RECRYSTALLIZATION AND FABRIC DEVELOPMENT IN PLAGIOCLASE

The microstructures and fabrics of naturally deformed intermediate composition plagioclase feldspars from the amphibolite-granulitic gneisses from the lower crust have been studied. The plagioclase feldspars (An40-50) have undergone extensive ductile deformation by intracrystalline slip and twinning. They show strong crystallographic preferred orientation which was produced by dominant (010) [001] slip. Dynamic recrystallization is indicated by fine-grained new grains (neoblasts) interspersed with deformed relicts (porphyroclasts). Optical microstructural evidence suggests that dynamic recrystallization occurred primarily by grain boundary migration with subsidiary subgrain rotation. We suggest that recrystallization-accommodated dislocation creep is an important process in the development of preferred orientations in plagioclase feldspars, which will result in geometric softening. -from Authors