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Geochemistry of a Neoarchean hot subduction volcanic suite discovered beneath the Cretaceous Deccan Traps, India

Tarun C. Khanna

Abstract

Arc as well as plume magmatism has sub equally contributed to the growth of continental crust on the Earth, since the Archean era. Unlike the crust that is exposed and accessible on the surface, the nature of the crust concealed beneath the volcanic igneous provinces such as Siberia and Deccan have remained enigmatic. Apparently, the voluminous lava pile deters access to the concealed basement, unless retrieved through deep continental drilling. Unlike the Siberian traps, the depth of lava in the Deccan does not exceed 1300 m, and therefore, penetrable through the underlying crust. CSIR-NGRI has drilled four scientific deep bore-holes (KBH-5, 8, 9 and 10) that penetrate the granitic basement to a depth of 1500 m. The volume of the basalt lava extracted from these well-cores extends to a depth of 1200 m. In comparison to the rest, KBH-5 is unique, in the sense that in this region the Deccan Traps are underlain by a Neoarchean (~2.58 Ga) volcanic sequence of ~300 m thick at -400 m m.s.l., instead of granites. This succession comprises of a hot subduction volcanic suite of rocks. The extension of this suite is traceable beyond 300 km on the surface, south of the Deccan Traps. This study provides first physical evidence and new information on the arc volcanic rocks of the Dharwar Supergroup extending further beneath the Deccan Traps. Unveiling of potentially similar scenarios entrapped beneath the vast canopy of continental flood basalts, would reveal new crustal growth events during Precambrian-Phanerozoic transition across the Earth.