Abstract

From Eocene times onwards southern-central Patagonia has been the site of a number of ridge-trench collisions (Cande & Leslsie, 1986; Ramos and Kay, 1992). Subduction of a spreading oceanic ridge beneath continental lithosphere is a rare event and the potential effects of ridge subduction on the overriding South American plate are still poorly understood. In order to better constrain the timing of igneous activity and the possible effect of tectonic rotations formed in response to ridge subduction events, *Ar-j9Ar radiometric age dating and palaeomagnetic studies of key outcrops were undertaken in the region south of Coyhaique between 45'30 and 47"s.