资源环境科技发展态势分析平台

Low-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 degrees. We use the palinspastic geometry of the preextensional Sevier orogen and critical Coulomb wedge (CCW) theory to constrain the friction coefficient, mu(D) 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 mu D 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 degrees to its present-day inclination of 11 degrees and extensional CCW theory implies that mu D 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.

Plain Language Summary Low-angle normal faults are widely regarded as playing an important role in crustal extension. Among influential examples, the Sevier Desert detachment is of broad interest because for more than 40 years it has represented a benchmark of detachment. We use a generally accepted palinspastic geometry of preextensional Sevier orogen and critical Coulomb wedge theory to investigate friction coefficients that may have existed along the Sevier Desert detachment during both compressional thrusting and subsequent extension. Our model can be tested by coring across the detachment and by measuring material properties and pore fluid pressure. Resolving the origin of this feature will have farreaching implications for mechanisms of crustal extension.