Sub-Moho lithospheric modification beneath the western Deccan Volcanic Province adjoining the Konkan plains: Evidence from Magnetotellurics

Abstract

The western continental margin of India consists of significant geomorphological features, namely the Konkan Coastal Plains (KCP), the coast parallel Western Ghat Escarpment (WGE), and the elevated Deccan plateau covered by massive lava flows, a product of mantle plume – lithosphere interaction. The region has also experienced multiple episodes of rifting. As a result, geophysical characterisation of the crust and mantle lithosphere is necessary to better understand the plume-lithosphere interaction process and its impact on the cratonic lithosphere beneath the western Deccan Volcanic Province (DVP). We present the results from 2-D and 3-D inversion of magnetotelluric (MT) data acquired along a 200 km long profile traversing in E-W direction across the KCP and the western Deccan plateau. The results reveal a distinct change in the regional geoelectric strike direction from N-S in the KCP to NW-SE in the Deccan plateau with the WGE forming the boundary between these two regions. The geoelectric model constructed from 2-D inversion of the MT data yields highly resistive fragmented eastward thickening cratonic blocks of the Dharwar Craton, dissected by faults/fracture zones of pre-eruptive times. The 3-D full-impedance tensor inversion shows similar resistive blocks along with a pronounced low electrical conductivity zone beneath the Deccan Plateau. The moderate-to-high conductivity zones underlying the resistive cratonic blocks possibly represent the relics of the interaction between the Indian lithosphere and the Réunion plume, and a zone of volatiles /long lived sulfide fluids due to the effect of residual thermal anomaly. We interpret this feature as an evidence for lithospheric modification through upwelling and decompressional melting of the volatile-enriched mantle. We infer that the persistent dynamic topography of the WGE is due to the presence of such fluids at the sub-Moho depths and uplifting of a low-to-intermediate strength lithosphere.