Abstract

This paper presents immobile trace elemental and Strontium-Neodymium (Sr-Nd) isotopic signatures of basalts encountered in Kerala-Konkan Offshore Basin of India. The results are compared with the basalts from Kutch and Mumbai Offshore Basins, Onland Deccan traps as well as Chagos Laccadive Ridge (CLR) and South Mascerene Plateau. The study suggests close affinity of Kerala Konkan Offshore basalts to Chagos-Laccadive Ridge and South Mascerene Plateau basalts. Further, the basalts from Kerala Konkan Offshore and Chagos-Laccadive Ridge/South Mascerene Plateau show Enriched Mid-Ocean Ridge Basalt (E-MORB) characteristics, a very significant finding being reported for the first time, while the basalts from Kutch and Mumbai Offshore fall in Within Plate Basalts (WPB) category similar to the on-land Deccan Traps. The geochemical and isotopic studies of basalts from Kerala Konkan Offshore suggest different petrogenetic history as compared to the basalts from Kutch and Mumbai Offshore and appear to have been derived from a more primitive deep mantle plume source. The Ar-Ar dating of basalts from wells KKD-AA and K-A-A of Kerala Konkan Offshore indicate their emplacement ~62 Ma which is coeval with the formation of northern part of Chagos- Laccadive Ridge. The magmatic episode in both the regions postdate the Deccan activity and were emplaced possibly by the interaction of the Reunion Plume and newly formed Carlsberg Ridge. In such kind of settings, the probability of occurrence of Mesozoic sediments below the E-MORB becomes meager. Present study also proposes a plausible model for emplacement of E-type MORB in the Kerala Konkan Offshore and the Chagos Laccadive Ridge.