Geology and Crustal Evolution

Introduction

The eastern segment of the Indian Precambrian shield preserves records of geological events spanning over Early Archean to Late Proterozoic time. There is a debate about the definition of the Eastern Indian craton. Should it comprise only the Archean basement rocks of South Singhbhum and some adjacent parts of Orissa and the banded iron formation (BIF)-bearing belts of supracrustal rocks flanking them? Or should it also include the physically contiguous and geologically related Proterozoic mobile belt of North Singhbhum and the Chhotanagpur Gneissic Complex (CGC), lying to the north of this belt. We, in the present context, define the area in its conventional sense, viz, from the Chhotanagpur Gneissic Complex in the north, upto the margin of Eastern Ghat granulite terrain in the south, and the eastern margin of the Mahanadi graben in the west to the last exposure of Precambrian rocks in the east. Considered in the context of crustal evolution of the region, these limitations should satisfy the definition of a craton (cf. Goodwin, 1996; Hoffman, 1988). However, the Archean granitic basement and the ancient supracrustal rocks of South Singhbhum–North Orissa may be considered to constitute the Archean cratonic nucleus (Fig.4.1.1).