Structural Investigation of the Ryôké Metamorphic Rocks of the Area between Iwakuni and Yanai, Southwestern Japan

Structural features of various scales were described, and, on the basis of geometrical and petrofabric analyses of these structures, the metamorphic history of the Ryôké metamorphic rocks has been discussed. The "Ryôké metamorphism" has been interpreted by predecessors as a progressive metamorphism of single generation, through which the Ryôké metamorphic rocks ranging from schistose hornfelses to banded gneisses and migmatites were produced. The metamorphic history of the area between Iwakuni and Yanai has, however, been considered by the present author as an overlapping series of events in which two phases have been discriminated: schistose hornfelses were formed during the first, earlier phase, and banded gneisses and migmatites during the second, later phase. The earlier phase is characterized by regional thermal metamorphism accompanied by penetrative movement, while the later phase by metasomatism or intense granitization under high temperature and relatively static condition.