COMBINING LOW-TEMPERATURE THERMOCHRONOLOGY AND COSMOGENIC RADIONUCLIDE DATING TO DOCUMENT FAULT INITIATION AND EXHUMATION IN THE ANDEAN PRECORDILLERA, SAN JUAN, ARGENTINA

The central Andean Precordillera has experienced active faulting and deformation from the early Miocene to present in a region with relatively stable and arid climate conditions persisting since at least ~10 Ma. Thus, landscape development has been driven primarily by tectonics rather than climate. We use a novel combination of low-temperature thermochronometry and cosmogenic radionuclide (CRN) techniques to quantify changes in recent and paleo-erosion rates in relationship to fault slip, fault growth patterns, and basin sedimentation. Eight vertical transects were collected across three active thrust faults in the eastern-most part of the Argentinian Precordillera between 30-31°S. Preliminary apatite (U-Th-Sm)/He data indicate the potential for partial resetting even in the highest elevation samples within our transects. Ages are between 30Ma and 2Ma and tend to be younger to the south, supporting previously published work suggesting fault activation migration from north to south. Initial erosion rates determined by our CRN data range from 22 – 1330 m/my, with generally lower rates in the north and higher rates to the south. Our CRN burial data are messy and indicate most burial ages are too old (>5Ma) for the technique, however, one sample in the north does record an isochron age of 2.5±0.3 My. Ongoing analysis and modeling of both thermochronology and CRN data will be used to constrain the most recent exhumation and erosion history in the central Andean Precordillera. Furthermore, we will be able to test the utility of combining thermochronology and CRN data to answer questions such as: Are landscape response (lag) times similar across different faults and/or along strike of the same fault? Do pulses detected in depositional sequences reflect pulses in fault-slip? Do paleo-erosion rates obtained via CRN analyses agree with paleo-erosion rates obtained through low-temperature thermochronologic analyses? Can burial and exposure information at the near-surface help refine rock cooling histories?