Stratigraphy and Geological Structure of the Crystaline Schist Region in Central Sikoku

The stratigraphical and structural analysis of crystalline schist region must be based on the mapping according to original rock-species from which the crystalline shcists were formed. , The identification of original rock-species is sometimes very difficult owing to the metamorphic differentiation under allochemical conditions. , The crystalline schists of Central Sikoku belong to the chlorite-zone or the green-schist facies of metamorphism of a regional scale. , They can be divided lithologically into the following groups and formations from the lower to the upper (Figs., 2 and 3): 1. , Nisiiya Group: The component members are mainly siliceous black-schists, interbedded with several thin beds of green-schists and pinkish or greenish quartz-schists. , It is supposed that the group includes some acid igneous rocks as quartz-porphyries, granite-porphyries, granites, quartz-diorites, etc., which are now represented by the pebbles in conglomerate-schists in the Oboke-Formation (This Journal, Vol., 56, No., 658, 1950, pp., 366-367). , The whole thickness of the group exceeds 800m. , 2. , Yosinogawa Group: 1) The lower sub-group is divided into the lower: Oboke Formation and the upper: Kawaguti Formation. , Oboke Formation: The component members are sandstone-schists interbedded with thin beds of black-schists. , In the middle and upper parts there are intercalated beds of conglomerate-schists 1-40m. , thick. , The whole thickness of the formation exceeds 1500m. , The lower limit of the formation is concealed beneath the Oboke anticline. , Kawaguti Formation: This formation is mainly composed of black-schists of pelitic origin, interbeded with 1-3 beds of green-schists. , The whole thickness varies from 500 to 1500m. , according to the change in thickness of the intercalated green-schists beds. , 2) The middle sub-group is divided into the lower Koboke Formation and the upper Minawa Formation. , In the region south of the Simomyo-Tuneyama fault, the Nisiiya Group is overlain by the Koboke Formation. , The relation between the two rock series is a distinct clilno-unconformity, called Minamihiura Unconformity. , Koboke Formation: The component members are mainly sandston-schists, interbedded with beds of black-schists and green-schists. , The whole thickness varies from 200 to 400m. , Minawa Formation: The formation comprises two or more beds of green-schists 100-400m. , in thickness. , The other members are greenish or pinkish quartz-schists (sometimes attaining to 100m., in thickness) and black-schists. , The whole thickness of the formation exceeds 800m. , 3) The upper sub-group is characterized by the presence of white siliceous rocks, which also characterize the non-metamorphic Palaeozoic formation in the Titibu-Zone. , The other members are black-schists, green-schists, sandstone-schists, calcareous schists, and semi-schists corresponding to them. , The lower and the middle sub-groups of the Yoshinogawa Group correspond respectively to the Oboke and the Bessi Series by T. , Ogawa (1902). , The geological structure of the region is characterized by domes or dome-like anticlines and basins or basin-like synclines in the non-spotted schists zones and by folds of recumbent types in the spotted schists zones. ,