The South Virgin-White Hills detachment fault, southeastern Nevada and northwestern Arizona: Significance, displacement gradient, and corrugation formation

Three major low-angle normal faults in the eastern Lake Mead area, Nevada and Arizona, are segments of a regional, 55-km-long, detachment fault. This fault, the South Virgin-White Hills detachment, consists of the Lakeside Mine, Salt Spring, and Cyclopic Mine fault segments. All three segments dip gently west and record top-to-the-west displacement. Based on apatite fission-track and apatite and titanite (U-Th)/He thermochronology of footwall rocks, tilt relations, and ⁴⁰ Ar/ ³⁹ Ar dates on tuffs and basalts within hanging-wall synextensional sedimentary sequences, signifi-cant extension along the South Virgin-White Hills detachment occurred between 16.5 and 14 Ma. Minor extension continued until ca. 8 Ma. Displacement on the South Virgin-White Hills detachment decreases from a maximum of∼17 km at the Gold Butte block in the north to 5-6 km at the Cyclopic Mine in the south. The along-strike, southward decrease in displacement is accompanied by a change in type of fault rock from mylonite along the Lakeside Mine fault (northern segment), to chloritic cataclasite along the Salt Spring fault (central segment), to unconsolidated fault breccia along the Cyclopic Mine fault (southern segment). Differences in fault rock may reflect decreasing exhumation of footwall rocks as a result of decreased displacement to the south. About 40% of the displacement gradient can be accommodated along a series of left-slip faults in the upper plate of the detachment. The Golden Rule Peak lineament, an east-trending alignment of structural and topographic features, may be a transverse structure that accommodates differential displacement between the Salt Spring and Cyclopic Mine faults. The trace of the South Virgin-White Hills detachment is highly sinuous in map view and is marked by three prominent salients that define west-plunging antiformal warps in the detachment surface. We interpret the corrugations in the South Virgin-White Hills detachment to have formed by a process of linkage of originally separate en echelon fault segments followed by eastward tilting of the footwall. Depositional patterns, particularly between the Lakeside Mine and Salt Spring segments, support this interpretation. The Grand Wash fault forms the present-day physiographic boundary between the Colorado Plateau and the Basin and Range Provinces; however, based on greater amount of displacement and exhumation, we suggest that the South Virgin-White Hills detachment is the principal structure accommodating regional extension in the eastern Lake Mead extensional domain.