Jadeite and jadeitite–bearing rock in the Sanbagawa and the Kamuikotan belts, Japan: A review

抄録

The mode of occurrence of jadeitic pyroxenes and their origins were reviewed using literatures published in the Sanbagawa belt (sensu lato), SW Japan, and the Kamuikotan belt, Hokkaido. Jadeite + quartz assemblage is found from tectonic blocks both in the Yorii area of the Kanto Mountains in the Sanbagawa belt and the Kamuikotan Gorge area, and its formation timing is predated to the main metamorphism in each area, where albite is stable along with metamorphic pyroxenes with lower jadeite contents (namely Jd_<50). The jadeite + quartz assemblage is recently found as inclusions in garnet grains in some rocks with peculiarly lower CaO and/or MgO bulk compositions, which suffered the eclogite facies metamorphism in the Sanbagawa belt of Shikoku area, although it is not detected from the matrix of the eclogite facies rocks. Recent zirconology applied to the jadeite + quartz rock in the Yorii area causes a hot argument on its origin, i.e., the wholesale metasomatic replacement origin or the vein precipitation origin. In either case, this methodology gave new insight on fluid activity recorded in Jurassic or post–Jurassic subduction zone.