Grain-size reduction of feldspars by fracturing and neocrystallization in a low-grade granitic mylonite and its rheological effect |
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| Authors: | Jin-Han Ree Hyeong Soo Kim Raehee Han Haemyeong Jung |
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| Institution: | aDepartment of Earth and Environmental Sciences, Korea University, Seoul 136-701, South Korea;bDepartment of Earth Science Education, Kyungpook National University, Daegu 702–701, South Korea;cInstitute of Geophysics and Planetary Physics, University of California, Riverside, California 92521, USA |
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| Abstract: | Feldspar grain-size reduction occurred due to the fracturing of plagioclase and K-feldspar, myrmekite formation and neocrystallization of albitic plagioclase along shear fractures of K-feldspar porphyroclasts in the leucocratic granitic rocks from the Yecheon shear zone of South Korea that was deformed under a middle greenschist-facies condition. The neocrystallization of albitic plagioclase was induced by strain energy adjacent to the shear fractures and by chemical free energy due to the compositional disequilibrium between infiltrating Na-rich fluid and host K-feldspar. With increasing deformation from protomylonite to mylonite, alternating layers of feldspar, quartz and muscovite developed. The fine-grained feldspar-rich layers were deformed dominantly by granular flow, while quartz ribbons were deformed by dislocation creep. With layer development and a more distributed strain in the mylonite, lower stresses in the quartz-rich layers resulted in a larger size of dynamically recrystallized quartz grains than that of the protomylonite. |
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| Keywords: | Granitic mylonite Grain-size reduction Granular flow Dynamic recrystallization Yecheon shear zone |
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