KINEMATIC EVOLUTION OF THE WASATCH MONOCLINE, CENTRAL UTAH

The Wasatch monocline forms the western front of the southern Wasatch Plateau, one of the dominant structural features of the geology of central Utah. The monocline is a key tectonic element within the complex Mesozoic-Cenozoic framework of central Utah, because it coincides spatially with the eastern limit of both the Sevier fold-thrust belt and the Basin and Range province. The Wasatch monocline is exposed between Milburn and Salina Canyon, Utah, trending 020-030° for approximately 89 km. The purpose of this research is to determine the kinematic history of the Wasatch monocline.

Bedding data from the length of the monocline documents a doubly plunging fold. Mesoscopic structures (faults, joints, and veins) were measured along four E-W profiles across the Wasatch monocline, including exposures along the crest and the west-dipping limb of the monocline. A graben occurs at the crest-limb hinge of the monocline. Fault analysis reveals that large-scale, antithetic faults have an orientation slightly oblique (counterclockwise) to the axial trace of the monocline. Mesoscopic fault striae dominantly indicate normal dip-slip motion, but also exhibit reverse dip-slip, oblique-slip, and strike-slip at some localities. These fault data document oblique shear and multiple slip events during monocline development. Fold-tests show that extensional joint and vein data typically are oriented perpendicular to bedding, compatible with joint studies by Hucka (1991) in the undeformed Wasatch Plateau coal field. Rotated fracture geometry suggests a pre-monocline origin for the fractures.

The timing and processes associated with development of the Wasatch monocline remain controversial. Several competing hypotheses for the origin of the monocline are proposed in the literature. Our new structural data helps establish the kinematic history associated with phases of Wasatch monocline development. The results are compared to existing models to help define the origin and evolution of the Wasatch monocline.