Hf- and O-isotope data from detrital and granitoid zircons reveal characteristics of the Permian-Triassic magmatic belt along the Antarctic sector of Gondwana

Permian-Triassic strata in the Transantarctic Mountains and West Antarctica carry a significant detrital component derived from a contemporaneous magmatic belt along the Gondwana margin. Hf- and O-isotope characteristics were determined for near-contemporaneous (as shown by U-Pb zircon geochronology) detrital igneous zircons in Upper Permian and Triassic sandstones. Zircons from six granitoids in the contemporaneous magmatic belt were also analyzed for Hf and O isotopes in order to gain insight into the potential detrital zircon sources. Although the ages of these granitoids only loosely correspond with the depositional ages of the sandstones, the initial ε_Hf and δ¹⁸O isotope compositions for these igneous zircon grains, in general, overlap those recorded for the detrital igneous zircon grains. Results demonstrate a range of ε_Hf and δ¹⁸O values. Features of particular interest are the very low δ¹⁸O values in two of the granitoids, and similar low values also recorded in the detrital igneous zircons in two sandstones. The distribution of Permian- Triassic granitoids must be much greater than is apparent from the existing outcrops in the extensively ice-covered region. The Permian and one of the Triassic granitoids have Hf-isotope characteristics similar to the Cretaceous granites and Devonian-Carboniferous plutons of West Antarctica, whereas the other Triassic granite differs from both. Importantly, the zircon isotopic data from the Permian-Triassic rocks suggest that an Hf-defined Upper Mesoproterozoic lithosphere underlies much of the magmatic belt.