Precambrian Geochronology of Peninsular India

Abstract

Geochronological data for the Precambrian formations of such a large region as Peninsular India are still far too few. However, with the available data, certain broad generalisations can be made regarding their relative ages, correlation, and stratigraphy.

Mysore, Kerala, Singhbhum, and Bundelkhand contain rocks nearly 3000 m.y. old. which probably represent the nuclei around which grew the continental mass of the Peninsula. The Dharwar craton appears to be the most ancient part of the Peninsula. The existing age determinations do not help, however, in determining which is the oldest rock formation in this region.

The Eastern Ghats belt was formerly considered to be about 1600 m.y. old, but it is now known to contain rocks ranging in age from 2100 to 2600 m.y. The base of the Cuddapahs is about 1400 m.y. old, and the Kurnools about 1150 m.y. Southernmost India contains rocks of a wide variety of ages. Some are very ancient being over 3000 m.y. old. There are also evidences of 500 m.y. and 700 m.y. events which have been recognised in Ceylon.

In Rajasthan many formations are now known to be much older than previously thought. The base of the Aravallis appears to be about 2500 m.y. old and the Delhis 1800 m.y. The Bundelkhand and Berach granites are of the same age (2555 ± 55 m.y.). The Banded Gneiss Complex has components varying in age from about 2100 to 950 m.y. The base of the Vindhyans is probably 1400 m.y. old, and the Upper Kaimur Series about 910 m.y. No dates are available for fixing the upper age limit of the Vindhyans. They probably span the Precambrian-Cambrian boundary.