岩石鉱物鉱床学会誌

有珠火山熔岩の化学組成変化とその岩石成因論的考察

大場与志男

1965 年 54 巻 6 号 p. 195-207
発行日: 1965/12/05
公開日: 2008/08/07

DOIhttps://doi.org/10.2465/ganko1941.54.195

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Detailed petrographic descriptions of the lavas from Usu volcano were made already by several researchers, but there has been no satisfactory petrological consideration on the remarkable difference in chemical composition between somma and dome-lavas.
The somma-lavas, forming a stratocone, are tholeiitic basalt or mafic andesite (SiO₂=49.36-53.46%); on the other hand, the succeeding dome-lavas and pumice are dacite or rhyolite (SiO₂=68.89-73.04%).
The present paper have applied Osborn's (1959) idea, which proposes two fractional crystallization trends depend on the Po₂ conditions, to interprete the genesis of the Usu lavas. If the chemical compositions of the lavas are plotted in the FeO+Fe₂O₃/FeO+Fe₂O₃+MgO-SiO₂ diagram, the sommalavas lie on a steep ascending trend while the dome-lavas lie on a gentle one. With some assumptions, the idealized fractional crystallization of the parental magma can be calculated as follows;
(1) The genesis of somma-lavas; Fractional crystallization on the tholeiite trend.
(2) The genesis of dome-lavas; Fractional crystallization on the talc-alkali rock trend.
For the dome-lavas, the trend of FeO and Fe₂O₃ contents could not be shown as a straight line; to maintain Po₂, 0.4% oxygen must be added to the andesitic magma.
After all, primary magma is solidified as crystal aggregates and residual felsic lava in proportions as shown in Figure 4.

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北海道積丹半島の地質と鉱床(II)

成田英吉, 岡部賢二, 河野純一

1965 年 54 巻 6 号 p. 208-215
発行日: 1965/12/05
公開日: 2008/08/07

DOIhttps://doi.org/10.2465/ganko1941.54.208

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駒込隕石について

島誠

1965 年 54 巻 6 号 p. 216-221
発行日: 1965/12/05
公開日: 2008/08/07

DOIhttps://doi.org/10.2465/ganko1941.54.216

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Within recent years, the meteorite has become an interesting material on the geochemistry and the cosmochemistry. The Komagome iron meteorite had been one of the doubtfull meteorite in Japan. According to literatures, it fell 18th April 1926 in Tokyo and was 238g (weight). The present paper describes the following results. Ni and Co contents of this iron meteorite were about 8.0% and about 0.5% respectively. On the distribution pattern of the schreibersite, it was shown by the electron probe X-ray microanalyzer. The schreibersite was always occupied the center of the troilite phase.

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カムチヤッカにおける第三紀花崗岩類の研究の展望

生出慶司

1965 年 54 巻 6 号 p. 222-234
発行日: 1965/12/05
公開日: 2008/08/07

DOIhttps://doi.org/10.2465/ganko1941.54.222

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