The Hidaka metamorphic belt of Hokkaido, Japan is a steeply dipping sequence of metamorphic and igneous rocks, similar to an island-arc type crust, which decrease in metamorphic grade from granulite facies in the west (base) to very low grade in the east (top). This island-arc type crust is thrust over a metamorphosed ophiolitic sequence to the west along the Hidaka Main Thrust. Twenty two biotite and two hornblende samples from metamorphic rocks and tonalites collected from the base to the top of the metamorphic sequence and from various topographic elevations of the Hidaka metamorphic belt yield similar K-Ar ages. These range from 19.1±0.4 Ma to 16.3±0.4 Ma regardless of rock type and metamorphic grade. These ages indicate that the present rock sequence and the steeply eastward dipping structure of the Hidaka metamorphic belt was already formed in or before the late Early Miocene. The steep tilt of the Hidaka island-arc resulted from a dextral thrust movement associated with the collision of the metamorphic belt with the ophiolitic sequence to the west. Their amalgamation, therefore, occurred before the late Early Miocene. A small difference in age of about 1 Ma between hornblende and biotite K-Ar ages indicates rapid uplift rates of 5.8 to 7.8mm/y during the late Early Miocene, using the closure temperatures of 300°C for biotite and 510°C for hornblende, and a geothermal gradient of 30°C/km. The rapid uplift of the metamorphic belt during that time is the result of the dextral transpression associated with the collision. The uplift rates decreased to 0.52 to 0.61mm/y from that time to the present according to the biotite K-Ar ages. Biotite K-Ar ages decrease with increasing topographic elevations of sample localities. This is the reverse of the trend that is usually observed, and suggests differential uplift due to differential movement along the steeply dipping schistosity surfaces within the metamorphic belt.

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Volcanic ash from 1992 eruption of Shinmoe-dake was investigated. Smectite and gypsum are present besides feldspar, pyroxenes, hornblende and cristobalite. An energy dispersive X-ray analysis indicates that the smectite is a Fe-rich smectite. The smectite resulted from rock alteration by a geothermal system within the cone at relatively low temperatures before the eruption.

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23.0±1.2 Ma was obtained by Rb-Sr method for a phlogopite-bearing spinel lherzolite from the Horoman peridotite complex in the Hidaka metamorphic belt, Hokkaido, Japan. The age is essentially identical to the oldest ages of the country metamorphic rocks reported so far in the Hidaka metamorphic belt, and may indicate the time of a metasomatic event which occurred in the wedge mantle. This metasomatic event may have occurred during uplift of this mantle fragment under mantle conditions contemporaneously with elevation of the Hidaka metamorphic belt resulting from collision between the Eurasian and North American plates.

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Raman spectra of carbonaceous material in the Paleozoic strata around the Hikami and the Kesengawa granites in the Southern Kitakami Mountains have been investigated. Two spectral lines, one occurring near 1350cm^-1, and another at about 1620cm^-1, indicate the degree of graphitization in terms of the I₁₃₅₀/I₁₆₂₀ intensity ratio. The I₁₃₅₀/I₁₆₂₀ intensity ratio decreases with advancing coalification and graphitization, and becomes zero above about 190Å in crystallite thickness L_c (002) determined by the X-ray diffraction techniques. X-ray parameters which indicate the degree of graphitization could not be obtained because of fluorides formation during chemical treatment for isolation of carbonaceous material. However, the I₁₃₅₀/I₁₆₂₀ value of the Raman spectra could determine the degree of graphitization even where other compounds coexist.
The Raman spectra of graphites collected from along the western edge of the Kesengawa granite show a single line at 1620cm^-1 rather than the 1580cm^-1 line of the theoretical E_2g2 mode in pristine graphite. The spectral line shift to higher frequency side suggests that these graphites might be graphite intercalation compounds.
I₁₃₅₀/I₁₆₂₀ values of the Siluro-Devonian Formations around the Hikami granite are above 0.2. These data indicate that the Silurian stratum was not thermally affected by the Hikami granite.
Laser Raman spectra of carbonaceous material in sedimentary and metamorphic rocks could be applied to evaluate the degree of graphitization, and to estimate thermal effects from granite plutons.

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Piemontite-bearing schist (Pm-schist) in the Yamagami metamorphic rocks, northeastern Abukuma Plateau, was studied in terms of bulk chemical composition, mineral assemblage and mineral chemistry.
The Pm-schist occurs as intercalating member of the albite-porphyroblastic muscovite-quartz schist and epidote-amphibolite. Petrographic features suggest that the primary mineral assemblage is quartz+muscovite+albite+chlorite+piemontite+tourmaline+hematite+rutile. Apatite, epidote and carbonate also occur as minor minerals. Veins formed of euhedral quartz and anhedral K-feldspar intruded into microgranoblastic quartz aggregation.
The compositions of piemontite range between Pm₁₁Ps₂₂Cz₆₇ and Pm₁₇Ps₁₈Cz₅₅. Muscovite is phengitic (Si 6.54-6.64 atoms per 22 oxygens) and contains moderate amount of hydromuscovite component. Chlorites are clinochlore with Fe/(Mg+Fe)=0.02 and pycnochlorite with Fe/(Mg+Fe)=0.38. Hematite contains Mn₂O₃ component.
The bulk chemical composition of the Pm-schist is characterized by the high silica content, 82.41 wt.%, and high oxidation ratio, (Fe³⁺×100)/(Fe³⁺+Fe²⁺)=93. MnO content is very low at 0.02 wt.%.
Appearance of piemontite, Mg-chlorite and hematite containing Mn₂O₃ component suggests that f_O2 condition during the metamorphism was very high, which is consistent with the extremely high oxidation ratio of the bulk composition. The extremely high f_O2 condition during metamor-phism may be explained by the dissociation equilibrium of H₂O with H₂ and O₂.

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We found high-Mg andesite (56.5 wt.% SiO₂ and 7.2 wt.% MgO) from Mikasayama in Wassamu town, northern Hokkaido. Its K-Ar age is 11.1±0.8 Ma. The high-Mg andesite is characterized by co-existence of Fo-rich olivine (Fo_90-85) and An-poor plagioclase (An_64-38) phenocrysts. The mineralogical evidence suggests that the high-Mg andesite from Mikasayama was produced by mixing of primitive basalt magma, containing Mg-rich olivine and clinopyroxene phenocrysts, and hornblende dacite magma.

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