Was Archean Dharwar Craton ever stable? A seismic perspective

Indian shield comprising a number of Archean-Proterozoic cratons, forms one of the most dynamic, sheared and deformed continental segment amongst all stable areas of the earth. However, for a long time it has been believed that its lithosphere remained unaffected by episodic tectono-thermal and volcanic perturbations. Using available seismic data, an attempt has been made to study the seismic structure of the south Indian shield in order to examine the effects of such mantle processes on its overall crust-mantle structure. Our study suggests that by and large, Indian crust is intermediate to mafic in composition. On an average, only a couple of kilometers of the initially formed upper (granitic-gneissic) crust now remains in place and a thick chunk of the original lower crust has been consumed by the underlying thermally buoyant mantle due to sub-crustal erosion and then subsequently replaced by possibly as much as about 16 km thick magma layer on either side of the Moho. This study throws a new light on the geologic and geodynamic evolution of this region and contradicts the hitherto believed paleo-stability of the Indian shield.