New insights on regional tectonics and basement composition beneath the eastern Sierras Pampeanas (Argentine back-arc region) from seismological and gravity data

Our seismic images have been combined with crustal density modeling in order to further investigate if the shear wave velocity structure obtained from the RF-SW joint inversion could explain the observed gravity variations. Our results show a crustal thickness varying from 35-40 km (east) to 45-50 km (west) with a Moho step at ~66°W. This step regionally presents a NW-SE orientation and is parallel to the trace at the surface of the Valle Fértil-La Huerta (VFLH) lineament (Cuyania-Pampia boundary). Our images also reveal the presence of a high wave velocity (high density) lower crust west of this Moho step, beneath the eastern Sierras Pampeanas (at 66-67°W). This observation suggests the east-dipping extension at depth of the VFLH structure and the underthrusting of the Cuyania lower crust under the Pampia terrane along this structure. Finally, we evidenced localized low velocity zones located at about 10 km beneath late Cenozoic volcanic fields (Pocho, Morro). We believe that these low velocity zones correspond to old magma chambers associated to the recent, slab flattening-related volcanism in the ESP.