Crustal structure of Bengal Basin and Shillong Plateau: Extension of Eastern Ghat and Satpura Mobile Belts to Himalayan fronts and seismotectonics

Gravity data from the East India and the Bangladesh are processed and compiled together to provide a composite complete Bouguer anomaly map of this region. Modelling of gravity profiles across the East Indian Shield (Chhotanagpur Granite Gneiss Complex, CGGC), the Shillong Plateau and the Bengal basin in Bangladesh, constrained from seismic studies suggest crustal thickness of 37–38 km and thrusted high density rocks in the middle crust under the East Indian Shield reducing to 30–32 km with thick sediments of 12–14 km under Bangladesh. Reduced crustal thickness under Bangladesh is attributed to oceanic type of crust, which is connected to Indian continent along Hinge zone characterized by linear gravity highs connecting east coast of India to the Shillong Plateau. Thrusted high density rocks under the CGGC and the Shillong Plateau are in comparison to those under the Eastern Ghat and the Satpura Mobile belts (EGMB, SMB) respectively suggest the north ward and east ward extensions of these orogenies. Margins of the thrusted block under Shillong Plateau when projected on surface coincide approximately with the south dipping Dauki and the Brahmaputra faults which coincides with central bulge due to lithospheric flexure indicating their surface expositions.