11:45 〜 12:00
[SVC30-11] Melt extraction from crystal mush leading to the 1593 explosive basaltic andesite eruption of Raung volcano, Indonesia: a preliminary study
キーワード：explosive basaltic, crystal mush, Plinian, Raung
Explosive basaltic eruptions, although uncommon, represent a significant volcanic phenomenon as it may cause massive destruction such as in Tarawera (New Zealand), Masaya (Nicaragua), and Etna (Italy). Understanding the magmatic processes that lead to such eruptions is important to recognize the precursor of similar eruptions in the future. Recent studies in the large silicic magma chamber suggest that melt extraction from crystal mush, along with volatile accumulation, can produce eruptible magma capable of causing explosive eruptions. The basaltic andesite scoria fall from the Raung 1593 eruption presents an important case study for similar phenomenon, particularly in mafic to intermediate magma system. We applied a comprehensive approach including petrography, SEM-EDS, mineral and glass chemistry analysis with EPMA, whole rock geochemistry, thermobarometer estimations, and crystallization modeling using rhyolite-MELTS. The Raung scoria (whole rock 54.2 wt% SiO2, groundmass glass 52-56 wt% SiO2) primarily contains mafic plagioclase antecrysts (An>80), olivine (Mg#62-76), and rare clinopyroxene (Mg#64-76). Crystallization modeling through Rhyolite-MELTS indicate that the basaltic andesite magma responsible for the Raung 1593 explosive eruption was produced by melt extraction from 80-90% crystallization of basaltic magma, under pressures of 2-3 kbar, and at approximately 1000°C. The crystal mush was continuously recharged by mafic magma, as evidenced by mingling texture, disequilibrium features, and fluctuation of plagioclase composition. This finding enhances our understanding of the magmatic processes leading to explosive basaltic eruptions and highlight the importance of studying pre-eruptive conditions to predict future volcanic activities.