“…The weight of published work thus suggests that dislocation flow processes dominate in shear zones, but this is somewhat misleading, because most of the studies have concentrated on zones in essentially monomineralic rocks, or on the outer (lower strain) parts of zones where dislocation flow dominates even in many polyphase rocks. Many polyphase rocks in retrograde shear zones are characterized, at least in their more highly strained portions, by unstrained, relatively equidimensional grains, low-energy grain shapes, uniform grain sizes, predominant contacts between unlike phases and commonly weak quartz c-axis preferred orientations (Ransom, 1969(Ransom, , 1971Vernon & Ransom, 1971;Bell & Etheridge, 1973. In other words, they are similar to progrude rocks of similar grade and composition.…”