RATES OF QUATERNARY DEXTRAL SLIP ON THE BENTON SPRINGS FAULT, CENTRAL WALKER LANE, WESTERN NEVADA, CONSTRAINED THROUGH U-SERIES DATING OF OFFSET ALLUVIAL FANS

The Walker Lane, a northwest-striking zone of dextral shear that accommodates ~25% of the relative motion between the Pacific and North American plates, extends from northeastern California, through western Nevada, into southeastern California. In the central Walker Lane between the Mina Deflection and the Carson Domain in Nevada, dextral shear is distributed across the northwest-striking dextral Agai-Pah, Indian Head, Gumdrop, Benton Springs (BSF), and Petrified Springs faults. Multiple geodetic studies of these faults suggested that combined they accommodate between ~3-10 mm/yr of dextral slip. Previous geodetic and geomorphological studies suggested that the BSF and Petrified Springs fault potentially accommodate the majority of the slip through this portion of the Walker Lane, with the BSF accommodating a minimum of ~1 mm/yr. New geomorphological mapping of offset alluvial deposits along the BSF was combined with terrestrial laser scanning, U-series dating of pedogenic carbonate from sub-surface clast coatings, and cosmogenic ³⁶Cl dating to constrain the rate of late Pleistocene-Holocene slip. Alluvial features offset along the BSF include channels, channel margins, ridges, and alluvial fan margins with dextral offsets ranging from ~1 m to 70 m. U-series ages at one site on the BSF yield minimum ages for fan deposition ranging from ~12-98 ka. A fan offset by ~31-34 m yields U-series ages of 12.7 ± 1.3 ka (all errors 2σ) on one side of the fault, and 12.2 ± 1.1 and 13.11 ± 0.88 ka on the other side. Taking the ~13 ka age as a minimum estimate of the fan’s age, these data indicate a slip rate of up to ~2-3 mm/yr. An adjacent fan offset a total of ~25-26 by multiple splays of the fault yields a preliminary cosmogenic ³⁶Cl depth profile age of 10.8 ± 2.5 ka suggesting a similar rate of ~2-3 mm/yr. Dating via the U-series and cosmogenic ³⁶Cl techniques provide mutually consistent ages for late Pleistocene-Holocene alluvial fans offset along the BSF and show that the fault accommodates a larger fraction of the slip within the central Walker Lane than previously demonstrated.