Parallel stretching lineations and fold axes oblique to a shear displacement direction—a model and observations

Spatial variations in shear strain rate are expected in ductile shear zones. Where the variation is a change in shear strain perpendicular to the displacement direction, the effect is to rotate the shear slip planes. This is a mechanism for giving a rotation of fold axes into parallelism with the slip and extension direction in a rock. If such a variation in shear strain affects rocks with a strong planar anisotropy it is possible to produce a fabric with an apparent stretching lineation parallel to fold axes, but both significantly oblique to the slip direction. A possible example of this is seen in strongly deformed quartz-mica schists from Syros, Greece, where a stretching lineation is seen parallel to fold hinges over a range of fold axes orientations of at least 40°.