Abstract

The Wyoming Province is a distinctive Archean craton in the northwestern United States that can be subdivided into three subprovinces, namely, from oldest to youngest, the Montana metasedimentary province, the Beartooth–Bighorn magmatic zone, and the Southern accreted terranes. Archean rocks of the Montana metasedimentary province and the Beartooth–Bighorn magmatic zone are characterized by (1) their antiquity (rock ages to 3.5 Ga, detrital zircon ages up to 4.0 Ga, and Nd model ages exceeding 4.0 Ga); (2) a distinctly enriched 207Pb/204Pb isotopic signature, which suggests that this part of the province was not produced by the amalgamation of exotic terranes; and (3) a distinctively thick (15–20 km), mafic lower crust. The Montana metasedimentary province and Beartooth–Bighorn magmatic zone were cratonized by about 3.0–2.8 Ga. Crustal growth occurred via continental-arc magmatism and terrane accretion in the Southern accreted terranes along the southern margin of the province at 2.68–2.50 Ga. By the end of the Archean, the three subprovinces were joined as part of what is now the Wyoming Province. Subsequent to amalgamation of the Wyoming crust to Laurentia at ca. 1.8–1.9 Ga, Paleoproterozoic crust (1.7–2.4 Ga) was juxtaposed along the southern and western boundaries of the province. Subsequent tectonism and magmatism in the Wyoming region are concentrated in the areas underlain by these Proterozoic mobile belts.

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