Tectonic setting and provenance of the Paleoproterozoic Willyama Supergroup, Curnamona Province, Australia: Geochemical and Nd isotopic constraints on contrasting source terrain components

The Curnamona Province Paleoproterozoic Willyama Supergroup was deposited in one of a series of basins developed along the eastern margin of the Proterozoic Australian continent. Linked tectonic evolutionary paths have previously been drawn between the northern and southern Australian cratons, based in part on similar depositional ages and stratigraphy, and tectonic evolutions of the sedimentary basins of this region. Detailed geochemical and Nd isotopic analyses from the Paleoproterozoic Willyama Supergroup suggest an intracratonic source for the lower parts of the sequence, with introduction of a significantly more juvenile source region for the ca. ≤1650 Ma uppermost part, marking a significant change in tectonic regime. The geochemical and Nd isotopic signature of both mature quartz-rich and pelitic sedimentary rocks of the lower part of the Willyama Supergroup support a dominant intracratonic central and northern Australian provenance, marked by a recycled and felsic upper crustal composition unusually enriched in REE and incompatible elements. Sedimentary REE abundance patterns double those of the Post-Archean Australian Shale average. Initial ɛNd values between −7 and −4 suggest old upper crustal recycled source basement. In contrast, the uppermost part of the Willyama sedimentary section has REE patterns much more like Post-Archean upper crustal shale average, and is characterised by more primitive initial ɛNd values of around −3 to 0. Significant ca. 1650 Ma felsic source terranes with such a juvenile Nd isotope signature are unknown in Australia. The data suggest proximity of a relatively juvenile as yet unidentified source to the present-day east of the basin. Some pre-Rodinian reconstruction models place eastern Australia proximal to southwestern Laurentia, which contains rocks of appropriate geochemical and isotopic signatures and could have delivered juvenile felsic sediment into the Willyama basin.