SOUTHERN TERMINATION OF THE WASATCH FAULT LOCALIZED BY EVAPORITE-CORED CRETACEOUS ANTICLINE, SEVIER VALLEY, UT

Structures inherited from the Sevier orogenic belt localized the southern terminus of the Wasatch fault and the transfer of its displacement to other faults. During the Sevier orogeny, Jurassic and Cretaceous rocks were folded into the Sevier-Sanpete anticline (SSA), which trends NNE under Sevier and Sanpete valleys in central Utah. The Wasatch fault terminates southward where it intersects the SSA. The Salina detachment, an eastward-rooting rolling hinge-style normal fault, was localized at the upper contact of weak evaporitic Jurassic Arapien Shale on the steep eastern limb of the SSA. Analysis of serial cross sections indicates that most of the displacement across the Wasatch fault is transferred across the SSA to the Salina detachment.

Basin and Range extension at 39° 10’ N latitude in central Utah is accommodated mainly by, from west to east, the Elsinore-Round Valley (ERV), Wasatch, and Sanpete faults. The faults strike north and accommodate ca. 9 km of divergence between the Pavant range to the west and the Wasatch Plateau to the east. Published maps show the Wasatch and Sanpete faults to terminate southward near 39° 10’ N, which would require the ERV fault to pick up displacement to the south. However, displacement across the ERV fault actually decreases southward from 2 km at 39° 10’ N to <500 m. The solution to this conundrum is that the Sanpete fault does not terminate, but rather continues southward as the Salina detachment. Three cross sections from the Pavant Range and the Wasatch Plateau, at latitudes 39° 10’ N, 39° 2’30" N, and 38° 55’ N, were constructed to analyze displacement transfer among the faults. Sections were constructed using the kink-fold method and assuming that faults with stratal separations of less than 100 m are oriented perpendicular to footwall bedding. Faults were restored successively eastward assuming a pin-line in the Wasatch Plateau. The cross sections yield a minimum heave estimate across the Salina detachment of approximately 7 km. We interpret these relations to indicate that the pre-existing evaporite-cored anticline governed the termination of the Wasatch fault and transfer of its heave to the Salina detachment.