We measured trace element abundances and ⁸⁷Sr/⁸⁶Sr ratios of andesites from Yufu-Tsurumi volcano group. The results and mineralogical data indicate that the andesite magma is a product of magma mixing and that mixing end-members are represented by dark inclusions from Yufu-Tsurumi volcano group and dacite from adjacent older volcano (Jissoji volcano).
Trace element abundances vs. SiO₂ plots of the andesites from a single variation trend between the inclusions at the mafic end and the dacite from the old volcano at the felsic end. ⁸⁷Sr/⁸⁶Sr rations of the andesites range from 0.7039 to 0.7044 and increase with increasing SiO₂ contents. In contrast, the inclusions have a narrow range of 0.7038 to 0.7040. Phenocrysts of the andesites are petrographically divided into two groups as follows; 1) olivine, Mg-rich clinopyroxene, pargasite and An-rich plagioclase, and 2) Mg-poor orthopyroxene, magnesio-hornblende, An-poor plagioclase and quartz. Phenocrysts of group 1) are derived from mafic magma, whereas those of group 2) from felsic magma. Plots of highly incompatible element concentration vs. highly/moderately incompatible element ratios show consistency between observed data and the mixing curves, which was calculated from the inclusions from Yufu-Tsurumi volcano group and the dacite from Jissoji volcano. As inferred from the bulk chemistry of andesites, proportions of the mixed basaltic magma increased with time. This temporal change agrees with modal compositions.
Magma mixing of Yufu-Tsurumi volcano group did not occur under static condition within a closed magma chamber but under dynamic condition during magma's ascent from a deeper chamber. Our proposed mixing model in Yufu-Tsurumi volcano group is that the basaltic and dacitic magmas commingled during ascent from a deeper magma chamber, and hybridized in a shallow chamber, then the hybrid magma erupted.

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Fifty-three volcanic rocks from Dogo island, Oki, Shimane Prefecture, southwestern Japa were analyzed for Sr isotopic compositions with two basement rocks. The rock samples consit of talc-alkali rock suite, Nagaoda shoshonite-banakite suite, Oki trachyte-rhyolite suite, Dogo mugearite suite, Hei trachyte and Tsuzurao rhyolite series, and Daimanjiyama, Ohmine, Kuroshima, Shiroshimazaki, Saigo, and Misaki alkali basalt groups in the order of probable eruption sequence. The volcanic rocks of calc-alkali suite and shoshonite-banakite suite were produced before Japan Sea opening (ca. 15 Ma), and both have ⁸⁷Sr/⁸⁶Sr ratios higher than 0.7068. Long after Japan Sea opening Oki trachyte-rhyolite suite was erupted (ca. 6.6 Ma); they have rather low ⁸⁷Sr/⁸⁶Sr ratios (0.7066-0.7081). Mugearites followed and have similar Sr isotopic composition, whereas 4.6 Ma old Daimanjiyama basalts have clearly low ⁸⁷Sr/⁸⁶Sr ratios (0.7050-0.7051). The rocks erupted 3-4 Ma seem to have the lowest ⁸⁷Sr/⁸⁶Sr ratios: they are Ohmine, Kuroshima, Shirosimazaki alkali basalt suites (0.7044-0.7048). The ⁸⁷Sr/⁸⁶Sr ratios of the Saigo basalts erupted 0.84 Ma are higher than those erupted 3-4 Ma. The latest volcanic products in Dogo island, Misaki basalt suite has even higher ⁸⁷Sr/⁸⁶Sr ratios (0.7054-0.7057) than the Saigo basalt suite. Thus, temporal and systematic variation of Sr isotopic compositions of the volcanic rocks from Dogo can be recognized. The ⁸⁷Sr/⁸⁶Sr ratios of the rocks were once as high as 0.7066 or even higher than 0.708, but they started decreasing down to ca. 0.7044-0.7048 4-3 Ma ago. Since then the ratios rebounded to 0.7049-0.7055. The Hei trachyte and Tsuzurao rhyolite series are not included in this temporal and systematic change. The mantle diapir associated with Japan Sea spreading might have caused the decrease in the ratios, and either Pacific Ocean plate or Philippine Sea plate subduction may be responsible for this rebound.

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Patches, veins and oriented zones of “incipient charnockites” occurring in the Precambrian granulite terrane of Sri Lanka provide compelling evidences for fluid-controlled granulite genesis. Transformation from gneiss to granulite involves breakdown of biotite or amphibole to orthopyroxene, with the resultant coarse charnockitic assemblage testifying to increased reaction kinetics aided by the influx of fluids. Fluid inclusion studies across a typical gneiss-charnockite reaction front at Kurunegala reveal that carbon dioxide was the ambient fluid species during incipient charnockite formation, with a melting temperature close to that for pure CO₂ and a density of 0.87g/cm³. Fluid evolution is traced from early pure carbonic through intermediate mixed carbonicaqueous to late aqueous regime. Visual decrepitation of carbonic inclusions in polished wafers indicate that the charnockite entrapped almost double the amount of CO₂ as compared to the gneiss, indicating external addition of fluids which effected dehydration. Combined solid-fluid equilibria define a P-T path characterized by its convexity towards the temperature axis, suggesting an isothemal uplift history. The close similarity between the decompression-related metamorphic uplift paths for Sri Lanka, South India and Antarctica strenghthen the current discussions on the juxtaposition of these continents in the Gondwana reconstruction.

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In the Na₂O:FeO:Fe₂O₃ and CaO:FeO:Fe₂O₃ (both by wt. %) diagrams, plots of composition of actinolite greenschists and associated glaucophane schists of the Sangun metamorphic belt are sharply separated from each other, those of the latter schists being distributed in the higher Fe₂O₃ area. Although the boundary is diffuse, the similar trend is observed also for the Sambagawa schists. The boundary for the Sangun schists are located in the lower Fe₂O₃/FeO position than that for the Sambagawa schists, and the stability field, in terms of Fe₂O₃/FeO, of alkali amphibole in basic schist seems to be wider in the former than in the latter belts. The association of calcic and alkali amphiboles are described in a few basic schists of the Sambagawa belt, whereas it is not reported from the Sangun belt. The pressure of metamorphism is inferred to have been higher, though slightly, in the Sangun than in the Sambagawa belts.

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