A tale of two basins? Stratigraphy and detrital zircon provenance of the Palaeoproterozoic Turee Creek and Horseshoe basins of Western Australia

Abstract The 2445–2010 Ma tectonic evolution of the southwestern Pilbara Craton is recorded by two depositional basins, but considering the time span involved it is pertinent to question whether only two are preserved and others have vanished. The first, the Turee Creek Basin, developed conformably on an ∼2450 Ma back-arc volcanic province, and was closed long before ∼2208 Ma. It was a retroarc basin sited in front of a magmatic fold-thrust belt on the southwestern margin of the craton. Its folded strata were intruded by ∼2208 Ma dolerite sills that are the preserved rock record of a large igneous province. The basin and dolerites were deformed by the N-verging ∼2195–2145 Ma Ophthalmia Fold-Thrust Belt. The second, the Horseshoe Basin, formed at ≤2050 Ma, unconformably truncating folded strata of the Turee Creek Basin and the ∼2208 Ma dolerites, and was closed prior to intrusion of ∼2008 Ma dolerite dykes. It was an intracontinental rift basin sited on the inverted fold-thrust belt. Detrital zircon age-spectra for the basins have poor fit to the zircon age-spectrum of the Pilbara, and differ significantly in their youngest modes. The youngest mode for the Turee Creek Basin is ∼2442 Ma, whereas the youngest mode for the Horseshoe Basin decreases upwards from ∼2276 Ma to ∼2206 Ma. Although differing in youngest detrital zircon age-modes, zircon age-spectra of the basins are otherwise similar, and broadly match the Glenburgh Terrane on the southwestern margin of the craton. While Turee Creek sediments were derived from the southwest, Horseshoe sediments were derived from the north and northeast. This conundrum is resolved by the Ophthalmia Fold-Thrust Belt, which tectonically loaded the craton to the north and northeast to form a now-vanished Ophthalmia foreland basin that derived sediment from the south and southwest, thereby emplacing zircon with an exotic age-spectrum on the North Pilbara. Inversion of tectonic elements occurred during formation of the Horseshoe Basin, with the fold-thrust belt subsiding beneath the rift while the foreland basin was uplifted. Recycling of the foreland basin inverted its detrital zircon age-spectrum, explaining why the youngest detrital zircon age-mode of the Horseshoe Basin decreases in age upwards.