Gravity Sliding: An Under-Recognized Phenomenon in the Basin and Range Province?

Differentiating between gravity slides and low-angle detachment faults is difficult but important, as the two phenomena have very different implications for estimates of crustal extension and geohazards. The Mormon Peak detachment in the Mormon Mountains of southeastern Nevada has been interpreted as an example of both mechanisms. Various criteria are identified that allow the predictions of these models to be tested.

Structure contours delimit discrete domains of motion. Kinematic indicators along the basal surfaces show motion most recently took place in a down dip direction. Apatite fission-track analysis shows exhumation of the range began around 23 - 17 Ma in a distributed fashion. The amount of material preserved in the hanging wall of the main low-angle fault in the range is a minimum of 10.9 km3, small compared with the size of the range. Restoration of predicted exhumation reveals no large-magnitude extension between the Mormon Mountains and surrounding ranges. Low angle detachments are temporally restricted to intervals between movement events on high-angle faults.

These criteria suggest the Mormon Peak detachment is a product of gravity sliding and may help future workers in other areas distinguish between rooted structures that accommodate crustal extension and rootless structures that do not.