Devonian-Carboniferous magmatism and glacial sedimentation in Tierra del Fuego, Chile: new evidence from the eastern Cordillera Darwin

Abstract

The Cordillera Darwin is the highest mountain range in the Fuegian Andes and exposes the oldest rocks of southernmost South America. This study presents new evidence of Devonian magmatism and the sedimentary environment of the late Paleozoic basement identified on the eastern margin of the Cordillera Darwin, specifically the Svea Granite and the Paso Las Lagunas Formation. The findings indicate a crystallization age of ca. 375 Ma for the Svea Granite, constituting the first documented occurrence of Late Devonian peraluminous magmatism in Tierra del Fuego. The granite was subsequently cooled during the latest Devonian, as indicated by a ca. 363 Ma 40Ar/39Ar muscovite age. The Paso Las Lagunas Formation comprises an approximately 400 m thick succession of immature sedimentary rocks of glacial to periglacial origin. Its depositional age is constrained by U-Pb zircon ages of ca. 350 Ma from an andesite intercalated within the upper section of the succession. The overlying sedimentary strata contain a youngest detrital zircon U-Pb age peak at ca. 340 Ma, indicating that deposition of the succession continued until at least this time in a periglacial environment. Together with the age of the andesite, the duration of deposition of the Paso Las Lagunas Formation is constrained to at least 10 Myr. These results suggest that the exhumation of the Svea Granite and its country rocks began prior to the deposition of the Paso Las Lagunas Formation. The study provides further support for the hypothesis that the Antarctic Peninsula may have been adjacent to Patagonia during the Devonian. Correlations between the studied rocks and broadly coeval geological units from Patagonia and the Antarctic Peninsula may indicate the existence of a Devonian-Carboniferous magmatic arc between Patagonia and Antarctica.