Tectonic geography of Mesoproterozoic Wilton package, north Australia

Abstract

The Mesoproterozoic is an important but relatively poorly explored interval in Earth history. It is a complicated system with dynamic interactions among tectonic, biosphere, atmospheric composition and ocean chemistry. One of the best sedimentary archives for probing the Mesoproterozoic Earth’s system is the Wilton package, greater McArthur Basin, north Australia. It covers the North Australia Craton in thousands kilometre-scale, forms temporal depositional records spanning over 600 million years, from ca. 0.9 Ga to 1.5 Ga. New constraints on this basin, therefore, contribute to a better understanding of the evolution of the Earth’s system during this period. In this thesis, we apply a multiproxy isotopic provenance approach to provide new constraints on the age of deposition, basin provenance, spatial intra basin correlation, and further, the paleogeography and tectonic evolution of the Mesoproterozoic North Australia Craton. Sedimentary rocks of the Wilton package were preserved in several geographically separated basins. The Roper Group of the Beetaloo Sub-basin, the depocentre of the Wilton package, is primarily focused. Data suggest that the Collara Subgroup (lower Roper Group) was sourced from southeast-southern sources. Whereas, the overlying Maiwok Subgroup (upper Roper Group) received more detritus from the eastern sources. This provenance change is interpreted to relate to exhumation of these eastern sources. They were uplifted as rift-shoulder highs, formed by contemporaneous extension between Proterozoic Australia and Laurentia, during the period of ca. 1.45 to 1.4 Ga. After that, progressively younger formations within the Maiwok Subgroup record another provenance shift to southern sources. This provenance change is interpreted to relate to closure of an ocean basin at ca. 1.35 to 1.32 Ga, which resulted in uplift of the southern margin of the North Australia Craton. The deposition of the Roper Group was punctuated by the intrusion of the ca. 1.31 Ga Derim Derim–Galiwinku LIP. The emplacement of Derim Derim–Galiwinku LIP progressively uplifted the basin from the north. Simultaneously, the increased weathering of Derim Derim–Galiwinku basaltic rocks increased nutrient (e.g. phosphorus) supply to the basin and presumably enhanced the primary production in the shallow marine settings, resulting in high organic carbon contents (TOC) that is seen in the top section of the Roper Group. Provenance consistence between the South Nicholson Group and the Roper Group indicates correlations between the Beetaloo-McArthur and the South Nicholson basins. The successions within the Birrindudu Basin, however, exhibit little similarities to the Roper Group. The Bulita Group of the Birrindudu Basin received detritus from northeast and northern sources, whereas, the younger Tijuna Group records a swamping of the basin by detritus from southerly sources. The Bulita and Tijuna groups demonstrate a provenance change to southern source regions, which is consistent with that is seen in the upper Maiwok Subgroup. These consistent southward provenance changes are interpreted to be related to the same ocean closure event at ca. 1.35 to 1.32 Ga. Despite the provenance dissimilarities in spatial scale, the co-evolution of provenance correlated the Beetaloo and Birrindudu basins temporally. Whereas, the inconsistency of their detrital zircon compositions is interpreted to relate to underwater bathymetries that blocked transportation of sediment. The supra-Wilton package successions is characterized by a series of unnamed sandstone and mudstone sedimentary units. These unnamed sedimentary units were deposited at least 300 million years after the deposition of the Wilton package, and are interpreted to be sourced from the Musgrave and the Arunta regions. Their significant provenance consistency with other early Neoproterozoic strata/groups indicates an extensive super basin with multiple depocentres.