The Process of formation of extremely high temperature zones in the deep crust beneath the Miocene Setouchi volcanic province

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The aim of this project is to investigate the crustal composition and structure, and the influence and nature of magmatic activity based on the research of metamorphic xenoliths enclosed in volcanic rocks and of intermediate and acidic volcanic rocks in the Miocene Setouchi volcanic province.1. Metamorphic xenoliths were collected from Nijozan (Kinki district), Amataki-yama and Amagiri-yama (Eastern Shikoku), and Kaminada dacite mass and Ishizuchi andesite formation and dikes (Western Shikoku). The xenoliths, except for those from Amagiri-yama, have been thermally metamorphosed and suffered partial melting at the wall of magma chambers which were formed in relatively shallow levels of the crust. The crust was heated to extremely high temperature, causing partial melting of crustal rocks to produce acidic igneous rocks. The original lithology of metamorphic xenoliths varies widely from mafic granulite and high grade pelitic gneisses to mafic and pelitic schists. The xenoliths from Amagiri-yama suffered varied thermal effects depending on the time they were holded in the magma, namely, on the level where they occurred. The crust is infered to consist, from shallow to deep, of Ryoke granite-gneisses, granulite facies gneisses and mylonites, Sanbagawa schists, and high temperature type gneisses.2. High temperature hornfels of Middle Miocene age have been found to occur in the Sanbagawa schists and revealed that they were formed by extremely high temperature fluid flows. The fluid flow is related to the Setouchi igneous activity, and directly derived from the magma chamber. This proves the shallow magma chamber beneath the Setouchi province.