抄録
Low-grade metamorphic rocks of the Ryoke belt in the study area grade northward into non-metamorphosed Jurassic strata of the Mino belt mainly composed of mudstone and sandstone, which are considered to be Late Jurassic in age on the basis of find of radiolarians. These strata include olistoliths of various size of Triassic chert, limestone and basic volcanic rocks. The Jurassic is intensely deformed. Deformation associated with the metamorphism is rather slight and deformation structures in the early stage are well preserved. Mesoscopic deformation structures, e. g. minor folds, microfaults and fragmentation of sandstone are frequently observed throughout the study area. The microscopic study reveals that 1) deformation of sand grains and axial plane cleavage are not recognized in the minor folds even at the hinge part of them, 2) cataclasis is little observed even in the adjacent part to the plane of microfault with large displacement and 3) the boundaries between sand-stone clasts and mudstone matrix are obscure in some cases. These facts suggest that soft-sediment deformation has extensively occurred in the latest Jurassic time.
