The Cordillera Principal at 36° to 39°S is an excellent place to address the relationship between tectonics and volcanism. Based on tectonostratigraphic analysis of the Cenozoic basins it has been possible to recognize a clear spatial coincidence between first order basin scale structures and Plio-Pleistocene volcanism. Cenozoic basins started in the Oligocene-Miocene as extensional depocenters, characterized by at least three north-south oriented sub-basins connected by two structural accommodation zones. Towards the Late Miocene this extensional system was tectonically inverted deforming and uplifting the previous extensional faults and sedimentary fill. The accommodation zones prevailed as first order structures and acted as weakened zones that enabled the volcanism and magmatism at the Nevados de Chillán and Copahue-Callaqui volcanic complexes. Each one of these volcanic complexes is characterized by an oriented series of emission centers, volcanic morphology and deposits that are subparallel to the underlying accommodation zone. © 2011 Servicio Nacional de Geología y Minería.