抄録
In the Chugoku zone in south-west Japan, ultra-basic bodies occur as "serpentine belt." The Komori Ultrabasic Mass is one of them and situated along the northern side of the Maizuru zone. It is lenticular in shape and has monoclinic structure, dipping steeply to the north. From the view point of the arrangement of rock facies and structure, four zones are recognized in the middle of the mass, from north to south. A-Zone: mainly dunite-I accompanying hornblendite B-Zone: mainly pyroxenite with small bodies of hornblendite C-Zone: mainly dunite-II with small bodies of diabase D-Zone: mainly gabbro-diabase These rock facies are cogenetic. The volume ratio of the rock facies in the mass is shown in Table 3. The difference between dunite-I and dunite-II were mainly caused during tectonic movement, prior to the granite intrusion. And "cleavable olivine" represents the sheared zones in the mass. The average chemical composition of the whole mass is estimated and shown in Table 4. It is peridotitic as a whole. Compared with "pyrolite model", Na2O, K2O and TiO2 are rather defficient in the mass.
