Abstract This chapter is intended to supplement rather than reproduce material presented in Transects B-1, B-2, and B-3 and their accompanying texts, although some overlap is unavoidable, particularly in summary descriptions of major lithological and structural packages that form the crust of this segment of the Cordillera. The chapter discusses results of recent studies by COCORP within the east-central part of the corridor of transect B-3A, and by LITHOPROBE within the corridors of B-2 and B-3A on and west of Vancouver Island and between B-2 and B-3 A in the east-central Cordillera (Fig. 1). The new results confirm the general principles on which the transects were constructed but constrain depths and attitudes of major lithological packages and structures and provide insights into processes within deeper parts of the crust. Transects B-1, B-2, and B-3 lie in the segment of the Cordillera that includes the southern half of British Columbia and Alberta in Canada, and Washington, northern Idaho, and Montana in the United States (Fig. 1). Each transect emphasizes a somewhat different aspect of Cordilleran geology. Transect B-1 (Yorath and others, 1985c) extends through a region between latitudes 51°N and 56°N and longitudes 126°W to 133°W. It exploits relatively abundant data in the offshore region to illustrate complex interactions near the plate junction between the Explorer (northern subplate of the Juan de Fuca Plate), Pacific, and North American plates and extends eastward across the granitic and high-grade metamorphic terrane of the Coast Mountains to terminate in the volcanogenic and sedimentary terranes of

Abstract This display illustrates the geological architecture,tectonic style and geophysical expression of the northern Canadian Pacific continental margin in the vicinity of the modern triple junction between the Pacific,America and Juan de Fuca Plates. In addition to active transform and convergent tectonics, the region embraces the junctions between allochthonous, or suspect terranes. The tectonic history, distribution and suture between two of these terranes, Wrangellia and the Alexander Terrane, is partly based upon interpretations of geophysical data beneath water-covered areas and, as such, is somewhat conjectural The sources of information for the display are published and unpublished maps, reports and data files of the Geological Survey of Canada, Earth Physics Branch, Departments of Geology and of Geophysics and Astronomy, both at the University of British Columbia, and the Geological Branch of the British Columbia Ministry of Energy Mines and Petroleum Resources. Unpublished geophysical and subsurface sample information has been provided by Chevron Standard Ltd. and Shell Canada Resources Ltd.

Abstract DNAG Transect B-1. Part of GSA’s DNAG Continent-Ocean Transect Series, this transect contains all or most of the following: free-air gravity and magnetic anomaly profiles, heat flow measurements, geologic cross section with no vertical exaggeration, multi-channel seismic reflection profiles, tectonic kindred cross section with vertical exaggeration, geologic map, stratigraphic diagram, and an index map. All transects are on a scale of 1:500,000.

Abstract The Canadian Cordilleran Orogen comprises the mountainous region of western Canada and includes the adjacent Pacific offshore area to the foot of the continental slope. Because the evolution of the orogen is linked directly to the dynamics of the nearby interacting lithospheric plates of the eastern Pacific Ocean, the Cordilleran volume deals with the oceanic region as far west as the spreading centres bounding the Juan de Fuca plate and the Queen Charlotte transform fault. (In this text, “Cordillera” implies “Canadian Cordillera” unless otherwise specified.) In general terms the geology of this region can be related to rifting that formed the western margin of ancestral North America, subsidence and sedimentation along the resultant passive continental margin and, finally, its interaction with allochthonous terranes that produced the varied tectonic styles, regional metamorphism, the various plutonic and volcanic suites, and controlled the physiographic evolution leading to the present landscape. Current concepts on plate-tectonics play an important role in interpretations of the evolution of the Cordillera and, therefore, the integration of geophysical, structural, stratigraphic, and sedimentological data from studies underway in the Pacific offshore region is particularly cogent to an understanding of the ancient history of the orogen. These concepts are stressed by organizing the volume into chapters dealing with assemblages of rocks deposited or emplaced in environments that for the most part have modern-day plate-tectonics analogues. This is an ideal time for an updated synthesis of Canadian Cordilleran geology. Since the last synthesis in 1970, a great deal of data have been collected and analyzed in the light of the revolutionary plate-tectonics concepts.