A Study of Quartz Orientation and its Relation to Movement in Shear Folds

Abstract

The orientation of quartz in small shear folds, which belong to two movement episodes, is considered to result from laminar flow along the axial plane surfaces. The locations of fabric maxima and girdles are controlled by the orientation of thea–kinematic axis, which in shear folds may not be normal to the fold axis, and the shear surfaces. The earlier fabric consists, essentially, of paired maxima arranged systematically about the axial plane;ac–girdles are absent. The explanation of the near-orthorhombic symmetry of the first fabric in terms of a late “flattening” overprinted upon the previously-formed fold is not favoured: quartz orientation developed during the first folding. The later fabric results from the recrystallization of quartz grains with their largest dimensions andc–axes parallel to the calculateda–kinematic axis of second folding.