THE CASE FOR COASTWISE DISPLACEMENTS: A PERSONAL VIEW

My stance as a protagonist for Cretaceous large-scale northward translation of tectonic elements along the margin of North America rests on four main pillars but has developed sequentially. (1) In the late 1960’s and 1970’s, the California narrative dominated our thinking about late Mesozoic tectonics in western North America. Plate convergence created the great triad: an on-land rock record comprising the Sierran arc, Great Valley forearc basin, and the Franciscan subduction complex. (2) Although coastwise displacements were not required to create the triad, some workers hypothesized that Cretaceous rock units in coastal Oregon and California that do not fit easily into the California template were translated coastwise from the south. (3) From the 1970’s into the 1990’s, paleomagnetic data from mid-Cretaceous rocks in northwest Washington and southwest British Columbia made a compelling case, not yet refuted in my opinion, for a southern origin. These data were the basis for our 1997 paper that proposed crucial tests for the Baja British Columbia hypothesis. (4) Independent geological evidence, especially from the San Juan Islands and North Cascades, indicates that the template for late Mesozoic California—the triad—does not extend northward into Washington and British Columbia. Paleomagnetic and geological evidence together indicate that the likeliest Cretaceous homeland for the diverse terranes was south of California.