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The scoria from the Kasa-yama volcano, Hagi, Yamaguchi Prefecture, is andesitic in composition, red brown in color and porous. Black scoria also occurs rarely. Phenocrysts of the scoria are olivine and clinopyroxene. In the present study, oxidation state of Fe in olivine phenocrysts in the scoria was investigated to evaluate the effect of oxidation at high temperature on the scoria. There is no precipitated material in olivine of the black scoria, and its Fo content ranges from 82 to 84 mol%, whereas olivine in the weakly reddish black scoria contains a small amount of opaque minerals, and its Fo content ranges from 81 to 88 mol%. Oxidation state of Fe in olivine was evaluated by means of the relative intensities of Fe Lbeta) and Fe L(alpha) X-rays. The [FeL(beta)/FeL(alpha)-ratios of olivine in the black scoria and weakly reddish black scoria is 0.67-0.72 and 0.64-0.69, respectively, which result in 0-4 and 1-8 % of Fe³⁺ against total Fe in olivine, respectively.

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Arsenate minerals as carminite, mimetite, beudantite-segnitite, and scorodite occur in quartz vein including galena, chalcopyrite, sphalerite, arsenopyrite, pyrite and bournonite at the Koganezawa mine, Koshu, Yamanashi Prefecture, Japan. The ore veins are developed in biotite-granite, which was altered to muscovite-chlorite rock around the ore veins.

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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Mineralization experiments are carried out at super-critical hydrothermal fluid flow condition with carbonate/silica contact configuration. Within 200µm from the original contact to carbonate phase, amorphous silica in vaterite pseudomorph occurred. Beyond the amorphous silica zone, wollastonite needle crystals precipitate from flowing hydrothermal fluid.

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Major and trace element analysis of rock samples with XRF: evaluation of analytical method with results on reference samples

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The Song Ma Suture zone in northern Vietnam is well-known as a micro-continental boundary between the South China and Indochina cratons. The mafic granulite from the suture zone was investigated in this study. Primary assemblage of the granulite is garnet, sodic clinopyroxene, amphibole and quartz. During the decompression, orthopyroxene- and plagioclase- bearing symplectites were formed. The granulite always associates micro-scale leucosome containing magmatic epidote and quartz with biotite + plagioclase + spinel + corundum symplectite. These microstructual features should be explained by amphibole (pargasite) dehydration melting at orthopyroxene- and plagioclase-free high-pressure condition and by later back reaction between residuous phases and melt. The results should be important to understand crustal melting under the extreme metamorphic conditions at continental collision zone.

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The late Pan-African voluminous igneous activities, younger than ca. 520Ma, occur in central to eastern Dronning Maud Land, East Antarctica. These igneous rocks contain granitic rocks with mafic enclaves. Dronning Maud Land has been believed to be a continental-collision zone related to the formation of Gondwana supercontinent during the Pan-African. The granitic rocks underwent little deformation and intruded the host high-grade metamorphic rocks that indicate clockwise P-T-t path. The mafic enclave and granitic rocks intimately intrudes the host high-grade metamorphic rocks; thereby, underplated basaltic magma combined with decompression of the lower crust would be generated by granitic magma. This tectonic process may be triggered by extensional collapse after the continental collision.

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We report here for the first time fluid inclusions from the Paleoproterozoic basement rocks in Bangladesh, reveals CO₂ and H₂O with hypersaline inclusions. Primary fluid inclusions comprise carbonic inclusions with melting temperature ranges from -56.6 to -57.9°C (granite) and -56.7 to -58.1°C (quartz vein), indicating that the dominant part of the trapped fluid is pure CO₂ . The homogenization temperature of inclusions ranges from -5.8 to 30°C and -6.8 to 29.8°C, respectively. These translate into carbonic inclusion densities in the range of 0.59 to 0.96 g/cm³ and 0.60 to 0.97 g/cm³, respectively. Isochore values are the indicative of the single stage of fluid activity and pressure of crystallization of the rocks ranges from 2.6 to 3.4 kbar at around 700°C.

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Thermally metamorphosed crystalline limestone on Mt. Kawara was systematically studied on the basis of field observation and analysed using the intercept method in CSD (crystal size distribution) theory. The mean intercept size (MIS) of all the calcite grain is 3.13 mm (SD=2.21), found in 6,436 grains of 16 specimens. The size of calcite grains tend to decrease as altitude of sample locality elevated. The samples of the lowest altitude locality and top of Mt. Ninotake (one of peaks in Mt. Kawara) are about 3.91 mm and about 1.89 mm in MIS, and temperatures are estimated as 764 and 585 degrees Celsius, respectively.

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