New constraints on the timing of magmatism and sedimentation in the Dajarra region, southern area of Western Fold Belt, Mt Isa Inlier, Australia: implication for stratigraphic successions during Paleoproterozoic

Mount Isa Inlier, located in northwest Queensland, consists of multiple Proterozoic volcano-sedimentary sequences intruded, deformed and metamorphosed during a complex tectonic history between ~1880 Ma and ~1490 Ma. The stratigraphy of the Mount Isa Inlier is generally interpretated to reflect the superposition of three major superbasin events, marked by discontinuities, and deformed and metamorphosed during the Isan Orogeny (1620-1500 Ma). The superbasin model proposes continuation of stratigraphy along the length of the inlier and the existence of corelative units across the inlier. According to this model, the stratigraphy in the Dajarra region (southern part of Western Fold Belt) consists of a series of units that are either continuous with or can be corelated along strike with units that occur further north. The oldest units are the Bottletree Formation and the Lower Haslingden Group, characterized by bimodal volcanics and siliciclastic rocks which were deposited during the 1800-1780 Ma Leichardt Superbasin. These units were unconformably overlain by the Warrina Park Quartzite and the Moondarra Siltstone accumulated during the 1690-1670 Ma Calvert Superbasin. However, there is no geochronological data available from the sedimentary units in the Dajarra region and these correlations remain speculative. In this study, we report new LA-ICP-MS ages from magmatic and detrital zircons that can help constrain the magmatic and sedimentary history of the rocks occurring in this region and evaluate the existing stratigraphic correlations. Two new magmatic events, between 1810-1780 Ma and between 1710-1690 Ma, are identified in the southern part of the Western Fold Belt. The detrital zircon data indicates that (1) siliciclastic rocks mapped as the Mount Guide Quartzite have the youngest detrital populations between 1885 Ma and 1850 Ma; (2) siliciclastic sediments from the Eastern Creek Volcanics and the Jayah Creek Metabasalt have the youngest detrital zircon populations between 1870 and 1850 Ma; (3) siliciclastic rocks mapped as the Timothy Creek Sandstone and as the Mount Isa Group have the youngest detrital populations between 1820 and 1780 Ma. The maximum depositional ages obtained in this study are significantly older compared to the same stratigraphic units mapped to the north indicating either a different source or that these units are indeed much older and represent a different stratigraphy not previously recognized in the Mount Isa Inlier.