The microfabrics of a porphyroclast-rich quartzitic mylonite, Mjølfjell, Jotun Nappe Complex, Norway

摘要: This paper describes the microfabrics of a quartzitic mylonite from shear zone which separates major tectonic units in Upper Jotun Nappe, part Nappe Complex. The is rich porphyroclasts, consisting variety minerals such as feldspar, garnet, clinopyroxene, epidote and titanite. porphyroclasts display large variation shape plate needle with extreme aspect ratios to ellipsoid sub-spherical. Many are asymmetric, fish-shaped, demonstrating top-to-ESE transport direction zone. Relict subgrain microstructures largest indicate that precursor was gneiss, deformed by dislocation creep. Compositional zoning common among porphyroclasts. In titanite this clear evidence diffusive mass transfer, indicates dissolution-precipitation creep dominant process shaping during mylonitisation. A change metamorphic environment demonstrated microstructures. These include (1) larger garnet enclosed corona-like mineral aggregate, includes new generation (2) silicification plagioclase suggests mylonitisation accompanied an influx silica-rich fluids. crystallographic preferred orientation adds no support recent reports plasticity may explain, at least partly, elongate shapes. Misorientation angles demonstrate close-range relationship, ascribed fragmentation drifting apart processes quartz matrix mediumto coarse-grained. fraction completely included these grains, formation followed annealing grain growth matrix. Quartz displays no, or very weak, shape-preferred but strong orientation, compatible glide on {m} system. This, together interlobate boundaries, lattice bending grades into microstructures, deformation lamellae, taken period combination under high-temperature conditions. Arrays transverse fracture systems tensile stresses set up exhumation cooling. Contrary earlier interpretation it argued origin stress system not distant local nature. Because petrological similarities nearby plutonic rocks considered unlikely quartzite has supracrustal origin, rather mangeritic highly enriched silica. Comparison geochronological data leads conclusion most likely time Sveconorwegian Orogeny.