Subducting serpentinites release reduced, not oxidized, aqueous fluids.

Autor: Piccoli F; University of Bern, Institute of Geological Sciences, Balzerstrasse 1+3, 3012, Bern, Switzerland. francesca.piccoli@geo.unibe.ch., Hermann J; University of Bern, Institute of Geological Sciences, Balzerstrasse 1+3, 3012, Bern, Switzerland., Pettke T; University of Bern, Institute of Geological Sciences, Balzerstrasse 1+3, 3012, Bern, Switzerland., Connolly JAD; Department of Earth Science, Swiss Federal Institute of Technology, Zurich, Switzerland., Kempf ED; University of Bern, Institute of Geological Sciences, Balzerstrasse 1+3, 3012, Bern, Switzerland., Vieira Duarte JF; University of Bern, Institute of Geological Sciences, Balzerstrasse 1+3, 3012, Bern, Switzerland.
Jazyk: angličtina
Zdroj: Scientific reports [Sci Rep] 2019 Dec 20; Vol. 9 (1), pp. 19573. Date of Electronic Publication: 2019 Dec 20.
DOI: 10.1038/s41598-019-55944-8
Abstrakt: The observation that primitive arc magmas are more oxidized than mid-ocean-ridge basalts has led to the paradigm that slab-derived fluids carry SO 2 and CO 2 that metasomatize and oxidize the sub-arc mantle wedge. We combine petrography and thermodynamic modelling to quantify the oxygen fugacity (fO 2 ) and speciation of the fluids generated by serpentinite dehydration during subduction. Silicate-magnetite assemblages maintain fO 2 conditions similar to the quartz-fayalite-magnetite (QFM) buffer at fore-arc conditions. Sulphides are stable under such conditions and aqueous fluids contain minor S. At sub-arc depth, dehydration occurs under more reducing conditions producing aqueous fluids carrying H 2 S. This finding brings into question current models in which serpentinite-derived fluids are the cause of oxidized arc magmatism and has major implications for the global volatile cycle, as well as for redox processes controlling subduction zone geodynamics.
Databáze: MEDLINE
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