RE-EVALUATION OF EXTENSIONAL FAULT GEOMETRY AND KINEMATICS AT AZURE RIDGE IN THE SOUTH VIRGIN MOUNTAINS, NEVADA

Azure Ridge, in the South Virgin Mountains, Nevada (central Basin and Range Province), is a key locality for demonstrating slip on low-angle normal faults (Brady et al., 2000). High-angle faults mapped as terminating downwards against the Million Hills Wash fault have been taken to indicate that the latter was active with a dip of no more than 11°. However, a re-evaluation of structural relations begun in 2005 suggests that the now gently inclined fault is locally offset by high-angle faults. If early results are borne out by further geological mapping planned for 2006, we suggest that Azure Ridge may be better interpreted according to the multiple-domino fault model. In this model, which is consistent with Andersonian mechanics, high-angle normal faults are tilted to lower inclinations during extension, and eventually are cross-cut by subsequent generations of high-angle normal faults. Since pre-extensional Miocene strata at Azure Ridge are only slightly discordant with Paleozoic rocks offset by the faults of interest, it should be possible to use cut-off angles combined with kinematic indicators to obtain a new palinspastic restoration of the structural development of this locality.