CHARACTER OF DEFORMATION ALONG THE BOUNDARY CANYON FAULT SYSTEM (BCF), DEATH VALLEY

The gently dipping BCF is exposed in the central and northern Funeral Mountains of Death Valley, and may represent a premier example of a tilted normal fault system that is exposed from the paleosurface to the ductile brittle transition zone in the crust. Its upper plate moved in a SE to NW direction with respect to lower plate rocks.

Building on mapping by Troxel and Wright (1993), we have investigated footwall deformation and how it varies with structural depth. To the SE, the Neoproterozoic Stirling Quartzite is undeformed and moderately SE dipping. To the NW, this section is rotated into near parallelism with the BCF by the Lee’s camp anticline and subsidiary folds and is cut and extended by small offset normal faults such that these units underlie ~22 of the ~38 km of exposed footwall in the fault slip direction. Folds measured in the Lee’s camp area have northeast/southwest trending axes and are both northwest- and southeast-vergent. In addition to map-scale normal faults with tens to hundreds of meters of offset, smaller scale faults with <20 cm of offset occur in quartzite layers bounded by siltstones or phyllites, and are ubiquitously developed from the Lee’s camp area to SE of Chloride Cliff to the northwest. The smaller scale faults all strike southwest/northeast but are variably rotated about an axis parallel to their strike and that of map-scale fault traces (~N35°E). Their slip directions (from slickensides/slip fiber lineations) are ~N66°W, parallel to stretching lineations measured in Monarch Canyon region in the deeper, ductile part of the footwall and fault corrugations along the BCF (~N60°W)

In the hanging wall of the BCF, Tertiary sedimentary and volcanic rocks, including the Oligocene Titus Canyon Formation and younger volcanic rocks (11.3 to 11.1 Ma), successively overlie the Stirling Quartzite, Wood Canyon Formation, and Zabriske Quartzite northwestward. Cumulative offset of the basal Titus unconformity by normal faults represents a minimum separation or slip estimate along the BCF of ~20 km. Existing geo/thermochronology and geologic mapping are compatible with a Miocene motion history of the BCF but footwall deformation appears to be progressively developed towards the NW and supports a variation of the rolling hinge model for the development of the BCF.