紀伊山地中央部の中・古生界(その4)

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書誌事項

タイトル別名
  • Mesozoic and Paleozoic Systems in the Central Area of the Kii Mountains, Southwest Japan (Part IV)
  • 紀伊山地中央部の中・古生界-4-高原川地域
  • キイ サンチ チュウオウブ ノ チュウ コセイカイ 4 タカハラガワ チイキ
  • 高原川地域
  • Mesozoic of the Takaharagawa District in Nara Prefecture

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抄録

This paper is part of our serial works on Paleozoic-Mesozoic systems in the Takaharagawa district. Five geological units are discriminated in the study area, namely Daihugendake,Wasabidani, Takahara, Obadanigawa, and Akataki Formations, intectonostratigra phically descending order. The Daihugendake.Wasabidani and Takahara Formations belong to the Chichibu Terrane, while the Obadanigawa and Akataki Formations belong to the Shimanto Terrane. The Daihugendake Formation is composed of chert-clastic sequences of Middle Triassic-Late Jurassic age. The sequences form an imbricate structure. The Wasabidani Formation is Late Jurassic melange including Middle-Late Triassic limestone, greenstone and chert blocks. The Takahara Formation comprises melange of early - middle Early Cretaceous age containing chert, limestone and greenstone blocks and the upper part of the formation is characterized by a dominance of sandstones. The Obadanigawa Formation consists mainly of Albian-Cenomanian sandstone-rich clastic sequences associated subordinately with melange which contains various blocks derived from the Chichibu Terrane. The Akataki Formation is Turonian melange containing red chert, red mudstone and green-stone blocks. These units have been stacked up to form a pile nappe structure, showing a younging age polarity from the upper unit to the lower one. Their contacts are marked by thrust faults parallel to the general trend of the strata. A slight structural discordance, however, is partly recognized between the Chichibu and Shimanto Terranes. This paper points out two possible interpretations concerning the tectonic evolution of the Chichibu and Shimanto Terranes. One interpretation is that the geological units of the two terranes were formed through successive accretionary processes from Late Jurassic to Cretaceous time. The other is that the Chichibu and Shimanto terranes were formed independently and the former has been thrust over the latter at a later stage, forming a large scale nappe structure.

収録刊行物

  • 地球科学

    地球科学 46 (3), 185-198, 1992

    地学団体研究会

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