Sodic-calcic amphiboles found from dolerite in the Nedamo Terrane, Northeast Japan

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  • Uchino Takayuki
    (AIST, Geological Survey of Japan, Institute of Geology and Geoinformation
  • Kawamura Makoto
    Department of Natural History Sciences, Graduate School of Science, Hokkaido University

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Other Title
  • 根田茂帯のドレライトから見出されたNa-Ca角閃石
  • 概報 根田茂帯のドレライトから見出されたNa-Ca角閃石
  • ガイホウ ネダモタイ ノ ドレライト カラ ミイダサレタ Na Caカクセンセキ

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Abstract

    Sodic-calcic amphiboles (winchite and richterite) occur in dolerite in the Nedamo Terrane, Early Carboniferous accretionary complex. Sodic-calcic amphiboles occur generally in high-P/T metamorphic terranes such as the Sambagawa Terrane, the Suo Terrane etc., whereas they also occur in manganese ore deposits and alkali igneous rocks. Sodic-calcic amphiboles of a high-P/T metamorphic type tend to show the feature of high-Al2O3 and low-TiO2. The sodic-calcic amphiboles of the dolerite in the Nedamo Terrane are difficult to be recognized as the high-P/T metamorphic type because they do not show the feature of high-Al2O3 and low-TiO2, that is they contain quite low glaucophane component. However, the sodic-calcic amphiboles could be formed as a metamorphic mineral in a subduction zone considering that some sodic-calcic amphiboles which show low glaucophane component occur certainly in high-P/T metamorphic rocks, bulk chemistry of the dolerite shows the feature of within-plate tholeiite, occurrence of the sodic-calcic amphiboles is different from that of sodic-calcic amphiboles in alkali igneous rock or contact aureole, and the dolerite does not undergo alteration or metasomatism.

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