Abstract

The massive eruption of Late Cretaceous Rajmahal Traps at the palaeocontinental margin of the Eastern Indian shield was in passive response to the rift-drift event of the Indian subcontinent. To understand the impact of the magmatic process that originated in the deep mantle on the lower crustal level the conspicuous gravity anomalies observed over the region were evaluated, integrating the available geophysical information. The region encompassing the Rajmahal Traps is well characterized by an elongated nature of relative high Bouguer anomaly in contrast to predominantly low Bouguer anomaly in its surroundings. The anomaly attains its peak amplitude over the shield edge along the western margin of the Rajmahal volcanics, with an average wavelength of 100 km in an east-west direction. That the relative gravity high extends beyond the metamorphic-Gondwana contact encompassing an even greater part of the Rajmahal volcanics, this long wavelength nature of the anomaly argues for a source at some deeper level; possibility of crustal accretion at the base of the crust cannot be ruled out. The maximum amplitude of the relative gravity high presents itself as the centre of the potential feeder channel for the Rajmahal Traps. It is suggested that the crustal accretion is the imprint of the mantle plum head, when the eastern margin of the eastern Indian shield passed over the hot spot. The nosing of the crustal accretion towards down south is the possible imprint of the subsequent magmatic intrusion along the plume path