Study on the relation between sedimentation and igenous activity in the forearc area.

根据主次元素分析，我们确定了日本西南部几个二叠纪至第三纪增生杂岩中玄武岩岩块的构造成因。玄武岩化学暗示了构造环境，即。板内热点成因玄武岩(碱性玄武岩或拉斑玄武岩)、大洋中玄武岩(N型或T型)和岛弧玄武岩。野外观测，特别是周围沉积物、盖层石灰岩或硅质岩之间的赋存方式、变形变质程度等与玄武岩的构造环境密切相关。MORB玄武岩变形变质程度较高，并被层状硅质岩覆盖，指示洋板俯冲过程中较深层次的底侵洋壳；热点型玄武岩变形变质较弱，被礁灰岩覆盖，指示剥离于浅层或海沟坍塌的海山。前者位于岛本带北部，后者位于Akiyoshi、Mino和Konose地体。

We defined the tectonic origin of basaltic rock blocks within several accretionary complex of Permian to Tertiary ages in Southwest Japan based on major and minor element analysis. Basalt chemistry suggests the tectonic settings, ie. within plate basalt of hotspot origin (alkalic or tholeiite), mid-oceanic basalt (MORB)(N-or T-type), and island arc basalt. The field observations, especially the mode of occurrence between the surrounding sediments, the capped limestone or chert, degree of deformation and metamorphism are intimately related to the tectonic settings of those basalts. Basalts which are of MORB are highly deformed and metamorphosed, and capped by bedded chert, indicating the underplated oceanic crust in the deeper levels during oceanic plate subduction, while basalts which are of hotspot origin are weakly deformed and metamorphosed, and capped by reef limestone, indicating the offscraped in the shallower levels or trench collapsed seamount. The former examples are in the Northern Shimanto belt, and the latter examples are in the Akiyoshi, Mino and Konose terranes.