In the Hanaoka mining area of the “Green Tuff” region, the Miocene submarine lavas and pyroclastic rocks with basaltic to andesitic compositions were recrystallized at low temperatures to form various secondary minerals. The upper metabasites are characterized by the mineral assemblage of prehnite-pumpellyite facies; i.e. chlorite+epidote+prehnite+pumpellyite, although zeolites occur in amygudules and veinlets. The microprobe data of secondary minerals, in addition to the microscopic observations, revealed the existence of several local domains with different effective bulk compositions within a single thin section. The metabasites of the upper cores (about 300m below the surface) of two drill holes also show secondary mineral assemblages of prehnite-pumpellyite facies, but those of the lower cores (at 900m depth) show actinolitebearing assemblages such as chlorite+epidote+prehnite+actinolite± pumpellyite. This indicates the transition to the prehnite-actinolite facies with increasing depth.

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Fe-Al-rich hornfels containing cordierite, olivine, orthopyroxene and spinel is found in the contact aureole of the Nogo-Hakusan granodiorite. Spinel is hercynitic and rich in V₂O₃ (up to 2.2 wt.%). Symplectites composed of olivine, cordierite and small amount of spinel are present around orthopyroxene. Phase relationships of cordierite, olivine, orthopyroxene and spinel in the system Mg-Fe²⁺-Al-Si-O-H have been experimentally determined. The experimental results and petrographical features suggest that the symplectites were formed by the following retrogressive reaction:
10 orthopyroxene+2 spinel=5 olivine+cordierite.
The maximum temperature of the metamorphism in the Nogo-Hakusan area was about 800°C at P_total=P_fluid=2-3 kb. The estimated f_o2 during the retrogressive metamorphism was relatively low, at least below the hematite-magnetite buffer curve.

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Petrological and geochemical study of volcanic rocks from Aguni-jima island, central Ryukyus has revealed their island-arc type characteristics. The volcanic rocks belong to Higashi Formation of early Pliocene age, and are divided into lower and upper units. Samples of lower unit are basaltic, whereas those of upper unit are andesitic. Trace element patterns are similar to those of island-arc volcanic rocks, and the rock suite may belong to the high-alumina basalt series. Major, trace and isotopic compositions show that the lower unit contains volcanic rocks of two different origins; one related to those of upper unit andesites, and the other unrelated ones. The basalt-andesite suite is possibly the result of low-pressure fractional crystallization of plagioclase, augite, magnetite, ±olivine and ±hypersthene.

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