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dc.contributor.author
Eberhard, Lisa
dc.contributor.author
Frost, Daniel J.
dc.contributor.author
McCammon, Catherine A.
dc.contributor.author
Dolejš, David
dc.contributor.author
Connolly, James
dc.date.accessioned
2023-11-28T15:51:06Z
dc.date.available
2023-11-26T07:00:50Z
dc.date.available
2023-11-28T15:51:06Z
dc.date.issued
2023-10
dc.identifier.issn
0022-3530
dc.identifier.issn
1460-2415
dc.identifier.other
10.1093/petrology/egad069
en_US
dc.identifier.uri
http://hdl.handle.net/20.500.11850/643717
dc.description.abstract
Serpentinites play an important role in the delivery of water into subduction zones. In addition, serpentinites also contain ferric Fe and can transport significant redox potential. We present high-pressure and high-temperature experiments and Mössbauer spectroscopy measurements on natural lizardite and antigorite samples equilibrated at various oxygen fugacities in order to quantify the relationship between the oxygen fugacity f(O₂) and the Fe³⁺/Feᵗᵒᵗ ratio in these two phases. In antigorite, Fe³⁺ partitions into the octahedral site and is charge balanced by tetrahedral Al. In lizardite, tetrahedral Fe³⁺ is observed only at low temperature as well as under high f(O₂), whereas Fe³⁺ prefers the octahedral site at temperatures exceeding 500 °C and at 3 to 5 GPa. Although metastable, lizardite remains in redox equilibrium in our experiments at conditions above the lizardite to antigorite phase transformation at 300 °C and demonstrates a similar stability to antigorite. The Al concentration of lizardite is found to be temperature dependent, and it was possible to reequilibrate the Fe³⁺/Feᵗᵒᵗ ratio of lizardite from 0.1 to 0.9 by using redox buffers such as Fe metal, graphite, graphite–calcite, Re–ReO₂ and Ru–RuO₂. Our experiments on antigorite demonstrate that antigorite does not adjust its Al concentration on experimental time scales. Since Fe³⁺ is charge balanced by Al, it was also not possible to manipulate the Fe³⁺/Feᵗᵒᵗ ratio of antigorite. The coexisting phases, however, show chemical equilibration with this antigorite composition. We have retrieved the standard Gibbs energy for Fe³⁺- and Al-endmembers of antigorite and lizardite and calculated the metamorphic evolution of subducting serpentinites. The lizardite to antigorite transformation does not cause a decrease in the bulk Fe³⁺/Feᵗᵒᵗ ratio under f(O₂) buffered conditions, in contrast to observations from some natural settings, but does result in the formation of additional magnetite due to antigorite having a lower Fe³⁺/Feᵗᵒᵗ ratio than lizardite at equilibrium. If the f(O₂) of antigorite serpentinite is buffered during subduction, such as due to the presence of graphite and carbonate, the bulk Fe³⁺/Feᵗᵒᵗ ratio decreases progressively. On the other hand, in a closed system where the bulk serpentinite Fe³⁺/Feᵗᵒᵗ ratio remains constant, the f(O₂) increases during subduction. In this scenario, the f(O₂) of an antigorite serpentinite with a typical Fe³⁺/Feᵗᵒᵗ ratio of 0.4 increases from the fayalite–magnetite–quartz to the hematite–magnetite f(O₂) buffer during dehydration. These f(O₂) results confirm earlier inferences that fluids produced by antigorite dehydration may not contain sufficient oxidised sulphur species to oxidise the mantle wedge. Sufficiently high levels of f(O₂) to mobilise oxidised sulphur species may be reached upon antigorite dehydration, however, if closed system behaviour maintains a high bulk redox potential across the lizardite to antigorite phase transformation. Alternatively, oxidation of the mantle wedge might be achieved by oxidising agents from sources in subducted oceanic crust and sediments.
en_US
dc.language.iso
en
en_US
dc.publisher
Oxford University Press
en_US
dc.subject
serpentine
en_US
dc.subject
subduction zone
en_US
dc.subject
redox
en_US
dc.subject
oxygen fugacity
en_US
dc.subject
Mössbauer spectroscopy
en_US
dc.title
Experimental Constraints on the Ferric Fe Content and Oxygen Fugacity in Subducted Serpentinites
en_US
dc.type
Journal Article
dc.date.published
2023-09-15
ethz.journal.title
Journal of Petrology
ethz.journal.volume
64
en_US
ethz.journal.issue
10
en_US
ethz.journal.abbreviated
J. petrol.
ethz.pages.start
egad069
en_US
ethz.size
18 p.
en_US
ethz.identifier.wos
ethz.identifier.scopus
ethz.publication.status
published
en_US
ethz.leitzahl
ETH Zürich::00002 - ETH Zürich::00012 - Lehre und Forschung::00007 - Departemente::02330 - Dep. Erdwissenschaften / Dep. of Earth Sciences::02725 - Institut für Geochemie und Petrologie / Institute of Geochemistry and Petrology::03592 - Schmidt, Max / Schmidt, Max
ethz.leitzahl.certified
ETH Zürich::00002 - ETH Zürich::00012 - Lehre und Forschung::00007 - Departemente::02330 - Dep. Erdwissenschaften / Dep. of Earth Sciences::02725 - Institut für Geochemie und Petrologie / Institute of Geochemistry and Petrology::03592 - Schmidt, Max / Schmidt, Max
ethz.date.deposited
2023-11-26T07:00:51Z
ethz.source
SCOPUS
ethz.eth
yes
en_US
ethz.availability
Metadata only
en_US
ethz.rosetta.installDate
2023-11-28T15:51:07Z
ethz.rosetta.lastUpdated
2024-02-03T07:15:48Z
ethz.rosetta.exportRequired
true
ethz.rosetta.versionExported
true
ethz.COinS
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