The Cuesta de Rahue Basement Inlier (Southern Neuquén Precordillera, Argentina): A Devonian to Triassic polyphase orogenic record in northern Patagonia.

Abstract

We present new geological, structural and microstructural data, together with K–Ar biotite and illite geochronological data, for the igneous–metamorphic rocks exposed in the Cuesta de Rahue Basement Inlier in the Southern Neuquén Precordillera, Argentina. We use these data to reconstruct the Late Paleozoic to Mesozoic tectonometamorphic and magmatic history of northwestern Patagonia. This block consists of a medium-grade metasedimentary sequence (the Cuesta de Rahue Metamorphic Complex), Late Carboniferous granitoids and a low-grade metavolcano-sedimentary unit (the Arroyo Coloco Metamorphic Complex). The Cuesta de Rahue Metamorphic Complex was deposited during the mid-Paleozoic and underwent Devonian low-pressure regional metamorphism, followed by the intrusion of granitoids at c. 300 Ma. By contrast, the Arroyo Coloco Metamorphic Complex records deformation and metamorphism under epizonal conditions (>300°C), constrained at c. 232–199 Ma by K–Ar and X-ray diffraction illite data. The Cuesta de Rahue Basement Inlier thus records a protracted orogenic evolution, recording Devonian metamorphism, Late Carboniferous–Permian Gondwanide tectonomagmatic processes, and Late Triassic deformation and metamorphism. This block was later affected by Mesozoic normal faulting and Miocene–Pliocene Andean deformation. The Andean deformation was intimately related to the reactivation of inherited basement fabrics, favouring a transpressional deformation regime.