NEW CONSTRAINTS ON THE STYLE, TIMING, AND RATES OF POST-MIDDLE-PLEISTOCENE DEFORMATION IN THE CONFIDENCE HILLS, SOUTHERN DEATH VALLEY, CALIFORNIA

New field studies and tephrochronology provide new insights into the style, timing, and rates of middle-Pleistocene-to-recent transpressional deformation in the Confidence Hills (CH), southern Death Valley. Movement on the active trace of the Southern Death Valley fault zone (SDVFZ) was preceded by earlier large-scale, northeast-vergent folding. This earlier folding involves several hundred meters of conformable late-Pliocene-to-middle-Pleistocene strata, which together form the common limb of a locally overturned fault-propagation fold pair. Geometric relations require that the blind thrust(s) responsible for earlier folding in the CH root well to the southwest of the active trace of the SDVFZ, which raises questions concerning previous flower structure models for earlier folding in the CH. Earlier folding began after deposition of Upper Glass Mountain tephra (0.9 Ma), which lies within the uppermost section of conformable, subvertical Confidence Hills strata, and ended prior to deposition of unconformably overlying, less-deformed fanglomerate, which contain tephra layers we tentatively correlate to the Bishop (0.76 Ma) and Lava Creek B (0.67 Ma). Earlier folding resulted in greater than 300 m structural relief and nearly 300 m of shortening in the span of roughly 140 ka, yielding a middle-Pleistocene shortening rate of ~2 mm/yr. Dextral slip along the mappable trace of the SDVFZ began after earlier fault-propagation folding and after deposition of the 0.76-0.67-Ma fanglomerates. Net right-lateral offset on the active trace of the SDVFZ is well constrained ~4-km south of Shoreline Butte, where a pre-existing high-angle fault, which strikes perpendicular to the SDVFZ, is offset ~700 m, yielding a post-middle-Pleistocene slip rate of ~1 mm/yr. The offset high-angle fault marks a profound lithologic and structural boundary between overturned fine-grained strata to the southeast and a thick section of upright volcanic-rich conglomerate to the northwest. We interpret the offset fault as an accommodation (i.e., tear) fault related to earlier folding in the CH. Earlier fault-propagation folding in the CH appears to be related to a short-lived episode of northeast-directed motion of the Owlshead Mountains block, which was likely accommodated, in part, by left-lateral slip along the Wingate Wash fault.