KINEMATICS OF LEFT-LATERAL FAULTING IN A DEXTRAL ZONE OF SHEAR – PRELIMINARY ASSESMENT OF THE OLINGHOUSE FAULT, NORTHERN WALKER LANE, WESTERN NEVADA, USA

The Walker Lane (WL) is a 700 km-long dextral shear zone that accommodates 15 - 25% of the motion between the Pacific and North American plates, several hundred km east of the main plate boundary along the San Andreas fault (SAF). Dextral shear in the WL is generally taken up on numerous subparallel N- to NW-striking faults. However, a few domains contain major NE-striking left-lateral faults. Cumulative dextral offset decreases to the north and essentially terminates near the latitude of the Mendocino triple junction and north end of the SAF, possibly indicating that the WL is propagating northward with the triple junction.

The Olinghouse fault is a NE-striking, 25-km –long, 6-km-wide, oblique sinistral-normal fault zone located just east of Reno, Nevada, in the northern WL. In addition to sinistral and normal fault strands, E-W trending folds occur in the fault zone. The faults cut a 2+ km thick sequence of Oligo-Miocene felsic to mafic volcanic and minor sedimentary rocks. Most fault strands are sub-parallel, striking N60-90E, and spaced 0.1-0.5 km. Faults generally dip near vertical, though a few faults dip as shallowly as 55 deg. Rakes of fault striae are mostly subhorizontal, with a few between 60 and 90 deg. Slip direction on the faults is generally left-lateral based on Riedel shears and rough facets, though a few strands have accommodated oblique or purely normal motion. Fault blocks are generally tilted 10-30 deg, though a few are tilted up to 60 deg. Quaternary alluvial fans are cut by several fault strands.

Understanding the kinematic role of the Olinghouse fault zone has implications for understanding processes of strike-slip fault and possibly continental transform development. Three possible models for the kinematic role of the Olinghouse fault zone include a secondary Riedel shear in a zone of NW-trending dextral shear, accommodation of vertical-axis block rotation (VABR), and/or an extensional transfer zone linking NW-striking dextral faults. Our preliminary kinematic data suggest that the extensional transfer model is unlikely. A secondary Riedel shear also seems unlikely, because the fault lies primarily west of the WL. The Olinghouse fault may therefore be accommodating VABR associated with a decrease in both NW-SE directed dextral shear and extension away from the WL in the western Great Basin.