Zircon U–Pb ages of the Kashiwagi Unit of the accretionary complex in the Northern Chichibu Belt, Kanto Mountains, central Japan

  • Tominaga Kohei
    Doctoral Program in Earth Evolution Sciences, Graduate School of Life and Environmental Sciences, University of Tsukuba (Research Assistant, AIST, Geological Survey of Japan, Research Institute of Geology and Geoinformation)
  • Hara Hidetoshi
    AIST, Geological Survey of Japan, Research Institute of Geology and Geoinformation
  • Tokiwa Tetsuya
    Faculty of Science, Shinshu University

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  • 関東山地に分布する北部秩父帯付加コンプレックス柏木ユニットのジルコンU–Pb 年代
  • 概報 関東山地に分布する北部秩父帯付加コンプレックス柏木ユニットのジルコンU-Pb年代
  • ガイホウ カントウ サンチ ニ ブンプ スル ホクブ チチブタイ フカ コンプレックス カシワギ ユニット ノ ジルコン U-Pb ネンダイ

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<p>The Kashiwagi Unit is the youngest unit in the Northern Chichibu accretionary complex. In this study, we measured zircon U–Pb ages from sandstone and felsic tuffaceous phyllite in the Kashiwagi Unit to determine their depositional ages. As a result, we obtained depositional age of 128.2±1.4 Ma and 126.7±2.0 Ma from two sandstone samples and 134.2±1.5 Ma from a felsic tuffaceous phyllite sample. The depositional age of this unit was previously estimated by radiolarian fossils from shale and siliceous shale, presenting a wide range from the Middle Jurassic to Early Cretaceous. The zircon U–Pb ages from the sandstones are assigned as the Early Cretaceous, presenting younger than the radiolarian age. Detrital zircon U–Pb ages of sandstone suggest that the uppermost age of the ocean plate stratigraphy of the Kashiwagi Unit is younger than the Barremian age.</p>

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