The Kamuikotan Gorge area, west of Asahikawa, is mainly underlain by the high-pressure Kamuikotan metamorphic rocks. In this area, the Kamuikotan metamorphic rocks form a coherent metamorphic sequence, and are classified into two formations, i. e., the Ino-gawa Green-stone Formation and the Harushinai Pelite Formation. In the latter formation, serpentinites are not uncommon, and sometimes enclose blocks of amphibolites, jadeite+quartz-bearing rocks, and metabasites.
In the Kamuikotan metamorphic rocks, lawsonite, epidote, pumpellyite, glaucophane, actinolite, sodic pyroxene, and chlorite commonly occur. Various mineral assemblages are observed in metabasite, and their stability relations were analyzed by Schreinemakers' method. The petrogenetic grids derived from this method indicate that the Kamuikotan metamorphism of the Kamuikotan Gorge area mainly belongs to a high pressure subfacies of the lawsonite-albite facies, in which aragonite is stable, and that the Harushinai Pelite Formation was metamorphosed at the higher-pressure field than that of the Ino-gawa Greenstone Formation in narrow tempera-ture range. Its metamorphic grade is similar to that of the Horokanai area.

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Cenozoic volcanism of Mishima Island in Japan Sea, 50 km off the coast of Yamaguchi Prefecture, is characterized by picritic basalts and associated andesites of alkaline suites and older sub-alkaline basalts. One picritic flow is of cummulative origin: it contains abundant (22-25%) olivine which shows disequilibrium with the host rock. Another flow (15% olivine, Fo=89%), however, shows equilibrium between olivine and host rock, and its pressure was estimated to be near 10 kb from the CMAS diagram. Associated basalts and andesites are not the fractionation products of this primary picritic basalt, because their K₂O contents are not as high as those expected by crystal fractionation model.

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Spatial compositional variations are found among the granitic rocks of the Tsukuba area, 50 km northeast of Tokyo. Coarse-grained granite of the northernmost body shows I-type character, whereas southernmost two-mica granite of later stage shows S-type character, and others being the intermediate of the two. These spatial variations may be related to the different intrusive environments; a regional metamorphism of low-pressure and high-temperature type is closely associated with the granite intrusion in the southern part, but no effect of regional metamorphism was observed in the north.

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Relic calcic plagioclase (An₈₈) was found in a clinopyroxene-rich harzburgite from the Mineoka belt, central Japan. It is most likely that saussurite commonly found in the Mineoka peridotites was derived from a calcic plagioclase like the one reported here. Calcic plagioclase was a solidus phase and coexisted with magnesian olivine (Fo_90-92), orthopyroxene, clinopyroxene and chromian spinel (Cr/Cr+Al atomic ratio, ca. 0.5). Combined with the age (mainly Miocene) and geographical position of intrusion, the Circum-Izu Massif serpentinites were derived from the upper mantle of the Shikoku Basin. The plagioclase-chromian spinel peridotite is the refractory residue formed only from a low-pressure (10 ?? 5 kb) mantle diapir in the inter-arc or back-arc
basins.

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