Intraplate alkali basalts related to end-Cretaceous Deccan magmatism: Implications to tectonomagmatic processes

摘要: This study aims to investigate the earliest imprint of Deccan rift magmatism as preserved in alkali basalts from the northwestern Indian shield. The alkali basalts are petrographically classified as nephelinites and basanites. They are silica undersaturated and their high Mg#, CaO/Al2O3, Cr and Ni indicate their primitive character. Geochemically, they are similar to global ocean island basalts; their bulk rock trace elements and Sr-Nd-Hf isotopic signatures suggest their derivation from garnet-bearing peridotite field. However, their elevated values of Sr/Sm, Sm/Hf, Zr/Hf, Nb/Ta; positive Ba, Sr and negative Zr, Hf spikes suggest that the magma source represents a mixture of garnet peridotites and carbonated melts. Estimated primary melt compositions closely follow the trajectory defined by the high pressure experimental partial melting trend of a low-carbonated peridotite source. The melting environment approximates …