STRUCTUAL EVOLUTION OF MÉLANGE UNIT IN THE UPPER CRETACEOUS SHIMANTO BELT, WAKAYAMA PREF., JAPAN
The mélange unit is composed of a sheared argillaceous “matrix” in which various sizes of tectonic lenses are incorporated. The tectonic lenses are intensely disrupted sandstone, mudstone, varicolored shale. The mélange structure seem to indicate the sinistral sense of shear due to an asymmetric orientation of the tales of the lenticular sandstone surrounded by scaly shale matrix and asymmetric varicolored shales. The asymmetric structure is characterized by boudin structure, pinch & swell structure and composite planar fabric. The deformation of sheared soft sediments are composed of highly sheared with layer of Y directions (Y-layer) and layer of P directions (P-layer oblique to Y-layer). A remarkable fact regarding the Y-layer is that composite planar fabric, Y-shears and P-foliations are developed by the deformation of sheared soft sediments. A comparative study between the first deformation structure and the later structures be able to present origin of mélange and mélange unit consist of sinistral sense of shear by the deformation of soft sediments.