STRUCTURAL CONFIGURATION OF TRANSTENSION IN A PORTION OF THE SOUTHWESTERN BASIN AND RANGE

We present new data and interpretations for the structural configuration of faults accommodating transtension in the southwestern Basin and Range province, California. The most obvious, active structural features are N-trending faults that bound valleys, but equally important are structures that cross the ranges: although most studies have focussed on range bounding structures, our work shows that intra-range faults can serve as important strain-transfer zones.

Active structures include: 1) normal faults on the west side of the Slate Range; and 2) normal and strike-slip faults in Panamint Valley. The western margin of the Slate Range is marked by a N-trending low-angle normal fault (dip <20° W) that cuts all units and features except the youngest shorelines and active washes. This fault continues northward and becomes the Manly Pass fault. The Manly Pass fault bends eastward and crosses the Slate Range into Panamint Valley. The Panamint Valley fault zone bounds the western side of the Panamint Range and consists of a complex array of normal and strike slip faults and these faults cut all features except for the currently active wash systems.

Although we have yet to determine slip rates on these faults, the current distribution of geomorphic features and scarps suggest that the Manly Pass fault feeds significant slip into the Panamint Valley system. The northeastward projection of the Manly Pass fault is defined by a zone of seismicity and the southern margin of a rhomb-shaped depression with a significant negative gravity anomaly. The projection also coincides with an area of complex faulting along the Panamint Valley fault zone. The Panamint Valley fault zone north of this point has abundant fault scarps and small alluvial fans, whereas to the south scarps are less pronounced and the fans are well developed, suggestive of higher rates of active deformation to the north.

Strain in the hanging wall of the Manly Pass system passes northward into northwestern Panamint Valley. Faults cut the Slate Range Crossing area and extend northward to become the Ash Hill fault. In addition, slip is fed northwestward along dominantly strike-slip faults into the Argus Range; this strain then is transferred into the more northerly-trending normal faults bounding Etcheron Valley.