Composition and age of the East Antarctic Shield in eastern Wilkes Land determined by proxy from Oligocene-Pleistocene glaciomarine sediment and Beacon Supergroup sandstones, Antarctica

Abstract

The Precambrian East Antarctic Shield played a central role in the tectonic evolution of Rodinia and Gondwana, as well as growth of the East Antarctic Ice Sheet, yet little is known about its ice-covered interior. Glaciogenic deposits of Oligocene-Miocene and Pleistocene age on the Wilkes Land margin include glaciomarine diamictons containing basement rock clasts and fine-grained siliciclastic detritus, which provide proxy samples of the continental basement. Rock clasts obtained by dredge (81% metamorphic, 14% igneous, and 5% sedimentary lithologies) provide petrographic, geochemical, and age information about the glacial source area. Igneous clasts with Ross orogen U-Pb zircon ages (ca. 500 Ma) include a notably old ca. 585 Ma granitoid; they and Ross-age metamorphic rocks give discrete inherited-zircon age populations of 670–780, 900–1300, 1740–2300, and >2700 Ma that reflect basement sources. Paleoproterozoic rock clasts (granitoid, charnockite gneiss, and granulite gneiss) range from ca. 1720 to 1740 Ma. Detrital zircon populations from glaciomarine sediments vary with depositional age but show common terrigenous provenance ages of 460–660, 1045–1315, 1545–1815, and 2420–2605 Ma, which overlap those from inherited zircons in the Ross granitoids. Detrital zircon ages from onshore Permian and Triassic terrestrial sedimentary rocks reveal a different provenance and indicate that the glaciogenic deposits do not contain significant second-cycle material from older interior basins. Together, these data suggest that metamorphic rock units with distinctive Neoproterozoic, Paleoproterozoic, and Archean ages dominate East Antarctic Shield basement inland from the eastern Wilkes Land margin, and that Ross-age granitoids either intruded or were derived by partial melting of this composite metamorphic basement.