Fig. 4

Optical microscope (a–d) and backscattered scanning electron microscope (e, f) images of the host sandstone (a) and deformed sandstones from the fault zone core (b–f). a Imbricated quartz grains sutured by pressure solution at grain contacts (arrows); b and c highly deformed sandstone with newly-formed white mica preferentially oriented along shear surface and as felpspar replacement. The white arrow indicates the vertical direction; d Shear surface with newly formed mica and chlorite; e SEM image of K-feldspar illitisation along a shear zone; f newly-formed white mica and chlorite preferentially oriented along a shear surface. The evidence of newly-formed phyllosilicates is shown by the interdigitate texture of chlorite and white mica. The black arrow indicates the vertical direction; Qz quartz, Fsd feldspar, Ms white mica, Chl chlorite; alt. Fsd altered feldspar