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Title: Oxidized Sulfur Species in Slab Fluids as a Source of Enriched Sulfur Isotope Signatures in Arcs
Abstract Recycling of oxidized sulfur from subducting slabs to the mantle wedge provides simultaneous explanations for the elevated oxygen fugacity (fO2) in subduction zones, their high hydrothermal and magmatic sulfur outputs, and the enriched sulfur isotopic signatures (i.e., δ34S > 0‰) of these outputs. However, a quantitative understanding of the abundance and speciation of sulfur in slab fluids consistent with high pressure experiments is lacking. Here we analyze published experimental data for anhydrite solubility in H2O‐NaCl solutions to calibrate a high‐pressure aqueous speciation model of sulfur within the framework of the deep earth water model. We characterize aqueous complexes, required to account for the high experimental anhydrite solubilities. We then use this framework to predict the speciation and solubility of sulfur in chemically complex fluids in equilibrium with model subducting mafic and ultramafic lithologies, from 2 to 3 GPa and 400 to 800°C at logfO2from FMQ‐2 to FMQ+4. We show that sulfate complexes of calcium and sodium markedly enhance the stability of sulfate in moderately oxidized fluids in equilibrium with pyrite atfO2conditions of FMQ+1 to +2, causing large sulfur isotope fractionations up to 10‰ in the fluid relative to the slab. Such fluids could impart oxidized, sulfur‐rich and high δ34S signatures to the mantle wedge that are ultimately transferred to arc magmas, without the need to invoke34S‐rich subducted lithologies.  more » « less
Award ID(s):
2032039
PAR ID:
10546209
Author(s) / Creator(s):
;
Publisher / Repository:
Geochemistry, Geophysics, Geosystems
Date Published:
Journal Name:
Geochemistry, Geophysics, Geosystems
Volume:
25
Issue:
7
ISSN:
1525-2027
Subject(s) / Keyword(s):
Anydrite solubility Sulfur in subduction zone fluids sulfur isotopic values
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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