Tectonic Evolution of Paleozoic and Mesozoic Andean Metamorphic Complexes and the Rocas Verdes Ophiolites in Southern Patagonia

Abstract

The petrology and geochronology of Paleozoic and Mesozoic metamorphic and ophiolitic complexes in southern Patagonia constrain the evolution of magmatic belts, marginal basins, and continental fragments that once formed part of the peripheral realm of the southwestern Gondwanan margin. The upper Paleozoic metasedimentary rocks exposed along the eastern slopes of the Andean ranges contain prominent zircon components of Devonian and earliest Carboniferous age. These strata were deposited in marine basins fed by sediment derived from almost coeval felsic magmatic belts and recycled units with Ordovician and Cambrian components; some of which have been identified to the east, in Argentina. Permian to Triassic metasedimentary complexes, mainly exposed along the western slope of the Southern Patagonian Andes and in the Antarctic Peninsula, show conspicuous peaks of Permian detrital zircons with sparse older age components, supporting their deposition near active magmatic belts in a convergent margin setting. It is proposed that rapid northward migration of Gondwana (between 330 and 270 Ma) promoted crustal extension and the establishment of an arc and back-arc marginal basin configuration during the Permian. Subsequent closure of the marginal basins occurred during the Late Triassic–Early Jurassic Chonide orogeny. Middle Jurassic fragmentation of Gondwana involved continental extension, synrift silicic and bimodal magmatism, and seafloor-spreading, leading to the oceanic-type Late Jurassic to Early Cretaceous Rocas Verdes basin. Once the Antarctic Peninsula microplate migrated southward, subduction was re-established in southern Patagonia in Early Cretaceous time, involving processes of subduction erosion and high-P/T metamorphism in the forearc region. The Rocas Verdes basin started to close in the latest Early Cretaceous involving underthrusting and subduction of its oceanic seafloor. These convergent processes culminated with the Late Cretaceous Patagonian and Fuegian orogeny involving the tectonic emplacement of ophiolitic complexes, collision of drifted crustal slivers against the continent, and development of the Magallanes–Austral foreland basin.