Cordilleran Section - 112th Annual Meeting - 2016

Paper No. 1-1
Presentation Time: 8:50 AM


CHOI, Na Hyung, College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, KIRBY, Eric, College of Earth, Ocean and Atmospheric Sciences, Oregon State University, Wilkinson 202D, Corvallis, OR 97331, MCDONALD, Eric, Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512, GOSSE, John, Earth Sciences, Dalhousie University, Halifax, NS B3J 3J5, Canada and HOFFMAN, William, ExxonMobil Development Company, Spring, TX 77389,

Despite decades of study, the significance of a mismatch between geodetic velocities and geologic fault slip rates across the eastern California shear zone (ECSZ) remains incompletely understood. Existing estimates of Late Pleistocene – Holocene slip rates along the Panamint Valley fault system (PVFS) are relatively slow (~2-3 mm/yr), but they are limited to a single site along the southernmost fault segment. In contrast, both geologic and geodetic rates suggest that the northernmost segment, the Hunter Mountain fault, may experience slip rates as high as ~5-6 mm/yr. Here, we present preliminary results from an investigation of displaced alluvial fan surfaces along the central PVFS, near Jail Canyon. This site is characterized by a relict channel system associated with a large alluvial fan complex derived from Jail Canyon. The channel is displaced dextrally across a ~500 m wide zone of distributed deformation. Restoration of the channel offsets with the aid of LiDAR suggests 120±10 m of net slip, oriented 300˚, across the PVFS. Without absolute age control, we rely on the degree of soil development and the degree of degradation of the channel risers. We exploit a chronosequence consisting of twelve soils in well-preserved alluvial deposits in Panamint Valley and the Mojave Desert; age control includes OSL, radiocarbon, and cosmogenic 10Be depth profiles. Profile development indices (PDI) of these soils suggest a strong correlation with age; extrapolation of this empirical chronofunction to soils at Jail Canyon implies that the displaced surfaces date 10-27 ka. Modeling the degradation of channel risers is consistent with this age. Calibration of a diffusivity constant against fault scarps and wave-cut shorelines of known age suggests a diffusivity range of 0.8-2.3 m2/ky. Applying this range to the degradation of channel risers at Jail Canyon results in an age range of 10-28 ka. The correspondence of these two independent techniques gives us confidence that the maximum age of the displaced surface is ~28 ka. Thus, our results imply that the minimum slip rate along this segment of the PVFS is ~4.3 mm/yr and could be higher. Our results confirm previous suggestions that the PVFS carries a large fraction of dextral shear in the ECSZ north of the Garlock Fault.