Tectonic denudation of Mesozoic contractile structures by a low-angle normal fault and associated faults, southern White Pine Range, Nevada
Abstract
The Blackrock Canyon area in the southern White Pine Range, Nevada mostly consists of the highly extended upper plate of a low-angle normal fault, the Blackrock fault, The post-31.3 Ma Blackrock fault places upper Paleozoic sedimentary rocks and overlying Tertiary volcanic rocks of the Garret Ranch Group in its hangingwall against a 50{dollar}\sp\circ{dollar} E-dipping homocline of Cambrian through Mississippian rocks in its footwall; The 15 to 30{dollar}\sp\circ{dollar} W-dipping Blackrock fault is non-planar and consists of two fault segments and a pronounced corrugation, the Bull Spring corrugation. These geometric irregularities suggest the slip direction on the fault was east-southeast or west-northwest. Additional geometric data such as dips of footwall strata and bedding-to-fault angles constrain the slip direction to west-northwest. This movement of the upper plate over the irregular Blackrock fault resulted in non-conservative deformation within the hangingwall block; Blackrock upper plate faults with diverse attitudes are approximately synchronous and orthorhombically symmetrical. Classical Andersonian conjugate faulting theory, which employs two-dimensional (plane) strain cannot explain these geometric and temporal fault relationships. Rather, these data suggest that nonconjugate processes generated these faults and that they represent three-dimensional or non-plane strain. A kinematic model, which invokes movement of the hangingwall block over a geometrically irregular detachment, explains the non-conservative, three-dimensional deformation observed in the Blackrock upper plate; In the Blackrock upper plate, Blackrock-related faults cut and Tertiary volcanic rocks cover Mesozoic contractile structures. Restored and retrodeformable cross sections allow the reconstruction of the pre-extensional structures. They indicate that normal movement on the Blackrock fault tectonically denuded and disrupted Mesozoic folds and a previously unrecognized thrust fault, which is here named the White Pine thrust; A restored and retrodeformable cross section across the Pancake Range, Duckwater Hills, and the White Pine Range reveals large-scale folds and thrust faults that are part of the central Nevada thrust belt. These structures correlate with previously reported folds and thrust faults that crop out in surrounding areas and consist of the Pancake thrust, McClure Spring syncline, Duckwater thrust, and the Easy Ridge or Green Springs thrust (Pipkin, 1956; Humphrey, 1960; Nolan and others, 1974; Perry and Dixon, 1993; Carpenter and others, 1993). This regional step-wise balanced and restored cross section, for the first time, allows (1) documentation of central Nevada thrust belt geometry across northern Railroad Valley and (2) examination of Tertiary extensional structural styles and the distribution of extension across this part of the belt. Together these findings suggest that northern Railroad Valley is an excellent petroleum prospect.