Opposite rotations in the Central Andes Bend: Tectonic scenario compared to other cases of opposite rotations and implications for long-term subduction at continental arcs

Abstract

A review confirms opposite paleomagnetic rotations on the northwest and southeast limbs of the Central Andes Bend in Peru, Bolivia, northern Chile and Argentina. Counter-clockwise rotations occur NW of an ENE-oriented axis extending from Arica on the Chile coast to Santa Cruz, Bolivia, with clockwise rotations to the south and SE. Rotations have been measured in all the curvilinear provinces from the Western Cordillera via the Altiplano/Puna to the Eastern Cordillera, InterAndean and SubAndean belts. Although several processes have been postulated, the zone coincides with flat-slab subduction, possibly related to underthrusting of oceanic plateaux. The curvilinear subduction zone is convex in the direction of subduction. Shortening associated with compression and uplift migrated east-northeastwards towards the SubAndean belt from Mid Eocene to Recent and is greatest at the axis of the bend. The area may be segmented with rotations facilitated by strike-slip fault zones: CCW rotations relate to sinistral strike-slip whereas CW rotations are associated with dextral strike-slip. Additional compartmentalisation is here suggested based on volcano distribution, regularly spaced giant copper porphyry deposits, offsets of thrust anticlines, and isolated foreland basins. This tectonic scenario is contrasted with other identified cases of opposite microplate rotations which are usually linked to rollback of a subduction zone which is concave in the direction of subduction. In these cases, CW rotations also relate to dextral strike-slip, and CCW rotations to sinistral strike-slip, but their distributions change if the slab changes from convex to concave in the direction of subduction. These observations provide a model for long-lived subduction at continental arcs where flat-slab subduction switches to rollback over time, such as Pacific China/Russia from 200 to 70 Ma, SW Gondwana from 220 to 145 Ma, western North America from 90 to 0 Ma, or Mexico from 16 to 0 Ma.