KINEMATICS OF THE PRINCE RUPERT SHEAR ZONE, BRITISH COLUMBIA

Abstract: The Western Fold and Thrust Belt in the Prince Rupert-Skeena area of British Columbia shows tops to the west thrusting and has yielded an inverted metamorphic sequence. Within the Western Fold and Thrust Belt is the Prince Rupert Shear Zone, a north-south striking structure located off the coast of Prince Rupert. A Kinematic analysis of four islands through which the Prince Rupert Shear Zone extends suggests that a late component of left handed strike slip shear exists.

The mean foliation for the islands strikes 314 +/- 10 ° with an average dip of 43 +/- 5 ° to the NE. Mineral lineations on Ridley and Lelu Islands trend 328 +/- 10 °, with a shallow plunge of 16 °. This data supports the interpretation of strike slip motions within the shear zone with a small dip slip component. The kinematics observed in the field as well as in thin section were principally left handed indicators, and include rotated porphyroblasts, asymmetric boudinage, mica fish, and S-C mylonites. No shear sense could be determined from either Coast or Kitson Island. On Kitson Island the mineral lineations trend 107 °, and plunge of 25 °.

An evaluation of the data suggests that the portion of the Prince Rupert Shear Zone that cuts through both Ridley and Lelu Islands has experienced left handed strike-slip shear with a slight dip slip component. Coast Island lies less than .5 km to the west of the shear zone, and demonstrates pure shear. An attempt to estimate the vorticity of the deformation will be done in order to demonstrate relationships between contradicting shear sense indicators. The variations in lineation measurements throughout the study area may record the collapse of the central dome structure within the adjacent Smith Island.