Magmatic Sulfur Dynamics in Arc Systems

Volcanic arcs, formed above subduction zones, are key sites for the cycling of sulfur between Earth’s interior and surface. As oceanic crust and sediments descend, sulfur is mobilised by slab-derived fluids into the overlying mantle wedge, where it influences the oxidation state of arc magmas and governs sulphide saturation. Within ascending magmas, sulfur speciation shifts between reduced (S2–) and oxidised (S6+) forms in response to oxygen fugacity and melt composition. Sulfide droplets nucleate and segregate early, controlling the distribution of chalcophile metals and setting the stage for magmatic-hydrothermal ore formation. On eruption, degassing releases sulfur gases that impact climate and atmospheric chemistry. Understanding these interconnected processes—from deep‐mantle inputs to surface emissions—is essential for assessing volcanic hazards, ore genesis and the global sulfur cycle.

Research from Nature Portfolio

Investigations into micrometric sulphide-volatile compound drops have revealed a mechanism by which sulphide blebs and gas bubbles coalesce at melt interfaces, oxidising to magnetite and efficiently transporting sulfur and chalcophile metals into shallow magmatic-hydrothermal systems. High-pressure studies of sub-arc mantle peridotites have identified both crystalline anhydrite and dissolved sulfate in melt inclusions, demonstrating S6+–Fe2+ redox coupling during slab-fluid percolation and confirming the role of slab-derived oxidising agents in arc magma genesis. Quantitative analyses of high-pressure rocks and vein assemblages show that most subducted sulfur remains reduced and is largely carried into the deep mantle, with only a modest flux reaching the mantle wedge—challenging previous assumptions about slab-to-wedge sulfate addition and its role in oxidising sub-arc magmas.

Magmatic Sulfur Dynamics in Arc Systems publication trend

The graph below shows the total number of articles in magmatic sulfur dynamics in arc systems across all publications each year (not limited to Nature Index journals).

Technical terms

Subducted slab: The descending plate of oceanic lithosphere carrying sediments and altered crust into the mantle.
Mantle wedge: The portion of the upper mantle above the subducting slab where arc magmas form.
Sulfide saturation: The condition when a silicate melt becomes capable of exsolving immiscible sulfide liquid.
Sulfur speciation: The oxidation state of sulfur in melts (e.g. S2– vs S6+), controlled by oxygen fugacity and melt chemistry.
Redox state (fO2): A measure of the oxidation potential of a melt, affecting mineral stability and volatile behavior.
Melt inclusion: A trapped pocket of melt within a crystal, preserving pre-eruptive volatile and trace element signatures.

References

1. Transfer of sulfur and chalcophile metals via sulfide-volatile compound drops in the Christiana-Santorini-Kolumbo volcanic field. Nature Communications (2024).
2. Oxidising agents in sub-arc mantle melts link slab devolatilisation and arc magmas. Nature Communications (2018).
3. Uncovering and quantifying the subduction zone sulfur cycle from the slab perspective. Nature Communications (2020).
4. Sulfur from the subducted slab dominates the sulfur budget of the mantle wedge under volcanic arcs. Earth and Planetary Science Letters (2023).
5. Compositional and temperature effects on sulfur speciation and solubility in silicate melts. Earth and Planetary Science Letters (2019).
6. The S content of silicate melts at sulfide saturation: New experiments and a model incorporating the effects of sulfide composition. American Mineralogist (2017).