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Savant Resources LLC, Tucson, AZ

Abstract: Structural Evolution Of The Uinta Salient And Tectonomagmatic Rejuvenation Of The Cheyenne Belt, North-central Utah

The Uinta thrust salient, a structural element superposed on the Cheyenne belt crustal suture, was formed by N-S and E-W oriented contractional fault systems which acted simultaneously from Late Cretaceous to late Eocene time. North-south oriented crustal shortening was accommodated by two basement involved thrusts systems. Thrusts involved in upper crustal deformation, capitalized on structural fabrics inherited from Proterozoic accretionary and rift related tectonism, and resulted in basin-inversion of the Proterozoic Uinta Mountains Group. A deeper set of blind thrusts, involving mainly the lower crust, facilitated underthrusting of Proterozoic Yavapai rocks beneath crust of the Archean-early Proterozoic Wyoming Craton.

Collectively, movements on these crustal thrust systems resulted in displacement and folding of the Uinta salient, crustal root development, and localization of crustal loads. Detachment of the Uinta salient along faults that formerly bounded the Proterozoic rift structure is important because once this rock-mass became a free-floating entity it was subject to gravitational spreading and resultant eastward tectonic transport. Crustal roots developed during this episode of crustal contraction became the sites of later normal faulting, flexural-isostatic exhumation and magmatism during late Paleogene-Neogene crustal extension.

Evidence to support this hypothesis is found in a collection of seemingly disparate structural relationships. These include: 1) thrust reactivation of the Charleston-Nebo and Hogsback thrusts by the Uinta sole fault, 2) flexural-isostatic exhumation and magmatism related to the Wasatch igneous belt and Cottonwood metamorphic core complex, 3) geographic limits of the Green River and Uinta basins, and 4) localization of crustal thickness anomalies.

AAPG Search and Discovery Article #90919©1999 AAPG Rocky Mountain Section Meeting, Bozeman, Montana