Abstract

Neoarchean supracrustal sequences in the south-central Wyoming Province are exposed as relatively small belts in Laramide uplifts. Some sequences are composed of materials derived mainly from pre-existing Wyoming province crust, but others are dominated by juvenile components. The latter include the Miners Delight Formation in the Wind River Range, the Rattlesnake Hills Group in the Granite Mountains, and the Bradley Peak succession in the Seminoe Mountains. U–Pb zircon dates from interbedded metavolcanic rocks suggest that these supracrustal belts are of at least two different ages: ca. 2.67 and ca. 2.72 Ga. We identify a time of contractional deformation and accretion of some of these supracrustal packages to the southern Wyoming Province at ∼2.65–2.63 Ga. Magmatism is nearly synchronous with deformation. Some granitoids intrude the Wyoming Province basement, as well as the juvenile rocks thrust onto this basement; these have Nd isotopic compositions indicating that these plutons assimilated some old continental basement during ascent. Plutons intruding the supracrustal rocks located farther from the margin do not show this continental influence. The time scale and geologic processes of deposition, contractional deformation, and plutonism appear analogous to Phanerozoic examples of oceanic terrane accretion, such as formed the Klamath Mountains Province of California and Oregon. We conclude that a major episode of Neoarchean crustal growth involved both the lateral accretion of juvenile terranes and the intrusion of arc magmas formed from mantle-derived and (or) juvenile crustal sources and was driven by geologic processes very similar to modern plate tectonics.

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