TECTONIC EVOLUTION OF THE CENTRAL WASATCH RANGE: GEOMETRIC, KINEMATIC AND AGE ANALYSES OF NOTABLE STRUCTURAL FEATURES

Structural features of the central Wasatch Range record multiple phases of deformation involving Early Proterozoic continental assembly, late Paleozoic basin development, Jurassic to Cretaceous shortening and Oligocene to Holocene magmatism and extension. These features provide a natural laboratory for students interested in deciphering the tectonic evolution of western North America. Students from BYU have assisted me in making the following discoveries. 1) Structural analysis of the Santaquin basement complex indicates mostly N-S horizontal stretching with a component of top to the south simple shear during continental assembly. 2) Exhumation of the basement complex coincides with Late Proterozoic rifting that formed the western edge of the North American craton. 3) Intracratonic basins, such as the Uinta graben and half-graben were inverted during Jurassic to Cretaceous east-directed shortening. Fault-propagation and tri-shear type folds developed on the flanks of the basins that document up to 40% strain during mostly eastward tectonic transport. 4) Some west-directed folds form above wedge thrust structures (triangle zones). 5) The final phases of shortening show NE directed structures with much less strain, but notable influences of inherited structure. 6) Oligocene to Holocene extensional deformation also may have localized along pre-existing structures that correspond with the eastern limit of previous deformation events. The Wasatch Range is a footwall horst bounded by the Wasatch Fault to the west and more distributed deformation to the east. Similar to the Death Valley region, the Wasatch Fault has many low-angle fault planes that dip between 25°-40°, including the Lone Peak turtle back structure. Slicken-lines and Holocene fault scarps 2 to 3 m in length and height, respectively, indicate nearly pure dip-slip motion capable of producing earthquakes > magnitude 7.0. 7) Deformation along the central Wasatch Fault over the past decade is measurable by repeat GPS surveys that indicate strain rates of 2-3 mm/yr.