Remagnetization and northward coastwise transport of Franciscan Complex rocks, northern California: a reinterpretation of the paleomagnetic data

Previous paleomagnetic studies of accreted oceanic rocks within the Franciscan Complex of northern California have concluded that these rocks originated far to the south of their present positions with respect to the North American continent. However, the plate motions implied by some of these paleomagnetic data are problematic (e.g., exceptional plate velocities), and uniform-polarity magnetizations in almost all of these rocks indicate the possibility of remagnetization. In this paper, Franciscan rocks in northern California are reinterpreted as having been remagnetized prior to accretion-related deformation. Paleolatitudes of subduction and remagnetization in the northern hemisphere (12?? to 33??) appear to be inversely proportional to age of accretion (middle Cretaceous to Oligocene) for the Franciscan rocks. Subsequent northward displacements (800 to 3700 km) and clockwise rotations (56?? and 154??) of these rocks inferred from the paleomagnetic data are consistent with potential displacements along the western margin of North America during late Mesozoic and Cenozoic time calculated using examples of modern subduction zones and current plate reconstruction models. -from Author