Age and Evolution of the Upper Cenozoic Andesitic Volcanism in Central-South Chile

The first ten potassium-argon determinations made on andesitic rocks of the Andes and Coastal ranges of central-south Chile, between latitudes 36° and 42° South, demonstrate the existence of at least two main cycles of volcanic activity; one in the Miocene and the other in the Pliocene to Holocene. The volcanic activity lines seem to have changed eastward from the present Coastal volcanic belt in Miocene times to about 100 km inland in Pliocene and Holocene times. During late Pleistocene to Holocene, a gradual inversion in the direction of migration of volcanism occurred. The geochronological asymmetry of the volcanic chains seems to be a highly important feature in this continental border and plate-contact zone.