Widespread silicic and alkaline magmatism synchronous with the Deccan Traps flood basalts, India

Abstract

Deccan Traps (DT) volcanism and the Chicxulub bolide impact have been suggested as potential triggers of the Cretaceous–Paleogene boundary (KPB) mass extinction. Recently published geochronology has established a timeline for the main basaltic sequence of the DT, showing that the majority of eruptions occurred within 700–800 kyr spanning the KPB. Silicic to alkaline magmatism linked to the DT, spatially associated with the Narmada lineament in central India, has been long known but not as well studied. Previous geochronology of some of the felsic magmatic centers has yielded dates that span many millions of years, making their temporal relationship with DT volcanism uncertain. We present zircon U-Pb ages from the Alech, Barda, Girnar, Rajula and Phenai Mata silicic–alkaline complexes, in addition to a series of trachytes on the coastal plain near Mumbai. While the trachytes are ∼64 Ma and mark the continental breakup of India ∼1.5 Myr after the main phase of DT eruptions, the silicic-alkaline complexes were all emplaced coevally with the main phase of DT volcanism ca. 66.2-65.7 Ma. Initial εHf in zircons (+10 to -20), whole-rock 87Sr/86Sr (0.702439-0.760932) and εNd (+1.11 to -35.7) for all five intrusive complexes suggest a hybrid origin involving juvenile sources as well as significant assimilation of older continental crust. Recognition that the silicic-alkaline complexes are coeval with basaltic magmatism and associated with a significant thermal imprint on the crust in and near the Narmada rift sedimentary strata supports the hypothesis that outgassing of organic-rich sediments may have contributed to the end-Maastrichtian warming and biologic crisis.