Regional tectonic features of the westem C•-mdian Cordillera can be interpreted in terms of Middle Jurassic accretion of a single composite supenerrane (Stikinia + Wrangellia + Alexander) to ancestral North America. Closure of the intervening Cache Creek-Bridge River ocean moved the continental edge to a new position west of the accreted superterrane. The Coast Belt is primarily a succession of superimposed Middle Jurassic to early Tertiary magmatic arcs related to prolonged subduction of Pacific Ocean lithosphere beneath the new North American margin. Discrete magmatic pulses, separated by lulls or periods of relative quiescence, successively overprinted the new margin. The Insular and Intermontane superterrane•, previously viewed as widely separate entities prior to mid-Cretaceous time, were already amalgamated before an initial Middle Jurassic overprint produced an ancestral Coast Belt. Late Jurassic to Early Cretaceous riftrelated(?) marine basins, mid to Late Cretaceous compressional structures, and early Tertiary extensional features coincident with the Coast Belt are subsidiary intraplate attributes that reflect extemal adjustments in plate motions within a primary, subduction-related Andean magmatic arc• Paper number 91•183. 0278-7407•92/91TC-02183510.00 model relates to a new east-dipping subduction zone beneath the accreted supenerrane. Recent work in the Coast Belt suggests that a magmatic arc linking the Insular superterrane to the Intermontane supenerrane may already have been established as far back as Middle Jurassic time [van der Heyden, 1989]. Other observations also argue against the concept of two superterranes, separated along the Coast Belt by a mid-Cretaceous oceanic suture. There is, for instance, no compelling record within the Coast Belt of Mesozoic oceanic lithosphere, subduction assemblage, or forearc basin between the supertermne•, and essentially concordant paleomagnetic signatmes suggest that the supertenanes were close together during early Mesozoic time [Irving and Wynne, 1990]. These observations, and others summarized in this paper, call for a critical evaluation of the mid-Cretaceous collision model. In recent years observations have also been made which have implications for the validity of the broader superterrane concept. In Monger et al.'s [1982] scenario, the Sfikine, Cache Creek, and Quesnel terranes were amalgamated into Intermontane superterrane by Late Triassic time, and Wrangellia and Alexander terrane were amalgamated into Insular superterrane by Late lurassic time. New stratigraphic, paleontologic, and geochronologic data suggest that Wrangellia and Alexander terranes were already together by Pennsylvanian time [Gardner et al., 1988] and that Stikinia was not accreted to the rest of the Intermontane superterrane until Middle lucassic time [Mo•er, 1986; Cordey et al., 1987, 1991; Rusmore et al., 1988; Rusmore and Woodsworth, 1991; also B. Ricketts, manuscript in preparation]. In combination, these observations suggest the possibility that Stikinia was already attached...
