日本地球惑星科学連合2018年大会

講演情報

[JJ] Eveningポスター発表

セッション記号 S (固体地球科学) » S-VC 火山学

[S-VC43] 火山・火成活動および長期予測

2018年5月20日(日) 17:15 〜 18:30 ポスター会場 (幕張メッセ国際展示場 7ホール)

コンビーナ:及川 輝樹(国立研究開発法人産業技術総合研究所)、長谷川 健(茨城大学理学部地球環境科学コース)、三浦 大助(一般財団法人 電力中央研究所 地球工学研究所 地圏科学領域、共同)、下司 信夫(産業技術総合研究所 活断層・火山研究部門)

[SVC43-P08] 雌阿寒岳,阿寒富士のマグマ供給システム

*佐藤 鋭一1和田 恵治2 (1.神戸大学大学教育推進機構、2.北海道教育大学旭川校)

キーワード:阿寒富士、雌阿寒岳、マグマ供給系

Akanfuji, situated in the Me-akan volcano of Eastern Hokkaido, started its eruption ca. 2.1 ka, and its activity continued for 1,100 years. During this period, 17 eruption deposits (Akf-1-Akf-17) can be discerned. The mode of the eruptions of this volcano was mainly of the scoriaceous sub-plinian type. Lava flows are often associated with the scoria eruption. The eruption history of Akanfuji is divided into five stages. In the first stage (Akf-1), scoria fall with many lithic fragments was deposited from northeast to east of the volcano. In the second stage (Akf-2-Akf-3), two larger eruptions occurred and coarse scoria falls were deposited to the northeast. In the third stage (Akf-4-Akf-13), some eruptions occurred and the scoria falls were dispersed in a northeast to southeast direction. This stage is characterized by the finding of orthopyroxene in the deposits. In the forth stage (Akf-14-Akf-16), three larger eruptions occurred and voluminous scoriae were deposited to northeast (Akf-14) and from southeast to south (Akf-15-Akf-16). In the final stage (Akf-17), fine scoria fall was deposited from northeast to southeast. Akanfuji had erupted basalts through its history. Two types of basalts (types I and II) are recognized on the basis of phenocrysts assemblage. Type I is orthopyroxene (opx) bearing olivine (ol)-crynopyroxene (cpx) basalt and Type II is cpx bearing ol-opx basalt. In the second stage, type I erupted, while in the stage 3, type II erupted. In the stages 4 and 5, the ejecta returned to the type I. Both types show mineralogical evidences of magma mixing, which are reaction products such as cpx overgrowth around opx phenocrysts, wide range of core compositions, and coexistence of normaly and reversely zoned plagioclase, olivine, and pyroxenes. We estimate the presence of A magma (cpx-rich) and B magma (opx-rich) and the types I and II are formed according to the degree of mixing of the A and B magmas.