Cenozoic dextral transpression and basin development at the southern edge of the Puna Plateau, northwestern Argentina

Abstract

In northwestern Argentina, the southern edge of the Altiplano-Puna is the most remarkable positive topographic anomaly (average altitude > 3700 m) of the Andean chain. To the south are the Sierras Pampeanas, a less elevated domain made of alternating compressive basins and ranges developed during the Cenozoic. At about 27°S, the transition between the Puna and the Sierras Pampeanas coincides with a substantial narrowing of the high chain and with a change in the dip of the Pacific subduction zone (Nazca plate), from 30°E below the plateau to subhorizontal below the Sierras Pampeanas. We argue that this structural transition, which can be identified at the scale of the Andean topography, is a major dextral transpressional transfer zone, the Tucumán Transfer Zone. In this region, ENE-WSW- to E-W-directed subhorizontal shortening related to bulk convergence between the Nazca and South American plates interferes with NW-SE-directed subhorizontal shortening strains, due to lateral influence of changes in the amount of crustal thickening on intraplate kinematics. Structural observations, digital mapping, SPOT satellite images and a microtectonic analysis of fault populations provide general insights into the Neogene kinematic evolution of transpressional basins and ranges at the edge of the Puna.