COUPLED TECTONIC, GEOMORPHOLOGICAL, AND MAGMATIC PROCESSES IN A RIFT ZONE: AN EXAMPLE FROM THE OWENS VALLEY RIGHT-SLIP TRANSTENSIONAL SYSTEM IN EASTERN CALIFORNIA

A key issue in the study of extensional tectonics is how the geometry of rift-bounding faults controls surface and deep-crustal processes during rift formation. To address this issue, we systematically examine the morphology, drainage systems, depocenters, distribution of active volcanic centers, and along-strike variation of slip on rift-bounding faults across the active right-slip transtensional Owens Valley system, eastern California. Our observations, together with existing studies, allow us to divide the rift zone into three segments from south to north. The southern rift zone is bounded by the east-dipping Sierra Nevada frontal fault zone along the western edge of the Owens rift valley. A parallel right-slip fault (the Owens Valley fault) lies along the axis of the valley while active volcanic centers are distributed across the western side of the rift in the down-dip direction of the fault. Highest topography of the western rift shoulder corresponds to the active depocenter of the rift valley and area of maximum slip on the Sierra Nevada frontal fault. The northern rift zone is bounded by the west-dipping transtensional White Mountains fault zone along the eastern edge of the valley. Active volcanic centers here are distributed across the eastern rift valley and rift shoulder in the down-dip direction of the fault. Highest topography correlates to maximum normal slip on the White Mountains fault, along with the active depocenter of the valley. The central rift zone is bounded by the southern extension of the White Mountains fault and the northern extension of the Sierra Nevada frontal fault and forms a symmetric graben system. Here, active volcanic centers are aligned linearly in a northeast direction. In order to explain the above observations, we suggest that the rift-bounding faults are low-angle within the lower crust, possibly extending across the Moho. Such structural geometry results in thinning of the mantle lithosphere, creating a magmatic plumbing system to transport mantle-derived melts to the surface across the thinnest part of the rift-zone crust.