CRITIQUING THE INTERPRETATION OF THE HURRICANE NORMAL FAULT AS A REACTIVATED LARAMIDE MONOCLINE, WESTERN GRAND CANYON, ARIZONA

The reactivation of particular geologic structures during repeated, kinematically opposed deformation events is a common theme in Grand Canyon geology. Many of the monoclinal folds in the upper Paleozoic rocks of the Grand Canyon region are interpreted to have formed during Laramide shortening as a result of inverse reactivation of Neoproterozoic normal faults. This scenario has been well documented in isolated examples. Many of the late Cenozoic normal faults of the central and western Grand Canyon, including the Hurricane fault, are commonly interpreted to be reactivated Laramide-age reverse faults. This interpretation is based primarily on the widespread occurrence of hanging-wall folds that resemble truncated monoclines associated with these normal faults. Few attempts have been made to describe this structural overprinting in detail.

Detailed observations of the Hurricane fault and related folds in Whitmore Canyon, near Colorado River mile 192, and in Diamond Creek Canyon, suggest that most structures associated with the Hurricane fault are explicable in terms of normal-fault processes. Moreover, the Hurricane fault appears to cross-cut, rather than reactivate, reverse structures locally exposed in the footwall. New apatite fission-track data also do not support the idea of a significant, Laramide age, west-side-up flexure in the location of the Hurricane fault. We therefore propose that the large hanging-wall fold associated with the Hurricane fault is related to late Cenozoic normal faulting, which locally overprints widespread but comparatively minor Laramide contractional features.