Characterisation and tracing of Permian magmatism in the south-western segment of the Gondwanan margin; U–Pb age, Lu–Hf and O isotopic compositions of detrital zircons from metasedimentary complexes of northern Antarctic Peninsula and western Patagonia

Abstract

Metasedimentary rocks in the Antarctic Peninsula and south-western Patagonia record detrital zircon evidence for significant Permian magmatic events along the Palaeo-Pacific margin of south West Gondwana. However, it is unclear where and how this magmatism formed due to the lack of outcropping Permian igneous sources at similar latitudes. Combined U–Pb, O, and Lu–Hf isotope analyses of detrital zircon grains in Permo–Triassic metasedimentary rocks indicate that the Permian magmatism resulted from the interaction of crust- and mantle-derived sources in an active continental margin. Permian detrital zircons from the Trinity Peninsula Group in the Antarctic Peninsula range from crustal signatures in the northern part (δ18O of ~8‰, initial εHf of ~−6) to mantle-like values in the south (δ18O of ~5‰, initial εHf of ~+3). Zircons from the northern domain have isotopic features similar to those from the Patagonian Duque de York Complex. They also share a secondary Ordovician component of ca. 470Ma. The Middle Jurassic Cape Wallace Beds in Low Island record a ca. 250Ma igneous source, with stronger crustal signatures (δ18O and initial εHf values of 7.5 to 10.8‰ and −3.2 to −14.2, respectively). In contrast, zircons from the upper Jurassic Miers Bluff Formation on Livingston Island and Cretaceous sediments on James Ross Island have similar Permian U–Pb ages, O and Hf trends to their Trinity Peninsula Group counterparts, suggesting reworking after the late Jurassic. Our results provide evidence for a Permian subduction-related magmatic arc, partly located in Patagonia and extending to West Antarctica. The southerly decrease in δ18O coupled with increasing initial εHf indicate fewer sedimentary components in the magma source and is consistent with a glaciated cold and dry climate. These conditions are comparable with West Antarctica climate settings, located close to the South Pole during the Carboniferous and Permian.