Magnetotelluric evidence for the thermotectonic architecture of a Paleoproterozoic rift basin in southwestern India

Abstract

The Kaladgi basin is one of the major Paleoproterozoic rift basins in Peninsular India. Here we attempt to reconstruct the architecture of the basin and evaluate the deep tectonics using magnetotelluric evidence. We identify thermo-tectonic rejuvenations of the lithospheric structure, with the continental lithosphere showing tectonic channeling of the thermo-magmatic fluxes in lateral and vertical directions. Our magnetotelluric profile passes adjacent to the Ramdurg, Kaladgi and Bilgi areas, crossing different geological formations. The 2-D electrical model was constructed from broadband magnetotelluric and long-period magnetotelluric data. The maximum thickness of the basin is identified as ~4,500 m with sediment resistivities less than 2,000 Ω-m overlying the high resistivity crystalline basement. The anticline and syncline-type structures of the basin were well-imaged, and an expansion of the basin was identified beneath the Cretaceous Deccan volcanic provinces. Deep-seated faults divide the crust into major blocks, representing an extension of the NW-SE trending faults (Bagalkot fault) towards the northwestern region. The low resistive area between the depth ranges of ~40–60 km defines the crust-mantle transition zone. The diffuse nature of the electrical Moho is evident beneath the basin, which suggests the decoupling between the crust and upper mantle lithospheric structure, which we correlate with the northward migration of the Indian plate during the Cretaceous-Tertiary period. We correlate the arti facts of the crustal conductive features with the fissure eruption of basalts. We also image the Archean Chi tradurga Suture Zone (CSZ) beneath the entire Kaladgi rift basin. Our study provides important insights into the architecture of one of the major Paleoproterozoic rift basins.