Sulfur loss from subducted altered oceanic crust and implications for mantle oxidation
Jesse B. Walters, Alicia Cruz‐Uribe, Horst R. Marschall
Abstract
Oxygen fugacity ( fO 2 ) is a controlling factor of the physics of Earth's mantle; however, the mechanisms driving spatial and secular changes in fO 2 associated with convergent margins are highly debated. We present new thermodynamic models and petrographic observations to predict that oxidised sulfur species are produced during the subduction of altered oceanic crust. Sulfur loss from the subducting slab is a function of the protolith Fe 3+ /Fe ratio and subduction zone thermal structure, with elevated sulfur fluxes predicted for oxidised slabs in cold subduction zones. We also predict bi-modal release of sulfur-bearing fluids, with a low volume shallow flux of reduced sulfur followed by an enhanced deep flux of sulfate and sulfite species, consistent with oxidised arc magmas and associated copper porphyry deposits. The variable SO x release predicted by our models both across and among active margins may introduce fO 2 heterogeneity to the upper mantle.