Fingerprinting windblown dust in south-eastern Australian soils by uranium-lead dating of detrital zircon

Abstract

The U-Pb ages of fine-grained zircon separated from 2 dust-dominated soils in the eastern highlands of south-eastern Australia and measured by ion microprobe (SHRIMP) revealed a characteristic age ‘fingerprint’ from which the source of the dust has been determined and by which it will be possible to assess the contribution of dust to other soil profiles. The 2 soils are dominated by zircon 400–600 and 1000–1200 Ma old, derived from Palaeozoic granites and sediments of the Lachlan Fold Belt, but also contain significant components 100–300 Ma old, characteristic of igneous rocks in the New England Fold Belt in northern New South Wales and Queensland. This pattern closely matches that of sediments of the Murray-Darling Basin, especially the Mallee dunefield, suggesting that weathering of rocks in the eastern highlands has contributed large quantities of sediment to the arid and semi-arid inland basins via internally draining rivers of the present and past Murray–Darling River systems, where it has formed a major source of dust subsequently blown eastwards and deposited in the highland soils of eastern Australia.