The North Patagonian Orogen: Meso-Cenozoic Evolution from the Andes to the Foreland Area

Abstract

In the last decades, an important amount of studies have dealt with the Patagonian orogen evolution. However, a holistic approach on the evolution of this sector has not been addressed yet. A review of recent advances in different aspects of the Patagonian orogen and its related broken foreland system reveals a close relation between the evolution of both sectors. This enabled us to integrate them in an evolutionary model connecting tectonic events from the North Patagonian Andes to the broken foreland area throughout the Mesozoic and Cenozoic. During the breakup of Western Gondwana, beginning in Jurassic times, several extensional basins developed in the Patagonian region. In late Early Cretaceous to Paleocene, a switch in the tectonic regime caused the initial uplift of the North Patagonian Andes and the fragmentation of the foreland area. Synchronously, an eastward magmatic arc expansion is documented at the retroarc zone. At this moment, a series of mid-ocean ridges collided one after another against the Patagonian margin. A causative relation between young lithosphere subduction, slab shallowing, oro- genesis and eruption of mafic magmatism at the arc and retroarc region has been proposed. In concert to regional compression, synorogenic foreland rifting occurred transversally to the main Andean trend in the San Jorge Gulf Basin, describing an exceptional setting for this type of rifting mechanism. From the Eocene to early Miocene, a westward retraction of the magmatic arc, possibly related to roll-back, was synchronous to the Traiguen Basin, formed over highly attenuated crust that splitted the arc and forearc areas. To the east, extensive intraplate magmatism began in the Patagonian foreland covering partially the broken foreland orogen. During the Neogene, an acceleration of the convergence rate between Nazca and South American plates caused the renewal of Patagonian Andes uplift and reactivation of the broken foreland system. Patagonian orogenesis along with the Late Cenozoic global cooling event triggered aridization of the foreland zone, having dramatic consequences for the Patagonian fauna and flora.