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The Sheahan Diamond Literature Reference Compilation - Scientific and Media Articles based on Major Keyword - Kimberlite
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 announcements called 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 Keyword Index
Sheahan Diamond Literature Reference Compilation - Scientific Articles by Author for all years
Each article reference in the SDLRC is tagged with one or more key words assigned by Pat Sheahan to highlight the main topics of the article. In an effort to make it easier for users to track down articles related to a specific topic, KRO has extracted these key words and developed a list of major key words presented in this Key Word Index to which individual key words used in the article reference have been assigned. In most of the individual Key Word Reports the references are in crhonological order, though in some such as Deposits the order is first by key word and then chronological. Only articles classified as "technical" (mainly scientific journal articles) and "media" (independent media articles) are included in the Key Word Index. References that were added in the most recent monthly update are highlighted in yellow.
Kimberlite is an igneous intrusion whose dominant content has a magmatic source at a depth of 150-400 km within the earth's mantle. Kimberlitic intrusions are unusual in that they appear to originate through discrete melting within the mantle whose resulting magma ascends through the mantle, entraining "xenoliths" of mantle material along the way, generally but not always entirely disaggregating the entrained material, exploiting zones of crustal weakness, and achieving emplacement by cooling within sub-vertical faults to form dykes or stratigraphic horizons to form sills, or gaining velocity and erupting explosively to form pipes with a classical morphology of a crater, diatreme, and root zone. References tagged with the keyword "kimberlite" are about kimberlites in general or specific kimberlites that have not become mines or scheduled for development. Commercial or potentially commercial kimberlites will usually have a key word in the format "Deposit - Venetia" or just "Venetia" which results in their articles showing up in the Deposits report.
Recherches Experimentales sur le Role Possible des Gaz a Hautes Temperatures Doues de Tres Fortes Pressions et Animes D'un Mouvement Fort Rapide dans Divers Phenomenes Geologiques.
Geological Society FRANCE (PARIS) Bulletin., Vol. 19, PP. 313-354.
Petrography of the Premier Kimberlite. I. a Microscopic And chemical Study of the Rock- Varieties of Blue Ground in The mine and Some Interesting Analytical Results.
Mining Engineering Journal of South Africa, Vol. 9, PT. 1, JULY 15TH. No. 436, PP. 819-820.
Petrography of the Premier Kimberlite. Ii. the Nodular Inclusions in the Blue Ground- an Interesting Graphite Bearing Specimen and the Problem of the Genetic Relationship.
Mining Engineering Journal of South Africa, Vol. 9, PT. 1, JULY 22ND. No. 437, PP. 857-858.
The Genesis of the Diamond. a Geological, Mineralogical, Crystallographical, Petrographical and Chemical Study of Kimberlite and its Associated Cognate and Accidental Inclusions.
Environment of Formation and Composition of the Continental deposits and Genetic Types of Diamond Placers in the Malo-botuobonskiy Region of Western Yakutia.
Experiments in Interpretation of the Regional Magnetic Field and the Relation of Magnetized Bodies to Tectonics in the Diamond Fields of Western Yakutia.
In: Symposium Primeneniye Aeromoetodoy Pri Poiskakh Korennykh Me, PP. 101-114.
Circumferential Faulting Around Wells Creek Basin, Houston And Stewart Counties, Tennessee- a Manuscript by Safford, J.m. and Lander, D.w.t. : Circa 1895.
Tennessee Academy of Science Journal, Vol. 41, No. 1, PP. 37-48.
Global
Kimberlite, Western Tennessee, Central States, Cryptoexplosion
Some Information on the Resolution Capacity of Aeromagnetic surveys As Applied to the Search for Anomalies Created by Bodies of Tubular Shape Under Complex Geologic Conditions.
Soviet Geology GEOPHYSICS, Vol. 15, No. 7, PP. 103-107.
Recovery Plant Practice at de Beers Consolidated Mines Limited, Kimberley with Particular Reference to Improvements Made for the Sorting of the Final Concentrates.
South African Institute of Mining and Metallurgy. Journal, Vol. 80, No. 9, PP. 317-328.
Use of Dipole Electric-magnetic Sounding in Determining The thickness of Alluvium During Exploration for Beach Diamond Placers in the Region of Anabar Bay.
Transform Faults Associated with the Antarctic and Tasman Sea Ridges and their Relationship to Continental Fractures And Kimberlitic Activity in Southeast Australia.
B.m.r. Rec. Min. Res. Geol. Geophys., 1979/2, PP. 33-34. (abstract.).
Methods for the Study, Processing and Interpretation of Magnetic and Gravimetric Fields in Prospecting for Kimberlite Bodies in Traps. Methodological Recommendations.
The Relationship of Geophysical and Remote Sensing Lineaments to Regional Structure and Kimberlite Intrusions in the Appalachian Plateau of Pennsylvania.
Geological Society of America (GSA), Vol. 11, No. 1, P. 48, (abstract.).
Metasomatism and Chemical Heterogeneity in the Sub-continental Mantle: Sr and Nd Isotopic Analysis of Apatite Rich Xenoliths and Alkaline Magmas from Eastern Australia.
Proceedings of Third International Kimberlite Conference, TERRA COGNITA, ABSTRACT VOLUME., Vol. 2, No. 3, P. 231, (abstract.).
Ultramafic Xenoliths from Lake Bulletinen Merri and Mt. Leura, South East Australia, and Their Bearing on the Evolution of The Continental Upper Mantle.
Proceedings of Third International Kimberlite Conference, TERRA COGNITA, ABSTRACT VOLUME., Vol. 2, No. 3, P. 230, (abstract.).
Edwards, D., Rock, N.M.S., Taylor, W.R., Griffin, B.J., Sun, S-S.
The Aries Diamondiferous kimberlite pipe, central Kimberley block, westernAustralia: mineralogy, petrology and geochem. of the pipe rock and indicators
Proceedings of Fifth International Kimberlite Conference held Araxa June 1991, Servico Geologico do Brasil (CPRM) Special, pp. 82-84
Comparison of Siberian and South African Diamondiferous kimberlites
Conference registration The Canadian Institute of Mining, Metallurgy and Petroleum (CIM) Xerox Tower Suite 1210, 3400 de Maissoneuve, Sept. 5-13, 1991 Fax 514 939-2714
Fort a la Corne kimberlites -exploration case history
Conference registration The Canadian Institute of Mining, Metallurgy and Petroleum (CIM) Xerox Tower Suite 1210, 3400 de Maissoneuve, Sept. 5-13, 1991 Fax 514 939-2714
Conference registration The Canadian Institute of Mining, Metallurgy and Petroleum (CIM) Xerox Tower Suite 1210, 3400 de Maissoneuve, Sept. 5-13, 1991 Fax 514 939-2714
Kimberlites : structural zonation and their productivity
Conference registration The Canadian Institute of Mining, Metallurgy and Petroleum (CIM) Xerox Tower Suite 1210, 3400 de Maissoneuve, Sept. 5-13, 1991 Fax 514 939-2714
Discovery of kimberlites in the Kirkland Lake area, northern Ontario, Canada. Part I: kimberlite discoveries, sampling, diamondcontent, age, emplacement
The Canadian Institute of Mining, Metallurgy and Petroleum (CIM) Exploration Mining Geology, Vol. 1, No. 4, October pp. 351-370
The Canadian Mining and Metallurgical Bulletin (CIM Bulletin) , Annual Meeting Abstracts approximately 10 lines, Vol. 86, No. 968, March POSTER ABSTRACT p. 69
Diamondiferous kimberlite in Saskatchewan, Canada- a biogeochemical SOURCE[ Journal of Geochemical Exploration,Special issue Proceedings of geochemical Exploration 1991 held Reno
Journal of Geochemical Exploration, Special issue Proceedings of, Vol. 47, No. 1-3, pp. 131-142
The tentative field identification of kimberlite and what should happennext: a short course definition, classification, petrology, mineralogy andprelim. eval. eval
Kimberlites and kimberlites or apples and orange(ite)s?
Mid-continent diamonds Geological Association of Canada (GAC)-Mineralogical Association of Canada (MAC) Symposium ABSTRACT volume, held Edmonton May, pp. 59-62.
Diamondiferous kimberlites in Saskatchewan, Canada: global, regional and local setting.
Mid-continent diamonds Geological Association of Canada (GAC)-Mineralogical Association of Canada (MAC) Symposium ABSTRACT volume, held Edmonton May, pp. 11-20.
The geochemistry (platinum group elements (PGE)) in kimberlites and constraints of the nature platinum group elements (PGE) insubcratonic lithospheric mantle.
International Symposium Upper Mantle, Aug. 14-19, 1994, Extended abstracts pp. 73-75.
Preliminary investigation: sedimentology and provenance of the Wood Mountain Formation and derived glacial and glaciofluival sediments - context for KIM anomalies.
Saskatchewan Geological Survey Summary of Investigations 2004, Vol. 2, pp. A 1-12.
Comtrasting Group I and Group II eclogite xenolith petrogenesis: petrological, trace element and isotopic evidence from eclogite, garnet websterite and akremite
Journal of Petrology, Vol. 46, 10, Oct. pp. 2059-2090.
Geochemistry and origin of the Proterozoic kimberlites, ultramafic and ultrapotassic magmatic rocks from Indravati Basin in Bastar Craton, central India.
Geological Society of India, Bangalore November Meeting Group Discussion on Kimberlites and Related Rocks India, Abstract p. 94-97.
Stable isotope composition of magmatic and deuteric carbonate phases in hypabyssal kimberlite, Lac de Gras field: implications for the composition of fluids...
Peltonen, P., Manttari, I., Huhma, H., Whitehouse, M.J.
Multi stage origin of the lower crust of the Karelian craton from 3.5 to 1.7 Ga based on isotopic ages of kimberlite derived mafic granulite xenoliths.
Precambrian Research, Vol. 147, 1-2, June 10, pp. 107-123.
Melting relations in the chloride carbonate silicate systems at high pressure and model for formation of alkalic diamond forming liquids in the upper mantle.
Earth and Planetary Science Letters, in press available
Compositional heterogeneity of the continental lithospheric mantle beneath the Early Precambrian and Phanerozoic structures: evidence from mantle xenoliths.
Geochemistry International, Vol. 45, 11, pp. 1077-1102.
Melluso, L., Lustrino, M., Ruberti, E., Brotzu, P., Barros Gomes, C., Morbidelli, Morra, Svisero, Amelio
Major and trace element composition of olivine perovskite, clinopyroxene, Cr Fe Ti oxides, phlogopite and host kamafugites and kimberlites, Alto Paranaiba,
Canadian Mineralogist, Vol. 46, no. 2 Feb. pp. 19-40.
The Majuagaa kimberlite dike, Maniitsoq region, West Greenland: constraints for an Mg rich silico carbonatite melt composition from groundmass mineralogy and bulk compositions.
Griffin, W.L., Kobussen, A.F., Babu, E.V.S.S.K., O'Reilly, S.Y., Norris, R., Sengupta, P.
A translithospheric suture in the vanished 1 Ga lithospheric root of South India: evidence from contrasting lithospheric sections in the Dharwar Craton.
Mineralogy and geochemistry of kimberlites NK-2 and KK-6 Narayanpet kimberlite field, eastern Dharwar Craton, southern India: evidence for transitional ...
The Canadian Mineralogist, Vol. 47, 5, pp. 1117-1135,
Chalapathi Rao, N.V., Lehmann, B., Mainkar, D., Belyatsky, B.
Petrogenesis of the end Cretaceous Diamondiferous Behradih orangeite pipe: implications for mantle plume - lithosphere interaction in the Bastar craton, India.
Contributions to Mineralogy and Petrology, Vol. 161, pp. 721-742.
Griffin, W.L., Kobussen, A.F., Babu, E.V.S.S.K., O'Reilly, S.Y., Norris, R., Sengupta, P.
A translithospheric suture in the vanished 1 Ga lithospheric root of South India: evidence from contrasting lithosphere sections in the Dharwar craton.
Schmadicke, E., Okrusch, M., Rupprecht-Gutowski, P., Will, T.M.
Garnet pyroxenite, eclogite and alkremite xenoliths from the off-craton Gibeon kimberlite field, Namibia: a window into the upper mantle of the Rehoboth Terrane.
Jelsma, H.,Krishnan, S.U., Perritt, S.,Kumar, M., Preston, R., Winter, F., Lemotlo, L., Costa, J., Van der Linde, G., Facatino, M., Posser, A., Wallace, C., Henning, A., Joy, S., Chinn, I., Armstrong, R., Phillips, D.
Kimberlites from central Angola: a case stidy of exploration findings.
10th. International Kimberlite Conference Feb. 6-11, Bangalore India, Abstract
Maier, W.D., Peltonen, P., McDonald, I., Barnes, S.J., Barnes, S-J., Hatton, C., Viljoen, F.
The concentration of platinum group elements and gold in southern African and Karelian kimberlite hosted mantle xenoliths: implications for the noble metal content of the Earth's mantle.
Girnis, A.V., Bulatov, V.K., Brey, G.P., Gerdes, A., Hofer, H.E.
Trace element partitioning between mantle minerals and silico-carbonate melts at 6-12 Gpa and applications to mantle metasomatism and kimberlite genesis.
Volatile fluxing causes cratonic flood basalt volcanism: case study of the Siberian Craton.
V.S. Sobolev Institute of Geology and Mineralogy Siberian Branch Russian Academy of Sciences International Symposium Advances in high pressure research: breaking scales and horizons ( Courtesy of N. Poikilenko), Held Sept. 22-26, 4p. Abstract
Repeated kimberlite magmatism beneath Yakutia and its relationship to Siberian flood volcanism: insights from in situ U-Pb and Sr-Nd perovskite isotope analysis.
Earth and Planetary Science Letters, Vol. 404, Oct. pp. 283-295.
Valentine, G.A., Graettinger, A.H, Macorps, E., Ross, P-S., White, J.D.L., Dohring, E., Sonder, I.
Experiments with vertically and laterally migrating subsurface explosions with applications to the geology of phreatomagmatic and hydrothermal explosion craters and diatremes.
Abstract: Carbon dioxide and water, being present in the Earth's mantle at concentration levels of tens to hundreds of ppm, greatly lower the peridotite solidus temperature and drastically modify the composition of produced melts. The presence of CO2 produces silica-poor, carbonate-rich liquids at the onset of melting, and these liquids shift toward silica rich compositions as the degree of melting increases. Numerous geochemical observations and experimental studies have revealed the complexity of the transition between carbonate-rich and silicate-rich melts. It is characterized by a strongly non-linear evolution and, under specific conditions, by immiscibility. To better constrain this transition, we have used the thermodynamic activity of silica as a probe of the mixing properties between molten carbonate and molten silicate. The activity of silica (aSiO2(l))aSiO2l was calculated for a large number of experimental liquids from two equilibria: olivine-orthopyroxene-melt and immiscible silicate-rich melt-carbonate-rich melt (491 data points ranging from 1 to 14 GPa and 1090 to 1800 °C). We modelled aSiO2(l)aSiO2l during incipient melting of the peridotite in presence of CO2 with a generalized Margules function. Our model reproduces well the silica activity-composition relationships of the experimental database, and can be used to predict the silica content of the melts coexisting with olivine and orthopyroxene. We show that water content and Ca/Mg ratio in the melts have an important influence on the aSiO2(l)aSiO2l. In contrast to a recent empirical model (Dasgupta et al., 2013), the analysis of the experimental database reveals that the transition from carbonate to silicate melt with decreasing depth should occur abruptly in oceanic mantle. Our model predicts that carbonatitic melts with ~ 5 wt.% SiO2 can be stabilized from ~ 150 km depth, at the onset of incipient melting by "redox melting", up to ~ 75 km, above which the liquid evolves abruptly to a carbonated silicate composition (> ~ 25 wt.% SiO2). In the cratonic mantle lithosphere, our model predicts that carbonatitic melts are prevailing up to shallow depth, and conflicts the recent model (Russell et al., 2012) of CO2-saturation triggered by orthopyroxene assimilation during kimberlite ascent.
Abstract: Xenoliths of mantle peridotite have been sampled from four kimberlite intrusions, Melton Wold, Hebron, Uintjiesberg and Markt, emplaced through the Mesoproterozoic Namaqua-Natal Belt, along the southern border of the Kaapvaal Craton. Although many of the xenoliths are heavily altered, constituent clinopyroxene, garnet and phlogopite are fresh and have been analysed by electron microprobe for major elements and by laser ablation ICP-MS for trace elements. Primitive mantle-normalised REE abundances in clinopyroxene are all strongly LREE enriched and show a range of patterns including uniformly MREE-HREE sloped (referred to here as ‘normal’), sinusoidal and humped sinusoidal patterns. HREE abundances are extremely low (Yb = 0.3-0.06 × PM). REEN patterns in coexisting garnets show a similar range of patterns. When normalised to primitive mantle values, trace element patterns in some clinopyroxenes show strong relative depletion in Rb-Ba, Ta-Nb and Ti, with some samples also being relatively depleted in Zr-Hf. These trace element characteristics are indistinguishable from those found in clinopyroxene and garnet from peridotites from the adjacent cratonic mantle. Numerical modelling of reactive porous flow of an enriched metasomatic melt through a geochemically depleted peridotite matrix can account for the full range in observed REEN patterns. The relative depletion in Rb-Ba, Ta-Nb and Ti can be accounted for by an early crystallisation of phlogopite from the percolating melt. The relative depletion in Zr-Hf in some clinopyroxenes requires either zircon to crystallise in the proximal metasomatic assemblage, or metasomatism by a carbonatitic melt. Modelling results, together with the absence of clinopyroxene with depleted or even partially enriched REEN patterns, suggest that all clinopyroxene has been modally introduced through metasomatism into an initially highly depleted harzburgitic protolith. The range in Sr and Pb isotopic composition of the clinopyroxenes indicates regional metasomatism by melts of various compositions. The strong HREEN depletion is interpreted to reflect the effect of initial melt depletion in the early Proterozoic, with melting extending into the spinel stability field requiring an oceanic realm, and again later in the Mesoproterozoic (Namaqua Orogeny). The superimposed incompatible element enrichment indicates subsequent multiple enrichment events by rising alkaline melts similar in composition to kimberlite or ultramafic alkaline lamprophyre, possibly related to Mesozoic plume upwelling beneath the region, that reintroduced clinopyroxene into the depleted Proterozoic harzburgite protolith.
Geochemistry, Exploration, Environment, Analysis, Vol. 16, pp. 62-84.
Canada, Northwest Territories
Kimberlite - Triple B mentioned
Abstract: In this study, results by direct portable XRF (‘pXRF’) on unsieved till samples were compared with those by established laboratory methods (aqua regia or fusion ICP-MS and ICP-ES) on the <0.063-mm fraction to determine if the application of direct pXRF in the field would serve as an acceptable guide for immediate follow-up work. Four test sites in Canada were chosen: the Halfmile Lake Cu-Pb-Zn VMS deposit; the intrusion-hosted W-Mo Sisson deposit; a Pb-Zn Mississippi Valley-type (MVT) deposit in the Pine Point district; and the Triple B kimberlite. Unsieved till samples from the GSC archive collection were used for this study and included samples from background areas, immediately overlying, and at various distances down-ice of each deposit. Ziploc® and Whirl-Pak® bags that were used to contain the samples in the field were tested for their properties of X-ray attenuation and contamination. In general, the performance of pXRF in the four test areas was very good where concentrations of elements of interest (indicator or pathfinder elements) were substantially above detection limits by this technique (in the low ppm range for many elements). The following elements, shown to be useful indicator elements (important constituents of the ore/commodity) or pathfinder elements (those associated with the commodity elements) by the established methodology, showed similar patterns by pXRF on the unsieved material: Zn, Cu, Pb, and As at Halfmile Lake; W, Mo, Cu, Zn, Pb, and As at the Sisson deposit; Zn, Pb, and Fe at Pine Point; and Ca, Sr, Cr, and Ni at Triple B. Pathfinder elements whose concentrations were too low for determination by pXRF include: Ag and Sb at Halfmile Lake; Ag and Cd at Sisson; Cd, S, and Se at Pine Point; and Co, Mg, P, U, and Th at Triple B. The high background for Bi by pXRF, equivalent to c. 50?ppm, and its noisy signal precluded its use at Halfmile Lake and Sisson. Elements which tended to show poor precision (three analyses each sample) by pXRF in some samples due to sample heterogeneity include Sn, V, and W. Mercury was erroneously reported for the majority of samples in the low ppm range by pXRF whereas its concentration in fact was in the low ppb range. Several Pb-, Zn- (c. 1% Pb, Zn) and Fe-rich (up to 16% Fe) samples demonstrated spectral interferences by: Pb on As, Th and Se; Zn on Cu; and Fe on Co. Results for six till samples analysed in Ziploc® and Whirl-Pak® bags showed that Ziploc® absorbs fewer low-energy photons and hence is preferable for determining light elements such as Si, K and Ca.
Abstract: The levels of brilliance (brightness and contrast), fire (flashes of rainbow color), and scintillation (intense sparkles when moved) of diamonds are unmatched by any other gemstone. Also diamonds of gem size and quality are relatively rare. As a result, gem diamonds are extremely valuable, yet the supply of diamonds is ultimately limited. This reality has pushed diamond exploration and mining into extreme environments, from the far Arctic North to the deserts of southern Africa and onto the ocean bed off the coast of Namibia. About two-thirds of the annual production of diamonds by weight comes from ancient volcanoes that consist of the rock types kimberlite, orangeite, or lamproite. Tracking down the remnants of these small volcanoes requires sophisticated and efficient collection and processing of samples for kimberlite indicator minerals (i.e., peridotite constituent minerals) and evaluation of enormous amounts of mineral data to constrain the diamond prospectivity of a region, cluster of pipes, or particular diatreme. The exploration sampling stage is usually followed by aero- or ground-geophysical measurements, target evaluation, and, finally, drill testing. Diamond exploration is expensive, but the rewards can be great. Diamond exploration in Finland started in 1985, and has been continuous, albeit with varying levels of activity, since that time. As a result, diamondiferous rocks have been found in three regions—namely, the Kuhmo-Lentiira area hosting a group of 1200 Ma orangeites, the Kuusamo-Hossa area containing several 760 Ma kimberlites, and the Kaavi-Kuopio area with a cluster of ?600 Ma kimberlites. Driven by the needs of these exploration activities, our understanding of the makeup of the Karelian craton, and our understanding of the magmas that have transported diamonds to the surface in this part of the world have benefitted enormously.
Earth and Planetary Science Letters, Vol. 447, pp. 151-160.
Mantle, Europe, Italy
Kimberlite formation, volcanism, melting
Abstract: Kimberlites are the most deep-seated magmas in the mantle and ascend to the surface at an impressive speed, travelling hundreds of kilometres in just hours while carrying a substantial load of xenolithic material, including diamonds. The ascent dynamics of these melts are buoyancy-controlled and certainly driven by outgassing of volatile species, presumably H2O and CO2, summing to concentration level of ca 15 -30 wt.% in kimberlite melts. We provide H2O -CO2 solubility data obtained on quenched glasses that are synthetic analogues of kimberlite melts (SiO2 content ranging from 18 to 28 wt.%). The experiments were conducted in the pressure range 100 to 350 MPa. While the CO2 solubility can reach 20 wt.%, we show that the H2O solubility in these low silica melts is indistinguishable from that found for basalts. Moreover, whereas in typical basalts most of the water exsolves at shallower pressure than the CO2, the opposite relationship is true for the low-SiO2 composition investigated. These data show that kimberlites can rise to depths of the upper crust without suffering significant degassing and must release large quantities of volatiles (>15 wt.%) within the very last few kilometres of ascent. This unconventional degassing path may explain the characteristic pipe, widening-upward from a ?2.5 km deep root zone, where kimberlites are mined for diamonds. Furthermore, we show that small changes in melt chemistry and original volatile composition (H2O vs. CO2) provide a single mechanism to explain the variety of morphologies of kimberlite pipes found over the world. The cooling associated to such massive degassing must freeze a large quantity of melt explaining the occurrence of hypabyssal kimberlite. Finally, we provide strong constraints on the primary volatile content of kimberlite, showing that the water content reported for kimberlite magma is mostly reflective of secondary alteration.
Contributions to Mineralogy and Petrology, Vol. 171, 7, 9p.
Mantle
Carbonatite, kimberlite
Abstract: Kimberlites are rare diamond-bearing volcanic rocks that originate as melts in the Earth’s mantle. The original composition of kimberlitic melt is poorly constrained because of mantle and crustal contamination, exsolution of volatiles during ascent, and pervasive alteration during and after emplacement. One recent model (Russell et al. in Nature 481(7381):352 -356, 2012. doi:10.1038/nature10740) proposes that kimberlite melts are initially carbonatitic and evolve to kimberlite during ascent through continuous assimilation of orthopyroxene and exsolution of CO2. In high-temperature, high-pressure experiments designed to test this model, assimilation of orthopyroxene commences between 2.5 and 3.5 GPa by a reaction in which orthopyroxene reacts with the melt to form olivine, clinopyroxene, and CO2. No assimilation occurs at 3.5 GPa and above. We propose that the clinopyroxene produced in this reaction can react with the melt at lower pressure in a second reaction that produces olivine, calcite, and CO2, which would explain the absence of clinopyroxene phenocrysts in kimberlites. These experiments do not confirm that assimilation of orthopyroxene for the entirety of kimberlite ascent takes place, but rather two reactions at lower pressures (<3.5 GPa) cause assimilation of orthopyroxene and then clinopyroxene, evolving carbonatitic melts to kimberlite and causing CO2 exsolution that drives rapid ascent.
India's fast Mesozoic drift linked to continental mantle lithosphere delamination: new insights from (U-Th)/He thermochronology of Dharwar craton kimberlites.
Proceedings National Academy of Sciences India , Vol. 82, 3, July special issue pp. 515-536.
India
Kimberlites, lamproites
Abstract: Major highlights of researches carried out on kimberlites, lamproites, lamprophyres, carbonatites, other alkaline rocks and mafic dykes from the Indian shield during 2012-2016 are presented. New findings involving field mapping, petrology, geochemistry (including high quality mineral based in situ isotopic studies) and geophysics have provided remarkable insights on the mode of their occurrence, timing of emplacement, mineralogy and bulk-rock composition, redox conditions, relative contribution of the lithosphere and asthenosphere, as well as their economic potential. Several large-scale geodynamic aspects such as plume-lithosphere interactions, ancient subduction events, layered structure of the sub-continental lithospheric mantle, spatial extent of the Precambrian large igneous provinces and supercontinent configurations could be unraveled from these studies on deep-mantle derived small-volume magmatic rocks.
Abstract: We present a new regional model for the depth-averaged density structure of the cratonic lithospheric mantle in southern Africa constrained on a 30? × 30? grid and discuss it in relation to regional seismic models for the crust and upper mantle, geochemical data on kimberlite-hosted mantle xenoliths, and data on kimberlite ages and distribution. Our calculations of mantle density are based on free-board constraints, account for mantle contribution to surface topography of ca. 0.5-1.0 km, and have uncertainty ranging from ca. 0.01 g/cm3 for the Archean terrains to ca. 0.03 g/cm3 for the adjacent fold belts. We demonstrate that in southern Africa, the lithospheric mantle has a general trend in mantle density increase from Archean to younger lithospheric terranes. Density of the Kaapvaal mantle is typically cratonic, with a subtle difference between the eastern, more depleted, (3.31-3.33 g/cm3) and the western (3.32-3.34 g/cm3) blocks. The Witwatersrand basin and the Bushveld Intrusion Complex appear as distinct blocks with an increased mantle density (3.34-3.35 g/cm3) with values typical of Proterozoic rather than Archean mantle. We attribute a significantly increased mantle density in these tectonic units and beneath the Archean Limpopo belt (3.34-3.37 g/cm3) to melt-metasomatism with an addition of a basaltic component. The Proterozoic Kheis, Okwa, and Namaqua-Natal belts and the Western Cape Fold Belt with the late Proterozoic basement have an overall fertile mantle (ca. 3.37 g/cm3) with local (100-300 km across) low-density (down to 3.34 g/cm3) and high-density (up to 3.41 g/cm3) anomalies. High (3.40-3.42 g/cm3) mantle densities beneath the Eastern Cape Fold belt require the presence of a significant amount of eclogite in the mantle, such as associated with subducted oceanic slabs. We find a strong correlation between the calculated density of the lithospheric mantle, the crustal structure, the spatial pattern of kimberlites, and their emplacement ages. (1) Blocks with the lowest values of mantle density (ca. 3.30 g/cm3) are not sampled by kimberlites and may represent the "pristine" Archean mantle. (2) Young (< 90 Ma) Group I kimberlites sample mantle with higher density (3.35 ± 0.03 g/cm3) than the older Group II kimberlites (3.33 ± 0.01 g/cm3), but the results may be biased by incomplete information on kimberlite ages. (3) Diamondiferous kimberlites are characteristic of regions with a low-density cratonic mantle (3.32-3.35 g/cm3), while non-diamondiferous kimberlites sample mantle with a broad range of density values. (4) Kimberlite-rich regions have a strong seismic velocity contrast at the Moho, thin crust (35-40 km) and low-density (3.32-3.33 g/cm3) mantle, while kimberlite-poor regions have a transitional Moho, thick crust (40-50 km), and denser mantle (3.34-3.36 g/cm3). We explain this pattern by a lithosphere-scale (presumably, pre-kimberlite) magmatic event in kimberlite-poor regions, which affected the Moho sharpness and the crustal thickness through magmatic underplating and modified the composition and rheology of the lithospheric mantle to make it unfavorable for consequent kimberlite eruptions. (5) Density anomalies in the lithospheric mantle show inverse correlation with seismic Vp, Vs velocities at 100-150 km depth. However, this correlation is weaker than reported in experimental studies and indicates that density-velocity relationship in the cratonic mantle is strongly non-unique.
Abstract: We want to know when plate tectonics began and will consider any important Earth feature that shows significant temporal evolution. Kimberlites, the primary source of diamonds, are rare igneous features. We analyze their distribution throughout Earth history; most are young (?95% are younger than 0.75 Ga), but rare examples are found as far back as the Archean (older than 2.5 Ga). Although there are differing explanations for this age asymmetry (lack of preservation, lack of exposure, fewer mantle plumes, or lack of old thick lithosphere in the Archean and Proterozoic), we suggest that kimberlite eruptions are a consequence of modern-style plate tectonics, in particular subduction of hydrated oceanic crust and sediments deep into the mantle. This recycling since the onset of modern-style plate tectonics ca. 1 Ga has massively increased mantle CO2 and H2O contents, leading to the rapid and explosive ascent of diamond-bearing kimberlite magmas. The age distribution of kimberlites, combined with other large-scale tectonic indicators that are prevalent only in the past ?1 Ga (blueschists, glaucophane-bearing eclogites; coesite- or diamond-bearing ultrahigh-pressure metamorphic rocks; lawsonite-bearing metamorphic rocks; and jadeitites), indicates that plate tectonics, as observed today, has only operated for <25% of Earth history.
Abstract: Cratons are old and strong continental cores where the lithosphere is thick and remains largely undeformed for 2-3 b.y. Unlike typical cratons, the Wyoming craton underwent pervasive deformation ca. 80-55 Ma during the Laramide orogeny in the west-central United States, and has been subsequently encroached upon by the Yellowstone hotspot since 2.0 Ma. However, the mechanism for the deformation and the craton-hotspot interaction are not well understood. We present here a three-dimensional shear wave velocity model beneath the Wyoming craton constrained from Rayleigh wave data, which reveal new details about the cratonic lithosphere. The average lithosphere thickness beneath the craton is ?150 km, significantly thinner than a normal cratonic root (>200 km). Continuous low velocities are observed beneath the Yellowstone hotspot and the Cheyenne belt. A low-velocity column is also present in the central-eastern craton at depths of 115-250 km. These low velocities can be explained by hot temperature and partial melting, implying mantle upwelling. A high-velocity anomaly with a dripping shape in central Wyoming extends to 200-250 km depth, indicating mantle downwelling and lithosphere erosion. Our model provides the first seismic evidence for complex small-scale mantle convection beneath the Wyoming craton. The convection probably developed during the subduction of the Farallon plate and has been reinforced by the Yellowstone hotspot. We propose that the combination of flat-slab subduction, small-scale convection, and hotspot activity can lead to massive destruction of a cratonic lithosphere.
Journal of Geochemical Exploration, Vol. 173, pp. 99-109.
Africa, Liberia
Kimberlite
Abstract: This report is brief in context and rich in unexpected discovery. With > 2 km of erosion, kimberlite models predict the near-complete removal of pipes with exposures to the pipe-root-zones of dikes. Exploration in NW Liberia has, indeed, uncovered eight kimberlite dikes (~ 10 m wide) but also an en echelon pipe, comparable in size to the Kimberley pipe and De Beers' pipe in South Africa. Discoveries are in a narrow 200-300 m wide valley of extraordinary thick bush, undergrowth, and organic overburden. Ilmenite and co-existing leucoxene were used as diagnostic tracers for detecting hard rock kimberlite in this tropical terrane. Micro-diamonds show that the redox state of ilmenite is a potentially useful proxy as an index for macro-diamond preservation. The tectonic control of kimberlites is complex, with diverse lithologies. Discoveries include a well-defined regional trend for kimberlite dikes along paleo-fracture zones, Precambrian in age (Liberia Trend), coupled with kimberlite dikes on the craton that are traced to Mesozoic oceanic transform faults (the Sierra Leone Trend). Although long predicted, this is the first report of kimberlite dike-trends in Liberia that are similar in orientation to those in Sierra Leone. An explosive blow on a Liberia-Trend dike demonstrates a similarity to the dynamics attendant in rich (50-500 cpht) diamond-bearing dikes in Sierra Leone, and in South Africa of comparable age. The potentially high grade dikes, along with the pipe (~ 500 × 50 m), now more reasonably accounts for the enormous number of alluvial diamonds (blood and non-conflict), recovered over more than seven decades, downstream from the discovery cluster. A neglected region since the classic work by Bardet (1974), and with few contributions on Liberia since then, an update is considered timely, particularly in the context of discoveries of diamond-bearing kimberlite.
International Journal of Mining Science, Vol. 3, 1, pp. 1-28.
Europe, Israel
Kimberlite, Lamproite
Abstract: An integrated analysis of several regional geological and geophysical factors allowed to select the Makhtesh Ramon area (northern Negev, Israel) for sesarching diamondiferous associations. The most important regional factor is the Middle Cretaceous maximum in the development of upper mantle hot spots brightly appearing in this area. Analysis of magnetic (paleomagnetic), self-potential and ionselective data inambogously indicate presence of some bodies possibly having kimberlite (lamproite) origin occurring at small depths (8 - 50 m) in the western Makhtesh Ramon. Repeated erosion processes in the area caused removing most part of sedimentary associations that significantly simplified the processes of mineral sampling and rock withdrawn for geochemical and petrological analyses. Comprehensive mineralogical analyses enabled to detect the following minerals-satellites of diamond associations: chrome-diopside, orange garnet, bright-crimson pyrope, picroilmenite, moissanite, corundum, black spinel, olivine, anatase and tourmaline (including black samples). These minerals do not rolled and oxidized that is an additional evidence of the neighboring occurrence of the indigenous rocks. Data of electronic microscopy show that the grains of (1) picroilmenite and (2) pyrope contain, respectively: (1) cobalt, chrome, magnesium and nickel and (2) chrome, magnesium and aluminum. This indicates that both picroilmenite and pyrope have the hyper-abyssal origin that also is an indicator of the possible occurring of diamondiferous pipes. List of secondary-importance satellite minerals includes feldspars, pyroxenes, magnetite, hematite, ilmenite, galenite, pyrite, limonite, mica, chromite, leucoxene, zircon, rutile, etc. These minerals (by their considering with the first group) are also indicators of diamond-bearing of the studied area. Identification of small plates of gold and silver as well as considerable traces of La, Ce, Th, Nb and Ta (Rare Earth Elements) also may be associated with the nearest kimberlite rock occurrence. The total number of recognized microdiamonds consists of more than 300 units; five diamonds (> 1 mm) were identified (sizes of the most largest crystals are 1.2 and 1.35 mm). Thus, on the basis of a set of geological-geophysical factors and identification of the mentioned minerals we can definitely estimate that the Makhtesh Ramon area is perspective for discovering diamondiferous rocks (kimberlite or lamproite pipes) as well as diamond crystals in loose deposits. Discovered silver- and gold-bearing and REE signatures may have independent importance.
Canadian Journal of Earth Sciences, Vol. 54, pp. 203-232.
Canada, Northwest Territories
kimberlite
Abstract: The Wopmay orogen is a Paleoproterozoic accretionary belt preserved to the west of the Archean Slave craton, northwest Canada. Reworked Archean crystalline basement occurs in the orogen, and new bedrock mapping, U–Pb geochronology, and Sm–Nd isotopic data further substantiate a Slave craton parentage for this basement. Detrital zircon results from unconformably overlying Paleoproterozoic supracrustal rocks also support a Slave craton provenance. Rifting of the Slave margin began at ca. 2.02 Ga with a second rift phase constrained between ca. 1.92 and 1.89 Ga, resulting in thermal weakening of the Archean basement and allowing subsequent penetrative deformation during the Calderian orogeny (ca. 1.88–1.85 Ga). The boundary between the western Slave craton and the reworked Archean basement in the southern Wopmay orogen is interpreted as the rifted cratonic margin, which later acted as a rigid backstop during compressional deformation. Age-isotopic characteristics of plutonic phases track the extent and evolution of these processes that left penetratively deformed Archean basement, Paleoproterozoic cover, and plutons in the west, and “rigid” Archean Slave craton to the east. Diamond-bearing kimberlite occurs across the central and eastern parts of the Slave craton, but kimberlite (diamond bearing or not) has not been documented west of ?114°W. It is proposed that while the crust of the western Slave craton escaped thermal weakening, the mantle did not and was moved out of the diamond stability field. The Paleoproterozoic extension–convergence cycle preserved in the Wopmay orogen provides a reasonable explanation as to why the western Slave craton appears to be diamond sterile.
Abstract: Although kimberlite magma carries large amounts of mantle-derived xenocrysts and xenoliths (with sizes up to meters), this magma ascends from the Earth's mantle (> 150–250 km) to the surface in a matter of hours or days, which enables diamonds to survive. The recently proposed assimilation-fuelled buoyancy model for kimberlite magma ascent emphasizes the importance of fluid CO2 that is produced via the reactive dissolution of mantle-derived orthopyroxene xenocrysts into kimberlite melt, which initially has carbonatitic composition. Here, we use a series of high-pressure experiments to test this model by studying the interaction of orthopyroxene (Opx) with an alkali-dolomitic melt (simplified to 0.7Na2CO3 + 0.3K2CO3 + 2CaMg(CO3)2), which is close to the melt that is produced by the partial melting of a kimberlite source, at P = 3.1–6.5 GPa and T = 1200–1600 °C, i.e., up to pressures that correspond to depths (~ 200 km) from where the ascent of kimberlite magma would start. During the first set of experiments, we study the reaction between powdered Opx and model carbonate melt in a homogeneous mixture. During the second set of experiments, we investigate the mechanism and kinetics of the dissolution of Opx crystals in alkali-dolomitic melt. Depending on the P-T conditions, Opx dissolves in the alkali-dolomitic melt (CL) either congruently or incongruently via the following reactions: Mg2Si2O6 (Opx) + CaMg(CO3)2 (CL) = CaMgSi2O6 (clinopyroxene) + 2MgCO3 (CL) and Mg2Si2O6 (Opx) = Mg2SiO4 (olivine) + SiO2 (CL). The experiments confirm that the dissolution of Opx causes gradual SiO2 enrichment in the initial carbonate melt, as previously suggested. However, the assimilation of Opx by carbonate melt does not produce fluid CO2 in the experiments because the CO2 is totally dissolved in the evolved melt. Thus, our results clearly demonstrate the absence of exsolved CO2 fluid at 3.1–6.5 GPa in ascending kimberlite magma and disprove the assimilation-fuelled buoyancy model for kimberlite magma ascent in the lithospheric mantle. We alternatively suggest that the extreme buoyancy of kimberlite magma at depths of 100–250 km is an exclusive consequence of the unique physical properties (i.e., low density, ultra-low viscosity and, thus, high mobility) of the kimberlite melt, which are dictated by its carbonatitic composition.
Russian Geology and Geophysics, Vol. 58, pp. 1093-1100.
Mantle
kimberlite
Abstract: New experimental data on the temperature and pressure dependences of the viscosity of synthetic hydrous kimberlite melts (82 wt.% silicate + 18 wt.% carbonate; degree of depolymerization: 100NBO/T = 313 for anhydrous melts and 100NBO/T = 247 for melts with 3 wt.% H2O) were obtained at a water pressure of 100 MPa and at lithostatic pressures of 5.5 and 7.5 GPa in the temperature range 1300-1950 °C. The temperature dependence of the viscosity of these melts follows the exponential Arrhenius-Frenkel-Eyring equation in the investigated range of temperatures and pressures. The activation energies of viscous flow for hydrous kimberlite melts were first shown to increase linearly with increasing pressure. Under isothermal conditions (T = 1800 °C), the viscosity of hydrous kimberlite melts increases exponentially by about an order of magnitude as the pressure increases from 100 MPa to 7.5 GPa. The new experimental data on the viscosity of hydrous kimberlite melts (error ± 30 rel.%) are compared with forecast viscosity data for anhydrous kimberlite and basaltic melts (100NBO/T = 51.5) and for hydrous basaltic melts (100NBO/T = 80). It is shown that at comparable temperatures, the viscosity of hydrous kimberlite melts at a moderate pressure (100 MPa) is about an order of magnitude lower than the viscosity of hydrous basaltic melts, whereas at a high pressure (7.5 GPa) it is more than twice higher. It is first established that water dissolution in kimberlite melts does not affect seriously their viscosity (within the measurement error) at both moderate (100 MPa) and high (7.5 GPa) pressures, whereas the viscosity of basaltic melts considerably decreases with water dissolution at moderate pressures (100 MPa) and remains unchanged at high pressures (P > 3.5 GPa).
Doklady Earth Sciences, Vol. 477, 1, pp. 1291-1294.
Russia
kimberlite, alnoite, carbonatite
Abstract: The results of geochemical typification of kimberlites and related rocks (alneites and carbonatites) of the North Anabar region are presented with consideration of the geochemical specification of their source and estimation of their potential for diamonds. The content of representative trace elements indicates the predominant contribution of an asthenospheric component (kimberlites and carbonatites) in their source, with a subordinate contribution of vein metasomatic formations containing Cr-diopside and ilmenite. A significant contribution of water-bearing potassium metasomatic parageneses is not recognized. According to the complex of geochemical data, the studied rocks are not industrially diamondiferous.
Earth and Planetary Science Letters, Vol. 484, pp. 1-14.
Mantle
kimberlite, origin, magmatism
Abstract: Kimberlite magmatism has occurred in cratonic regions on every continent. The global age distribution suggests that this form of mantle melting has been more prominent after 1.2 Ga, and notably between 250-50 Ma, than during early Earth history before 2 Ga (i.e., the Paleoproterozoic and Archean). Although preservation bias has been discussed as a possible reason for the skewed kimberlite age distribution, new treatment of an updated global database suggests that the apparent secular evolution of kimberlite and related CO2-rich ultramafic magmatism is genuine and probably coupled to lowering temperatures of Earth's upper mantle through time. Incipient melting near the CO2- and H2O-bearing peridotite solidus at >200 km depth (1100-1400?°C) is the petrologically most feasible process that can produce high-MgO carbonated silicate melts with enriched trace element concentrations akin to kimberlites. These conditions occur within the convecting asthenospheric mantle directly beneath thick continental lithosphere. In this transient upper mantle source region, variable CHO volatile mixtures control melting of peridotite in the absence of heat anomalies so that low-degree carbonated silicate melts may be permanently present at ambient mantle temperatures below 1400?°C. However, extraction of low-volume melts to Earth's surface requires tectonic triggers. Abrupt changes in the speed and direction of plate motions, such as typified by the dynamics of supercontinent cycles, can be effective in the creation of lithospheric pathways aiding kimberlite magma ascent. Provided that CO2- and H2O-fluxed deep cratonic keels, which formed parts of larger drifting tectonic plates, existed by 3 Ga or even before, kimberlite volcanism could have been frequent during the Archean. However, we argue that frequent kimberlite magmatism had to await establishment of an incipient melting regime beneath the maturing continents, which only became significant after secular mantle cooling to below 1400?°C during post-Archean times, probably sometime shortly after 2 Ga. At around this time kimberlites replace komatiites as the hallmark mantle-derived magmatic feature of continental shields worldwide. The remarkable Mesozoic-Cenozoic ‘kimberlite bloom’ between 250-50 Ma may represent the ideal circumstance under which the relatively cool and volatile-fluxed cratonic roots of the Pangea supercontinent underwent significant tectonic disturbance. This created more than 60% of world's known kimberlites in a combination of redox- and decompression-related low-degree partial melting. Less than 2% of world's known kimberlites formed after 50 Ma, and the tectonic settings of rare ‘young’ kimberlites from eastern Africa and western North America demonstrate that far-field stresses on cratonic lithosphere enforced by either continental rifting or cold subduction play a crucial role in enabling kimberlite magma transfer to Earth's surface.
Abstract: A classification suggested for alkaline ultramafic rocks of the Ary-Mastakh and Staraya Rechka fields, Northern Anabar Shield, is based on the modal mineralogical composition of the rocks and the chemical compositions of their rock-forming and accessory minerals. Within the framework of this classification, the rocks are indentified as orangeite and alkaline ultramafic lamprophyres: aillikite and damtjernite. To estimate how much contamination with the host rocks has modified their composition when the diatremes were formed, the pyroclastic rocks were studied that abound in xenogenic material (which is rich in SiO2, Al2O3, K2O, Rb, Pb, and occasionally also Ba) at relatively low (La/Yb)PM, (La/Sm)PM, and not as much also (Sm/Zr)PM and (La/Nb)PM ratios. The isotopic composition of the rocks suggests that the very first melt portions were of asthenospheric nature. The distribution of trace elements and REE indicates that one of the leading factors that controlled the diversity of the mineralogical composition of the rocks and the broad variations in their isotopic-geochemical and geochemical characteristics was asthenosphere-lithosphere interaction when the melts of the alkaline ultramafic rocks were derived. The melting processes involved metasomatic vein-hosted assemblages of carbonate and potassic hydrous composition (of the MARID type). The alkaline ultramafic rocks whose geochemistry reflects the contributions of enriched vein assemblages to the lithospheric source material, occur in the northern Anabar Shield closer to the boundary between the Khapchan and Daldyn terranes. The evolution of the aillikite melts during their ascent through the lithospheric mantle could give rise to damtjernite generation and was associated with the separation of a C-H-O fluid phase. Our data allowed us to distinguish the evolutionary episodes of the magma-generating zone during the origin of the Triassic alkaline ultramafic rocks in the northern Anabar Shield.
Canadian Journal of Earth Science, Vol. 55, pp. 130-137.
Global
Kimberlite morphology
Abstract: We use analogue experimentation to test the hypothesis that host rock competence primarily determines the morphology of kimberlite pipes. Natural occurrences of kimberlite pipes are subdivided into three classes: class 1 pipes are steep-sided diatremes emplaced into crystalline rock; class 2 pipes have a wide, shallow crater emplaced into sedimentary rock overlain by unconsolidated sediments; class 3 pipes comprise a steep-sided diatreme with a shallow-angled crater emplaced into competent crystalline rock overlain by unconsolidated sediments. We use different configurations of three analogue materials with varying cohesions to model the contrasting geological settings observed in nature. Pulses of compressed air, representing the energy of the gas-rich head of a kimberlitic magma, are used to disrupt the experimental substrate. In our experiments, the competence and configuration of the analogue materials control the excavation processes as well as the final shape of the analogue pipes: eruption through competent analogue strata results in steep-sided analogue pipes; eruption through weak analogue strata results in wide, shallow analogue pipes; eruption through intermediate strength analogue strata results in analogue pipes with a shallow crater and a steep-sided diatreme. These experimental results correspond with the shapes of natural kimberlite pipes, and demonstrate that variations in the lithology of the host rock are sufficient to generate classic kimberlite pipe shapes. These findings are consistent with models that ascribe the pipe morphologies of natural kimberlites to the competence of the host rocks in which they are emplaced.
Abstract: The cratonic part of Greenland has been a hotspot of scientific investigation since the discovery of some of the oldest crust on Earth and of significant diamond potential in the underlying lithospheric mantle, the characterization of which remains, however, incomplete. We applied a detailed petrographic and in situ analytical approach to a new suite of fresh kimberlite-borne peridotite xenoliths, recovered from the North Atlantic craton in SW Greenland, to unravel the timing and nature of mantle metasomatism, and its link to the formation of low-volume melts (e.g. kimberlites) and to geophysically detectible discontinuities. Two types of mineralogies and metasomatic styles, occurring at two depth intervals, are recognized. The first type comprises lherzolites, harzburgites and dunites, some phlogopite-bearing, which occur from ?100-170?km depth. They form continuous trends towards lower mineral Mg# at increasing TiO2, MnO and Na2O and decreasing NiO contents. These systematics are ascribed to metasomatism by a hydrous silicate melt precursor to c. 150?Ma kimberlites, in the course of rifting, decompression and lithosphere thinning. This metasomatism was accompanied by progressive garnet breakdown, texturally evident by pyroxene-spinel assemblages occupying former coarse grains and compositionally evident by increasing concentrations of elements that are compatible in garnet (Y, Sc, In, heavy rare earth elements) in newly formed clinopyroxene. Concomitant sulphide saturation is indicated by depletion in Cu, Ni and Co. The residual, more silica-undersaturated and potentially more oxidizing melts percolated upwards and metasomatized the shallower lithospheric mantle, which is composed of phlogopite-bearing, texturally equilibrated peridotites, including wehrlites, showing evidence for recent pyroxene-breakdown. This is the second type of lithology, which occurs at ?90-110?km depth and is inferred to have highly depleted protoliths. This type is compositionally distinct from lherzolites, with olivine having higher Ca/Al, but lower Al and V contents. Whereas low Al may in part reflect lower equilibration temperatures, low V is ascribed to a combination of intrinsically more oxidizing mantle at lower pressure and oxidative metasomatism. The intense metasomatism in the shallow cratonic mantle lithosphere contrasts with the strong depletion recorded in the northwestern part of the craton, which at 590-550?Ma extended to >210?km depth, and suggests loss of ?40?km of lithospheric mantle, also recorded in the progressive shallowing of magma sources during the breakup of the North Atlantic craton. The concentration of phlogopite-rich lithologies in a narrow depth interval (?90-110?km) overlaps with a negative seismic velocity gradient that is interpreted as a mid-lithospheric discontinuity beneath western Greenland. This is suggested to be a manifestation of small-volume volatile-rich magmatism, which paved the way for Mesozoic kimberlite, ultramafic lamprophyre, and carbonatite emplacement across the North Atlantic craton.
Mineralogy and Petrology, in press available, 11p.
Mantle
kimberlite ascent
Abstract: The sustained transportation of particles in a suspension commonly results in particle attrition leading to grain size reduction and shape modification. Particle attrition is a well-studied phenomenon that has mainly focussed on sediments produced in aeolian or fluvial environments. Here, we present analogue experiments designed to explore processes of attrition in the kimberlite system; we focus on olivine as it is the most abundant constituent of kimberlite. The attrition experiments on olivine use separate experimental set-ups to approximate two natural environments relevant to kimberlites. Tumbling mill experiments feature a low energy system supporting near continual particle-particle contact and are relevant to re-sedimentation and dispersal processes. Experiments performed in a fluidized particle bed constitute a substantially higher energy environment pertinent to kimberlite ascent and eruption. The run-products of each experiment are analysed for grain size reduction and shape modification and these data are used to elucidate the rates and extents of olivine attrition as a function of time and energy. Lastly, we model the two experimental datasets with an empirical rate equation that describes the production of daughter products (fines) with time. Both datasets approach a fines production limit, or plateau, at long particle residence times; the fluidized system is much more efficient producing a substantially higher fines content and reaches the plateau faster. Our experimental results and models provide a way to forensically examine a wide range of processes relevant to kimberlite on the basis of olivine size and shape properties.
Contributions to Mineralogy and Petrology, 10.1007/ s00410-018- 1480-3, 27p.
Russia, Siberia
kimberlite
Abstract: We studied olivines from the Devonian pre-trap (the Ilbokich occurrence) and the Triassic post-trap (the Chadobets occurrence) carbonate-rich ultramafic lamprophyres (UMLs) in the southwestern portion of the Siberian craton. On the basis of detailed investigations of major, minor, and trace-element distributions, we have reconstructed the main processes that control the origins of these olivines. These include fractional crystallisation from melt, assimilation, and fractional crystallisation processes with orthopyroxene assimilation, melt-reaction diffusive re-equilibration, alkali enrichment, and CO2 degassing of the melt. Furthermore, we inferred the composition of the sources of the primary UML melt and their possible correlations with proto-kimberlitic melts, as well as the influence of the Triassic Siberian plume on the composition of the lithospheric mantle. The main differences between olivines from the Ilbokich and the Chadobets aillikites were that the olivines from the former had more magnesium-rich cores (Mg# = 89.2 ± 0.2), had Mg- and Cr-rich transition zones (Mg# = 89.7 ± 0.2 and 300-500 ppm Cr), had lower Ni (up to 3100 ppm) and Li (1.4-1.5 ppm), and had higher B (0.8-2.6 ppm) contents, all at higher Fo values (90-86), relative to the olivines from the latter (Mg# = 88-75; 200-300 ppm Cr; up to 3400 ppm Ni; 1.4-2.4 ppm Li; 0.4-2.2 ppm B). The Siberian aillikite sources contained a significant amount of metasomatic material. Phlogopite-rich MARID-type veins provided the likely metasomatic component in the pre-trap Devonian Ilbokich aillikite source, whereas the Triassic Chadobets aillikitic post-trap melts were derived from a source with a significant carbonate component. A comparison of UML olivines with olivines from the pre-trap and post-trap Siberian kimberlites shows a striking similarity. This suggests that the carbonate component in the aillikitic source could have been produced by evolved kimberlite melts. The differences in the lithospheric metasomatic component that contributed to pre-trap and post-trap aillikitic melts can be interpreted as reflections of the thermal impact of the Siberian Traps, which reduced phlogopite-bearing metasomes within the southwestern Siberian sub-continental lithospheric mantle.
Earth and Planetary Science Letters, Vol. 481, 1, pp. 143-153.
Mantle
kimberlite
Abstract: Rare garnet crystals from a peridotite xenolith from the Wesselton kimberlite, South Africa, have distinct zones related to two separate episodes of mantle metasomatism. The garnet cores were firstly depleted through melt extraction, then equilibrated during metasomatism by a potentially diamond-forming carbonate-bearing or proto-kimberlitic fluid at 1100-1300?°C and 4.5-5.5 GPa. The garnet rim chemistry, in contrast, is consistent with later overgrowth in equilibrium with a kimberlite at around and . This suggests that the rock was physically moved upwards by up to tens of kilometres between the two metasomatic episodes. Preserved high Ca, Al and Cr contents in orthopyroxenes suggest this uplift was tectonic, rather than magmatic. Diffusion profiles were measured over the transitions between garnet cores and rims using electron microprobe (Mg, Ca, Fe for modelling, plus Cr, Mn, Ti, Na, Al) and nano Secondary Ion Mass Spectrometry (NanoSIMS; 89Y, along with 23Na, Ca, Cr, Fe, Mn and Ti) analyses. The short profile lengths (generally <10 ?m) and low Y concentrations (0.2-60 ppm) make the NanoSIMS approach preferable. Diffusion profiles at the interface between the zones yield constraints on the timescale between the second metasomatic event and eruption of the kimberlite magma that brought the xenolith to the surface. The time taken to form the diffusion profiles is on the order of 25 days to 400 yr, primarily based on modelling of Y diffusion along with Ca, Fe and Mg (multicomponent diffusion) profiles. These timescales are too long to be produced by the interaction of the mantle xenolith with the host kimberlite magma during a single-stage ascent to the crust (hours to days). The samples offer a rare opportunity to study metasomatic processes associated with failed eruption attempts in the cratonic lithosphere.
International Journal of Earth Sciences, Vol. 107, 7, pp. 2627-2633.
Africa, Botswana
kimberlites
Abstract: Glassy beads were found in the sand cover associated with known and suspected kimberlites on the Kalahari plateau, Botswana. Morphology and chemistry were examined by ESEM and EDAX. The polymetallic and quartzose "beads", here described for the first time and termed fulguroids, formed at very high temperatures, well in excess of those reached by the kimberlites. They solidified in free fall. We propose that they were melted in the atmosphere by lightning strikes on Kalahari overburden entrained when the kimberlites erupted.
Mineralogy and Petrology, doi:10.1007/ s00710-018-0568-9 15p.
Africa, South Africa
deposit - Group I, orangeites Group II
Abstract: The West Coast of Namaqualand in South Africa hosts extensive detrital diamond deposits, but considerable debate exists as to the provenance of these diamonds. Some researchers have suggested derivation of the diamonds from Cretaceous-Jurassic kimberlites (also termed Group I kimberlites) and orangeites (also termed Group II kimberlites) located on the Kaapvaal Craton. However, others favour erosion of diamonds from the ca.300 Ma Dwyka Group sediments, with older, pre-Karoo kimberlites being the original source(s). Previous work has demonstrated that 40Ar/39Ar analyses of clinopyroxene inclusions, extracted from diamonds, yield ages approaching the time(s) of source kimberlite emplacement, which can be used to constrain the provenance of placer diamond deposits. In the current study, 40Ar/39Ar analyses were conducted on clinopyroxene inclusions from two similar batches of Namaqualand detrital diamonds, yielding (maximum) ages ranging from 117.5?±?43.6 Ma to 3684?±?191 Ma (2s) and 120.6?±?15.4 Ma to 688.8?±?4.9 Ma (2s), respectively. The vast majority of inclusions (88%) produced ages younger than 500 Ma, indicating that most Namaqualand diamonds originated from Cretaceous-Jurassic kimberlites/orangeites, with few, if any, derived from the Dwyka tillites. The provenance of the Namaqualand diamonds from ca.115-200 Ma orangeites is consistent with Late Cretaceous paleo-drainage reconstructions, as these localities could have been sampled by the ‘paleo-Karoo’ River and transported to the West Coast via an outlet close to the current Olifants River mouth. At ca.90 Ma, this drainage system appears to have been captured by the ‘paleo-Kalahari’ River, a precursor to the modern Orange River system. This latter drainage is considered to have transported diamonds eroded from both ca.80-90 Ma kimberlites and ca.115-200 Ma orangeites to the West Coast, which were subsequently reworked along the Namibian coast, forming additional placer deposits.
Mineralogy and Petrology, doi:10.1007/ s00710-018-0568-9 15p.
Africa, South Africa
deposit - Group I, orangeites Group II
Abstract: The West Coast of Namaqualand in South Africa hosts extensive detrital diamond deposits, but considerable debate exists as to the provenance of these diamonds. Some researchers have suggested derivation of the diamonds from Cretaceous-Jurassic kimberlites (also termed Group I kimberlites) and orangeites (also termed Group II kimberlites) located on the Kaapvaal Craton. However, others favour erosion of diamonds from the ca.300 Ma Dwyka Group sediments, with older, pre-Karoo kimberlites being the original source(s). Previous work has demonstrated that 40Ar/39Ar analyses of clinopyroxene inclusions, extracted from diamonds, yield ages approaching the time(s) of source kimberlite emplacement, which can be used to constrain the provenance of placer diamond deposits. In the current study, 40Ar/39Ar analyses were conducted on clinopyroxene inclusions from two similar batches of Namaqualand detrital diamonds, yielding (maximum) ages ranging from 117.5?±?43.6 Ma to 3684?±?191 Ma (2s) and 120.6?±?15.4 Ma to 688.8?±?4.9 Ma (2s), respectively. The vast majority of inclusions (88%) produced ages younger than 500 Ma, indicating that most Namaqualand diamonds originated from Cretaceous-Jurassic kimberlites/orangeites, with few, if any, derived from the Dwyka tillites. The provenance of the Namaqualand diamonds from ca.115-200 Ma orangeites is consistent with Late Cretaceous paleo-drainage reconstructions, as these localities could have been sampled by the ‘paleo-Karoo’ River and transported to the West Coast via an outlet close to the current Olifants River mouth. At ca.90 Ma, this drainage system appears to have been captured by the ‘paleo-Kalahari’ River, a precursor to the modern Orange River system. This latter drainage is considered to have transported diamonds eroded from both ca.80-90 Ma kimberlites and ca.115-200 Ma orangeites to the West Coast, which were subsequently reworked along the Namibian coast, forming additional placer deposits.
Mineralogy and Petrology, doi.org/10.1007/ s00710-018-0628-1 14p.
Africa, Angola
kimberlites
Abstract: Based on a comprehensive analysis of kimberlite pipes of Angola, including the near surface structural setting, deep lithospheric structure, pipe morphology and emplacement, mineralogical and petrographic features, diamond characteristics and locations of secondary deposits four geographical regions have been outlined within Angola representing four types of diamond bearing potential. These areas include high diamond bearing potential pipes, possible potential, no potential, and unclear potential areas. It was found that the depth of magmatism and diamond potential of kimberlites increases from the Atlantic coast in southwestern Angola into the continent in the north-easterly direction. Areas prospective for the discovery of new primary diamond deposits have been identified.
Earth and Planetary Science Letters, Vol. 502, pp. 244-252.
Russia, Canada, Ontario, Attawapiskat
kimberlite, core boundary
Abstract: Mantle plumes are hot buoyant upwellings that rise from Earth's core-mantle-boundary to its surface where they can produce large igneous provinces (LIPs) and volcanic tracks, such as the Siberian Traps and the Hawaiian Emperor chain, respectively. We show that flattened mantle plume heads, which can have radii of >1200 km in the uppermost mantle, can heat the overlying lithospheric mantle to temperatures above the diamond stability field. As a consequence, they can destroy diamonds within the roots of Archean cratons, the principal source of diamonds in kimberlites. We quantitatively demonstrate that there is a ‘sour spot’ for this effect that occurs when lithospheric thicknesses are 165-185 km and the plume has a temperature of >150?°C above background mantle. Our model explains why the kimberlites associated with the 370 Ma Yakutsk-Vilyui plume in the Siberian craton are diamondiferous whilst those associated with the younger 250 Ma Siberian Traps plume are barren. We also show that the time required to restore the pre-plume thermal structure of the lithosphere is ca. 75-120 Myr, and that destroyed diamonds may regrow once the plume's thermal effect dissipates. The 1100 Ma Kyle Lake and adjacent 180-150 Ma Attawapiskat kimberlites in the southern Superior craton exemplify this, where the older kimberlites are associated with a narrower diamond window (<30 km) in comparison with the ca. 85 km diamond window of the younger Attawapiskat field.
Geological Society of America Annual Meeting, Vol. 50, 4, 1p. Abstract
United States, Kansas
kimberlite
Abstract: The Critical Zone is the realm where rocks meet life. This study examines the physicochemical interactions that occur when interbedded limestone-shale systems and kimberlitc eruptive materials weather to form soils. Fast weathering with extensive soil loss has been a major environmental concern in the Flint Hills. Knowledge of soil formation processes, rates of formation and loss and understanding how these processes differ in different systems are critical for managing soil as a resource. The kimberlites of Riley County, KS, are CO2-rich igneous rocks that are high in Mg and Fe; they are compositionally distinct from the Paleozoic limestones and shales found throughout the rest of the region. Bulk composition and mineralogy of the soils overlying these different bedrock types have been analyzed using X-Ray Fluorescence (XRF), X-Ray diffraction of <2mm soil fraction and <2µm soil clay fraction, bulk elemental extraction, and particle size analyses. Results show that the kimberlitic soils have higher concentrations of Fe, Mg, Ca, K and some trace elements (e.g. Ti, Ni, Cu). The weathering products differ mineralogically as well, e.g. lizardite is abundant in kimberlitic soils and absent from the limestone terrane. As a result, kimberlite-sourced soils have significantly different physical properties than the thin limestone-sourced soils surrounding them. Particle size analysis shows that the limestone-shale soils have a higher proportion of silt-sized particles whereas the kimberlitic soils have more clay (10.55% vs. 8.06%) and significantly more sand (36.12% vs. 14.83%). Mineralogy was determined for all <2mm fractions and for some <2µm soil clay fraction to understand the association and mobility of these major and trace elements in the respective soils. Interestingly some of the similarities between the kimberlite and limestone-shale soils suggests that loess/wind-blown sediment is making a significant contribution to the soil profile. Kimberlite-sourced and limestone-shale-sourced soils produce different weathering products and could potentially have agricultural significance in terms of ionic and nutrient mobility.
Abstract: Porphyritic olivine kimberlitic breccia, discovered in the Dörbed Banner of Inner Mongolia, Western China, is referred to as Longtou Shan Kimberlite in our study. This kimberlite occurs as a pipe in the Halahuogete Formation of Bayan Obo Group. Zircon U-Pb ages of Longtou Shan Kimberlite reveals a Mesoproterozoic age of ~1,552 Ma, constraining the deposition age of Halahuogete Formation to the Mesoproterozoic. Compared with Mesoproterozoic kimberlite of the ancient landmass, it can be inferred that the North China Craton is a member of the Ur ancient continent of the Columbia supercontinent. Furthermore, according to the tectonic background of the Bayan Obo Group, we raise this possibility that “Bayan Obo Aulacogen” should be renamed the "Bayan Obo Continental Rift."
Earth and Planetary Science Letters, Vol. 506, pp. 38-52.
Mantle
kimberlite genesis
Abstract: Low-degree partial melts from deeply subducted, carbonated ocean crust are carbonatite liquids with ?35-47 wt% CO2. Their reactions with the overlying mantle regulate the slab-mantle interaction and carbon transport in the deep upper mantle but have not been investigated systematically. Here we present new multi-anvil experiments and parameterized phase relation models to constrain the fate of slab-derived carbonatite melts in the upper mantle. The experiments were conducted at 7 GPa/1400 °C and 10 GPa/1450 °C, and used starting compositions mimicking the ambient mantle infiltrated by variable carbonatite fluxes (0-45 wt%) from the slab surface. Kimberlitic melts (CO2 = 14-32 wt%, SiO2 = 15-33 wt%, and MgO = 20-29 wt%) were produced from experiments with 5.8-25.6 wt% carbonatite influxes. Experimental phase relations demonstrate a reactive melting process in which the carbonatite influx increases in proportion by dissolution of olivine, orthopyroxene, garnet and precipitation of clinopyroxene. This manifests a feasible mechanism for slab-derived carbonatite melts to efficiently transport in the ambient mantle through high-porosity channels. The melt and mineral fractions from this study and previous phase equilibria experiments in peridotite + O systems were empirically parameterized as functions of temperature (900-2000 °C), pressure (3-20 GPa), and bulk compositions (e.g., CO2 = 0.9-17.1 wt% and Na2O + K2O = 0.27-2.51 wt%). Applications of the phase relation models to prescribed melting processes indicate that reactive melting of a carbonatite-fluxed mantle source could produce kimberlitic melts with diverse residual lithologies under various melting conditions. However, reactive melting at the slab-mantle interface can only commence when the slab-released carbonatite melt conquers the carbonation freezing front, i.e., the peridotite solidi suppressed by infiltration of CO2-rich melts in an open system. Depending on temperatures and local influxes, reactive melting and carbonation/redox freezing can occur simultaneously above the slab-mantle interface, yielding heterogeneous lithologies and redox conditions as well as various time-scales of carbon transport in Earth's mantle.
Abstract: Kimberlite magmas entrain, transport and erupt large volumes of mantle-derived olivine grains. Characteristically, the olivine crystals found in kimberlite are rounded and ellipsoidal in shape. The origin of their ellipsoidal morphologies remains somewhat enigmatic given their origin from disaggregation of lithospheric mantle rocks. Explanations include rounding by magmatic corrosion and dissolution (Kamenetsky et al. 2008; Pilbeam et al. 2013) or mechanical milling (Arndt et al. 2006; Arndt et al. 2010; Russell et al. 2012; Jones et al. 2014; Brett et al. 2015). Here, we focus on mechanical processes that operate during turbulent mantle ascent, facilitating reshaping and resurfacing of olivine. During transport orthopyroxene and other mantle minerals are assimilated by the kimberlite magma. One effect of the assimilation is to raise the melt’s SiO2 content, thereby causing a reduction in CO2 solubility and the spontaneous exsolution of a CO2-dominated fluid phase (Brooker et al. 2011; Russell et al. 2012; Moussallam et al. 2015). This assimilation-driven exsolution of a fluid phase provides a continuous decrease in density, an increase in buoyancy, and an accelerating ascent. Additionally, there is strong evidence that, during kimberlite magma ascent through the mantle lithosphere, substantial mechanical modification of the suspended cargo occurs (Jones et al. 2014; Brett et al. 2015). Brett et al. (2015) hypothesized that the ascending dyke segregates into a turbulent gas-rich head where particleparticle interactions dominate followed by a trailing tail of less gas-charged magma. This ascending dyke continually modifies its cargo from initial disaggregation to ultimately, eruption. Here, we present data from a series of novel, scaled, analogue attrition experiments that inform on the rates, efficiency and timings of mechanical modification possible during transport through the mantle lithosphere.
Abstract: In situ U-Pb and Hf analyses were used for crustal zircon xenocrysts from Triassic kimberlites exposed in the Rangnim Massif of North Korea to identify components of the basement hidden in the deep crust of the Rangnim Massif and to clarify the crustal evolution of the massif. The U-Pb age spectrum of the zircons has a prominent population at 1.9-1.8 Ga and a lack of Archaean ages. The data indicate that the deep crust and basement beneath the Rangnim Massif are predominantly of Palaeoproterozoic age, consistent with the ages of widely exposed Palaeoproterozoic granitic rocks. In situ zircon Hf isotope data show that most of the Palaeoproterozoic zircon xenocrysts have negative ?Hf ( t ) values (?9.7 to +0.7) with an average Hf model age of 2.86 ± 0.02 Ga (2 ? ), which suggests that the Palaeoproterozoic basement was not juvenile but derived from the reworking of Archaean rocks. Considering the existence of Archaean remanent material in the Rangnim Massif and their juvenile features, a strong crustal reworking event is indicated at 1.9-1.8 Ga, during which time the pre-existing Archaean basement was exhausted and replaced by a newly formed Palaeoproterozoic basement. These features suggest that the Rangnim Massif constitutes the eastern extension of the Palaeoproterozoic Liao-Ji Belt of the North China Craton instead of the Archaean Liaonan Block as previously thought. A huge Palaeoproterozoic orogen may exist in the eastern margin of the Sino-Korean Craton.
Contributions to Mineralogy and Petrology, Vol. 174, 23p.
Europe, Greenland
kimberlites
Abstract: We report highly siderophile element (HSE) abundances and Re-Os isotope compositions, obtained by isotope dilution inductively coupled plasma mass spectrometry, of olivine separates from a suite of multiply metasomatised peridotite xenoliths entrained in kimberlites from SW Greenland. Combined with petrographic and compositional observations on accessory base metal sulphides (BMS), the results reveal new insights into the chemical, physical and mineralogical effects of multi-stage rifting and associated melt percolation on the Archaean lithospheric mantle. Refertilised lherzolites are dominated by rare to frequent small (tens of µm) BMS inclusions in olivine, whereas modally metasomatised phlogopite-bearing lherzolite and wehrlites have higher proportions of more Ni-rich BMS, including abundant large interstitial grains (hundreds of µm). The olivine separates display depleted HSE systematics with Primitive Upper Mantle (PUM)-normalised Pd/Ir of 0.014-0.62, and have both depleted and enriched 187Os/188Os (0.1139-0.2724) relative to chondrite that are not correlated with 187Re/188Os. Four out of ten olivine separates retain similarly depleted Os corresponding to Re-depletion model ages of 2.1-1.8 Ga. They may reflect Palaeoproterozoic refertilisation (lherzolitisation) during Laurentia plate assembly, with re-introduction of clinopyroxene and Os-rich BMS into the originally refractory mantle lithosphere by asthenosphere-derived basaltic melts, followed by recrystallisation and occlusion in olivine. Unradiogenic Os is observed regardless of lithology, including from peridotites that contain abundant interstitial BMS. This reflects addition of Os-poor BMS (<1 ppm) during more recent wehrlitisation and phlogopite-introduction, and control of the Os isotopic signature by older Os-rich BMS that precipitated from the basaltic melt. Depletions in compatible HSE (0.5?×?PUM for Ru, Ir, Os) in all but one olivine separate reflect nugget effects (amount of depleted vs. metasomatic BMS inclusions) and/or loss due to sulphide dissolution into oxidising small-volume melts that invaded the lithosphere during recurrent rifting, the latter supported by similar depletions in published bulk peridotite data. Combined, these multiple metasomatic events destroyed all vestiges of Mesoarchaean or older inheritance in the olivine separates investigated here, and highlight that caution is needed when interpreting Proterozoic Os model ages in terms of Proterozoic lithosphere stabilisation.
Abstract: Primary melt composition of kimberlites remains poorly constrained due to the contamination from mantle and crustal rocks, loss of volatiles during emplacement, significant alteration, and the lack of any quenched melts. Additionally, kimberlite bodies have multiple morphologies of which their emplacement mechanism remains elusive. Apatite is a common accessory mineral in kimberlite. Its structure incorporates many trace elements of which partitioning depends on the composition of the melt. Concentrations of trace elements in kimberlitic apatite can help to assess the content of carbonate and silicate components in kimberlite melt. Apatite is also often used as an indicator mineral of magma degassing in igneous systems. As such, it should be applied to kimberlitic systems to study the volatile behaviour during emplacement. However, the existing estimates for the trace elements partitioning in apatite provide controversial estimates for carbonatitic melts and estimates for silicate melts use compositions very different than the composition of kimberlites. This study experimentally determines partition coefficients of trace elements and kimberlite-like melts. The experiments were done in piston cylinder apparatus at 1250-1350 °C and 1-2 Gpa. Partition coefficients for Nb, Sr, Rb, Zr, Sm, Cs, Hf, La, Yb, and Eu were examined in synthetic compositions representing evolved kimberlite melts: three lamproitic compositions (17-23 wt % SiO2 and 9-33 wt % CO2) and a composition modelled after a magmatic kimberlite (14-29 wt % SiO2 and 7-33 wt % CO2). The effects of melt composition, temperature, pressure, water, and oxygen fugacity have been tested. The obtained partition coefficients were applied to natural kimberlitic apatites from Ekati Mine (Canada) and Orapa cluster (Botswana) to model kimberlite melt composition. Observed variation in the presence, textures, and composition of natural apatites relative to depth in kimberlite pipes of differing lithologies is compared to experimental run products to infer crystallization conditions of different kimberlite bodies.
Frontiers in Earth Science, Vol. 7, pp. 134-145. pdf
Global
kimberlite genesis
Abstract: Kimberlite magmas transport cratonic mantle xenoliths and diamonds to the Earth's surface. However, the mechanisms supporting the successful and efficient ascent of these cargo-laden magmas remains enigmatic due to the absence of historic eruptions, uncertainties in melt composition, and questions concerning their rheology. Mantle-derived xenocrystic olivine is the most abundant component in kimberlite and is uniquely rounded and ellipsoidal in shape. Here, we present data from a series of attrition experiments designed to inform on the transport of low-viscosity melts through the mantle lithosphere. The experimental data suggest that the textural properties of the mantle-derived olivine are records of the flow regime, particle concentration, and transport duration of ascent for kimberlitic magmas. Specifically, our results provide evidence for the rapid and turbulent ascent of kimberlite during their transit through the lithosphere; this transport regime creates mechanical particle-particle interactions that, in combination with chemical processes, continually modify the mantle cargo and facilitate mineral assimilation.
Brazil Journal of Geology, Vol. 47, 3, pp. 383-401. pdf
South America, Brazil
kimberlites, kamafugites, Tres Ranchos, Coromandel
Abstract: Magmatism associated with the Alto Paranaíba structural high comprises kimberlites, kamafugites, and alkaline complexes, forming an approximately 400 x 150 km NW-SE belt in the southern São Francisco Craton. Dating of some intrusions reveals ages between 120 and 75 Ma. Chemical analyses of garnet recovered in alluvium from traditional diamond digging areas indicate peridotitic garnet windows in Três Ranchos and Coromandel. Six hundred and eighty (680) diamonds acquired or recovered during mineral exploration in the digging areas of Romaria, Estrela do Sul, Três Ranchos and Coromandel show unique characteristics, certain populations indicating young, proximal and primary sources (YPP). Analyses of 201 stones from Santo Antônio do Bonito, Santo Inácio and Douradinho rivers alluvium, Coromandel, present no evidence of transport, characterizing a proximal source. Within these river basins, exposures of the Late Cretaceous Capacete Formation basal conglomerate contain mainly small rounded and/or angular quartzite pebbles and of basic and ultrabasic rocks, as well as kimberlite minerals (garnet, ilmenite, spinel, sometimes diamond). A magnetotelluric profile between the Paraná and Sanfranciscana basins shows that the thick underlying lithosphere in the Coromandel region coincides with the peridotitic garnet window and with a diamond population displaying proximal source characteristics. Diamond-bearing kimberlite intrusions occur in different areas of Alto Paranaíba.
Abstract: n situ U-Pb and Hf analyses were used for crustal zircon xenocrysts from Triassic kimberlites exposed in the Rangnim Massif of North Korea to identify components of the basement hidden in the deep crust of the Rangnim Massif and to clarify the crustal evolution of the massif. The U-Pb age spectrum of the zircons has a prominent population at 1.9-1.8 Ga and a lack of Archaean ages. The data indicate that the deep crust and basement beneath the Rangnim Massif are predominantly of Palaeoproterozoic age, consistent with the ages of widely exposed Palaeoproterozoic granitic rocks. In situ zircon Hf isotope data show that most of the Palaeoproterozoic zircon xenocrysts have negative ?Hf(t) values (?9.7 to +0.7) with an average Hf model age of 2.86 ± 0.02 Ga (2?), which suggests that the Palaeoproterozoic basement was not juvenile but derived from the reworking of Archaean rocks. Considering the existence of Archaean remanent material in the Rangnim Massif and their juvenile features, a strong crustal reworking event is indicated at 1.9-1.8 Ga, during which time the pre-existing Archaean basement was exhausted and replaced by a newly formed Palaeoproterozoic basement. These features suggest that the Rangnim Massif constitutes the eastern extension of the Palaeoproterozoic Liao-Ji Belt of the North China Craton instead of the Archaean Liaonan Block as previously thought. A huge Palaeoproterozoic orogen may exist in the eastern margin of the Sino-Korean Craton.
Yellowknife Forum NWTgeoscience.ca, abstract volume p. 42-43.
Canada, Northwest Territories
kimberlite
Abstract: Mineral exploration in northern latitudes is challenging in that undiscovered deposits are likely buried beneath significant glacial overburden. The development of innovative exploration strategies and robust techniques to see through cover is imperative to future discovery success. Microbial communities are sensitive to subtle environmental fluctuations, reflecting these changes on very short timescales. Shifts in microbial community profiles, induced by chemical differences related to geology, are detectable in the surficial environment, and can be used to vector toward discrete geological features. The modernization of genetic sequencing and big-data evaluation allows for efficient and cost-effective microbial characterization of soil profiles, with the potential to see through glacial cover. Results to date have demonstrated the viability of microbial fingerprinting to directly identify the surface projection of kimberlites in addition to entrained geochemical signatures in till. Soils above two kimberlites in the Northwest Territories, have undergone microbial community profiling. These community-genome derived datasets have been integrated with chemistry, mineralogy, surface geology, vegetation type and other environmental variables including Eh and pH. Analyses show significant microbial community shifts, correlated with the presence of kimberlites, with a distinct community response at the species level directly over known deposits. Diversity of soil bacteria is also depressed in the same regions of the microbial community response. The relationship between microbial profiles and buried kimberlites has led to the application of microbial fingerprinting as a method to accurately delineate potential ore deposits in covered terrain. The integration of microbial community information with soil chemistry and landscape development coupled with geology and geophysics significantly improves the drill / no-drill decision process and has proven to be far more accurate than traditional surficial exploration methods. There is high potential for application as a field-based technique as microbial databases for kimberlites in northern regions are refined, and as sequencing technology is progressively developed into portable platforms.
Earth and Planetary Science Letters, Vol. 534, 8p. Pdf
Europe, Greenland
kimberlite genesis
Abstract: Archean cratons are composites of terranes formed at different times, juxtaposed during craton assembly. Cratons are underpinned by a deep lithospheric root, and models for the development of this cratonic lithosphere include both vertical and horizontal accretion. How different Archean terranes at the surface are reflected vertically within the lithosphere, which might inform on modes of formation, is poorly constrained. Kimberlites, which originate from significant depths within the upper mantle, sample cratonic interiors. The North Atlantic Craton, West Greenland, comprises Eoarchean and Mesoarchean gneiss terranes - the latter including the Akia Terrane - assembled during the late Archean. We report U-Pb and Hf isotopic, and trace element, data measured in zircon xenocrysts from a Neoproterozoic (557 Ma) kimberlite which intruded the Mesoarchean Akia Terrane. The zircon trace element profiles suggest they crystallized from evolved magmas, and their Eo-to Neoarchean U-Pb ages match the surrounding gneiss terranes, and highlight that magmatism was episodic. Zircon Hf isotope values lie within two crustal evolution trends: a Mesoarchean trend and an Eoarchean trend. The Eoarchean trend is anchored on 3.8 Ga orthogneiss, and includes 3.6-3.5 Ga, 2.7 and 2.5-2.4 Ga aged zircons. The Mesoarchean Akia Terrane may have been built upon mafic crust, in which case all zircons whose Hf isotopes lie within the Eoarchean trend were derived from the surrounding Eoarchean gneiss terranes, emplaced under the Akia Terrane after ca. 2.97 or 2.7 Ga, perhaps during late Archean terrane assembly. Kimberlite-hosted peridotite rhenium depletion model ages suggest a late Archean stabilization for the lithospheric mantle. The zircon data support a model of lithospheric growth via tectonic stacking for the North Atlantic Craton.
Geochimica et Cosmochimica Acta, Vol. 278, pp. 78-83.
Canada, Northwest Territories
kimberlites
Abstract: Kimberlite-borne granulite xenoliths provide rare insights into the age, chemical composition and tectonothermal evolution of the otherwise largely inaccessible deep cratonic crust. The formation and transformation of the lower continental crust (LCC) beneath the central Slave craton (Canada) is here illuminated using whole-rock trace-element and Sr-Nd isotope compositions of nine metabasaltic (MBG), one gabbroic (MGG) and two metasedimentary/hybrid (MSG) granulite xenoliths. On the one hand, published sulphide Re-Os and a few zircon U-Pb data indicate that at least a portion of the LCC beneath the central Slave craton has a Palaeoarchaean origin (?3.3?Ga), which apparently coincides with a period of juvenile crust and deep lithospheric mantle formation during plume impingement beneath the pre-existing cratonic nucleus. On the other hand, enrichment in Li, Sr, LREE, Pb and Th, but relative depletion in Ti, Hf and HREE, suggest formation of (picro)basaltic protoliths by partial melting of a subduction-modified garnet-bearing source, Crystallisation in the crust after fractionation of plagioclase is inidicated by their Sr and Eu negative anomalies, which are complementary to the positive anomalies in the MGG. Samarium-Nd isotopes in MBG and MGG show large scatter, but fall on Neo- or Mesoarchaean age arrays. These elemental systematics are suggested to fingerprint deserpentinisation fluids plus small amounts of sedimentary melt as the main contaminants of the mantle source, supporting the operation of at least regional and transient subduction at 3.3?Ga. Evidence for quasi-coeval plume impingement and subduction beneath the central Slave craton in the Mesoarchaean is reconcilable in a dynamic regime where vertical tectonics, though waning, was still active and plate interactions became increasingly important. Unradiogenic 87Sr/86Sr (down to 0.7017) is consistent with significant loss of Rb and probably other heat-producing elements (K, Th, U) plus H2O during Neoarchaean metamorphism, which helped to enhance LCC viscosity and stabilise the cratonic lithosphere.
Proceedings Natural Science Academy, Vol. 86, 1, pp. 301-311.
India
kimberlite, lamproites
Abstract: Highlights of researches on kimberlites, lamproites and lamprophyres (and their entrained xenoliths) during 2016-2019 from the Indian context are presented. A few previously unknown occurrences have been brought to light, and a wealth of petrological, geochemical and isotopic data on these rocks became available. All these studies provided new insights into the nomenclatural as well as geodynamic aspects such as subduction-tectonics, mantle metasomatism, lithospheric thickness, supercontinent amalgamation, and break-up and nature of the sub-continental lithospheric mantle from the Indian shield.
Abstract: FOZO-PREMA is an ubiquitous component of oceanic basalts and was originally defined by the convergence of Sr- Nd-Pb isotope trends of ocean island basalts (OIBs) from individual island-seamount chains [1]. FOZO-PREMA is also widespread in juvenile continental magmas, which argue for a global relevance of this component irrespective of the tectonic settings. Early studies proposed that FOZO-PREMA could be a physically discrete reservoir derived from depletion of primitive mantle based on the combination of geochemically depleted 143Nd/144Nd combined with elevated 3He/4He ratios [2]. Conversely, later models showed that isotopic compositions spanning the FOZO-PREMA field can be obtained by mixing recycled oceanic crust and mantle material previously depleted by crust extraction [3]. Kimberlites can provide a new perspective on this debate because a recent study of the Nd and Hf isotope compositions of kimberlite through time shows that these magmas sample a deep, long-lived, homogeneous reservoir, which might contain remnants of early Earth differentiation processes [4]. We critically review the Sr, Nd and Hf isotope compositions of kimberlites that were emplaced from ~2.1 Ga. After screening kimberlite isotopic data for the effects of lithospheric contamination and secondary alteration, we show that kimberlites through time have been derived from a mantle source with FOZO-PREMA composition. This observation makes it unlikely that FOZO-PREMA derives from continuous mixing of depleted and recycled components because the composition of subducted lithologies, pressure and temperature conditions in subduction zones, and temperature and oxygen fugacity conditions of the convective mantle have changed throughout Earth history. We therefore conclude that FOZO-PREMA is a long-lived component of Earth’s mantle, which must have existed for at least the last 2.1 Ga, the wider implications of which will be discussed.
Journal of Petrology, https://doi.org/ 10.1093/petrology /egaa040 50p. Pdf
Africa, South Africa
kimberlites
Abstract: Eclogite xenoliths, together with garnet pyroxenites and some mafic garnet granulites, found in kimberlites located along the southern margin of the Kaapvaal craton in southern Africa have been analysed by electron microprobe and mass spectrometry techniques to determine their geochemical characteristics. The majority of eclogites are bimineralic with garnet and omphacitic clinopyroxene in subequal proportions, with rutile as the main accessory phase; a few contain kyanite. Based on K2O in clinopyroxene and Na2O in garnet, the eclogites can be classified as Group II eclogites, and the majority are high-Ca in character. Garnet pyroxenites comprise garnet clinopyroxenites and garnet websterites. Major and trace element concentrations and isotope ratios of reconstituted bulk rock compositions of the eclogites and garnet pyroxenites allow constraints to be placed on depth of origin and likely protolith history. Calculated Fe–Mg exchange equilibration temperatures for the eclogites range from 815 to 1000?°C, at pressures of 1·7?±?0·4?GPa as determined by REE partitioning, indicating that they were sampled from depths of 50–55?km; i.e. within the lower crust of the Namaqua–Natal Belt. The garnet pyroxenites show slightly lower temperatures (686–835?°C) at similar pressures of equilibration. Initial 143Nd/144Nd and 87Sr/86Sr ratios (calculated to time of kimberlite emplacement) of both lithologies overlap the field for lower crustal samples from the Namaqua–Natal Belt. Further evidence for a crustal origin is found in the similar REE patterns shown by many of the associated garnet granulite xenoliths. Garnet pyroxenites are interpreted to have a similar origin as the associated eclogites but with the mafic protolith having insufficient Na (i.e. low modal plagioclase) to allow for development of omphacitic pyroxene. Metamorphism of the mafic protoliths to these eclogites and garnet pyroxenites is inferred to have occurred during crustal shortening and thickening associated with the collision of the Namaqua–Natal Belt with the Kaapvaal craton at 1–1·2?Ga.
Earth and Planetary Science Letters, Vol. 548, 12p. Pdf
Mantle
kimberlite ascent
Abstract: A wide variety of magmas entrain, transport and erupt mantle material in the form of xenoliths and xenocrysts. The host magmas are often low viscosity in nature and range from basalt to more esoteric compositions such as kimberlite, nephelinite and basanite. Here we focus on kimberlite magmas which are particularly successful at transporting deep mantle cargo to the surface, including economically important quantities of diamond. Collections of mantle-derived xenoliths and xenocrysts are critical to our understanding of the structure, stability, composition, thermal state, age, and origin of the lithosphere. However, they also inform on magma transport conditions. Through a series of scaled analogue experiments, we document the relative mechanical stability of olivine, garnet, orthopyroxene, clinopyroxene and diamond xenocrysts during magma ascent. Our experiments fluidized these mantle minerals at a constant gas flux for variable amounts of time approximating transport in a high velocity, turbulent, fluid-rich (supercritical fluid or gas, depending on depth) magma. The evolution of mineral surface features, morphology and grain size distributions is analyzed as a function of residence time. We show that on timescales consistent with magma ascent, each mantle mineral is subject to mechanical modification resulting in mass loss and reshaping (rounding) by grain size reduction and surface pitting. We further discuss the chemical consequences of producing fine particle chips that are highly susceptible to dissolution. Lastly, we utilize an empirical model that relates textural observations (e.g. impact pit size) on xenocrysts to differential particle velocities. Our approach applied to natural kimberlitic olivine and garnet xenocrysts indicates differential velocities of - the first direct estimate for velocity in an ascending kimberlite magma.
IN: Nemeth, K., Carrasco-Nunez, G., Aranda-Gomez, J.J., Smith, I.E.M. eds. Monogenetic volcanism GSL Special Volume, Vol. 446, 22p. Pdf * note date
Europe
kimberlite, maars
Abstract: Most kimberlite maar-diatreme volcanoes erupted during the Tertiary or earlier and therefore their tephra rings and, less often, their near-surface diatreme-filling deposits have usually been eliminated by erosion. Poorly eroded Quaternary non-kimberlite maar-diatreme volcanoes, especially those of mafic and ultramafic magma types, have the same diatreme size range (diameter and depth) as kimberlite pipes and show similar internal volcaniclastic diatreme lithofacies. In addition, these young volcanoes often have a more or less preserved tephra ring consisting of hundreds to perhaps a few thousand thin tephra beds. Volcanological analyses of the xenolith-rich primary volcaniclastic deposits both within these diatremes and in the tephra ring beds reflect phases of explosive pipe growth and are of convincingly phreatomagmatic origin. The similarities between non-kimberlite pipes and kimberlite pipes suggest to some researchers that phreatomagmatic processes were also responsible for pipe excavation processes in kimberlite maar-diatreme volcanoes. In contrast, other researchers have suggested that kimberlite maar-diatreme volcanoes were emplaced largely by magmatic processes as a consequence of exsolution and the explosive expansion of juvenile volatiles. We therefore analysed and compared some key geological features of kimberlite and ultrabasic to basic ‘basaltic’ maar-diatreme volcanoes to determine similarities and differences with respect to their emplacement behaviour. The following problems were addressed - the layout of the abstract; an amendment to the caption of Fig. 1; and some changes to Zimanowski's references in the reference list.
Revista Brasileira de Geociencas*** ENG, Vol. 31, 4, pp. 653-660. pdf
South America, Brazil
kimberlites
Abstract: Garne ts from couc eru ratc from the vargcm l kimberl ite pipe show a long compos itional range and reveallong lincar tre nds within the lherzolite field in a Cr~Ol - CaO% dia gram (Sobolcv et til. 1974) (lip (0 11% MgO). fon ned by grains of different dimensions with fcw deviations to harzburg itcs . Larger grains (fraction +3) arc higher in CaO with less Cr~01 (to 5.5%). TIle Cr20 1 freq uen cy reduc es in hyperbo lic function for each fraction . IImenites reve;1142-56% Ti0 2l..'Olllpositionai range with linear FeO - MgO correhuions but 3(4) separate groups for A I ~01 suggest different proport ion of co-prccipimted gimlet , probably due to polybn ric Irncnonanon. lncreasing Cr~O l nnd r"t..-Q% conte nt (fractionation uegn:e ) with red ucing TiO~ is in accord with Ar c mod el.. Ganict xenolith fnnnldnin II pipe with large Ga r- Cpxgrains and fine Mica-Curb bearing mat rix refer to 60 kbcr and 35 mv/m2 gcothcrm . 11displays enr iched trace c lement pat ter ns but not completely equilibrated compositions for Ga r anti Cpx. sugges ting low degree me lting of rela tively fertile mantle. St udied uuuc rinlmay s uggcsrmcrasomu tized, relat ively fertile and irre gularly heated mantle bene ath Sombcrn Bra zil as found by (Carvalho & Lccnnrdos 1997).
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.
Proceedings of the National Academy of Sciences PNAS, Vol. 118, 1 e201521118 9p. Pdf
Mantle
kimberlite
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.
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.
Physics of the Earth and Planetary Interiors, Vol. 315, 106708, 13p. Pdf
India
kimberlites
Abstract: Complex geological structures and processes that took place in the Dharwar craton formation make it difficult to understand the evolution history. 3-D magnetotelluric inversion is a challenging task for the imaging of sub-surface structures. Data at 40 stations in a gridded fashion are used in this study for inversion. A controversy exists regarding the subduction polarity between the eastern and western Dharwar craton. Based on the conductivity anomalies mapped in the sub-surface, the lithosphere can be divided into the shallower and deeper lithosphere. The study delineated several crustal and lithospheric upper mantle conductors. In the crustal region, several conductive features (~10 ?-m) are imaged in the western part, central, and eastern part of the profile. A new finding of this 3-D study is a conductor in the eastern Dharwar craton in the depth range of 65-140 km. The base of this conductor shows the graphite diamond stability field and is correlated with the kimberlites/lamproites present in the region. An uppermost mantle conductor is present at the depth range of 80-200 km in the central part of the study area. Sulphides and carbon-rich fluids could be one cause of the conductors mapped in the crust. The low electrical resistivity imaged in the deeper lithosphere could be due to the refertilization of the mantle scar in the Cretaceous age by the passage of several hotspots. The lithospheric thickness estimated beneath the Dharwar craton in this study is more than 200 km. This study reveals geophysical evidence for the eastward subduction polarity in the Dharwar craton.
Book: Diamonds from the Arkangelk Province, NW Russia., July doi.10.1007/978-3-030-35717-7_1 30p.
Russia, Archangel
kimberlites
Abstract: The chapter headlines the historical perspective of discovering the Arkhangelsk Diamondiferous Region, previously was also called the Arkhangelsk Diamondiferous Province (hereinafter named ADR), offers the contemporary concept of the ADR geology, and location of kimberlite fields and magmatic rock bodies in its area. It describes the layout, structure, mineralogical characteristics and lithology of pipes from the Grib and Lomonosov deposits. It gives a snapshot of the alkaline ultrabasic rocks’ representatives from the Zimny Bereg area of the ADR that is not covered by the deposits.
Journal of Geophysical Research: Solid Earth , preprint available 40p. Pdf
Africa
kimberlites
Abstract: The tectonic history of Southern Africa includes Archean formation of cratons, multiple episodes of subduction and rifting and some of the world's most significant magmatic events. These processes left behind a compositional trail that can be observed in xenoliths and measured by geophysical methods. The abundance of kimberlites in southern Africa makes it an ideal place to test and calibrate mantle geophysical interpretations that can then be applied to less well-constrained regions. Magnetotellurics (MT) is a particularly useful tool for understanding tectonic history because electrical conductivity is sensitive to temperature, bulk composition, accessory minerals and rock fabric. We produced three-dimensional MT models of the southern African mantle taken from the SAMTEX MT dataset, mapped the properties of $\sim36000$ garnet xenocrysts from Group I kimberlites, and compared the results. We found that depleted regions of the mantle are uniformly associated with high electrical resistivities. The conductivity of fertile regions is more complex and depends on the specific tectonic and metasomatic history of the region, including the compositions of metasomatic fluids or melts and the emplacement of metasomatic minerals. The mantle beneath the $\sim 2.05$ Ga Bushveld Complex is highly conductive, probably caused by magmas flowing along a lithospheric weakness zone and precipitating interconnected, conductive accessory minerals such as graphite and sulfides. Kimberlites tend to be emplaced near the edges of the cratons where the mantle below 100 km depth is not highly resistive. Kimberlites avoid strong mantle conductors, suggesting a systematic relationship between their emplacement and mantle composition.
Lithos, Vol. 406-407. doi: 10.1016/j.lithos.2021.106499 77p. Pdf
Russia
kimberlite genesis
Abstract: Major and trace element variations in picroilmenites from Late Devonian kimberlite pipes in Siberia reveal similarities within the region in general, but show individual features for ilmenites from different fields and pipes. Empirical ilmenite thermobarometry (Ashchepkov et al., 2010), as well as common methods of mantle thermobarometry and trace element geochemical modeling, shows long compositional trends for the ilmenites. These are a result of complex processes of polybaric fractionation of protokimberlite melts, accompanied by the interaction with mantle wall rocks and dissolution of previous wall rock and metasomatic associations. Evolution of the parental magmas for the picroilmenites was determined for the three distinct phases of kimberlite activity from Yubileynaya and nearby Aprelskaya pipes, showing heating and an increase of Fe# (Fe# = Fe / (Fe + Mg) a.u.) of mantle peridotite minerals from stage to stage and splitting of the magmatic system in the final stages. High-pressure (5.5–7.0 GPa) Cr-bearing Mg-rich ilmenites (group 1) reflect the conditions of high-temperature metasomatic rocks at the base of the mantle lithosphere. Trace element patterns are enriched to 0.1–10/relative to primitive mantle (PM) and have flattened, spoon-like or S- or W-shaped rare earth element (REE) patterns with Pb > 1. These result from melting and crystallization in melt-feeding channels in the base of the lithosphere, where high-temperature dunites, harzburgites and pyroxenites were formed. Cr-poor ilmenite megacrysts (group 2) trace the high-temperature path of protokimberlites developed as result of fractional crystallization and wall rock assimilation during the creation of the feeder systems prior to the main kimberlite eruption. Inflections in ilmenite compositional trends probably reflect the mantle layering and pulsing melt intrusion during melt migration within the channels. Group 2 ilmenites have inclined REE enriched patterns (10–100)/PM with La / Ybn ~ 10–25, similar to those derived from kimberlites, with high-field-strength elements (HFSE) peaks (typical megacrysts). A series of similar patterns results from polybaric Assimilation + fractional crystallization (AFC) crystallization of protokimberlite melts which also precipitated sulfides (Pb < 1) and mixed with partial melts from garnet peridotites. Relatively low-Ti ilmenites with high-Cr content (group 3) probably crystallized in the metasomatic front under the rising protokimberlite source and represent the product of crystallization of segregated partial melts from metasomatic rocks. Cr-rich ilmenites are typical of veins and veinlets in peridotites crystallized from highly contaminated magma intruded into wall rocks in different levels within the mantle columns. Ilmenites which have the highest trace element contents (1000/PM) have REE patterns similar to those of perovskites. Low Cr contents suggest relatively closed system fractionation which occurred from the base of the lithosphere up to the garnet–spinel transition, according to monomineral thermobarometry for Mir and Dachnaya pipes. Restricted trends were detected for ilmenites from Udachnaya and most other pipes from the Daldyn–Alakit fields and other regions (Nakyn, Upper Muna and Prianabarie), where ilmenite trends extend from the base of the lithosphere mainly up to 4.0 GPa. Interaction of the megacryst forming melts with the mantle lithosphere caused heating and HFSE metasomatism prior to kimberlite eruption.
International Geology Review, Vol. 64, 8, pp. 1119-1138.
Russia, Siberia
kimberlite magmatism
Abstract: Zircon xenocrysts from two diamond-barren kimberlite pipes (Leningrad and Ruslovaya) in the West Ukukit kimberlite field opened a ‘window’ to the buried crustal basement in the northern Siberian craton. Zircon U-Pb ages reveal a close affinity of the basement of the Khapchan belt to the Archaean Anabar province and a significant tectonomagmatic reworking in the Paleoproterozoic (~2.1-1.8 Ga) due to collision between the Anabar province and the Olenek province. The West Ukukit kimberlite field experienced multiple tectonomagmatic reactivation from ~670 to 144 Ma, which can be attributed to interaction of the deep crust with mantle-derived melts. Hf isotope composition of zircon xenocrysts reveals significant addition of juvenile material into the crust during the Paleoproterozoic orogeny in diamond-barren kimberlite fields, which is different from the reworking crust in the southern Yakutia diamondiferous kimberlite fields. Eruption of the Leningrad and Ruslovaya pipes were constrained as the Late Jurassic, much later than the well-known Late Silurian-Earth Devonian kimberlites in the West Ukukit kimberlite field. A NE-trending, >2000 km long kimberlite corridor is proposed to account for a prolonged lithospheric channel for episodic eruption of kimberlites in the Siberian craton. The diamond storage in the lithosphere beneath the West Ukukit kimberlite field may have been largely reduced by the Paleoproterozoic orogeny and Phanerozoic reworking.
Abstract: In the experiments at 3.0-6.3 GPa and 1200-1350°C, it is found that under P-T parameters close to the conditions in ascending kimberlite magma, the carbonate melt enriched in potassium and volatiles is able to dissolve effectively the entire amount of xenogenic peridotite material that can potentially transport. As a result of this process, the melt is enriched in SiO2 (up to 30 wt %) and is transformed from carbonate to a kimberlite-like one. In the range of parameters studied, due to the high solubility of CO2 in the melt and the appearance of magnesite, an equilibrium fluid phase is not formed in the system. The interaction realized in the experiments may be the most important factor at the initial stage of magma evolution. The calculations performed in this work show that even after the dissolution of 30-50 wt % of lherzolite, the volatile-rich carbonate-silicate melt has a high degree of depolymerization (the ratio of the number of nonbridging oxygen atoms to the number of tetrahedrally coordinated ions (100NBO/T from 250 to 390) remains low-viscous (0.3-32.6 Pa s) and able to ascend to the surface rapidly. The obtained data indicate that immiscibility occurs between the potassium-rich carbonate-silicate and highly silicate melts only at 5.5 GPa and 1350°C and is likely to have a minor impact on the evolution of magma.