Deep electrical structure over the Paleoproterozoic intracratonic Kaladgi rift basin in southwestern India imaged from magnetotelluric studies

Abstract

The disintegration of the Columbia supercontinent during the late Paleoproterozoic generated major rift basins in the constituent continental fragments. The Kaladgi basin, located between the southern part of the Deccan volcanic province (DVP) and the northern part of the Dharwar craton, is a Columbia rift- related basin in southwestern India that preserves a complex history from initial fault-controlled mechan- ical subsidence during rifting, thermal subsidence along a collision zone, crustal thinning due to stretch- ing and erosion associated with doming. The Paleoproterozoic basins worldwide show higher uranium concentration and many deposits are also established in the Purana basins of India. In the present study, the lithotectonic architecture of this basin using broadband magnetotelluric ( ∼320 Hz–30 0 0 s) soundings in the western segment of the Kaladgi rift basin along two profiles. Two-dimensional (2-D) inversion of data using a 2-D nonlinear conjugate gradient algorithm along both profiles provides insights into the deeper structure of the basin. Our results reveal a thin sheet of Deccan volcanic, sedimentary successions belonging to the Badami and Bagalkot groups, and Proterozoic sediments from top to bottom beneath this basin. The crustal structure is highly heterogeneous and associated with deep-seated faults, and its thick- ness increases from the eastern Dharwar craton ( ∼30 km) to the western Dharwar craton ( ∼45 km). The crustal conductors are interpreted as mafic intrusions derived from the underplated basalts. The mod- erate conductive features may correspond to carbonate fluids trapped within the faults/fractures zone during basin initiation. The conductive features in the lower crust and the Moho are interpreted as flu- ids derived from underplated intrusions through plume impact. The NNW trending Chitradurga Suture Zone (CSZ) signature and the Bababudan-Nallur Shear (BNS) in the crust and upper mantle depth are imaged along both MT profiles. This study provides insights into the lithology and tectonic architecture of a long-lived rift basin involved in multiple tectonic events from the late Paleoproterozoic to the late Cretaceous.