Abstract

The Archean rocks in western Wyoming, including the Teton Range, the northern Wind River Range, and the western Owl Creek Mountains, preserve a record of a 2.68–2.67 Ga orogenic belt that has many of the hallmarks of modern plate tectonics. A 2683 Ma tholeiitic dike swarm is undeformed and unmetamorphosed in the western Owl Creek Mountains. In the Wind River Range, these dikes have been deformed and metamorphosed during thrusting along the west- to southwest-directed Mount Helen structural belt, which was active at the time that the 2.67 Ga Bridger batholith was emplaced. In the northern Teton Range, the Moose Basin gneiss, which contains relict granulitefacies assemblages, appears to have been thrust upon the amphibolite-grade layered gneiss. The syntectonic Webb Canyon orthogneiss was intruded into the thrust at or before 2673 Ma. We interpret these relations, along with isotopic data indicating that the layered gneiss in the Teton Range consists of juvenile components, to indicate that the western Wyoming Province was the site of active margin tectonics at 2.68–2.67 Ga. This involved a magmatic arc in the present Wind River Range and back-arc spreading in the Owl Creek Mountains. The immature, juvenile layered gneiss in the Teton Range probably represents an accretionary prism or fore-arc basin onto which high-pressure rocks containing a mature sedimentary sequence were thrust at 2.67 Ga. Although it may be questioned as to when modern-style plate tectonics began in other cratons, it was certainly operating in the Wyoming Province by 2.67 Ga.

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