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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  • Petrology of an epizonal gabbroic suite: the Batow pluton, Yamizo Mountains, Central Japan
    Hisao Tanaka, Chung-Hsi Huang, Youichi Nakamura, Etsuo Kurokawa, Masah ...
    1987 Volume 82 Issue 12 Pages 419-432
    Published: December 05, 1987
    Released on J-STAGE: August 07, 2008
    DOIhttps://doi.org/10.2465/ganko1941.82.419
    JOURNAL FREE ACCESS
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    The Batow pluton, an epizonal gabbroic body, Central Japan, was studied to delineate its geologic, petrographic and geochemical characteristics. Though the pluton is small, it exhibits a wide compositional range from melagabbro to granodiorite and varies from 42.8 to 62.7 wt.% SiO2. The Batow rocks have similar features to calc-alkaline, magnetite-series and I-type plutonic rocks and are characterized by high abundances of lithophile elements, comparable to those in a shoshonite rock association.
    Crystallization path calculations and petrographic observations suggest that the wide compositional variation was brought mainly by amphibole- and plagioclase-dominated fractionation of a gabbroic magma with minor fractionation of clinopyroxene, biotite and potash feldspar. This fractionation occurred at a comparatively shallow crustal level, deeper than 2kb, before upward migration.
    The granitic rocks characterized by an abundance of amphibole (up to 39%) and a scarcity of biotite (less than 4%) were formed at a higher P H2O and lower temperature than early-crystallized gabbros. The close association of clinopyroxene- and biotite-rich gabbro, whose clinopyroxene and plagioclase often show reverse zoning in the Mg/(Mg+Fe*) ratio and An content, with amphibole-rich gabbro suggests that P H2O had increased rapidly during crystallization of the gabbroic melt. The intrusion of H2O-saturated granodioritic melt to the gabbroic melt may have caused the rapid increase of P H2O.
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  • Age of formation for the Ishikawa composite mass, Abukuma mountains, inferred from Nd and Sr isotopic systematics
    Ken Shibata, Tsuyoshi Tanaka
    1987 Volume 82 Issue 12 Pages 433-440
    Published: December 05, 1987
    Released on J-STAGE: August 07, 2008
    DOIhttps://doi.org/10.2465/ganko1941.82.433
    JOURNAL FREE ACCESS
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    Sm-Nd and Rb-Sr isotopic compositions and REE abundances were measured on the Ishikawa composite mass, which is one of the older granitic rocks in the Abukuma mountains. Three mineral and two whole-rock samples define a Sm-Nd isochron yielding an age of 111±42 Ma with an initial 143Nd/144Nd ratio of 0.51251±3. Eight whole-rock samples give a Rb-Sr isochron age of 106±16Ma with an initial 87Sr/86Sr ratio of 0.70518±15. These ages are interpreted to represent the time of intrusion, supporting the Jurassic age of the Gosaisho metamorphic rocks confirmed by the fossil evidence.
    The Nd model ages of the Jshikawa mass relative to CHUR are as young as intrusion ages, whereas those relative to DM are 600-800Ma. On the basis of the REE patterns and εNd-εSr relationship, the Ishikawa mass is thought to be derived from the source material similar to CHUR. It is therefore suggested that the intrusion of the Ishikawa mass occurred subsequently to the differentiation of the source magma from the mantle.
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  • Conversions between SI and CGS units for rock magnetism
    Hirotomo Ueno
    1987 Volume 82 Issue 12 Pages 441-444
    Published: December 05, 1987
    Released on J-STAGE: August 07, 2008
    DOIhttps://doi.org/10.2465/ganko1941.82.441
    JOURNAL FREE ACCESS
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    Conversion factors between SI and CGS units for magnetic susceptibility and other magnetic quantities are described. The relationship between the volume magnetic susceptibility χSI in SI units and the specific magnetic susceptibility χCGS in CGS units is given by the formula χSI=4πρχCGS, where ρ is the density of rocks. A nomogram for their conversion is shown.
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  • Haruo Ohashi “Reexamination of the pressure-composition diagram for the system NaCrSi2O6-NaAlSi2O6”
    Discussion on “Haruo Ohashi-Relxamenation of the pressurec-composition diagram for the system NaCrSi2O6-NaAlSi2O6”
    Shohei Banno
    1987 Volume 82 Issue 12 Pages 445
    Published: December 05, 1987
    Released on J-STAGE: August 07, 2008
    DOIhttps://doi.org/10.2465/ganko1941.82.445
    JOURNAL FREE ACCESS
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  • “Reexamination of the pressure-composition diagram for the system NaCrSi2O6-NaAlSi2O6” Reply to S. Banno
    Haruo Ohashi
    1987 Volume 82 Issue 12 Pages 446-447
    Published: December 05, 1987
    Released on J-STAGE: August 07, 2008
    DOIhttps://doi.org/10.2465/ganko1941.82.446
    JOURNAL FREE ACCESS
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