Paper No. 265-3
Presentation Time: 9:00 AM-6:30 PM
RATES OF QUATERNARY DEXTRAL SLIP WITHIN THE CENTRAL WALKER LANE, WESTERN NEVADA
The ~700 km long 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, and into eastern California. In the central Walker Lane, Nevada, between the Mina Deflection and the Carson Domain, dextral shear is distributed across five faults: the Agai-Pah, Indian Head (IHF), Gumdrop (GHF), Benton Springs (BSF), and Petrified Springs (PSF) faults. We have precisely measured Quaternary fault offsets along these faults using field observations and DEMs generated with Terrestrial Laser Scanning and Structure from Motion using Agisoft Photoscan applied to dextrally offset thalwegs, fan edges, channel margins, and ridges. We used a published MATLAB GUI, LadiCaoz, which calculates an optimal offset based on the goodness of fit of geomorphic markers correlated across the faults. Dextral offset magnitudes vary with age of offset features and range from ~2-50 m on the IHF, ~10-20 m on the GHF, ~1-35 m on the BSF, and ~8-99 m on the PSF. Clast counts of offset deposits support our reconstructions. We calculate the first Quaternary slip rates for these faults using modern techniques by combining measured offsets with terrestrial cosmogenic nuclide dating (TCN) of samples from depth profiles and U-series dating of carbonate clast-coatings. Preliminary 10Be ages from a deposit at one site on the BSF with a channel edge offset by ~34 m yielded ages of ~21-31 ka, indicating a late Pleistocene minimum slip rate between ~1.1-1.6 mm/yr. At one site on the GHF, dextrally offset channels and margins on two splays within a fan show a minimum offset of ~20 m on one splay and ~13 m on the second splay. Combined with preliminary 10Be ages of ~67 and ~63 ka for the fan at each splay, we obtain a minimum late Pleistocene dextral slip rate of ~0.5 mm/yr. Recently published block modeling suggests modern dextral rates of ~0.5 mm/yr on the IHF, ~1 mm/yr on the BSF (slightly less than our late Pleistocene rate), and ~0.6 mm/yr on the PSF. TCN and U-series dating of other offset surfaces on these faults are in progress and will further constrain the patterns of Quaternary slip in this segment of the Walker Lane, yielding insights into the proportion of slip accommodated by each of these faults throughout the Quaternary.