STACKED DETACHMENTS, HYDROTHERMAL FLUID FLOW, AND BASIN-AND-RANGE FORMATION; EVIDENCE FROM THE WHITE PINE RANGE, EAST-CENTRAL NEVADA

In their landmark 1968 paper and map on the White Pine and Grant Ranges, east-central Nevada, Eldridge Moores and his coauthors established the importance of low-angle younger-over-older faults in Great Basin evolution. We present a model of stacked detachment faults as major components of mid-Tertiary attenuation and Basin and Range formation. Primary evidence for this model comes from the Currant Gap region at the southern end of the White Pine Range, although regional mapping provides corroborating evidence covering a 50 by 80 km region of the eastern Great Basin.

We mapped two detachment faults in ductile units at Currant Gap, the White Pine detachment (WPD; Walker et al, 1992) in the Mississippian Chainman Shale, and the Currant Gap detachment (CGD) in the Cambrian Lincoln Peak Formation. The WPD is continuous from the ranges into the adjacent Railroad Valley, with over 20,000 feet of relief and no observable offset by a valley-bounding steep normal fault (Francis and Walker, 2001). Vertical separation between detachments ranges from over 500m to essentially zero in the Currant Gap area; similar coalescence of detachments exists elsewhere in the White Pine Range and also in the Schell Creek Range. Field evidence for the detachments consists of: 1) low-angle fault down cutting into the lower plate, 2) thin topographically subdued breccia zones, primarily with lower plate fragments, and 3) silicification, expressed as jasperoid along the WPD and stockwork vein replacement of limestone along the CGD. In the White Pine Range the CGD is exposed only at Currant Gap due to uplift along post-detachment N-S steeply dipping faults.

A major E-W strike-slip “Currant Summit fault,” previously mapped between the White Pine and Grant Ranges, does not exist as it does not offset the detachments. Apparent offset at the surface could be due to rotating blocks above the detachment(s). Silicification, and stable isotopic data from host rock and veins, document an extensive meteoric-hydrothermal system active during detachment faulting in the brittle regime. Boiling is indicated by a negative correlation between fluid inclusion δD and bulk δ¹⁸O values from replacement silica. Rotating normal faults could act as conduits for fluid flow, and magma, evidenced by a hydrothermally altered sill in the CGD lower plate, could be a heat source.