3D Lithosphere density structure of southern Indian shield from joint inversion of gravity, geoid and topography data

Abstract

We present the 3D crustal and lithospheric structure and crustal average density distribution of southern Indian shield (south of 18°N), Sri Lanka and adjoining oceans. The model is based on the assumption of local isostatic equilibrium and is derived from joint inversion of free air gravity and geoid anomalies and topography data. The derived crustal thickness of 10–25km in the oceanic region increases to 34–35km along the coast. A crustal thickness of 34–38km is obtained beneath the Eastern Dharwar Craton and 36–45km beneath the Western Dharwar Craton and the Southern Granulite Terrain. Sri Lanka has a thinner crust of 30–35km. The lithosphere–asthenosphere boundary is located at depths of 70–120km under oceanic regions and ∼150–180km below the Dharwar Craton and the Northern block of Southern Granulite Terrain. A notably thinned lithosphere of ∼130km near Bangalore in the Eastern Dharwar Craton, ∼140km beneath the Southern block of Southern Granulite Terrain and ∼130km in Sri Lanka is observed. The thickness of the lithosphere (∼130km) near Bangalore is inferred as the frozen in signature of a small fossil mantle plume and/or tectono-compositional effect of a rifted margin and a suture. Considerable stretching and/or convective removal of pristine lithosphere in the Southern block of Southern Granulite Terrain and adjoining Sri Lanka, before disappearing completely in the Archaean Northern block of Southern Granulite Terrain and Dharwar Craton, is suggested.