Tuff beds in Kurnool subbasin, southern India and implications for felsic volcanism in Proterozoic intracratonic basins

A first report on tuff beds from the Owk Shale in the Proterozoic Kurnool sub-basin in southern India is presented. The rhyolitic to rhodacitic tuffs, overlying shelfal limestones formed at depths below storm wave base, have rheomorphic features indicative of viscoplastic flow, and geochemical signatures of rhyolitic to rhyodacitic unwelded to welded tuffs, similar to those described from other Proterozoic intracratonic basins like Vindhyan and Chhattisgarh basins in India. Fragmentary nature of altered glass with perlitic cracks and local admixture with intrabasinal sediments suggest phreatomagmatic reactions. The widespread and repeated occurrences of felsic tuffs in these basins, possibly derived from low degree melting of continental crust, suggest intermittent tectonothermal instability which likely influenced basinal topography and cyclic development of the carbonate platforms.

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► First report of rhyodacitic tuff beds and their geochemistry from the Proterozoic Owk Shale, southern India.
► Geochemical discrimination indicates affinity with Volcanic Arc Granites, in spite of supposed intracratonic basinal setting.
► Contribution of submarine ash flow interpreted from texture and marine sediment association.