Crustal geoelectric structure of the Indian plate at the western extremity of the Bundelkhand craton and Sharda Depression in the Ganga Basin

The latest episode in the geodynamic evolution of the Ganga Basin invokes continent-continent collision, Himalayan mountain building, and flexure of the Indian plate, which resulted in deposition of thick alluvial sediments in the basin masking the geological heterogeneities of the Indian plate. In recent years, a series of magnetotelluric (MT) studies in the central Ganga Basin have brought out information about its basement and crustal structure. In the present study, we have covered the region between Gwalior and Tanakpur falling at the western extremity of the Bundelkhand craton (BKC) in south and the super-deep Sharda Depression in north (at the Himalayan foothills) by a 330 km long profile to delineate the crustal structure of the region. The geoelectric model of the crustal structure derived from 2-D inversion of broadband MT data reveals the presence of the BKC underneath the alluvial sediments as a resistive northward dipping block in this region also, implying that the BKC extends northward of its presently known boundary shown in the geological map of the region. This cratonic block is buried beneath about 5 km thick moderately resistive rocks of the Vindhyan Supergroup. The results also reveal the presence of an upper-thick Proterozoic rift basin with its deepest part more than 30 km thick within the Sharda Depression, and two lithospheric mantle conductors in the central sector of the profile indicating the possibility of the presence of a significant conductive anomaly at deep lithospheric level. The top conducting layer in the model consisting of the Shiwaliks and Recent alluvium deposited in the flexural environment gradually thickens northward and attains a thickness of about 5 km at the foothills. The results reveal that the crustal structure of this part of the Ganga Basin is highly heterogeneous across the basin.