Abstract
The first-generation structures of the Quetico Metasedimentary Belt are large-scale recumbent folds which, in the Kashabowie area, are northwestward vergent and facing, that is, they face towards the centre of the metasedimentary belt. During this folding, basaltic pillows were elongated normal to fold hinges and a schistosity was developed. Subsequent deformation has largely destroyed the schistosity, but the pillow elongation remains, although reoriented. Second-generation tight to isoclinal upright folds are characteristic of the belt, and have an associated prominent, but not perfectly axial planar schistosity (S 2 ). Refolding of earlier folds causes second-generation folds to be either upward or downward facing, depending upon whether the present exposure level is either above or below the earlier fold axial surface. Third-generation close to tight, asymmetric folds, which become markedly disharmonic or convoluted at the highest metamorphic grades, crenulate and fold the subvertical S 2 schistosity towards the centre of the belt. Folding and generation of S-planes pre-dates the metamorphic peak in the central part of the belt, and post-dates metamorphism at the belt margin; but deformation continued as the belt cooled. Post-folding ‘brittle’ and ‘brittle—ductile’ structures such as: extension gashes, shear fractures, tension gashes and boudinage of post-folding quartz veins all indicate layer-parallel extension throughout the belt. Anisotropy within the metagrey-wackes and metapelites controls the location of many of these minor structures. The orientation and geometry of the structures indicate that an early period of gravitational instability in the adjacent Shebandowan Volcanic Belt (granite—greenstone terrain) produced recumbent folds directed towards the metasedimentary belt. Subsequently, the Quetico Metasedimentary Belt experienced subhorizontal shortening normal to, and subhorizontal extension parallel to, its axis for most of its history, including both the heating and cooling stages.
Published Version
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