岩石鉱物鉱床学会誌

本邦産火成岩のK-Adating (I)

河野義礼, 植田良夫

1964 年 51 巻 4 号 p. 127-148
発行日: 1964/04/05
公開日: 2008/08/07

DOIhttps://doi.org/10.2465/ganko1941.51.127

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Since 1958, the authors have planned the K-A dating of rocks and minerals, and been engaged in preparation of apparatus. By the installation of multiplier to the mass spectrometer at the end of last year, the accuracies of measurement have been remarkably increased. The mass spectrometer can be kept at high vacuum of 10-9mm Hg and the specimen belonging to such a young age as late Cenozoic can be measured under static operation. In this paper, the experiments which were carried out in our laboratory and the workings of the mass spectrometer are briefly described.
In order to ascertain the dependability of the machine through the whole operation such as argon extraction, spike argon mixing and argon isotope measurement by mass spectrometer, repeated measurements on the same specimen were done, and the reproducibility was examined. As a result, it was confirmed that the reproducibility could be obtained within the maximum errors of ±5%.
Age measurements on different minerals such as biotite and K-feldspar from the same rock were also attempted. From two specimens, 10% younger K-feldspar ages than biotite ones were measured, and from one specimen almost the same age was obtained, while from another specimen, younger biotite age than that of K-feldspar was dated due to the thermal metamor-phism at the later stage.
Regarding to granitic rocks, samples from following districts such as Ichinohe, Kitakami Mountains, Abukuma Mountains, Backbone District of Northeastern Japan, Ashio Mountainblock, Kofu Basin and Outer Zone of Southwestern Japan were dated. The most ages of the specimens from
these districts belong to Cretaceous, but the samples from Hinokami-yama, Kitakami Mountains indicated the Triassic age, and the specimens from Kofu Basin the Pliocene.
For the Cenozoic volcanics of which the stratigraphic horizons had been established, K-A datings were also done, and a high degree of consistency to geologic evidences has been found.

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京都府,河守鉱山付近の超塩基性岩体中に発見された2種類の無色雲母

黒田吉益, 佐藤満雄, 小倉義雄, 橋田栄一

1964 年 51 巻 4 号 p. 149-157
発行日: 1964/04/05
公開日: 2008/08/07

DOIhttps://doi.org/10.2465/ganko1941.51.149

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京都府,河守鉱山付近にはダンかんらん岩がかなり大きく露出しているが,その一部にpyroxeniteがあり,その中に巾数cm～数10cmの優白質脈が存在する。それは,ゆうれん石と2種の無色雲母からなるアプライト状の組織をもつ岩石である。
2種の無色雲母は,微小の液体包有物(?)をもつよごれた感じのものと,きれいなものとである。また,前者は屈折率がやや低く,後者はやや高いのではつきり区別できる。これらの光学性,化学成分,X線データなどを検討した結果,前者はmuscoviteで,後者はparagoniteとmargariteの中間的なもの(固溶体)と考えた。
Euguster and Yoderのmuscovite-paragonite joinは正しいが,化学的条件によつてはparagonite-margariteはより固溶体をつくりやすいだろうと推定した。

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舞鶴地帯の古生層の輝緑凝灰岩と貫入岩・変成岩類のうけた低度変成作用

関陽太郎

1964 年 51 巻 4 号 p. 158-161
発行日: 1964/04/05
公開日: 2008/08/07

DOIhttps://doi.org/10.2465/ganko1941.51.158

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Mafic volcanic and pyroclastic rocks forming Permian formation, mafic-ultramafic intrusive rocks and high-grade metamorphosed rocks (amphibolite and biotite-or biotite-garnet gneiss) were generally altered into the assemblages of the following minerals: chlorite, sericite, calcite, prehnite, pumpellyite, albite and quartz.
These mineral assemblages and other geological evidences show that the Maizuru Zone must have suffered the low-grade regional metamorphism of the Sangun belt in late Paleozoic or early Mesozoic time.

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鉄-ニッケル系の金属相鉱物

都城秋穂

1964 年 51 巻 4 号 p. 162-172
発行日: 1964/04/05
公開日: 2008/08/07

DOIhttps://doi.org/10.2465/ganko1941.51.162

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