Aqueous fluids are effective oxidizing agents of the mantle in subduction zones

Aqueous fluids produced by dehydration of the downgoing slab facilitate chemical exchange in subduction zones, but the efficiency of fluid-mediated redox transfer as a mechanism to deliver oxidized material from the slab to the sub-arc mantle remains hotly debated. Here we report the first direct me...

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Bibliographic Details
Published in:Contributions to mineralogy and petrology 2020-03, Vol.175 (4), Article 36
Main Authors: Iacovino, Kayla, Guild, Meghan R., Till, Christy B.
Format: Article
Language:English
Subjects:
Analysis
Basalt
Computational fluid dynamics
Dehydration
Earth and Environmental Science
Earth Sciences
Equations of state
Fluctuations
Fluids
Flux
Geology
Magma
Mantle
Mineral Resources
Mineralogy
Modelling
Original Paper
Oxidation
Oxidizing agents
Oxidoreductions
Petrology
Sensors
Serpentinite
Subduction
Subduction (geology)
Subduction zones
Subduction zones (Geology)
Thermodynamic models
Thermodynamics
Valence
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Summary:Aqueous fluids produced by dehydration of the downgoing slab facilitate chemical exchange in subduction zones, but the efficiency of fluid-mediated redox transfer as a mechanism to deliver oxidized material from the slab to the sub-arc mantle remains hotly debated. Here we report the first direct measurements of the oxidation state of experimentally produced slab fluids using in situ redox sensors. Our experiments show that the dehydration of natural antigorite serpentinite at shallow subduction zone conditions (1 GPa, 800 °C) produces moderately oxidizing fluids (QFM + 2) with elevated concentrations of Na, K, Ca, and Mg. The composition and redox of the experimental fluids are then used to parameterize a thermodynamic reactive transport model to investigate the interaction of slab fluid with the sub-arc mantle from 1–4 GPa and 700–900 °C. Recently determined equation of state parameters for aqueous fluids at high pressures now enables thermodynamic modeling of aqueous fluid–rock interactions at conditions relevant to deep subduction zones for the first time. Our thermodynamic modeling demonstrates that aqueous fluid can efficiently oxidize Fe in mantle minerals via the reduction of H + to H 2 in the fluid. We estimate that 
ISSN:0010-7999
1432-0967
DOI:10.1007/s00410-020-1673-4