EVIDENCE FOR A RELEASING BEND AT THE SOUTHERN MARGIN OF THE PUNA PLATEAU, ARGENTINE ANDES

Fault data from northwestern Argentina's Cordillera de San Buenaventura, a Late Cenozoic, E-W trending volcanic range at the southern margin of the Puna plateau adjacent to the modern volcanic arc at 27°S, constrain its tectonic and volcanic evolution. Faults in this region dominantly strike roughly E-W, with lengths reaching at least 30-40 km. Fault motion, where measurable, has been normal, commonly with a right-lateral component. Scarps displace alluvium and dated Quaternary lava domes and flows, intermediate to felsic in composition, with throws of 1-100 m. Previous studies in the surrounding southern Puna have reported ~NNW-SSE extension along N-S to NNE-SSW striking right-slip faults active since at least 2 Ma. The new data, combined with existing data, suggest that the Cordillera de San Buenaventura represents an active releasing bend along a regional strike-slip system. We propose that opening of this releasing bend triggered an episode of prolific, but non-explosive, magmatism at the surface during the latest Tertiary or Early Quaternary. Magmatic addition filled in the topographic depression created by the releasing bend and, together with thermal uplift, constructed the topographically high Cordillera de San Buenaventura.