Age data on pegmatites of South Kerala and their tectonic significance

K/Ar mica age of chrysoberyl-bearing pegmatites from four localities of Trivandrum district, Kerala ranges from 445 to 474 m.y., with a mean around 460 m.y. There is a close agreement between the ages of the concordant and cross-cutting pegmatites, between muscovite and biotite ages, as 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 pressure or temperature, 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 of south-western India are younger compared to those of other localities viz., Rajasthan, Bihar, Nellore and Mysore. (author)