The Transitional Zone Between the Southern Central and Northern Patagonian Andes (36–39°S)

Abstract

The transition zone from the Southern Central to the North PatagonianAndes is characterized by a low topography and low shortenings. During its evolution,an extensional event in late Oligocene times affected the western section ofthe Late Cretaceous to Eocene fold and thrust belt. Late early Miocene contractionthen constructed most of the eastern Andean slope as in sequence structures stackedin the frontal sector of the fold and thrust belt. However, out of sequence structuresderived mainly from the inversion of the late Oligocene extensional depocentersuplifted the axial Andean zone at these latitudes. Contractional and extensionalstages coincide with periods in which the arc expanded and retracted, respectively.Shortening gradients from 30 km in the north to only 11 km in the south anddevelopment of synorogenic depocenters are linked to arc dynamics.