Mid-Mesozoic Multiphase Folding Along the Border of the Shuswap Metamorphic Complex
The high-grade regional metamorphism of the extensive Shuswap metamorphic complex of southeastern British Columbia has been considered by most geologists to be Precambrian in age. On the basis of structural analysis, it is now apparent that low-grade Triassic rocks of the nearby Slocan Group have undergone the same three generations of folding as the Shuswap, beginning with that accompanying regional metamorphism. Intense isoclinal recumbent folding of the first generation accompanied regional metamorphism and development of a schistosity parallel to the axial surfaces of these folds and a penetrative lineation parallel to their axes. Following regional metamorphism, a second deformation, accompanying formation of nearly upright macroscopic folds, formed a strain-slip cleavage by crenulation of the schistosity. Subsequent intrusion of granitic plutons developed mesoscopic folds having coplanar axes in any single domain. This third deformation refolded the nearly constant eastward plunge of earlier folds and lineations into small cones. Deformation accompanying regional metamorphism of the Shuswap complex must have occurred since the Triassic and probably during the Jurassic period.