2:30 PM - 2:45 PM
[SVC37-04] Probing magmatic processes just prior to historic eruptions at Sakurajima volcano: Toward understanding “magma pre-charge”
Keywords:Sakurajima volcano, magnetite, diffusion
Magnetite is a mineral suitable for investigating short-timescale pre-eruptive processes because of its fast element diffusion (i.e., high time resolution) compared to common phenocrystic silicates. We have analysed chemical compositions of more than 300 magnetite phenocrysts in pumices and lavas from the historic eruptions. The magnetite phenocrysts showed scarce zoning in each crystal (mostly within 1 Usp mol%), while their compositional range is wide (e.g., 27–45 Usp mol% for the 1914–1915 eruption). This indicates that the eruptions had initiated from a magma reservoir heterogeneous in at least either temperature, melt composition, or oxygen fugacity, and that this heterogeneity had not been perturbed prior to the eruptions. Therefore, widely accepted models for eruption trigger, such as new magma injection and overturn of stratified magma reservoir are not likely to apply to these historic Plinian eruptions.