Slickenlines and the kinematics of the Crowsnest Deflection in the southern Rocky Mountains of Canada

In the vicinity of the Crowsnest Pass, in the southern Rocky Mountains of Canada, the strike of the structural grain deviates significantly from the regional 325° Bow Valley–northern Montana trend. This deviation is known as the Crowsnest Deflection.The preferred azimuths for slickenlines on bedding north and south of the deflection is 056°; that is almost exactly perpendicular to the Bow Valley–northern Montana trend. Within the deflection, however, the preferred azimuth appears to be composite, ranging from 051° (Beaver Mines) to 082° (Frank, Alberta). The temporal relations of intersecting striae in the coal measures of Bow Valley would suggest, moreover, that these preferred slip directions are not sequential but may be partially or wholly concurrent.These kinematic fabric data, in conjunction with the alignment of remanent magnetic dipoles in mid-Proterozoic (Helikian) rocks, support the hypothesis that within the Crowsnest Deflection the curviplanar shape of contraction faults in the eastern Cordillera of Canada was controlled by the ancestral shape of the Cordilleran shelf-miogeocline.The proposed origin and tectonic significance of the Crowsnest Deflection may be similar to that of other great arcs, including the northeastward salient of the Mackenzie Mountains in the northern Cordillera of Canada, and of the northwestward salient of the central Appalachians of Pennsylvania.