Fig. 4

a SEM micrograph of a polished surface with slickensides in top view. A slickenside riser perpendicular to shear direction can be seen in the upper part of the image with linear striae visible (arrow b) parallel to slip direction. b High-resolution SEM micrograph of a showing nm-wide, platy clay particles aligned parallel to the slickensided surface. c BIB–SEM micrograph of a µm-thin shear zone in side view (above dashed line). Note the shear zone-parallel alignment of clay minerals. Authigenic illite can be seen as thin curvy fibres above the dashed line. Location of micrograph is given in Fig. 5d. d SEM image showing side view of a slickenside with a nano-sized thin band of clay particles (indicated by arrows), possibly authigenic illite. e Photograph and f sketch of a gouge band from the upper boundary of the Main Fault. The darker gouge is sharply separated by µm-thin shear zones from bordering scaly clay. Note the brighter clasts of scaly clay within the gouge. Dark lines in f are traced shears