著者

後藤 芳彦 合地 信生

出版者

特定非営利活動法人日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.36, no.1, pp.37-50, 1991-04-15

被引用文献数

2

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Quaternary subaqueous volcanic rocks are widely distributed in the Shiretoko Peninsula, Northeast Hokkaido, Japan. They are composed of andesitic to basaltic hyaloclastites, which are associated with comagmatic dykes and epiclastic volcanic breccias. The geology, petrography and major element compositions of these volcanic rocks from the Cape Shiretoko area were examined to reconstruct the submarine volcanoes in the area. The volcanic rocks in the area are composed of hyaloclastites and epiclastic volcanic breccias. Hyaloclastites are divided into two types. One is composed of pillows with concentric fractures and angular fragments in a cogenetic matrix, and the other is composed of angular fragments in a cogenetic matrix. Epiclastic volcanic breccias are composed of subrounded to rounded volcanic fragments in a fine matrix. These volcaniclastic rocks are overlapped one another, and form two dome structures which are intruded by radial swarms of comagmatic dykes. One of the radial dyke swarm has a volcanic neck in the center. These facts are suggestive of two submarine volcanic cones with radial dyke swarms. The authors revealed two submarine polygenetic volcanoes which have been formed by island arc volcanism with a wide range of composition (SiO_2 = 48 - 65 wt%) during the early to middle Pleistocene.