Figure 4

Rock volumes immediately below slip surfaces after (a to d) 1.5 mm and (e to f) 5 mm displacement.

All images originate from FIB-SEM specimens cut perpendicular or parallel to the slip direction (shear sense arrows in Figs (a,e)). (a) Calcite grains cracked along bend cleavage planes (dashed lines). (b) High-resolution TEM image showing a nanograin (grain size: 5–50 nm) volume immediately below the slip surface, within the nanocrystalline domain. (c) Inter-cleavage crystal domains (dashed lines) exhibit complex TEM diffraction contrast due to a high degree of crystal defects, i.e. dislocations. High dislocations domains (arrow heads) remain either crystallographically coherent or develop a polycrystalline (see SAED pattern) mosaicism nanostructure, dashed area in c. (d) The high defect domains terminate abruptly into domains of low defect density. (e) After 5 mm displacement a semi-coherent amorphous carbon a–c layer develops across the slip surface. (f) Enlargement of Fig. (e) showing compositional layering of a–c and CaO-bearing phase immediately beneath the slip surface. Both Figs (e,f) are HAADF-STEM images. (g) EDS analysis confirms the presence of (a–C) in (f). Stars denote the analysed areas.