Petrological constraints on magma storage conditions during ongoing post-caldera volcanism at Ioto volcano, Ogasawara, Japan

Active volcanism occurs at post-caldera volcanoes, which are often characterized by rapid crustal uplift due to the development of resurgent domes. Post-caldera volcanism has been attributed to the behavior of volcanic fluids in a magma storage region beneath the caldera. However, few studies have provided petrological constraints on magma storage during ongoing post-caldera volcanism. In this paper, we describe the petrological characteristics of the eruptive products from the 2022 eruption at Ioto volcano, Ogasawara, Japan, which provide a unique opportunity to examine magma storage conditions. The 2022 Ioto magma is characterized by a trachytic composition and contains ~7 vol.% phenocrysts (plagioclase, clinopyroxene, olivine, and magnetite). The clinopyroxene–liquid geothermometer and plagioclase–liquid hygrometer yield a temperature of 970 ± 30°C and water content of 1.4 ± 1.1 wt.% for the Ioto magma. The water content corresponds to a pressure of 25 ± 22 MPa, implying magma is stored at a depth of 1.2 ± 1.0 km beneath the volcano. This depth is consistent with the funnel-shaped magma body at 1–2 km depth inferred from geophysical data. As such, we conclude that the 2022 eruption was sourced from magma stored at ~1.2 km depth. Intrusion of magma through a cone sheet may have contributed to the block-like uplift of Motoyama, which is part of the ongoing post-caldera volcanism at Ioto volcano.