Co-operative research of granite mylonites in Japan

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In this co-operative research have been performed descriptions of granite mylonites in Japan and their formation processes and tectonics have been discussed. Granite mylonites are developed as large-scale zones in the Hida belt, Ryoke belt, Abukuma-Kitakami belt, Hidaka belt and Greentuff belt as magma-arcs. They are zones of strain concentration in magma-arcs. In order to understand tectonic of magma-arcs, therefore, it is very important to clarify formation processes and movement pictures of large-scale granite mylonite zones. Granite mylonite zone in the Hida belt has been studied by Komatsu (1992) and Hara (1992) clarifying that it was developed during two phases, Unazuki phase for tectonics related to the uplifting of medium P/T type schists and Hunatsu phase for tectonics related to the intrusion of Hunatsu granites. Large-scale mylonite zone in the Ryoke belt, which is placed along the Median Tectonic Line, has been studied by Ui and Yokoyama (1992), Takagi (1992), Hara (1992) a … More nd Takeshita (1992) clarifying that it was developed as a flat-lying shear zone. Its movement picture has bee analyzed during the period from the phase of Cretaceous granite intrusion to the phase of the Japan-sea spreading. Large-scale mylonite zones in the Abukuma-Kitakami belt have been studied by Koshiya (1992) and Hara (1992), clarifying that they were developed as upright shear zones with horizontal shear unlike the case of the Ryoke belt, though the shear zones in both belts are of the same generation. Large-scale mylonite zone in the Hidaka belt has been studied by Toyoshima (1992) and Toyoshima and Hara (1990), clarifying that it was developed as flat-lying shear zone during two phases, phase of intrusion of MORB type magma and phase of intrusion of calcalkaline magma, and then the shear zone with igneous intrusion was moved into upright attitude giving rise to great mylonite zone (Hidaka western margin mylonite zone). Mylonite zone in the greentuff belt is developed along the Itoigawa-Shizuoka tectonic line. Its microtextures and movement picture have been analyzed by Kosaka and Takizawa (1992), Takizawa and Kosaka (1992) and Shimamoto (1992). Microtextures, formation processes, movement pictures andstress estimation of mylonites have been discussed by Masuda et al. (1992), Takizawa and Kosaka (1992), Hara et al. (1992), Kang et al. (1992), Koshiya (l992) and Simamoto (1992). Less