Age data on pegmatites of south Kerala and their tectonic significance.

The K/Ar mica age of chrysoberyl-bearing pegmatites from four localities of Trivandrum district, Kerala, SW India, ranges 445- 474 m.y., with a mean of approx 460 m.y. Close agreement exists between the ages of the concordant and crosscutting pegmatites, between muscovite and biotite ages, and also between various size fractions. Chrysoberyl occurs within feldspars in association with quartz and muscovite. Since the formation of chrysoberyl-quartz association requires a higher P or T, the reported age would indicate the time of emplacement of the chrysoberyl-bearing pegmatites at the closing phase of a major tectonomagmatic event. It is interesting to note that these pegmatites are younger compared with those of other localities such as Rajasthan, Bihar, Nellore and Mysore. -T.R.