Continent-ocean transitions in western North America between latitudes 46 and 56 degrees: Transects B1, B2, B3
J.W.H. Monger, R. M. Clowes, D. S. Cowan, C. J. Potter, R. A. Price, C. J. Yorath, 1994. "Continent-ocean transitions in western North America between latitudes 46 and 56 degrees: Transects B1, B2, B3", Phanerozoic Evolution of North American Continent-Ocean Transitions, Robert C. Speed
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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
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This volume presents syntheses in twelve chapters of the tectonic evolution of continent-ocean transitions of North America (Canada-Mexico-U.S.A.) since the Precambrian. The syntheses are interpretations based on the 19 continent-ocean transects across North American margins published by GSA as part of its Decade of North American Geology (DNAG) series. The transitional region is the part of North America between the craton, little deformed in Phanerozoic time, and the modern ocean basins. The region developed heterogeneously within plate boundary zones that led to sequences of passive, collisional, and active margins that differ place to place. Nine chapters address individual segments of the transitional region, two consider active and passive margin tectonics topically, and one treats the evolution of Phanerozoic transitions of North America as a whole.