Late Cretaceous to recent plate motions in western South America revisited

Abstract

The Andean Cordillera has evolved since the Late Cretaceous in the context of subduction of oceanic lithosphere beneath continental lithosphere, making the kinematics between South America and its adjacent oceanic plates in the Pacific basin valuable to analyze the development of the Andean orogen. The latest Cretaceous–Cenozoic convergence history in western South America may be divided into three stages. The youngest Stage 1 (25–0Ma) is characterized by ENE directed convergence of the Nazca plate toward most of South America, and by ~E–W subduction of the Antarctic plate beneath southern Patagonia. The Nazca–South America convergence rate in Stage 1 shows a continuous decrease from the highest values in the Cenozoic (~15cm/yr) to the present day values from GPS measurements (~7cm/yr). Stage 2 (47–28Ma) is characterized by NE directed subduction of Farallon with the convergence rate remaining almost constant during the entire interval. In those times obliquity was dextral in Chile, sinistral in southern Peru, while almost head-on convergence occurred in central and northern Peru. During latest Cretaceous to Early Eocene times (Stage 3) the Farallon plate was subducted beneath Perú and the Phoenix plate was subducted farther south, where a triple junction migrated southward along the Chilean margin. The subduction of the Farallon plate was rather slow with variable direction imposed by the position of the triple junction, whereas subduction of the Phoenix plate was rapid (>10cm/yr) and ESE directed. We present a working hypothesis suggesting no major changes in the age of subducted lithosphere in the Chile trench from Middle Eocene to Late Oligocene, followed by subduction of progressively older oceanic lithosphere in the early Neogene and progressively younger lithosphere during the late Neogene and the Quaternary. In addition, it is shown that South American motion as predicted by available hotspot models has insufficient resolution to be applied to the analysis of Cenozoic Andean deformation.