紀伊半島西部の三波川変成帯の地質

その他

The Sambagawa metamorphic belt in the Mt. Iimori district, westem Kii Peninsula, is divided into two geologic units, i. e. , the Tomobuchi unit and structurally overlying limori unit. The highgrade schists, referred as the Funaokayama schists, which are different in metamorphic grade and mode of deformation from the surrounding schists of the limori unit, occur in the northern parts of this district. The geologic structure of the Mt. Iimori district is characterized by the E-W trending limori syncline plunging westward at low angle.
The Tomobuchi unit, more than 1800 m in thickness, is composed mainly of pelitic schists with subordinate amounts of basic, siliceous and psammitic schists, but in the southernmost parts of this district, psammitic schists are predominant. The most parts of the Tomobuchi unit belong to the chlorite zone based on the mineral assemblage of pelitic schists, but minor parts near the border with the limori unit reach to the low-grade garnet zone.
The limori unit, more than 900 m in thickness, is composed mainly of pelitic and basic schists with subordinate amounts of siliceous and psammitic schists. The upper portions of this unit around Mt. Ryumon, are dominated by pelitic schists. The limori unit belongs mairily to the garnet zone, but partly to the albite-biotite zone. Many ultramafic and mafic bodies (e.g. Ryumon ultramafic body) occur within this unit.
The boundary between the Tomobuchi and the limori units, which corresponds to the boundary between the non-spotted and spotted schist zones, is possibly a fault because of the contrast of geologic structure and metamorphic grade.
The Funaokayama schists occur as a tectonic block or a thrust sheet within the limori unit, and consist mainly of pelitic and basic schists with minor siliceous. Oligoclase often rims porphyroblastic albite in pelitic and basic schists, suggesting that at least parts of the Funaokayama schists reach to the oligoclase-biotite zone. Mylonitic textures such as ribbon quartz and mica fish are developed in the Funaokayama schists.