八重山変成岩類の地質構造
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概要
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The Yaeyama metamorphic rocks distributed in the Yaeyama Islands of south Ryukyus are divided into Tomuru and Fusaki formations. The Tomuru formation is composed of mafic schist, pelitic schist, metagabbro and siliceous schist of blue schist facies and the Fusaki formation is of deformed conglomerate, chert, sandstone, mudstone and crystalline limestone which are weakly metamorphosed. Deformation analysis of the rocks revealed five stages. I: Folding with NW-SE axis parallel to mineral and corrugation lineations associated with the principal metamorphism. II: Deformation producing the corrugation lineation with N-S direction though the folding axis is not clear. III: E-W fold axis and corrugation lineation printed over the I and II stages structures. ？: Kink fold with E-W axis. V: Kink fold with NE-SW axis. The Fusaki formation shows the fold axis parallel to the III stage deformation of the Tomuru formation with out I and II stage deformations. Therefore, the Fusaki formation should be deposited during the I and II stages and after, but before the III stage. The radiometric age of the metamorphism of the Tomuru formation indicates Jurassic so that the Fusaki formation could be the Jurassic to Cretaceous sediments. The deformation of the III stage should have occurred in early Paleogene because the Miyara formation of Eocene is not subjected by intense deformation but tilting. Later the Tomuru formation thrusted up to the Nosoko formation at the central part of the Ishigaki-jima associated with serpentinite intrusions so that the thrusting occurred in Oligocene. It is succeeded by the emplacement of Miocene granite.
- 日本地質学会の論文
- 1983-03-30
著者
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