4:15 PM - 4:30 PM
[SVC46-01] A petrological test of the earthquake-trigger model of the Mt. Fuji Hoei eruption
Keywords:Fuji Volcano, Hoei Eruption, Hoei Earthquake, Eruption Trigger, Tracer Element Diffusion
We found reverse zonings of plagioclase phenocrysts in the basaltic scoriae. The phenocrysts were considered to have been derived from the dacite magma because their core compositions are consistent with those in the silicic magma initially erupted in the Hoei sequence. Based on the measured MgO concentration profiles, we can estimate the timescale of magma mixing and then test the scenario that the Hoei eruption was triggered by the Hoei earthquake. The temperature of basaltic magma of the Hoei eruption was estimated to be 1080-1180 (Sato & Hara, 1990). With this temperature range, the timescales of magma mixing were calculated to be 45.9, 9.6 and 2.2 days at 1080, 1130 and 1180 ℃, respectively. Because these estimated timescales are shorter than 49 days, the mixing should have started after the Hoei earthquake. On the other hand, the estimated timescales are longer than the duration of the Hoei eruption, showing that the mixing was not syn-eruptive but preeruptive. These results support a model that the Hoei earthquake triggered the injection of basaltic magma into the shallow dacite magma chamber, leading to the Hoei eruption.