Sebastián Bascuñan

Mechanisms and Episodes of Deformation Along the Chilean–Pampean Flat-Slab Subduction Segment of the Central Andes in Northern Chile

The knowledge of the tectonic architecture, timing, and the mechanisms of deformation that affected the western slope of the Chilean–Pampean flat-slab subduction segment of the Central Andes in northern Chile are a key to understand the complete evolution of this Andean segment. In Chile, this segment is composed of two tectonic provinces: The Coastal and the Frontal Cordilleras. Traditionally, this broad intracontinental deformation zone that characterized this segment has been compared with the Rocky Mountains, in terms of structural styles and age of deformation, although the complex interaction between extensional Mesozoic structures and different styles of contractional structures suggest that this segment resulted from multiple episodes of deformation. We present the results of a study developed along the Coastal and Frontal Cordillera of northern Chile (27°–28° S), based on regional fieldwork, structural analysis, and geochronological dating of synorogenic deposits. Our results have revealed that the structure of this region consists of NNE-striking inverted and basement-involved contractional structures. The occurrence of these structural styles suggests that a hybrid tectonic mechanism dominated by tectonic inversion and basement-involving thrusting was responsible of its current configuration. On the other hand, the U–Pb ages determined in the synorogenic deposits exposed on the footwall of the main faults indicate that the Andean deformation could have initiated during the Late Cretaceous in the Coastal Cordillera associated with tectonic inversion and then this migrated to the east as basement-involved thrusting during the Paleocene–Miocene times.