Geochronological and genetic characterization of basaltic basement from western offshore basins in India

⁴⁰Ar-³⁹Ar geochronology, geochemistry, and Sr-Nd isotopic compositions of 30 core samples from 24 offshore drill wells in the Western offshore basins have been used to characterize the genetics of the volcanic basement from the Kutch, Mumbai, and Kerala-Konkan offshore basins. Findings from the volcanic basement rocks demonstrate extremely varied isotopic and geochemical fingerprints, which are suggestive of significantly diverse parent magma compositions and emplacement processes.

Basaltic tholeiitic basement from Kutch Offshore basin has Ar-Ar ages that range between 60 Ma and 62 Ma. This basement is characterised by a within-plate basalt signature, with depleted isotopic signatures similar to least contaminated Deccan Traps basalts, and a component of subducted crustal material. Basaltic basement from Mumbai Offshore Basin has eruption ages between 63 Ma and 65 Ma and show a strong within-plate OIB affinity. Geochemical and isotopic signatures are consistent with Renuion lavas and an enriched-end member of Deccan Traps basalts. However, Kerala-Konkan Offshore Basin shows significant E-MORB affinity and is characterized by primitive-mantle signatures and least contamination from the upper continental crust, with ages of eruption between 60 Ma and 61 Ma based on obtained ⁴⁰Ar-³⁹Ar ages.

The study suggests that the Mumbai Offshore Basalts’ mode of the eruption was comparable with onshore Deccan volcanism, whereas the basaltic basement in Kutch Offshore was formed after the main phase of Deccan eruption and may have been an offshoot of a “tail” of the main Deccan volcanism. The parent magma for the volcanic E-MORB basement in the Kerala-Konkan Offshore Basin is thought to have come from mixing along the Carlsberg Mid-Oceanic Ridge and the material from the Réunion plume with the northward movement of the Indian Plate during the Early Paleocene. This is thought to have occurred concurrently with the formation of the Chagos-Laccadive Ridge.