Three-dimensional lithospheric mapping of the eastern Indian shield: A multi-parametric inversion approach

Abstract

We analyzed satellite gravity and geoid anomaly and topography data to determine the 3D lithospheric density structure of the Singhbhum Protocontinent. Our density model shows that distinct vertical density heterogeneities exist throughout the lithosphere beneath the Singhbhum Protocontinent. The crustal structure identified includes a lateral average crustal density variation from 2800 to 2890kg/m3 as well as a relatively flat Moho at 35–40km depth in Singhbhum Protocontinent and Bastar Craton. A similar Moho depth range is found for the Mahanadi, Damodar, and Bengal basins. In the northern part of the area, Moho undulates between more than 40km under the confluence of Mahanadi–Damodar Gondwana basins and the Ganga foreland basin, and 36–32km under the Eastern Ghats Mobile belt and finally reaches 24km in the Bay of Bengal. The lithosphere–asthenosphere boundary (LAB) across the Singhbhum Protocontinent is at a depth of about 130–140km. In the regions of Bastar Craton and Bengal Basin, the LAB dips to about 155±5km depth. The confluence of Mahanadi and Damodar Gondwana basins toward the north-west and the foreland Ganga Basin toward the north are characterized by a deeper LAB lying at a depth of over 170 and 200km, respectively. In the Bay of Bengal, the LAB is at a shallower depth of about 100–130km except over the 85 0E ridge (150km), and off the Kolkata coast (155km). Significant density variation as well as an almost flat crust–mantle boundary indicates the effect of significant crustal reworking. The thin (135–140km) lithosphere provides compelling evidence of lithospheric modification in the Singhbhum Protocontinent. Similarities between the lithospheric structures of the Singhbhum Craton, Chhotanagpur Gneiss Complex, and Northern Singhbhum Mobile Belt confirm that the repeated thermal perturbation controlled continental lithospheric modification in the Singhbhum Protocontinent.