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

Abstract

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 εHf 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 εHf 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. Show more