Abstract
The region in question is composed of the crystalline schist system which constitutes the Iimori syncline and adjoining districts. The Iimori syncline is asymmetric with respect to its stratigraphy and geologic structure, and is subsidiary to the main synclinorium of the Sambagawa geosyncline. The crystalline schist system is characterized by thick basic schists and ultrabasic rocks in the middle part. The system is divided into three formations, namely the Tomobuchi alternation, the Iimori greenschists, and the Ryumon alternation, in ascending order. The Tomobuchi formation is. distributed in the transitional zone between the southern anticlinorium and the Iimori syncline, while the Iimori and the Ryumon formations were deposited in the synclinal zone. The Iimori formation tends to become thicker towards the north, suggesting a downward movement of the geosynclinal basin. Moreover, the Iimori and the Ryumon formations have thickness differing from east to west. This reflects a fluctuation of the downward movement in that direction in the course of sedimentation. In the Iimori syncline the axis of fold plunges towards the west in the eastern part, but towards the east in the weatern part. The upper part of the synclinal structure has a shape similar to the bottom of a ship. The lower part is characterized by a trench-shaped structure forming a root of the syncline, which must have been formed by lateral compression accompanying the downward movement. Therefore, the syncline has a highly disharmonic structure. The Iimori syncline is bordered with flexure zones on both sides, and adjoining the northern flexure zone occurs the Ozu folded zone which is characterized by predominance of minor folds accompanied by axial plane foliation crossing the bedding foliation at high angles. Crystalline schists in the southern anticlinorium belong generally to the greenschist facies, although glaucophane-schists can be found locally. The Iimori syncline and the Ozu folded zone consist of rocks characterized by larger grain-size and the presence of albitic plagioclase porphy-roblasts, and their metamorphic facies is the epidote-amphibolite facies. The grade of metamorphism tends to become higher towards the inner part of the syncline structure.
Many ore deposits of the bedded cupriferous pyritic deposit type have been known from the region. Most of the ore deposits occur within the Iimori greenschists formation stratigraphycally, and within or near the flexture zone of the Iimori syncline tectonically. The limited occurrence of the ore deposits suggests their genetic relationship to the downward movement of the geosynclinal basin and associated submarine volcanism.
