日高変成帯,札内川七ノ沢におけるIタイプ・Sタイプトーナル岩マグマの起源:Sr・Nd同位体比からの検討  [in Japanese] Origin of the I- and S-type tonalite magma in the Satsunai-gawa Shichino-sawa river region of the Hidaka metamorphic belt, Hokkaido, northern Japan: Inferences from Sr and Nd isotopic compositions  [in Japanese]

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Author(s)

Abstract

日高変成帯中部地域に分布する37 MaのIタイプとSタイプトーナル岩のSrとNdの同位体比組成から,トーナル岩類の成因を検討した.<br>Iタイプの角閃石黒雲母トーナル岩は砂泥質変成岩類に貫入し,その周囲にSタイプの白雲母黒雲母トーナル岩を形成している.その同位体比組成変化は壁岩の砂泥質岩との同化分別結晶作用に起因する.また,Nd<i>I</i>は変成帯下部層の苦鉄質変成岩類と一致しない.このことから,角閃石黒雲母トーナル岩マグマの起源物質は苦鉄質変成岩類ではない.その候補となるのは,音調津地域のノーライトを形成した苦鉄質マグマと同等の物質であろう.

The Hidaka Metamorphic Belt (HMB) is a tilted crustal section of a magmatic arc formed by magmatic activities at 37 and 19 Ma. We investigated the Sr and Nd isotopic compositions of the 37-Ma I- and S-type tonalites distributed in the central part of the HMB to clarify their origins.<br>Emplacement of I-type hornblende-biotite tonalite magma triggered partial melting of metamorphic pelitic-psammitic country rocks, resulting in the <i>in situ</i> formation of migmatitic S-type muscovite-biotite tonalite. The Sr and Nd isotopic ratios of the hornblende-biotite tonalites are increasingly enriched with increasing whole-rock SiO<sub>2</sub> concentrations, suggesting that the magma experienced fractional crystallization and assimilated gneissic country rocks<br>The discordance of the Nd isotopic compositions of the hornblende-biotite tonalites compared with the mafic metamorphic rocks in the lower sequence of the HMB indicates that the hornblende-biotite tonalite magma was not derived exclusively from mafic metamorphic sources. Isotopic signatures show that the magma source was likely similar to that of synchronous norites in the Oshirabetsu region.

Journal

  • The Journal of the Geological Society of Japan

    The Journal of the Geological Society of Japan 120(11), 393-412, 2014

    The Geological Society of Japan

Codes

  • NII Article ID (NAID)
    130004756759
  • NII NACSIS-CAT ID (NCID)
    AN00141768
  • Text Lang
    JPN
  • ISSN
    0016-7630
  • NDL Article ID
    025939720
  • NDL Call No.
    Z15-174
  • Data Source
    NDL  J-STAGE 
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