漸新統紅葉山層の流紋岩質凝灰岩中に見い出された変成岩片とその意義 : 北海道中央部の古第三紀テクトニクスに関連して  [in Japanese] Finding of metamorphic rock fragments in rhyolitic tuff beds of the Oligocene Momijiyama Formation, central Hokkaido, Japan : implications in the Paleogene tectonism of central Hokkaido  [in Japanese]

Access this Article

Search this Article

Author(s)

    • 川上 源太郎 KAWAKAMI Gentaro
    • 北海道大学大学院理学研究科地球惑星科学専攻 Division of Earth and Planetary Sciences, Graduate School of Science, Hokkaido University
    • 川村 信人 KAWAMURA Makoto
    • 北海道大学大学院理学研究科地球惑星科学専攻 Division of Earth and Planetary Sciences, Graduate School of Science, Hokkaido University
    • 在田 一則 ARITA Kazunori
    • 北海道大学大学院理学研究科地球惑星科学専攻 Division of Earth and Planetary Sciences, Graduate School of Science, Hokkaido University

Abstract

北海道中央部夕張川地域に分布する下部漸新統紅葉山(もみじやま)層に挟在する流紋岩質凝灰岩層から,砂泥質岩起源の変成岩片を見い出した.流紋岩質凝灰岩層は典型的な逆級化-正級化構造を示し,重力流堆積物であると考えられる.変成岩片の大部分は砕屑物として混入したもので,起源となる変成岩類が珪長質火山活動場の基盤浅部を構成していたと考えられる.変成岩片には,多様な変成度のものが認められる.斑状変晶ザクロ石はMnやCaに富む化学組成のものが多く,緑色片岩相~角閃岩相の変成度を示す.日高変成帯は紅葉山層堆積盆の近傍に位置する高温型変成帯であり,これらの変成岩片の起源として想定される.とりわけザクロ石の化学組成の特徴は,日高変成帯と一連の変成作用で形成された冬島変成岩類のザクロ石とよく類似する.日高変成帯の陸化は一般に後期中新世とされているが,下部漸新統からの変成岩片の発見は,日高変成帯の低変成度部がそれよりも早期に上昇したことを示す.

Pelitic and psammitic metamorphic rock fragments are found in rhyolitic tuff beds of the Lower Oligocene Momijiyama Formation in Yubari-gawa area of central Hokkaido, Japan. The host rhyolitic tuff bed shows typical inverse-to-normal grading, and is interpreted as sediment-gravity-flow deposits. Except for a few cases, the metamorphic rock fragments are considered to be derived as detrital fragments from the metamorphic rocks composing shallow basement beneath felsic volcanics. The metamorphic rock fragments show various metamorphic grades up to the amphibolite facies. Chemical composition of garnets in metamorphic rock fragments and detrital garnets in the tuff bed is characteristically rich in Mn and/or Ca, indicating the greenschist facies to amphibolite facies. The Hidaka metamorphic belt is a nearby low P/T metamorphic belt that is supposed to be a source region of the metamorphic rock fragments. Chemical composition of the garnet grains is similar to that of the Fuyushima metamorphic rocks, a possible low-grade equivalent of Hidaka metamorphic rocks. Timing of the exhumation of the Hidaka metamorphic rocks is generally supposed to be the Late Miocene. The finding of metamorphic rock fragments from the Lower Oligocene tuff beds, however, suggests earlier uplifting of the low-grade Hidaka metamorphic rocks.

Journal

  • The Journal of the Geological Society of Japan

    The Journal of the Geological Society of Japan 108(4), 235-248, 2002-04-15

    The Geological Society of Japan

References:  46

Cited by:  2

Codes

  • NII Article ID (NAID)
    110003013237
  • NII NACSIS-CAT ID (NCID)
    AN00141768
  • Text Lang
    JPN
  • Article Type
    Journal Article
  • ISSN
    00167630
  • NDL Article ID
    6148075
  • NDL Source Classification
    ZM49(科学技術--地球科学--地質)
  • NDL Call No.
    Z15-174
  • Data Source
    CJP  CJPref  NDL  NII-ELS  J-STAGE 
Page Top