A gravity slide origin for the Mormon Peak detachment: Re-examining the evidence for extreme extension in the Mormon Mountains, southeastern Nevada, U.S.A.

摘要

The Mormon Peak detachment is an enigmatic, low-angle surface that cuts almost all other structures in the Mormon Mountains of southeast Nevada. It has been described as both a large-magnitude offset, low-angle normal fault and as a rootless gravity slide. The two models have been tested, and the gravity slide model explains the geology exposed in the range better than the extreme extension model. Kinematic indicators on the detachment show down-dip motion. Structure contours delimit discrete domains. Exhumed structures reveal no large-magnitude offset between the Meadow Valley and Mormon Mountains. Thermochronological modeling indicates basin-wide exhumation beginning at ∼23--17 Ma. Field mapping documents a pervasive role for long-lived high-angle normal faults with spatially and temporally restricted detachment formation events, and measurements of the volume of rock contained in the hanging wall show it required only a small source area with respect to the size of the range.;Regional crustal extension from the Meadow Valley Mountains to the Beaver Dam Mountains is approximately 25%, an order of magnitude less than previously interpreted. The conclusions from the Mormon Mountains were applied to several interpreted detachment faults elsewhere and a set of criteria developed to help future workers distinguish between rooted structures that accommodate crustal extension and rootless structures that do not.