Spatial and temporal variations in the Andean subduction zone.

The age-dependence of subduction is of special interest in understanding the Late Cainozoic history of the Andean subduction zone. Many of the complexities of this zone result from the peculiar circumstances that the zone is in transition from an early stage of consumption of old lithosphere (> 70 m.y.) towards the latest stage of consumption of young lithosphere. This has induced an evolutionary pattern with significant temporal variations, notably changes in dip and length of the subducted slab. Many of the temporal and spatial variations in lithospheric age at the trench originate from the re-organization in plate configuration which started with the break-up of the Farallon plate into the Cocos plate and the Nazca plate about 25 m.y. ago. (This and the following 11 abstracts represent all but one of a thematic series on the Geology of the Andes).-R.A.H.