Three types of andalusite porphyroblasts occur in the Ryoke metamorphic rocks from the Nukata area, Aichi Prefecture. The first type porphyroblast has only one kind domain (oblique Si domain) of which inclusion trail (Si) is oblique to the schistosity of the matrix (Se). The second type has another kind domain (parallel Si domain) of which Si is parallel to the Se. The third type porphyroblast consists of two kinds of domains: central oblique Si domain and outer parallel Si domains. From the systematic distribution of these type porphyroblasts in the area, the oblique and parallel Si domains are considered to have grown during regional and contact metamorphic events, respectively.

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A 1, 400m-long core was obtained in Lake Biwa. Mineralogical study was carried out for the core samples. Main constituent minerals are quartz, feldspar, smectite, chlorite, illite and kaolinite. Small amounts of zeolites, amphibole and siderite are found in the samples. Quartz and feldspar are present in every sample, and considerable amounts of illite, chlorite and kaolinite are found in almost every sample. Smectite is not present or hardly detectable in some samples. Based on the results of this study, it is possible to estimate the changes of sizes of Lake Biwa in the past. High concentration of smectite in the samples indicates that the size of Lake Biwa was big at that time, and low concentration of smectite indicates that the Lake Biwa was small. Judging from the changes of the amounts of smectite, quartz and feldspar, it can be estimated that several environmental changes on the sediments happened.

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Significant amounts of MgO, and excess SiO₂ and Al₂O₃ in anorthites from the island of Miyakejima are estimated by EPMA and X-ray diffraction analysis. The role in the crystal structure establishes Mg, Si and Al cations as CaMgSi₃O₈, ?? Si₄O₈ and AlAl₃SiO₈ endmembers for the anorthite solid solution. Syntheses under dry conditions of anorthites along the joins CaAl₂Si₂O₈- ?? Si₄O₈ and CaAl₂Si₂O₈-CaMgSi₃O₈ conduced to ascertaining the partial solubility limits of these endmembers in the solid solutions, compared with the anomalous anorthites from Miyakejima. The maximum limit of partial solubility of CaMgSi₃O₈ is about 25 mol% to CaAl₂Si₂O₈, and that of ?? Si₄O₈ is nearly 8 mol%. Nevertheless inhomogeneous distribution of Mg cation within this single crystal has an implication for the unstable behavior of Mg cation in the anorthite structure. Chemical shift of MgKαI in the synthetic anorthites affords infallible discrimination of solubility of CaMgSi₃O₈ endmember rather than MgAl₂Si₂O₈.
Condensation of natural occurrences and syntheses of plagioclases with small amounts of CaMgSi₃O₈ and ?? Si₄O₈ components purifies that anorthites from Miyakejima may have been originally crystallized by super-cooling in SiO₂-saturated and Mg-rich host magma at the hightemperature more than 1, 000°C, and that the phenomenon in anorthite similar to Tschermak substitution, Mg+Si⇔2Al, goes to prove the charge-coupled substitution of Mg+Si in only tetrahedral sites. Emphasis is placed upon experimental verification and comparison to observed data is made where possible.

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Rb-Sr whole rock isochron age has been determined on the Early Cretaceous Monai volcanic rocks occurring in Okushiri Island, Northeast Japan Sea. Five samples of dolerite, andesite and rhyolitic welded tuff give a well defined whole rock isochron with an age of 101.3±4.8 Ma and an initial ⁸⁷Sr/⁸⁶Sr ratio of 0.70532±0.00007 (2σ). These results almost agree with the mineral and whole rock isochron ages and the initial Sr isotopic ratios determined by the previous workers for the pre-Tertiary granitoids occurring in Okushiri Island and the western margin of southwest Hokkaido. This facts indicate the concurrence of the pre-Tertiary volcanism and plutonism in these areas and the similarity in isotopic compositions of the source materials for the Monai volcanic rocks and these granitoids. The initial Sr isotopic ratio of the Monai volcanic rocks are much higher than those of the Early Cretaceous volcanic rocks from the region to the west of Hidaka Mountains and the eastern margin of the Kitakami Mountains.
Comparative investigations of initial Sr isotopic ratios reported by the previous and present workers for the Early Cretaceous volcanic rocks and granitoids from the NE Japan arc and Hokkaido indicate that initial Sr isotopic ratios for these igneous rocks increase from the eastern tholeiitic volcanic zone to the western calc-alkaline volcanic-plutonic zone, in contrast to the across-arc variation of the Sr ratios of the Quaternary volcanic rocks from the NE Japan arc.

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