The geometry of folded tectonic shear sense indicators

The geometry of refolding of early stretching lineations and associated sense of shear indicators is often not fully considered and can potentially lead to grossly incorrect tectonic interpretations of orogens and orogenic events. Sense of shear is not inverted or ‘flipped’ in all cases of refolding by folds with closure angle <90°. The geometry of inversion of ‘flipping’ of shear sense is determined entirely by the angle (φ) between the stretching lineation and the latter fold axes. Folding around an axis orthogonal to the stretching lineation (φ=90°) does not result in shear sense inversion. This is a special case; if there is any degree of obliquity (φ<90°) between fold axis and stretching lineation, there is a change in the orientation of the stretching lineation on alternate limbs and if φ<45° the sense of shear is inverted in alternate limbs.