40 K/ 40 Ar Ages of a Suite of Lower Palaeozoic Post-Tectonic Granitoids, Southern India

Four ⁴⁰K/⁴⁰Ar mica ages of the granitoid suite around Kadavur range from 475 to 527 Ma with a mean around 500 Ma. Since (i) there is a close agreement in mica ages between variants of the granitoid suite and between size fractions and (ii) the dated minerals are from post-tectonic, undeformed and unmetamorphosed rocks, this mean age appears to closely approximate the age of intrusion of the granitoids. One hornblende separate from the older invaded hornblende leuco-gabbro of the Kadavur gabbro-anorthosite complex with a ⁴⁰K/⁴⁰Ar age of 492 Ma is most probably a thermally reset age.