CHARACTER AND TIMING OF DEFORMATION IN THE FUNERAL MOUNTAINS METAMORPHIC CORE COMPLEX, DEATH VALLEY, CALIFORNIA AND NEVADA

The gently dipping Boundary Canyon fault (BCF) exposed in the central and northern Funeral Mountains of Death Valley represents a premier example of a tilted normal fault system exposed from the Miocene paleosurface to the ductile brittle transition zone at depth in the crust. As one of numerous metamorphic core complexes distributed throughout the North American Cordillera, the Funeral Mountains host lower plate rocks that were exhumed from mid-crustal depths and thus provide a valuable record of deformational and metamorphic processes associated with the deeper levels of fault zones. Despite decades of study in this MCC and others worldwide, the details of the tectonic processes responsible for exhuming rocks from the middle to deep crust towards the surface remain unclear. This study focuses on the brittle portion of BCF, the structural deformation of the footwall rocks and the offset of Cenozoic sedimentary successions in order to better understand the evolution of this fault system to its current configuration.
This study builds on mapping by Wright and Troxel (1993) and investigates how footwall deformation varies as a function of structural depth. A Neoproterozoic-Early Cambrian sequence including the Stirling Quartzite, Wood Canyon Formation, and Zabriske Quartzite serves as an excellent marker to monitor deformation related to the formation and evolution of the BDF within the central and northern Funeral Mountains. Within the central Funeral Mountains, exposures of the Stirling Quartzite proximal to the BDF are undeformed and moderately to steeply SE dipping. To the NW in the northern Funeral Mountains, this stratigraphic package is transposed into near parallelism with the BCF by the Lee’s camp anticline and subsidiary folds. All exposures of Stirling Quartzite are successively cut and extended by small offset normal faults. As a result of the normal displacements along these structures, Stirling Quartzite underlies ~22 km of the ~38 km of exposed footwall in the fault slip direction. As these faults increase in offset to the NW, they are inferred to post-date and cut the BCF as mapped in the central Funeral Mountains.
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 mm’s to ~20 cm of offset occur in quartzite layers bounded by siltstones or phyllites. These smaller scale faults are ubiquitously developed from the Lee’s camp area to SE of Chloride Cliff to the northwest. The minor 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 to fault corrugations along the BCF (~N60°W).
In the hanging wall of the BCF, Cenozoic sedimentary and volcanic rocks successively unconformably overlie the Stirling Quartzite, Wood Canyon Formation, and Zabriske Quartzite from southeast to northwest. These include the Eocene- Oligocene Titus Canyon Formation and younger sedimentary and volcanic rocks. Sixteen detrital zircon suites were dated from the Titus Canyon Formation in three localities, Titus Canyon, the head of Monarch Canyon and in the upper plate klippe of the BCF in the central Funeral Mountains. Basal redbeds have locally derived zircons from the erosion of Triassic, Jurassic and Cretaceous plutons of the Sierran arc. An influx of chert-rich pebble and cobble conglomerate has latest Eocene-Early Oligocene detrital zircon populations and distinctive clast compositions that indicate sources in north-central Nevada. The BCF cuts a sedimentary unit that yields a maximum depositional age of 12.7 ± 0.8 Ma (10.8 youngest single grain age), requiring slip to postdate this time period. This result is consistent with previously reported geo/thermochronology and geologic mapping that collectively indicate a Late Miocene history of motion on the BCF.