SINISTRAL SLIP ALONG THE NACIMIENTO-CABORCA-DURANGO-ZACATECAS FAULT (75-60 MA)

Finite-element paleogeologic restoration at 60 Ma shows the western edge of Cretaceous granodiorite plutons, formed as a continuous magmatic arc above the Franciscan subduction zone, offset 370-480 km in southern California. This offset is successfully restored by reversing sinistral slip along a proposed Nacimiento-Caborca-Durango-Zacatecas (NCDZ) fault trace (active 75-60 Ma). The Franciscan trench west of the finite-element model can be restored by extending the NCDZ fault northward through coastal Franciscan terrane, where it formed a trench-trench-fault triple junction (TTFtj). As the TTFtj migrated southeastward along the continental margin, a new forearc margin was exposed sequentially from NW to SE, beneath which the Pelona-Orocopia-Rand schist (POR) was underplated. This scenario is consistent with NW to SE younging of POR and initial forearc sediments deposited on newly exposed plutonic crust. NCDZ fault displacement occurred concurrently with Laramide flat-slab subduction and intersection of the continental margin with an aseismic oceanic ridge. The TTFtj would have tracked the intersection point of the NE-SW ridge with the NW-SE continental margin. Tests of this model (following palinspastic restoration) include: 1. POR Schist should young NW-SE; 2. initiation of forearc deep-marine sedimentation directly on Mesozoic magmatic-arc basement of Salinia should young NW-SE; 3. detrital-zircon age spectra and other provenance indicators should correlate with potential source areas; 4. metamorphic and plutonic belts of the batholithic belt should realign; 5. Great Valley forearc belts should realign; 6. Franciscan belts should realign. Additional supporting observations include: 1. Truncation of the Franciscan trench in the SF Bay area, where the TTFtj may have initiated, provide a mechanism for initiating downcutting of major submarine canyons in the Sacramento Valley; 2. recent documentation of sinistral-slip kinematic indicators along the west side of the northern San Gabriel block (southern Salinia) are consistent with this model.