Paleogeographic reconstruction of regional accretionary complex architecture, Franciscan Complex, northwestern San Francisco Bay Area, California, USA

Abstract The Franciscan Complex of western California, USA, the archetypal subduction accretionary complex, cannot serve as a model complex unless its local-to-regional architecture is clearly understood. Yet, architectural details are not understood in many regions, including northwestern San Francisco Bay Area. Here, Cenozoicage, dextral strike-slip faulting on faults Andreas System fragmented original architecture, forming crustal blocks and juxtaposing fragments rock different tectonostratigraphy. One little-known Cenozoicage fault block boundary, Tamarancho Shear Zone, separates northeastern that dominated by rocks from southwestern with significantly have abbreviated stacks at least one blueschist-facies unit, whereas lack units either westward-and-downward–younging tectonostratigraphy or thrustsheet composed partial sequences ocean-plate stratigraphy rocks. Area bounded southwest (sensu stricto) northeast Petaluma Valley–Point Richmond–Silver Creek fault. Using paleogeographic reconstruction, can be partially reconstructed removing separations enhanced unfolding Cenozoic folds. Accretionary were originally assembled ~190 km southeast their present locations, west southern Diablo Range. Reconstruction location considerations require Novato Block, located Mt. Tamalpais to southwest, separated along across strike complex. Either dual zone faulted plate geometries produced segment each highlights possibilities along- across-strike variations structure history