Wyoming Craton
Younger metamorphic dates (1.81–1.71 Ga) also typify the eastern and northern Wyoming province peripheries in the western Dakotas and southeastern Montana.
The Montana metasedimentary province and Beartooth–Bighorn magmatic zone were established as cratons by about 3.0–2.8 Ga. Crustal growth occurred through a combination of continental-arc magmatism resulting from oceanic crust subducted beneath continental crust on an adjacent plate, creating an arc-shaped mountain belt, together with 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 craton.
Based on imaging by the "Deep Probe" analysis, a thick lower crustal layer corresponds geographically with the Bighorn subprovince and may be an underplate associated with ca.
The Sweetwater subprovince is characterized by an east–west-tending tectonic grain that was established by three or more roughly contemporaneous late Archean, pulses of basin development, shortening, and arc magmatism.
This tectonic grain, including the 2.62 Ga Oregon Trail structure, controlled the locations and orientations of Proterozoic rifting and uplifts related to the Laramide orogeny.
If there has been any net crustal growth of the Wyoming Province since 3.0 Ga, it has involved a combination of mafic underplating and arc magmatism.
As a result of the collision, older, Archean rocks of the Wyoming province were intensely deformed and metamorphosed for at least 75 km inboard from the suture, which is marked today by the Laramie Mountains.
Both the anorthosite and granite transect the Cheyenne belt in the Laramide Mountains, and intrude crystalline rocks of the Wyoming province.
[4] Long after its assembly, the Wyoming Craton owes its spectacular mountainous terranes mainly to a regional episode of compressional deformation during the Laramide orogeny (ca.60 Ma).
