Nature of the lithosphere-asthenosphere boundary beneath the Eastern Dharwar Craton of the Indian Shield

Abstract

• Thickness and nature of lithosphere-asthenosphere boundary has been discussed. • Partial melts may explain the shallow and sharp lithosphere-asthenosphere boundary. • Plume induced lithospheric thinning argued beneath the Eastern Dharwar Craton . • The Eastern Dharwar Craton lithosphere has been substantially modified. The lithosphere-asthenosphere boundary (LAB) is a fundamental element of the plate tectonic hypothesis that accommodates the differential motion of rigid lithosphere over the weaker asthenosphere . In recent times, various usages have been used to define the LAB, depending on the nature of their measurements. Here, we investigate the lithospheric structure beneath the Eastern Dharwar Craton (EDC) of the Indian Shield using geochemical, thermal and seismological data sets. We analysed S-receiver functions from the stations deployed in the EDC along with the surface wave dispersion tomography. We also added thermal measurements from 5 different locations and geochemical data from 34 Kimberlite/Lamproite xenolith samples to constrain the nature of the LAB. The seismological measurements using Rayleigh wave dispersion and receiver function analysis indicate the lithospheric thickness of 98–118 and 94–118 km respectively, with sharp transition across the LAB. The P-T results from xenoliths are interpreted in concurrence with the heat-flow measurements suggesting a thick thermal lithosphere of ∼ 200 km for the normal mantle solidus with cold geotherm. To reconcile our observations, we invoke partial melts or melts enriched in volatiles, which significantly lowers the viscosity of mantle rocks inducing a zone of weakness between the rigid lithosphere (∼125 km) and the convective asthenosphere. Further, we favour the view that the thick lithosphere beneath the Indian plate has been thinned by a plume during the Gondwanaland breakup at ∼ 130 Ma. The presence of younger kimberlites from the Indian shield support that it is further degenerated by the delamination leading to an uneven topography in the LAB.