Delineation of lithosphere structure below Northwest Indian Shield (India) through constrained geopotential field modelling : geodynamic evolution

Abstract

<p>The Northwest Indian shield (NWIS) comprises of Archean Bundelkhand, Marwar and Dharwar cratons, Proterozoic mobile belts of Aravalli Delhi fold belts (ADFB) and Central Indian tectonic zone (CITZ), and the basins such as Vindhyan (VB), Cambay (CR) and the Kutch (KR). The major area of the NWIS is covered by the Cretaceous Deccan Volcanic Province (DVP) that makes it difficult to assess the lithosphere structure in this region. Here we present the seismically constrained multi-scale geopotential field interpretation of  gravity, magnetic and geoid across the major Precambrian terrains of NWIS to delineate the lithosphere structure and further to understand the evolution of these terrains. The Bouguer gravity anomaly map shows overall high gravity values except the Bundelkhand and Dharwar cratonic parts over the NWIS region. The subsurface extension of the Precambrian  terrains of the NWIS are indicated by the distinct anomaly signatures in regional gravity anomaly map. The residual gravity anomaly map is able to delineate the shallow source bodies and boundaries between various terranes that correlat well with the surface geological expressions. The constrained geopotential modelling carried out along SW-NE trending profile across the region reveals that the Moho and  Lithosphre Asthenosphere Boundary (LAB) below the DVP and CR is relatively shallow as compared to the ADFB. It has also been noticed that a high density layer at the base of the lower crust, represents the presence of  underplated crust. The shallower lithosphere structure observed below the CR region might indicate the Cretaceous reworking. The imprints of the Deccan magmatism through intrusive bodies and the modelled structure below NWIS have implications on the lithosphere evolution in the region. </p>