Redox-variability and controls in subduction zones from an iron-isotope perspective

Nebel, Oliver; Sossi, Paolo A.; Bénard, Antoine; Wille, Martin; Vroon, P.Z.; Arculus, R. J.

doi:10.1016/j.epsl.2015.09.036

Cited by 83 publications

(74 citation statements)

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“…Subsequent melting of the metasomatised heavy-Fe upper mantle may in turn be source of OIBs with elevated δ 56 Fe values (Konter et al 2016), supporting a deep mantle cycle. By contrast, arc lavas display a lighter Fe isotopic signature than MORB (Sossi et al 2016), reflecting extensive melt-depletion and preferential removal of Fe 3+ over Fe 2+ during prior melting, leaving a light Fe isotopic signature of the residue in the sub-arc mantle wedge (Nebel et al 2013(Nebel et al , 2015. These recent studies emphasise negligible influence of slab-derived fluids on the Fe isotopic composition of the mantle wedge.…”

Section: Implications For the Mantle Fe Isotopic Compositionmentioning

confidence: 90%

“…Despite its high Fe 3+ /ΣFe ratio, blueschist GR 12b has a δ 56 Fe value similar to rocks with a lower Fe 3+ /ΣFe ratio. While largescale transfer of oxidised Fe from sediments to the mantle wedge is not considered as a significant oxidising process (Nebel et al 2015), local Fe isotope re-equilibration between sample GR 12b and sediment-derived sulfate-rich and/or hypersaline fluids may have been responsible for the decoupling of δ 56 Fe and Fe 3+ /ΣFe. Fig.…”

Section: Effect Of Hydrothermal Alteration On Fe Isotope Fractionationmentioning

confidence: 99%

“…A recent study has determined δ 56 Fe values of subducting sediments from +0.05 to +0.18‰ [average: +0.12 ± 0.04 (2σ SD); Nebel et al 2015 Fig. A2).…”

Section: Effect Of Hydrothermal Alteration On Fe Isotope Fractionationmentioning

confidence: 99%

“…5a, b; Electronic Appendix, Fig. A1) Schuessler et al 2009;Craddock and Dauphas 2011;Konter et al 2016), or in island arc basalts and lavas (IAB, IAL) (−0.04 to +0.15‰; Dauphas et al 2009;Nebel et al 2015) (Fig. 6).…”

Section: Fe Isotope Fractionation During Retrograde Greenschist Faciesmentioning

confidence: 99%

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Iron isotope fractionation in subduction-related high-pressure metabasites (Ile de Groix, France)

Korh

Luais

Deloule

et al. 2017

Contrib Mineral Petrol

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1during metamorphism: newly-formed Fe-rich minerals allowed preserving bulk rock Fe compositions during metamorphic reactions and hampered any Fe isotope fractionation. Greenschists have δ 56 Fe values (+0.17 ± 0.01 to +0.27 ± 0.02‰) similar to high-pressure rocks. Hence, metasomatism related to fluids derived from the subducted hydrothermally altered metabasites might only have a limited effect on mantle Fe isotope composition under subsolidus conditions, owing to the large stability of Fe-rich minerals and low mobility of Fe. Subsequent melting of the heavy-Fe metabasites at deeper levels is expected to generate mantle Fe isotope heterogeneities.Keywords Fe isotopes · Metabasites · Subduction · HP-LT metamorphism · Blueschists · Eclogites · Greenschists · Basaltic protoliths IntroductionHigh-pressure/low-temperature (HP-LT) rocks are remnants of ancient subduction zones. They provide information on geochemical processes and deep fluid-rock interactions occurring at present-day active convergent margins. Fluid infiltration during high-and lowtemperature hydrothermal alteration of the oceanic crust at mid-ocean ridges and on the seafloor is responsible for the hydration of basic rocks and serpentinisation of the lithospheric mantle. During subduction, the hydrothermally altered oceanic crust dehydrates continuously and releases large amounts of H 2 O at a relatively shallow level in the subduction zone (50-80 km) (Schmidt and Poli 1998;Rüpke et al. 2004). Deserpentinisation of the lithospheric mantle occurs at deeper levels (100-200 km), where fluids are expected to be the source of arc melting (Ulmer and Abstract Characterisation of mass transfer during subduction is fundamental to understand the origin of compositional heterogeneities in the upper mantle. Fe isotopes were measured in high-pressure/low-temperature metabasites (blueschists, eclogites and retrograde greenschists) from the Ile de Groix (France), a Variscan high-pressure terrane, to determine if the subducted oceanic crust contributes to mantle Fe isotope heterogeneities. The metabasites have δ 56 Fe values of +0.16 to +0.33‰, which are heavier than typical values of MORB and OIB, indicating that their basaltic protolith derives from a heavy-Fe mantle source. The δ 56 Fe correlates well with Y/Nb and (La/Sm) PM ratios, which commonly fractionate during magmatic processes, highlighting variations in the magmatic protolith composition. In addition, the shift of δ 56 Fe by +0.06 to 0.10‰ compared to basalts may reflect hydrothermal alteration prior to subduction. The δ 56 Fe decrease from blueschists (+0.19 ± 0.03 to +0.33 ± 0.01‰) to eclogites (+0.16 ± 0.02 to +0.18 ± 0.03‰) reflects small variations in the protolith composition, rather than Fe fractionation

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Section: Implications For the Mantle Fe Isotopic Compositionmentioning

confidence: 90%

Section: Effect Of Hydrothermal Alteration On Fe Isotope Fractionationmentioning

confidence: 99%

“…A recent study has determined δ 56 Fe values of subducting sediments from +0.05 to +0.18‰ [average: +0.12 ± 0.04 (2σ SD); Nebel et al 2015 Fig. A2).…”

Section: Effect Of Hydrothermal Alteration On Fe Isotope Fractionationmentioning

confidence: 99%

Section: Fe Isotope Fractionation During Retrograde Greenschist Faciesmentioning

confidence: 99%

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Iron isotope fractionation in subduction-related high-pressure metabasites (Ile de Groix, France)

Korh

Luais

Deloule

et al. 2017

Contrib Mineral Petrol

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“…For instance, d 51 V becomes isotopically lighter in progressively depleted (clinopyroxene-poor) peridotites (Prytulak et al, 2013). This is an important observation because the arc mantle wedge has been inferred to be markedly depleted (e.g., Woodhead, 1993;Nebel et al, 2015) with respect to the source of MORB. In the absence of a common source, observations of similar V/Sc and d V with progressive depletion thus negates a simple explanation of isotope fractionation during melt extraction (Prytulak et al, 2013).…”

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confidence: 87%

Stable vanadium isotopes as a redox proxy in magmatic systems?

Prytulak¹,

Sossi²,

Halliday³

et al. 2016

Geochem. Persp. Let.

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Recycling pathways of multivalent elements, that impact our understanding of diverse geological processes from ore formation to the rise of atmospheric oxygen, depend critically on the spatial and temporal variation of oxygen fugacity ( fO 2 ) in the Earth's interior. Despite its importance, there is currently no consensus on the relative fO 2 of the mantle source of mid-ocean ridge basalts compared to the sub-arc mantle, regions central to the mediation of crust-mantle mass balances. Here we present the first stable vanadium isotope measurements of arc lavas, complemented by non-arc lavas and two co-genetic suites of fractionating magmas, to explore the potential of V isotopes as a redox proxy. Vanadium isotopic compositions of arc and non-arc magmas with similar MgO overlap with one another. However, V isotopes display strikingly large, systematic variations of ~2 ‰ during magmatic differentiation in both arc and non-arc settings. Calculated bulk V Rayleigh fractionation factors (1000 lna min-melt of -0.4 to -0.5 ‰) are similar regardless of the oxidation state of the evolving magmatic system, which implies that V isotope fractionation is most influenced by differences in bonding environment between minerals and melt rather than changes in redox conditions. Thus, although subtle fO 2 effects may be present, V isotopes are not a direct proxy for oxygen fugacity in magmatic systems.

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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

Inglis

Debret

Burton

et al. 2017

Geochem Geophys Geosyst

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Arc lavas display elevated Fe 31 /RFe ratios relative to MORB. One mechanism to explain this is the mobilization and transfer of oxidized or oxidizing 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-bearing and C-bearing fluids, this suggests that relatively small amounts of Zn are mobilized from the mafic lithologies in within these types of dehydration fluids. Conversely, metagabbros from the Queyras that are in proximity to metasediments display a significant Fe isotope fractionation. The covariation of d 56 Fe 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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Redox-variability and controls in subduction zones from an iron-isotope perspective

Cited by 83 publications

References 83 publications

Iron isotope fractionation in subduction-related high-pressure metabasites (Ile de Groix, France)

Iron isotope fractionation in subduction-related high-pressure metabasites (Ile de Groix, France)

Stable vanadium isotopes as a redox proxy in magmatic systems?

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

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