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 ε<inf>Hf</inf> of ~-6) to mantle-like values in the south (δ18O of ~5‰, initial ε<inf>Hf</inf> 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 ε<inf>Hf</inf> 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 ε<inf>Hf</inf> 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. Show more