CONICET | Buscador de Institutos y Recursos Humanos

In northern Chile (24.5°-26°S) two depocenters of the Pre-Andean cycle are relatively well exposed: the Cifuncho basin along the Coastal Cordillera, and El Profeta basin in the Precordillera. The study of these basins is an important proxy in order to characterize the geodynamic framework of the Late Triassic-Early Jurassic evolution of the southwestern margin of Gondwana during the transition to the Andean orogeny. Furthermore, an important number of mesoscopic synrift structures are well preserved in some ravines. The kinematic analysis of these structures allow us to compare the strain field along the Cifuncho-El Profeta basins with those reported in Argentina for the same period. In order to unravel the geologic evolution during this period and to evaluate the possible influence of the subduction process in the strain field of the crust, we are currently carrying a tectonostratigraphic study of these basins. Here, we present the first report of synrift structures affecting Late Triassic successions of the El Profeta depocenter. The kinematic analysis shows a variability in the bedding-corrected orientation of tensional axis (T) from a main NW to subordinate NE directions. Most of the corrected extensional structures show normal faulting with little strike-slip component except the Quebrada Doña Ines Chica data which correspond to a main sinistral faulting with a minor extensional component. On the other hand, no correlation with the age of the synrift strata is observed, suggesting that the principal directions distribution could be reflecting local variations in the strain field across the El Profeta basin during the aperture of Pre-Andean depocenters more than a temporal variation. The main NW-NNW direction of extension could be related with the local predominance of a NE-ENE trending extensional faulting instead of a NNW far field rifting.