日本列島の基盤構造と活断層の形成位置との関係に関する基礎的研究

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In order to prove the relationships between active faults and the basement strcutures, especially. ancient ductile and brittle faults, we have investigated and analyze shear planes in a deep crustal section tectonically uplifted as the Ryoke metamorphic belt, and an active fault system apparently superposed on the thrust fault of the crustal section. The study areas are 1) Yawatahama-Oshima island. 2) Wada-Misakubo region of the Ryoke metamorphic belt, and 3) Kawauchi, south to Matsuyama.1) In the high-grade metamorphic thrust sheet of the Yawatahama-Oshima island, pseudotachylite veins are extensively developed in granodioritic gneisses, concentrated in three zones of brittle fault. : The gneisses have suffered two stages of ductile shearing and one stage of brittle before pseudotachylite, and one stage each of ductile shearing and of brittle shearing after pseudotachylite. The pseudotachylite veins associate with sharp slip planes such as Y, R1 and P, and fructures high angle to the … More slip planes. The main slip planes (Y) are parallel to the pre-existing mylonite foliation of first stage, and cut very narrow cataclastic veins. At the base of the thrust sheet, pseudotachylite veins are partly deformed in a ductile manner ; country rock fragments within veins deform to lenticular shape, quartz has preferred lattice orientations and glass are recrystallised to submicroscopic mica and opaque minerals, oriented parallel to shear planes in country rocks.2) Sharp slip planes are generally parallel with strong mylonite foliations in the basal part of the Ryoke belt. an exposed deep crustal section, in the Wada-Misakubo area, central Japan. The basal thrust gently dips northwestward, and cut by an active fault, known as the Median Tectonic Line. The active fault is not related to the foregoing thrust or brittle faults in the Ryoke belt.3) The conclusion is also supported by geld tracing of an active fault in the Kawauchi area, south to. Matsuyama, which is a part of the MTL active fault system. The active fault has been considered to marge into tha basal thrust of the Ryoke Belt, but it is not the case in this area. Less