Plate motions, Andean orogeny, and volcanism above the South Atlantic convection cell

The geometric and kinematic evolution of the Andes provides insight onto the nature of the force balance beneath the South American plate. While the Andean load is opposed on its western edge by the force induced by subduction of the Nazca plate, its more elusive eastern counterpart, which we explore herein, requires some contribution from the mantle beneath the South Atlantic. Using a mantle flow model, we show that the Andes owe their existence to basal drag beneath South America caused by a cylindrical convection cell under the South Atlantic. We find that the observed Andean uplift requires both westward push from active upwelling beneath Africa and westward drag toward the downgoing Nazca slab. These mutuallyreinforcing downwellings and upwellings amount to 38% and 23% of the total driving force, respectively. Further decomposition reveals that the South Atlantic cell is most vigorous near its center, rendering the net drag force higher where the Andes also *Manuscript Click here to view linked References in su -0 06 65 61 3, v er si on 1 6 Fe b 20 12 Author manuscript, published in "Earth and Planetary Science Letters 316-317 (2012) 126-135" DOI : 10.1016/j.epsl.2011.11.040