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Journal of the Geological Society

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Spatial and temporal variations in the Andean subduction zone

A comprehensive global study of the process of subduction of oceanic lithosphere has made it evident that a major role is played by the age of the subducted lithosphere. The age-dependence of subduction is of special interest in an understanding of the late Cenozoic history of the Andean subduction zone. Many of the complexities of this zone result from the peculiar circumstance that the zone is in transition from an early stage of consumption of old lithosphere (>70 Ma, producing deep earthquakes) towards the latest stage of consumption of young lithosphere (without deep earthquakes). This transition has induced an evolutionary pattern with significant temporal variations, notably changes in dip and length of the subducted slab. Moreover, the various segments of the South American subduction zone are in different stages of this evolution. In comparison with the other segments, the northern Chile segment is in the earliest stage and, therefore, shows a much closer resemblance to the ‘classic’ deep subduction zones in the Western Pacific than do other parts of the South American zone. A roughly N–S symmetry in development is found around northern Chile, with the Ecuadorian and southern Chilean (near 40–45°S) segments representing the latest stage. To a large extent the temporal and spatial variations in lithospheric age at the trench originate from the reorganization in plate configuration which started with the break-up of the Farallon plate into the Cocos plate and the Nazca plate at about 25 Ma.