日本海拡大時の中央および西南日本前弧域テクトニクス Tectonics in the Forearc Region of Central and SW Japan during the Japan Sea Opening

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 Studies on geologic structures including some deformation microstructures in both areas along the Median Tectonic Line (MTL) in western Shikoku and of the South Fossa Magna indicate that N-S trending horizontal compression tectonics prevailed in these areas during the earliest Middle Miocene (<i>ca.</i> 15 Ma). Also, a review of structural development in Nankai province indicates that similar compression tectonics prevailed during the periods from the Early to earliest Middle Miocene (<i>ca.</i> 20-15 Ma). These periods are nearly coeval with the timing of the Japan Sea opening. Although there is uncertainty about the reactivation of the MTL around this time, south-dipping normal faults were formed in the Sambagawa belt truncating the MTL to produce the Kuma basin (18-16 Ma), which were later reactivated as thrusts (Tobe and Hanayama thrusts), indicating inversion tectonics. In the South Fossa Magna region, not only a large amount of shortening—as much as 40-50%—was caused in the Momonoki Subgroup (earliest Middle Miocence, 16-15 Ma) by folding strata, but also the constituent quartz grains were moderately plastically deformed and microcracked followed by healing (<i>i.e.</i> healed microcracks), indicating deformation under brittle-ductile transition conditions (<i>ca.</i> 300°C) at <i>ca</i>. 15 Ma. Furthermore, slaty cleavage caused by pressure solution developed in the strata constituting the Oligocene-Early Miocene (>20 Ma) Southern Shimanto belt, and forearc sediments (18-15 Ma) as thick as 4000 m overlying these sediments with angular unconformity (<i>e.g.</i> Tanabe and Kumano Groups in the Kii peninsula) were also deformed by folding with a shortening ratio of 10-20%. All these onland geological facts in the forearc region indicate that the forearc region was in a regime of compression, while the back-arc region was in a regime of extension at the same time during the Japan Sea opening. Similar tectonics also occurred in Italy, where the Tyrrhenian Sea (back-arc basin) has opened since the Pliocene (5 Ma), while shortening tectonics shown by the development of fold and thrust belts and deep (>7 km) basins occurred at the same time in the forearc region. Although these concurrent back-arc extension and forearc shortening are difficult to interpret, they may be caused by ridge push force (<i>i.e.</i> gravity tectonics) after back-arc spreading commences so that extensional force is no longer sustained in the arc.

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  • 地學雜誌

    地學雜誌 119(2), 347-361, 2010-04-25

    公益社団法人 東京地学協会

参考文献:  45件中 1-45件 を表示

被引用文献:  3件中 1-3件 を表示

各種コード

  • NII論文ID(NAID)
    10030368979
  • NII書誌ID(NCID)
    AN00322536
  • 本文言語コード
    JPN
  • 資料種別
    ART
  • ISSN
    0022135X
  • NDL 記事登録ID
    10704955
  • NDL 雑誌分類
    ZM41(科学技術--地球科学)
  • NDL 請求記号
    Z15-169
  • データ提供元
    CJP書誌  CJP引用  NDL  J-STAGE 
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