Decratonised lithosphere associated with mantle plume upwelling in the Singhbhum craton, eastern India based on geophysical and geodynamic perspective

Abstract

The mode of crustal and lithospheric mantle evolution of cratonic blocks and their subsequent deformation and decratonisation due to regional plate tectonics and continued intraplate geodynamic process, are not well understood. This is especially true for the highly complex Eoarchean Singhbhum craton, located in the eastern part of the Indian shield, which underwent prolonged episodes of intraplate volcanism, mafic dyke intrusions, rifting, collision and widespread sedimentation lasting for over two billion years, leaving behind noticeable imprints in the crust and mantle lithosphere. Our detailed analysis of the geophysical characteristics indicates high crustal velocities and presence of a pronounced metasomatised zone between the depth 14 km and 30 km, which is characterised by drop in Vs from 3.93 km/s to 3.76 km/s. This zone is further followed by 14 km thick high velocity magmatic crust above the Moho. A substantial part of the upper crust has been eroded away from this craton due to thermal-induced uplifting and massive crustal exhumation, caused by the multiple hot mantle plume interactions during Precambrian period, in which mantle potential temperature and pressure reached as high as 1700 oC and 4.4 GPa respectively. This craton is conspicuously associated with highly positive gravity anomalies (up to +10mGal), which are well correlated with high elevation and the location of mafic volcanic suites. It is also characterised by an unusually thin lithosphere (∼ 60-128 km), high Moho temperatures (910°C) and high dose of heat flow (47mW/m2) emanating from the mantle, which conforms with the estimated low effective elastic thickness of ∼30 km. Transient effects of the paleo-thermal anomalies possibly still persist due to periodic rejuvenation of surrounding rift valleys and suture zones. Eventually, this craton now shows geophysical characters of more or less a mobile belt, not of a typical craton. Since, almost 150-200 km thick mantle lithosphere from the bottom has been eroded away from this region due to persistent thermo-geodynamic activities and mantle upwelling induced rise of mantle isotherms, our study does not favour the idea of cratonic stability and preservation of deep continental roots.