徳島県美馬市南部の三波川変成帯の変堆積岩の原岩層  [in Japanese] The parentage of low-grade metasediments in the Sanbagawa Metamorphic Belt, southern area of Mima City, Tokushima Prefecture, Japan  [in Japanese]

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Author(s)

    • 戸田 祐貴 TODA Yuki
    • 山口大学理学部地球科学教室 Department of Earth Sciences, Faculty of Science, Yamaguchi University

Abstract

構造層序や化石年代から三波川変成帯(緑泥石帯)の砂質・泥質片岩の原岩は,後期ジュラ紀以降に堆積したと推定される.徳島県美馬市南部の三波川変成帯の原岩層を特定するために,同地域の砂質片岩および泥質片岩の全岩化学分析を行った.調査地域の三波川帯は,岩相や地質構造から北部と南部に区分される.調査域の砂質片岩の地球化学的特徴は,その原岩層が南部秩父帯の中-上部ジュラ系ではないことを示している.砂質片岩と泥質片岩の地球化学的な特徴は,北部と南部がそれぞれ四万十帯北帯のKS-IIユニット(コニアシアン-カンパニアン)とKS-Iユニット(アルビアン?-前期コニアシアン)を原岩層としていることを示している.これらの結論は,四国の三波川変成帯の低度変成岩の多くがアンダープレーティングに由来する四万十帯北帯の深部相であることを意味している.<br>

Tectonostratigraphic relationships and paleontological evidence suggest a post-Middle Jurassic depositional age for the protoliths of the Sanbagawa psammitic/pelitic schists. In order to identify the parentage of low-grade metasediments in the Sanbagawa Metamorphic Belt in the southern area of Mima City, Tokushima Prefecure, we have studied the bulk chemistry of psammitic and pelitic schists in the Sanbagawa Belt. The Sanbagawa Belt in the study area can be divided into northern and southern parts on the basis of lithology and structure. Some geochemical signatures of psammitic schists differ from those of the Middle/Late Jurassic sandstones in the Southern Chichibu Belt. The geochemistry of the psammitic and pelitic schists suggests that the parents of the northern and southern parts are the KS-II Unit (Coniacian-Campanian) and KS-I Unit (Albian?-Early Coniacian) of the Northern Shimanto Belt, respectively. These conclusions imply that most of the low-grade metasediments of the Sanbagawa Belt in Shikoku are an underplated, deeper facies of the Cretaceous Shimanto accretionary complex.<br>

Journal

  • The Journal of the Geological Society of Japan

    The Journal of the Geological Society of Japan 113(4), 158-167, 2007-04-15

    The Geological Society of Japan

References:  40

Cited by:  5

Codes

  • NII Article ID (NAID)
    110006250933
  • NII NACSIS-CAT ID (NCID)
    AN00141768
  • Text Lang
    JPN
  • Article Type
    Journal Article
  • ISSN
    00167630
  • NDL Article ID
    8808023
  • 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 
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