Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

Sisir K. Mondal ¹

Affiliations
1 Department of Geological Sciences, Jadavpur University, Kolkata, IN

Abstract

No Abstract.

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Sisir K. Mondal ¹

Affiliations
1 Department of Geological Sciences, Jadavpur University, Kolkata - 700032, IN

Abstract

The Archaean cratonic nuclei of the continents are important as they contain the most significant evidences for the evolution of Earth e.g. the greenstone sequences. In the Indian Shield, one of the important cratons is the Singhbhum craton, where nearly 95% of the Indian chromite deposits and only PGE deposits are located which are hosted within Mesoarchaean ultramafic-mafic rock sequences. The ultramafic units occur as sill like intrusions within the Iron Ore Group (IOG) greenstone belts and often associated with gabbroic intrusions. In the Nuasahi and Sukinda mining districts of these occurrences, detailed petrological, geochemical and isotopic studies have been carried out in the last decades. Petrological and geochemical studies indicate a supra-subduction zone (SSZ) tectonic settings in Archaean for the origin of these ultramafic-mafic sequences. The Os isotopic and platinum group element (PGE) geochemical studies of chromites from the two mining districts indicate presence of a subchondritic source mantle domain beneath and within the Singhbhum craton similar to the Zimbabwean craton of southern African continent. The Os model age calculation indicates melt extraction from a subcontinental lithospheric mantle (SCLM) before 3.7 Ga which is similar to the other ancient cratons. As a whole the study supports the premise that India was part of the African continent in pre-Gondwana times and even in early Archaean and suggest possible amalgamation and building up of a supercontinent during late Archaean. However, in comparison with other occurrences, the Singhbhum craton of the Indian Shield and the Zimbabwean craton in southern Africa are characterized by the presence of subchondritic lithospheric mantle domains within the SCLM, which were developed prior to 3.7 Ga.

Keywords

Chromite, PGE, Os Isotope, SCLM, Plate Tectonics, Supercontinent, Greenstone Belt, Archaean, Singhbhum Craton.

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Sisir K. Mondal ¹

Affiliations
1 Department of Geological Sciences, Jadavpur University, 188 Raja S.C. Mullick Road, Kolkata - 700 032, IN

Abstract

Platinum group elements (PGE: Os, Ir, Ru, Rh, Pt, Pd) are important geochemical and cosmochemical tracers. Depending on physical and chemical behaviour the PGEs are divided into two subgroups: IPGE (Ir, Os, Ru) and PPGE (Pd, Pt, Rh). Platinum group elements show strong siderophile and chalcophile affinity. Base metal sulfides control the PGE budget of the Earth's mantle. Mantle xenoliths contain two types of sulfide populations: (1) enclosed within silicate minerals, and (2) interstitial to the silicate minerals. In terms of PGE characters the included variety shows IPGE enriched patterns - similar to the melt-depleted mantle harzburgite, whereas the interstitial variety shows PPGE enriched patterns - resembling the fractionated PGE patterns of the basalt. These PGE characters of the mantle sulfides have been interpreted to be representative of multi-stages melting process of the mantle that helped to shape the chemical evolution of the Earth.

Keywords

Mantle Xenoliths, Base Metal Sulfides, Platinum Group Element (PGE), Os Isotope, Mantle Heterogeneity.

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Sisir K. Mondal ¹

Affiliations
1 Department of Geological Sciences, Jadavpur University, Kolkata - 700032, IN

Abstract

This year, the 21^st Annual V. M. Goldschmidt Conference was held at Prague, Czech Republic from 14^th to 19^th August. The Goldschmidt Conference_TM is the premiere international conference on geochemistry (http://www.goldschmidt 2011.org/). This conference was organized and sponsored by The European Association of Geochemistry and The Geochemical Society (USA). This year the main theme of the conference was ‘Earth, Life and Fire’ under which there were 23 sub-themes in the conference. The different subjects that were covered under these themes include Cosmochemistry-Planet Formation, Primitive Earth: From Core to Atmosphere, Evolution and Dynamics of the Deep Earth, Mantle to Crust: Ocean Ridge and Intraplate Volcanism, Continental Crust Formation and Evolution, Recycling: Subduction, The Mantle Wedge and Arc Volcanism, Earth Resources: Energy, Earth’s Resources: Ores etc. There were 175 numbers of Sessions under the various themes in the conference. A total of 3800 abstracts were submitted in the conference by participants of more than hundred countries across the globe. There was an additional special plenary session focusing on the Fukushima accident (Japan) and its geochemical consequences. The plenary presentations in the conference were given by Samuel Mukasa (‘Volatiles in the Mantle: Impact on Intraplate Magmatism), Marc Hirchmann (‘Deep Earth Volatile Cycles: From Ancient to Modern’), Edouard Bard (‘Geochemical Profiles to Study the Last Deglaciation and its impact on Rivers’), Frank Selsis (‘Exoplanet Atmospheres: From Hot to Habitable Worlds’) and Victoria Orphan (‘Microbial Partnerships and Methene-Oxidation in the Deep Sea’).

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