Abstract
Many active landslides are developed in the Sambagawa metamorphic terrain at Motoyama, Kochi Prefecture, central Shikoku. The clay minerals such as sericite, interstratified clay mineral and kaolin together with gibbsite were identified in the debris of landslide deposits at Yoshinobu and Furuta districts. Under the microscope, the whity-debris shows a texture of albitophyre. A large amount of sericite having 2M polytype in association with kaolin and interstratified mineral occurs in the groundmass and replacing albite crystals. The sericite may have been formed by hydrothermal alteration. A. clayey-debris is mainly composed of an interstratified mineral in association with sericite, kaolin and gibbsite. X-ray analysis indicates the interstratified mineral is a regulerly interstratification of sericite (0.55) and swellinglayer (0.45). It may be concluded the sericite converts into kaolin and/or gibbsite through interstratified mineral of sericite and swelling-layer by weathering closely related to activity of landslides developed in this area.
