Extensional Inversion of the Central Utah Thrust Belt: More than Just the Sevier Desert Detachment

Coogan, James C.
Western State College of Colorado, Gunnison, CO

     The Sevier Desert detachment (SDD) is proposed as a low-angle Cenozoic normal fault that formed by inversion of slip along a former Cretaceous thrust fault, the Pavant thrust. Seismic imaging of Miocene-Pliocene growth strata above the SDD provides the most widely cited evidence for Basin and Range extension along the detachment. However, structural and stratigraphic reconstruction of the basin indicates that pre-Basin and Range extension accounts for over a third of the 45-50 km total SDD displacement constrained from hanging wall and footwall cutoffs and piercing points. Inversion of the Pavant thrust along the SDD is just one component of Oligocene and younger low-angle normal faulting that reactivated the Pavant and all major thrust systems to the east. Growth strata of the Oligocene Goldens Ranch Formation are particularly well dated and imaged across the relay zone between the Juab and Sevier grabens, where normal faults sole downward into Pavant footwall thrusts. Normal reactivation of the Paxton thrust occurred beneath the Sevier Valley south of the Gunnison Plateau, where the Sevier normal fault is interpreted to sole westward into the Paxton thrust system. Eastward rollover of the Oligocene Crazy Hollow and Aurora Formations and the thick overlying volcanic succession is evident along the east flank of the Pavant Range above the sole fault, although definitive evidence of growth is absent. Finally, growth strata in the Moroni Formation document Oligocene normal inversion of the Sanpete Valley backthrust along the west side of the frontal triangle zone east of the Gunnison thrust.

AAPG Search and Discovery Article #90071 © 2007 AAPG Rocky Mountain Meeting, Snowbird, Utah