Neotectonic deformation of the southern Puna Plateau, northwestern Argentina

Abstract

Continental plateaus have been likened to pressure gauges that record the mechanical state of the lithosphere involved in mountain building. We outline the kinematic state of the southern Puna Plateau and bounding foreland provinces of the NW Argentine Andes based on surficial fault slip data and crustal seismicity. Kinematic analysis of about 350 faults, measured in a transect from the northern Sierras Pampeanas into the southern Puna, document a relatively uniform late Tertiary history of thrust faulting and vertical extension, followed by a more variable Quaternary history. During the latter, the plateau has undergone horizontal extension on strike-slip and normal faults whereas the thick-skinned foreland continues to experience thrust kinematics. The extension in the plateau, however, is not perpendicular to the trend of the Andes, but sub-parallel to it. A regional survey of all available kinematic data in the Central Andes between 12° and 32°S shows a similar style of kinematics characterizes the northern termination of the Altiplano in southern Peru and northernmost Bolivia. Although kinematic data do not exist for most of the Bolivian Altiplano, the lack of crustal earthquakes and scarcity of modern fault scarps tentatively suggest that the neotectonic activity is concentrated at both ends of the plateau. We interpret this apparent concentration in terms of an edge effect, related to along-strike narrowing topography and diminishing foreland shortening, which in turn are probably related to variations in the underlying geometry of the subducted Nazca Plate.