The Journal of the Japanese Association of Mineralogists, Petrologists and Economic Geologists
Online ISSN : 1883-0765
Print ISSN : 0021-4825
ISSN-L : 0021-4825
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Volume 72, Issue 11
Displaying 1-4 of 4 articles from this issue
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  • THE STABILITY OF ANDRADITE IN H2O-CO2 MIXTURES
    TETSUYA SHOJI
    1977 Volume 72 Issue 11 Pages 399-411
    Published: November 05, 1977
    Released on J-STAGE: August 07, 2008
    DOIhttps://doi.org/10.2465/ganko1941.72.399
    JOURNAL FREE ACCESS
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    The stability field of andradite in H2O-CO2 mixtures has been calculated on the basis of previous work in the systems CaO-SiO2-CO2 and CaO-FeOX-SiO2-O2, and the thermo-chemlcai data. Under relatively high oxygen fugacities where hedenbergite is unstable, the andradite field is restricted by the following reactions:
    (1) andradite+CO2=calcite+magnetite+quartz+O2
    (2) andradite+CO2=calcite+hematite+quartz.
    Compared with the grossular field, the andradite field extends towards the low-temperature and CO2-rich side in the T-XCO2 diagram. For example, where the oxygen fugacity is represented by the NNO buffer, the equilibrium boundary for Reaction (1) at 2000 bars passes approximately through the points: XCO2=13mole%, T=500°C, and XCO2=0.44mole%, T=300°C.
    Since grandite garnet occurs commonly in skarn-type ore deposits, the upper limit of the amount of CO2 in fluids under which ore-bearing skarn can be formed is inferred to be 3 mole % at 400°C. This suggestion agrees with the fact that CO2-rich inclusions are not common in ore deposits of this type.
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  • A Rb-Sr ISOTOPIC STUBY ON THE OJIKA AND ICHINOHE GABBROIC COMPLEXES IN THE KITAKAMI MOUNTAINS, NORTHEAST JAPAN
    KAZUYA KUBO
    1977 Volume 72 Issue 11 Pages 412-418
    Published: November 05, 1977
    Released on J-STAGE: August 07, 2008
    DOIhttps://doi.org/10.2465/ganko1941.72.412
    JOURNAL FREE ACCESS
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    Rb and Sr concentrations and Sr isotopic compositions were analyzed for the Ojika gabbroic complex, the S-mass in the Aji islet and the Ichinohe complex in the Kitakami mountains. The initial 87Sr/86Sr ratios of 0.7045_??_0.7050 for the former two is somewhat higher than that of 0.7041 for the latter.
    For the Inchinohe complex, 105±30 m. y. is obtained as the whole rock isochron age, which shows well-agreement with the biotite-whole rock isochron age of 101_??_110m. y. These ages indicate the age of emplacement of the Ichinohe complex.
    The low initial 87Sr/86Sr ratios for these complexes indicate that incorporation of crustal materials in the original magmas is eliminated.
    The K/Rb ratios of the present district is 72_??_287. These values are somewhat lower than those of some other granitic rocks in Japan.
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  • Ca-Fe-RICH PYROXENES IN MIOCENE PERLITES FROM THE TSUGAWA AND TADAMI AREAS, NORTHEAST JAPAN
    MITSUO SHIMAZU, MASAKI TAKANO
    1977 Volume 72 Issue 11 Pages 419-427
    Published: November 05, 1977
    Released on J-STAGE: August 07, 2008
    DOIhttps://doi.org/10.2465/ganko1941.72.419
    JOURNAL FREE ACCESS
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    Phenocrysts of Ca-Fe-rich pyroxenes such as ferroaugite and ferrohedenbergite were found in perlite lavas, which occur in the Middle Miocene formations in the Tsugawa and Tadami areas, although many of acid volcanic rocks in the areas consist of phenocrysts of biotite or hornblende. These perlites consist of phenocrysts of plagioclase (andesine-oligoclase), ferroaugite or ferrohedenbergite, altered olivine and titanomagnetite in a pale brown glassy groundmass.
    Ferroaugite and ferrohedenbergite occur in the British and Icelandic Tertiary acid glass and the late stages of the Skaergaard and Bushveld intrusions. Such pyroxenes also occur in some alkaline rocks. On the Ca-Mg-Fe quadilateral, chemical compositions of Ca-Fe-rich pyroxenes from the perlites are plotted near the trend curve of pyroxenes of tholeiitic rocks and are lower TiO2, A12O3 and K2O contents than those from alkaline rocks.
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  • X-RAY STUDIES ON THE ALKALI FELDSPAR FROM OKI ISLANDS
    Tateo Ueda, Kazumi Toda
    1977 Volume 72 Issue 11 Pages 428-432
    Published: November 05, 1977
    Released on J-STAGE: August 07, 2008
    DOIhttps://doi.org/10.2465/ganko1941.72.428
    JOURNAL FREE ACCESS
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    Alkali feldsapr from Kaminishi, Oki Islands has been examined. Its chemical component is 0r46Ab49An5. By taking X-ray rotation and Weissenberg photographs cell-dimensions and axial angles have been measured. Results obtained are as follows: a=8.560Å, b=12.995Å, c=7.171Å, α=90°, β=116°00', γ=90°. Its space group is C2/m. Accordingly, the alkali feldspar was crystallized as soda-sanidine. In X-ray Weissenberg photographs strong and medium reflexions are accompanied with a diffuse streak. The diffuse streaks extend along the direction of the a*-axis in the a*-b* reciprocal plane and slant at about 10 degrees against the a*-axis in the a*-c* reciprocal plane. Hence, the diffuse streaks are almost in the direction parallel to the line which connect origin to 107 reciprocal lattice point in reciprocal space. Some considerations have been given to the occurrence of the diffuse reflexions with a sharp spot in center.
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