Chapter Two - Indian Peninsular Shield

Abstract

The Indian peninsular shield is a mosaic of crustal blocks of independent evolutionary history. Rocks as old as 3800Ma are exposed here. It comprises the low-grade granite-greenstone of the Dharwar craton in the north and the high-grade granulite terrane in the south. In order to determine the configuration of the crust in the Indian peninsular shield, seismic studies have been conducted in two phases. In the first phase, refraction and postcritical reflection studies were carried out along two east-west profiles, across the Proterozoic-Archean Cuddapah Basin and the Dharwar craton. The crustal velocity models for these regions have been highlighted and various crustal features are explained. In the second phase the refraction, postcritical reflection and also deep reflection studies were carried out along a profile crossing the southern granulite terrane, including the Cauvery shear zone, in a north-south direction. The evolutionary model of this region suggests that composition of the crust in the Cauvery shear zone system is different from the Archean Dharwar craton in the north and the Archean-Proterozoic Madurai block to the south. The shear zones of this system separating the two crustal blocks to the north and south represent terrane boundaries. Crustal growth in these shear zones is a result of two-way mass transfer between the mantle and the crust, in the form of delamination and underplating.