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 73, Issue 7
Displaying 1-4 of 4 articles from this issue
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  • PETROLOGIC STUDY OF SILLIMANITE-GARNET-CORDIERITE-BEARING PEGMATITE INTRUSIVES FROM TAKATO, CENTRAL JAPAN
    AKIRA ONO
    1978 Volume 73 Issue 7 Pages 185-190
    Published: July 05, 1978
    Released on J-STAGE: August 07, 2008
    DOIhttps://doi.org/10.2465/ganko1941.73.185
    JOURNAL FREE ACCESS
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    Sillimanite+garnet+cordierite+graphite-bearing pegmatites were found in Takato. Chemical compositions of constitutent minerals are similar to those of the surrounding metamorphic rocks. Mineral assemblages, chemical compositions of minerals and modes of occurrences of the Takato pegmatites suggest that the pegmatite magmas were produced by partial melting of high temperature parts of the Ryoke metamorphic rocks and rised to the crustal level of upper amphibolite facies.
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  • SOLUBILITY OF CaAl2SiO6 IN CaScAlSiO6-PYROXENE
    Haruo OHASHI
    1978 Volume 73 Issue 7 Pages 191-196
    Published: July 05, 1978
    Released on J-STAGE: August 07, 2008
    DOIhttps://doi.org/10.2465/ganko1941.73.191
    JOURNAL FREE ACCESS
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    Six clinopyroxenes between the two end members along the join CaScAlSiO6-CaA12SiO6 have been synthesized at 1 atm and higher pressure. Their unit-cell dimensions have been determined by X-ray powder method. All the cell dimensions (a, b, c and β) were found to change linearly against the change of mol% along the join CaScAlSiO6-CaA12SiO6. Judging from the linear changes of unit-cell dimensions this series of clinopyroxenes is expected to form a complete series of solid solutions at high pressure. The maximum solubility of CaAl2SiO6 in CaScAlSiO6-pyroxene at 1 atm is about 32 mol% at about 1400°C. Lowering of the melting point of the pyroxene solid solution, relative to that of CaScAlSiO6 end member, is rather small and about 120°C for the composition 30 mol% CaA12SiO6.
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  • DIFFERENTION OF BORE HOLE HO-1 DOLERITE SILL, ODATE CITY
    Ken-ichiro Aoki, Toshiharu Tokoyo, Hisashi Aoki
    1978 Volume 73 Issue 7 Pages 197-201
    Published: July 05, 1978
    Released on J-STAGE: August 07, 2008
    DOIhttps://doi.org/10.2465/ganko1941.73.197
    JOURNAL FREE ACCESS
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    The bore hole HO-1 dolerite sill, which is about 120m thick and well-differentiated sill, intruded into the Okuzu formation (middle Miocene), about 5km NNW of Odate city, northeastern Japan in the middle Miocene age, after the formation of the Kuroko ore deposits in this district. After the intrusion, a magma having about 10 per cent by volume of olivine and auigte phenocrysts formed several segregation veins composed of soda monoznite and/or soda syenite subparallel to the contact by fractionation in situ.
    Thirteen representative rocks have been analyzed chemically (Table 1). Petrographically, the HO-1 dolerite belongs to the calc-alkalic basalt having high-alkali tholeiite (Kuno, 1968b) or olivine tholeiite (Yoder and Tilley, 1962) in composition. The compositions of olivine dolerite-soda syenite suite vary widely with the fractionation, showing the clear increase of SiO2 and Na2O and the decrease of CaO and MgO. The crystallization trend of the dolerite magma does not follow that of calc-alkalic series, but follows alkalic series. Such unusual trend would be attributable to the presence of small amounts of water in the magma.
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  • “KOMATIITE-LIKE” PERIDOTITE IN THE HIGO METAMORPHIC BELT, KUMAMOTO PREFECTURE
    Toshio Mizuta
    1978 Volume 73 Issue 7 Pages 202-215
    Published: July 05, 1978
    Released on J-STAGE: August 07, 2008
    DOIhttps://doi.org/10.2465/ganko1941.73.202
    JOURNAL FREE ACCESS
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    Peridotites characterized by the texture of elongated olivine crystals, are found in the Higo metamorphic belt mainly composed of psammitic gneiss. The peridotite mainly consists of olivine, orthopyroxene, tremolite, serpentine, and talc. Spinifex-like olivine crystals, partly altered to serpentine and magnetite, consist of randomly oriented plates parallel to (010). The elongated olivine crystals in same handspecimen are chemically homogeneous, and the compositional zonation of the crystals has not been observed by microprobe analysis. However, the chemical composition of olivine ranges from FO83 to FO92 in different handspecimens. The NiO content of olivine varies from 0.2 to 0.5 weight per cent and the MnO content from 0.1 to 0.2 weight per cent. The NiO and MnO contents are about the same as those of komatiitic olivines. On the other hand, the olivines in the Higo perioditite contain a negligible amount of CaO and remarkabIly differ from those of extrusive peridotite (komatiite). The rocks are free from clinopyroxene and contain large and prismatic orthopyroxene. The extremely Ca-depleted orthopyroxenes (En89-En92) are interlocked with tabular olivines in each other. The Al2O, and Cr2O3 contents of orthopyroxenes are relatively lower than those of orthopyroxenes in alpine peridotites.
    From the mineral assemblages of peridotites and metamorphic rocks, and from the chemical composition of olivine and orthopyroxene, it is suggested that the peridotite bodies suffered from the regional metamorphism of amphibolite facies (approximately 700°C, 3-4kb). This conclusion is also supported by the data concerning Mg-Fe2+ distribution between olivine and chromian spinel in the Higo peridotite.
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