The early Paleoproterozoic was a time of unprecedented change in Earth’s climate and surface environment. The key to resolving some of the controversies surrounding the timing and causes of these changes lies with supracrustal sequences, such as the 2.45–2.22 Ga Turee Creek Group in the southern Pilbara craton, northwestern Australia. The group preserves a predominantly siliciclastic sequence; however, its precise age, tectonic setting, and postdepositional history are disputed. Although it is interpreted to have been deposited in a foreland basin setting shortly after 2.45 Ga, the oldest well-recognized deformational event, marked by northward folding and thrusting, is the 2.20–2.15 Ga Ophthalmia orogeny. Evidence for a pre-Ophthalmia fabric-forming tectonic event north of the Archean Sylvania Inlier, southeast Pilbara craton, which is marked by tight to isoclinal folding, has been largely overlooked. In this area, we report in situ U-Pb geochronology of authigenic monazite and xenotime in shale with a well-developed tectonic cleavage from the ca. 2.63 Ga Jeerinah Formation. Monazite porphyroblasts, which are locally wrapped by strain fringes aligned in a tectonic cleavage, yielded weighted mean 207Pb/206Pb ages at 2370 ± 11 Ma and 2312 ± 8 Ma, whereas xenotime, which overprints a crenulation cleavage, gave a weighted mean 207Pb/206Pb age of 2291 ± 11 Ma, constraining fabric development to between 2.31 Ga and 2.29 Ga. Our results confirm the existence of a pre-Ophthalmia deformational event in the southeastern Pilbara craton, herein referred to as the Sylvania orogeny, which is part of an ~300 m.y. interval (2.45–2.15 Ga) of northward-directed compression (“Hamersley orogenic cycle”). This orogenic cycle is marked by east-west and northwest-southeast folding, cleavage development, veining, hydrothermal gold mineralization, and isotopic resetting across the southern Pilbara craton. Our results indicate that the syn–Great Oxidation Event Turee Creek Group was deposited in one or more foreland basins after 2.45 Ga. Our results provide a new tectonostratigraphic and geodynamic framework for understanding the timing and origin of geochemical records in a key succession deposited during an interval of global environmental change.
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Research Article|
May 12, 2022
U-Pb dating reveals multiple Paleoproterozoic orogenic events (Hamersley orogenic cycle) along the southern Pilbara margin (Australia) spanning the onset of atmospheric oxygenation
Birger Rasmussen;
Birger Rasmussen
1
School of Earth Sciences, The University of Western Australia, Stirling Highway, Perth, WA 6009, Australia2
State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China
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Jian-wei Zi;
Jian-wei Zi
2
State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China
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Janet Muhling
Janet Muhling
1
School of Earth Sciences, The University of Western Australia, Stirling Highway, Perth, WA 6009, Australia
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Geology (2022)
Article history
received:
11 Aug 2021
rev-recd:
05 Jan 2022
accepted:
21 Mar 2022
first online:
12 May 2022
Citation
Birger Rasmussen, Jian-wei Zi, Janet Muhling; U-Pb dating reveals multiple Paleoproterozoic orogenic events (Hamersley orogenic cycle) along the southern Pilbara margin (Australia) spanning the onset of atmospheric oxygenation. Geology 2022; doi: https://doi.org/10.1130/G50010.1
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