Deformation and metamorphic reactions in polyphase rocks
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Detail of granodiorite mylonite; pure quartz regions deformed by regime 3 dislocation creep while fine-grained mixed phase matrix deformed by grain boundary sliding - diffusion creep.
Detail of granodiorite mylonite. The fine-grained portions consist of a mixture of albite + epidote/clinozoisite + quartz + white mica. The coarse-grained portion consists of pure quartz, which is dynamically recrystallized by regime 3 dislocation creep. The phase mixture has a finer grain size due to rapid nucleation of new phases and grain boundary pinning, and this finer grain size allowed a switch to grain boundary sliding and diffusion creep.