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 The first part of this chapter deals with the concepts of morphogeological belts, tectonic assemblages and terranes. These concepts are fundamental to the understanding of Canadian Cordilleran evolution and play an important role in the organization of the volume. Part B is mainly devoted to recent paleontological studies and their significance relative to the characterization of Cordilleran terranes. No attempt is made to synthesize the full scope of paleontology in the context of Cordilleran geology, a subject beyond the purview of this volume, but the importance of this discipline will be apparent in the chapters on stratigraphy. Part C presents a synthesis of crustal geophysical surveys including refraction and reflection seismology, seismicity, heat flow, geomagnetism, gravity, isostasy and magnetotellurics. Although many of these studies are in their infant stages they have already provided a wealth of data on the nature of the deep crust and processes contributing to its evolution.

Abstract The pre-Late Devonian Cordilleran miogeocline consisted of extensive shallow-water platforms upon which carbonate-clastic deposits accumulated. They were flanked to the west by deep-water environments where shale and carbonate accumulated (Rocky Mountains Assemblage). Clastic sediments were largely craton-derived. During the Late Devonian sedimentation patterns changed dramatically as turbiditic, chert-rich clastics, derived from the west and north, flooded the northern Cordillera (Earn and Imperial assemblages). Shale (Besa River Assemblage) was deposited far out onto the miogeocline and InteriorPlatform; the carbonate front of the Rundle Assemblage retreated far to the east and south of its Middle Devonian position. By mid-Mississippian time the clastic influx waned and normal marine shelf carbonate and clastic sedimentation resumed, once again with clastics derived from the craton. Devono-Mississippian plutonism occurred only in northernmost Yukon Territory, and volcanism was restricted to central Yukon and south-central British Columbia.Pre-Late Mississippian folding occurred in northern Yukon but elsewhere deformation is expressed only by local high-angle faults and disconformities. Devono-Mississippian tectonism in the northern Yukon involved uplift and granitic intrusion in Frasnian to Early Mississippian time, resulting in an upward shoaling and southward-prograding clastic wedge. The sequence consists of shale at the base, flyschoid sediments near the middle, and partly fluvial-deltaic strata at the top. Deformation migrated southward from the area of uplift until the clastics themselves were folded prior to the mid-Carboniferous. The source of Devono-Mississippian sediments in the central Cordillera was uppermost Precambrian quartzose clastics and lower Paleozoic chert from the western miogeocline. Western coarse clastics are typified

Abstract The dominant elements of structural style in the Canadian Cordillera are related to the Insular, Coast, Intermontane, Omineca, and Foreland morphogeological belts, of which the Coast and Omineca belts represent greatly uplifted granitic and metamorphic orogenic core zones. Structures commonly verge outward from the core zones so that, in cross-section, the Cordilleran orogen contains two symmetrical suborogens (Fig. 17.1, in pocket). The first to develop was the Omineca Belt wherein Mesozoic deformation is attributed to the collision of the Intermontane Superterrane with ancestral North America. Orogenesis in the Coast Belt is attributed to the long-lived development of a volcanic-plutonic arc perhaps coupled with collision of the Insular and Intermontane superterranes beginning in Jurassic time. Subsequent dextral strike-slip faulting greatly modified the distribution of components of the amalgamated terranes. Mesozoic and Cenozoic structures in the Insular Belt comprise two main elements: 1) contractional, subduction or accretion related faults and folds in the Saint Elias Mountains and Vancouver Island and 2) dextral strikeslip faults and transpressive folds in the Queen Charlotte Islands. In the Saint Elias Mountains contractional structures are cut by Late Jurassic and Early Cretaceous plutons, and, in the southern Insular Belt, both extension and contraction structures are associated with hypabyssal, felsic dykes, sills and small plutons. On Vancouver Island northwest-trending anticlinoria and northerly trending Early and Middle Jurassic plutons dominate the structural grain; on the Queen Charlotte Islands, similar plutons are of Late Jurassic age. The structurally symmetrical Coast Belt consists of a western part with westward verging

Abstract This pamphlet supplements the display sheets of Transect B2. It provides (1) descriptions of terranes on the line of Transect B2, (2) comments on gravity, magnetic and heat flow data and seismicity by R.P. Riddihough, (3) description of the seismic cross-section by R.M. Clowes, (4) bases for the compilation of Cross-section II and (5) references. The geological Strip Map and Cross-section I were taken by the contributors listed on the display sheets from both published and unpublished material and modified for this presentation. Monger was responsible for integrating the data and preparing the display sheets. He was guided through the intricacies of the geology of the eastern Cordillera by R.L. Brown, R.A. Price, P.S. Simony and J.O. Wheeler, through the Coast Plutonic Complex by G.J. Woodsworth, and through the off-shore area by C.J. Yorath. R.A. Price and P.S. Simony made the interpretation of the deep crust in the Omineca Crystalline Belt. R.L. Armstrong (principal reviewer), R.C. Speed and S. Stahl reviewed the first version of Transect B2 and made many valuable suggestions, which have modified this version, although some interpretations made herein probably are not ones that would be made by the reviewers, or even all contributors. Proterozoic and (?)Paleozoic crustal extension and rifting were responsible for creating the ancient western margin of North America (e.g. Stewart, 1976; Sears and Price, 1978). Episodes of Paleozoic(?), Mesozoic and Cenozoic crustal convergence involved not only subduction of Panthalassic/Pacific oceanic lithosphere with extensive, concomitant upper plate magmatism and intraplate, pericratonic compression, but also