A tectonic model of the Antarctic Gondwana margin with implications for southeastern Australia: isotopic and geochemical evidence

Abstract

Abstract Geochemical studies of Paleozoic granites in northern Victoria Land (NVL) and the central Transantarctic Mountains (CTM) are integrated with structural and lithologie studies into a model for the tectonic development of the Antarctic-south-east Australian Gondwana margin in late Precambrian-middle Paleozoic time. Isotopic data (Nd, Sr, O) are used to define crustal basement age boundaries and subduction polarity and thus help identify suspect terranes. In the CTM, three basement age-blocks are recognized: The outboard two provinces are inferred to be allochthonous, with accretion to the Gondwana margin occurring between ≈ 750 and ≈ 500 Ma. This tectonic scenario is inferred to apply also to NVL and southeastern Australia (SEA). In the CTM and NVL, chemical and isotopic polarity of ca. 500 Ma granitoids indicate a cratonward-dipping subduction zone. In NVL, terranes outboard of the belt of ca. 500 Ma granites contain Devonian (ca. 400 Ma) I-type granites with chemical and isotopic polarity opposed to that of the ca. 500 Ma granites. In the furthest outboard position, S-type granites emplaced at ca. 600 and 525 Ma occur with ca. 400 Ma granites and indicate the presence of early Proterozoic basement. This NVL terrane collage is allochthonous; it was assembled, intruded by Devonian granites, and then tectonically accreted to the Gondwana margin between latest Devonian and Permian time. Terrane correlations with SEA imply that much of the latter was accreted to the Gondwana margin after Devonian time. Other fragments of this allochthonous continental collage are probably in Marie Byrd Land (West Antarctica) and New Zealand (including the Campbell Plateau).