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There is a lack of consensus regarding the roles of sulfide saturation versus volatile degassing on the partitioning of Cu and Ag during differentiation and eruption of convergent margin magmas. Because of their oxidized character, volatile‐rich magmas from the Eastern Manus Back‐arc Basin (EMBB) only reach sulfide saturation following magnetite‐driven reduction of the melt: the so‐called “magnetite crisis.” If sulfide saturation typically precedes volatile saturation, the magnetite crisis will limit the proportion of Cu and Ag that can partition from the melt into an exsolving volatile‐rich phase, which may contribute to the sporadic occurrence of magmatic‐hydrothermal ore deposits at convergent margins. However, it is unclear whether the magnetite crisis is a common or rare event during differentiation of volatile‐rich magmas. We report major and trace element data for submarine volcanic glasses from the Tonga arc …