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 Patagonian Andes is characterized by a low topography and low shortenings. During its evolution, an extensional event in late Oligocene times affected the western section of the Late Cretaceous to Eocene fold and thrust belt. Late early Miocene contraction then constructed most of the eastern Andean slope as in sequence structures stacked in the frontal sector of the fold and thrust belt. However, out of sequence structures derived mainly from the inversion of the late Oligocene extensional depocenters uplifted the axial Andean zone at these latitudes. Contractional and extensional stages 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 and development of synorogenic depocenters are linked to arc dynamics.