U–Pb geochronology of volcano–sedimentary moraine sediments of the Bunger Hills: implications for Mesoproterozoic evolution of East Antarctica

Abstract

The Bunger Hills and adjacent areas of Wilkes Land and Queen Mary Land occupy the very western periphery of the Musgrave–Albany–Fraser Orogen, and represent one of the few exposures within east Antarctica with direct correlations to Australian constituent terrains of this continental-scale system. U–Pb analyses of detrital zircons from volcano–sedimentary moraine sediments of the Bunger Hills yield concordant 206Pb/238U ages ranging from ca. 1364 Ma to ca. 1040 Ma (n = 842), with a main late Mesoproterozoic magmatic zircon population clustered at ca. 1179–1161 Ma. Strong parallels with the time profile of in-situ rocks from the Stage 2 Albany–Fraser Orogen (AFO), the Bunger Hills and Windmill Islands, suggest these were the likely provenances for the associated moraine detritus. The Bunger Hills lie downstream from outcrops of the geographically inaccessible Sandow Group, which comprises clastic and mafic volcanoclastic rocks. It is interpreted that the sedimentary moraine materials of the Bunger Hills were derived from the glacial erosion of the Sandow Group supracrustal successions. The lithological character, sedimentary fill pattern and advanced diagenesis suggest that the Sandow Group formed within an active intra-continental rift-basin and represents the upper-crustal expression of extensional tectonism. Reconnaissance U–Pb geochronology of authigenic titanite suggests basin development occurred close to or within the time frame of the high-grade metamorphism recorded in the Bunger Hills. Therefore basin development was probably directly associated with the second major thermo–tectonic phase of the AFO (Stage 2; ca. 1215–1140 Ma). Due to the essentially non-metamorphosed volcano–sedimentary nature of the detritus in the sedimentary rocks, it seems likely that the evolving Mesoproterozoic orogenic system was not deeply exhumed during basin development.