GPS CONSTRAINTS ON CRUSTAL SHORTENING IN AN ACTIVE FOLD-THRUST BELT, NORTHWEST ARGENTINA

Abstract:

We present new crustal velocities for five stations from the Puna-Andes GPS Array (PAGA) for the six-year observation period between March 2009 and February 2015. PAGA is a continuously recording GPS (cGPS) network operating in the Puna Plateau and adjacent fold-thrust belt of the Central Andes (~24°S), it is the first ever high-resolution (~100 km station spacing) cGPS exploration of the Andean retroarc at these latitudes. We present the PAGA velocities, realized in a South America fixed reference frame, in the context of the regional crustal velocity field derived from established cGPS networks in the region. We rotate a subset of seven of the velocities, which form a thrust-perpendicular transect, into a thrust front perpendicular/parallel coordinate system to investigate the magnitude and distribution of interseismic strain accumulation. From this subset, we document ~8 mm/yr of thrust-perpendicular shortening accommodated over ~400 km. Additionally, we utilize published regional balanced cross sections and geologically determined frontal thrust slip rates to constrain an elastic edge-dislocation model for the décollement and quantify the degree misfit between the model and the observed crustal velocity field. Finally, we explore penetrative deformation within the wedge, rigid block rotation and ramp-flat detachment geometry as potential sources of motion to reduce the discrepancy between observed and model predicted shortening rates.