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Alteration and submergence of basalts in Kachchh, Gujarat, India: implications for the role of the Deccan Traps in the India–Seychelles break-up

By
Souvik Mitra
Souvik Mitra
Department of Geology & Geophysics, Indian Institute of Technology Kharagpur – 721 302, India
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Kaushik Mitra
Kaushik Mitra
Department of Geology & Geophysics, Indian Institute of Technology Kharagpur – 721 302, India
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Saibal Gupta
Saibal Gupta
Department of Geology & Geophysics, Indian Institute of Technology Kharagpur – 721 302, India
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Satadru Bhattacharya
Satadru Bhattacharya
Space Applications Centre, Indian Space Research Organization, Ahmedabad – 380 015, India
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Prakash Chauhan
Prakash Chauhan
Space Applications Centre, Indian Space Research Organization, Ahmedabad – 380 015, India
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Nirmala Jain
Nirmala Jain
Space Applications Centre, Indian Space Research Organization, Ahmedabad – 380 015, India
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Published:
January 01, 2017

Abstract

The Deccan Trap flood basalt volcanism has commonly been considered to have initiated the break-up of India from the Seychelles (c. 62.5 Ma). In Kachchh, Gujarat, western India, the sedimentary succession in the Paleocene Matanomadh Formation was deposited on highly weathered Deccan Trap basalts that were altered to kaolinite before basin formation. This contrasts with the weathering pattern on flat-topped hills of the Deccan Traps outside the Cenozoic rift basins in the Kachchh region and other parts of India, where basalt is dominantly altered to smectitic minerals. As basalts that are altered to smectite and kaolinite occur just across the faults that bound the Matanomadh Basin, the differential weathering cannot be attributed to climate. Geochemical modelling shows that kaolinite stabilizes in preference to smectite if CO2- and O2-buffered rainwater interacts with well-drained basaltic rock at high water:rock ratios. Such conditions can be accomplished by rainfall on a slope created by Cenozoic rifting that exposes the graben flank and basin floor basalts to continuously flowing water, the composition of which is buffered by equilibration with the atmosphere. As the rift post-dates both the eruption of the basalts and subsequent smectite formation, the associated extensional tectonics must be unrelated to flood basalt volcanism, and is most likely to correspond to the India–Seychelles break-up.

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Geological Society, London, Special Publications

Tectonics of the Deccan Large Igneous Province

S. Mukherjee
S. Mukherjee
Department of Earth Sciences, Indian Institute of Technology Bombay, Mumbai 400 076, Maharashtra, India
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A. A. Misra
A. A. Misra
Exploration, Reliance Industries Ltd, Mumbai 400 701, Maharashtra, India
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G. Calvès
G. Calvès
Université Toulouse 3, Paul Sabatier, Géosciences Environnement Toulouse, 14 avenue Edouard Belin, 31400, Toulouse, France
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M. Nemčok
M. Nemčok
EGI at University of Utah, 423 Wakara Way, Suite 300, Salt Lake City, UT 84108, USAEGI Laboratory at SAV, Dúbravskácesta 9, 840 05 Bratislava, Slovakia
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Geological Society of London
Volume
445
ISBN electronic:
9781786203281
Publication date:
January 01, 2017

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