Evidence of underplating from seismic and gravity studies in the Mahanadi delta of eastern India and its tectonic significance

Abstract

[1] We have imaged the crustal configuration of the Mahanadi delta of eastern India by modeling both wide-angle seismic and Bouguer gravity data. This delta has undergone several stages of rifting, subsidence, sedimentation, and uplift. It is one of the important Gondwana sedimentary basins of India where widespread volcanic activity occurred during the Early Cretaceous along the rift zones. This volcanic activity corresponds to the breakup of greater India from east Gondwana (e.g., present Antarctica and Australia). We have derived a five-layer crustal model with velocities of 6.0, 6.5, 6.0, 7.0, and 7.5 km/s having estimated densities of 2.7, 2.8, 2.65, 2.9, and 3.05 g/cm3, respectively. The velocity-density relation along with heat flux and other geological/geochronological information indicates typical rift-related evolution of the delta with a midcrustal low-velocity (6.0 km/s) and low-density (2.65 g/cm3) zone and a ∼10 km thick high-velocity (7.5 km/s) and high-density (3.05 g/cm3) layer at the base of the crust, presumably due to underplating. The Moho upwarping or crustal thinning in the rift zone and emplacement of thick, high-velocity material at the base of the crust strongly suggests basaltic underplating probably due to the Kerguelen hot spot activity. These activities are synchronous with ∼117 Ma Rajmahal volcanism in northeast India and the Lambert graben in East Antarctica and are closely associated with the Gondwana breakup in the India-Antarctica sector. The rifting stages are closely correlated with the sedimentation phases of the lower and upper Gondwana deposits in the Mahanadi delta, which evolved parallel to the Lambert graben in East Antarctica.