Geochronology of the Indian Precambrian

Abstract

Precambrian geochronology of India is now known with greater precision because of the dating of samples carefully se lected , in respect of geological consideration and set up, from several areas in the pas t decade. Vestiges of older nuclei dating more than 3000 m.y. have been identified in southern, eastern and western India. The Charnockite-Khonda­ lite supergroup (c.2900-2600 m.y.) is now considered to be older than the Dharwar super­ group; the Eastern Ghats (sensu stricto) rocks are now considered belonging to the Charnoc­ kite-Khondalite supergroup proper but with impress of event s at 1650 m.y. and 1400 m.y . a t about the same time as events in Cuddapah Basin, Nellore Schist Belt and Amgaon group. The Aravalli, Bailadila, Bengpal and Iron Ore groups are correlated wi th the Dharwar and range in age from c.2500-<:.2000 m.y. The Delhi supergroup appears to be coeval with the lavas of the Gwalior 'series'. Vindhyan sedimentation which started at c.1400 m.y. continued into Cambrian (?) un­ like the Cuddapah supergroup where sedimentation ended by about 1300 m.y. The success­ ively younger dates for the mobile belts from south to north, with respect to the southern nucleus, indicates a migration of geosynclin es in the same direction. The Satpura 'group' despite valid e.vidences for it s aboliti on as a supergroup appears to indicate the reactivation of the Narmada-Son lineament at 950/ 1000 m.y. in part or eastern India. The manifestation of carbonatite and anorogenic granites dating 725 m.y. in southern India, high-level granites in western India, dating 730 m.y., Mylliem granite at 765 m.y. in eastern India and carbona­ tite in Rajasthan at 960 m.y. appear to be rel ated to reacti vat ion of lineaments in these areas at these dates. The overprint of minera I ages at c.500 m.y. along th e east coast is also suggest­ ive of activity of lineaments but further studies are necessa ry to confirm this view.