Abstract

Rocks of the early Proterozoic orogenic system that fringes the Archean-aged Wyoming province are exposed along the Uinta fault in the northeastern Uinta Mountains of Utah and Colorado. Exposed here are the Red Creek Quartzite, an early Proterozoic-type miogeoclinal metasedimentary sequence more than 4 km thick, and an underlying, newly recognized, Archean gneiss complex more than 2.7 b.y. old. During the Hudsonian orogenic period, the miogeoclinal sequence was emplaced northward over the Archean complex by tectonic translation along a thick mylonite zone in the waning phases of upper amphibolite metamorphism. The orogen was disrupted by east-trending block faults with several kilometres displacement during initiation of the Uinta aulacogen and was buried by more than 7 km of middle Proterozoic sediments of the Uinta Mountain Group. The middle Proterozoic block faults were reactivated with reversed sense of displacement during the Laramide uplift of the Uinta Mountain block.

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