Lithospheric Mantle Deformation beneath the Indian Cratons.

The nature of deformation of the deep continental roots beneath the Archean-Early Proterozoic terrains opens the question whether these ancient terrains have had stable roots since the Precambrian or whether recent plate motions have deformed them. In view of this, we make an attempt to study the thermal structure beneath the cratonic regions of the Indian shield, which vary in lithospheric thickness from 65 km in the Singhbhum craton to 148 km in the Archean Dharwars. The average depth of 104 km to the top of the underlying asthenosphere is consistent with other termination methods and is in fact less than half the 200-400-km depth found in other stable areas of the earth. Similarly, the average reduced heat flow of about 35 mW/m2 and Moho temperature of about 550 degrees C (range: 400 degrees -730 degrees C) for the Indian cratons are also much higher than their counterparts elsewhere. Our study indicates a large-scale deformation of the cratonic mantle lithosphere beneath the Indian shield since the Mesoproterozoic caused by various geodynamic causes, challenging the idea of stability of deep continental roots.