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In the Cleaverville area of Western Australia, the Regal, Dixon Island, and Cleaverville Formations preserve a Mesoarchean lower-greenschist-facies volcano-sedimentary succession in the coastal Pilbar...a Terrane. These formations are distributed in a rhomboidal-shaped area and are unconformably overlain by two narrowly distributed shallow-marine sedimentary sequences: the Sixty-Six Hill and Forty-Four Hill Members of the Lizard Hills Formation. The former member is preserved within the core of the Cleaverville Syncline and the latter formed along the northeast-trending Eighty-Seven Fault. Based on the metamorphic grade and structures, two deformation events are recognized: D1 resulted in folding caused by a collisional event, and D2 resulted in regional sinistral strike-slip deformation. A previous study reported that the Cleaverville Formation was deposited at 3020 Ma, after the Prinsep Orogeny (3070–3050 Ma). Our SHRIMP U–Pb zircon ages show that (1) graded volcaniclastic–felsic tuff within the black shale sequence below the banded iron formation in the Cleaverville Formation yields an age of (3114 ±14) Ma; (2) the youngest zircons in sandstones of the Sixty-Six Hill Member, which unconformably overlies pillow basalt of the Regal Formation, yield ages of 3090–3060 Ma; and (3) zircons in sandstones of the Forty-Four Hill Member show two age peaks at 3270 Ga and 3020 Ga. In this way, the Cleaverville Formation was deposited at 3114–3060 Ma and was deformed at 3070–3050 Ma (D1). Depositional age of the Cleaverville Formation is at least 40–90 Myr older than that proposed in previous studies and pre-dates the Prinsep Orogeny (3070–3050 Ma). After 3020 Ma, D2 resulted in the formation of a regional strike-slip pull-apart basin in the Cleaverville area. The lower-greenschist-facies volcano-sedimentary rocks are distributed onlywithin this basin structure. This strike-slip deformation was synchronous with crustalscale sinistral shear deformation (3000–2930 Ma) in the Pilbara region.続きを見る
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