日本海形成に伴う西南日本の火山岩類の岩石化学-化学組成と同位体組成からの検討

已经进行了三个项目。第一个项目涉及对松江市半径5公里范围内出露的11 Ma老松江组玄武岩进行取样和分析。对代表性样品进行了主元素和微量元素氧化物、稀土元素以及^<87>Sr/^<86>Sr和^<143>Nd/^<144>Nd的分析。三个样品用K/Ar全岩定年。初步结果表明，存在两种玄武岩类型，一种代表同位素贫化地幔源的熔融，而另一个，同位素和微量元素富集源的熔融。大多数松江组玄武岩是这两种端元的混合物。同位素化学范围跨越了整个日本西南部。松江组玄武岩有限的年龄和范围被解释为代表了一个小的地幔柱与上覆的相对亏损的地幔的相互作用。第二个项目涉及整个松江组玄武岩。岩石和同位素分析，以及隐岐十善岛中新世火山岩的K/Ar年龄测定。这种方法修正了火山历史，表明隐岐十善岛的中央锥粗面岩和正长岩作为早期岩浆相一起演化，早期的研究认为，中央锥状粗面岩第三个项目是研究第四纪火山的全岩和同位素化学，

Three projects have been undertaken.The first involved sampling and analysis of ll Ma old basalts of the Matsue Formation,which outcrops within a 5 km radius of Matsue city.Representative samples were analysed for major and trace element oxides,rare earth elements,and ^<87>Sr/^<86>Sr and ^<143>Nd/^<144>Nd.three samples were dated by K/Ar whole rock.Preliminary results show that two basalt types are present,one representing melting of an isotopically depleted mantle source,and the other,melting of an isotopically and trace element enriched source.Most Matsue Formation basalts are mixtures of these two end members.The range in isotope chemistry spans that known for all of southwest Japan.The limited age and extent of the Matsue Formation basalts is interpreted as representing interaction of a small mantle plume with overlying relatively depleted mantle.The second project has involved whole-rock and isotope analysis,with K/Ar age dating of Miocene volcanic rocks from Oki Dozen Island.This approach has revised the volcanic history,showing that the central cone trachyte,and syenite on Oki Dozen evolved together as an early igneous phase,before the eruption of basaltic through to rhyolitic rocks that make up the main volcanic shield.Earlier studies had argued that the central cone trachyte occurred part the way through the shield building phase,and the position of the syenite was unknown.The third project has been to examine the whole-rock and isotope chemistry of Quaternary volca