Deformation-induced Japan twinning in quartz during incipient mylonitization

Many crystalline rocks of the continental crust contain coarse-grained quartz as a main mineral (e.g., granitoids). Incipient deformation coarse quartz, which likely controls accumulation bulk strain in heterogeneously deformed crustal rock volumes, commonly develops microshear zones (MSZs) localized recrystallization. At mid-crustal conditions, where is mostly accomplished by subgrain rotation recrystallization, grains MSZs can show an abrupt change crystallographic orientation (large misorientation angle) with respect to host that still not fully understood. We analyzed (20–200 μm thick) from (millimeter grain size) veins Austroalpine Schobergruppe (Eastern Alps). Electron backscatter diffraction analysis reveals are characterized nearly 90° angle between c-axes and new grains, also share one {m} {1122} pole, compatible Japan twinning. This switch c-axis promote geometrical softening shear localization. So far, twinning has been interpreted growth feature. deformation-induced including Dauphiné twinning, play important role initiation crystal-plastic within crust.