Geological and petrological recovery of Paleo-Mesozoic seamounts in the southwest Japan

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Geochemistry of Paleo-Mesozoic greenstones give petrological and geological constraints on geotectonic settings of Japanese Islands. This project deals with the greenstones collected from basement greenstones of Akiyoshi, Taishaku and Atetsu of the Inner belt, Shikoku Karst, Nakatsu Myojin of the Outer belt of southwest Japan. Ages of the greenstones are younger than overlain limestones which are biostratigraphically estimated from upper Carboniferous to Permian by including fusulinid.Abundance of whole REE in massive basalt lava from Taishaku limestone plateau is exceedingly higher in alkaline metabasalt and enriched in light REE than that of tholeiite. In alkaline basalts Ce rangews from 70 to 120 ppm and La content is from 34 to 57 ppm, whereas in tholeiite, abundances of these elements are low from 28 to 38 and 12 to 15ppm respectively. Heavy REE contents are nearly the same to both rock types. Yb concentration is 1 to 2 ppm and does not depend on rock type. Basalt lava from Shikoku Karst characterized by Ti and Al rich purple colored augite phenocryst have lower concentration of REE than Taishaku metabasalts.Chondrite normarized REE patterns of the Taishaku greenstone exhibit LREE enriched steep inclined pattern. The LREE enriched inclined pattern is characteristic of recent intra-plate ocean island or seamount basalts. Alkaline ocean island basalts which bear total REE more than 250 ppm and chondrite normarized value of La more than 200 as revealed from Taishaku greenstones suggest partial melting in the large ionic lithophile elements enriched mantle.