10Be surface exposure dating reveals strong active deformation in the central Andean backarc interior

EZEQUIEL GARCÍA MORABITO; CARLA M. TERRIZZANO; ROLAND ZECH; SEAN WILLETT; MARCELA G. YAMÍN; NEGAR HAGHIPOUR; LORENZ WUETHRICH; MARCUS CHRISTL; JOSE M. CORTES; VICTOR A. RAMOS

Viena

Congreso; EGU General Assembly 2016; 2016

Understanding thedeformation associated with active thrust wedges is essential toevaluate seismic hazard. How is active faulting distributedthroughout the wedge, and how much deformation is taken up byindividual structures?We address thesequestions for our study region, the central Andean backarc ofArgentina. We combined a structural and geomorphological approachwith surface exposure dating (10Be) of alluvial fans andstrath terraces in two key localities at ~32° S: the Cerro Salinas,located in the active orogenic front of the Precordillera, and theBarreal block in the interior of the Andean mountain range. Weanalysed 22 surface samples and 6 depth profiles. At the thrustfront, the oldest terrace (T1) yields ages of 100-130 ka, theintermediate terrace (T2) ages between 40-95 ka, and the youngestterrace (T3) ages of ~20 ka. In the Andean interior, T1´ dates to117-146 ka, T2´ to ~70 ka, and T3´ to ~20 ka, allcalculations assuming negligible erosion and using the scaling schemefor spallation based on Lal 1991, Stone 2000. Verticalslip rates of fault offsets are 0.3-0.5 mm/yr and of 0.6-1.2 mm/yr atthe thrust front and in the Andean interior, respectively.Ourresults highlight: i) fault activity related to the growth of theAndean orogenic wedge is not only limited to a narrow thrust frontzone. Internal structures have been active during the last 150 ka,ii) deformation rates in the Andean interior arecomparable or even higher that those estimated and reported along theemerging thrust front, iii) distribution of active faulting seemsto account for unsteady state conditions, and iv) seismichazards may be more relevant in the internal partsof the Andean orogen than assumed so far.