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

古中生代绿岩地球化学为日本列岛大地构造背景提供了岩石地质约束。该项目处理了从日本西南部内带的秋吉、大坂和Atetsu，四国喀斯特，外带的中津Myojin的基底绿岩中收集的绿岩。绿岩的年龄比上石炭统至二叠统的上覆灰岩要年轻。太白库灰岩高原块状玄武岩熔岩整体稀土元素丰度在碱性变质玄武岩中异常高，轻稀土元素富集于拉斑岩。在碱性玄武岩中，Ce含量在70 ~ 120ppm之间，La含量在34 ~ 57ppm之间，而在拉斑岩中，这些元素的丰度分别在28 ~ 38ppm和12 ~ 15ppm之间。两种岩石的重稀土元素含量基本相同。Yb浓度为1 ~ 2ppm，与岩石类型无关。四国喀斯特玄武岩熔岩以富钛、富铝的紫色亮辉岩斑晶为特征，其稀土元素含量低于太崎变质玄武岩。太白绿岩的球粒陨石归一化稀土模式表现为LREE富集陡斜模式。轻稀土富集倾斜模式是近代板块内洋岛或海山玄武岩的特征。太初古绿岩显示，碱性洋岛玄武岩总REE大于250ppm，球粒陨石正态化La值大于200，表明其在富集大离子亲石元素的地幔中有部分熔融作用。

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.