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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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2021 Technical Reference Compilation
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.
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.
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.
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.
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.
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.
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.
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.
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 (SREEs) 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 d18OV-SMOW values range between 7.48 and 10.05‰, while d13CV-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 d13CV-PDB and d18OV-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.
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.
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.
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.
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.
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).
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.
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; eHfe: +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; eHfe: -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 (eHfi?=?+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, eNdi?=?+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.
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, a = 83.458(6)°, ß = 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.
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.
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.
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.
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.
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 SREEs, 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 SREEs (REEdef), the studied deposits can be considered as promising to highly promising REE ores and could represent a profitable alternative source for critical REEs.
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.
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.
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 µm 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.
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
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?
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.
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.
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.
Cherry, J.The future of pink diamonds.Gems&Jewellery, Vol. 30, 1, pp. 32-35.Globalmarkets
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.
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.
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.
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 Eskisehir-Kizilcaören (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 Kizilcaören 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 Karapinar limestone, which hosts the F-REE-Th mineralization in contact zones. A carbonatite sample from the Kizilcaören region displays both a total rare earth element (TREE) concentration (4795 ppm) and d11B (-6.83‰) isotope composition consistent with mantle-derived carbonatite; whereas it is characterized by heavier d13C (+1.43‰) and d18O (+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 d13C (-0.14 to -0.75‰), d18O (+27.36 to +30.61‰), and d11B (+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 Kizilcaören and the Kuluncak regions consist of hydrothermally metasomatized carbonatite and limestone, respectively. The mineralization in the Kizilcaören 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.
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.
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
Cohen, T.Crowning glory ( Almod Diamonds) patented diamond cut.Gems & Jewellery, Vol. 29, 4, pp. 42-44. pdfUnited States, New Yorkdiamond cutting
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.
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.
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.
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.
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 (eNd = +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 (eNd = -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.
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
De Wit, M.Paleozoic diamond deposits of the NW Province, South Africa.Wits Geotalk recorded, https://youtu.be/ BajbGtkTqpEAfrica, South Africaalluvials
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.
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.
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.
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.
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
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 (d13C = -4.1 ± 1.9‰ [PDB] and dl8O = 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.
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 µ-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.
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 d18?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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Evans, R.Grading fancy shaped diamonds. Gems & Gemology , Vol. 29, 4, p. 31. pdfGlobalgemmology
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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 d18O 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.
Fritsch, E.Revealing the formation secrets of the Matryosha diamond.Journal of Gemmology, Vol. 37, 5, pp. 528-533.Russiadiamond genesis
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.
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.
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
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.
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.
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.
Geophysics ContractorsCompiled List of geophysical contractors sent out to members of SEGMIN. *** not specific to diamonds Geophysical contractors, SEGMIN website 13p. PdfGlobalgeophysics
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.
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.
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.
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
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.
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.
Gonzales, A.New rating system for coloured gemstones.Gems&Jewellery, Vol. 30, 1, p. 31.Globalgemstones
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.
Goodden, R.Ocean diamonds - alluvialsGems & Jewellery, Vol. 29, 4, pp. 14-16. pdfAfrica, Namibiaalluvials
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.
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 (d13C?
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.
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.
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.
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.
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 µW/m3 (n = 3) whereas mafic granulites have an average heat production of 0.13 ± 0.03 µW/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 µW/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.
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.
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*, eSr and eNd widely used in magmatic petrology.
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.
Hainschwang, T.Wrestling with radiation ( diamonds)Gems & Jewellery, Vol. 29, 4, pp. 28-41.Globaldiamond colour
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.
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.
Harlow, G.The American Museum of Natural History Gem exhibit.Gems&Jewellery, Vol. 30, 1, pp. 18-20.United States, New YorkGem exhibit
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.
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.
Hills, S.Fluorescence microscopy: the revolution revolving.Carnegiescience.edu, June 8, 2pm. ESTGlobalfluorescence
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
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.
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.
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.
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.
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 <<10,000). Total PGE abundance in BMS range from 0.17 to 223 ppm. We recognise four end-member compositions (types i to iv), distinguished by total PGE abundance and Pt/Pd and Au/Pd ratios. The majority of BMS have low PGE abundances (< 10 ppm) but Type iv BMS have the highest concentration of PGE recorded in eclogites so far (> 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.
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 eNd and eHf, 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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?µm 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.
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.
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.
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.
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 eNd(i) and variably radiogenic Sr(i), whereas the rocks of the Permian lamprophyre association of anorogenic affinity are characterized by positive eNd(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.
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 Certák and Repište 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.
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.
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
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.
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.
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.
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 O-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.
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 d¹³? = -10.52‰ VPDB t? -12.82‰ VPDB (average d¹³? = -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.
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 megablocks are interpreted as subsided portions of the maar ejecta ring. Sedimentary megablocks originate either from above, or from the same level, relative to their current location, i.e. no megablock has a net upward displacement. Small-volume debris avalanche deposits are poorly sorted deposits resulting from gravitational destabilization of the surrounding country rocks into the syn-eruptive crater. Small-volume debris avalanches and individual megablock collapse are the main ways in which the crater grew in size laterally during the eruption. We combine the componentry of the disturbed bedded pyroclastic facies, the non-bedded pyroclastic facies and the pyroclastic megablocks with a series of conceptual models for country rock fragmentation. This exercise further allows us to estimate diatreme wall slopes of 70° below the Bidahochi Formation to approximately the depth of the root zone around 440 m below the pre-eruptive surface. Lithic fragments at the current level of exposure come from elevations up to 190 m above (i.e., up to the pre-eruptive surface) and up to 250 m below (i.e., down to the root zone) their current locations. Pyroclastic units displaying the richest content of lithic clasts with a deep origin are typically the non-bedded facies interpreted to have formed from debris jets during the eruption.
Lawley, C.J.M., Somers, A.M., Kjarsgaard, B.A.Rapid geochemical imaging of rocks and minerals with handheld laser induced breakdown spectroscopy. ( LIBS)Journal of Geochemical Exploration, Vol. 222, 106694, 16p. PdfCanada, Nunavutdeposit - Jericho, Muskox

Abstract: Geochemical imaging is a powerful tool for unravelling the complex geological histories of rocks and minerals. However, its applications have until recently been restricted to geological research in a lab environment due to the cost and size of conventional instrumentation, long analysis times, and extensive sample preparation for some methods. Herein we present a rapid, qualitative geochemical imaging method for rocks and minerals using handheld LIBS. Analyses were completed directly on sawed drill core surfaces for a suite of kimberlite-hosted mantle xenoliths (Jericho and Muskox kimberlites, Nunavut, Canada). Semi-automated LIBS spectral processing following a new open-source workflow allows stitching of multiple small-area maps (each approximately 3 × 3 mm that take 2-3 min to complete) to produce cm-scale geochemical images of variably altered mantle xenolith samples (total data acquisition in 1-2 h). Replicate analyses of a Znsingle bondAl alloy reference material (NZA-1; CANMET) that were undertaken during standard-sample bracketing suggests that the relative standard deviation (RSD) is typically 15-20% for sum-normalized emission intensities above the estimated background. We demonstrate with open-source machine learning tools how qualitative LIBS spectral data can be converted to Feature-Of-Interest (FOI) maps to distinguish a variety of metasomatic and alteration features (e.g., Cr-diopside, kelyphite rims on pyrope garnet, and calcite veinlets) from the primary mantle mineralogy (e.g., olivine and orthopyroxene). Our results further demonstrate that the resolution of handheld LIBS-based geochemical imaging is sufficient to map veinlets and grain boundaries lined with metasomatic minerals. The LIBS approach is particularly sensitive for mapping the microscale distribution of elements with low atomic number (e.g., Li and Na). These light elements are difficult to detect at low concentrations with other handheld and field-portable technologies, but represent important geochemical tracers of hydrothermal and magmatic processes. Rapid LIBS mapping thus represents an emerging geochemical imaging tool for unravelling the complex geological history of rocks and minerals in the field with minimal to no sample preparation.
Le Pape, F., Jones, A.G., Jessell, M.W., Hogg, C., Siebenaller, L., Perrouty, S., Tour, A., Oiuya, P., Boren, G.The nature pf the southern West Africa craton lithosphere inferred from its electrical resistivity.Precambrian Research, Vol. 358, 106190, 15p. Pdf Africageophysics

Abstract: The West-African craton is defined by a combination of Archean and Palaeoproterozoic rocks that stabilised at ~2 Ga towards the end of the Paleoproterozoic Eburnean Orogeny, and therefore may reflect the transition from Archean to modern tectonic processes. Exploring its present lithospheric architecture aids further understanding of not only the craton’s stability through its history but also its formation. We investigate the lithospheric structure of the craton through analysing and modelling magnetotelluric (MT) data from a 500-km-long east-west profile in northern Ghana and southern Burkina Faso crossing part of the Baoulé-Mossi Domain and reaching the Volta Basin in the south-eastern part of the craton. Although the MT stations are along a 2D profile, due to the complexity of the structures characterising the area, 3D resistivity modelling of the data is performed to obtain insights on the thermal signature and composition of the subcontinental lithosphere beneath the area. The thermal structure and water content estimates from different resistivity models highlight a strong dependence on the starting model in the 3D inversions, but still enable us to put constraints on the deep structure of the craton. The present-day thermal lithosphere-asthenosphere boundary (LAB) depth is estimated to be at least 250 km beneath the Baoulé-Mossi domain. The area likely transitions from a cold and thick lithosphere with relatively low water content into thinner, more fertile lithosphere below the Volta Basin. Although the inferred amount of water could be explained by Paleoproterozoic subduction processes involved in the formation of the Baoulé-Mossi domain, later enrichment of the lithosphere cannot be excluded.
Le Pichon, X., Jellinek, M., Lenardic, A., Sengor, A.M.C., Imren, C.Pangea migration.Tectonics, e2020TC006585 42p. PdfMantleplate tectonics

Abstract: We confirm the proposition of Le Pichon et al. (2019) that Pangea was ringed by a hemispheric subduction girdle from its formation 400 Ma to its dispersal 100 Ma. We quantify the northward migration, that we attribute to True Polar Wander (TPW), of its axis of symmetry, between 400 Ma and 150 Ma, from southern latitudes to the equatorial zone. The spatial stabilizing within the equatorial zone of the axis of symmetry in a fixed position with respect to lower mantle, was marked by alternating CW and CCW oscillations between 250 Ma and 100 Ma that we relate to tectonic events. A subduction girdle is predicted to set up lateral temperature gradients from relatively warm sub-Pangean mantle to cooler sub-oceanic mantle. Over time, this effect acts to destabilize the Pangea landmass and its associated subduction girdle. Quantitatively, a scaling theory for the stability of the subduction girdle against mantle overturn constrains the maximum magnitude of sub-Pangean warming before breakup to be order 100 oC, consistent with constraints on Pacific-Atlantic oceanic crustal thickness differences. Our predictions are in line with recent analyses of Jurassic-Cretaceous climate change and with existing models for potential driving forces for a TPW oscillation of Pangea across the equator. The timing and intensity of predicted sub-Pangean warming potentially contributed to the enigmatically large Siberian Traps and CAMP flood basalts at 250 Ma and 201 Ma, respectively.
Lebel, D.Geological survey of Canada 8.0: mapping the journey towards predictive geoscience.Hill, P.R., Lebel, D., Hitzman, M., Smelror, M., Thorleifson, H. eds The changing role of Geological Surveys . GSL SP 499, Vol. 499, pp. 28-30. pdfCanadatechnology

Abstract: The Geological Survey of Canada (GSC) has been furthering the geoscientific understanding of Canada since its inception in 1842, the equivalent of seven generations ago. The evolution of the activities of the GSC over this period has been driven by evolving geographic, economic and political contexts and needs. Likewise, new technologies and evolving scientific methods and models shaped broadly the successive generations of GSC geoscience activities. The most recent GSC generation presented a mixed portfolio of large framework mapping geoscience programmes, and more targeted, hypothesis-driven geoscience research, and the development of decision support products for a range of government, industry and other stakeholders needs. Entering its eighth generation, the GSC and related organizations are embracing digital technologies for applications such as the evaluation of mineral resource potential, the evaluation of risks and the early warning of earthquakes. In order to do so, the GSC will need to develop new methods and systems in co-operation with other geological survey organizations, and target its data acquisition and research to further advance its ability to respond to the evolving needs of society to navigate geology through space and time, from the past to the present, and from the present to the future.
Letnikova, E.F., Izokh, A.E., Kosticin, Y.A., Letnikov, F.A., Ershova, V.B., Federyagina, E.N., Ivanov, A.V., Nojkin, A.D., Shkolnik, S.I., Brodnikova, E.A.High-potassium volcanism approximately 640 Ma in the southwestern Siberian platform ( Biryusa uplift Sayan region).Doklady Earth Sciences, Vol. 496, 1, pp. 53-59.Russia, Siberiaalkaline rocks

Abstract: On the basis of petrographic and mineralogical studies, we have established the presence of clastic rocks with a strong predominance of K-feldspar among the rock-forming fragments within the Late Precambrian sedimentary sequence in the southwestern part of the Siberian Platform. Two types of mineralogical occurrence of K-feldspars are determined: (1) huge zonal crystal clasts with increased Ba concentrations in the central parts of the grains and (2) the main mineral phase in the form of a decrystallized glassy mass. In both cases, low concentrations of Na (lower than 0.1 wt %) are detected. K-feldspars of the second type contain intergrowths of idiomorphic rhombic dolomite with a high ankerite component. Dolomite grains contain inclusions of K-feldspar. The prevailing accessory minerals are F-apatite (with high concentrations of REEs), zircon (with high concentrations of Th), magnetite, rutile, monacite, and sinchizite. Encasement minerals with an idiomorphic shape are identified, with K-feldspar being located in the center, while the middle shell is formed by apatite with a high REE content, and the outer shell is formed by apatite without rare earth elements. These rocks are products of high-potassium volcanic activity. The age of this event has been established on the basis of U-Pb zircon dating to about 640 Ma. The Lu-Hf zircon systematics for these rocks indicates the connection of volcanism with igneous events of mantle genesis within its range. The products of explosive eruption, which are widespread within the Biryusa uplift of the Siberian Platform, were erroneously considered earlier as Riphean sedimentary rocks of the Karagas Series.
Li, W., Xie, X., Song, J., Xie, R., Wang, J., Li, G.,Hou, H., Lu, J.Assessment and source identification of toxic metals in an abandoned synthetic diamond production plant from Anhui Province, China.Environmental Forensics, Vol. 22, 3-4, pp. 340-350. abstract onlyChinasynthetics

Abstract: In this study, soil and sediment samples along with groundwater samples were collected and analyzed from an abandoned synthetic diamond production plant in Anhui Province, South China. Chemical analysis, pollution characteristics analysis, and correlation analysis were conducted to assess and to determine the source(s) of the toxic metal and organic pollutions in the study sites. The Co and Ni concentrations of soil samples collected from the production area exceed the risk screening value for contaminated development land in Soil Environment Quality Standards for soil pollution risk control on construction land (Trial) of China, while the concentrations of other toxic elements such as Cr, Cu, and Zn are lower than the screening value. The PCA and HCA results are consistent with the correlation coefficient analysis and indicate that industrial activities are the main sources of Co and Ni. The chemical composition and source analysis results of soil and groundwater show that toxic metals originating from catalyst and low pH value from acid waste water should be the main point of concern in the synthetic diamond production plant.
Li, Y., Sun, J., Shuling, L., Leao-Santos, M.A paradigm shift in magnetic data interpretation; increased value through magnetization inversions.Geophysics Leading Edge, Vol. 40, 2, pp. 89-98.Canada, South America, Brazilgeophysics

Abstract: Magnetic data are sensitive to both the induced magnetization in rock units caused by the present earth's magnetic field and the remanent magnetization acquired by rock units in past geologic time. Susceptibility is a direct indicator of the magnetic mineral content, whereas remanent magnetization carries information about the formation process and subsequent structural movement of geologic units. The ability to recover and use total magnetization, defined as the vectorial sum of the induced and remanent magnetization, therefore enables us to take full advantage of magnetic data. The exploration geophysics community has achieved significant advances in inverting magnetic data affected by remanent magnetization. It is now feasible to invert any magnetic data set for total magnetization. We provide an overview of the state of the art in magnetization inversion and demonstrate the informational value of inverted magnetization through a set of case studies from mineral exploration problems. We focus on the methods that recover either the magnitude of the total magnetization or the total magnetization vector itself.
Liang, Y., Ji, Z., Liu, B.What can we learn from REE abundances in clinopyroxene and orthopyroxene in residual mantle peridotites?Contributions to Mineralogy and Petrology, 176, 19p. PdfMantleREE

Abstract: Clinopyroxene and orthopyroxene are the two major repositories of rare earth elements (REE) in spinel peridotites. Most geochemical studies of REE in mantle samples focus on clinopyroxene. Recent advances in in situ trace element analysis has made it possible to measure REE abundance in orthopyroxene. The purpose of this study is to determine what additional information one can learn about mantle processes from REE abundances in orthopyroxene coexisting with clinopyroxene in residual spinel peridotites. To address this question, we select a group of spinel peridotite xenoliths (9 samples) and a group of abyssal peridotites (12 samples) that are considered residues of mantle melting and that have major element and REE compositions in the two pyroxenes reported in the literature. We use a disequilibrium double-porosity melting model and the Markov chain Monte Carlo method to invert melting parameters from REE abundance in the bulk sample. We then use a subsolidus reequilibration model to calculate REE redistribution between cpx and opx at the extent of melting inferred from the bulk REE data and at the closure temperature of REE in the two pyroxenes. We compare the calculated results with those observed in clinopyroxene and orthopyroxene in the selected peridotitic samples. Results from our two-step melting followed by subsolidus reequilibration modeling show that it is more reliable to deduce melting parameters from REE abundance in the bulk peridotite than in clinopyroxene. We do not recommend the use of REE in clinopyroxene alone to infer the degree of melting experienced by the mantle xenolith, as HREE in clinopyroxene in the xenolith are reset by subsolidus reequilibration. In general, LREE in orthopyroxene and HREE in clinopyroxene are more susceptible to subsolidus redistribution. The extent of redistribution depends on the modes of clinopyroxene and orthopyroxene in the sample and thermal history experienced by the peridotite. By modeling subsolidus redistribution of REE between orthopyroxene and clinopyroxene after melting, we show that it is possible to discriminate mineral mode of the starting mantle and cooling rate experienced by the peridotitic sample. We conclude that endmembers of the depleted MORB mantle and the primitive mantle are not homogeneous in mineral mode. A modally heterogeneous peridotitic starting mantle provides a simple explanation for the large variations of mineral mode observed in mantle xenoliths and abyssal peridotites. Finally, by using different starting mantle compositions in our simulations, we show that composition of the primitive mantle is more suitable for modeling REE depletion in cratonic mantle xenoliths than the composition of the depleted MORB mantle.
Lima, N.M., Azzone, R.G., Chmyz, L.Petrographic, geochemical and isotopic evidence of crustal assimilation processes in the Indiaia-II kimberlite, Alto Paranaiba Province, southeast Brazil.The Canadian Mineralogist, Vol. 58, pp. 563-585.South America, Brazil, Paranaibadeposit - Indiaia-II

Abstract: The Indaiá-I and Indaiá-II intrusions are hypabyssal, small-sized ultrabasic bodies belonging to the Cretaceous magmatism of the Alto Paranaiba Alkaline Province (southeast-central western Brazil). While Indaiá-I is classified as an archetypal group-I kimberlite, Indaiá-II (its satellite intrusion) presents several petrographic and chemical distinctions: (1) an ultrapotassic composition (similar to kamafugites), (2) lower volumes of olivine macrocrysts, (3) diopside as the main matrix phase (in contrast with the presence of monticellite in Indaiá-I), (4) high amounts of phlogopite, and (5) abundant felsic boudinaged and stretched microenclaves and crustal xenoliths. Disequilibrium features, such as embayment and sieve textures in olivine and clinopyroxene grains, are indicative of open-system processes in Indaiá-II. Mineral reactions observed in Indaiá-II (e.g., diopside formed at the expense of monticellite and olivine; phlogopite nearby crustal enclaves and close to olivine macrocrysts) point to an increase in the silica activity of the kimberlite magma; otherwise partially melted crustal xenoliths present kalsilite, generated by desilification reactions. The high Contamination Index (2.12-2.25) and the large amounts of crustal xenoliths (most of them totally transformed or with evidence of partial melting) indicate a high degree of crustal assimilation in the Indaiá-II intrusion. Calculated melts (after removal of olivine xenocrysts) of Indaiá-II have higher amounts of SiO2, Al2O3, K2O, slightly higher Rb/Sr ratios, lower Ce/Pb and Gd/Lu ratios, higher 87Sr/86Sr, and lower 143Nd/144Nd than those calculated for Indaiá-I. Crustal contamination models were developed considering mixing between the calculated melts of Indaiá-I and partial melts modeled from the granitoid country rocks. Mixing-model curves using major and trace elements and isotopic compositions are consistent with crustal assimilation processes with amounts of crustal contribution of ca. 30%. We conclude that (1) Indaiá-II is representative of a highly contaminated kimberlitic intrusion, (2) this contamination occurred by the assimilation of anatectic melts from the main crustal country rocks of this area, and (3) Indaiá-I and Indaiá-II could have had the same parent melt, but with different degrees of crustal contamination. Our petrological model also indicates that Indaiá-II is a satellite blind pipe linked to the main occurrence of Indaiá-I.
Litasov, K.D., Kagi, H., Bekker, T.B., Makino, Y., Hirata, T., Brazhkin, V.V.Why Tolbachik diamonds cannot be natural.The American Mineralogist, Vol. 106. pp. 44-53. pdfRussiadeposit - Kamchatka

Abstract: Taking into account recent publications, we provide additional comprehensive evidence that type Ib cuboctahedral diamonds and some other microcrystalline diamonds from Kamchatka volcanic rocks and alluvial placers cannot be natural and undoubtedly represent synthetic materials, which appear in the natural rocks by anthropogenic contamination. The major arguments provided in favor of the natural origin of those diamonds can be easily disproved. They include the coexistence of diamond and deltalumite from Koryaksky volcano; coexistence with super-reduced corundum and moissanite, Mn-Ni silicide inclusions, F-Cl enrichment and F/Cl ratios, and carbon and nitrogen isotopes in Tolbachik diamonds, as well as microtwinning, Mn-Ni silicides, and other inclusions in microcrystalline diamond aggregates from other Kamchatka placers. We emphasize the importance of careful comparison of unusual minerals found in nature, which include type Ib cuboctahedral diamonds and super-reduced phase assemblages resembling industrial slags, with synthetic analogs. The cavitation model proposed for the origin of Tolbachik diamonds is also unreliable since cavitation has only been shown to cause the formation of nanosized diamonds only.
Liu, J., Pearson, D.G., Wang, L.H., Mather, K.A., Kjarsgaard, B.A., Schaeffer, A.J., Irvine, G.J., Kopylova, M.G., Armstrong, J.P.Plume-driven recratonization of deep continental lithospheric mantle.Nature, doi.org/101038/ s41586-021-03395-5 5p. PdfCanada, Northwest Territoriescraton

Abstract: Cratons are Earth’s ancient continental land masses that remain stable for billions of years. The mantle roots of cratons are renowned as being long-lived, stable features of Earth’s continents, but there is also evidence of their disruption in the recent1,2,3,4,5,6 and more distant7,8,9 past. Despite periods of lithospheric thinning during the Proterozoic and Phanerozoic eons, the lithosphere beneath many cratons seems to always ‘heal’, returning to a thickness of 150 to 200 kilometres10,11,12; similar lithospheric thicknesses are thought to have existed since Archaean times3,13,14,15. Although numerous studies have focused on the mechanism for lithospheric destruction2,5,13,16,17,18,19, the mechanisms that recratonize the lithosphere beneath cratons and thus sustain them are not well understood. Here we study kimberlite-borne mantle xenoliths and seismology across a transect of the cratonic lithosphere of Arctic Canada, which includes a region affected by the Mackenzie plume event 1.27 billion years ago20. We demonstrate the important role of plume upwelling in the destruction and recratonization of roughly 200-kilometre-thick cratonic lithospheric mantle in the northern portion of the Slave craton. Using numerical modelling, we show how new, buoyant melt residues produced by the Mackenzie plume event are captured in a region of thinned lithosphere between two thick cratonic blocks. Our results identify a process by which cratons heal and return to their original lithospheric thickness after substantial disruption of their roots. This process may be widespread in the history of cratons and may contribute to how cratonic mantle becomes a patchwork of mantle peridotites of different age and origin.
Liu, Y., Huang, R., Wu, Ye, Zhang, D., Zhang, J., Wu, X.Thermal equation of state of phase egg ( AlSi03OH): implications for hydrous phases in the deep Earth.Contributions to Mineralogy and Petrology, Vol. 176, 8 doi.org/10.1007 /s00410-020- 01758-1 10p. PdfMantlesubduction
Liu, Z., Shea, J., Foley, S., Bussweiler, Y., Rohrbach, A., Klemme, S., BerndtClarifying source assemblages and metasomatic agents for basaltic rocks in eastern Australia using olivine phenocryst compositions. Basanites, melilititesLithos, in press available, 74p. PdfAustraliametasomatism

Abstract: Many Cenozoic basaltic rocks in Eastern Australia exhibit an age-progressive trend from north to south, leading to the suggestion that one or more mantle plumes passed beneath the Australian plate. Trace element patterns indicate that the source regions have been metasomatised by infiltrating melts, but the source rock assemblages have never been closely identified. Here, trace element analyses of olivine and whole rock geochemistry for several occurrences in New South Wales (Bingara-Inverell, Dubbo, Barrington and Ebor) are combined to characterize the mineralogy of the source and identify the nature of the melts that caused the metasomatic enrichment. According to Ni/Mg against Mn/Fe and Zn/Fe ratios in olivines, Zn/Fe and FC3MS (FeOT/CaO-3*MgO/SiO2) parameters in whole rocks, tholeiite, alkali basalt, and basanite rich in olivine xenocrysts from Dubbo were derived from pyroxenite-dominated mixed source, mixed pyroxenite+peridotite source, and peridotite-dominated source, respectively. Similarly, basalts from Ebor and Bingara/Inverell are suggested to originate from a mixed pyroxenite+peridotite source based on their high FC3MS values. In contrast, the source of basanite and picrobasalt from Barrington was peridotite with little pyroxenite. High Li and Zn in olivines, high P2O5/TiO2 and Zr/Hf at low Ti/Eu in whole rocks illustrate that the pyroxenite sources of basanites from Bingara/Inverell, Barrington and Dubbo resulted from variable degrees of carbonatitic metasomatism. Partial melting of peridotite metasomatised by carbonatite melts at around the spinel-garnet peridotite transition depth produced basalts and basanites from Dubbo, Barrington, Ebor, Bingara/Inverell and Buckland (Queensland). Carbonatitic metasomatism is widespread in the eastern Australian mantle lithosphere, occurring seaboard of a ledge between thick lithosphere beneath the Australian continent that stretches from Queensland, through New South Wales to Victoria.
Live ScienceA remnant of a protoplanet may be hiding inside Earth.livescience.com, March 29, 2p.Mantlecore - boundary
Lock, N.Use and misuse of historical estimates and data - examples from diamond projects.saimm.co.za, 8p. PdfAfrica, South Africaeconomics

Abstract: Projects with long histories must be documented in current disclosures with transparency and materiality, using historical data and historical estimates. Historical data may be of great value if it is from a reliable source, and the raw data can be validated and/or duplicated. Historical estimates can and should be reported, but with qualification of the ever-changing economic parameters of ‘Reasonable Prospects for Eventual Economic Extraction’ (RPEEE). The SAMREC Code requires current sampling results and diamond valuations, without which RPEEE cannot be assessed; consequently, historical estimates cannot ever be declared as current Diamond Resources or Reserves. The SAMREC Code defines historical estimates and provides guidance on the use of historical data. Examples from real projects and reports in the public domain are reviewed in this paper. Opinions on use and misuse are those of the writer; judgment on good or bad practice is not the intention and is left to the opinion of the reader. Comparison, with both the JORC Code (Australasia) and CIM Definition Standards and National Instrument 43-101 (Canada), is provided. The SAMREC Code appears to be more closely aligned with the Canadian standards.
Lollar, B.S., Heuer, V.B., McDermott, J., Tille, S., Warr, O., Moran, J.J., Telling, J., Hinrichs, K-U.A window into the abiotic carbon cycle - acetate and formate in fracture waters in 2.7 billion year-old host rocks of the Canadian shield. ( Not specific to diamonds just interest)Geochimica et Cosmochimica Acta, Vol. 294. pp. 295-314. pdfCanadacarbon

Abstract: The recent expansion of studies at hydrothermal submarine vents from investigation of abiotic methane formation to include abiotic production of organics such acetate and formate, and rising interest in processes of abiotic organic synthesis on the ocean-world moons of Saturn and Jupiter, have raised interest in potential Earth analogs for investigation of prebiotic/abiotic processes to an unprecedented level. The deep continental subsurface provides an attractive target to identify analog environments where the influence of abiotic carbon cycling may be investigated, particularly in hydrogeological isolated fracture fluids where the products of chemical water-rock reactions have been less overprinted by the biogeochemical signatures of the planet’s surficial water and carbon cycles. Here we report, for the first time, a comprehensive set of concentration measurements and isotopic signatures for acetate and formate, as well as the dissolved inorganic and organic carbon pools, for saline fracture waters naturally flowing 2.4?km below surface in 2.7 billion year-old rocks on the Canadian Shield. These geologically ancient fluids at the Kidd Creek Observatory were the focus of previous investigations of fracture fluid geochemistry, microbiology and noble gas-derived residence times. Here we show the fracture waters of Kidd Creek contain high concentrations of both acetate and formate with concentrations from 1200 to 1900?µmol/L, and 480 to 1000?µmol/L, respectively. Acetate and formate alone account for more than 50-90% of the total DOC - providing a very simple "organic soup". The unusually elevated concentrations and profoundly 13C-enriched nature of the acetate and formate suggest an important role for abiotic organic synthesis in the deep carbon cycle at this hydrogeologically isolated site. A variety of potential abiotic production reactions are discussed, including a radiolytically driven H, S and C deep cycle that could provide a mechanism for sustaining deep subsurface habitability. Scientific discoveries are beginning to reveal that organic-producing reactions that would have prevailed on Earth before the rise of life, and that may persist today on planets and moons such as Enceladus, Europa and Titan, can be accessed in some specialized geologic settings on Earth that provide valuable natural analog environments for the investigation of abiotic organic chemistry outside the laboratory.
Lou, W., Zhang, D., Bayless, R.C.Review of mineral recognition and its future. AI techniquesApplied Geochemistry, Vol. 122, 104727, 10p. PdfGlobalmineralogy

Abstract: Mineral identification is a basic skill in geological studies, and is useful for characterizing rocks and tracing diagenesis and mineralization processes. Traditional methods of observation under a microscope are subject to many complex factors such as the limitations of resolution and magnification, so they are poor in qualitative analysis, and inefficient. With the expansion of geological prospecting, it is necessary to provide information for all minerals, pores and trace elements in rocks. So, mineral identification has started to rely on advanced microbeam mineral analysis techniques. This paper summarizes the common mineral analysis techniques such as Raman spectroscopy, X-ray fluorescence spectrometry (XRF), X-ray diffraction (XRD), Scanning electron microscopy (SEM), and Automated mineralogy (AM) systems. These microbeam technologies now approach a semi-automated analysis process, and most of these methods mainly detect the chemical composition of the mineral, rather than the mineral's optical characteristics which are the most basic properties of minerals. Therefore, this study proposes a method that can use mineral's optical features for automatic classification, mineral recognition based on convolutional neural network (CNN) and face recognition technology. The feasibility, research status and outlook of this method are also discussed. The proposed method uses convolution neural network technology to automatically extract the optical characteristics of minerals for mineral identification. Successful application of these techniques will have profound application value by reducing the cost and time needed to process and identify minerals.
Luo, Y., Korenaga, J.Efficiency of eclogite removal from continental lithosphere and its implications for cratonic diamonds. CLMGeology, in press available 5p. PdfMantlemelting

Abstract: Continental lithospheric mantle (CLM) may have been built from subducted slabs, but the apparent lack of concurrent oceanic crust in CLM, known as the mass imbalance problem, remains unresolved. Here, we present a simple dynamic model to evaluate the likelihood of losing dense eclogitized oceanic crust from CLM by gravitational instability. Our model allowed us to assess the long-term evolution of such crust removal, based on how thermal and viscosity profiles change over time across the continental lithosphere. We found that the oceanic crust incorporated early into CLM can quickly escape to the asthenosphere, whereas that incorporated after a certain age would be preserved in CLM. This study provides a plausible explanation for the mass imbalance problem posed by the oceanic ridge origin hypothesis of CLM and points to the significance of preservation bias inherent to the studies of cratonic diamonds.
Lv, M., Dorfman, S.M., Badro, J., Borensztajin, S., Greenberg, E., Prakapenka, V.B.Reversal of carbonate-silicate cation exchange in cold slabs in Earth's lower mantle. Nature Communications, doi.org/10.10.1038 /s41467-021-21761-9 8p. PdfMantlediamond inclusions

Abstract: The stable forms of carbon in Earth’s deep interior control storage and fluxes of carbon through the planet over geologic time, impacting the surface climate as well as carrying records of geologic processes in the form of diamond inclusions. However, current estimates of the distribution of carbon in Earth’s mantle are uncertain, due in part to limited understanding of the fate of carbonates through subduction, the main mechanism that transports carbon from Earth’s surface to its interior. Oxidized carbon carried by subduction has been found to reside in MgCO3 throughout much of the mantle. Experiments in this study demonstrate that at deep mantle conditions MgCO3 reacts with silicates to form CaCO3. In combination with previous work indicating that CaCO3 is more stable than MgCO3 under reducing conditions of Earth’s lowermost mantle, these observations allow us to predict that the signature of surface carbon reaching Earth’s lowermost mantle may include CaCO3.
Magna, T., Viladar, S., Rapprich, V., Pour, O., Hopp, J., Cejkova, B.Nb-V enriched sovites of the northeastern and eastern part of the Amba Dongar carbonatite ring dike, India - a reflection of post-emplacement hydrothermal overprint?Geochemistry, Vol. 80, doi.org/10.1016 /j.chemer.2019 .125534 11p. PdfIndiadeposit - Amba Dongar

Abstract: Wakefieldite-(Ce,La) and vanadinite in coarse-grained calciocarbonatites (sovites) are for the first time reported from the northeastern part of the worldwide largest fluorite deposit at the Amba Dongar carbonatite ring dike, India. Sovite in this part of the carbonatite ring dike is rich in pyrochlore, calcite and magnetite. Pyrochlore makes up almost 50% of some sovite samples and shows core-to-rim compositional changes. The core of pyrochlore consists of primary fluorcalciopyrochlore with high F and Na contents while the margins gained elevated amounts of Pb, La and Ce with the associated loss of F and Na due to circulation of hydrothermal solutions. The presence of wakefieldite-(Ce,La) and vanadinite points to an exceptionally high V abundance in hydrothermal solutions formed towards the end of the carbonatite magma activity. This investigation thus opens new promising areas for Nb and REE prospection in the eastern part of the Amba Dongar carbonatite body.
Malkovets, V.G., Shatsky, V.S., Dak, A.I., Gibsher, A.A., Yakovlev, I.V., Belousova, E.A., Tsujimori, T., Sobolev, N.V.Evidence for multistage and polychronous alkaline-ultrabasic Mesozoic magmatism in the area of diamondiferous placers of the Ebelyakh River basin, ( eastern slope of the Anabar shield).Doklady Earth Sciences, Vol. 496, 1, pp. 48-52.Russiadeposit - Anabar

Abstract: New mineralogical and isotope-geochemical data for zircon megacrysts (n = 48) from alluvium of Kholomolokh Creek (a tributary of the Ebelakh River) are reported. Using the geochemical classification schemes, the presence of zircons of kimberlitic and carbonatitic genesis was shown. The U-Pb dating of zircons revealed two major age populations: the Triassic (258-221 Ma, n = 18) and Jurassic (192-154 Ma, n = 30). Weighted mean 206Pb/238U ages allowed us to distinguish the following age stages: 155 ± 3, 161 ± 2, 177 ± 1.5, 183 ± 1.5, 190 ± 2, 233 ± 2.5, and 252 ± 4 Ma. It is suggested that the Ebelyakh diamonds could have been transported from the mantle depths by kimberlite, as well as by other related rocks, such as carbonatite, lamprophyre, lamproite, olivine melilitite, etc. Diamonds from the Ebelyakh placers most likely have polygenic native sources and may be associated with polychronous and multistage Middle Paleozoic and Mesozoic kimberlite and alkaline-ultrabasic magmatism in the eastern slope of the Anabar Shield (the Ebelyakh, Mayat, and Billyakh river basins).
Manning, C.E., Frezzotti, M.L.Subduction-zone fluids. Deep fluidsElements, Vol. 16, pp. 395-400.Mantlewater

Abstract: Fluids are essential to the physical and chemical processes in subduction zones. Two types of subduction-zone fluids can be distinguished. First, shallow fluids, which are relatively dilute and water rich and that have properties that vary between subduction zones depending on the local thermal regime. Second, deep fluids, which possess higher proportions of dissolved silicate, salts and non-polar gases relative to water content, and have properties that are broadly similar in most subduction systems, regardless of the local thermal structure. We review key physical and chemical properties of fluids in two key subduction-zone contexts-along the slab top and beneath the volcanic front-to illustrate the distinct properties of shallow and deep subduction-zone fluids.
Marshall, T., Ward, J.D., de Wit, M.C.Alluvial diamond deposits across Africa - a travelogue.Geological Society of South Africa presentation, https://www.youtube.com/watch?v=1tsWuXo6fB4&t=23sAfrica, Lesotho, Cote d'Ivoire, Democratic Republic of Congo, Tanzania, Angola, South Africa, Ghana, Mauritania, Zimbabwe, Namibia, Central African Republic, Cameroon, Swaziland, Mali, Sierra Leone, Liberia, Guineaalluvials
Marshall, T.R.Evaluation of secondary diamond ( and gemstone) deposits according to SAMREC code.saimm.co.za, 6p. PdfAfrica, South Africaalluvials

Abstract: Alluvial diamond and other gemstone deposits have, typically, been exploited by small artisanal operations with little or no geological control. Over the last decade, however, alluvial deposits have become more interesting to larger (often listed), mid-tier companies wishing to benefit from the higher incomes generated by high-quality stones. The difficulties associated with evaluation and valuation of such alluvial diamond/gemstone deposits are widely known but, regrettably, often not widely understood - leading to several misconceptions over what can and cannot be expected from such deposits. Fortunately, there is a reasonably well-established body of knowledge on alluvial diamonds that has resulted in accepted industry-standard practices of how to evaluate these deposits. The 2016 version of the SAMREC Code includes several sections specific to the requirements of secondary diamond and gemstone deposits, both alluvial and marine. Consequently, it is possible to define Diamond/Gemstone Resources in accordance with the major international Committee for Mineral Reserves International Reporting Standards (CRIRSCO) type codes. This paper outlines some of the requirements and some of the pitfalls that need to be appreciated while estimating Diamond/Gemstone Resources and/or Reserves on such deposits.
Martin, E.L., Spencer, C.J., Collins, W.J., Thomas, R.J., Macey, P.H., Roberts, N.M.W.The core of Rodinia formed by the juxtaposition of opposed retreating and advancing accretionary orogens.Earth-Science Reviews, Vol. 211, doi.org/10.1016 /j.earscirev.2020 .103413 17p. Pdf Globalcratons

Abstract: Long-lived (800?Ma) Paleo- to Mesoproterozoic accretionary orogens on the margins of Laurentia, Baltica, Amazonia, and Kalahari collided to form the core of the supercontinent, Rodinia. Accretionary orogens in Laurentia and Baltica record predominately radiogenic zircon eHf(t) and whole-rock Pb isotopic compositions, short crustal residence times (ca. 0.5?Ga), and the development of arc-backarc complexes. The accretionary orogenic record of Laurentia and Baltica is consistent with a retreating accretionary orogen and analogous to the Phanerozoic western Pacific orogenic system. In contrast, the Mesoproterozoic orogens of Amazon and Kalahari cratons record unradiogenic zircon eHf(t) values, ca. 0.8?Ga crustal residence times, and more ancient whole-rock Pb isotopic signatures. The accretionary orogenic record of Amazonia and Kalahari indicates the preferential incorporation of cratonic material in continental arcs of advancing accretionary orogens comparable to the Phanerozoic eastern Pacific orogenic system. Based on similarities in the geodynamic evolution of the Phanerozoic circum-Pacific orogens peripheral to Gondwana/Pangea, we suggest that the Mesoproterozoic accretionary orogens formed as peripheral subduction zones along the margin of the supercontinent Nuna (ca. 1.8-1.6?Ga). The eventual collapse of this peripheral subduction zone onto itself and closure of the external ocean around Nuna to form Rodinia is equivalent to the projected future collapse of the circum-Pacific subduction system and juxtaposition of Australia-Asia with South America. The juxtaposition of advancing and retreating accretionary orogens at the core of the supercontinent Rodinia demonstrates that supercontinent assembly can occur by the closure of external oceans and indicates that future closure of the Pacific Ocean is plausible.
Martirosyan, N.S., Efthimiopoulos, I., Pennacchioni, L., Wirth, R., Jahn, S., Koch-Muller, M.Effect of catonic substitution on the pressure -induced phase transition in calcium carbonate.American Mineralogist, Vol. 106, pp. 549-558. pdfMantledeep carbon cycle
Mason, E, Wieser, P.E., Liu, E.J., Edmonds, M., Ilyinskaya, E., Whitty, R.C., Mather, T.A., Elias, T., Nadeau, P.A., Wilkes, T.C., McGonigle, A.J.S., Pering, T.D., Mims, F.M., Kern, C., Schneider, D.J., Oppenheimer, C.Volatile metal emissions from volcanic gassing and lava-seawater interactions at Kilauea volcano, Hawaii.Earth & Environment Communications, 10.1038/s43247-021-00145-3 16p. PdfUnited States, Hawaiimagmatism

Abstract: Volcanoes represent one of the largest natural sources of metals to the Earth’s surface. Emissions of these metals can have important impacts on the biosphere as pollutants or nutrients. Here we use ground- and drone-based direct measurements to compare the gas and particulate chemistry of the magmatic and lava-seawater interaction (laze) plumes from the 2018 eruption of Kilauea, Hawai’i. We find that the magmatic plume contains abundant volatile metals and metalloids whereas the laze plume is further enriched in copper and seawater components, like chlorine, with volatile metals also elevated above seawater concentrations. Speciation modelling of magmatic gas mixtures highlights the importance of the S2- ligand in highly volatile metal/metalloid degassing at the magmatic vent. In contrast, volatile metal enrichments in the laze plume can be explained by affinity for chloride complexation during late-stage degassing of distal lavas, which is potentially facilitated by the HCl gas formed as seawater boils.
Massonne, H-J., Li, B.Zoning of eclogitic garnet cores - a key pattern demonstrating the dominance of tectonic erosion as part of the burial process of worldwide occurring eclogites.Earth-Science Reviews, Vol. 210, doi.org/10.1016 /j.earscirev.2020. 103356 27p. Pdf MantleUHP, geodynamics

Abstract: Eclogites are witnesses of geodynamic processes that are commonly related to subduction of oceanic crust. Information on the part of these processes that refers to the burial of this rock type is rarely published but stored in the eclogitic garnet core and inclusions therein. To better understand general aspects of the burial process, a literature search on the chemical characteristics of garnet in worldwide occurrences of eclogite was undertaken. In most cases extended garnet cores show either a prograde growth zoning with increasing Mg, starting at a few percent of pyrope component, and decreasing Mn contents (type I eclogite) or a (nearly) constant chemical composition frequently with pyrope contents significantly above 10 percent (eclogites of types II and III). Only in minor cases, it is difficult to assign the reported garnet core to an eclogite type. The growth zoning of garnet was thermodynamically modelled for the chemical composition of a basalt following different burial paths. These paths are characterized either by a trajectory along a low geothermal gradient (type I eclogite), as expected for the subducting upper portion of oceanic crust, or a one characterized by nearly isothermal burial at temperatures above 500 °C reaching peak pressures up to 2.1 GPa (type III eclogite), as possibly due to crustal thickening during continent-continent collision, or more (type II eclogite) when basic rocks are tectonically eroded from the overriding continental plate before deep subduction. In addition, diffusion modelling was undertaken on mm-sized garnet demonstrating that the characteristics of the core zoning are not fully obliterated even during residence at temperatures of 800-850 °C within 10 million years. The scrutiny of more than 200 eclogites reported in the literature led to the following result: about half of them are type II eclogites; a third and a sixth can be related to type I and type III, respectively. Among type III are almost all of the few Proterozoic eclogites considered. To demonstrate the benefit of our study, we link the core zoning of eclogitic garnet from various (ultra)high-pressure terranes in Phanerozoic orogenic belts to the geodynamics shaping corresponding orogens. The eclogites in these belts are dominated by type II. Thus, we propose that some of the material of the lower portion of the overriding continental crust was tectonically eroded by a subducted oceanic plate and brought to great depth. Afterwards, this material was exhumed first in a deep subduction channel and then in an exhumation channel during continent-continent collision where a contact with the upper continental plate was re-established. Furthermore, we suggest that type II eclogite can also occur in extrusion wedges as far as oblique subduction took place.
Massuyeau, M., Gardes, E., Rogerie, G., Aulbach, S., Tappe, S., Le Trong, E., Sifre, D., Gaillard, F.MAGLAB: A computing platform connecting geophysical signatures to melting processes in Earth's mantle.Physics of the Earth and Planetary Interiors, doi.org/10.1016/ j.pepi.2020.106638 51p. PdfMantlegeophysics - magnetics

Abstract: Decompression melting of the upper mantle produces magmas and volcanism at the Earth's surface. Experimental petrology demonstrates that the presence of CO2 and H2O enhances peridotite melting anywhere within the upper mantle down to approximately 200-300?km depth. The presence of mantle melts with compositions ranging from carbonate-rich to silicate-rich unavoidably affects the geophysical signals retrieved from Earth's mantle. Geochemical investigations of erupted intraplate magmas along with geophysical surveys allow for constraining the nature and volume of primary melts, and a sound formalism is required to integrate these diverse datasets into a realistic model for the upper mantle including melting processes. Here, we introduce MAGLAB, a model developed to calculate the composition and volume fraction of melts in the upper mantle, together with the corresponding electrical conductivity of partially molten mantle peridotites at realistic pressure-temperature conditions and volatile contents. We use MAGLAB to show how the compositions of intraplate magmas relate to variations in lithosphere thickness. Progressive partial melting of a homogeneous peridotitic mantle source can in theory create the diversity of compositions observed among the spectrum of intraplate magma types, with kimberlite melts beneath thick continental shields, alkaline magmas such as melilitite, nephelinite and basanite beneath thinner continents and relatively old plus thick oceanic lithospheres, and ‘regular’ basalts beneath the youngest and thinnest oceanic lithospheres as well as beneath significantly thinned continental lithospheres. MAGLAB calculations support recent experimental findings about the role of H2O in the upper mantle on producing primary kimberlitic melts in addition to CO2. We demonstrate the robustness of MAGLAB calculations by reproducing the compositions of erupted melts as well as associated mantle electrical conductivities beneath the Society hotspot in the Pacific Ocean. A comparison of our simulations with magnetotelluric surveys at various oceanic settings shows that the heterogeneities in electrical conductivity of Earth's upper mantle are related to variations in volatile content via the presence of small (generally <<1?wt%) and heterogeneously distributed fractions of CO2-H2O-bearing melts.
Matende, K., Mickus, K.Magnetic and gravity investigation of kimberlites in north-central Botswana.Geophysics, Vol. 86, 2, B67-78.Africa, Botswanageophysics

Abstract: The Orapa kimberlite field of Botswana is one of the world’s major diamond producing regions. Within this field, there are several small kimberlite pipes that have not been completely explored in terms of their lateral extent, depth, and diamond potential. Two such pipes, BK54 and BK55, were found during a ground gravity and magnetic survey, and subsequent drilling confirmed the presence of kimberlite material. To determine the physical properties of these pipes, their lateral extent, depth, and thickness were estimated using a gravity and magnetic analysis and 2.5D and 3D modeling. Tilt derivatives of the magnetic data indicated that BK54 has a northwest-trending elliptical shape and BK55 has a roughly circular shape. Residual gravity anomaly maps indicate that BK54 does not have a density anomaly whereas BK55 is associated with a gravity maximum. The 3D gravity and magnetic inversion modeling constrained by magnetic susceptibility measurements indicates that BK54 is smaller in volume than BK55 and that neither pipe is thicker than 125 m. The difference in shape and the lack of a gravity anomaly over BK54 implies a different formation mechanism for each kimberlite pipe. Although several mechanisms are suggested, BK54 may have formed by a more explosive eruption producing more tuffistic material in the crater and diatreme facies. The gravity and magnetic analysis also found that the kimberlite pipes, while small, are larger in extent than was determined by drilling and warrant additional drilling to determine their economic potential.
Mazzero, F.C., Rocco, I., Tucker, R.D., Morra, V., D'Antonio, M., Melluso, L.Olivine melilitites, mantle xenoliths, and xenocrysts of the Takarindiona district: petrogenesis, magmatic evolution, and the sub-continental lithospheric mantle of east-central Madagascar.Journal of African Earth Sciences, Vol. 174, 104059, 17p. PdfAfrica, Madagascarmelilitites

Abstract: The olivine melilitites from the southern part of the 6.8 Ma-old Takarindiona volcanic field (Eastern Madagascar) are olivine ± chromite -phyric lavas, with zoned titanaugite, perovskite, melilite, nepheline, monticellite, Ba-Ti-mica and Fe-Ti oxides as microphenocrysts and groundmass phases. The rocks are very primitive, rich in incompatible trace elements (e.g., Ba = 1049 ± 153 ppm, Sr = 1050 ± 167 ppm, Nb = 98 ± 13 ppm; La/Ybn = 41 ± 5; La/Nb = 0.88 ± 0.05), and have restricted ranges of initial 87Sr/86Sr (0.70391-0.70410) and 143Nd/144Nd (0.51272-0.51282). The rocks follow a differentiation trend controlled by ab. 20% removal/addition of phenocryst olivine ± chromite. The olivine melilititic magmas are the product of small degrees of partial melting (1-3%) of a peridotitic source, enriched in highly incompatible trace elements by CO2-, F-, and H2O-rich melts, located within the garnet stability field (3-3.5 GPa and ~100 km depth) of sub-continental lithospheric mantle, where carbonates (dolomite) and possibly phlogopite were stable phases. Mantle xenoliths within the volcanics are mostly spinel harzburgites having mineral modes and chemical compositions suggesting variable degrees of "basalt" melt extraction. Based on textural and chemical evidence, and quantitative thermobarometric estimates, the xenoliths were incorporated at a pressure of ~1.1 GPa (~35-40 km depth), far shallower than the source of the melilititic magmas, and along a predictably cool geotherm beneath Archean continental lithosphere. Highly resorbed orthopyroxene xenocrysts mantled by augite indicate that the melilitites may have also entrained lower crustal materials or underplated subalkaline rocks. The mantle sources of the lavas and mantle xenoliths of the Takarindiona district indicate stratification of the lithospheric mantle, and help constraining the lithospheric features and the magmatic history of the Eastern Madagascar craton.
McElhenny, G., Turner, M., Breeding, C.M.Corundum inclusions in gem diamond.Gems & Gemology , Vol. 56, 1, pp. 129-131.Technologydiamond inclusions

Abstract: Inclusions can tell us a great deal about a diamond’s formation history. Inclusions such as olivine, garnet, and chromite are more common, while others such as kyanite, zircon, and corundum (Al2O3) can be quite rare. Regardless of their rarity, diamond inclusions are often quite fascinating as they trap a small bit of the deep earth that cannot otherwise be sampled.
Melnik, A.E., Korolev,N.M., Skublov, S.G., Muller, D., LiL, Q-L., Li, X-H.Zircon in mantle eclogite xenoliths: a reviewGeological Magazine, https://doi.org/ 10.1017/ S0016756820001387Africa, Angola, Central African Republic, GabonKasai craton

Abstract: Very few zircon-bearing, kimberlite-hosted mantle eclogite xenoliths have been identified to date; however, the zircon they contain is crucial for our understanding of subcratonic lithospheric mantle evolution and eclogite genesis. In this study, we constrain the characteristics of zircon from mantle eclogite xenoliths based on existing mineralogical and geochemical data from zircons from different geological settings, and on the inferred origin of mantle eclogites. Given the likely origin and subsequent evolution of mantle eclogites, we infer that the xenoliths can contain zircons with magmatic, metamorphic and xenogenic (i.e. kimberlitic zircon) origins. Magmatic zircon can be inherited from low-pressure mafic oceanic crust precursors, or might form during direct crystallization of eclogites from primary mantle-derived melts at mantle pressures. Metamorphic zircon within mantle eclogites has a number of possible origins, ranging from low-pressure hydrothermal alteration of oceanic crustal protoliths to metasomatism related to kimberlite magmatism. This study outlines a possible approach for the identification of inherited magmatic zircon within subduction-related mantle eclogites as well as xenogenic kimberlitic zircon within all types of mantle eclogites. We demonstrate this approach using zircon grains from kimberlite-hosted eclogite xenoliths from the Kasai Craton, which reveals that most, if not all, of these zircons were most likely incorporated as a result of laboratory-based contamination.
Merdith, A.S., Williams, S.E., Collins, A.S., Tetley, M.G., Mulder, J.A., Blades, M.L., Young, A., Armistead, S.E., Cannon, J., Zahirovic, S., Muller, R.D.Extending full plate tectonic models into deep time: linking the Neoproterozoic and the Phanerozoic.Earth Science Reviews, Vol. 214, 44p. PdfMantleplate tectonics

Abstract: Recent progress in plate tectonic reconstructions has seen models move beyond the classical idea of continental drift by attempting to reconstruct the full evolving configuration of tectonic plates and plate boundaries. A particular problem for the Neoproterozoic and Cambrian is that many existing interpretations of geological and palaeomagnetic data have remained disconnected from younger, better-constrained periods in Earth history. An important test of deep time reconstructions is therefore to demonstrate the continuous kinematic viability of tectonic motions across multiple supercontinent cycles. We present, for the first time, a continuous full-plate model spanning 1 Ga to the present-day, that includes a revised and improved model for the Neoproterozoic-Cambrian (1000-520 Ma) that connects with models of the Phanerozoic, thereby opening up pre-Gondwana times for quantitative analysis and further regional refinements. In this contribution, we first summarise methodological approaches to full-plate modelling and review the existing full-plate models in order to select appropriate models that produce a single continuous model. Our model is presented in a palaeomagnetic reference frame, with a newly-derived apparent polar wander path for Gondwana from 540 to 320 Ma, and a global apparent polar wander path from 320 to 0 Ma. We stress, though while we have used palaeomagnetic data when available, the model is also geologically constrained, based on preserved data from past-plate boundaries. This study is intended as a first step in the direction of a detailed and self-consistent tectonic reconstruction for the last billion years of Earth history, and our model files are released to facilitate community development.
Meyer, N.Diamonds and their inclusions from the Koffiefontein pipe provide insights into the formation and evolution of the Kaapvaal craton.Vancouver Kimberlite Cluster, Feb. 24, recorded update https://www.youtube.com/ channel/UCcZvayDnqDD azIHAh1Otreg gets you into the VKCAfrica, South Africadeposit - Koffiefontein

Abstract: Diamonds and their mineral inclusions preserve mantle processes over space and time. Forming over a protracted period, diamonds also provide snapshots of early craton formation and mantle evolution over much of Earth’s history. The lithosphere beneath Koffiefontein is extremely depleted and is characterised by high-Mg# olivine and low-Ca garnet. In addition to garnet LREE enrichment, Koffiefontein experienced a unique K-Nb-Ta-rich metasomatism event that resulted in new minerals. The lack of clinopyroxene and co-existing garnet-orthopyroxene assemblages lead to the use of the electron microprobe for trace element analysis of Al in olivine. Geothermobarometry indicates that upper mantle diamond formation conditions are 1100-1300 °C and 4-7 GPa. Koffiefontein diamonds have a main d13C mode for both peridotitic and eclogitic diamonds similar to mantle carbon. Relationships of d15N-[N] and d13C-d15N indicate that nitrogen was derived from subducted sources and suggests that formation of not only eclogitic but also peridotitic diamonds involved fluids derived from altered oceanic crust. Lower mantle diamonds with coexisting ferropericlase and former bridgmanite indicate formation at or below 660 km. The high bulk Mg# of this assemblage is consistent with the diamond substrate originating from the depleted lithospheric mantle portion of an oceanic slab. Diamond formation at Koffiefontein dominantly takes place in depleted peridotite at both lithospheric and lower mantle depths. The d13C-d15N systematics suggest the same subducted source for both peridotitic and eclogitic diamonds. Subduction has played an important role in the formation and evolution of the Kaapvaal Craton and subsequent diamond formation.
Mikhail, S., Rinaldi, M., Mare, E.R., Sverjensky, D.A.A genetic metasomatic link between eclogitic and peridotitc diamond inclusions.Geochemical Perspectives Letters, Vol. 17, pp. 33-38. pdfMantlediamond inclusions

Abstract: Diamond inclusions sample the otherwise inaccessible archive of Earth’s deep interior. The geochemical and petrological diversity of diamond inclusions reflects either pre-metasomatic upper mantle heterogeneity or metasomatism coeval with diamond formation. We focus on the origin of lithospheric garnet and clinopyroxene inclusions by simulating metasomatic reactions between eclogitic fluids and mantle peridotites at 5 GPa, 1000 °C, and across a range of redox conditions (logfO2?=?-1 to -6 ?FMQ). Our results demonstrate that fluid-rock interaction can result in the formation of eclogitic, websteritic, and peridotitic silicates from a single fluid during a single diamond-forming metasomatic event. Ergo, the petrogenesis of diamond and their inclusions can be syngenetic, and the petrological diversity of diamond inclusions can reflect metasomatism coeval with diamond formation. Furthermore, during the metasomatism, refractory peridotite can be converted to fertile websterite which could become a pyroxenitic mantle source for oceanic basalts.
Mikhailenko, D.S., Korsakov, A.V., Ohfuji, H., Sobolev, N.V.Silicate inclusions in metamorphic diamonds from the ultra-high pressure Kokchetav complex, Kazakhstan.Doklady Earth Sciences, Vol. 496, pp. 142-145.Russia, Kazakhstandeposit - Kokchetav

Abstract: Mineral inclusions in cubic diamonds from garnet-clinopyroxene rock of the Kokchetav massif were studied. The coexistence of fluid and silicate inclusions in the central part of the diamond of the G0 sample was revealed by means of transmission electron microscopy. Silicate inclusions are represented by intergrowths of garnet and mica, which are spatially related with the carbonate and fluid inclusions. The first finding of silicate inclusions in the cubic diamonds from the UHP complex discovered over 50 years of their study is apparently due to a selective capture of the silicate minerals in the process of the diamond crystallization from the carbonate-bearing C-O-H fluid. The processes of diamond crystallization in the metamorphic deeply subducted rocks and upper mantle rocks, which are carried to the surface as xenoliths by kimberlite melts, have much in common.
Mints, M.V., Dokukina, K.A., Afonina, T.B.Precambrian lithosphere beneath Hudson Bay: a new geological model based on the Hudson Bay lithospheric experiment ( HuBLE), Canadian shield.Tectonophysics, Vol. 799, 15p. Doi.org/10.1016/ j.tecto.2020.228701Canada, Ontario, Quebectomography

Abstract: The oval-shaped basin of Hudson Bay occurs near the center of the round-oval Archaean crustal domain of the North American continent. This paper presents models of the geological structure and evolution of the subcontinental lithospheric mantle underlying Hudson Bay and surrounding tectonic provinces based on geological interpretations of regional geological and geophysical data and results of seismic tomography investigations that have been conducted under the Hudson Bay Lithospheric Experiment. The experiment was aimed at lithospheric processes directly related to the origin of the North American craton and the Hudson Bay basin. Hudson Bay is located directly above the lithospheric keel of North America. The geological history demonstrates systematic "renovation" of the basin: (1) origin and evolution of the Neoarchaean Lake Minto basin (~2.75 Ga); (2) accumulation of the Palaeoproterozoic volcanic-sedimentary filling of the epicontinental basin, relics of which is preserved on its passive margins (2.03-1.87 Ga); (3) origin of Ordovician-Late Devonian sedimentary sequence whose maximum thickness reaches 2.5 km; and (4) the development of Late Jurassic-Miocene sediment-filled ring-shaped trough immediately above the lithospheric keel. The Hudson Bay basin occurs above the lithospheric keel in compliance with thermomechanical model of ascending plume. Tomography studies have not detected evidence of either production or transformation of the lithosphere in the Palaeoproterozoic, which are implied by the model of the United Plates of America. Interpretations of tomography data reveal a vertical axial zone in the lithosphere beneath Hudson Bay, which extends from the lithosphere-asthenosphere boundary to the base of the crust or, perhaps, even to the present day surface. The zone is made up of relatively light low-velocity igneous rocks, probably a swarm of kimberlite dikes or pipes. At 2.75 Ga, the North American continent was a single continental mass with Hudson Bay at its center.
Mitchell, R.H.Comment on Vladykin, N.V. & Piranjo, F. -Types of carbonatites; geochemistry, genesis and mantle sources.Lithos, Vol 386-387, 105982 3p. PdfGlobalcarbonatites
Mitchell, R.H., Dawson, J.B.Mineralogy of volcanic calciocarbonatites from the Trig Point Hill debris flow, Kerimasi volcano, Tanzania: implications for the altered natrocarbonatite hypothesis.Mineralogical Magazine, 12p. PdfAfrica, Tanzaniadeposit - Trig Point Hill

Abstract: A major debris flow, the Trig Point Hill flow, originating from Kerimasi volcano (Tanzania) contains numerous blocks of extrusive/pyroclastic carbonatites similar to those exposed at the rim of the currently inactive crater. The blocks of calcite carbonatite consist of: (1) large clasts of corroded and altered coarse grained calcite; (2) primary prismatic inclusion bearing phenocrystal calcite; and (3) a matrix consisting primarily of fine-grained prismatic calcite. The large clasts are inclusion free and exhibit a ‘corduroy-like’ texture resulting from solution along cleavage planes. The resulting voids are filled by brown Fe-Mn hydroxides/oxides and secondary calcite. The prismatic or lath-shaped phenocrystal calcite is not altered and contains melt inclusions consisting principally of primary Na-Ca carbonates which contain earlier-formed crystals of monticellite, periclase, apatite, Mn-Mg-magnetite, Mn-Fe-sphalerite and Nb-perovskite. Individual Na-Ca carbonate inclusions are of uniform composition, and the overall range of all inclusions analysed (wt.%) is from 28.7 to 35.9 CaO; 16.7-23.6 Na2O; 0.5-2.8 K2O, with minor SO3 (1.1-2.2) and SrO (0.34-1.0). The Na-Ca carbonate compositions are similar to that of shortite, although this phase is not present. The Na-Ca carbonates are considered to be primary deuteric phases and not secondary minerals formed after nyerereite. Monticellite shows limited compositional variation and contains 2-4 wt.% MnO and 12 wt.% FeO and is Mn-poor relative to monticellite in Oldoinyo Lengai natrocarbonatite. Periclase is Fe-bearing with up to 13 wt.% FeO. Spinels are Cr-free, Mn-poor and belong to the magnetite-magnesioferrite series in contrast to Mn-rich spinels of the magnetite-jacobsite series occurring in Oldoinyo Lengai natrocarbonatite. The matrix in which the ‘corduroy’ clasts and phenocrystal calcite are set consists of closely packed small prisms of calcite lacking melt inclusions, with interstitial fine-grained apatite, baryte, strontianite and minor fluorite. Pore spaces are filled with secondary Mn-Fe hydroxides/oxides, anhydrite and gypsum. The hypothesis that flow-aligned calcite in volcanic calciocarbonatites from Kerimasi, Tinderet, Homa and Catanda is altered nyerereite is discussed and it is considered that these calcite are either primary phases or altered melilite. The nyerereite alteration hypothesis is discussed with respect to the volumetric and compositional aspects of pseudomorphism by dissolution-precipitation replacement mechanisms. This study concludes that none of the volcanic calciocarbonatites containing flow-aligned calcite phenocrysts are altered natrocarbonatite.
Modise, E.G., Zungeru, M.A., Chuma, J.M., Prabaharan, S.R.S., Mtengi, B., Ude, A., Nedev, Z.The new paradox of dual modality x-ray diamond sorting.IEEE Photonics Journal, Researchgate 35102286, April, 28p. PdfGloballuminescence

Abstract: Modern-day diamond sorting is achieved through the application of x-ray luminescence (XRL) and x-ray transmission (XRT) techniques. Sorting with XRL is limited to the class range of 1.25mm to 32mm because of self-absorption associated with larger diamonds, greater than 32mm. The effect of self-absorption is also a high-energy phenomenon in XRL. XRT is limited to sorting large size diamonds as the technique suffers poor contrast for diamonds smaller than 10mm. XRT measurements are immune to self-absorption for all sample sizes, while XRL measurements have good contrast for particles smaller than 32mm. The applications of these techniques have hitherto been used independently of each other and have subsequently progressed mutually exclusively. Here we analytically show a new paradox of a dual-modality X-ray diamond sorting combining XRL and XRT techniques' strengths. Key features of our new paradoxical model performance are contrast mitigation for small particles and self-absorption rejection for a large particle at high energy as well as improved particle detectability and classification.
Mohammed, A. Al Deep, M.Depth to the bottom of the magnetic layer, crustal thickness, and heat flow in Africa: inferences from gravity and magnetic data.Journal of African Earth Sciences, Vol. 179, 104204, 17p. PdfAfricaEMAG2

Abstract: Data from the Earth Gravitational Model (EGM2008) and the Earth Magnetic Anomaly Grid (EMAG2) were used to develop a continental scale crustal thickness model for Africa, and to estimate the depth to the bottom of the magnetic layer (DBML) and the geothermal gradient and heat flow. The results are: (1) the estimated DBML from the magnetic data varies from ~23.0 to ~37.2 km. The shallowest DBML values are located in the northern, eastern, and western parts of the continent, whereas the deepest values are observed in the central and southern regions. (2) The estimated crustal thickness based on gravity data varies from ~29.9 km in the northern and western parts of Africa to ~48.0 km in its southern regions, with an average thickness of 35.1 km for the whole continent. (3) The estimated heat flow varies between high values of 46-59 mW/m2, observed in the northern, eastern, and western regions to low values of ~< 41 mW/m2, observed in the central and southern parts of the continent. (4) The geothermal gradient values vary between 14.5 and 23.6 °C/km (5) The East African rift zone is underlain by shallow DBML characterized by high heat flow values that vary between 42 and 59 mW/m2 (6) The heat flow anomalies in Egypt and Libya may be associated with the zone of the Pelusium megashear system, and it shows heat flow values that vary between 36.3 and 59.0 mW/m2. The current study has taken advantage of the availability of the EGM2008 and EMAG2 datasets to map crustal thickness variations and DBML beneath the continental landmass of Africa.
Muruganathan, M., Mizuta, H.Boron vacancy color center in diamond: An initio study.Diamond & Related Materials, Vol. 114, 108341 6p. PdfGlobaldiamond colours

Abstract: The color centers in diamond are crucial for emerging single-photon sources, quantum technologies, and biological sensors. Even though boron is commonly used as a dopant for diamond, its functionality as a vacancy color center depends on the capability to excite electrons optically between the well-defined gap states. Here we show by using density functional theory calculations that the negatively charged boron-vacancy (BV-1) center in diamond possesses such well-isolated gap states and enables the spin-conserved triplet excitation. Formation energy of different charge states of boron vacancy center is calculated by including the corrections of electrostatic interactions between the periodic images of the charged defects and the defect-induced bands shift. Wavefunctions of diamond BV-1 center defect states are elucidated and its zero phonon line is calculated as 3.22 eV. These characteristics manifest that the BV-1 center can be harnessed as an alternative promising color center for diamonds.
Nathan, E.M., Hariharan, A., Florez, D., Fischer, K.M.Multi-layer seismic anisotropy beneath Greenland.Geochemistry, Geophysics, Geosystems, 10.1029/2020G C009512 17p. PdfEurope, Greenlandgeophysics - seismic

Abstract: Measurements of seismic anisotropy (the direction-dependent variation in seismic wavespeed) provide useful information about the orientation of deformation in the Earth. We measured seismic anisotropy using shear waves refracted through the outer core and recorded by stations in Greenland. Due to new stations and data, this study includes more measurements of the effects of anisotropy than previously possible. We show that a model with two layers of anisotropy explains dominant patterns in the fast vibration direction of the shear waves as a function of the angle at which they approach each station. We suggest that the shallow layer reflects coherent deformation in the continental lithosphere of Greenland due to its history of plate collisions and that the lower layer reflects deformation in the asthenospheric mantle induced by the motion of the plate above or a second layer of lithospheric anisotropy.
Neil, B.J.C., Gibson, H.D., Pehrsson, S.J., Martel, E., Thiessen, E.J., Crowley, J.L.Provenance, stratigraphic and precise depositional age constraints for an outlier of the 1.9 to 1.8 Ga Nonacho Group, Rae craton, Northwest Territories, Canada.Precambrian Research, Vol. 352, 105999, 15p. PdfCanada, Northwest Territoriesgeochronology

Abstract: The Nonacho Group comprises six formations of continental clastic rocks that were deposited between 1.91 and 1.83?Ga. The Nonacho Group is part of a broader assemblage of conglomerate and sandstone that was deposited atop the Rae craton in response to the amalgamation of Laurentia and supercontinent Nuna, but the details of its tectonic setting are contentious. This paper documents an outlier of Nonacho Group rocks ~50?km east of the main Nonacho basin. Field observations and LA-ICPMS (laser ablation inductively coupled plasma mass spectrometry) U-Pb detrital zircon geochronology are integrated with previous studies of the main basin to better understand the group’s depositional history, provenance and tectonic setting. The lithology and detrital zircon age spectra of the outlier allow for its correlation to the upper two formations of the Nonacho Group. CA-ID-TIMS (chemical abrasion isotope dilution thermal ionization mass spectrometry) analyses of two fragments of the youngest detrital zircon provide a maximum depositional age of 1901.0?±?0.9?Ma. A felsic volcanic cobble dated at ca. 2.38?Ga provides evidence of volcanism during the Arrowsmith orogeny. Detrital zircon dates recovered from the outlier (ca. 3.4-3.0, 2.7, 2.5-2.3 and 2.0-1.9?Ga) are consistent with derivation from topography of the Taltson and/or Thelon orogens on the western margin of the Rae craton. Taltson-Thelon (2.0 to 1.9?Ga) aged detritus is only abundant in the upper two formations of the Nonacho Group, marking a change in provenance from the lower formations. This change in provenance may have coincided with a period of renewed uplift and the unroofing of Taltson-Thelon plutons. The detrital zircon provenance and depositional age of the Nonacho Group is consistent with models that link its deposition to the Taltson and/or Thelon orogens. However, tectonism associated with the 1.9 to 1.8?Ga Snowbird and Trans-Hudson orogens to the east could also have affected basin formation or the change in provenance from the lower to upper Nonacho Group. This study highlights the importance of CA-ID-TIMS in establishing accurate and precise maximum depositional ages for sedimentary successions.
Nemeth, P., McColl, K., Smith, R., Murri, M.Diamond-Graphene composite nanostructures.Nano Letters, doi.10.1021/acs/ nanolett.Oc0556 10p. PdfGlobalnanodiamond

Abstract: The search for new nanostructural topologies composed of elemental carbon is driven by technological opportunities as well as the need to understand the structure and evolution of carbon materials formed by planetary shock impact events and in laboratory syntheses. We describe two new families of diamond-graphene (diaphite) phases constructed from layered and bonded sp3 and sp2 nanostructural units and provide a framework for classifying the members of this new class of materials. The nanocomposite structures are identified within both natural impact diamonds and laboratory-shocked samples and possess diffraction features that have previously been assigned to lonsdaleite and postgraphite phases. The diaphite nanocomposites represent a new class of high-performance carbon materials that are predicted to combine the superhard qualities of diamond with high fracture toughness and ductility enabled by the graphitic units and the atomically defined interfaces between the sp3- and sp2-bonded nanodomains.
Nestola, F.How to apply elastic geobarometry in geology.American Mineralogist, Vol. 106, pp. 669-671. pdfGlobalgeobarometry

Abstract: Pressure and temperature estimates of rocks provide the fundamental data for the investigation of many geological processes such as subduction and exhumation, and yet their determination remains extremely challenging (Tajcmanova et al. 2020). A wide variety of methods are constantly being developed to tackle the ambitious objective of pinpointing the geological history of rocks through the many complex processes often interacting with one another at depth in our planet. Analytical advances are being pushed to the limit of conventional methods, allowing information preserved by mineral, fluid, and solid inclusions to be used for high spatial resolution determinations that can unravel a large variety of processes occurring at the micro- to the nano-scale. Among these, chemical geothermobarometry that is often challenging in many rock types due to alteration processes, chemical re-equilibration, diffusion, and kinetic limitations has been increasingly coupled with elastic geothermobarometry (e.g., Anzolini et al. 2019; Gonzalez et al. 2019). Elastic geothermobarometry of host-inclusion systems, in paper Mazzucchelli et al. 2021, this issue, is a new and complementary non-destructive method (see Fig. 1 for an example) to determine the pressures (P) and temperatures (T) of inclusion entrapment (i.e., the P-T conditions attained by rocks and minerals at depth in the Earth) from the remnant stress or strain measured in inclusions still trapped in their host mineral at room conditions (e.g., Nestola et al. 2011; Howell et al. 2012; Alvaro et al. 2020).
Neves, S.P.Comparative geological evolution of the Borobrema province and Sao Francisco craton ( eastern Brazil): decratonization and crustal reworking during west Gondwana assembly and implications for paleogeographic reconstructions.Precambrian Research, Vol. 355, 106119, 23p. PdfSouth America, Brazil, Paraibacraton

Abstract: 70-80% of the continental crust was produced during the 4.0-2.0 Ga time span, but the preserved area of Archean/early Paleoproterozoic cratons is smaller than 40%. Part of this deficit can be accounted for by the presence of reworked old crust in the basement of mid-Paleoproterozoic to Phanerozoic orogenic belts. Here, I compare the crustal evolution of the Brasiliano-Pan-African Borborema Province (BP) with that of the São Francisco Craton (SFC) in eastern Brazil and highlight numerous geological aspects, several of which are uncommon in other cratons/orogenic belts, indicating their shared evolution for most of the Precambrian. These include: 1. Presence of the oldest rocks (Eo- to Paleoarchean) from the South American Platform. 2. Occurrence of Siderian (2.5-2.3 Ga) rocks. 3. Generation of juvenile crust and reworking of pre-existing rocks during the Transamazonian event (2.2-2.0 Ga). 4. Intermittent rifting and intraplate magmatic events between 1.78 and 1.50 Ga. 5. Intrusion of mafic dykes and A-type granites at 1.0-0.85 Ga. 6. Intrusion of mafic rocks, syenites and granitoids with intraplate signature between ca. 0.71 and 0.64 Ga. 7. The lack of evidence for igneous and tectonic activity between ca. 1.95 and 1.78 Ga, during most of the Mesoproterozoic, and between 0.85 and 0.73 Ga. The temporal coincidence of Rhyacian orogenic events in the SFC and BP favors the hypothesis that they were part of a continent formed by the accretion of Archean/early-Paleoproterozoic blocks and of juvenile arc crust during the Transamazonian Orogeny. In addition, the recording of several intraplate tectonomagmatic events from the late-Paleoproterozoic to the Neoproterozoic indicates that they remained united until at least the mid-Neoproterozoic. In this context, BP can be interpreted as a fragment of the SFC re-accreted and reworked during the Brasiliano-Pan-African Orogeny (ca. 640-550 Ma). Recent studies demonstrate that most of the basement of the Brasília and Araçuaí belts, which occur to the west and east, respectively, of the SFC, also resulted from its reworking. Therefore, an area c. two times larger than the current outline of the SFC can be inferred, indicating an intense process of decratonization during the Brasiliano-Pan-African Orogeny. The intermittent late Paleoproterozoic to early Neoproterozoic extension-related magmatism in this Greater São Francisco paleocontinent contrasts with the worldwide occurrence of orogenic episodes accompanying the amalgamation of the Columbia supercontinent, its fragmentation, and the build-up of Rodinia. These differences suggest that Greater São Francisco was not part of these supercontinental assemblages.
Ngwenya, N.S., Tappe, S.Diamondiferous lamproites of the Luangwa Rift in central Africa and links to remobilized cratonic lithosphere.Chemical Geology, in press available 31p. PdfAfrica, Zambialamproite

Abstract: Mesozoic diamondiferous lamproite pipes occur along the Kapamba River within the Luangwa Valley of eastern Zambia, which is a ca. 300-200?Ma old Karoo-age precursor branch to the East African Rift System. The Luangwa Rift developed above a reactivated mega-shear zone that cuts through the Proterozoic Irumide Belt between the Congo-Tanzania-Kalahari cratons and thus it provides a rare snapshot of early-stage cratonic rift evolution. The primary mineralogy of the fresh volcanic rocks suggests that they represent a continuum between primitive olivine lamproites and slightly more evolved olivine-leucite lamproites. Mineral compositions and evolutionary trends, such as the strong Al-depletion at Tisingle bondF enrichment in groundmass phlogopite and potassic richterite, resemble those of classic lamproite provinces in circum-cratonic settings (e.g., the Leucite Hills of Wyoming and the West Kimberley field in Australia). However, there are some similarities to orangeites from the Kaapvaal craton (formerly Group-2 kimberlites), type kamafugites from the East African Rift, and ultramafic lamprophyres from a key region of the rifted North Atlantic craton, which implies a complex interplay between source-forming and tectonic processes during Karoo-age lamproite magma formation beneath south-central Africa. The bulk compositions of the Kapamba volcanic rocks fall within the range of ‘cratonic’ low-silica lamproites, but there is overlap with orangeites, in particular with the more evolved leucite- and sanidine-bearing orangeite varieties. Modelling of the process by which most of the original leucite was transformed into analcime suggests that the primitive alkaline magmas at Kapamba contained ~6-9?wt% K2O and had high K2O/Na2O ratios between ~1.6-6.2 at >10?wt% MgO - confirming the ultrapotassic nature of the mantle-derived magmatism beneath the Luangwa Rift. The virtually CO2-free, H2O-F-rich Kapamba lamproites present an extension of the geochemical continuum displayed by the members of the CO2-H2O-rich kamafugite / ultramafic lamprophyre group. Hence, we suggest that the Kapamba lamproites and the type kamafugites, located within separate branches of the East African Rift System, represent melting products of similar K-metasomatized cratonic mantle domains, but their formation occurred under contrasting volatile conditions at different stages during rift development (i.e., incipient versus slightly more advanced rifting). Temperature estimates for peridotite-derived olivine xenocrysts from the Kapamba lamproites suggest that the Luangwa Valley is an aborted cratonic rift that retained a relatively cold (=42?mW/m2) lithospheric mantle root down to ~180-200?km depth during the Mesozoic. Olivine major and trace element compositions support the presence of an Archean mantle root (up to 92.4?mol% forsterite contents) that is progressively metasomatized toward its base (e.g., increasing Tisingle bondCu contents with depth). For south-central Africa, it appears that significant volumes of Archean cratonic mantle domains ‘survived’ beneath strongly deformed and granite-intruded Proterozoic terranes, which suggests that the continental crust is more strongly impacted during collisional or rift tectonics than the ‘stabilizing’ mantle lithosphere.
Nieto, I.E.M., Prieto, G.A.Structural signatures of the Amazonian Craton in eastern Columbia from gravity and magnetometry data interpretation.Tectonophysics, Vol. 800, 228705, 15p. PdfSouth America, Colombiageophyics - magnetics, gravity

Abstract: Geophysical interpretation of potential field data plays an important role in the integration of geological data. Estimation of density and magnetic susceptibility variations within the upper crust helps evaluating the continuity of geological structures in the field. In the present study we use gravity and magnetic data in NW Amazonian Craton in Colombia. Total horizontal gradient of the reduction to magnetic pole were used to delineate magnetic lineaments and domains showing four zones, each with its own features. Multiscale edge detection (worming) of the data help delineate upper crustal structures that we interpret as tectonic boundaries that correlate with the four zones identified. 3D density and magnetic susceptibility inversion showed high density and/or high magnetic susceptibility sources correlated with these crustal structures. Zone (1) is located south of the Guaviare River, with predominant NW-SE and NE-SW magnetic lineaments; zone (2), located from south of the Guaviare River to the north, present nearly E-W magnetic lineaments and a deep E-W edge interpreted as a possible shear zone parallel to Guaviare, Orinoco and Ventuari rivers; zone (3) from south of the Vichada River to the north, with NE-SW and NW-SE lineaments; N-S zone (4) cuts the zones (2) and (3), characterized by high density/magnetic susceptibility source bounded by N-S deep edges. A more complete tectonic evolution interpretation requires further work, but we speculate that the zone (4) could indicate an aborted rift/collision suture and that the zone (2) is indicative of a younger deformation event. Shear direction at (2) is not clear: geological maps show NEE-SWW right-lateral faulting, but geophysical anomalies suggest left-lateral displacement, highlighted by left dislocation of the Orinoco River. We also speculate that a N-S edge located at the SE of the area can be related with the Atabapo Belt and the limit of Ventuari-Tapajós and Rionegro geochronological provinces.
Nikolenko, E.I., Sharygin, I.S., Rezvukhin, D.I., Malkovets, v.G., Tychkov, N.S., Pokhilenko, N.P.Sulfide-bearing polymineralic inclusions in mantle-derived garnets from lamprophyres of the Chompolo field, (Central Aldan, Siberian Craton).Doklady Earth Sciences, Vol. 497, pp. 300-304.Russia, Siberiadeposit - Chompolo

Abstract: Sulfide-bearing polymineralic inclusions in mantle-derived chromium pyrope garnets of lherzolite paragenesis from lamprophyres of the Chompolo field (Aldan shield, southern Siberian craton) have been studied. The inclusions are composed of either only sulfides or sulfides in association with other minerals (carbonates, silicates, oxides, etc.). The sulfide part of the inclusions is represented by up to four minerals. Among the sulfides, minerals rich in Cu and Ni have been found, whereas Fe sulfides (pyrrhotite, troilite) are absent. This distinguishes the inclusions studied from the majority of sulfide inclusions in mantle minerals and diamonds, as well as in mantle xenoliths from kimberlites. The formation of polymineralic inclusions in chromium garnets of the Chompolo field is attributed to the effect of a carbonate-silicate metasomatic melt/fluid on mantle peridotites, as evidenced by the mineral suite associated with the sulfides. The research results indicate significant differences in the nature of metasomatic processes that occurred in the lithospheric mantle of the southern and central parts of the Siberian craton.
Ohtani, E.Hydration and dehydration in Earth's interior.Annual Review of Earth Planetary Sciences, Vol. 49, pp. 253-278.Mantlewater

Abstract: Hydrogen and deuterium isotopic evidence indicates that the source of terrestrial water was mostly meteorites, with additional influx from nebula gas during accretion. There are two Earth models, with large (7-12 ocean masses) and small (1-4 ocean masses) water budgets that can explain the geochemical, cosmochemical, and geological observations. Geophysical and mineral physics data indicate that the upper and lower mantles are generally dry, whereas the mantle transition zone is wetter, with heterogeneous water distribution. Subducting slabs are a source of water influx, and there are three major sites of deep dehydration: the base of the upper mantle, and the top and bottom of the lower mantle in addition to slabs in the shallow upper mantle. Hydrated regions surround these dehydration sites. The core may be a hidden reservoir of hydrogen under the large water budget model.
Oliveira, B., Alfonso, J.C., Tilhac, R.A disequilibrium reactive transport model for mantle magmatism.Journal of Petrology, Vol. 61, 9, egaa067, 35p. PdfMantlemagmatism

Abstract: Besides standard thermo-mechanical conservation laws, a general description of mantle magmatism requires the simultaneous consideration of phase changes (e.g. from solid to liquid), chemical reactions (i.e. exchange of chemical components) and multiple dynamic phases (e.g. liquid percolating through a deforming matrix). Typically, these processes evolve at different rates, over multiple spatial scales and exhibit complex feedback loops and disequilibrium features. Partially as a result of these complexities, integrated descriptions of the thermal, mechanical and chemical evolution of mantle magmatism have been challenging for numerical models. Here we present a conceptual and numerical model that provides a versatile platform to study the dynamics and nonlinear feedbacks inherent in mantle magmatism and to make quantitative comparisons between petrological and geochemical datasets. Our model is based on the combination of three main modules: (1) a Two-Phase, Multi-Component, Reactive Transport module that describes how liquids and solids evolve in space and time; (2) a melting formalism, called Dynamic Disequilibirum Melting, based on thermodynamic grounds and capable of describing the chemical exchange of major elements between phases in disequilibrium; (3) a grain-scale model for diffusion-controlled trace-element mass transfer. We illustrate some of the benefits of the model by analyzing both major and trace elements during mantle magmatism in a mid-ocean ridge-like context. We systematically explore the effects of mantle potential temperature, upwelling velocity, degree of equilibrium and hetererogeneous sources on the compositional variability of melts and residual peridotites. Our model not only reproduces the main thermo-chemical features of decompression melting but also predicts counter-intuitive differentiation trends as a consequence of phase changes and transport occurring in disequilibrium. These include a negative correlation between Na2O and FeO in melts generated at the same Tp and the continued increase of the melt’s CaO/Al2O3 after Cpx exhaustion. Our model results also emphasize the role of disequilibrium arising from diffusion for the interpretation of trace-element signatures. The latter is shown to be able to reconcile the major- and trace-element compositions of abyssal peridotites with field evidence indicating extensive reaction between peridotites and melts. The combination of chemical disequilibrium of major elements and sluggish diffusion of trace elements may also result in weakened middle rare earth to heavy rare earth depletion comparable with the effect of residual garnet in mid-ocean ridge basalt, despite its absence in the modelled melts source. We also find that the crystallization of basalts ascending in disequilibrium through the asthenospheric mantle could be responsible for the formation of olivine gabbros and wehrlites that are observed in the deep sections of ophiolites. The presented framework is general and readily extendable to accommodate additional processes of geological relevance (e.g. melting in the presence of volatiles and/or of complex heterogeneous sources, refertilization of the lithospheric mantle, magma channelization and shallow processes) and the implementation of other geochemical and isotopic proxies. Here we illustrate the effect of heterogeneous sources on the thermo-mechanical-chemical evolution of melts and residues using a mixed peridotite-pyroxenite source.
Oparin, N., Oleynikov, O.Picroilmenite from kimberlite pipes of central Yakutia.IOP Conference series: Earth and Environmental Science, 609, 01028 8p. PdfRussia, Yakutiadeposit - Manchary, Aprelskaya

Abstract: Picroilmenite is one of the most important indicator minerals of kimberlite rocks, which can be used in solving petrological problems and in the search for diamond deposits. The present study shows the results of studying picroilmenite grains from the Manchary and Aprelskaya pipes within the Khompu-May kimberlite field (Central Yakutia). The rocks composing the pipes are represented by porphyritic kimberlite and kimberlite breccia, between which there are gradual transitions. Rocks forming the upper pipe horizons are highly carbonatized and supergenetically altered. Porphyritic segregations are represented by carbonatized serpentine pseudomorphs from macro-, megacrysts and olivine phenocrysts. Pyrope, picroilmenite mega-, macrocrysts and chromospinellide macrocrysts are found in both pipes. Most weakly altered parts of mesostasis are microgranular and formed mostly by phlogopite, with xenomorphic segregations of calcite and serpentine. Picroilmenite in both kimberlite bodies occurs as irregular and rounded macrorysts ranging from 0.7 to 10 mm and megacrysts ranging from 10 to 25 mm. Micrograins of this mineral were not diagnosed in the mesostasis. Individual grains of picroilmenite from the Manchary pipe are surrounded by a polymineral rim composed of either ferrospinel and magnetite, or perovskite and magnetite. High-and low-chromium varieties which correspond to two parageneses are identified among the picroilmenite grains from the Manchary pipe. Crystallization trend of high-chromium ilmenites from the Manchary pipe is clearly seen in the diagram in the coordinates Fe2O3-FeTiO3-MgTiO3 and associated with the presence of Cr-rich phlogopite from lherzolites xenoliths. Picroilmenite grains from the Aprelskaya kimberlite pipe are more magnesian in comparison with similar grains from the Manchary pipe. Picroilmenite from both pipes in the coordinates Fe2O3-FeTiO3-MgTiO3 is characterized by a magmatic kimberlite trend of the mineral composition evolution. The distribution of mineral composition points from the studied pipes in the diagram in the coordinates MgO - Cr2O3 has form of the "Haggerty parabola" (Haggerty, 1975) - typical for picroilmenites from kimberlites of industrial diamond-bearing middle Paleozoic pipes of Yakutia (Aikhal, Mir, Udachnaya). In general, picroilmenite of Central Yakutia pipes differs from picroilmenite of the Aikhal, Mir and Udachnaya pipes by the presence of the parabola right branch in the Haggerty diagram and an indistinct left branch. The Aikhal, Mir, and Udachnaya pipes are characterized by a clear demonstration of the left branch and a weak right. At the same time, the composition points of the high-chromium picroilmenite variety from the Manchary pipe in the Haggerty diagram coincide with the high-chromium picroilmenite from the Grib kimberlite pipe (Arkhangelsk diamondiferous province). Thus, the study showed the genetic polygeny of picroilmenite from the Manchary and Aprelskaya kimberlite pipes, and also the correlation with mineralogical diamond potential of both pipes traced by comparison with the known industrial ilmenite diamondiferous pipes of Yakutia and Arkhangelsk region.
Otter, L.M., Forster, M.W., Belousova, E., O'Reilly, P., Nowak, D., Parlk, S., Clar, S., Foley, S.F., Jacob, D.E.GGR cutting-edge review nanoscale chemical imaging by photo-induced force microscopy: technical aspects and application to the geosciences. ( not specific to diamonds)Geostandards and Geoanalytical Research, doi:10.111/ GGR.12373. 51p. PdfGlobalspectroscopy, mineralogy

Abstract: Photo-induced force microscopy (PiFM) is a new-frontier technique that combines the advantages of atomic force microscopy with infrared spectroscopy and allows for the simultaneous acquisition of 3D topographic data with molecular chemical information at high spatial (~ 5 nm) and spectral (~ 1 cm-1) resolution at the nanoscale. This non-destructive technique is time efficient as it requires only conventional mirror-polishing and has fast mapping rates on the order of a few minutes that allow the study of dynamic processes via time series. Here, we review the method’s historical development, working principle, data acquisition, evaluation, and provide a comparison with traditional geochemical methods. We review PiFM studies in the areas of materials science, chemistry, and biology. In addition, we provide the first applications for geochemical samples including the visualisation of faint growth zonation in zircons, the identification of fluid speciation in high-pressure experimental samples, and of nanoscale organic phases in biominerals. We demonstrate that PiFM analysis is a time- and cost-efficient technique combining high-resolution surface imaging with molecular chemical information at the nanoscale and, thus, complements and expands traditional geochemical methods.
Palyanov, Y.N., Borzdov, Y.M., Sokol, A.G., Btaaleva, Y.V., Kupriyanov, I.N., Reitsky, V.N., Wiedenbeck, M., Sobolev, N.V.Diamond formation in an electric field under deep Earth conditions.Science Advances, Vol. 7, 4, eabb4644 doi: 10.1126/ sciadv.abb4644 28p. PdfMantlegeophysics

Abstract: Most natural diamonds are formed in Earth’s lithospheric mantle; however, the exact mechanisms behind their genesis remain debated. Given the occurrence of electrochemical processes in Earth’s mantle and the high electrical conductivity of mantle melts and fluids, we have developed a model whereby localized electric fields play a central role in diamond formation. Here, we experimentally demonstrate a diamond crystallization mechanism that operates under lithospheric mantle pressure-temperature conditions (6.3 and 7.5 gigapascals; 1300° to 1600°C) through the action of an electric potential applied across carbonate or carbonate-silicate melts. In this process, the carbonate-rich melt acts as both the carbon source and the crystallization medium for diamond, which forms in assemblage with mantle minerals near the cathode. Our results clearly demonstrate that electric fields should be considered a key additional factor influencing diamond crystallization, mantle mineral-forming processes, carbon isotope fractionation, and the global carbon cycle.
Pamato, M.G., Novella, D., Jacobs, D.E., Oliveira, B., Pearson, D.G., Greene, S., Alfonso, J.C., Favero, M., Stachel, T., Alvaro, M., Nestola, F.Protogenetic sulfide inclusions in diamonds date the diamond formation event using Re-Os isotopes. Victor, JerichoGeology , Vol. 49, 4, 5p. Canada, Ontario, Nunavutdiamond inclusions

Abstract: Sulfides are the most abundant inclusions in diamonds and a key tool for dating diamond formation via Re-Os isotopic analyses. The manner in which fluids invade the continental lithospheric mantle and the time scale at which they equilibrate with preexisting (protogenetic) sulfides are poorly understood yet essential factors to understanding diamond formation and the validity of isotopic ages. We investigated a suite of sulfide-bearing diamonds from two Canadian cratons to test the robustness of Re-Os in sulfide for dating diamond formation. Single-crystal X-ray diffraction (XRD) allowed determination of the original monosulfide solid-solution (Mss) composition stable in the mantle, indicating subsolidus conditions of encapsulation, and providing crystallographic evidence supporting a protogenetic origin of the inclusions. The results, coupled with a diffusion model, indicate Re-Os isotope equilibration is sufficiently fast in sulfide inclusions with typical grain size, at mantle temperatures, for the system to be reset by the diamond-forming event. This confirms that even if protogenetic, the Re-Os isochrons defined by these minerals likely reflect the ages of diamond formation, and this result highlights the power of this system to date the timing of fluid migration in mantle lithosphere.
Parashuramulu, V., Shankar, R., Sarma, V.S., Nagaraju, E., Babu, N.R.Baddeleyite Pb-Pb geochrnology and paleomagnetic poles for ~1.89-~1.86 Ga mafic intrusions from the Dharwar craton, India, and their paleogeographic implications.Tectonophysics, Vol. 805, 228789 18p. PdfIndiamagmatism

Abstract: We present new key paleomagnetic pole at 13°S, 152°E (k = 21, A95 = 7.8°) for recently identified 1864.4 ± 2.7 Ma (weighted mean age of four Pbsingle bondPb ages) mafic magmatic event, based on a detailed paleomagnetic study of dolerite dykes and sills intruding Archean basement rocks and Tadipatri formation of the Cuddapah basin, Dharwar craton respectively. The Pbsingle bondPb baddeleyite geochronology yields a crystallisation age of 1867.1 ± 1.0 Ma (MSWD = 1.02) for N77°E trending dyke in the southern region to Cuddapah basin. This new age obtained, confirms the presence of ~1864 Ma magmatic episode with a spatial extent of ~400 km in the Eastern Dharwar craton, within the brief period of ~5 Ma. The paleomagnetic results in these dykes revealed reverse polarity magnetisation direction with mean D = 107°, I = 24° (N = 13 sites, a95 = 10°). Here, we also update the normal polarity magnetic directions on ~1.89 Ga swarm, and the corresponding paleopole situated at 21°N, 336°E (N = 79 sites, A95 = 3.6°). The paleoposition of India is constrained around the equator during ~1.89-1.86 Ga time. The paleogeographic reconstructions were also been attempted at ~1.89 Ga and ~ 1.86 Ga with available key poles from other cratons, indicates the possibility of single plume acting as a source for two distinguishable radial emplacement of mafic dyke swarms across India (Dharwar and Bastar craton) and Western Australia (Yilgarn craton) within a time span of ~35 Ma. The individual movement of India, Baltica and Siberia with a drift rate of ~5.55 cm/yr towards the south, whereas Amazonia craton has moved rapidly to the north (~24.9 cm/yr), do not suggest the amalgamation of a supercontinent (Columbia/ Nuna) during ~1.88-1.86 Ga time.
Pardieu, V., Sangsawong, S., Cornuz, L., Raynaud, V., Luetrakulprawat, S.Update on emeralds from the Mananjary-Irondo area, Madagascar.Journal of Gemology, Vol. 37, 4, pp. 416-425.Africa, Madagascaremerald
Pattnaik, J., Demouchy, S., Ghosh, S.Low hydrogen concentrations in Dharwar cratonic lithospheric inferred from peridotites, Wajrakarur kimberlite field: implications for mantle viscosity and carbonated silicate melt metasomatism.Precambrian Research, Vol. 352, doi.org/1016 /j.precamres .2020.105982 15p. PdfIndiadeposit - Wajrakarur

Abstract: Hydrogen as an atomic impurity in mantle minerals is recurrently proposed as a key element impacting significantly on many mantle properties and processes such as melting temperature and mechanical strength. Nevertheless, interpretation based on the natural samples remains weak as we do not have yet a robust world-wild database for hydrogen concentrations in mantle minerals and rocks. Here, we report the first hydrogen concentrations in nominally anhydrous minerals from a rare selection of ultramafic rocks and minerals embedded in Mesoproterozoic Wajrakarur kimberlites (Eastern Dharwar craton, India). Based on key chemical elements, we demonstrate that olivine, pyroxenes and garnet from the Dharwar craton are of mantle origin. We quantify the hydrogen concentrations using Fourier transform infrared spectroscopy (FTIR) and mineral-specific FTIR calibrations. Calculated hydrogen concentrations are, in average, 18 ppm wt H2O in olivine, 70 ppm wt H2O in orthopyroxene and 207 ppm wt H2O in clinopyroxene. Garnet has highly variable hydrogen concentration ranging from 0 to 258 ppm wt H2O, probably influenced by nano-scale inclusions. The average of clean garnet spectra yields 14.5 ppm wt H2O. The reconstructed hydrogen bulk concentrations of Dharwar peridotites yields ppm wt H2O. This value is two to five times lower than the estimated hydrogen concentration in the lithospheric mantle, and agree well with the lower range of hydrogen bulk concentration from the current data base for the upper mantle minerals transported by kimberlites from other cratons (e.g., South Africa, Siberia). The low hydrogen concentration in mantle minerals, together with petrological and geochemical evidence of carbonated silicate melt metasomatism in Dharwar cratonic lithospheric mantle, suggest that these xenoliths are possibly related to proto-kimberlite melts with low water activity prior to being transported to the surface by the Mesoproterozoic Wajrakarur kimberlites. These observations, valid to a depth of ~165-km, suggest that cratonic lithosphere beneath the Dharwar craton may not be particularly indicative of an abnormal hydrogen-rich southern Indian lithosphere in the late Archean and that hydroxylic weakening in olivine would induced a negligible effect on the mantle viscosity of Indian subcontinent.
Pavlushkin, A., Loginova, A., Seryotkin, Y.Crystallographic orientation and geochemical features of mineral inclusions in diamonds.Russian Geology and Geophysics, doi:10.15372 /RG2020144 21p. PdfRussiadeposit - Mir, Udachnaya, Aikal, Yubileinya

Abstract: The orientation of 76 mineral inclusions represented by olivine (25 inclusions), pyrope (13 inclusions), and magnesiochromite (38 inclusions) was measured in 16 diamond samples from the major primary diamond deposits of Yakutia: Mir, Udachnaya, Internatsionalnaya, Aikhal, and Yubileynaya kimberlite pipes. The novelty of the study is that it provides a special purposeful approach to selection of samples containing not only olivine inclusions that have been extensively studied in the most recent years after the publication of the book Carbon in Earth (2013). The present collection accounts for more than 25% of all samples studied across the world and includes the most typical mineral inclusions of the predominant peridotitic paragenesis in almost all known kimberlites. Both this experiment and similar studies conducted by foreign colleagues in 2014-2019 have found no inclusions whose orientation meets the epitaxial criterion. Only single magnesiochromite inclusions in three diamonds demonstrate an orientation close to the regular one. A significant correlation between the carbon isotope composition and the mineral composition of inclusions of peridotitic and eclogitic paragenesis diamonds as well as the lack of a correlation with other properties may be considered one of the geochemical features. However, given the numerous published and proprietary data demonstrating the complex diamond growth history and, in some cases, wide variations in the composition of mineral inclusions in different zones, along with the difference in their morphology, the authors a believe that syngenetic and protogenetic inclusions can coexist in the same diamond. This is also confirmed by the discoveries of diamondiferous peridotite and eclogite xenoliths in kimberlites where diamonds are completely enclosed in garnet or olivine. Of particular note is the constant presence of heavy hydrocarbons (rel.%), from pentane (C5H12) to hexadecane (C16H34), that are predominant in fluid inclusions in kimberlite and placer diamonds as well as in pyrope and olivine of diamondiferous peridotite xenoliths.
Pavlushkin, A., Zedgenizov, D., Vasilev, E., Kuper, K.Morphology and genesis of ballas and ballas-like diamonds.MDPI Crystals, Vol. 11, 17 dx.doi.org/ 103390/ Qcrystal11010017 24p. PdfRussia, Yakutia, Urals, South America, Brazildeposits - Mir, Udachnaya, Aikal, Yubilenya

Abstract: Ballas diamond is a rare form of the polycrystalline radial aggregate of diamonds with diverse internal structures. The morphological features of ballas diamonds have experienced repeated revision. The need that this paper presents for development of a crystal-genetic classification was determined by a rich variety of combined and transitional forms of ballas-like diamonds, which include aggregates, crystals, and intergrowths. The new crystal-genetic classification combines already-known and new morphological types of ballas as well as ballas-like diamonds discovered in the placers of Yakutia, the Urals, and Brazil. The ballas-like diamond forms include spherocrystals, aggregates with a single crystal core, split crystals, radial multiple twin intergrowths, and globular crystals. The crystal genetic scheme of the evolution of ballas and ballas-like diamonds is a sequence of the morphological types arranged in accordance with the conventional model of the dependence of the mechanism and diamond growth from carbon supersaturation developed by I. Sunagawa. The evolution of the growth forms of ballas and ballas-like diamonds was tracked based on the macrozonal structure of diamonds varying from a flat-faced octahedron to a fibrous cuboid with its transition forms to the radiating crystal aggregates. The morphological diversity of the ballas-like diamonds depends on the level of supersaturation, and abrupt changes of the level of supersaturation engender abrupt changes in a mechanism of crystal growth. The change in the rate of growth under the influence of adsorption and absorption of the mechanic impurities accompanied the sudden appearance of the autodeformation defects in the form of splitting and multiple radial twinning of crystals. The spherical shape of Yakutia ballas-like diamonds is due to the volumetric dissolution that results in the curved-face crystals of the "Urals" or "Brazilian" type associated with ballas diamonds in placers.
Pearson, D.G., Li, D., Xu, Y., Liu, S-A., Chu, Z., Chen, L-H., Li, S.Oxidation of the deep mantle wedge by recycled carbonates: constraints from highly siderophile elements and osmium isotopes.Geochimica et Cosmochimica Acta, Vol. 295, pp. 207-223.Chinanephelinites, basanites

Abstract: Widespread Cenozoic intraplate basalts from eastern China offer the opportunity to investigate the consequences of interaction between the stagnant Pacific slab and overlying asthenosphere and chemical heterogeneity within this “big mantle wedge”. We present and compile a comprehensive study of highly siderophile elements and Mg-Zn isotopes of this magmatic suite (60 samples including nephelinites, basanites, alkali basalts and tholeiites). The large-scale Mg-Zn isotopic anomalies documented in these basalts have been ascribed to mantle hybridization by recycled Mg-carbonates from the stagnant western Pacific plate. Our results reveal that the nephelinites and basanites are characterized by unfractionated platinum-group element (PGE) patterns normalized to primitive upper mantle (PUM) (e.g., PdN/IrN normalized to PUM?=?1.1?±?0.8, 1s), relatively high total PGE contents (e.g., Ir?=?0.25?±?0.14?ppb) and modern mantle-like 187Os/188Os (0.142?±?0.020). These characteristics are coupled with lighter Mg isotope (d26Mg?=?-0.48?±?0.07‰) and heavier Zn isotope (d66Zn = +0.46?±?0.06‰) compositions compared to the mantle values (d26Mg: -0.25?±?0.07‰; d66Zn: +0.18?±?0.05‰). Together, these data are interpreted to reflect the oxidative breakdown of low proportions of mantle sulfides in the sources of these small-degree melts, likely caused by recycled carbonates, which then release chalcophile-siderophile elements into carbonatitic melts. By contrast, the contemporaneous alkali basalts and tholeiites are characterized by highly fractionated PGE patterns (e.g., PdN/IrN?=?4.4?±?3.3; Ir?=?0.037?±?0.027?ppb) and radiogenic 187Os/188Os (0.279?±?0.115) coupled with less fractionated Mg-Zn isotope compositions (d26Mg: -0.39?±?0.05‰; d66Zn: +0.35?±?0.03‰). In combination with other isotopic (e.g., Sr-Nd) and chemical (SiO2, Ce/Pb, Ba/Th, Fe/Mn) constraints, the alkali basalts and tholeiites were derived from higher degree melting of ancient pyroxenite-bearing mantle in addition to mixing with the aforementioned nephelinitic and basanitic melts. Collectively, we suggest that deep recycled carbonates promoted melting within the "big mantle wedge" leading to the generation of Cenozoic intraplate basalts across eastern China and the "redox freezing of carbonates" may cause the oxidation of Fe0 and S2-. This process may provide an important mechanism to oxidize mantle sulfides and transfer precious metals from deep mantle to crust.
Pearson, G.Exploring for diamonds and what they tell us about how the Earth works. *** April 29Carnegie Institute Lecture April 29, 6.30 pm est, Please click this URL to join.Globaldiamond genesis

Abstract: Finding and evaluating diamond deposits is one of the hardest tasks in mineral resource development. In this talk, we will delve a little into the techniques used to find diamonds and how to evaluate the deposits. We will then examine why diamonds-the deepest derived of all natural materials—are unique in their ability to illuminate processes taking place over 700 km beneath Earth's surface, and up to 3.5 billion years back into its history. Click to register for Upcoming April 29, 2021 Webinar.
Pearson, G.D.Exploring for diamonds and what they tell us about how the Earth works. April 29Carnegiescience.edu, https://youtu.be /23M235RKAqA Globaldiamond genesis

Abstract: Finding and evaluating diamond deposits is one of the hardest tasks in mineral resource development. In this talk, we will delve a little into the techniques used to find diamonds and how to evaluate the deposits. We will then examine why diamonds-the deepest derived of all natural materials-are unique in their ability to illuminate processes taking place over 700 km beneath Earth's surface, and up to 3.5 billion years back into its history.
Perchuk, A.L., Sapegina, A.V., Safonov, O.G., Yapaskurt, V.O., Shatsky, V.S., Malkovets, V.G.Reduced amphibolite facies conditions in the Precambrian continental crust of the Siberian craton recorded by mafic granulite xenoliths from the Udachnaya kimberlite pipe, Yakutia.Precambrian Research, Vol. 357, 1061022, 14p. PdfRussia, Yakutiadeposit - Udachnaya

Abstract: It is widely accepted that granulite xenoliths from kimberlites provide a record of granulite facies metamorphism at the basement of cratons worldwide. However, application of the phase equilibria modeling for seven representative samples of mafic granulites from xenoliths of the Udachnaya kimberlite pipe, Yakutia, revealed that a granulitic garnet + clinopyroxene + plagioclase ± orthopyroxene ± amphibole ± scapolite mineral assemblage was likely formed in the middle crust under amphibolite facies conditions (600-650 °C and 0.8-1.0 GPa) in a deficiency of fluid. Clinopyroxene in the rocks is characterized by elevated aegirine content (up to 10 mol.%) both in the earlier magmatic cores and in the later metamorphic rim zones of the grains. Nevertheless, the phase equilibrium modeling for all samples indicates surprisingly reduced conditions, i.e. oxygen fugacity 1.6-3.3 log units below the FMQ (Fayalite-Magnetite-Quartz) buffer. In contrast, the coexistence of Fe-Ti oxides indicates temperatures of 850-990 °C and oxygen fugacity about lg(FMQ) ± 0.5, conditions which correspond to earlier stages of rock evolution. Reduction of oxygen fugacity during cooling is discussed in the context of the evolution of a complex fluid. The reconstructed P-T conditions for the final equilibration in the mafic granulites indicate that temperatures were ~250 °C higher than those extrapolated from the continental conductive geotherm of 35-40 µW/m2 deduced from peridotite xenoliths of the Udachnaya pipe. Although the granulites resided in the crust for a period for at least 1.4 Ga, they did not re-equilibrate to the temperatures of the geotherm, likely due to the blocking of mineral reactions under relatively low temperatures and fluid-deficient conditions
Pessano, P.C., Ganade, C.E., Tupinamba, M., Teixeira, W.Updated map of the mafic dike swarms of Brazil based on airborne geophysical data.Journal of South American Earth Sciences, in press available, 16p. PdfSouth America, Brazilgeophysics

Abstract: Identification of mafic dike swarms and LIPs (Large Igneous Provinces) are of vital importance in geologic history because they provide information on geodynamics, mantle geochemistry, and paleomagnetism. These data provide key information for paleogeographic reconstructions with the aid of barcode matches and precise radiometric ages. Considering such issues, the Brazilian Precambrian shield can be used as a case for refining the cartography of the relevant intraplate activity (e.g., dikes, sills, flood basalts) in space and time. This work presents an updated map of Brazilian mafic dike swarms produced from airborne geophysical maps (Series 1000 - Geological Survey of Brazil). Linear and strong anomalies found on aeromagnetic maps using First Vertical Derivative of the Magnetic Field and Amplitude of the Analytic Signal were mapped on a GIS platform. The obtained data were compared to ternary radiometric maps and geological maps in order to exclude those that do not correspond to mafic dikes. The remaining structures - those believed to represent mafic dikes - were classified based on data compiled from the literature. The updated map exhibits more than 5000 elements, including dikes and magmatic suites, in which about 75% were geologically identified and divided into 60 dike swarms and 10 igneous suites and/or units. The dikes were grouped into sixteen extensional episodes from the Archean to the Cenozoic, although some are related to extension/transtension domains within regional compressive zones akin to orogenic settings. The most frequent records refer to the Proterozoic, representing intraplate episodes, some of them consistent with LIPs. The dataset also includes a large record of the Mesozoic age, which corresponds to major LIP events related to the opening of the Atlantic Ocean and the fragmentation of Gondwana.
Petrovskii, M.N.Rare earth minerals from carbonatite veins in the Soustov pluton, Kola Peninsula, as an indicator of its ore specialization.Geology of Ore Deposits, Vol. 62, 8, pp. 754-763. pdfRussia, Kola PeninsulaREE

Abstract: This paper presents the results of the first geological, isotope, geochemical, and mineralogical study of carbonatite veins that were previously unknown in the Soustov pluton. The studied veins are similar in the Sm-Nd isotope composition and model age to the host rocks, which implies a common formation processs. High contents of light lanthanides, Sr, and Nb in carbonatite veins were measured. These elements are concentrated in bastnäsite, strontianite, monazite, and pyrochlore. These data significantly enlarge our concepts of the geochemical and ore specialization of the massif.
Piccolo, A., Kaus, B.J.P., White, R.W., Palin, R.M., Reuber, G.S.Plume - Lid interactions during the Archean and implications for the generation of early continental terranes.Gondwana Research, Vol. 88, pp. 150-168. 19p. PdfMantlegeodynamics

Abstract: Many Archean terranes are interpreted to have a tectonic and metamorphic evolution that indicates intra-crustal reorganization driven by lithospheric-scale gravitational instabilities. These processes are associated with the production of a significant amount of felsic and mafic crust, and are widely regarded to be a consequence of plume-lithosphere interactions. The juvenile Archean felsic crust is made predominantly of rocks of the tonalite-trondhjemite-granodiorite (TTG) suite, which are the result of partial melting of hydrous metabasalts. The geodynamic processes that have assisted the production of juvenile felsic crust, are still not well understood. Here, we perform 2D and 3D numerical simulations coupled with the state-of-the-art of petrological thermodynamical modelling to study the tectonic evolution of a primitive Archean oceanic plateau with particular regard on the condition of extraction of felsic melts. In our numerical simulations, the continuous emplacement of new, dry mafic intrusions and the extraction of the felsic melts, generate an unstable lower crust which drips into the mantle soon after the plume arrival. The subsequent tectonic evolution depends on the asthenosphere TP. If the TP is high enough (= 1500 °C) the entire oceanic crust is recycled within 2 Myrs. By contrast at low TP, the thin oceanic plateau slowly propagates generating plate-boundary like features.
Pilchin, A.N., Eppelbaum, L.V.Plate tectonics and Earth evolution: a conceptual review.ANAS Transactions, Earth Sciences, Vol. 2, pp. 3-32. pdf doi: 10.33677 /ggianas20200200043Mantlegeodynamics

Abstract: Numerous attempts have been made to understand the rules of Earth’s tectono-geodynamic processes over the past centuries. While no paradigm has offered comprehensive answers to all of the questions, the present review aims to acquaint readers with the modern state of developments in the tectonic insights of Earth's evolution. A number of very interesting and unique processes and features took place during the evolution of early Earth. Most of these, however, were largely erased over the course of Earth’s ensuing evolution; some leaving only traces of their existence and some remnant phenomena, especially those taking place in the Hadean and Early to Late Archean. Among such processes and features are: the planetary accretion of Earth, formation of unique rock complexes, initiation of the plate tectonics phenomenon, main forces driving plate tectonics, significant influence of thermal parameters, role of overpressure under different physical-geological environments, stratification of Earth's crust and lithosphere by density, and various other thermodynamic models. Nearly all of these remain enigmatic, due to considerable uncertainty in the timing and methods of their evolution, and the ambiguity of their secondary processes and tectono-geophysical indicators. At the same time, majority of tectono-geodynamic processes and features are also interrelated, and the simultaneous fluctuation of myriad different factors played a significant role in their influence to the geological medium. Some of these intricate questions are discussed in this paper. For instance, what is the role of the plate tectonics phenomenon and when did this process initiate on Earth? Especial attention is paid in the review to the sophisticated methods of understanding tectonic processes over the course of various generations of geoscientists. In the conducted analyses, certain physical data derived from other planets of the Solar System were utilized as well.
Podolsky, M.Primary asset development standard model - deposit to reserve desktop to feasibility governance - example Gahcho Kue mine, Northwest Territories, Canada.Vancouver Kimberlite Cluster recorded,  https://youtu.be/ GMyoKHoQrJECanada, Northwest Territoriesdeposit - Gahcho Kue

Abstract: A primary rock-hosted diamond Deposit to Reserve Asset Development Standard model governed under the 2014 Canadian Institute of Mining, Metallurgy and Petroleum definition standards on Mineral Resources and Reserves and 2016 Toronto Stock Exchange National Instrument 43-101 - Standards of Disclosure for Mineral Projects, is presented and discussed. The Gahcho Kué Mine De Beers Canada - Mountain Province Diamonds joint venture project roadmap from exploration commencing in 1992 to definitive Feasibility Study in 2010 is reviewed under the incorporated 2003 Guidelines for the Reporting of Diamond Exploration Results and 2008 Estimation of Mineral Resources and Mineral Reserves Best Practices Guidelines for Rock Hosted Diamonds. Karowe and Ekati-Sable diamond mines histories are also compared. The Asset Development Standard model utilizes a published De Beers system of kimberlite Deposit to Reserves geo-scientific scorecard classification, that is aligned with reporting of Desktop, Conceptual and Pre-Feasibility to Feasibility Studies.
Popov, M., Bondarenko, M., Kulnitskiy, B., Zholudev, S., Blank, V., Terentyev, S.Impulse laser cutting of diamond accompanied by phase transitions to fullerene -type onion.Diamond & Related Materials, Vol. 113, 108281, 6p. PdfGlobalraman spectroscopy
Presser, J.Lampoites in Leucite HillsLinkedin, https://www.linkedin.com/ posts/jaime-l-b-presser -179a0415_and-the-paleo- volcanoes-of-lamproites -in-activity-6781902573 998759936-4fEnUnited States, Wyominglamproite
Presser, J.B.Lamproites of the Kaapvaal type, two reference mines: Finch with 59.9 cpht and Dokolwayo with 30 cpht. Others …..https://www.linkedin.com/in/jaime-I-b-presser, Jan. 7, 8p. Africa, South Africa, Australia, South America, Paraguaylamproite
Presser, J.L.B.Peridotite geotherms of the Rio de la Plata craton-archon core. *** in EngHistoria Natural , Vol. 10, 3, pp. 5-10. pdfSouth Americageothermometry

Abstract: At the Rio de la Plata Craton archon-core environment were inferred, based on 1D Vs profiles (on 208 numbers of points), of the peridotitic geotherms. Values for the archon-core environment, it was estimated 38.5 to 40 mW/m2 in its central northern portion and southern portion and in its edges/southern portion 40 to 42 mW/m2. Geotherm values that allowed estimate LAB between 243 to 237 km depth (northern portion) and 225 to 213 km depth (southern portion). The same 1D Vs information allowed recognizing for this geothermal environment the depth of the graphite-to-diamond phase transition, finding that it is located at ~135 km. depth. So, projecting 70-90 Km. (southern portion) to 102-108 km. (northern portion) thickness of the “diamond window” for the Rio de la Plata craton archon-core. "Diamond window" thickness very close to those of the Kalahari archon craton where the highest grade of diamond deposit is the Kimberley with 200 cpht. Thus, it is estimated for eventual diamond deposit, in the Río de la Plata craton core, are quite similar to Kimberley diamond deposits could be also expected in the archon-core of Río de la Plata craton.
Presser, J.L.B., Benitez, P.Eclogitic geotherms of the Rio de la Plata craton archon-core: Estancia Trementina and Puentesino, Dpto. Of Concepion - Paraguay. Compared to two large diamond deposits Argyle ( lamproitic) and Orapa ( Kimberlitic).Linked in, 20p. PdfSouth America, Paraguaygeothermometry
Priestley, K., Ho, T., McKenzie, D.The formation of continental roots.Geology, Vol. 49, pp. 190-194. pdfMantlegeophysics, seismics, tomography

Abstract: New evidence from seismic tomography reveals a unique mineral fabric restricted to the thick mantle lithosphere beneath ancient continental cratons, providing an important clue to the formation of these prominent and influential features in Earth’s geological history. Olivine, the dominant mineral of Earth’s upper mantle, has elastic properties that differ along its three crystallographic axes, and preferential alignment of individual olivine grains during plastic deformation can affect the bulk nature of seismic-wave propagation. Surface-wave tomography has shown that over most of Earth, deformation of the mantle lithosphere has oriented olivine crystals with the fast axis in the horizontal plane, but at depths centered at ~150 km within cratonic continental-lithosphere roots, the fast crystallographic axis is preferentially aligned vertically. Because of the high viscosity of the cratonic roots, this fabric is likely to be a vestige from craton formation. Geochemical and petrological studies of upper-mantle garnet-peridotite nodules demonstrate that the cratonic mantle roots are stabilized by their reduced density, which was caused by melt removal at much shallower depths than those from which the nodules were subsequently extracted. The mineral fabric inferred from surface-wave tomography suggests that horizontal shortening carried the depleted zone downward after the melt-depletion event to form the thick continental roots, stretching the depleted material in the vertical dimension by pure shear and causing the fast crystallographic axis to be aligned vertically. This seismological fabric at ~150 km is evidence of the shortening event that created the cratonic roots.
Prokopyev, I.R., Doroshkevich, A.G., Zhumadilova, D.V., Starikova, A.E., Nugumanova, Ya.N., Vladykin, N.V.Petrogenesis of Zr-Nb ( REE) carbonatites from the Arbarastakh complex ( Aldan Shield, Russia): mineralogy and inclusion data.Ore Geology Reviews, Vol. 131, 104042, 15p. Pdf.Russiadeposit - Arbarastakh

Abstract: The Arbarastakh Neoproterozoic ultramafic carbonatite complex is located in the southwestern part of the Siberian Craton (Aldan Shield) and contains ore-bearing Zr-Nb (REE) carbonatites and phoscorites. Carbonatites are mainly represented by calcite and silicocarbonatite varieties. The primary minerals composing the carbonatites are calcite and dolomite, as well as phlogopite, clinopyroxene, fluorapatite, amphibole, fluorite, K-feldspar and feldspathoids. Olivine (forsterite), Ti-magnetite, apatite, phlogopite, calcite, dolomite and the minor spinel group minerals form the primary phoscorites. The ore-bearing Zr-Nb mineral assemblages of the phoscorites and carbonatites include accessory zircon, zirconolite, perovskite, pyrochlore and baddeleyite. The Ba-Sr-REE hydrothermal mineralisation consists of ancylite-(Ce), bastnaesite-(Ce) and burbankite, as well as barite-celestite, strontianite, barytocalcite, and rare Cu-Fe sulphides. The silicocarbonatites and carbonatites formed in multiple stages from a single alkaline Ca-Na-K-silicocarbonatite melt, while the phoscorites are products of differentiation of the carbonatitic melt and were crystallised from an Fe-rich phosphate-carbonate melt at temperatures of more than 720 °C. The silicate-phosphate-carbonate melts were responsible for the Zr-Nb mineralisation of the carbonatites at temperatures of more than 540-575 °C; the hydrothermal REE-bearing mineral assemblages crystallised from saline (60-70 wt%) carbonatitic fluids of Na-Ca-Mg-F-carbonate composition at a minimum temperature range of 350-300 °C. The Ca-Sr-carbonate as well as the Na-hydro-carbonate fluids were responsible for the Ba-Sr-REE mineralisation of the phoscorites at ~500-480 and 450-430 °C.
Pujol-Sola, N., Dominguez-Carretero, D., Proenza, J.A., Haissen, F., Ikenne, M., Gonzales-Jiminez, J.M., Colas, V., Maacha, L., Garcia-Casco, A.The chromitites of the Neoproterozoic Bou Azzer ophiolite ( central Anti-Atlas, Morocco) revisited.Ore Geology Reviews, Vol. 134, 104166, 24p. PdfAfrica, Moroccomoissanite

Abstract: The Neoproterozoic Bou Azzer ophiolite in the Moroccan Anti-Atlas Panafrican belt hosts numerous chromitite orebodies within the peridotite section of the oceanic mantle. The chromitites are strongly affected by serpentinization and metamorphism, although they still preserve igneous relicts amenable for petrogenetic interpretation. The major, minor and trace element composition of unaltered chromite cores reveal two compositional groups: intermediate-Cr (Cr# = 0.60 - 0.74) and high-Cr (Cr# = 0.79 - 0.84) and estimates of parental melt compositions suggest crystallization from pulses of fore-arc basalts (FAB) and boninitic melts, respectively, that infiltrated the oceanic supra-subduction zone (SSZ) mantle. A platinum group elements (PGE) mineralization dominated by Ir-Ru-Os is recognized in the chromitites, which has its mineralogical expression in abundant inclusions of Os-Ir alloys and coexisting magmatic laurite (RuS2) and their products of metamorphic alteration. Unusual mineral phases in chromite, not previously reported in this ophiolite, include super-reduced and/or nominally ultra-high pressure minerals moissanite (SiC), native Cu and silicates (oriented clinopyroxene lamellae), but “exotic” zircon and diaspore have also been identified. We interpret that clinopyroxene lamellae have a magmatic origin, whereas super-reduced phases originated during serpentinization processes and diaspore is linked to late circulation of low-silica fluids related to rodingitization. Zircon grains, on the other hand, with apatite and serpentine inclusions, could either have formed after the interaction of chromitite with mantle-derived melts or could represent subducted detrital sediments later incorporated into the chromitites. We offer a comparison of the Bou Azzer chromitites with other Precambrian ophiolitic chromitites worldwide, which are rather scarce in the geological record. The studied chromitites are very similar to the Neoproterozoic chromitites reported in the Arabian-Nubian shield, which are also related to the Panafrican orogeny. Thus, we conclude that the Bou Azzer chromitites formed in a subduction-initiation geodynamic setting with two-stages of evolution, with formation of FAB-derived intermediate-Cr chromitites in the early stage and formation of boninite-derived high-Cr chromitites in the late stage.
Rabinowitz, Y., Etinger, A., Litvak, B., Yahalom, A., Cohen, H., Pinhasi, Y.Millimeter wave spectroscopy for evaluating diamond color grades.Diamond & Related Materials, Vol. 116, 108386 10p. PdfGlobalspectroscopy

Abstract: One of the most important parameters affecting the value of natural colorless diamonds is its light transparency, defined as its color grade. The regular range of color grades in the trade is denoted by alphabet letters in the range D-M, where D represents the best commercial quality. The color grade of diamonds is largely influenced by their nitrogen content (when nitrogen atoms substitute carbon atoms in the crystal) and can be determined from this property. Diamonds absorb electromagnetic radiation in the UV-visible as well as in the Infrared spectral range and therefore, their color grade is measured via spectroscopic light absorption in these frequency range. The electromagnetic properties of different polished diamonds having several nitrogen concentrations in the frequency range of 100-110 GHz (W band) have been studied. The results indicate that there is a good correlation between the amount of nitrogen impurities and the Free Spectral Range (FSR) parameter of a reflection signal, S11, in the antenna. From the study It is concluded that measuring the diamonds dielectric properties via spectroscopic analysis in the millimeter wavelength range, can determine the color grading. In addition, the FSR measurements were correlated well with the FTIR measurements. The methodology of the new color determination mode and a novel color estimate, based on the FSR vs the nitrogen correlation, has been tested on 26 diamonds with a success rate higher than 70%.
Ramokgaba, L., Le Roex, A., Robey, J.Phlogopite-rich and phlogopite-poor kimberlite intrusions within the Du Toitspan kimberlite pipe, South Africa: petrogenetic relationships and localised source heterogeneity.Lithos, in press available, 35p. PdfAfrica, South Africadeposit - Du Toitspan

Abstract: Samples from three petrographically distinct, intrusive kimberlite bodies and associated kimberlite dykes from the eastern lobe of the Du Toitspan kimberlite pipe, Kimberley, South Africa, have been analysed for their bulk rock major and trace element compositions and their olivine and phlogopite compositions. The two dominant intrusive bodies (D13, D14) are distinguished by the one (D13) being phlogopite-rich and best classified as a macrocrystic hypabyssal phlogopite kimberlite, and the other (D14) being phlogopite-poor and best classified as a macrocrystic hypabyssal monticellite kimberlite. The minor D17 intrusive body is classified as a macrocrystic transitional hypabyssal serpentinized phlogopite kimberlite. The associated kimberlite dykes range texturally from aphanitic to macrocrystic and are classified as calcite kimberlites. The major kimberlite intrusions and their associated dykes show no evidence of crustal contamination and are characterised by broadly overlapping geochemistry except for distinctly higher K2O (> 2?wt%) and Al2O3 (>3?wt%) and flattening HREE patterns (Gd/YbN?=?6.5-7.0) in the D13 - phlogopite kimberlite compared to the D14 - monticellite kimberlite and the calcite kimberlite dykes (Gd/YbN?=?9.6-12.1). These distinguishing geochemical features of the D13 - phlogopite kimberlite are comparable to typical Group II kimberlites in southern Africa. However, their diagnostic incompatible trace element ratios (for example, Th/Nb, La/Nb, Ce/Pb, and Ba/Nb) are instead comparable to other kimberlite intrusions analysed in this study and to southern African Group I kimberlites in general. Semi-quantitative modelling suggests that these kimberlite intrusions could have derived by low (<1%) degrees of partial melting of a source region that is enriched in LREE (Lan?=?~6.1; Ybn?~?1.47) comparable to metasomatised peridotites from the underlying lithospheric mantle. The composition of the D13 phlogopite kimberlite is consistent with a partial melt of a modally metasomatised source containing a higher proportion of residual clinopyroxene relative to garnet (compared to that giving rise to the D14 monticellite kimberlite and calcite kimberlite dykes), as well as accessory amounts of phlogopite, i.e. a garnet phlogopite peridotite (GPP). The absence of K-anomalies on primitive mantle normalized diagrams for the D13 phlogopite kimberlite requires that phlogopite was not a residual phase during partial melting and was exhausted shortly before or at the moment of melt segregation. The higher Gd/Yb ratios and lower K2O in the D14 monticellite kimberlite and calcite kimberlite dykes can be explained by partial melting of a cryptically metasomatized, phlogopite - free, garnet peridotite (GP) source, containing a higher proportion of garnet relative to clinopyroxene. The low absolute K and strong negative K-anomaly on primitive mantle normalized diagrams for the D14 monticellite kimberlite were inherited from a source region that previously experienced cryptic metasomatism by a differentiated fluid already carrying a negative K-anomaly.
Razgulov, A.A., Lyanpin, S.G., Novikov, A.P., Ekimov, E.A.Low-temperature photoluminescence study of SnV centers in HPHT diamond.Diamond & Related Materials, Vol. 116, 108379 9p. PdfGlobaldiamond colours

Abstract: Here we report on the study of temperature shift and broadening of the zero phonon line (ZPL) of SnV center in HPHT microcrystalline diamond in the temperature range of 80-300 K. To separate contributions of lattice thermal expansion and electron-phonon coupling, the study of the pressure effect on the ZPL was conducted. A strong nonlinearity observed in the electron-phonon part of the ZPL temperature shift appeared to be in good agreement with well-known polynomial law ?E(T) = cT^2-dT^4 and, therefore, can be related to the effect of the strong softening of elastic springs.
Regis, D., Pehrsson, S., Martel, E., Thiessen, E., Peterson, T., Kellett, D.Post - 1.9 Ga evolution of the south Rae craton ( Northwest Territories), Canada: a paleoproterozoic orogenic collapse system.Precambrian Research, Vol. 355, 106105, 29p. PdfCanada, Northwest Territoriessunduction

Abstract: The Trans-Hudson Orogen (THO), formed from the convergence between the Superior craton and the composite Churchill Upper Plate (CUP), is one of the best-preserved examples of a collisional orogen in the Paleoproterozoic. Similar to modern collision systems such as the Himalayan orogen, it is characterized by a composite upper plate in which terrane accretion established a continental plateau that was tectonically and magmatically active for >100 myr. Our study presents new petrological and geochronological data for four samples collected in three lithotectonic domains of the south Rae craton (one of the CUP terranes). The results presented here allow us to re-define the previously proposed extent of THO reworking in the CUP and afford the opportunity to study and compare the evolution of various fragments that illustrate differing levels of a collapsed plateau in the CUP hinterland. The new data indicate that the south Rae craton locally preserves evidence for burial at 1.855-1.84 Ga with peak metamorphic conditions at approximately 790 °C and 9.5-12.5 kbar followed by rapid cooling and decompression melting (P < 6 kbar) at ca. 1.835-1.826 Ga. These results, which provide important and so far missing Pressure-Temperature-time (P-T-t) constraints on the evolution of the south Rae craton in the Northwest Territories at Trans-Hudson time, coupled with existing regional geochronological and geochemical data, are used to propose an updated model for the post-1.9 Ga THO collision and extensional collapse. Our results reveal that: i) initial thickening in the upper plate started at Snowbird time (ca. 1.94 Ga), then continued via Sask collision (with high-grade metamorphism recorded in the south Rae craton, ca. 1.85 Ga), and ended with Superior collision (ca. 1.83 Ga); ii) the extent of the THO structural and metamorphic overprint in the SW CUP is much broader across strike than previously recognized, and iii) T-t data in the south Rae are indicative of relatively fast cooling rates (8-25 °C/Ma) compared to other known Precambrian orogens. We suggest that the Paleoproterozoic THO represents the first record of a major ‘modern-style’ orogenic plateau collapse in Earth’s history.
Renfro, N., Palke, A.Microfeatures of gems: geologic implications ( diamond and other gemstones)gia.org and knowledge session utube, 44266Globaldiamond inclusions

Abstract: Inclusions are more than imperfections or clarity characteristics. They can teach us much about gemstones’ journeys and reveal otherwise inaccessible information about Earth’s formation. What stories do diamond inclusions tell about Earth’s mantle? What do rutile needles and three-phase inclusions teach us about corundum and emerald, respectively? Follow Manager of Gem Identification Nathan Renfro and Senior Manager of Research Dr. Aaron Palke as they offer an up-close look into the microworld of gems and show us how this world reveals secrets about Earth’s geologic processes at large.
Rezvukhina, O.V., Korsakov, A.V., Rezvukin, D.I., Mikhailenko, D.S., Zamyatin, D.A., Greshnyakov, E.D., Shur, V.Y.Zircon from diamondiferous kyanite gneisses of the Kokchetav massif: revealing growth stages using an integrated cathodluminescence- Raman spectroscopy- electron microprobe approach.Mineralogical Magazine, in press 28p. https://doi.org /10.1180/mgm.2020.95RussiaKokchetav
Rezvukhina, O.V., Skublov, S.G., Rezvukhin, D.I., Korsakov, A.V.Rutile in diamondiferous metamorphic rocks: new insight from trace element composition, mineral/fluid inclusions, and U-Pb-ID-TIMS dating.Lithos, Vol. 394-395, 7p. PdfRussia, Kazakhstandiamond inclusions

Abstract: This study highlights the usefulness of rutile when applied for reconstruction of the metamorphic evolution of ultrahigh-pressure rocks containing diamond. Within the diamondiferous kyanite gneiss (Kokchetav massif, Northern Kazakhstan), rutile shows three distinct textural positions: (i) rounded/irregular-shaped grains in the rock matrix; (ii) monomineralic inclusions in garnet, kyanite, quartz, and zircon; and (iii) grains in polyphase inclusions within garnet and kyanite porphyroblasts. High Nb (1990-3197 ppm) and relatively low Cr (404-703 ppm) concentrations in rutile indicate its metapelitic derivation. The Zr content in rutile varies from 480 to 798 ppm and the average temperature estimates yielded by the Zr-in-rutile geothermometer for 5 GPa are 880 °C. Rutile-hosted Zn-rich (up to 1.74 wt% ZnO) staurolite is interpreted as a record of the prograde metamorphic stage formed as a result of gahnite+pyrophyllite+diaspore breakdown at 0.3-0.8 GPa, 400-450 °C. Inclusions of diamond±CO2 ± carbonate±garnet in rutile originated near the peak of metamorphism (~5 GPa and ~ 880 °C). U-Pb ID-TIMS dating of a representative rutile separate yielded a concordant age of 519 ± 1.6 Ma that is younger than the previously estimated U-Pb crystallization ages of the peak metamorphic assemblages of the Kokchetav massif (528 ± 3 Ma). The obtained age represents the timing of cooling to the closure temperature for Pb diffusion in rutile (Tc; 420-640 °C). The cooling of the rocks from the peak temperatures to Tc occurred with the rates of 27-51 °C/Ma, whereas the exhumation rates (from 880 °C and 5 GPa to 420-640 °C and 0.5-1 GPa) were 1.3-1.5 cm/year. The peak temperature estimates as well as rapid cooling and exhumation rates reported here are in agreement with published data on zircon from similar diamondiferous Kokchetav gneisses. This work demonstrates that rutile provides a beneficial tool in studies dealing with reconstruction of the metamorphic evolution of diamondiferous rocks.
Ribeiro da Costa, I., Roseiro, J., Figueiras, J., Rodrigues, P.C.R., Mateus, A.Pyrochlore from the Bailundo carbonatite Complex ( Angola): compositional variation and implications to mineral exploration.Journal of African Earth Sciences, Vol. 177, 104154, 16p. PdfAfrica, Angoladeposit - Bailundo

Abstract: Pyrochlore is a common accessory in carbonatite rocks and its composition can provide useful insights on petrogenetic and post-magmatic metal-enrichment processes, especially those which favour its occurrence and concentration. Comprehensive compositional and textural characterization of a large set of pyrochlores from the Bailundo Carbonatite Complex (SW Angola) and associated surface rocks was the basis to (i) evaluate the main effects of metasomatism and weathering as causes of metal leaching or concentration; and (ii) assess pyrochlore compositions as potential petrogenetic or metallogenetic tools, with particular emphasis on pyrochlore enrichment in economic components, such as Ta, REE, U, Th and Pb, during weathering processes. Unweathered fluor- and hydroxyl-calciopyrochlores from deep-seated carbonatitic rocks (provided by a 600 m-deep drill-core) often present high Ta/Nb ratios, as well as high U and Th contents, and comparatively low overall REE concentrations. Metasomatic effects are not easy to assess, given the extreme compositional variability of these pyrochlores. On the other hand, some systematic trends can be established in pyrochlores from weathered surface rocks: these pyrochlores usually show strong depletion in most A-site cations (e.g., Na, Ca, U), and clear enrichment in Nb and in large-ion metals (e.g., Ba, Sr, Pb) usually absent in unweathered pyrochlores. REE seem to be relatively immobile and to become concentrated during weathering. Along with some REE phosphates and oxides, pyrochlore is often present in several domains of the weathering profile, occurring in the outcropping weathered carbonatite as well as in the regolith immediately overlying the intrusion. Thus, both the Bailundo carbonatite intrusion and its weathering products, concentrated inside the ridge formed by differential erosion of the fenitic aureole, constitute good exploration targets for Nb (±Ta ± REE). However, future exploration work should also include a 3-D understanding of the chemical and geological processes at work in both geological environments.
Rimmer, A.Flawless precision. DiamondsGems&Jewellery, Vol. 30, 1, pp. 28-30.Globalmarkets
Rocheleau, J.Modeling the creation of cratons, Earth's secret keepers.Eos 102 , https://doi.org/ 10.1029/ 2021EO153324Mantleperidotites

Abstract: Geoscientists have long been trying to answer the complicated questions of how and why Earth’s continents formed. New research suggests a solution that surprised even the investigators themselves.
Roseiro, J., Figueiras, J., Rodrigues, P.C.N., Mateus, A.M. Nb-bearing mineral phases in the Bailiundo carbonatite complex, ( Angola): implications of Nb geochemistry in metallogenesis.Comminocacoes Geologicas ( Researchgate), July, 7p. PdfAfrica, Angoladeposit - Bailundo

Abstract: Pyrochlore group minerals are common accessory phases in many rock types of the Bailundo Carbonatite Complex. These minerals record compositional and textural features that provide useful information regarding their genesis and accumulation, monitoring magmatic, metasomatic and weathering events. In drill core samples, primary compositions (significant Ta and U contents, and relatively low Nb and F values) are found in relict cores of strongly metasomatized pyrochlore grains; irregular patches in pyrochlore rims, typically enriched in F, Na and Nb, reflect fluid alteration fronts. At shallower levels, preserved pyrochlores show well-defined concentric zoning and substantially higher values of F and Nb. In the weathering profile, alteration processes include replacement of F, Na and Ca by Ba, Sr, Pb and H2O. These data suggest the possibility of Nb concentration in late-magmatic fluids as fluoride complexes, and its subsequent mobilization and crystallization in the form of pyrochlore at shallower levels of the Bailundo Carbonatite Complex.
S & P Global Market IntelligenceWorld Exploration Trends 2021S & P for PDAC, 13p. PdfGlobalmarkets
S&P GlobalThe socialeconomic and environmental impact of large-scale diamond mining.Trucost, https://dpawordpress.s3. amazonaws.com/ Trucost _Socioeconomic_and_Environmental_Impact_ of_Large-Scale_ Diamond_ Mining+(2)-min.pdf 37p.Globaldiamond mining

Abstract: In 2017, the DPA engaged Trucost, part of S&P Global, to undertake a world-first comprehensive analysis of the total value contribution of the DPA members, considering all material socioeconomic and environmental benefits and impacts. The study sought to capture not only the economic benefits of diamond mining, which are well understood, but also the social and environmental benefits and impacts associated with the production process. The Trucost Total Value methodology seeks to quantify and capture the full value of these benefits and impacts to provide an assessment of the value created by the DPA members.
Salazar-Mora, C., Sacek, V.Lateral flow of thick continental lithospheric mantle during tectonic quiescence.Journal of Geodynamics, Vol. 146, 101830, 9p. PdfMantlecraton

Abstract: The amalgamation of continental blocks naturally results in a lithosphere with lateral variations in thickness due to the juxtaposition of thicker cratonic and thinner orogenic lithospheres, which in turn evolve together through time. After the amalgamation, this mosaic of continental blocks can experience longstanding periods of relative tectonic quiescence until the next tectonic event, for instance continental rifting. Using geodynamic numerical models, we explored the internal deformation of the continental lithosphere during periods of tectonic quiescence taking into account lateral variations of lithospheric thickness. We observed that the orientation of lateral flow of the thick cratonic lithosphere depends primarily on the compositional density contrasts (??) between the asthenosphere and continental lithospheric mantle and on the width of the juxtaposed mobile belt lithosphere. In the case of mobile belts wider than 300 km, the margin of the thick craton flows towards (or underplates) the base of the thin lithosphere when ?? = 32-48 kg/m3, whereas for smaller ?? values, the thick cratonic margin flows away from mobile belt, preserving a sharp thickness variation. For mobile belts narrower than 300 km, the ?? threshold between underplate or outward behavior decreases with the mobile belt width. Underplating of cratonic lithosphere beneath the thin lithosphere is efficient in mobile belts narrower than 300 km and for higher ??, which allows them to cool, thicken and stiffen. Lateral flow of cratonic lithosphere is not efficient to underplate wide mobile belts thoroughly, so the latter are influenced by asthenospheric heat for prolonged periods and thus remain less rigid. Therefore, we propose that protracted tectonic quiescence of supercontinents can develop lithospheric rheological inheritances that may or may not facilitate post-quiescence continental lithospheric rifting.
Savage, N.Quantum Diamond Sensors Synthetic versions of the super-hard gem stone are driving the development of a class of device with applications in biomedicine and beyond.https://youtu.be/VCT0wDLyvSs, https://www.nature.com/articles /d41586-021-00742-4? utm_source=Nature+Briefing&utm_campaign=d5a18a3501- briefing-dy-20210329& utm_medium=email&utm_term= 0_c9dfd39373- d5a18a3501-42627851Globalsynthetic - uses
Savard, J.J., Mitchell, R.H.Petrology of ijolite series rocks from the Prairie Lake ( Canada) and Fen ( Norway) alkaline rock-carbonatite complexes.Lithos, Vol. 396-397, 106188 20p.Canada, Ontariodeposit - Prairie Lake

Abstract: This study reports the mineralogy and petrology, together with the major and trace element composition of pyroxenes, garnets and apatite from ijolite series rocks occurring at the Prairie Lake carbonatite complex, northwestern Ontario, with comparative data for ijolites from the Fen complex, Norway. The ijolites and calcite ijolites (hollaites) of Prairie Lake record the effects of magma mixing, crystal settling, solid-state re-equilibration and deuteric alteration. The Prairie Lake complex was formed by at least three stages of intrusion. The initial stage was predominantly biotite pyroxenite and associated coarse carbonatite veins. The second stage is represented primarily by members of the ijolite series together with meta-ijolites created by solid state re-equilibration of previously crystallized rocks. Differentiation of the magmas which formed the ijolite suite resulted in the formation of calcite ijolites (hollaites) and malignites (potassic nepheline syenites). The final stage was the intrusion of the heterogeneous carbonatites derived from different batches of carbonatite related magmas. These rocks contain xenoliths of ijolite suite rocks, pyroxene apatitite, wollastonite apatitite, and phoscorite. Pyroxene compositions show an evolutionary trend from diopside in biotite pyroxenites through Fe-enriched diopside-augite in ijolites to aegirine in malignites. Clinopyroxene major and trace element data show that the cores of clinopyroxene in biotite pyroxenites formed as antecrysts at depth and were emplaced as part of a later event. Trace element data from pyroxenes, garnets and apatite from Prairie Lake and Fen are similar to each other and those found in carbonatite complexes worldwide. It is proposed that a continuously-filled fractionating magma chamber was not present at Prairie Lake and that the ijolite-malignite members of the complex formed as result of small intrusions of nephelinitic magma into pre-existing ijolites. Similar styles of magmatic evolution by fractional crystallization are indicated for the Prairie Lake, Fen, and Belaya Zima ijolite-carbonatite complexes and there is no evidence that liquid immiscibility played any role in their petrogenesis.
Schmetzer, K., Martayan, G., Ortiz, J.G.History of the Chivor emerald mine, Part 1 ( 1880-1925): from rediscovery to early production. Part 2 listed previouslyGems & Gemology , Vol. 56, 1, pp. 66-109.South America, Colombiaemerald

Abstract: The history of the Chivor emerald mine in Colombia is rife with legend and adventure. The tale traces from early exploitation by indigenous people, to work by the Spanish in the sixteenth and seventeenth centuries, to 200 years of abandonment and jungle overgrowth. The story then picks up with rediscovery near the turn of the twentieth century by the Colombian mining engineer Francisco Restrepo using clues from a historical manuscript. Still the saga continued, with repeated shortages of investment funds driving multiple ownership changes and little progress toward mining the largely inaccessible deposit. The German gem merchant Fritz Klein, in cooperation with Restrepo, pursued limited mining activities with a small number of workers for a few months prior to the outbreak of World War I. After the war, the American company Colombian Emerald Syndicate, Ltd., took ownership, and mining operations resumed under the new leadership. Ownership changed yet again in the 1920s, followed by multiple cycles of expanding and shrinking mining activity, interrupted by completely unproductive periods.
Schmitz, M., Ramirez, K., Mazuera, F., Avila, J., Yegres, L., Bezada, M., Levander, A.Moho depth map of northern Venezuela on wide-angle seismic studies.Journal of South American Earth Sciences, Vol. 107, 103088, 17p. PdfSouth America, VenezuelaGeophysics - seismics

Abstract: As part of the lithosphere, the crust represents Earth's rigid outer layer. Some of the tools to study the crust and its thickness are wide-angle seismic studies. To date, a series of seismic studies have been carried out in Venezuela to determine in detail the crustal thickness in the southern Caribbean, in the region of the Caribbean Mountain System in northern Venezuela, as well as along the Mérida Andes and surrounding regions. In this study, a review of the wide-angle seismic data is given, incorporating new data from the GIAME project for western Venezuela, resulting in a map of Moho depth north of the Orinoco River, which serves as the basis for future integrated models. Differences in Moho depths from seismic data and receiver function analysis are discussed. From the Caribbean plate, Moho depth increases from 20 to 25 km in the Venezuela Basin to about 35 km along the coast (except for the Falcón area where a thinning to less than 30 km is observed) and 40-45 km in Barinas - Apure and Guárico Basins, and Guayana Shield, respectively. Values of more than 50 km are observed in the Maturín Basin and in the southern part of the Mérida Andes.
Semple, A.G., Lenardic, A.Feedbacks between a non-Newtonian upper mantle, mantle viscosity structure and mantle dynamics.Geophysical Journal International, Vol. 224, 2, pp. 961-972.Mantlegeophysics - seismics

Abstract: Previous studies have shown that a low viscosity upper mantle can impact the wavelength of mantle flow and the balance of plate driving to resisting forces. Those studies assumed that mantle viscosity is independent of mantle flow. We explore the potential that mantle flow is not only influenced by viscosity but can also feedback and alter mantle viscosity structure owing to a non-Newtonian upper-mantle rheology. Our results indicate that the average viscosity of the upper mantle, and viscosity variations within it, are affected by the depth to which a non-Newtonian rheology holds. Changes in the wavelength of mantle flow, that occur when upper-mantle viscosity drops below a critical value, alter flow velocities which, in turn, alter mantle viscosity. Those changes also affect flow profiles in the mantle and the degree to which mantle flow drives the motion of a plate analogue above it. Enhanced upper-mantle flow, due to an increasing degree of non-Newtonian behaviour, decreases the ratio of upper- to lower-mantle viscosity. Whole layer mantle convection is maintained but upper- and lower-mantle flow take on different dynamic forms: fast and concentrated upper-mantle flow; slow and diffuse lower-mantle flow. Collectively, mantle viscosity, mantle flow wavelengths, upper- to lower-mantle velocities and the degree to which the mantle can drive plate motions become connected to one another through coupled feedback loops. Under this view of mantle dynamics, depth-variable mantle viscosity is an emergent flow feature that both affects and is affected by the configuration of mantle and plate flow.
Shaikh, A.M., Tappe, S., Bussweiler, Y., Patel, S.C., Ravi, S., Bolhar, R., Viljoen, F.Clinopyroxene and garnet mantle cargo in kimberlites as probes of Dharwar craton architecture and geotherms, with implications for post -1.1 Ga lithosphere thinning events beneath southern India.Journal of Petrology, Vol. 61, 9, egaa087 23p. PdfIndiadeposit - Wajrakarur

Abstract: The Wajrakarur Kimberlite Field (WKF) on the Eastern Dharwar Craton in southern India hosts several occurrences of Mesoproterozoic kimberlites, lamproites and ultramafic lamprophyres, for which mantle-derived xenoliths are rare and only poorly preserved. The general paucity of mantle cargo has hampered the investigation of the nature and evolution of the continental lithospheric mantle (CLM) beneath cratonic southern India. We present a comprehensive study of the major and trace element compositions of clinopyroxene and garnet xenocrysts recovered from heavy mineral concentrates for three c.1•1?Ga old WKF kimberlite pipes (P7, P9, P10), with the goal to improve our understanding of the cratonic mantle architecture and its evolution beneath southern India. The pressure-temperature conditions recorded by peridotitic clinopyroxene xenocrysts, estimated using single-pyroxene thermobarometry, suggest a relatively moderate cratonic mantle geotherm of 40 mW/m2 at 1•1?Ga. Reconstruction of the vertical distribution of clinopyroxene and garnet xenocrysts, combined with some rare mantle xenoliths data, reveals a compositionally layered CLM structure. Two main lithological horizons are identified and denoted as layer A (~80-145?km depth) and layer B (~160-190?km depth). Layer A is dominated by depleted lherzolite with subordinate amounts of pyroxenite, whereas layer B comprises mainly refertilised and Ti-metasomatized peridotite. Harzburgite occurs as a minor lithology in both layers. Eclogite stringers occur within the lower portion of layer A and at the bottom of layer B near the lithosphere-asthenosphere boundary at 1•1?Ga. Refertilisation of layer B is marked by garnet compositions with enrichment in Ca, Ti, Fe, Zr and LREE, although Y is depleted compared to garnet in layer A. Garnet trace element systematics such as Zr/Hf and Ti/Eu indicate that both kimberlitic and carbonatitic melts have interacted with and compositionally overprinted layer B. Progressive changes in the REE systematics of garnet grains with depth record an upward percolation of a continuously evolving metasomatic agent. The intervening zone between layers A and B at ~145-160?km depth is characterized by a general paucity of garnet. This ‘garnet-paucity’ zone and an overlying type II clinopyroxene-bearing zone (~115-145?km) appear to be rich in hydrous mineral assemblages of the MARID- or PIC kind. The composite horizon between ~115-160?km depth may represent the product of intensive melt/rock interaction by which former garnet was largely reacted out and new metasomatic phases such as type II clinopyroxene and phlogopite plus amphibole were introduced. By analogy with better-studied cratons, this ‘metasomatic horizon’ may be a petrological manifestation of a former mid-lithospheric discontinuity at 1•1?Ga. Importantly, the depth interval of the present-day lithosphere-asthenosphere boundary beneath Peninsular India as detected in seismic surveys coincides with this heavily overprinted metasomatic horizon, which suggests that post-1•1?Ga delamination of cratonic mantle lithosphere progressed all the way to mid-lithospheric depth. This finding implies that strongly overprinted metasomatic layers, such as the ‘garnet-paucity’ zone beneath the Dharwar craton, present structural zones of weakness that aid lithosphere detachment and foundering in response to plate tectonic stresses.
Sharma, J., Kumar, M.R., Roy, K.S., Pal, S.K., Roy, P.N.S.Low velocity zones and negative radial anisotropy beneath the plume perturbed northwestern Deccan volcanic province.Journal of Geophysical Research: Solid Earth, 126, e2020JB02 0295. https://doi.org/ 10.1029/ 2020JB020295Indiageophysics - seismic

Abstract: The Deccan volcanic province (DVP) witnessed a massive outpouring of flood basalts of ~2 million km3 volume, at ~65 Ma, in less than a Myr. The volcanic eruption is concomitant with crustal extension, lithospheric thinning and magma influx beneath the major rift systems namely Cambay, Narmada, and Kutch. In this study, we investigate the anisotropic and isotropic variations within the crust and upper mantle beneath the northwestern DVP by estimating the shear wave velocity (VSV, VSH, and VSoigt) and radial anisotropy (?oigt) models using the Surface Wave Tomography technique. A joint inversion of the regionalized Rayleigh and Love wave group velocities is performed, using the genetic algorithm approach. Our results reveal different intracrustal layers, lid, and a low-velocity zone (LVZ). This LVZ comprises of a uniform asthenospheric low-velocity layer (LVL) of average VSV 4.44 km/s and VSH 4.47 km/s, and another LVL below, of average VSV 4.45 km/s and VSH 4.41 km/s. Furthermore, the LVZ represents a negative anomaly with reference to different global models (AK135, STW105, PREM, and S2.9EA). A negative ?oigt is observed in the LVZ, indicating dominance of vertical flow. This could be related to presence of partials melts, volatile materials and/or a thermal anomaly. We also identified the Moho (~34-40 km) and lithosphere-asthenosphere boundary (~84-123 km). The low VS values, negative ?oigt and a thin lithosphere (~84 km) in the vicinity of Gulf of Cambay affirm the presence of a plume head beneath it, in concurrence with the hypothesis of Indian Plate-Reunion plume interaction.
Shatskiy, A., Arefiev, A.V., Podborodnikov, I.V., Litasov, K.D.Effect of water on carbonate-silicate liquid immiscibility in the system KAlSi3O8-CaMgSiO6-NaAlSiO6-CaMg(CO3)2 at 6 Pa: implications for diamond forming melts.American Mineralogist, Vol. 106, pp. 165-173. pdfMantlemelting

Abstract: To evaluate the effect of Na on the carbonate-silicate liquid immiscibility in the diamond stability field, we performed experiments along some specific joins of the system KAlSi3O8-CaMg(CO3)2 ± NaAlSi2O6 ± Na2CO3 at 6 GPa. Melting in all studied joins begins at 1000-1050 °C. The melting in the Kfs + Dol system is controlled by the reaction 6 KAlSi3O8 (K-feldspar) + 6 CaMg(CO3)2 (dolomite) = 2 (Can,Mg1-n)3Al2Si3O12 (garnet) + Al2SiO5 (kyanite) + 11 SiO2 (coesite) + 3 K2(Ca1-n,Mgn)2(CO3)3 (carbonatitic melt) + 3 CO2 (fluid), where n ~ 0.3-0.4. A temperature increasing to 1300 °C yields an appearance of the silicic immiscible melt in addition to carbonatitic melt via the reaction K2CO3 (carbonatitic melt) + Al2SiO5 (kyanite) + 5 SiO2 (coesite) = 2 KAlSi3O8 (silicic melt) + CO2 (fluid or solute in melts). The silicic melt composition is close to KAlSi3O8 with dissolved CaMg(CO3)2 and molecular CO2. An addition of NaAlSi2O6 or Na2CO3 to the system results in partial decomposition of K-feldspar and formation of K-bearing carbonates, (K, Na)2Mg(CO3)2 and (K, Na)2Ca3(CO3)4. Their melting produces carbonatite melt with the approximate composition of 4(K, Na)2CO3•6Ca0.6Mg0.4CO3 and magnesite. Besides, the presence of NaAlSi2O6 in the studied system shifts the lower-temperature limit of immiscibility to 1500°?, while the presence of Na2CO3 eliminates the appearance of silicic melt by the following reaction: 2 KAlSi3O8 (in the silicic melt) + Na2CO3 = 2 NaAlSi2O6 (in clinopyroxene) + K2CO3 (in the carbonatitic melt) + SiO2 (coesite). Thus, an increase of the Na2O content in the system Na2O-K2O-CaO-MgO-Al2O3-SiO2-CO2 consumes Al2O3 and SiO2 from silicic melt to form clinopyroxene. We found that grossular-pyrope and diopside-jadeite solid solutions can coexist with CO2 fluid at 900-1500 °C and 6 GPa. Thus, CO2 fluid is stable in the eclogitic suite in the diamond stability field under temperature conditions of the continental lithosphere and subducting slabs. Variations in the Na2O content observed in carbonatitic melts trapped by natural in diamonds exceed those derived by the pelite melting. The present experiments show that an addition of NaAlSi2O6 to the Kfs + Dol system does not cause an increase of the Na2O content in the carbonatitic melt, whereas the addition of Na2CO3 at Na2O/Al2O3 > 1 yields the formation of the melts with the Na2O contents covering the entire range of natural compositions. Thus, only the presence of additional salt components can explain the elevated Na2O content in the melts trapped in lithospheric diamonds. In addition to carbonates, sodium can be hosted by chlorides, sulfates, etc.
Shatskiy, A., Podborodnikov, I.V., Arefiev, A.V., Bekhtenova, A., Vinogradova, Y.G., Stepanov, K.M., Litasov, K.D.Pyroxene-carbonate reactions in the CaMgSi206+-NaAlSi206+MgC03+-Na2C03+-K2C03 system at 3-6 Gpa: implications for partial melting of carbonated peridotite.Contributions to Mineralogy and Petrology, Vol. 176, 34 21p. PdfMantlecarbonatites

Abstract: The reactions between pyroxenes and carbonates have been studied in the CaMgSi2O6 + MgCO3 (Di + 2Mgs), CaMgSi2O6 + NaAlSi2O6 + 2MgCO3 (Di + Jd + 2Mgs), CaMgSi2O6 + Na2Mg(CO3)2 (Di + Eit), and CaMgSi2O6 + K2Mg(CO3)2 (Di + K2Mg) systems at pressures of 3.0 and 4.5 GPa in the temperature range 850-1300 °C and compared with those established previously at 6.0 GPa. The Di + 2Mgs solidus locates at 1220 °C / 3 GPa and 1400 °C / 6 GPa. Near-solidus melt is carbonatitic with SiO2 < 4 wt% and Ca# 56. The Di + Jd + 2Mgs solidus locates near 1050 °C at 3 GPa, rises to 1200 °C at 4.5 GPa, and 1350 °C at 6 GPa. The solidus is controlled by the reaction: 4NaAlSi2O6.2CaMgSi2O6 (clinopyroxene) + 12MgCO3 (magnesite) = 2MgAl2SiO6.5Mg2Si2O6 (clinopyroxene) + 2[Na2CO3.CaCO3.MgCO3] (liquid) + 6CO2. As pressure increases, the composition of solidus melt evolves from 26Na2CO3·74Ca0.58Mg0.42CO3 at 3 GPa to 10Na2CO3·90Ca0.50Mg0.50CO3 at 6 GPa. Melting in the Di + Eit and Di + K2Mg systems is controlled by the reactions: CaMgSi2O6 (clinopyroxene) + 2(Na or K)2 Mg(CO3)2 (eitelite) = Mg2Si2O6 (orthopyroxene) + 2[(Na or K)2CO3·Ca0.5Mg0.5CO3] (liquid). The Di + Eit solidus locates at 925 °C / 3 GPa and 1100 °C / 6 GPa, whereas the Di + K2Mg solidus is located at 50 °C lower. The resulting melts have alkali-rich carbonate compositions, (Na or K)2CO3·Ca0.4Mg0.6CO3. The obtained results suggest that most carbonates belong to the ultramafic suite would survive during subduction into the deep mantle and experience partial melting involving alkaline carbonates, eitelite or K2Mg(CO3)2, under geothermal conditions of the subcontinental lithospheric mantle (35-40 mW/m2). On the other hand, the jadeite component in clinopyroxene would be an important fluxing agent responsible for the partial melting of carbonated rocks under the rift margin geotherm (60 mW/m2) at a depth of about 100 km, yielding the formation of Na-carbonatite melt.
Shearman, R.What is the story behind Aether and how did the business start? Gems & Gemology , Vol. 29, 4, pp. 22-24. pdfEurope, Switzerlandsynthetics
Shribak, M., Cesare, B.Polychromatic polarization and the good old microscope: new avenues for the microstructural imaging of geological materials.( not specific to diamonds)Researchgate conference paper, 3p. PdfGlobalmicroscope

Abstract: The polarizing microscope, fundamental tool for any first characterization of geological materials, suffers from one major limitation, namely the poor ability to image microstructures where minerals have a retardance <400 nm and display interference colors in the gray scale. This problem, so far considered as intrinsic and unsolvable, has prevented detailed optical observation of many low-birefringence (e.g., quartz, feldspars, leucite) or quasi-isotropic (e.g., garnet) rock-forming minerals. For the microstructural analysis of these phases, alternative microscopic techniques, mostly electronic, have been developed and are routinely used. Polychromatic polarization microscopy (PPM, [1]) is a new optical technique that overcomes the above limitations and allows inspection of materials with retardation from 1 to 400 nm. This is achieved by means of a full spectrum color palette where the hue depends on orientation of the slow axis and the saturation depends on the retardance amount. We have applied PPM to regular, glass-covered 30 µm rock thin sections, with particular interest for the subtle birefringence of garnet, due both non-cubic growth[2] or to strain induced by external stresses or by mineral inclusions. PPM produces striking, colorful images that highlight different types of microstructures in very low retardance phases, which are virtually undetectable by conventional polarizing microscopy. The calibrated hue scale provides straightforward measurement of the orientation of optical axes in the thin section (Fig. 1). PPM will open new avenues for microstructural analysis of geological materials. We highlight two of them. On one hand the direct detection and imaging of microstructures will provide a fast and cheap alternative (or complement) to time-consuming and more expensive SEM-based analyses such as, e.g., EBSD. On the other hand this powerful imaging method will provide-again in a very fast way-a much better texturally constrained basis for the location of targets for cutting-edge applications such as, e.g., FIB-TEM or Atom Probe. Figure 1-The same crystal of tetragonal garnet studied in [2] viewed under crossed-polarizers (left), with the ? plate (center), and under PPM (right). The thin section is glass-covered and has a regular 30-µm thickness.
Shubin, I.I., Filina, M., Kogarko, L.Evolution of pyroxenes of the Lovozero rare metal deposit ( Lower zone).Geochemistry International, Vol. 59, pp. 92-98. pdfRussiaREE

Abstract: This paper reports the results of the first study of pyroxenes from the deepest zones of the Lovozero deposit. The geochemical and mineralogical study of these rocks is of great scientific interest, as they are the least differentiated rocks and provide insight into the composition of a parental magma. According to microprobe analysis, clinopyroxenes evolve from early diopside-hedenbergite-augite to later alkaline aegirine-augite species. Upsection, the contents of Na, Fe3+ and Ti increase, while Mg, Ca, Fe2+, and Zr decrease. Thus, isomorphic substitution in pyroxenes of the lower zone follows the scheme (Ca, Mg, Fe2+, Zr) ? (Na, Fe3+, Ti).
Shumilova, T.Diamond fossils as an important new key for astrobiology.Researchgate conference paper, 2p. PdfRussiaimpact craters Kara, Popigai

Abstract: Astrobiology is one of the actively studied fields aimed to answer the question about the Earth life origin. The detail studies of the organic matter could give a key for understanding about possible conditions for preservation of the biological material at the extreme conditions of the giant impact events and meteorite fallings. In the context of the astrobiological problem the recent discovery of diamond fossils is very informative and impressive [1, 2]. Here we describe in short the features of the impact-preserved organic relicts in the diamond state having relict fragments of cellulose and lignin, pointing to possibility to save organics even under the conditions of diamond formation. Impact Diamonds: Almost 50 years have passed since the discovery of impact diamonds. Currently, several varieties of impact diamonds are known in natural geological objects, determined by the type of carbon precursor, that define their formation mechanisms and structural features. Actually, aftergraphite, after-coal and after-organic diamonds are known [1-5]. The latter usually present in the form of diamond fossils after plant fragments. After-Graphitic Impact Diamonds: The aftergraphitic diamonds were discovered in the 70s of the XX century in the largest Popigai astrobleme with a diameter of about 100 km, bearing giant reserves of valuable technical diamond raw materials [3, 4]. This type of impact diamonds is formed by solid-state transformation of the graphite precursor structure to diamond with a diffusion-free mechanism forming micropolycrystalline aggregates with submicrometersized crystals [1]. This variety is characterized by polyphase aggregates with possible substantial amount of hexagonal packaging defects (named “lonsdaleite”) within the cubic diamond structure [6]. It may also include an admixture of relict graphite, amorphous and onion-like carbon [7, 8]. Currently, apographic diamonds have been discovered in several deposits, for example diamond-rich Popigai and Puchezh-Katunki in Russia, Ries (Germany), Sudbury (Canada). After-Coal Impact Diamonds: After-coal impact diamonds were discovered a bit later, they were found in the giant Kara astrobleme in 80s of the XX century [3, 4]. This diamond type was formed by short-distance diffusion mechanism from coalificated carboniferous particles from the host sedimentary rocks, described in detail in [5]. The diamonds have crystallites size about 20-50 nm, differ from the after-graphitic variety by presence of ideal octahedral crystallite shapes and dislocation-free (lonsdaleite-free) structure [2]. By present the after-coal diamonds are known only at the Kara astrobleme and near-set Ust`-Kara impactites. After-Organic Diamonds (Diamond Fossils): The diamond fossils have been just discovered. The first find has been found out within melt fragment within suevitic breccia at the Kara astrobleme (Fig. 1). The diamonds are presented with well preserved relict cell micromorphology and have very specific structure, composition and spectroscopic features studied and described in detail in [1].
Simbanegavi, G.The mining mindset…. BlueRock story.Gems & Gemology , Vol. 29, 4, pp. 19-21. pdfAfrica, South Africamining
Singh, A.P., Kumar, N., Nageswara Rao, B., Tiwari, V.M.Geopotential evidence of missing lithospheric root beneath the eastern Indian shield: an integrated approach.Precambrian Research, Vol. 356, 106116Indiageophysics - seismic

Abstract: The eastern Indian shield consists of Archaean Singhbhum Craton and Proterozoic Chhotanagpur Gneissic Complex sandwiching the Singhbhum Mobile Belt. Since the cratonization of the Singhbhum Craton in Archaean, the growth of the eastern Indian shield took place in time and space through tectono-magmatic processes. The stability of cold and thick lithosphere is fundamental to long-term survival of cratons, whereas the geophysical studies have detected the lithosphere-asthenosphere boundary (LAB) under the eastern Indian shield at depths too shallow to be called stable. We analysed the terrestrial Bouguer gravity anomaly, and satellite-based free-air anomaly, geoid undulation, and elevation data to ascertain the 2D lithospheric density structure across the region. Our density model illustrates that the density inhomogeneity exists in the crust across the three tectonic domains of the eastern Indian shield. The derived crustal model shows an upper and lower crustal density variation from 2740 to 2770 kg/m3, and from 2930 to 2940 kg/m3, respectively, and a reasonably smooth Moho at 37-41 km depth. Towards the north, the Moho undulates from 40 to 43 km under the foreland Ganga basin, whereas in the south, it varies from 38 to 30 km under the Eastern Ghats Mobile Belt and lastly moves to ~20 km in the Bay of Bengal. In the southern part of the Singhbhum Craton, an undissipated lithospheric mantle root is found at a depth of ~150 km. Otherwise, the LAB shallows to ~132 km in the northern Singhbhum Craton and Singhbhum Mobile Belt and then thickens to about 135-140 km depth beneath the Chhotanagpur Gneissic Complex. The foreland Ganga basin toward the extreme north is characterized by a more in-depth LAB lying at a depth of over 200 km. The LAB, in the Bay of Bengal, is at a depth of 112-125 km, except for the Kolkata coast (135 km). Moderate crustal density difference in various crustal domains, as well as an almost smooth crust-mantle boundary at 37-40 km depth, suggests the effect of substantial mafic-ultramafic crustal intrusion and together with the thin (135-140 km) lithosphere reinforces the evidence of thermo-chemical processes that controlled the lithospheric modification in the eastern Indian shield.
Sizyakov, V.M., Kawalla, R., Brichkin, V.N.Geochemical aspects of the mining and processing of the large tonne mineral resources of the hibinian alkaline massif.Geochemistry, Vol. 80, doi.org/10.1016 /j.chemer.2019 .04.002 5p. PdfRussiadeposit - Khibiny

Abstract: This article presents an analysis of the influences of nature and production factors relating to the chemical-mineralogical composition of products that formed at the stages of mining and processing apatite-nepheline ores in the Khibiny Mountain Massif. It is shown that all main production processes are connected to the formation of dump waste products that are subject to further changes under the influence of exogenous factors, which include conditions of outdoor storage in dumps and sludge accumulators. According to the dead tails (stale tails) of apatite production, the characteristic changes in the chemical-mineralogical composition and grain-size distribution are determined and have a significant effect on the indicators of their mineral processing. The experimental study of dead tails includes processing a set of technological operations, and their flowsheets are also determined. These flowsheets provide a nepheline concentrate of the required composition with indicators no worse than when processing the tailings of the current composition. It is shown that the existing flowsheets for apatite or nepheline concentrate processing lead to the accumulation of significant amounts of mulls associated with the separation of less valuable components of raw materials into the dump waste products, including calcium and silica. The experimental work also demonstrates the conversion process of gypsum wastes produced during the production of phosphoric acid and shows the importance of additional hydrochemical treatment of belite mull to achieve an economically justified ratio of the main and by-products in the processing of aluminosilicate raw materials.
Skublov, S.G., Tolstov, A.V., Baranov, L.N., Melnik, A.E., Levashova, E.V.First data on the geochemistry and U-Pb age of zircons from the kamaphorites of the Tomtor alkaline-ultrabasic massif, Arctic Yakutia.Geochemistry, Vol. 80, doi.org/10.1016 /j.chemer. 2019.04.001 11p. PdfRussiadeposit - Tomtor

Abstract: Zircon from Tomtor syenites and kamaphorites was dated following the U-Pb method (SHRIMP-II), and the distribution of trace and rare-earth elements (REE) was studied at the same zircon point using an ion microprobe. The main zircon population from syenites was dated at 402?±?7 Ma, while the age range of single zircon grains was 700-660 M?. Different-aged zircon groups from syenites exhibited the characteristics of magmatic zircon, but their concentrations of REE and other trace elements differed markedly. The REE distribution in 700-660-M? zircon is consistent with that of the typical zircon from syenites (Belousova et al., 2002), while the heavy rare-earth elements (HREE), P, Ti, and Y concentrations of ca. 400-Ma zircon differ from those of older zircon. This is the first isotope-geochemical study of zircon from kamaphorites, and the U-Pb age of ca. 400 M? is within the error limits with of the main zircon population from syenites. The considerable enrichment of REE, C?, Ti, Sr, Y, Nb, and Ba in zircon from kamaphorites may be partly due to the presence of burbankite microinclusions. The trace-element distribution pattern of zircon from kamaphorites is very similar to the geochemical characteristics of zircon from Tiksheozero carbonatites (Tichomirowa et al., 2013).The new age dates for Tomtor syenites and kamaphorites, consistent with 700-660 M? and ca. 400 M? events, support the zircon (Vladykin et al., 2014) and pyrochlore (Antonov et al., 2017) age dates determined following the U-Pb method and those of biotite obtained following the 40Ar-39Ar method (Vladykin et al., 2014).
Skuzovatov, S.Yu., Shatsky, V.S., Ragozin, A.L., Wang, K-L.Ubiquitous post-peak zircon in an eclogite from the Kumdy-Kol, Kokchetav UHP-HP massif ( Kazakhstan): significance of exhumation-related zircon growth and modification in continental-subduction settings.Island Arc, doi:10.1111/ iar.12385 29p. PdfRussia, Kazakhstandeposit - Kumby-Kol

Abstract: U-Pb geochronological, trace-element and Lu-Hf isotopic studies have been made on zircons from ultrahigh-pressure (UHP) mafic eclogite from the Kumdy-Kol area, one of the diamond-facies domains of the Kokchetav Massif (northern Kazakhstan). The peak eclogitic assemblage equilibrated at >?900?°C, whereas the bulk sample composition displays light rare-earth element (LREE) and Th depletion evident of partial melting. Zircons from the eclogite are represented by exclusively newly formed metamorphic grains and have U-Pb age spread over 533-459?Ma, thus ranging from the time of peak subduction burial to that of the late post-orogenic collapse. The major zircon group with concordant age estimates have a concordia age of 508.1?±4.4?Ma, which corresponds to exhumation of the eclogite-bearing UHP crustal slice to granulite- or amphibolite-facies depths. This may indicate potentially incoherent exhumation of different crustal blocks within a single Kumdy-Kol UHP domain. Model Hf isotopic characteristics of zircons (eHf(t) +1.5 to +7.8, Neoproterozoic model Hf ages of 1.02-0.79?Ga) closely resemble the whole-rock values of the Kumdy-Kol eclogites and likely reflect in situ derivation of HFSE source for newly formed grains. The ages coupled with geochemical systematics of zircons confirm that predominantly late zircon growth occurred in Th-LREE-depleted eclogitic assemblage, that experienced incipient melting and monazite dissolution in melt at granulite-facies depths, followed by amphibolite-facies rehydration during late-stage exhumation-related retrogression.
Slezak, P., Spandler, C., Border, A., Whittock, K.Geology and ore genesis of the carbonatite-associated Yangibana REE district, Gascoyne Province, Western Australia.Mineralium Deposita, 10.1007/s00126-020-01026-z 20p. PdfAustraliaREE

Abstract: The Yangibana rare earth element (REE) district consists of multiple mineral deposits/prospects hosted within the Mesoproterozoic Gifford Creek Carbonatite Complex (GCCC), Western Australia, which comprises a range of rock types including calcite carbonatite, dolomite carbonatite, ankerite-siderite carbonatite, magnetite-biotite dykes, silica-rich alkaline veins, fenite, glimmerites and what have historically been called “ironstones”. The dykes/sills were emplaced during a period of extension and/or transtension, likely utilising existing structures. The Yangibana REE deposits/prospects are located along many of these structures, particularly along the prominent Bald Hill Lineament. The primary ore mineral at Yangibana is monazite, which is contained within ankerite-siderite carbonatite, magnetite-biotite dykes and ironstone units. The ironstones comprise boxwork-textured Fe oxides/hydroxides, quartz, chalcedony and minor monazite and subordinate rhabdophane. Carbonate mineral-shaped cavities in ironstone, fenite and glimmerite alteration mantling the ironstone units, and ankerite-siderite carbonatite dykes altering to ironstone-like assemblages in drill core indicate that the ironstones are derived from ankerite-siderite carbonatite. This premise is further supported by similar bulk-rock Nd isotope composition of ironstone and other alkaline igneous rocks of the GCCC. Mass balance evaluation shows that the ironstones can be derived from the ankerite-siderite carbonatites via significant mass removal, which has resulted in passive REE concentration by ~?2 to ~?10 times. This mass removal and ore tenor upgrade is attributed to extensive carbonate breakdown and weathering of ankerite-siderite carbonatite by near-surface meteoric water. Monazite from the ironstones has strong positive and negative correlations between Pr and Nd, and Nd and La, respectively. These relationships are reflected in the bulk-rock drill assays, which display substantial variation in the La/Nd throughout the GCCC. The changes in La/Nd are attributed to variations in primary magmatic composition, shifts in the magmatic-hydrothermal systems related to CO2 versus water-dominated fluid phases, and changes in temperature.
Smart, K.A., Tappe, S., Woodland, A.B., Greyling, D.R., Harris, C., Gussone, N.Constraints on Archean crust recycling and the origin of mantle redox variability from delta 44/40 Ca - delta 18O - fO2 signatures of cratonic eclogites.Earth and Planetary Science Letters, doi.org/10.1016/ j.epsl.2020. 116720 19p. PdfAfrica, South Africadeposit - Bellsbank

Abstract: The nature of the deep calcium geochemical cycle through time is unresolved, in part due to the dearth of information about the calcium isotope composition of Archean recycled oceanic crust. Remnants of such ancient oceanic crust are preserved in the form of cratonic mantle eclogites, brought to surface as xenoliths in kimberlite magma eruptions. The d 44 / 40Ca of fresh mantle-derived eclogite xenoliths (i.e., garnet and omphacite mineral separates) from the Bellsbank kimberlite on the Kaapvaal craton in South Africa are presented here in combination with their trace element compositions, garnet Fe3+ contents and d18O values. The studied Bellsbank eclogite xenoliths have geochemical compositions that indicate oceanic crustal protoliths, with bulk Al2O3 from 15 to 27 wt.%, Eu anomalies from 0.8 to 2.6 and, significantly, garnet d18O values from +2.7 to +6.2‰. Garnet Fe3+/SFe contents yield logfO2(?FMQ) values between -4.0 and -1.2 for a depth range of 110-180 km, recording strong redox heterogeneity of the eclogite component within the Archean Kaapvaal mantle lithosphere. Reconstructed bulk eclogite MgO contents correlate negatively with fO2, suggesting that the redox compositions are related to magmatic differentiation during oceanic crust formation, excluding secondary metasomatic overprints. These data may thus emphasize that Archean basaltic oceanic crust had a similarly variable redox composition to modern MORB-type crust. Reconstructed bulk d 44 / 40Ca values for the Bellsbank eclogites range from +0.28 to +1.56‰. Although some of the xenoliths have d 44 / 40Ca values that overlap with the average mantle composition and modern MORB (+0.94 ± 0.1 and +0.83 ± 0.05‰), half of our dataset shows excursions to more extreme Ca isotopic compositions. Both higher and lower d 44 / 40Ca relative to mantle compositions are recorded by the eclogites, with a general negative correlation with d18O suggestive of seawater-alteration of oceanic crust. The combined low d 44 / 40Ca (+0.28‰) and d18O (+3.4‰) measured for one eclogite xenolith may record a subtle imprint by carbonate-rich mantle melts, which are known to contain isotopically light calcium contributed by recycled sediments. In contrast, the high d 44 / 40Ca of up to +1.56‰ for some eclogite xenoliths, coupled with strong LREE depletion, can be explained by calcium isotope fractionation during partial melting. The protracted history of recycled oceanic crust as probed by cratonic mantle eclogites is recorded by their highly variable d 44 / 40Ca-d18O-fO2 signatures. Whereas some of this heterogeneity can be linked to processes that operated on the Archean ocean floor such as seawater-alteration of basaltic crust, other sources of compositional variability are introduced by loss and addition of melts during subduction recycling and mantle residence. The observed d 44 / 40Ca complexity of ancient recycled oceanic crust components at the scale of a single mantle-derived eclogite xenolith suite implies that mantle plume sourced intraplate magmas should reveal similarly strong calcium isotope variations contributed by apparently essential recycled crust components - as observed in the global oceanic island basalt record.
Smith, E.A look at kimberlites: the volcanoes that carry diamonds.gia.org and knowledge session utube, 44280Globalkimberlite genesis

Abstract: Natural diamonds crystallize at great depths, far deeper than we can dig or drill into the Earth. So how is it that diamonds can be found among us? The answer lies in rare and unusual volcanoes called kimberlites. These deeply-seated volcanic eruptions can sometimes pick up diamonds, along with other minerals and rock fragments, and blast them to the top. Think of kimberlites as elevators that diamonds use to ride up to Earth’s surface! Tune in as GIA Research Scientist Dr. Evan Smith digs deeper into these super-charged volcanoes and uncovers the role they play, not just in transporting gem diamonds, but in revealing the geological workings of the Earth.
Smith, E.Deep diamonds contain evidence of deep Earth recycling processes.Phys.org, https://phys-org.cdn.amp project.org/c /s/phys.org/news /2021-03-deep-diamonds- evidence-deep-earth- recycling.ampMantlesubduction
Smith, E., Ni, P., Shirey, S.B., Richardson, S.H., Wang, W., Shahar, A.Heavy iron in large gem diamonds traces deep subduction of serpentinized ocean floor.Science Vol. 74, https://advances. sciencemag.org /content/7/14/ eabe9773 9p.Mantlesubduction

Abstract: Subducting tectonic plates carry water and other surficial components into Earth’s interior. Previous studies suggest that serpentinized peridotite is a key part of deep recycling, but this geochemical pathway has not been directly traced. Here, we report Fe-Ni-rich metallic inclusions in sublithospheric diamonds from a depth of 360 to 750 km with isotopically heavy iron (d56Fe = 0.79 to 0.90‰) and unradiogenic osmium (187Os/188Os = 0.111). These iron values lie outside the range of known mantle compositions or expected reaction products at depth. This signature represents subducted iron from magnetite and/or Fe-Ni alloys precipitated during serpentinization of oceanic peridotite, a lithology known to carry unradiogenic osmium inherited from prior convection and melt depletion. These diamond-hosted inclusions trace serpentinite subduction into the mantle transition zone. We propose that iron-rich phases from serpentinite contribute a labile heavy iron component to the heterogeneous convecting mantle eventually sampled by oceanic basalts.
Smith, E.M., Nestola, F., Paqualetto, L., Zorzi, F., Secco, L., Wang, W.The new mineral crowningshieldite: a high temperature NiS polymorph found in a type IIa diamond from the Letseng mine, Lesotho.American Mineralogist, Vol. 106, pp. 301-308. pdfAfrica, Lesothodeposit - Letseng

Abstract: Crowningshieldite is the natural analog of the synthetic compound a-NiS. It has a NiAs-type structure and is the high-temperature polymorph relative to millerite (ß-NiS), with an inversion temperature of 379 °C. Crowningshieldite is hexagonal, space group P63/mmc, with a = 3.44(1) Å, c = 5.36(1) Å, V = 55.0(2) Å3, and Z = 2. It has an empirical formula (Ni0.90Fe0.10)S and dcalc = 5.47(1) g/cm3. The five strongest lines in the powder X-ray diffraction data are [dmeas in angstroms (I) (hkl)]: 1.992 (100) (102), 1.718 (55) (110), 2.978 (53) (100), 2.608 (35) (101), and 1.304 (17) (202). Crowningshieldite was found as part of a multiphase inclusion in a gem-quality, colorless, type IIa (containing less than ~5 ppm N) diamond from the Letseng mine, Lesotho. The inclusion contains crowningshieldite along with magnetite-magnesioferrite, hematite, and graphite. A fracture was observed that extended from the inclusion to the diamond exterior, meaning that fluids, possibly kimberlite-related, could have penetrated into this fracture and altered the inclusion. Originally, the inclusion might have been a more reduced, metallic Fe-Ni-C-S mixture made up of cohenite, Fe-Ni alloy, and pyrrhotite, akin to the other fracture-free, pristine inclusions within the same diamond. Such metallic Fe-Ni-C-S primary inclusions are a notable recurring feature of similar type IIa diamonds from Letseng and elsewhere that have been shown to originate from the sublithospheric mantle. The discovery of crowningshieldite confirms that the a-NiS polymorph occurs in nature. In this case, the reason for its preservation is unclear, but the relatively iron-rich composition [Fe/(Fe+Ni) = 0.1] or the confining pressure of the diamond host are potential factors impeding its transformation to millerite. The new mineral name honors G. Robert Crowningshield (1919-2006) (IMA2018-072).
SmithsonianEarth's oldest minerals date onset of plate tectonics to 3.6 billion years ago: ancient zircons from the Jack Hills of western Australia hone date of an event that was crucial to making the planet hospitable to life. *** not specific to diamondsScience Daily, www.sciencedaily.com /releases/2021/05/ 210514134159.htmMantletectonics

Abstract: Scientists provide new evidence that modern plate tectonics, a defining feature of Earth and its unique ability to support life, emerged roughly 3.6 billion years ago. The study uses zircons, the oldest minerals ever found on Earth, to peer back into the planet's ancient past.
Sokol, A.G., Kruk, A.N.Role of CO2 in the evolution of kimberlite magma: experimental constraints at 5.5GPa and 1200-1450 C.Lithos, in press available, 13p. PdfGlobalmagmatism

Abstract: According to the existing models of kimberlite origin, free exsolution CO2 may be an important agent in the evolution of primary kimberlite magma and initiation of crack propagation. We study the reaction of garnet lherzolite with carbonatitic melt rich in molecular CO2 and H2O in experiments at 5.5 GPa and 1200-1450 °C. The experimental results show that carbonation of olivine with formation of orthopyroxene and magnesite can buffer the contents of molecular CO2 in the melt, which impedes immediate separation of CO2 fluid from melt equilibrated with the peridotite source. The solubility of molecular CO2 in the melt decreases from 20 -25 wt% at 4.5-6.8 wt% SiO2 typical of carbonatite to below 7-12 wt% in more silicic melts with 26-32 wt% SiO2. Interaction of garnet lherzolite with carbonatitic melt (at a weight proportion of 2:1) in the presence of 2-3 wt% H2O and 17-24 wt% of total CO2 at 1200-1450 °C yields low-SiO2 (<10 wt%) alkali-carbonated melts, which shows multiphase saturation with magnesite-bearing garnet harzburgite. Thus, carbonatitic melts rich in volatiles can originate in a harzburgite source at moderate temperatures common to continental lithospheric mantle (CLM). Excessive volatiles may be present in carbonatitic melts not equilibrated with the peridotitic source due to the formation of metasomatic reaction zones. Having separated from the source, carbonatitic magma enriched in molecular CO2 and H2O can rapidly become more silicic (>25 wt% SiO2) by dissolution and carbonation of entrapped peridotite. Furthermore, interaction of garnet lherzolite with carbonatitic melt rich in K, CO2, and H2O at 1350 °C produces immiscible carbonate-silicate and K-rich silicate melts. Quenched silicate melt develops globules of foam-like vesicular glass. Differentiation of immiscible melts early during their ascent may equalize the compositions of kimberlite magmas generated in different CLM sources. The fluid phase can release explosively from ascending magma at lower pressures as a result of SiO2 increase which reduces the solubility of CO2 and due to the decarbonation reaction of magnesite and orthopyroxene.
Sonin, V.M., Zhimulev, E.I., Chepurov, A.A., Lindenblot, E.S., Loginova, A.M., Shcheglov, D.V., Pomazanskii, B.S., Afanasiev, V.P., Chepurov, A.I.Dissolution of natural octahedral diamonds in an Fe-S melt at high pressure.Geology of Ore Deposits, Vol. 62, 6, pp. 497-507. pdfRussia, Yakutiadeposit Yubileinaya

Abstract: An experimental study was carried out on the dissolution of natural octahedral diamonds from the Internatsionalnaya and Yubileinaya kimberlite pipes (Yakutia) in an Fe-S melt at 4 GPa and 1450-1500°C with different sulfur contents (10-25 wt %). It was found that with an increase in sulfur content in the iron melt, the degree of diamond dissolution sharply decreases. The stationary (final) shape of diamond crystal dissolution under the achieved conditions corresponds to an octahedroid with trigonal etching layers, which is confirmed by photogoniometry. Diamonds with similar morphology are common in kimberlite pipes, especially in mantle xenoliths from kimberlites. It was concluded that diamonds with this shape did not undergo natural dissolution in a kimberlite magma, but, similar to flat-faced octahedra, were probably isolated from it in xenoliths. Therefore, the higher the content of octahedroid-shaped diamonds with trigonal layers in a deposit, the smaller the direct influence of an aggressive kimberlite magma on the diamond content.
South African Diamond Producers OrganizationStrategy for short and medium term.SAPP, 9p. Pdf executive summaryAfrica, South Africaalluvials, legal
Spengler, D., Alifirova, T.A.Formation of Siberian cratonic mantle websterites from high - Mg magmas.Lithos, in press available 13p. PdfRussiadeposit - Mir, Obnazhennaya, Udachnaya

Abstract: Garnet-(olivine) websterite xenoliths from the lithospheric mantle of the central and northeastern parts of the Siberian Craton contain exsolution microstructures after Si- and Ti-rich precursor garnets. We petrographically, geochemically, and thermobarometrically investigated 13 such xenoliths from the Mir, Obnazhennaya, and Udachnaya kimberlite pipes. All samples contain garnet grains with needle- to lamellae-shaped precipitates (up to 3.0?vol%), including Ti-oxide and/or pyroxene. Orthopyroxene and clinopyroxene grains host oriented lamellae of complementary Ca-rich and Ca-poor pyroxene, respectively, in addition to lamellae of garnet and Ti- and/or Cr-oxides. The common exsolution lamellae assemblages in garnet and pyroxene imply that exsolution occurred during cooling from high-temperature precursors. Exsolution is unlikely to have resulted from variations in pressure, given experimental and thermodynamic constraints. Host mineral partitioning of transition metal and lanthanide elements with different diffusivities record temperatures that range between those of local geotherms and a dry pyroxenite solidus. Inferred magmatic minimum temperatures of 1500-1700?°C satisfy the physical conditions predicted from experimental studies of the solubility of excess Si and Ti in garnet. Granular inclusions of all major minerals within each other imply an overlapping crystallisation history. The reconstructed compositions of the websterite whole-rocks have high MgO contents (15.7-35.7?wt%). A plot of MgO/SiO2 versus SiO2 forms an array, apart from the compositions of natural websterites that formed by interaction of peridotite with basaltic or siliceous melts. The array overlaps the compositional range of komatiite flows from Commondale and Barberton, South Africa, including spinifex, massive, and cumulate subtypes of komatiites. Other major and minor element abundances and ratios of the Siberian websterite suite resemble those of South African Al-enriched komatiites and are distinct from melt-rock reaction websterites. Therefore, the mineral microstructures and geochemistry of the Siberian websterites are suggestive of the former presence of a thermal anomaly. We propose that mantle plume activity or a similar form of lower-mantle ascent played a major role in stabilising cratonic nuclei before amalgamation of the present-day Siberian Craton.
Stagno, V.Carbon, carbides, carbonates and carbonatitic melts in the Earth's interiors. *** NOTE DATEresearchgate, doi:10.31223/ osf.io/uhSc8 40p. PdfMantlecarbonatite

Abstract: Over recent decades, many experimental studies have focused on the effect of CO2 on phase equilibria and melting behaviour of synthetic eclogites and peridotites as a function of pressure and temperature. These studies have been of fundamental importance to understanding the origin of carbonated magmas varying in composition from carbonatitic to kimberlitic. The occurrence of diamonds in natural rocks is further evidence of the presence of (reduced) carbon in the Earth's interior. The oxygenation of the Earth's interior (i.e. its redox state) through time has strongly influenced the speciation of carbon from the mantle to mantle-derived magmas and, in turn, to the volcanic gases released to the atmosphere. This paper explains how the knowledge of the oxygen fugacity recorded by mantle rocks and determined through the use of appropriate oxy-thermobarometers allows modelling of the speciation of carbon in the mantle, its mobilization in the asthenospheric mantle by redox partial melting, and its sequestration and storage during subduction by redox freezing processes. The effect of a gradual increase of the mantle fO2 on the mobilization of C is here discussed along with the main variables affecting its transport by subduction into the mantle.
Stanley, S.Subduction may recycle less water than thought.Eos, 102, doi.org/10.1029 /2021EO154530Mantlesubduction

Abstract: When one tectonic plate dives beneath another at a subduction zone, it recycles huge amounts of water and other chemicals into Earth’s mantle. The sinking plate carries seawater trapped in sediments and crust or chemically bound in minerals like serpentine. Later release of this water in the mantle contributes to key geological processes, such as earthquakes and the formation of volcano-feeding magma. By volume, the largest portion of a subducting plate is its bottom layer, which comprises upper mantle material. Estimates of the amount of water in downgoing slabs of upper mantle vary widely: Some suggest that worldwide, subduction zones have swallowed more than two oceans’ worth of water in the past 540 million years. However, new research by Miller et al. suggests that water transport at the Middle America Trench subduction zone is an order of magnitude less than previously estimated. As a plate approaches a subduction zone, it bends downward, causing faults to form. Models and earlier observations have suggested that this bending and faulting allow seawater to infiltrate into the upper mantle, where it fills cracks in fault zones, reacts with olivine to produce serpentine, and is later carried deeper into the subduction zone. Previous estimates of how much water reaches the upper mantle along bending faults have relied on measurements of the speed of seismic waves as they pass through a subducting plate. However, those measurements and estimates could not discern whether the upper mantle layer is uniformly hydrated or whether water is confined to bending fault zones. To address that limitation, the new study accounted for seismic anisotropy characterizing how the speed of seismic waves depends on the direction they travel through a material. The researchers used data collected by seafloor seismometers to measure seismic anisotropy along the Middle America Trench near Nicaragua, which enabled a much more detailed picture of upper mantle hydration. The data revealed that in the region studied, water storage in the upper mantle is limited to serpentinized fault zones that thin rapidly with depth, suggesting that fault dynamics and serpentinization reaction kinetics prevent seawater from hydrating the mantle between bending faults. New estimates of water transport that incorporate this finding are an order of magnitude lower than previous estimates for the Middle America Trench. Because the same processes occur at other subduction zones, the researchers report that far less water may be transported worldwide than previously estimated. (Journal of Geophysical Research: Solid Earth, https://doi.org/10.1029/2020JB020982, 2021)
Steele-MacInnis, M., Manning, C.E.Hydrothermal properties of geologic fluids.Elements, Vol. 16, pp. 375-380.Mantlewater

Abstract: Aqueous fluids are critical agents in the geochemical evolution of Earth’s interior. Fluid circulation and fluid-rock reactions in the Earth take place at temperatures ranging from ambient to magmatic, at pressures from ambient to extreme, and involve fluids that range from nearly pure H2O through to complex, multicomponent solutions. Consequently, the physical and chemical properties of hydrothermal fluids vary widely as functions of geologic setting; this variation strongly impacts fluid-driven processes. This issue will focus on the nature of geologic fluids at hydrothermal conditions and how such fluids affect geologic processes in some major settings.
Stern, R.J.The Mesoproterozoic single - lid tectonic episode: prelude to modern plate tectonics.GSA Today, Vol. 30, pp. 4-10. pdfMantletectonics

Abstract: The hypothesis that the Mesoproterozoic (1600-1000 Ma) tectonic regime was a protracted single-lid episode is explored. Single-lid tectonic regimes contrast with plate tectonics because the silicate planet or moon is encased in a single lithospheric shell, not a global plate mosaic. Single-lid tectonics dominate among the Solar System’s active silicate bodies, and these show a wide range of magmatic and tectonic styles, including heat pipe (Io), vigorous (Venus), and sluggish (Mars). Both positive and negative evidence is used to evaluate the viability of the Mesoproterozoic single-lid hypothesis. Four lines of positive evidence are: (1) elevated thermal regime; (2, 3) abundance of unusual dry magmas such as A-type granites and anorthosites; and (4) paucity of new passive continental margins. Negative evidence is the lack of rock and mineral assemblages formed by plate-tectonic processes such as ophiolites, blueschists, and ultra high-pressure terranes. Younger plate-tectonic-related and Mesoproterozoic mineralization styles contrast greatly. Paleomagnetic evidence is equivocal but is permissive that Mesoproterozoic apparent polar wander paths of continental blocks did not differ significantly. These tests compel the conclusion that the Mesoproterozoic single-lid hypothesis is viable.
Stoudmann, N., Reibelt, L.M., Rakotomalala, A.G., Randriamanjakahasina, O., Garcia, C.A., Waeber, P.O.A double edged sword: realities of artisanal and small scale mining for rural people in the Alaotra region of Madagascar. ** not specific to diamondsNatural Resources Forum, Vol 45 pp. 87-102. pdfAfrica, Madagascaralluvials

Abstract: A growing number of people are entering the artisanal and small-scale mining (ASM) sector worldwide. In Madagascar, millions of individuals depend on this informal activity. Through a case study in the Alaotra-Mangoro region of Madagascar, our research aimed to understand the "bottom-up" dynamics and ripple effects of the sector, by looking at the realities for rural communities where inhabitants are both directly and indirectly affected by ASM. We were interested in community members' and miners' perceptions of the socio-economic and environmental impacts of ASM, and in identifying the factors attracting people living in one of the country's agricultural hubs to this activity. Our results show a wide diversity of push and pull factors leading people to enter the sector. Although many positive impacts of ASM exist for miners and communities within the vicinity of mines, most miner participants considered themselves worse off since starting to mine, highlighting the high risk and low probability of return of ASM. ASM's potential for local and national development will remain squandered if its negative impacts continue to go unmanaged. Accounting for local contexts and the ripple effects of ASM will be crucial in achieving safety and security for miners, and to tap into the benefits it may offer communities while minimising environmental damage.
Sudholz, Z.I., Yaxley, G.M., Jaques, A.L., Chen, J.Ni-in-garnet geothermometry in mantle rocks: a high pressure experimental recalibration between 1100 and 1325 C. ( diamond potential)Contributions to Mineralogy and Petrology, 176, 16p. PdfMantlegeothermobarometry

Abstract: The temperature-dependent exchange of Ni and Mg between garnet and olivine in mantle peridotite is an important geothermometer for determining temperature variations in the upper mantle and the diamond potential of kimberlites. Existing calibrations of the Ni-in-garnet geothermometer show considerable differences in estimated temperature above and below 1100 °C hindering its confident application. In this study, we present the results from new synthesis experiments conducted on a piston cylinder apparatus at 2.25-4.5 GPa and 1100-1325 °C. Our experimental approach was to equilibrate a Ni-free Cr-pyrope-rich garnet starting mixture made from sintered oxides with natural olivine capsules (Niolv ? 3000 ppm) to produce an experimental charge comprised entirely of peridotitic pyrope garnet with trace abundances of Ni (10-100 s of ppm). Experimental runs products were analysed by wave-length dispersive electron probe microanalysis (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). We use the partition coefficient for the distribution of Ni between our garnet experimental charge and the olivine capsule (lnDNigrt/olv;NigrtNiolv), the Ca mole fraction in garnet (XCagrt; Ca/(Ca?+?Fe?+?Mg)), and the Cr mole fraction in garnet (XCrgrt; Cr/(Cr?+?Al)) to develop a new formulation of the Ni-in-garnet geothermometer that performs more reliably on experimental and natural datasets than existing calibrations. Our updated Ni-in-garnet geothermometer is defined here as: T(°C)=-8254.568((XCagrt×3.023)+(XCrgrt×2.307)+(lnDNigrtolv-2.639))-273±55 where DNigrt/olv=NigrtNiolv, Ni is in ppm, XCagrt = Ca/(Ca?+?Fe?+?Mg) in garnet, and XCrgrt= Cr/(Cr?+?Al) in garnet. Our updated Ni-in-garnet geothermometer can be applied to garnet peridotite xenoliths or monomineralic garnet xenocrysts derived from disaggregation of a peridotite source. Our calibration can be used as a single grain geothermometer by assuming an average mantle olivine Ni concentration of 3000 ppm. To maximise the reliability of temperature estimates made from our Ni-in-garnet geothermometer, we provide users with a data quality protocol method which can be applied to all garnet EPMA and LA-ICP-MS analyses prior to Ni-in-garnet geothermometry. The temperature uncertainty of our updated calibration has been rigorously propagated by incorporating all analytical and experimental uncertainties. We have found that our Ni-in-garnet temperature estimates have a maximum associated uncertainty of ± 55 °C. The improved performance of our updated calibration is demonstrated through its application to previously published experimental datasets and on natural, well-characterised garnet peridotite xenoliths from a variety of published datasets, including the diamondiferous Diavik and Ekati kimberlite pipes from the Lac de Gras kimberlite field, Canada. Our new calibration better aligns temperature estimates using the Ni-in-garnet geothermometer with those estimated by the widely used (Nimis and Taylor, Contrib Mineral Petrol 139:541-554, 2000) enstatite-in-clinopyroxene geothermometer, and confirms an improvement in performance of the new calibration relative to existing versions of the Ni-in-garnet geothermometer.
Sudholz, Z.J., Yaxley, G.M., Jaques, A.L., Brey, G.P.Experimental recalibration of the Cr-in-clinpyroxene geobarometer: improved precision and reliability above 4.5 Gpa.Contributions to Mineralogy and Petrology, Vol. 176, 10.1007/s0041 0-020-01768-z 21p. PdfMantlegeothermometry

Abstract: The pressure dependence of the exchange of Cr between clinopyroxene and garnet in peridotite is applicable as a geobarometer for mantle-derived Cr-diopside xenocrysts and xenoliths. The most widely used calibration (Nimis and Taylor Contrib Miner Petrol 139: 541-554, 2000; herein NT00) performs well at pressures below 4.5 GPa, but has been shown to consistently underestimate pressures above 4.5 GPa. We have experimentally re-examined this exchange reaction over an extended pressure, temperature, and compositional range using multi-anvil, belt, and piston cylinder apparatuses. Twenty-nine experiments were completed between 3-7 GPa, and 1100-1400 °C in a variety of compositionally complex lherzolitic systems. These experiments are used in conjunction with several published experimental datasets to present a modified calibration of the widely-used NT00 Cr-in-clinopyroxene (Cr-in-cpx) single crystal geobarometer. Our updated calibration calculates P (GPa) as a function of T (K), CaCr Tschermak activity in clinopyroxene (acpxCaCrTs), and Cr/(Cr?+?Al) (Cr#) in clinopyroxene. Rearranging experimental results into a 2n polynomial using multiple linear regression found the following expression for pressure: P(GPa)=11.03+(-T(K) ln(acpxCaCrTs)×0.001088)+(1.526×ln(Cr#cpxT(K))) where Cr#cpx=(CrCr+Al), acpxCaCrTs=Cr-0.81·Cr#cpx·(Na+K), with all mineral components calculated assuming six oxygen anions per formula unit in clinopyroxene. Temperature (K) may be calculated through a variety of geothermometers, however, we recommend the NT00 single crystal, enstatite-in-clinopyroxene (en-in-cpx) geothermometer. The pressure uncertainty of our updated calibration has been propagated by incorporating all analytical and experimental uncertainties. We have found that pressure estimates below 4 GPa, between 4-6 GPa and above 6 GPa have associated uncertainties of 0.31, 0.35, and 0.41 GPa, respectively. Pressures calculated using our calibration of the Cr-in-cpx geobarometer are in good agreement between 2-7 GPa, and 900-1400 °C with those estimated from widely-used two-phase geobarometers based on the solubility of alumina in orthopyroxene coexisting with garnet. Application of our updated calibration to suites of well-equilibrated garnet lherzolite and garnet pyroxenite xenoliths and xenocrysts from the Diavik-Ekati kimberlite and the Argyle lamproite pipes confirm the accuracy and precision of our modified geobarometer, and show that PT estimates using our revised geobarometer result in systematically steeper paleogeotherms and higher estimates of the lithosphere?asthenosphere boundary compared with the original NT00 calibration.
Sun, J., Zhu, X-K., Belshaw, N.S., Chen, W., Doroshkevich, A.G., Luo, W.J., Song, W.L., Chen, B.B., Cheng, Z.G., Li, Z.H., Wang, Y., Kynicky, J., Henderson, G.M.Ca isotope systematics of carbonatites: insights into carbonatite source and evolution.Geochemical Perspectives Letters, Vol. 17, pp. 11-15. pdfMantlecarbonatites

Abstract: Carbonatite, an unusual carbonate-rich igneous rock, is known to be sourced from the mantle which provides insights into mantle-to-crust carbon transfer. To constrain further the Ca isotopic composition of carbonatites, investigate the behaviour of Ca isotopes during their evolution, and constrain whether recycled carbonates are involved in their source regions, we report d44/42Ca for 47 worldwide carbonatite and associated silicate rocks using a refined analytical protocol. Our results show that primary carbonatite and associated silicate rocks are rather homogeneous in Ca isotope compositions that are comparable to d44/42Ca values of basalts, while non-primary carbonatites show detectable d44/42Ca variations that are correlated to d13C values. Our finding suggests that Ca isotopes fractionate during late stages of carbonatite evolution, making it a useful tool in the study of carbonatite evolution. The finding also implies that carbonatite is sourced from a mantle source without requiring the involvement of recycled carbonates.
Tagawa, S., Sakamoto, N., Hirose, K., Hernlund, J., Ohishi, Y., Yurimoto, H.Experimental evidence for more hydrogen in Earth's core than in the oceans.Nature Communications, doi.org/10.1038/s41467-021-22035-0 Vol. 12 8p. PdfMantlehydrogen

Abstract: Hydrogen is one of the possible alloying elements in the Earth’s core, but its siderophile (iron-loving) nature is debated. Here we experimentally examined the partitioning of hydrogen between molten iron and silicate melt at 30-60 gigapascals and 3100-4600?kelvin. We find that hydrogen has a metal/silicate partition coefficient DH?=?29 and is therefore strongly siderophile at conditions of core formation. Unless water was delivered only in the final stage of accretion, core formation scenarios suggest that 0.3-0.6?wt% H was incorporated into the core, leaving a relatively small residual H2O concentration in silicates. This amount of H explains 30-60% of the density deficit and sound velocity excess of the outer core relative to pure iron. Our results also suggest that hydrogen may be an important constituent in the metallic cores of any terrestrial planet or moon having a mass in excess of ~10% of the Earth.
Taguchi, T., Kouketsu, Y., Igami, Y., Kobayashi, T., Miyake, A.Hidden intact coesite in deeply subducted rocks.Earth and Planetary Science Letters, Vol. 558, 115763, 6p. PdfEurope, ItalyUHP

Abstract: The stabilization of coesite is a diagnostic indicator of ultrahigh-pressure metamorphism and in many cases it implies that a rock has been subducted to a minimum depth of 80 km. Coesite typically occurs as rare relicts in rigid host minerals, but most commonly transforms into a-quartz pseudomorphs during exhumation. The abundance of coesite-bearing rocks in orogens worldwide is a contentious issue in the petrological community, despite evidence from numerical modeling that suggests that coesite formation should be a common geological process during ultrahigh-pressure metamorphism. This knowledge gap must be addressed to improve the understanding of the geological aspects of subduction-zone geodynamics. Here we report that minuscule coesites (<20 µm) occur as abundant inclusions in garnet-rich layers from the Italian Western Alps. The discovery of such intact inclusions may fill the gaps in the predicted and observed abundances of coesite worldwide. Through integrated approaches with resolutions down to the nano-scale, we show that these garnet-hosted inclusions are composed entirely of coesite. Our results suggest that common coesite-derived quartz pseudomorphs are less typical structures in ultrahigh-pressure metamorphic rocks and the minuscule coesite in many rocks may be overlooked because of its size. These findings open up new research directions for constraining the extent of deeply subducted rocks and their rheology.
Tang, Li., Wagner, T.,Fusswinkel, T., Zhang, S-T., Xi, B., Jia, L-H., Hu, X-K. Magmatic-hydrothermal evolution of an unusual Mo-rich carbonatite: a case study using LA-ICP-MS fluid inclusion microanalysis and He-Ar isotopes from the Huangshuian deposit, Qinling, China.Mineralium Deposita, 10.1007/s00126 -021-01055-2 18p. PdfChinacarbonatites

Abstract: The Huangshui'an deposit located in East Qinling (China) is an unusual case of a Si-rich carbonatite hosting economic Mo and minor Pb and REE mineralization. The role of mantle-sourced carbonatite melts and fluids in the formation of the Mo mineralization remains poorly understood. Our integrated study based on field geology, petrography, microthermometry, and LA-ICP-MS analysis of single fluid inclusions, and noble gas isotopes of pyrite permits to reconstruct the source characteristics, the magmatic-hydrothermal evolution of the carbonatitic fluids, and their controls on Mo mineralization. Fluid inclusions hosted in calcite in the carbonatite dikes have the highest concentrations of Mo (9.9-62 ppm), Ce (820-9700 ppm), Pb (1800-19500 ppm), and Zn (570-5800 ppm) and represent the least modified hydrothermal fluid derived from the carbonatite melt. Fluid inclusions hosted in calcite (Cal) and quartz (Qz2 and Qz3) of the stage I carbonatite dikes have different metal concentrations, suggesting that they formed from two distinct end member fluids. The FIA in calcite represent fluid A evolved from carbonatite melt with relatively high-ore metal concentrations, and those in quartz characterize fluid B having a crustal signature due to metasomatic reactions with the wall rocks. The FIA in quartz (Qz1) within the altered wall rock have overlapping elemental concentrations with those of massive quartz (Qz2) and vuggy quartz (Qz3) in carbonatite. This suggests that the volumetrically significant quartz in the Huangshui'an carbonatite has been formed by the introduction of Si by fluid B. The positive correlations between Rb, B, Al, Cl, and Sr in stage II fluid inclusions in late fluorite + quartz + calcite veins indicate that this late mineralization formed from the mixing of primary hydrothermal fluid B with meteoric water. The He-Ar isotope data, in combination with available C-O-Sr-Nd-Pb isotope data, constrain the carbonatite source as an enriched mantle source modified by contributions from crustal material which was probably the fertile lower crust in the region. This distinct source facilitated the enrichment in Mo, REE, and Pb in the primary carbonatite magma. The carbonatite magmatism and Mo mineralization at 209.5-207 Ma occurred in the regional-scale extensional setting at the postcollision stage of the Qinling Orogenic Belt.
Tang, M., Ji, W-Q., Chu, X., Wu, A., Chen, C.Reconstructing crustal thickness evolution from europium anomalies in detrital zircons.Geology, Vol. 49, pp. 76-80. pdfAsia, Tibetzircons

Abstract: A new data compilation shows that in intermediate to felsic rocks, zircon Eu/Eu* [chondrite normalized Eu/ graphic] correlates with whole rock La/Yb, which has been be used to infer crustal thickness. The resultant positive correlation between zircon Eu/Eu* and crustal thickness can be explained by two processes favored during high-pressure differentiation: (1) supression of plagioclase and (2) endogenic oxidation of Eu2+ due to garnet fractionation. Here we calibrate a crustal thickness proxy based on Eu anomalies in zircons. The Eu/Eu*-in-zircon proxy makes it possible to reconstruct crustal thickness evolution in magmatic arcs and orogens using detrital zircons. To evaluate this new proxy, we analyzed detrital zircons separated from modern river sands in the Gangdese belt, southern Tibet. Our results reveal two episodes of crustal thickening (to 60-70 km) since the Cretaceous. The first thickening event occurred at 90-70 Ma, and the second at 50-30 Ma following Eurasia-India collision. These findings are temporally consistent with contractional deformation of sedimentary strata in southern Tibet.
Tchoukeu, C.D.N., Baseka, C.A., Djomani, Y.P., Rousse, S., Etame,J., Llubes, M., Seoane,L., Mbang, C.S., Yomba, A.E.Crustal thickness, depth to the bottom of magnetic sources and thermal structure of the crust from Cameroon to Central African Republic: preliminary results for a better understanding of the origin of the Bangui Magnetic Anomaly.Journal of African Earth Sciences, Vol. 179, 104206, 21p. pdfAfrica, Cameroon, Central African Republicgeophysics

Abstract: The Bangui Magnetic Anomaly (BMA) is one of the largest magnetic anomalies in the world whose origin is still not known. This research investigated the crustal thickness, Curie depths and thermal structures in the Central African sub-regions - Cameroon, Central African Republic and adjacent countries - which are largely characterized by the Bangui Magnetic Anomaly. To achieve a better understanding and clearer idea of the location of the possible sources of the BMA, analyses of geothermal structures were conducted. Two potential methods were used: gravity to evaluate the crustal thickness and magnetics for geothermal analysis. Spectral analysis of gravity data shows that crustal thickness range between 14 and 55 km. The highest depths were found in Central African Republic. The lower values of crustal thickness were obtained in South-Chad basin with a minimum of roughly 14 km. Geothermal analysis is carried out using the Curie point depth, thermal gradient and heat-flow evaluations. The results show that the BMA is related to a thick crust of roughly 40 km. Depth to the bottom of possible sources does not exceed the lower crust. The mean Curie point depth estimated is 38 km with an error of ±2 km. Geothermal results also show the difference in the thermal behaviour between the crust in the Pan African and Precambrian domain. The mobile zone which constitutes the Pan African domain is associated with a thin crust of high heat-flow values of 65 mW/m2. However, the Precambrian domain beneath the BMA is associated with a thick crust with lower heat-flow values (roughly 45 mW/m2). The difference between crustal thickness and Curie point depths shows that all the sources of the BMA are crustal. The present results are in favour of a geological origin for the Bangui Magnetic anomaly.
Thomson, A.R., Kohn, S.C., Prabhu, A., Walter, M.J.Evaluating the formation pressure of diamond-hosted majoritic garnets; a machine learning majorite barometer.Journal of Geophysical Research, Solid Earth, in press available, 34p.Globaldiamond inclusions

Abstract: Natural diamonds, as well as being a cherished commodity, are valuable for scientists studying the Earth's interior because they only grow at depths greater than 140 km. When diamonds grow, they may trap tiny fragments of surrounding materials as sub-millimetre defects. Study of these inclusions can provide insights into the materials and processes occurring deep inside our planet. Sub-lithospheric diamonds are a relatively rare subset of natural diamonds, believed to have grown deeper than 250 km, and are thought to be the deepest Earth materials that have been transported to the surface. Ideally, we would be able to estimate their formation depths accurately. Inclusions of majoritic garnet provide a unique opportunity for this, as their chemistry is known to change systematically with formation depth. However, this behaviour is highly complex, and previous attempts to parameterise the depth dependence of inclusion chemistries have limitations. Here we have used data science to train a "Machine Learning" algorithm that improves the accuracy of estimating the formation pressures of majoritic garnet inclusion. The approach confirms that many natural diamonds containing inclusions of majoritic garnet must have originally formed at depths of 400 - 660 km.
Thomson, A.R., Kohn, S.C., Prabhu, A., Walter, M.J.Evaluating the formation pressure of diamond-hosted majoritic garnets: a machine leaning majorite barometer.Journal of Geophysical Research Physical Review B., http://doi.org/10 /1029/2020JB020 604 21p. PdfMantlediamond inclusions

Abstract: Natural diamonds, as well as being a cherished commodity, are valuable for scientists studying the Earth's interior because they only grow at depths greater than 140 km. When diamonds grow, they may trap tiny fragments of surrounding materials as sub-millimeter defects. Study of these inclusions can provide insights into the materials and processes occurring deep inside our planet. Sub-lithospheric diamonds are a relatively rare subset of natural diamonds, believed to have grown deeper than 250 km, and are thought to be the deepest Earth materials that have been transported to the surface. Ideally, we would be able to estimate their formation depths accurately. Inclusions of majoritic garnet provide a unique opportunity for this, as their chemistry is known to change systematically with formation depth. However, this behavior is highly complex, and previous attempts to parameterize the depth dependence of inclusion chemistries have limitations. Here we have used data science to train a "machine learning" algorithm that improves the accuracy of estimating the formation pressures of majoritic garnet inclusion. The approach confirms that many natural diamonds containing inclusions of majoritic garnet must have originally formed at depths of 400-660 km.
Thrane, K.The oldest part of the Rae craton identified in western Greenland.Precambrian Research, Vol. 357, 106139, 14p. PdfEurope, Greenlandcraton

Abstract: New U-Pb zircon data from a range of Archean rocks from the Paleoproterozoic Rinkian Belt in the North-West and central West Greenland provide new constraints on the crystallisation and formation of the Archean basement to this Paleoproterozoic orogen. The results show that the protoliths of the oldest orthogneisses were emplaced in the central part of the Rinkian Belt at c. 3150-3100 Ma. This was followed in the southern part of the belt by the crystallisation of igneous rocks at c. 3000-2900 Ma, including rhyolites that are well preserved. This event is not recorded in the northern part of the belt and may represent southward growth away from a cratonic core at this time. The orthogneisses across the entire belt were subsequently affected by a metamorphic event at c. 2730-2660 Ma, which included intrusions of granites and northward cratonic growth. A few samples also yield evidence of a younger Paleoproterozoic overprint associated with the formation of the 1.90-1.80 Ga Rinkian Belt. The Archean basement rocks of the Rinkian Belt have previously been correlated with similar rocks exposed in northeast Canada and, consequently, they have been referred to as the Greenland part of the Rae craton. The new data support this correlation in general but reveal that Greenland contains the oldest rocks of the Rae craton discovered so far. The new data also show that the Rinkian Belt has a significantly different Archean history than the basement underlying the Nagssugtoqidian orogen to the south. This supports former models that envision two separate Archean cratons colliding during the Paleoproterozoic and that a suture of this age is situated in the central Disko Bugt area.
Titkov, S.V., Yakovleva, V.V., Breev, I.D., Anisimov, A.N., Baranov, P.G., Dorofeeva, A.I., Bortnikov, N.S.Distribution of nitrogen-vacancy NV centers in cubic diamond crystals from Anabar placers as revealed by ODMR and PL tomography.Doklady Earth Sciences, Vol. 496, 1, pp. 45-47. pdfRussiadeposit - Anabar

Abstract: Nitrogen-vacancy NV- centers, which are of considerable interest for quantum electronics, are artificially produced in the diamond structure by irradiation and sub