HR: 0830h
AN: T51D-0194    [PDF]
TI: Neotectonics of the Panamint Valley fault zone: Active slip on a low-angle normal fault system
AU: * Kirby, E
EM: ekirby@geosc.psu.edu
AF: Dept. of Geosciences, Penn State Univ., University Park, PA 16802 United States
AU: Snyder, N
EM: nsnyder@usgs.gov
AF: USGS Pacific Science Center, 1156 High. St., Santa Cruz, CA 95064 United States
AU: Whipple, K
EM: kxw@mit.edu
AF: Dept. of EAPS, MIT, Cambridge, MA 02139 United States
AU: Walker, J D
EM: jdwalker@ku.edu
AF: Dept. of Geology, Univ. of Kansas, Lawrence, KS 66045 United States
AU: Andrew, J
EM: jeandrew@ysu.edu
AF: Dept. of Geological and Environmental Sciences, Youngstown State Univ., Youngstown, OH 44555 United States
AB: The mechanical feasibility of active normal-sense displacement on low-angle ($<$ 30$\deg$) fault systems has been the subject of debate for the past quarter-century. Although the significance of these fault systems has now been recognized in both extensional and collisional orogens across the globe, relatively few have been shown to be presently or recently active. Rather, observations of high-angle normal faults which displace young alluvial deposits near or at the range front are commonly interpreted to indicate that low-angle faults observed within the range have been abandoned in favor of newly-formed structures. Here we assess this hypothesis with new mapping and observations of late Pleistocene - Holocene alluvial deposits and fault scarps along $\sim$60km of the central and southern Panamint Valley fault zone. Four lines of evidence indicate that slip on these young fault scarps is a direct consequence of displacement on a low-angle master detachment. First, the geometry of fault scarps within alluvium mimics range-scale variations in strike on the curviplanar, low-angle detachment fault, suggesting that scarps merge with the detachment at depth. Second, the kinematics of recent faulting inferred from displaced geomorphic markers suggests oblique-normal slip, consistent with the long-term slip vector inferred from piercing lines across the Hunter Mountain fault (e.g., Burchfiel et al., 1987). Third, alluvium of late Pleistocene age (inferred from soil and surface characteristics) is juxtaposed against bedrock across a $\sim$25-30$\deg$ fault surface characterized by well-developed fault gouge. Finally, direct observations of 3-5 meter fault scarps at the intersection of the low-angle range-front fault with the valley floor indicate recent (probably seismogenic) slip on the detachment system itself. We are forced to conclude that the neotectonics of the Panamint Valley fault zone reflect active slip above a low-angle detachment fault.
DE: 8107 Continental neotectonics
DE: 8109 Continental tectonics--extensional (0905)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting