Shear strain analysis and periodicity within shear gradients of metagranite shear zones

The distribution of natural ductile strain is studied by mapping continuous shear strain gradients across shear zones with widths of the order of tens of centimetres. The shear zones are derived from granites and the most ductile mineral (quartz) accommodates most of the rock deformation. Shear strain maps are based on quartz gram orientation, and finite strain maps on the shape of quartz grams measured by image analysis. Shear strain distribution shows discrete hands parallel to the shear plane, which reflect the strain localization. Strain profiles across the strain maps are compared to exponentially decreasing profiles. The significant variations of shear strain after subtraction of the smoothed profile are checked by Fourier analysis in terms of wavelengths. With this information at hand, we argue that shear strain distribution in shear gradients is periodic.