Basement and lithospheric structure of the central Ganga Basin between the Bundelkhand craton and the Sharda Deep by magnetotellurics

Abstract

The geological and tectonic fabric of the Indian plate in the Ganga Basin is masked by alluvial sediments. Geophysical exploration of the basin for hydrocarbons yielded information on the presence of transverse basement ridges and Cenozoic as well as some pre-collision stratigraphy of the basin. However, the depth of the basement especially in the northern part of the basin and the nature of the underlying crust and mantle lithosphere is largely unknown. We have carried out a magnetotelluric (MT) study along a 300-km-long profile between the Bundelkhand craton (BC) and the Sharda Deep (at the Himalayan foothills) across the central Ganga Basin to delineate the basement and the lithospheric structure. The electrical resistivity image obtained by 2-D inversion of broadband MT data reveals significant lateral heterogeneity in the subsurface structure along the profile. The model yields a super-thick sedimentary basin in the Sharda Deep consisting of multiple stages of basin formation, including a Proterozoic paleo-rift, and a highly heterogeneous lithospheric structure of the Indian plate north of the BC. The model consists of two major upper mantle conductors connected to the conductors within the lower crust. It is surmised that enhanced conductivity could be due to the presence of fluids and the upper mantle conductors are feeding to the crustal conductors. However, an in-depth analysis of the genesis of these conductors would require other independent geophysical information which is not available at present. This is the first reporting of such a heterogeneous nature of the Indian continental lithosphere beneath the Ganga Basin at a regional scale. Our model further supports the presence of the electrical Moho in the BC and, together with earlier published MT results along another profile, suggests that the BC extends much farther north than its presently known northern limit.