LOW-ANGLE NORMAL FAULTING IN THE VICINITY OF DEATH VALLEY, CALIFORNIA

Of the many subjects on which Bennie Troxel and Lauren Wright wrote over the course of their long professional careers, none is more topical than the origin and significance of gently inclined normal faults. Our data from several parts of the Basin and Range Province are consistent with the interpretation of J.M. Proffett (1977, GSAB 88, 247-266) in the Yerington district, Nevada, that mid- to late Cenozoic extension was accommodated in brittlely deformed rocks for the most part by moderately to steeply inclined normal faults that tilted to lower dip during deformation, and were cut by one or more generations of younger, more favorably oriented faults. Such back-tilting of faults is well displayed along the Black Mountains on the east side of central Death Valley (M.B. Miller, 1991, Geology, 19, 372-375). A regional-scale rolling hinge model for the Black Mountains and ranges to the east is nonetheless incompatible with the tilt history of those blocks, particularly the Resting Spring Range (M.M. Tremblay, 2012, Barnard College, senior thesis, 70 p.), and with right- rather than left-lateral displacement on the Sheephead fault (B. Renik, 2010, Columbia University, Ph.D. dissertation, 238 p.). Evidence for Pleistocene displacement on turtleback faults dipping as gently as 19° (N.W. Hayman et al., 2003, Geology, 31, 343-346) is reinterpreted as landslides making use of former faults (e.g., M.B. Miller, 1999, GSA Special Paper 333, 367-376).

The seismological observations of P. Bodin et al. (this session) are intriguing, but problematic. First, they suggest contemporary deformation to the east of the Black Mountains front, for which there appears to be no surface expression or GPS evidence. Second, the inferred fault must cut across the high-angle fault system responsible for exhumation of the Black Mountains because it is difficult to account for an original footwall depth of 10-12 km on a fault dipping at 9° given current constraints on the magnitude of crustal extension. Unlike the Sevier Desert detachment, for which we have recently estimated a friction coefficient of 0.13 (X.P. Yuan et al., GRL, in review), it is not possible to ascribe weakness to a pre-existing thrust fault. An explanation is needed for why an optimally oriented normal fault was replaced by one that is severely misoriented.