Tectonostratigraphic evolution and timing deformation in the Miocene Paso del Sapo Basin: Implications for the Patagonian broken foreland

Abstract

Several segments of the Central and Southern Andes show deformation evidences located far away from the orogenic front. As a result, a landscape constituted by fault-blocks mountains and intermontane basins occurs. The spatial-temporal distribution of the deformation in these Broken Foreland Systems is still uncertain. Some works suggest that change in space and time of rock uplift along the structures is controlled mainly by older crustal discontinuities. However, other authors propose, a particular deformation pattern between the Andean and extra Andean regions, such as eastward-westward migration of the orogenic front related to subduction zone dynamics. In this work we analyse new structural, geomorphological and tectono-stratigraphical data together with previous chronological scheme (based on U-Pb and magnetostratigraphic ages) of one of the Patagonian Broken Foreland depocenters: the Paso del Sapo Basin. The results allow to perform the tectonostratigraphic evolution of the basin and constrain the timing of deformation in Paso del Sapo Basin at 15–11.5 Ma. Different tectonic structures were activated and de-activated in this time interval, while an older crustal discontinuity – the Río Chubut Medio fault, located at the eastern border of the basin – recorded a continuous tectonic activity throughout the entire evolution of the basin. These evidences show a synchronous tectonic activity for the Andean and extra-Andean Patagonian regions at those times. In addition, the presence of a climax deformation constrained to 15–14.6 Ma and the deceleration of the Río Chubut Medio Fault at 12.2 Ma could be related to eastward expansion and westward retraction of the orogenic front respectively. Therefore, our data indicate that both the presence and absence of a deformation pattern in extra-Andean regions should be considered to suggest alternative lithospheric-scale models.