Deformation mechanisms in the mylonite/ultramylonite transition

摘要: Abstract The deformation mechanisms and controls that operate in the mylonite/ultramylonite transition are interpreted from microstructural observation. investigated mylonites ultramylonites were derived a granitic protolith which was deformed under greenschist facies conditions, presence of fluid, regional-scale shear zone northwest Argentina. Several recognized to simultaneously different domains microstructure at each particular stage evolution. This continuously mobile partitioning, present throughout evolution, ceases abruptly ultramylonite stage, where stable-state is achieved. Domainal quartz c-axis fabrics indicate deforms by crystal-plastic processes initial intermediate stages deformation, but solution-transfer become predominant stage. Plagioclase progressively transformed into muscovite through retrograde softening reactions. K-feldspar fine-grade aggregates via cataclastic flow incipient recrystallization. Mica kinking basal slip, with progressive development fine-grained, morphologically oriented aggregates. disappearance as well intrafolial microfolds characterize between mylonitic ultramylonitic domains. Disruption these represent ultimate control on localization bands.