Stable isotope evidence for ca. 2.7-Ga-old Archean cap carbonates from the Dharwar Supergroup, southern India

Sharma, Subrata Das and Srinivasan, R (2015) Stable isotope evidence for ca. 2.7-Ga-old Archean cap carbonates from the Dharwar Supergroup, southern India. In: CURRENT SCIENCE, 108 (12). pp. 2223-2229.

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Abstract

Carbon isotope compositions of carbonate rocks from similar to 2.7-Ga-old Neoarchean Vanivilas Formation of the Dharwar Supergroup presented earlier by us are re-evaluated in this study, besides oxygen isotope compositions of a few silica dolomite pairs. The purpose of such a revisit assumes significance in view of recent field evidences that suggest a glaciomarine origin for the matrix-supported conglomerate member, the Talya conglomerate, which underlies the carbonate rocks of the Vanivilas Formation. An in-depth analysis of carbon isotope data reveals preservation of their pristine character despite the rocks having been subjected to metamorphism to different degrees (from lower greenschist to lower amphibolite facies). The dolomitic member of Vanivilas Formation of Marikanive area is characterized by highly depleted delta C-13 value (up to -5 parts per thousand VPDB) and merits as the Indian example of ca. 2.7-Ga-old cap carbonate. This inference is further supported by estimated low temperature of equilibration documented by a few silica dolomite pairs from the Vanivilas Formation collected near Kalche area. These pairs show evidence for oxygen isotopic equilibrium at low temperatures (similar to 0-20 degrees C) with depleted water (delta O-18 = -21 parts per thousand to -15 parts per thousand VSMOW) of glacial origin. We propose that the mineral pairs were deposited during the deglaciation period when the ocean temperature was in its gradual restoration phase. The dolomite of Marikanive area is the first record of cap carbonates from the Indian subcontinent with Neoarchean antiquity.

Item Type:	Journal Article
Publication:	CURRENT SCIENCE
Publisher:	INDIAN ACAD SCIENCES
Additional Information:	Copy right for this article belongs to the INDIAN ACAD SCIENCES, C V RAMAN AVENUE, SADASHIVANAGAR, P B #8005, BANGALORE 560 080, INDIA
Keywords:	Carbonate rocks; carbon and oxygen isotopes; Dharwar Craton; glaciomarine deposit; Neoarchean
Department/Centre:	Division of Mechanical Sciences > Centre for Atmospheric & Oceanic Sciences
Date Deposited:	31 Jul 2015 15:01
Last Modified:	31 Jul 2015 15:01
URI:	http://eprints.iisc.ac.in/id/eprint/51994

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