The Monashee décollement at Cariboo Alp, southern flank of the Monashee complex, southern British Columbia, Canada

Abstract

The Monashee décollement is a crustal-scale compressional shear zone in the southern Canadian Cordillera; it is well exposed in alpine terrane and is imaged in the subsurface by LITHOPROBE seismic-reflection profiles. The décollement separates middle- to upper-crustal allochthonous assemblages from underlying middle- to lower-crustal rocks of the orogen. Development of the exposed part of the décollement at Cariboo Alp in the southern Thor-Odin culmination has included formation of major isoclinal folds, superposition of smaller scale folds during progressive deformation, and transposition of early formed fabrics and stratigraphic boundaries into the dominant SW-dipping mylonitic planar fabric. Hinge lines of early folds have been rotated toward the strong consistent SW-plunging mineral stretching lineation. As a result of NE-directed shearing of fold limbs and thrust-stacking of these folded sheets between a basal shear zone and overlying allochthonous assemblages, an imbricate zone developed within the middle crust during peak metamorphic conditions.