By the beginning of Neogene time, some 24 Ma ago, the Kula Plate had disappeared and the Pacific-Farallon spreading ridge had collided with the western margin of North America north of Queen Charlotte Islands. During the early Neogene the Pacific-North America-Farallon triple junction migrated southeastward to a position adjacent to the northern end of Vancouver Island where it has remained relatively fixed for the past 10 Ma. The early Neogene shift in the position of the triple junction was accompanied by a rapid decrease in the size of the easterlysubducting Farallon Plate. The present small remnants of the Farallon Plate have been renamed the Juan de Fuca and Explorer plates, and the active spreading centre (Farallon-Pacific spreading ridge) which bounds them on the west has been renamed the Juan de Fuca Ridge system. Motion vectors relative to the absolute (hotspot) framework indicate that the western Canadian part of the North American Plate moved southwestward at about 22 mm per year for most of Neogene time.
Dextral transcurrent faulting, which dominated the early Tertiary tectonics of the Intermontane Belt, was greatly reduced during the Neogene, and confined to faults at or near the continental margin. Movement on the Totschunda and Border Ranges fault systems accompanied profound Neogene uplift, folding and northeasterly directed thrusting in the Saint Elias Mountains. During this time the Intermontane Belt remained relatively stable whereas the axis of the Coast Belt was greatly uplifted and deeply dissected.
throughout the offshore regions of the Insular Belt, on parts
Figures & Tables
Geology of the Cordilleran Orogen in Canada
Seven stratigraphic chapters cover time slices from Precambrian to Neogene; also included are chapters covering tectonic framework, paleomagnetism, physiographic evolution, Quaternary glaciation, volcanic and plutonic regimes, metamorphism, structural styles, metallogeny, energy and ground resources, and natural hazards. A tectonic synthesis chapter and a summary of outstanding problems round out the volume. Accompanying plates include physiographic, tectonic assemblage, terrane and metamorphic maps, correlation charts, structural cross sections, and special maps showing distribution of Proterozoic and Miocene plutonic suites and the metallogeny of terranes.