Remnant plume head under Neoproterozoic Malani Igneous Suite, western India

Abstract

The plumbing architecture of the Neoproterozoic Malani Igneous Suite (MIS), representing one of the largest, intraplate, anorogenic rhyolitic volcanism in western Rajasthan, is poorly constrained. We present a crustal scale model from gravity anomaly modelling also supported by other geological and geophysical observations. The regional-residual separation using frequency filtering technique reveals the presence of high-density discreet bodies at different crustal levels. A 2½D forward and 3D constrained inversion of the residual gravity anomaly suggests the presence of sediments covering MIS, and 6–8 km thick high-density sills emplaced in upper crust down to ~9 km depth. The high gravity anomalies in the remaining part of the Bouguer anomaly could be explained by the presence of 10–12 km thick high-density magmatic intrusion at the base of the Moho below 32–38 km depth. These high-density bodies may be attributed to mafic/ultramafic cumulates during MIS magmatism. It appears that the magmatic melts migrated upwards from the mantle to lower crustal magma reservoirs may alter the bulk magma composition by crustal assimilation. The ensuing density contrast would lead to the upward migration of the dominant felsic melt and their emplacement at shallower depths.