Geology and petrology of volcanic conduits and lava domes

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Research results are summarized as follows : 1) Geological, petrographical and geochemical studies have carried out for origin of shoshonite, trachyte and rhyolite magmas, and features of volcanic conduits of evolved magmas which are widely distributed in the Oki Islands. Some rhyolite magmas were generated by partial melting of crustal materials under different P-T conditions and degree of partial melting. Magma mixing took place during uprising of magma or in conduit. 2) There are some granulite xenoliths including partial melt glasses with rhyolitic composition in late Cenozoic basalts in the west San'in region. This demonstrates the potential for generation of felsic magma beneath the west San'in region in late Cenozoic time. 3) The temperature of pyroclastic flow was estimated by ^<13>C/^<12>C isotope ratio, H/C ratio and infrared spectroscopy (absorption) of carbonaceous woods made under given temperature and times. ^<13>C/^<12>C isotope ratio is not available, but H/C ratio and infrared spectroscopy (absorption) are very affectable, especially in the case of less than 400ﾟC.4) Many Quanternary volcanoes with dacite compositions are sporadically distributed from the San'in region to northern Kyushu. Systematic differences of chemical characteristics are recognized from Daisen and Sambe volcanoes to Taradake volcano through Oetakayama, Aonoyama and Kunisaki Peninsula. 5) Fluid components, such as S,CO_2, Cl and F,in volcanic glass from Sambe dacite lava and pyroclstics have been analyzed for examination of relationship between eruption and non-eruption felsic magmas.