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Abstract

Northern Vancouver Island lies in the southern part of the Wrangellia tectonostratigraphic terrane which is bounded on the east by plutonic rocks of the Coast Belt and underplated on the west by the Pacific Rim and Crescent accretionary terranes (Wheeler and McFeely, 1991). Amalgamation of Wrangellia to the Alexander Terrane to form the Insular Superterrane appears to have occurred as early as Late Carboniferous time (Gardner et al., 1988). Subsequent accretion of the Insular Superterrane to inboard terranes of the Coast and Intermontane belts may have occurred as late as the mid-Cretaceous (Monger et al., 1982) or as early as the mid-Jurassic when a single superterrane may have been accreted to the North American continental margin (van der Heyden, 1991). There is an accumulating body of geophysical evidence (T. J. Lewis, C. Lowe and T. Hamilton, personal communications, 1993) to suggest that since this accretionary event, the northern tip of Vancouver Island may have been involved in the formation of the Queen Charlotte Basin, a Tertiary trans-tensional province related to oblique convergence of the Pacific and Juan de Fuca plates with the North American plate (Riddihough and Hyndman, 1991). The southern boundary of this extensional regime appears to be marked by the northeasterly trending Brooks Peninsula fault zone which is coincident with Tertiary dike swarms (Nixon et al., 1993a) and young (8 to 2 Ma) calcalkaline lavas of the Alert Bay volcanic belt (Figure 1). The tectonic setting of the Alert Bay suite has been linked to a descending plate-edge

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