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。第一项研究是对松江组的所有Ma古老玄武岩进行取样和分析，这些玄武岩在松江市半径5公里范围内露头。分析了代表性样品的主要元素和微量元素氧化物、稀土元素、^<87>Sr/^<86>Sr和^<143>Nd/^<144>Nd。三个样品用K/Ar全岩测年。初步结果表明，该区存在两种玄武岩类型，一种为同位素贫源熔融玄武岩，另一种为同位素富源熔融玄武岩。大多数松江组玄武岩是这两个端元的混合物。同位素化学的范围横跨整个日本西南部。松江组玄武岩的有限年龄和范围被解释为代表了一个小的地幔柱与上覆相对枯竭的地幔的相互作用。第二个项目涉及全岩和同位素分析，对Oki Dozen岛中新世火山岩进行K/Ar年龄测定。这种方法修正了火山历史，表明在玄武岩喷发到流纹岩形成主要火山盾之前，Oki Dozen上的中央锥粗面岩和正长岩在早期火成岩阶段一起演化。早期的研究认为，在盾构阶段，中心锥粗面形成了一部分，正长岩的位置尚不清楚。第三个项目是第四纪火山岩的全岩和同位素化学研究

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