THE SOUTHERN SIERRA-SALINIA SUPRASUBDUCTION ZONE METAMORPHIC CORE COMPLEX, CALIFORNIA

For ~500 km the Sierra Nevada batholith (SNB) and coupled Great Valley exhibit continuous arc exhumation and forearc basin deposition patterns. Continuing ~50 km southward the SNB and its forearc are tilted up and distorted westward, and exposed to ~35 km depths where the low-angle Rand fault system truncates the Cretaceous crust. This fault system places Franciscan-affinity Rand schist (RS) beneath the deep SNB along the Late Cretaceous Rand thrust, and high-level eastern SNB rocks above both the deep SNB rocks and RS along latest Cretaceous ~S-directed detachment faults. This fault system continues into the western Mojave Desert and Salinia with conventional pre-Neogene palinspastic restorations. Sparse remnants of deep-level thrust plate rocks, and more common higher-level detachment plates remain as a relatively thin batholithic veneer above RS throughout the western Mojave. The detachment plate(s) extend into the Gabilan Range of Salinia, where they rest directly on Rand-equivalent schist (Sierra de Salinas). To the west of the Gabilan Range the principal Salinia schist exposure emerges as a faulted antiform, and is mantled to the west along deep ductile faults by 30-35 km deep batholithic rocks of the Santa Lucia Range. Emplacement of the Franciscan-affinity schists throughout the restored southern Sierra-Salinia arc segment is hypothesized to have arisen from the subduction of a shallow slab segment affecting the southern California region during the onset of the Laramide orogeny. The tilted crustal section of the southern SNB marks the crustal response along the slab segmentation inflection. Extensional collapse of the disrupted arc segment followed crustal shortening and schist underplating in response to slab rollback during the demise of the shallow slab segment. Such extensional tectonism resulted in regional core complex deep crustal exhumation patterns extending from the southern SNB southward into Mojave-Salinia. This occurred above the still active SW Cordilleran subduction zone, and resulted in the westward breachment of the southern SNB-Salinia arc segment across its forearc and quite likely into its inner trench wall environment where its outer zones were liable for tectonic erosion.