Naturally deformed quartzo-feldspathic rocks
Figure caption
weak deformation (Mulwaree) / strong deformation (Mulwaree) / mylonites (Redbank) / ultramylonites (Redbank)
76
Detail of granodiorite mylonite deformed at mid greenschist conditions by fracturing of feldspars and coalescence of weaker quartz and biotite.
Higher magnification view of granodiorite mylonite shown in photo #75. Biotite is completely recrystallized and quartz is present as largely recrystallized ribbon grains; these two phases form continuous and almost planar layers over large distances. Most of the deformation is accommodated by these quartz and/or biotite layers. Fractured feldspar grains are concentrated in layers. The dominant deformation process in these granitoids is intracrystalline plasticity in weak monophase layers (quartz or biotite), which formed by gradual coalescence. Feldspar has not changed chemically and has not recrystallized, but deformed by fracturing.