Multiple constraints on oxygen fugacity of the highly evolved magmas of Changbaishan volcano (China/North Korea)

Silicic caldera volcanoes normally cause adverse effects on human life since they often generate some of the largest and most catastrophic volcanic eruptions and eject massive amounts of gases (e.g., H₂O, CO₂, S, Cl, and F) into the stratosphere, potentially leading to extreme climate conditions. Oxygen fugacity (fO₂) is a vital chemical parameter controlling the geochemical behavior of multivalent elements (e.g., Fe, V, S, and C) but also influences magma degassing and magmatic evolution processes. Thus, studying the relationships between redox states and magma evolution is essential for the interpretation of mineral and residual liquid compositions in peralkaline felsic magmas.

Changbaishan is located on the border between the Democratic People’s Republic of Korea and China and has violently erupted large-volume volcanic lavas and ashes in the past 250,000 years. Previous works have shown that the eruptions of Changbaishan volcano produced a large variety of different rocks ranging from basalt over trachyte to rhyolite. Up to now, only few studies focused on the pre-eruptive fO₂ range of the highly evolved magmas of Changbaishan volcano and on the possible impact of redox state on eruption explosivity and liquid lines of descent.

In this study, we evaluated the redox states of Changbaishan magmas using Fe-Ti oxide and magnetite-melt oxybarometry. Our results reveal that trachyte and rhyolite magmas exhibit a broad range in oxygen fugacity spanning from FMQ+1 to possibly FMQ-3, where rhyolitic magmas indicate more reducing conditions than trachytic magmas. Different possible hypotheses are discussed to explain this feature, including degassing of sulfur species (notably SO₂), magma mixing or crustal contamination. This work provides new insights into the evolution of pre-eruptive redox states in magma reservoirs of Changbaishan volcano and potential critical factors controlling eruption explosivity.