INTRAFORMATIONAL CLASTIC DIKES OF THE UPPER CRETACEOUS NANAIMO GROUP (BRITISH COLUMBIA, CANADA): EVIDENCE FOR TERRANE DOCKING

The Baja-British Columbia hypothesis stipulates that British Columbia originated from latitudes akin to Baja California and was tectonically translated northward to its present location rapidly across the Mesozoic-Cenozoic transition. Intraformational clastic dikes occur throughout finer grained strata of the Upper Cretaceous Nanaimo Group of British Columbia. Assuming that the principal stress directions of the dikes orient perpendicular to the trench, we note a significant (~80˚) rotation upsection that suggests a shift from an oceanic arc system to the continental arc of North America. The ca. 80 Ma age for terrane docking implied by the Nanaimo Group clastic dike orientations suggests that a majority of the tectonic translation was accomplished along an ancient transcurrent fault system yet to be identified, but possibly cloaked by Late Cretaceous plutonism in the Cascade Mountains and elsewhere along the Cordillera.