Crustal configuration of the Narmada-Tapti region (India) from gravity studies

Abstract

The Narmada-Tapti region has a special significance in the realm of Deccan volcanism. The region is covered by a thick pile of lava flows and characterized by several hidden tectonic features and complex geophysical signatures. Though the four deep seismic sounding (DSS) profiles in the region provide some vital information about its crustal configuration, its origin and evolution have remained unsolved. An analysis of the Bouguer gravity anomaly along the DSS profiles indicates the presence of a 15–20 km thick anomalous density (3.02 g/cm 3) layer at the base of the crust beneath the region. The thickness of this anomalous layer decreases gradually towards the east. The unusually high density layer coincides with the area of estimated high heat flow and a number of existing hot springs exceeding 80 °C. The geothermal signatures of the adjacent west coast of India suggest that the asthenosphere has upwarped considerably and is located at a depth of about 40 km. This indicates the existence of partial melting conditions at shallow depths. It is suggested that the massive Deccan flood basalt eruption were associated with a huge magmatic intrusion (magmatic underplating) at the base of the crust, similar to that seen at other volcanic continental margins worldwide. The anomalously thinned thermal lithosphere and the lateral movement of intruding magma at the crust/mantle boundary may also be responsible for the highly contaminated nature of the Deccan flood basalts.