北上山地,岩泉・階上・宮古花崗岩類の化学的性質 : 特に「乙茂型」花崗岩類について
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概要
- 論文の詳細を見る
The Iwaizumi, Hashikami and Miyako granites, which are Cretaceous intrusives in northern Kitakami mountains, belong to zone II (KATADA, 1974). On the whole, they have many common characters in regard to mode of occurrence, petrography, petrochemistry and mineral chemistry. With respect to petrochemical features, however, the Miyako granites are partially different from other two. In the Iwaizumi and Hashikami granites, so-called "Otomo type" granites which are characterized by high SiO_2 and Na_20 and low K_2O occur. In Miyako granites, resemblances to the "Otomo type" occur. Both the "Otomo type" granite and its resemblance contain low Th and U. The Iwaizumi granites have a narrow range of δ^<18>O values, which are rather lower than those of the Ryoke and San-yo granites. From δ^<18>O value assimilation of ^<18>O-rich material in granitic magma, which was proposed as genesis of "Otomo type" by KANO (1959), was not supported. Judging from the following evidences it is considered that magma of the "Otomo type" have been rich in water: mutual relation between quartz and biotite crystals observed under the microscope, oxygene isotopic ratio of quartz and biotite, and experiments carried out by MAALE and WYLLIE (1975) and others. The granitic rocks showing high SiO_2, Na_2O and low K_2O in composition are found in "Tertiary granites", however other compositions of the granites are different from those of "Otomo type" granites. This suggests that origin of "Otomo type" granites is different from that of "Tertiary granites".
- 日本地質学会の論文
- 1979-09-20