Mechanical Properties of the Sevier Desert Detachment: An Application of Critical Coulomb Wedge Theory

Abstract

AbstractLow‐angle normal faults are widely regarded as playing an important role in crustal extension. Among the most influential examples, the Sevier Desert detachment (SDD) has been imaged in seismic reflection profiles beneath the Sevier Desert basin of west‐central Utah. An extensional offset of as much as 47 km is thought to have occurred since the late Oligocene at or near its present dip of 11°. We use the palinspastic geometry of the preextensional Sevier orogen and critical Coulomb wedge (CCW) theory to constrain the friction coefficient, μD of the inferred detachment. It is assumed that the SDD is at least in part a reactivated strand of the Pavant thrust system. Compressive CCW theory suggests μD values of 0.2–0.24 for thrust faults when crustal shortening ceased in the early Paleocene. A decrease in the dip of the SDD from a maximum of 30° to its present‐day inclination of 11° and extensional CCW theory implies that μD decreased from 0.2–0.24 initially to 0.13 today. Salt, for which the normal‐stress dependence of the friction equation disappears with even shallow burial, is widespread in the Sevier Desert basin and presents locally also in Jurassic strata of central Utah. Elevated pore fluid pressure may have played a role in reducing the effective normal stress. Our model can be tested directly by coring across the detachment and by measuring material properties and the pore fluid pressure in the vicinity of the contact.