Fig. 6

Microstructures of the deformed samples after the velocity-stepping friction tests at normal stresses of a, b 2 MPa, c, d 10 MPa and e, f 20 MPa, under optical (a, c, f) and electron (b, d, f) microscopes. Shear sense is top-to-the-left. a The boundary shear zone (BZ), the lower boundary of which is delimited by the dotted white line, is located along the upper edge of the sample. The black box gives the position of b. b A close-up view of the boundary shear zone characterized by < 20 μm small grains, located above the dotted yellow line. c The dotted lines indicate cataclastic P foliations formed in the upper part of the sample. The black box gives the position of d. d A close-up view of elongated plagioclase fragments, demarcated by the dotted yellow line, forming the cataclastic foliation. e The P foliation (dotted lines) is pervasive across the bulk sample, and sometimes offset by left-lateral Riedel shears (solid white line). The black box gives the position of f. f A close-up view of the Riedel micro-shear zone bounded by the dotted yellow lines. Pl, plagioclase; Opx, orthopyroxene; Cpx, clinopyroxene; Hem, hematite