Variations in ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd ratios of basalt-andesite lavas from the Quaternary volcanoes of the southwestern Kurile arc show seesaw lateral trends toward the back-arc side. Combining trace element data, the complex lateral variations in the isotopic compositions can be ascribed to addition of fluids released from amphibole in the mantle wedge beneath the volcanic front and from phlogopite in the wedge on the back-arc side. The basalts of Rishiri volcano, which is located farthest away from the trench, shift to MORB composition because addition of fluids from the subducted oceanic lithosphere is not expected. It seems that interaction between the subducted oceanic lithosphere and mantle wedge governs the geochemical characteristics of arc magmas.

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We obtained a K-Ar age of 3.32 Ma (Pliocene epoch) for an alkali basalt sample from Kyuroku-shima Island in the northeast margin of Japan Sea. The sample is normally magnetized and probably correlates to the Gauss normal epoch. The N-type MORB-normalized incompatible element pattern and the K₂O/TiO₂ ratio. indicate that the alkali basalt has a character of typical island arc. The petrography and chemistry of the alkali basalt is similar to those of basalts from present Chokai Volcanic Zone, especially those from Oshima-Oshima volcano. A regional study of Pliocene volcanoes by Shuto (1989) and ours revealed an existence of the lateral variation back then at least within our study area.

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High-grade metamorphic rocks such as garnet amphibolite and garnet-biotite gneiss were found in Ohshima, Yawatahama city, western Shikoku. They occur in the Sanbagawa metamorphic belt and are in fault contact with greenstones of the pumpellyite-actinolite facies. Common occurrences of almandine garnet in the amphibolite and cummingtonite-quartz assemblage suggest that they belong to the amphibolite facies of the intermediate-pressure type metamorphism, distinct from the surrounding Sanbagawa metamorphic rocks. Two biotites and two amphiboles from the high-grade rocks have a narrow range of K-Ar age from 90 to 100 Ma. Although present occurrence of the high-grade rocks may be explained by thrusting over the Sanbagawa metamorphic rocks, there has been so far no report of a suitable candidate corresponding to the parental body of the high-grade metamorphic rocks.

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The effect of radioactive radiation on ESR signals of zircon has been studied. Natural zircons and synthetic zircons doped with Ca, U, Al-U, and Ca-P were irradiated with thermal neutrons and γ-rays. ESR measurements performed on these and also on non-irradiated syn-thetic zircons containing various elements, revealed that ESR signals in a range from g=2.000 to g=2.009 are attributed to various radiations and not to impurity ions. Among them, the signal g=2.008₃ changes little in intensity with the irradiations and is considered to be related only to α-decay. This has been demonstrated from the nuclear reaction ⁴⁰Ca (n, α)³⁷ Ar in the Ca-doped zircon. Since the intensity of the signal g=2.008₃ in natural zircons is roughly proportional to their fission track age, it is probably caused by disintegration of radioactive elements in the zircons. The other signals with g=2.000₁, 2.001₀, 2.001₈. and 2.003₀. become stronger in intensity after the neutron and γ-ray irradiations.

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New trace-element data on several Ueno basaltic rocks, obtained by instrumental neutron activation and X-ray fluorescence analyses, show significantly low Ta and Nb values, thereby indicating that the rocks are “arc type” basalts. Most of old analyses on the Ueno basaltic rocks, cited by Ujike (1989), seem to have overestimated the Ta content. Therefore, Ujike's (1989) genetic model, in which these rocks could be derived from a “non-arc type” mantle material, a potential source of the Neogene alkalic volcanic rocks in west Japan, should be abandoned.

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Chemical analyses of the following rocks and minerals from the Sangun metamorphic terrain, Nichinan-cho, Tottori Prefecture are given: two chlorites, two muscovites and their host pelitic schists, two chlorites and one epidote of basic schists carrying barroisite. The muscovites of the pelitic schists are distinctly phengitic.

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