Isotopic age study of pre-Alpine rocks in the basal units on Naxos, Sikinos and Ios, Greek Cyclades

Abstract

Isotopic dating proves the existence of pre-Alpine basement rocks on the islands of Naxos, Sikinos and Ios in the Greek Cyclades. The U-Pb systematics of a suite of zircons from the migmatite dome on Naxos shows that the main generation of zircons of late Paleozoic age contains a minor amount of old radiogenic lead. Rb-Sr analysis of whole rock samples of a metadiorite on Sikinos substantiates the existence of a late Paleozoic or early Mesozoic basement. K-Ar analysis of white micas from the augengneiss on Ios revealed ages of about 125 Ma to about 23Ma, intermediate between the Hercynian and the Alpine orogenesis. On the basis of textural- and chemical characteristics it is suggested that some of these micas represent partially reset Hercynian micas, other Alpidic micas with excess radiogenic Ar, and a few reflect a complete rejuvenation during the Alpine orogenesis.