RELATIVE MOTIONS BETWEEN PACIFIC BASIN OCEANIC PLATES AND NORTH AMERICA AND THEIR IMPRINT IN THE FRANCISCAN COMPLEX

The convergence between the Pacific, Farallon and Kula oceanic plates and the North American plate has provided a driving force for tectonic processes that have shaped the western margin of North America. But reconstructions of plate motions in the Pacific basin have traditionally relied on the assumption of fixed hotspots. In the last decade, substantial Cretaceous and Paleogene motion between the Pacific and Atlantic hotspots has been defined using paleomagnetic data. Geodynamic modeling suggests that rapid migration of the Hawaiian hotspot may have been caused by the cessation of mantle ridge flow that had captured the plume conduit (Tarduno et al., Science, 2009). These data and hypotheses provide motivation for reevaluating the history of relative motion between Pacific oceanic plates and North America by means of plate circuit reconstructions. We contrast two plate circuits (Doubrovine and Tarduno, JGR, 2008) and their associated reconstructions and examine the implications for formation of the Franciscan Complex and, more generally, the western margin of North America.