Archaean-Proterozoic Boundary in India

Greenstone belts in India are predominantly Archaean with minor development in Proterozoic. The important greenstone belts of India, like the Dharwar of South India, Iron-Ore Group of Eastern India and Bailadilla Group of Central India, are of Late Archaean age and show characteristics transitional to Proterozoic. The end of the Archaean is marked by a burst of granitic activity.

Two independent continental blocks-a southern Peninsular Block and a northern Foreland Block are recognised. The Early Proterozoic successions in India are formed in rifted basins fringing these two Archaean cratonic blocks. These Early Proterozoic cover-rocks and the Archaean basement have invariably been deformed together in Middle Proterozoic, pointing to substantial crustal shortening. The narrow continuous fold belts like those of Aravalli, Delhi, and Satpura, mark the sites of the coming together of the different continental blocks to form a single Indian continent as we see today. A comparable situation is that of the Great Lakes Tectonic Zone of Central North America. Geological, geochronological, geochemical, palaeo-magnetic and palaeobiological considerations which help in demarcating the boundary are outlined.

Ideally, in order to more precisely demarcate the stratigraphic boundary, specific rock units have to be identified in the rock succession in each of the regions. Present data is insufficient and the available maps are on too large a scale to permit identification of boundary stratotypes.