High-temperature microstructures and rheology of deformed granite, Erzgebirge, Bohemian Massif

Three stages of granite deformation were recognized in porphyric granitoids sheared under amphibolite facies conditions in the Erzgebirge Mts: (1) weakly deformed granite in lozenge-shaped pods, (2) S—C orthogneiss, and (3) thin zones of banded mylonites. deformed granite forms a load-bearing framework (LBF) structure in which quartz and feldspar aggregates exhibit similar strain intensities and shapes. K-feldspar deforms by fracturing and onset of dynamic recrystallization along clast margins, plagioclase recrystallizes completely and quartz shows effects of grain boundary migration recrystallization and activity of basal (a) slip. S—C orthogneiss is interpreted as an interconnected weak layer (IWL) structure with high viscosity contrast between quartz and both feldspars. Concentration of deformation into thin quartz layers is indicated by intense strain of quartz, grain size variations of recrystallized quartz and dominant prism (a) slip. Feldspars show well annealed structures and slip on (010)(001). Banded mylonite is marked by similar strain intensity of quartz and feldspar aggregates and low viscosity contrast between constituent phases. Quartz shows evidence for grain size increase and rhomb (a + c) slip. Fully recrystallized feldspars show evidence for (010)(100) slip. ole microstructural sequence and the transitions from LBF structure to IWL structures show the dependence of microstructural evolution of different materials on the bulk strain intensity.