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- 矢嶋 一仁
- 東北大学大学院理学研究科地学専攻 現所属: ニチアス株式会社鶴見研究所
書誌事項
- タイトル別名
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- Two types of chemical trends found in low-Ca boninite suite from Chichijima, Ogasawara (Bonin) arc
- オガサワラ グントウ チチジマ ニ サンスル テイ Ca ボニナイト ケイレツガン ノ 2ツ ノ ソセイ ヘンカ トレンド
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抄録
Chichijima, located in Ogasawara (Bonin) arc, Japan has been known as the type locality of boninite. Meanwhile, extremely evolved volcanics (SiO2>70 wt%) also occur together with the high-magnesian andesites. The evolved rocks have been considered as the products of differentiation from the boninitic parental magma by fractional crystallization processes. The differentiation processes are considered to produce low-Ca boninite through bronzite-andesite, dacite, quartz-dacite and quartz-rhyolite. Some of the quartz-dacites, however, would not be necessarily regarded as differentiates from the dacite magma. Quartz-dacites are enriched in SiO2 for the fractional crystallization products from dacite. Some quartz-dacites show mineralogical evidences of magma mixing, while such features can not be observed in the dacites. Quartz phenocrysts in the silica rich quartz-rhyolite exhibit euhedral form, but quartz-dacites have corroded quartz phenocrysts. The compositions of mafic pyroxene phenocrysts in quartz-dacites are similar to those in bronzite-andesites. Groundmass pyroxenes in some quartz-dacites include orthopyroxene and augite. In contrast, pigeonite and augite are ubiquitous groundmass pyroxenes in the quartz-free dacites. These chemical and petrographical features imply that the quartz-dacites have calc-alkalic affinities, whereas the dacites have tholeiitic affinities. The tholeiitic trend of the dacites might be formed by fractional crystallization under low fO2 conditions, judging from the crystallization of Fe-rich pigeonite phenocrysts, and the quartz-rhyolite would be produced from the dacite magma by fractional crystallization in the tholeiite suite. Mixing calculations between bronzite-andesite and quartz-rhyolite reproduce the observed chemical variations of quartz-dacites. Therefore, calc-alkalic trend of the quartz-dacites might be formed by internal magma mixing between the bronzite-andesite magma and the quartz-rhyolite magma.
収録刊行物
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- 岩石鉱物科学
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岩石鉱物科学 32 (2), 51-67, 2003
一般社団法人 日本鉱物科学会
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詳細情報 詳細情報について
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- CRID
- 1390001206525741312
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- NII論文ID
- 130000253540
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- NII書誌ID
- AA1146088X
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- COI
- 1:CAS:528:DC%2BD3sXlvFels74%3D
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- ISSN
- 13497979
- 1345630X
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- NDL書誌ID
- 6630389
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- 本文言語コード
- ja
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- データソース種別
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- JaLC
- NDL
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- 使用不可