Linking accretionary orogens with continental crustal growth and stabilization: Lessons from Patagonia.

Abstract

The origin of the continental crust and the tectonic significance of Paleozoic magmatic rocks of Patagonia (southernmost South America) remain one of the main enigmas in the history of the Gondwana supercontinent. Here, new whole-rock geochemistry together with coupled zircon U-Pb and Lu-Hf isotopic data of Devonian to Permian intrusive rocks of northern Patagonia are integrated with a revised geochemical and isotopic database of the region, providing a novel model for the tectonomagmatic evolution and related crustal growth mechanisms. The development of a Devonian retreating accretionary orogen associated with crustal thinning was succeeded by a late Carboniferous to Permian advancing orogen and crustal shortening, resulting from slab shallowing. The latter was related to the Gondwanide Orogeny, a major transpressional tectonic event that led to the maturation and stabilization of the continental crust of Patagonia due to widespread magmatism and crustal thickening, which culminated with Permian-Triassic slab break-off. Addition of juvenile mantle-derived magmas is more significant during the Devonian, whereas a progressively increase in crustal reworking is documented from the late Carboniferous to the Permian due to crustal thickening. Therefore, this non-collisional model favors an in situ middle to late Paleozoic crustal growth of Patagonia during changing dynamics of accretionary orogens at the proto-Pacific margin of southwestern Gondwana.