CRUSTAL EVOLUTION OF THE CAPRICORN OROGEN (WA): INSIGHT FROM A PROVENANCE STUDY OF ITS MAJOR MESOPROTEROZOIC SEDIMENTARY BASINS

Many unsolved aspects remain on the origin of the Mesoproterozoic Edmund and Collier basins in the centre of the Capricorn orogenic belt (Western Australia). Their stratigraphy made of 4-10 Km thick siliciclastic and volcanoclastic rocks sequences is characterized by numerous lateral and vertical facies transitions and sharp changes that recorded the concurrence of several sources for the sediment supply and environmental modifications. Although the Yilgarn Craton, Glenburgh Terrane and Pilbara Craton are recognised as main source regions, their role is not clear because little is known on the tectonic activity that ultimately controlled their exposure and erosion. Thus, the depositional history of the Edmund and Collier basins depend on a complex mosaic of sources that needs to be investigated to resolve the sediment origin and the tectonic evolution of the orogen.

To do so more than 3000 detrital zircons were analysed and studied with a new approach to the traditional provenance study. The zircon U-Pb isotopes and trace elements were measure on a recently developed Laser-Ablation Split Stream – ICPMS facility (LASS-ICPMS) at the Curtin University. The U-Pb age data were visually and statistically compared with published data, through stacked cumulative probability plots, Kolmogorov-Smirnov test probabilities and multidimensional scaling plots (MDS), with the aim to reveal potential source terrains and sediment transportation patterns. The outcomes were then analysed under the light of the geochemical signature of the detrital zircons through: (i) chemical discrimination diagrams with rock types compositional fields (ii) chemical discrimination diagrams containing compositional fields established on geochemical data, analysed in the same way, from magmatic zircons selected for some granite suites of the Capricorn. The elemental matching between detrital and magmatic zircons constrained distinct sources for the sediments that would be otherwise invisible within the U-Pb age modes. Moreover, this methodology set a new base for provenance study, where a higher detail in the distinction of source terrains can be achieved.