Role of the plate margin curvature in the plateau buildup: Consequences for the central Andes

The influence of convergent plate boundary curvature on the stress distribution in an overriding plate is explored using analytical and numerical modeling techniques. Trench‐parallel compression can be produced near the symmetry axis of a seaward‐concave plate boundary if the interplate friction is high and/or if the subducting lithosphere has a low flexural rigidity, which produces little nonhydrostatic normal stress on the plate boundary. This situation favors the formation of trench‐parallel thrusts with minor trench‐parallel component of slip. Trench‐parallel compression is reduced along the most oblique parts of the plate boundary, which favors the formation of strike slip faults with major trench‐parallel slip. Both the stress conditions on the interplate zone and the 3‐D geometry of this zone control whether the trench‐parallel stress in the center of a seaward‐concave curvature is a tension or compression. Low dip angle and high convergence obliquity angle favor trench‐parallel compression. In the central Andes, N‐S minor shortening in the center of the Arica bend and strike slip systems north and south of the symmetry axis suggest that the effect of shear traction dominated during Cenozoic time when the curvature of the plate boundary was forming. This result suggests that the processes responsible for the formation of the plate boundary curvature were assisted by enhanced interplate friction and/or reduced compressive nonhydrostatic normal stress. For a geometry resembling the present‐day South American plate margin, estimations of normal and shear stresses on the plate boundary suggest that the trench‐parallel stress in the center of the curvature is compressive.