[SVC50-P10] Eruption history and magma plumbing system of Akanfuji in the Me-akan volcano, eastern Hokkaido, Japan
Keywords:Me-akan volcano, Akanfuji, Magma mixing
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. 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. Zoning profiles of these phenocrysts show timing of magma mixing. We can estimate the time from mixing of the basaltic magmas to the eruption.