STRUCTURAL RELATIONSHIPS OF THE SKEENA FOLD BELT WEST OF THE BOWSER BASIN, NORTHWEST BRITISH-COLUMBIA

The Skeena Fold Belt is a regional fold and thrust belt that extends across most of the width of the northern Intermontane Belt of the Canadian Cordillera. Structural and stratigraphic relationships at its northeast margin show that it developed between latest Jurassic(?) and early Tertiary time, that it involved strata at least as low as Lower and Middle Jurassic Hazelton Group, and that it is characterized by northeast-verging folds and thrust faults. The structures accommodated at least 44% shortening and appear to root to the west. Most of the fold belt is distinguished by folds in thinly layered Jurassic and Cretaceous clastic rocks of the Bowser and Sustut basins. Its boundary is difficult to establish west of the Bowser Basin in poorly layered Middle Jurassic and older strata. However, map relationships show that Hazelton Group strata are folded with Bowser Lake Group. It is suggested here that the fold belt continues westward to the east margin of the Coast Plutonic Complex, where the increase in metamorphic grade and dominance of plutonic rocks effectively mark the western boundary of the Skeena Fold Belt. The difference in structural style between the Bowser Lake Group and massive volcanic rocks of the Hazelton Group is attributed to their difference in competency. Shortening by thrust faults and large-scale folds in volcanic rocks west of the Bowser Basin may balance with shortening by folds and related detachments in Bowser Lake Group farther east.