Age-dependent subduction of oceanic lithosphere beneath western South America

A recently established relation between the penetration depth of oceanic lithosphere and the lithospheric age appears to be of special interest to the understanding of the South American subduction zone. The main characteristics of this complicated zone, such as the absence of deep-focus earthquakes south of 30°S, the variations in the dip angle of the descending Nazca plate and the gap in seismic activity between depths of approximately 300 and 525 km, can be understood if the spatial and temporal variations in the age of the descending oceanic lithosphere are taken into account. In view of the significance of local aspects of the subduction process the South American-Nazca plate interaction cannot simply be considered as a type-example of the interaction between a continental and an oceanic plate.