Convergence in the western margin of South America during the Cenozoic: Subduction of Nazca, Farallon and Aluk plates

Abstract

New late Cretaceous to recent reconstructions between South America and the oceanic plates in the Pacific basin allow the division of the corresponding convergence history into three stages. The convergence parameters for the 72-47 Ma time span suggest the migration of the Farallón-South America-Aluk triple junction from northern Chile (southern Perú?) up to the southern Patagonian Andes. Some deformational and magmatic events in the upper plate could be attributed to subduction of the Farallón-Aluk ridge by those times. The 47-28 Ma stage is characterized by subduction of Farallón plate in most (all?) of the margin. The convergence rate and direction remained almost constant during this stage. The 26-0 Ma stage corresponds to the subduction of Nazca plate beneath most of the South American trench. The beginning of this stage coincides with a strong increase in convergence rate which gradually decreased during the last 10 m.y., whereas the direction of convergence remained rather constant during the entire stage. Variations of subduction rate during this younger stage may be related with some deformational and magmatic events in the upper plate, including the uplift of the Central Andes.