北海道中央部, 五色ヶ原火山の形成史

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The Goshikigahara volcano, situated at the northern part of the Tomuraushi volcano group in Central Hokkaido, Japan, is a large Quaternary composite volcano consisting of a basal volcanic edifice (Kaundake volcano) and three overlying volcanic edifices (Ponkaundake, Chubetsudake, and Goshikidake volcanoes). The volcanic activity began with eruptions of andesitic and dacitic lava flows and pyroclastics, and produced a large stratovolcano Kaundake (ca. 1.1 Ma - 0.95 Ma). Subsequent to this activity, a dacitic stratovolcano Ponkaundake has grown on the western flank of the Kaundake cone. The main part of the Ponkaundake cone constructed prior to about 0.8 Ma. The next period of volcanic activity began at the eastern and southeastern flanks of the Kaundake cone, building up two andesitic lava plateaus, Chubetsudake (0.75 Ma) and Goshikidake (0.74 Ma), concurrently.The rock types of the Goshikigahara volcano are medium-K, calc-alkaline, two-pyroxene andesites and dacites. The eruptives from each of the four eruption centers show distinct whole-rock major element trends. Differences also exist between the modal characteristics of the eruptive products from the four centers. The petrographic and geochemical differences between the four volcanoes suggest each volcanic center had its own crustal magma chamber.
日本鉱物科学会の論文
2004-01-30