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.
Bibliographical noteFunding Information:
This research was supported by National Science Foundation grant ANT 0944662 to Elliot. The Jeffrey Head granodiorite (collected by Terry Wilson in 2014), the Guy Peaks hornblende diorite (collected by Campbell Craddock and Craig White in 1968), and the Ohio Range sandstone (collected by William E. Long in the 1963-1964 field season) were provided by the U.S. Polar Rock Repository at Ohio State University. Steve Weaver kindly provided the zircons from the Mount Murphy granite. Elliot wishes to acknowledge significant support over many years from the Office of Polar Programs at the National Science Foundation. Comments by the associate editor and two anonymous reviewers greatly improved the manuscript. Byrd Polar and Climate Research Center Contribution #1579.