Seismic Imprints of Plume-Lithosphere Interaction Beneath the Northwestern Deccan Volcanic Province

Abstract

The interaction of the Indian continental lithosphere with the Reunion plume resulted in massive outpouring of basalts manifested in the Deccan Volcanic Province. Although it is postulated that preexisting weak rift zones facilitated the eruption, deeper signatures of the plume remain contentious. In this study, we investigate the shear wave velocity (Vs) structure of the crust and upper mantle by inverting regionalized group velocity dispersion data in the period range of 6 to 100 s, down to 220 km depth, using the genetic algorithm technique. We used 1,286 dispersion curves derived from waveforms of 77 regional earthquakes recorded at 38 broadband stations. Our results reveal distinct intracrustal layers, Moho, mantle lid, and asthenospheric low-velocity layer. Signatures of magmatic underplating are recognized in terms of high Vs and a thick crust beneath the Kutch seismic zone and Western Ghats. The lithospheric thickness varies from 80 to 124 km, being thinnest at the junction of Cambay and Narmada rifts, which could be the source zone of volcanic eruption. A thin lithosphere has also been observed beneath the Kutch seismic zone. A low-velocity zone at depths ~80 km can be related with upwarping of the asthenosphere and/or presence of partial melts. A predominant low-velocity zone beneath the Cambay, Saurashtra, and adjoining regions may be due to the effect of a residual thermal anomaly. A thin lithosphere beneath northwestern Deccan Volcanic Province could be the result of weakening due to plume-lithosphere interaction, which facilitated volcanism through preexisting rift zones.