High‐Sulphur Arc Volcano at Mt. Pinatubo Induced by Ridge Subduction

ABSTRACT Sulphur dioxide is a poisonous volatile released during volcanic eruptions, which may reach fatal concentrations in arc volcanoes. Mt. Pinatubo is a high‐sulphur volcano that released nearly 15–20 Mt of SO 2 into the stratosphere. The mechanism for sulphur enrichment remains obscure. Here we propose that the subduction of the young (∼ 15 Ma) Huangyan seamount chain with abundant coral reefs, and a consequently opened slab window, may have contributed to the high SO 2 and CO 2 emissions. The subducted young oceanic crust undergoes partial melting, especially at slab tear locations, generating oxidized sulphate‐rich adakitic dacite magma with total sulphur concentrations up to ∼1.2 wt%. Meanwhile, reduced magmas with high sulphide/sulphate ratios, formed through asthenosphere upwelling during slab window opening, probably inject into the adakitic dacite magma chamber. The mixing of these two types of magmas forms abundant SO 2 through sulphate reduction. The consequently significant SO 2 degassing ultimately promotes explosive eruptions.