南部北上帯の奥火の土花崗岩体は先シルル紀基盤か?

  • 足立 守
    Department of Earth and Planetary Sciences, School of Science, Nagoya University
  • 鈴木 和博
    Department of Earth and Planetary Sciences, School of Science, Nagoya University
  • 与語 節生
    Department of Earth and Planetary Sciences, School of Science, Nagoya University
  • 吉田 鎮男
    Geological Institute Faculty of Science, University of Tokyo

書誌事項

タイトル別名
  • The Okuhinotsuchi granitic mass in the South Kitakami terrane: pre-Silurian basement or Permian intrusives.

抄録

Chemical Th-U-total Pb isochron (CHIME) ages were determined on monazite, xenotime and zircon from coarse-grained leucogranite, quartzose pegmatite and residual arkose (weathered granite) of the Okuhinotsuchi granitic mass (Okuhinotsuchi Mass) in the South Kitakami terrane, Northeast Japan. Leucogranite, characterized by higher K2O/Na2O and lower CaO/(Na2O+K2O) ratios, yields latest Permian ages of 250-260 Ma for monazite and/or zircon. Some of the granite contains xenocrysts of Th-rich monazite or zircon that yields late Silurian to early Devonian ages of 400-410 Ma. Quartzose pegmatite or quartz vein, cutting in places leucogranite and rarely sediments of the Lower-Middle Silurian Okuhinotsuchi Formation, yields unequivocal CHIME ages of 240-250 Ma for Th-poor monazite, zircon and/or xenotime. Residual arkose that occurs immediately below the unconformity, is more disintegrated, altered and depleted in K2O than leucogranite. The arkose contains Th- and U-bearing minerals with different CHIME ages: (1) both Th-rich (420 Ma) and Th-poor (260 Ma) monazites, (2) zoned xenotime grains with 410-420 Ma core mantled by 350 or 250 Ma rim, (3) euhedral ca. 250 Ma zircon, or (4) rounded inherited zircon grains of ca. 500-1000 Ma. All the CHIME age data demonstrate that the Okuhinotsuchi Mass is unlikely to be the pre-Silurian basement.<br> The CHIME geochronology also reveals that the leucogranite of the Okuhinotsuchi Mass is a remnant of the source rock for some Permian granitoid clasts in the Usuginu Conglomerate in the South Kitakami terrane, whose provenance has long been an open problem.

収録刊行物

  • 岩鉱

    岩鉱 89 (1), 21-36, 1994

    一般社団法人 日本鉱物科学会

被引用文献 (3)*注記

もっと見る

詳細情報 詳細情報について

  • CRID
    1390001206216966400
  • NII論文ID
    130003884788
  • DOI
    10.2465/ganko.89.21
  • COI
    1:CAS:528:DyaK2cXislGrsbo%3D
  • ISSN
    18813275
    09149783
    http://id.crossref.org/issn/09149783
  • 本文言語コード
    en
  • データソース種別
    • JaLC
    • Crossref
    • CiNii Articles
  • 抄録ライセンスフラグ
    使用不可

問題の指摘

ページトップへ