Crustal structure of the Indian plate underneath the alluvial plains of the central Ganga basin by broadband magnetotellurics

Abstract

The Ganga basin consists of thick Cenozoic sediments that mask the tectonic fabric of the underlying Indian plate. Despite the availability of fairly good information on the intra-basin structure, especially at the foothills of the Himalaya due to hydrocarbon exploration activities, very little is known about the basement and the crustal/lithospheric structure although composition and thermomechanical properties of the underthrusting Indian plate are expected to have a significant role in controlling the deformation and seismicity along the Himalayan arc. Here, we present a two-dimensional geoelectric model of the crustal structure along a 285-km-long profile across the central Ganga basin. The results were obtained by inversion of decomposed TE- and TM-mode impedance tensors derived from broadband magnetotelluric data recorded at 45 sites along the profile. The results reveal three main features: (i) the highly resistive Bundelkhand massif (BKC) extends northward beneath the sediments up to Lucknow; (ii) the massif is constituted of two blocks separated by a 10-km-wide moderately resistive nearly vertical zone; and (iii) a super-deep sedimentary basin constituted of highly conductive sedimentary succession exists in the northern segment of the profile. We report the presence of an electrical Moho at 40–45 km depth for the buried BKC and a crustal shear zone within the craton masked by the alluvial sediments. These results shall facilitate in furthering our understanding of the evolution of the BKC as well as the lithospheric/flexural deformation of the Indian continental lithosphere.