伊豆半島,多賀火山初期噴出物としての畑玄武岩類 : 静岡県丹那盆地付近の地質とK-Ar年代

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Taga Volcano, in northern part of the Izu Peninsula, central Japan, is a large Quaternary strato volcano made of andesite and basalt. The Hata Basalts underlying the Taga volcanic rocks is a pile of pyroclastics with some lava flows mainly of basalts which include the most mafic basalt in the late Tertiary to Quaternary volcanic rocks of north Izu and Hakone region. This Basalts has been treated as the late Tertiary product by previous workers. In order to clarify the volcano-stratigraphic relationship between the Hata Basalts and the Taga volcanic rocks, geologic investigations were carried out in and around the Tanna Basin, and the core and cuttings samples from three 500-600 m drill holes in the Tanna Basin were examined. The Hata Basalts is lithologically characterized by dominant pyroclastics, especially high-temperature oxidized, reddish-brown agglutinate, whereas the products of Taga Volcano are characterized by dominant lava flows. The Hata Basalts is overlain by the Taga volcanic rocks (TV_4 and TV_5) unconformably at the eastward of the Tanna Basin, and overlain by the Shimo-Tanna Shales and the Taga volcanic rocks unconformably at the westward. Petrography and major elements chemistry suggest that both the Hata Basalts and the Taga volcanic rocks are petrologically very similar to each other. K-Ar dating of two rock samples of the Hata Basalts and one sample of Taga Volcano revealed that they were products of almost the same age, around 600-700 ka. All the samples dated can be correlated to the Brunhes normal polarity epoch. We conclude that the Hata Basalts is the early stage products of Taga Volcano.
特定非営利活動法人日本火山学会の論文
1993-04-01

伊豆半島,多賀火山初期噴出物としての畑玄武岩類 : 静岡県丹那盆地付近の地質とK-Ar年代

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