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The behavior of iron and zinc stable isotopes accompanying the subduction of mafic oceanic crust: A case study from Western Alpine Ophiolites

The behavior of iron and zinc stable isotopes accompanying the subduction of mafic oceanic crust: A case study from Western Alpine Ophiolites
The behavior of iron and zinc stable isotopes accompanying the subduction of mafic oceanic crust: A case study from Western Alpine Ophiolites
Arc lavas display elevated Fe3+/ΣFe ratios relative to MORB. One mechanism to explain this is the mobilization and transfer of oxidised or oxidising components from the subducting slab to the mantle wedge. Here we use iron and zinc isotopes, which are fractionated upon complexation by sulfide, chloride and carbonate ligands, to remark on the chemistry and oxidation state of fluids released during prograde metamorphism of subducted oceanic crust. We present data for metagabbros and metabasalts from the Chenaillet massif, Queyras complex and the Zermatt-Saas ophiolite (Western European Alps), which have been metamorphosed at typical subduction zone P-T conditions and preserve their prograde metamorphic history. There is no systematic, detectable fractionation of either Fe or Zn isotopes across metamorphic facies, rather the isotope composition of the eclogites overlaps with published data for MORB. The lack of resolvable Fe isotope fractionation with increasing prograde metamorphism likely reflects the mass balance of the system, and in this scenario Fe mobility is not traceable with Fe isotopes. Given that Zn isotopes are fractionated by S- and C-bearing fluids, this suggests that relatively small amounts of Zn are mobilised from the mafic lithologies in within these types of dehydration fluids. Conversely, metagabbros from the Queyras that are in close proximity to metasediments display a significant Fe isotope fractionation. The covariation of δ56Fe of these samples with selected fluid mobile elements suggests the infiltration of sediment derived fluids with an isotopically light signature during subduction.
1525-2027
2562–2579
Inglis, Edward C.
4932ad3c-6b03-4925-a249-d0bff9909a51
Debret, Baptiste
57e5f529-7ff3-485b-a641-304901c80904
Burton, Kevin W.
b17a2651-0697-4369-bfa7-ece9a9f0a3f1
Millet, Marc-Alban
c5ba8664-967e-48af-930d-4cd1abac19dd
Pons, Marie-Laure
1d4ee012-8e8f-4e5c-a3de-c6186dcdf5ed
Dale, Christopher W.
b6d29356-455c-4eb1-b4df-8c57cd4381ac
Bouilhol, Pierre
bb200fd6-93c9-499e-880b-c2a9c213e0f1
Cooper, Matthew
54f7bff0-1f8c-4835-8358-71eef8529e7a
Nowell, Geoffrey M.
cae7ee78-7392-4be1-b526-da026d388740
McCoy-West, Alex
0a3c42b2-6e57-4256-98d7-f505fdd89b11
Williams, Helen M.
fb96383f-76f8-4d68-baa6-826402c4ff7a
Inglis, Edward C.
4932ad3c-6b03-4925-a249-d0bff9909a51
Debret, Baptiste
57e5f529-7ff3-485b-a641-304901c80904
Burton, Kevin W.
b17a2651-0697-4369-bfa7-ece9a9f0a3f1
Millet, Marc-Alban
c5ba8664-967e-48af-930d-4cd1abac19dd
Pons, Marie-Laure
1d4ee012-8e8f-4e5c-a3de-c6186dcdf5ed
Dale, Christopher W.
b6d29356-455c-4eb1-b4df-8c57cd4381ac
Bouilhol, Pierre
bb200fd6-93c9-499e-880b-c2a9c213e0f1
Cooper, Matthew
54f7bff0-1f8c-4835-8358-71eef8529e7a
Nowell, Geoffrey M.
cae7ee78-7392-4be1-b526-da026d388740
McCoy-West, Alex
0a3c42b2-6e57-4256-98d7-f505fdd89b11
Williams, Helen M.
fb96383f-76f8-4d68-baa6-826402c4ff7a

Inglis, Edward C., Debret, Baptiste, Burton, Kevin W., Millet, Marc-Alban, Pons, Marie-Laure, Dale, Christopher W., Bouilhol, Pierre, Cooper, Matthew, Nowell, Geoffrey M., McCoy-West, Alex and Williams, Helen M. (2017) The behavior of iron and zinc stable isotopes accompanying the subduction of mafic oceanic crust: A case study from Western Alpine Ophiolites. Geochemistry, Geophysics, Geosystems, 18 (7), 2562–2579. (doi:10.1002/2016GC006735).

Record type: Article

Abstract

Arc lavas display elevated Fe3+/ΣFe ratios relative to MORB. One mechanism to explain this is the mobilization and transfer of oxidised or oxidising components from the subducting slab to the mantle wedge. Here we use iron and zinc isotopes, which are fractionated upon complexation by sulfide, chloride and carbonate ligands, to remark on the chemistry and oxidation state of fluids released during prograde metamorphism of subducted oceanic crust. We present data for metagabbros and metabasalts from the Chenaillet massif, Queyras complex and the Zermatt-Saas ophiolite (Western European Alps), which have been metamorphosed at typical subduction zone P-T conditions and preserve their prograde metamorphic history. There is no systematic, detectable fractionation of either Fe or Zn isotopes across metamorphic facies, rather the isotope composition of the eclogites overlaps with published data for MORB. The lack of resolvable Fe isotope fractionation with increasing prograde metamorphism likely reflects the mass balance of the system, and in this scenario Fe mobility is not traceable with Fe isotopes. Given that Zn isotopes are fractionated by S- and C-bearing fluids, this suggests that relatively small amounts of Zn are mobilised from the mafic lithologies in within these types of dehydration fluids. Conversely, metagabbros from the Queyras that are in close proximity to metasediments display a significant Fe isotope fractionation. The covariation of δ56Fe of these samples with selected fluid mobile elements suggests the infiltration of sediment derived fluids with an isotopically light signature during subduction.

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Accepted/In Press date: 2 June 2017
e-pub ahead of print date: 13 July 2017
Published date: July 2017
Organisations: Ocean and Earth Science, Geochemistry

Identifiers

Local EPrints ID: 411160
URI: http://eprints.soton.ac.uk/id/eprint/411160
ISSN: 1525-2027
PURE UUID: 7c374a82-756e-47e0-b47d-bacd526d5aae
ORCID for Matthew Cooper: ORCID iD orcid.org/0000-0002-2130-2759

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Date deposited: 15 Jun 2017 16:31
Last modified: 27 Apr 2022 01:43

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Contributors

Author: Edward C. Inglis
Author: Baptiste Debret
Author: Kevin W. Burton
Author: Marc-Alban Millet
Author: Marie-Laure Pons
Author: Christopher W. Dale
Author: Pierre Bouilhol
Author: Matthew Cooper ORCID iD
Author: Geoffrey M. Nowell
Author: Alex McCoy-West
Author: Helen M. Williams

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