積丹半島西南部の地質と火成活動 : とくに,層序とハイアロクラスタイトについて

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The southwestern coast of the Shakotan Peninsula consists of Neogene Tertiary formations, such as the Kayanuma, Tomari, and Tohmarugawa formations in ascending order. A granodiorite-quartz porphyry and many dikes of altered andesite, basaltic andesite and hornblende dacite intruded in the Tomari formation. The Tomari formation can be divided into four members viz. the Furushiki conglomerate, Maenokogawa mudstone-tuff, Kozawa sandstone-tuff, and Kabuto volcaniclastic rocks members in ascending order. The Kabuto volcaniclastic rocks member is subdivided into the lower, middle, and upper beds. The lower and middle beds are mainly composed of hyaloclastites of altered quartz bearing hornblende andesite, whereas the upper bed is largely composed of those of hypersthene augite andesite. The andesitic hyaloclastites seem to have formed by jointing and fragmentation of viscous auto-intrusive bodies due to quenching and the ir movement at the time of eruption. They are largely divided into two types, i.e. hyaloclastites with and without pillows. The difference in forms of hyaloclastites may probably depend on difference in the viscosity of magma. The trend of the auto-intrusive body swarms, from which the hyaloclastites were fed, is considerably uniform within each bed, but different from each other in the these beds of the Kabuto volcaniclastic rocks member. The Middle Miocene sedimentary basin in this area was generated at the western part of the axial upheaval zones of the Shakotan Peninsula trending from NW to SE, then the submarine andesitic volcanism characterized by fissure eruptions in a tensional field is considered to have occurred yielding a number of auto-intrusive bodies and other dikes.
日本地質学会の論文
1979-03-30

積丹半島西南部の地質と火成活動 : とくに,層序とハイアロクラスタイトについて

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