Cenozoic Deccan Traps. 2. Geochemical Characteristics

Published and own data on geochemistry of Cenozoic traps of Deccan have been generalized. Tholeiitic basalts dominating the formation are more rich in incoherent elements as compared to the mid-oceanic ridges of similar matrix composition. This is interpreted to be a consequence of the mantle substrate being different beneath the continents and oceans in the zones where tholeiitic magmas melt out. In the basalt group as a whole, concentrations of most rare elements appear to depend on the rock composition regardless of alkalinity suggesting their close genetic relationship. On the basis of data on geochemistry of stable isotopes the supposition is made that the mantle beneath platforms is heterogeneous and there are additional sources of incoherent elements supplied to the zones of magma production by mantle metasomatism. The trap-associated acidic rocks, trachytes and rhyolites, have independent sources of matter and are derivatives of basic and acidic substrate of the crust, respectively.