores and the surface facies of the crust of carbonatites, but serve as evidence of their later formation due to the reductive epigenesis of carbonatite weathering products under the influence of solutions draining the overlying coaliferous rocks. Wide distribution of the phenomena of colloidal liquid layering into manganese and ferruginous fractions was established for the first time in surface facies of the weathering crust of carbonatites, and active lateral colloidal migration of Ti from the host rocks was revealed.
DS202103-0392
2020
Latutrie, B., Ross, P-S.What lithic clasts and lithic-rich facies can tell us about diatreme processes: an example at Round Butte, Hopi Buttes volcanic field, Navajo Nation, Arizona.Journal of Volcanology and Geothermal Research ( researchgate), 34p. PdfUnited States, Arizonadiatremes

Abstract: Round Butte (Hopi Buttes volcanic field, Arizona) exposes a diatreme 170-190 m across, 190 m below the pre-eruptive surface. The central part of the massif is 130-150 m in diameter, displaying 20-30 m-high subvertical cliffs. The well-known layer-cake stratigraphy of the sedimentary rocks of the Colorado Plateau permits identification of the largest lithic fragments preserved in the Round Butte diatreme. We define three main groups of pyroclastic facies: undisturbed beds, disturbed beds and non-bedded rocks. Two other minor facies groups were mapped: megablocks (blocks over 2 m in long axis), and small-volume debris avalanche deposits. Pyroclastic megablocks are finer grained and richer in lithic clasts than most diatreme rocks surrounding them. These pyroclastic megablo