長野県北部～東部における新生代後半の構造運動と火山活動

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書誌事項

タイトル別名
  • Late Neogene Tectonisms and Volcanisms in the Northern-Eastern Part of Nagano Prefecture, Central Japan
  • ナガノケン ホクブ トウブ ニ オケル シンセイダイ コウハン ノ コウゾウ
  • (特集「新生代末期の火成活動」(第29回総会シンポジウム))
  • (Symposium 「Igneous Activities in Late Cenozoic Era in Japan」(Memoirs of the 29th General Meeting of the Association for the Geological Collaboration in Japan))

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説明

Late Neogene volcanic rocks in the northern-eastern part of Nagano Prefecture were distributed in two regions separately. One is in the western area of the Central Uplifting Belt (Fossa Magna Reserch Group, 1958), the other is in the western area of it. In this paper we arranged these volcanisnis from the view point of tectonic developments. The Middle Miocene to Early Pliocene marine sediments has a wide distribution in the western area of the central Uplifting Belt. Depositions and distributions of these materials may be controled by the basin-forming movement during the Middle Miocene to Early Pleistocene time. The Komiji, the Takafu and the Hikage synclines were main sedimentary basins which generated during this time. The syncline axes in these areas has a NNE-SSW direction. During the Middle Pliocene to Late Pliocene time, a new tectonic movement may be generated in this area. This movement is characterized by the basaltic-andesitic volcanics which were composed of pyroxene andesite-hornblende andesite lava flows and pyroclastics. They were restricted in Hijiriyama, Arakurayama and Togakushiyama districts. It is remarkable that the Pliocene volcanism had taken place in this depression area with NE-SW direction. Because the NE-SW direction in the western area seems represents the Late Pliocene-Early Pleistocene tectonic movement. On the other hand, the characters of tectonism and volcanism in the eastern area of the Central Uplifting Belt seems very different from those in the western area. Since the Middle Miocene (Bessho stage), this area might have a tendency of uplifting, so during the Late Miocene to Early Pliocene time there might be no sedimentary basins in the greater part of this area. The Komoro and The Enrei sedimentary basins had being in existence in the Middle Pliocene to Early Pleistocene time. The former is in NNE-SSW tectonic direction, the later one is in NW-SE direction. In these basins, violent volcanisms had taken place rapidly and it supplied a large quantity of pyroclastics and lava flows. The upper part of them was characterized by so called flat lavas, which consist of mainly hypersthene augite andesite and hornblende andesite lava flows.

収録刊行物

  • 地球科学

    地球科学 30 (2), 73-80, 1976

    地学団体研究会

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