This is a thre-part analytical program to investigate fundammental aspects of Deccan-related volcanism using existing well-documented smaples; the goal is to expand knowledge outward from the intensively studied southwestern region, to begin to understand the huge Deccan episode ina plate-tectonic framework and with respect to other large continental flood basalts. 1) Existing chemical evidence shows that the lower six formations of the western Deccan do not simply repeat the geochemistry of the Five later, upper level formations, now quite well understood. A Nd, Pb, and Sr isotopic study of otherwise thoroughly characterized lavas from the lower formations is proposed. The combined chemical and isotopic data will be used to evaluate the nature and evolution of their mantle source(s), the roles and mechanisms of contamination early in the Deccan succession, and relationships to the overlying formations. In particular, were ancient lithospheric mantle sources supplanted by asthenospheric sources; and did AFC processes dominate early on, as has been predicted? 2) An even earlier suite of flood basalts from southern and eastern Madagascar represents a stage of volcanism (70-80 Myr) in India proper. Nd, Sr, and Pb isotopic ratios will be measured on a set of Madagascar lavas, in conjunction with petrographic, major and trace element, and geochronological work by Frency collegues, in order to trace the beginning phases of volcanic activity. 3) Though a huge anticlinal structure incorporating the western Deccan formations has been indentified recently, the geochemical stratigraphy of the province in a W-E direction remains completely unknown. On extreme view holds that lavas in the central and northeastern Deccan are simply distal fringes of the western formations (up to 1000 km or more away); another that most or all of the former were erupted more locally from dikes along the Narmada-Son Lineament and thus should reflect their own unique petrogenesis. Isotopic, chemical, and petrographic data on sections running W-I from Aurangabad, Chikaldara, and Nagpur areas will directly text these two conflicting but critical hypotheses.
