SPATIAL AND TEMPORAL CHARACTERIZATION OF VOLCANIC-FILLED PALEOVALLEYS DEXTRALLY OFFSET ACROSS THE PETRIFIED SPRINGS FAULT IN THE CENTRAL WALKER LANE, NEVADA

Motion across the PA-NA plate boundary results in ~50 mm/yr of dextral shear, ~25% of which is accommodated in the Walker Lane, an intracontinental dextral fault system. In the Central Walker Lane (CWL), Nevada five NW-striking faults are hypothesized to accommodate most of the dextral slip, but displacement magnitudes and fault initiation ages are poorly constrained. Review of published 30+ year-old geologic maps suggests Cenozoic volcanic-filled paleovalleys (PVs) record dextral offset across the five CWL faults, including the Petrified Springs fault (PSF). To test the hypothesis that PVs act as geologic markers across the PSF, we completed new geologic mapping and structural studies. The CWL is predominantly Mesozoic metasedimentary and intrusive rocks overlain unconformably by Oligocene and Miocene tuffs, lavas, and sedimentary rocks. Observations of paleosol developed stratigraphically on top of Mesozoic rocks and structural measurements in the overlying Cenozoic rocks document the geometry of the unconformity and offset magnitude across the PSF. The PSF is a NW-striking dextral fault that extends ~65 km along strike and offsets four Cenozoic geologic markers. The oldest marker is a series of four, nested PVs filled with Cenozoic lavas and tuffs. Dividing the 10.3 ± 2.5 km offset magnitude across the PSF by the 27.11 ± 0.07 Ma Ar/Ar age reported for the youngest nested unit, the Mickey Pass Tuff (Henry & Faulds, 2010), yields a minimum slip rate of ~0.4 mm/yr. A younger PV is offset 9.6 ± 2.0 km and filled with a 16.03 ± 0.05 Ma andesite lava (preliminary Ar/Ar age), yielding a minimum slip rate of ~0.6 mm/yr. A third PV is offset 1.8 ± 0.4 km across one splay and filled with a presumed Pliocene basalt (Ar/Ar geochronology in progress). The fourth marker is a basin-bounding normal fault, truncated and dextrally offset across the PSF. Dividing the 3.3 ± 1.0 km offset magnitude by the ~10.7 Ma K/Ar age of the basin fill (Evernden et al., 1964) yields a ~0.3 mm/yr minimum slip rate. Our ~0.4 mm/yr long-term slip rate is within error of reported minimum slip rates along both the dextral, west-adjacent CWL faults: the Gumdrop Hills and Benton Springs faults (Mayberry & Lee, 2017; Dubyoski et al., 2016), and is within error of GPS-based block-model estimates for recent slip on the PSF of ~0.6 mm/yr (Bormann et al., 2016).