巻号一覧
80 巻, 2 号
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富田 克利, 金井 敏正, 小林 哲夫, 大庭 昇1985 年 80 巻 2 号 p. 49-54
発行日: 1985/02/05
公開日: 2008/08/07
ジャーナル フリー1983年5月22日の桜島火山の噴火で,火山豆石が生成し降下した。火山豆石のX線粉末回折分析,示差熱分析および走査電子顕微鏡観察により,火山豆石中には石膏が生成しているのが認められた。また,多くの火山豆石中には球状の空隙があり,これはある程度の水分の存在下で細粒の火山灰集合体内にできた泡と考えられる。これまで桜島火山の噴火で降った新鮮な火山灰には石膏が認められないが,これらの火山灰を水で湿らすと石膏の結晶が生ずる。火山豆石中の石膏と泡の存在は,細粒火山灰とある程度の水分が,火山豆石に関する多くの生成条件の中で最も基本的なものであることを示唆する。抄録全体を表示PDF形式でダウンロード (3437K) -
周藤 賢治, 八島 隆一, 滝本 俊明1985 年 80 巻 2 号 p. 55-72
発行日: 1985/02/05
公開日: 2008/08/07
ジャーナル フリーHigh magnesian olivine basalts of lower Miocene age are distributed in the Ryozen district of the northeastern part of Fukushima Prefecture, Northeast Japan. Olivine basalts have low FeO*/MgO ratios (0.68-1.17) and high Cr contents (323-1193ppm). The olivine basalt R09 is sparsely phyric (phenocrysts of olivine and chromite 10⟨vol%), and the olivine phenocrysts have narrow compositional range (Fo=85-89) and high NiO contents (0.24-0.32%). The olivine phenocrysts of the olivine basalt R09 contain chromite only as inclusion. Fe-Mg partitioning of the olivine basalt R09 suggests that phenocryst of magnesian olivine (Fo=87) is in equilibrium with coexisting liquid (=groundmass).
These features strongly indicate that the olivine basalt R09 has primitive nature in chemical composition and may represent the primary olivine tholeiitic magma generated in the upper mantle.
Differentiated basalts having relatively high FeO*/MgO ratios may be produced from the primary magma by the fractionation of magnesian olivine, chromite and clinopyroxene.抄録全体を表示PDF形式でダウンロード (825K) -
造岩鉱物の化学組成林 信太郎, 青木 謙一郎1985 年 80 巻 2 号 p. 73-82
発行日: 1985/02/05
公開日: 2008/08/07
ジャーナル フリーChemical compositions of the rock-forming minerals in a high-alumina basalt, calc-alkaline basalts, calc-alkaline andesites from Chokai volcano were analyzed with the electron microanalyzer. The rocks of the Chokai volcano can be divided into olivine-bearing and olivine-free types on the basis of their mineralogical character. The cores of phenocryst (orthopyroxene, clinopyroxene, plagioclase and magnetite) in the olivine-free calc-alkaline andesite of stage I are unimodal in chemical compositions, and the rim of phenocrysts and microphenocrysts have similar composition to the core of the respective phenocryst. These phenocrysts tend to change the chemical composition with increasing differentiation of the host andesite. The olivine-free andesite of stage IIc is also characterized by the unimodal phenocryst compositions. The phenocrysts of olivine-bearing rocks (high-alumina basalt and olivine-bearing calc-alkaline andesite of stage I, and most of the rocks from stage II and stage III) have normally-zoned phenocrysts (olivine, calcic plagioclase and magnesian clinopyroxene) and reversely-zoned phenocrysts (sodic plagioclase, ferriferous clinopyroxene and hypersthene) in the same rock. The cores of the phenocrysts are almost constant in composition regardless of the bulk chemical compositions of the host rocks.抄録全体を表示PDF形式でダウンロード (639K)
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