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Subducting serpentinites release reduced, not oxidized, aqueous fluids.
F Piccoli1, J Hermann2, T Pettke2
1University of Bern, Institute of Geological Sciences, Balzerstrasse 1+3, 3012, Bern, Switzerland. francesca.piccoli@geo.unibe.ch.
Scientific Reports
|December 22, 2019
Summary
Serpentinite dehydration during subduction produces reducing fluids, challenging the idea that these fluids cause oxidized arc magmatism. This impacts understanding of mantle wedge metasomatism and global volatile cycles.
Area of Science:
- Geochemistry
- Petrology
- Mineral Physics
Background:
- Primitive arc magmas exhibit higher oxidation states than mid-ocean-ridge basalts.
- A prevailing model suggests slab-derived fluids, rich in sulfur dioxide (SO2) and carbon dioxide (CO2), oxidize the sub-arc mantle wedge.
Purpose of the Study:
- To quantify oxygen fugacity (fO2) and fluid speciation during serpentinite dehydration in subduction zones.
- To evaluate the role of serpentinite-derived fluids in arc magmatism's oxidation.
Main Methods:
- Integration of petrographic analysis with thermodynamic modeling.
- Quantification of oxygen fugacity (fO2) and fluid composition.
Main Results:
- At fore-arc conditions, serpentinite dehydration yields fluids with minor sulfur under oxidizing conditions (near quartz-fayalite-magnetite buffer).
- At sub-arc depths, dehydration occurs under more reducing conditions, generating fluids rich in hydrogen sulfide (H2S).
Conclusions:
- The study challenges the paradigm that serpentinite-derived fluids are the primary cause of oxidized arc magmatism.
- Findings have significant implications for understanding subduction zone geodynamics, global volatile cycling, and redox processes.
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