巻号一覧
68 巻, 3 号
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仲井 豊, 山口 満寿美, 中西 由美子1973 年 68 巻 3 号 p. 71-77
発行日: 1973/03/05
公開日: 2008/08/07
ジャーナル フリーThe Ibaragi granitic complex comprises four rock types, that is, (I) medium-grained quartz diorite, (II) medium-grained adamellite, (III) fine-grained porphyritic granite and (IV) fine-grained adamellite. These granitic rocks intruded into Paleozoic formations successively from type I to IV in the late Cretaceous age.
Zircon crystals from these granitic complex have been studied on their crystal habit, length along the c-axis and breadth along the a1 or a2 axis.
A crystal habit which has two prisms and one pyramid increases towards the later intrusion. A growth trend of zircon populations is indicated by the “a” value, that is, ratio of standard deviation of length by that of breadth. The “a” value decreases towards the later intrusion.
The metamict zircon is most abundant in the fine-grained adamellite that is the latest intrusive rocks.
Parameters such as crystal habit or “a” value vary continuously with the characters of the host rocks.抄録全体を表示PDF形式でダウンロード (1780K) -
その3.形成機構と成因的考察矢内 桂三1973 年 68 巻 3 号 p. 78-86
発行日: 1973/03/05
公開日: 2008/08/07
ジャーナル フリーThe acidic rocks in northern Ashio mountains area are classified into following groups, based on their stuctural state and chemical composition of feldspars, and scale of the rock bodies. Matsuki and Sori granitic rocks are larger bodies, the lowest temperature type (430-480°C apparent temperature after Barth), the lowest content of Ab (9-14 wt%) in K-feldspars and low temperature plagioclase. Adamellites and granodiorite in Chuzenji acidic rocks are of intermediate scale, containing high temperature type (530-580°C) and high Ab content (17-24%), and low-intermediate plagioclase. Porphyries and welded tuffs contain the highest type (530-730°C) and highest Ab content (18-33%), and structurally high state plagioclase. Then, it is expected that adamellites and granodiorite are not related in origin to Matsuki and Sori granitic rocks, but porphyries and welded tuffs. This opinion agrees with field occurrences, ages of emplacement and others (Yanai, 1972, 1973).
Igneous activities of Chuzenji acidic rocks was taken place as follows (Fig. 2), formation of the magma reservoir, eruption of rhyolite lava, consolidation of vents and increasing vapor pressure in magma reservoir, eruption of voluminous acidic pyroclastic flows, caldera collapse, intrusion of serverl porphyries, and intrusion of granitic rocks at the latest stage.
Formation of caldera coincides well with the negative Bouguer anomaly.抄録全体を表示PDF形式でダウンロード (446K) -
1973 年 68 巻 3 号 p. 87-96
発行日: 1973年
公開日: 2012/07/13
ジャーナル フリーPDF形式でダウンロード (1015K)
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