Three-dimensional Moho depth model of the eastern Indian shield and its isostatic implications

摘要

Abstract The Singhbhum Craton, Singhbhum Mobile Belt along its northern, eastern, and western edges, and Chotanagpur Gneissic Complex farther north are all parts of the Precambrian eastern Indian shield. Modern isotope dates and associated geological evidence suggest that these crustal units may be one cratonic block that developed sequentially between 3.55 and 1.00 Ga. The region has always been the focus of numerous geoscientific studies due to its complex evolutionary history and abundant mineralisation. We used the terrestrial gravity data from the Gravity Map Series of India and the EGM2008 global gravity dataset in the Bay of Bengal to model the 3D Moho geometry of the eastern Indian shield and the adjoining Bay of Bengal by inverting the gravity data. The Bouguer gravity data were filtered at several levels before applying the Parker–Oldenburg iterative inversion procedure. The Moho depth measurement is then computed by presuming a constant density contrast. The effects of sediments were eliminated from gravity data by collecting thickness and density details of the sediment from a worldwide sedimentary thickness map CRUST1.0 and applying a correction comparable to the Bouguer correction that uses the density difference of 0.24 g/cm3. Spectral analysis is used to fix a reference depth level and the low-frequency range associated with Moho deflection in the Bouguer anomaly filtered for sedimentary overburden. We subsequently executed the gravity inversion of a basic two-layer structure having a constant density difference of 0.40 g/cm3 across the Moho fixed at an average depth of 35 km. The gravity inversion analysis shows that the Moho depth within the Bay of Bengal is between 18 and 24 km. In the continent, the Moho depth varies from 34 km near the coastline to 38 km towards the Singhbhum Craton and Chhotanagpur Gneiss Complex. In the northern portion of the region, the Moho depth increases to over 40 km underneath the convergence of the Mahanadi–Damodar Gondwana basins and the Ganga foreland basin.