The nature and thickness of lithosphere beneath the Archean Dharwar Craton, southern India: A magnetotelluric model

Abstract

The Dharwar Craton in the southern Indian shield region occupies a key position in reconstructions of the earliest supercontinent “Ur” as well as in the global Neoarchean configurations of continental assembly. Here we synthesize the available geophysical data that include heat flow, seismic tomography, temperature profile derived from xenoliths and magnetotellurics (MT) from the Dharwar Craton. A thickness of more than 200km is identified for the lithosphere beneath this craton by magnetotelluric model. Our inference lends support to the models from recent seismological investigations that argue for the presence of a thick lithosphere, as well as the upper mantle structure derived from the analysis of mantle xenoliths. A synthesis of recent geophysical and geochemical data, together with our magnetotelluric model indicate the existence of a thick lithospheric root beneath the Dharwar Craton and suggest that not much of the lithosphere has been eroded since Precambrian in this region, leading to the conclusion that the Dharwar Craton preserves an Archean tectosphere. An increase in the lithospheric thickness from east to west in the Dharwar Craton and the Lithosphere–Asthenosphere Boundary (LAB) migration to shallower levels observed from geophysical data towards the east is interpreted as a probable reflection of the Mesoproterozoic subduction-erosion of the Archean cratonic keel.