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

- We model 3D lithospheric density structure of the Singhbhum Protocontinent.
- The lithosphere is apparently thinned to about 135-140 km in the region.
- Structure reflects a moderate modification of relict, buoyant Archaean lithosphere.
- Study further supports a continental like structure of the Bay of Bengal.

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 2890 kg/m3 as well as a relatively flat Moho at 35-40 km 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 40 km under the confluence of Mahanadi-Damodar Gondwana basins and the Ganga foreland basin, and 36-32 km under the Eastern Ghats Mobile belt and finally reaches 24 km in the Bay of Bengal. The lithosphere-asthenosphere boundary (LAB) across the Singhbhum Protocontinent is at a depth of about 130-140 km. In the regions of Bastar Craton and Bengal Basin, the LAB dips to about 155 ± 5 km 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 200 km, respectively. In the Bay of Bengal, the LAB is at a shallower depth of about 100-130 km except over the 85 0E ridge (150 km), and off the Kolkata coast (155 km). Significant density variation as well as an almost flat crust-mantle boundary indicates the effect of significant crustal reworking. The thin (135-140 km) 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.