Picrite basalt was found in the Paleogene Kobotoke Group, central Japan. The picrite basalt occurs as a small mass enclosed by greenish sandstone and mudstone having clasts derived from picrite basalt and related rocks. The picrite basalt mass is a large boulder emplaced in a similar stratigraphical position to serpentinite masses in the Kobotoke Group. Phenocrysts of magnesian olivine (Fo_89-90) with opaque spinel inclusions occupies more than 50 volume % of the rock. The spinel is Cr-rich, having the Cr/(Cr+Al) atomic ratio of around 0.7, and is also Ti-rich, having 1 to 3 wt % of TiO₂. The rock is characterized by high Ti/(Na+K) and Na/(Na+K) ratios. The picrite basalt from the Kobotoke belt is quite similar to those from other Circum-Izu massif areas (the Mineoka and Setogawa belts) in terms both of the mineral chemistry and of the wholerock chemistry. It is noteworthy that the petrological characteristics of the Circum-Izu massif picrite basalts are identical to those of the Hawaiian tholejites.

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Thermodynamic calculations on the stability relations among various tungsten species are performed in order to elucidate the possible form of tungsten during the transportation in hydrothermal solution, using the knowledge of the fluoride and chloride concentrations.
Based on the fluorine contents in micas and topaz and the fluid inclusion data, it is calculated that HF/H₂O and HC1/H₂O fugacity ratios in the natural hydrothermal solutions responsible for major Japanese tungsten deposits at the Kaneuchi, Ohtani, Takatori, Fujigatani, Kiwada, and Kuga range from 10^-3.15 to 10^-5.91 and are less than 10^-3.33, respectively. Pressure and temperature conditions for the formation of the studied deposits are summarized and calculated to be from 1 to 2 kbars, and from 300° to 600°C, respectively. Oxygen fugacities are assumed to be those defined by the C-CO-CO₂ buffer as the most reducing condition encountered.
Based on the pressure, temperature, f(O₂), f(HF)/f(H₂O), and f(HCl)/f(H₂O) conditions evaluated for the studied deposits, thermodynamic calculations are performed to compare the stabilities of halogen-bearing species with those of tungstates. Calculated results show that H₂WO₄ may be a predominant species in the natural hydrothermal solutions responsible for the formation of major Japanese tungsten deposits.

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Alkali amphibole-bearing schist is found in the Sambagawa metamorphic terrane, central Kii Peninsula where the zone of the glaucophane schist facies has never been recognized.
Alkali amphibole is rimmed or included by actinolite and coexists with epidote, chlorite, albite and quartz, occasionally associated with stilpnomelane, muscovite, sphene and calcite. Microprobe analyses of the alkali amphiboles reveal that they fall into the two compositional fields of glaucophane and crossite to magnesioriebeckite. The petrological evidence shows that the metamorphic grade in the study area has attained to the glaucophane schist facies; actinolite enclosing the alkali amphibole is regarded as being formed during a later probably low-pressure phase of the metamorphism.

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Rb, Sr, Sm and Nd concentrations, and Sr and Nd isotopic compositions have been determined for gabbroic inclusions in Pliocene calc-alkaline andesites from the Umikawa and Arakurayama areas in northern Fossa Magna region, Central Japan. These gabbroic inclusions may be derived from the deepest part of the lower crust beneath the northern Fossa Magna region. Sr and Nd isotope data indicate that the gabbroic inclusions are not in equilibrium with host andesite, suggesting accidental origin of the gabbros in andesitic magmas. ¹⁴³Nd/¹⁴⁴Nd ratios of nine gabbroic inclusions have very narrow range between 0.51274 and 0.51279 while they have a wide range of ⁸⁷Sr/⁸⁶Sr ratios between 0.70389 and 0.70568. In the ∈ Sr and ∈ Nd diagram, the gabbroic inclusions plot to the right of the mantle array. The following explanations for the Sr and Nd isotope variations of the gabbroic inclusions reported here are possible; 1) the inclusions may represent the residues after formation of the intermediate to acid magmas by partial melting of a lower crust source material, or 2) the strontium isotopic compositions of the inclusions were affected by seawater interaction prior to eruption of Pliocene andesitic magmas.

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