Evolution of Fe redox state in serpentine during subduction

Debret, Baptiste; Andréani, M.; Muñoz, Manuel; Bolfan-Casanova, Nathalie; Carlut, Julie; Nicollet, Christian; Schwartz, Stéphane; Trcera, Nicolas

doi:10.1016/j.epsl.2014.05.038

Cited by 94 publications

(80 citation statements)

References 84 publications

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“…Recent studies have shown that variations in the nature and mode of metasomatic processes result in variable effects on Fe isotope composition of mantle rocks (Weyer and Ionov 2007;Poitrasson et al 2013). Fe solubility, transport and isotope fractionation in subduction zone fluids strongly depends on its oxidation state and relative abundance, as well as on the fluid composition (Polyakov and Mineev 2000;Manning 2004;Hill et al 2010;Debret et al 2014Debret et al , 2016. Our results confirm that the subducted oceanic crust may be a source for mantle iron isotope heterogeneities at different depth levels:…”

Section: Implications For the Mantle Fe Isotopic Compositionsupporting

confidence: 77%

“…Fluids were mainly equilibrated with the subducted metabasites of the Ile de Groix during dehydration reactions, as fluid-rock interactions mostly occurred at low fluid/rock ratios and slow fluid migration rates (El Korh et al 2011. Large-scale transport of Fe from the basaltic crust to the mantle wedge requires Cl and/or SO X to be released in the fluid phase (Manning 2004;Debret et al 2014) and Fe to be mobilised during metamorphic reactions (i.e. breakdown of a Fe-rich phase).…”

Section: Implications For the Mantle Fe Isotopic Compositionmentioning

confidence: 99%

“…As Ti is relatively immobile during HP metamorphism, the absence of a correlation between the Fe/ Ti ratio and the δ 56 Fe indicates that Fe isotopic signatures were also preserved during dehydration reactions. Fe is transported as Fe 2+ -chloride or Fe 2+ -sulphate complexes in subduction zone fluids (Manning 2004;Debret et al 2014), which enhances light-Fe mobility. Hence, light Fe-enriched fluids would be released during dehydration reactions associated to prograde metamorphism.…”

Section: Fe Isotope Fractionation During Subduction Zone Metamorphismmentioning

confidence: 99%

“…Hypersaline brines, supercritical fluids, silicate-rich C-bearing fluids, silicate melts or sulphate-bearing fluids derived from the oceanic lithosphere are recognised as effective metasomatic oxidising agents in the lithospheric mantle (Kelley and Cottrell 2009;Malaspina et al 2010;Debret et al 2016). The prograde transition from lizardite to antigorite results in a decrease of the serpentine Fe 3+ / ΣFe ratio and magnetite modal percentage under eclogite facies conditions (Debret et al 2014). Fe mass transfer accompanying the release of oxidised fluids (e.g.…”

Section: Introductionmentioning

confidence: 99%

“…Fe mass transfer accompanying the release of oxidised fluids (e.g. SO X , H 2 O, CO 2 ) leads to Fe reduction in serpentinites (Debret et al 2014).…”

Section: Introductionmentioning

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 Compositionsupporting

confidence: 77%

Section: Implications For the Mantle Fe Isotopic Compositionmentioning

confidence: 99%

Section: Fe Isotope Fractionation During Subduction Zone Metamorphismmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…Fe mass transfer accompanying the release of oxidised fluids (e.g. SO X , H 2 O, CO 2 ) leads to Fe reduction in serpentinites (Debret et al 2014).…”

Section: Introductionmentioning

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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Magnetic signatures of serpentinization at ophiolite complexes

Bonnemains

Carlut

Escartı́n

et al. 2016

Geochem Geophys Geosyst

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International audienceWe compare magnetic properties of 58 variably serpentinized peridotites from three ophiolite complexes (Pindos, Greece; Oman; Chenaillet, France) and the mid-Atlantic Ridge near the Kane fracture zone (MARK). The Pindos and Oman sites show low susceptibility and remanence (K < 0.02 SI; M s < 0.4 Am 2 / kg), while the Chenaillet and MARK sites show instead high susceptibility and remanence (K up to 0.15 SI; M s up to 6 Am 2 /kg), regardless of serpentinization degree. Petrographic observations confirm that Pindos and Oman samples contain serpentine with very little magnetite, while Chenaillet and MARK samples display abundant magnetite in serpentine mesh cells. Bulk rock analyses show similar amounts of ferric iron at a given serpentinization degree, suggesting that iron is oxidized during the serpentinization reaction in both cases, but that its distribution among phases differs. Microprobe analyses show iron-rich serpentine minerals (5–7 wt % FeO) in low-susceptibility samples, while iron-poor serpentine minerals (2–4 wt % FeO) occur in high susceptibility samples. The contrasted magnetic properties between the two groups of sites thus reflect different iron partitioning during serpentinization, that must be related to distinct conditions at which the serpentinization reaction takes place. We propose that magnetic properties of ophiolitic serpen-tinites can be used as a proxy to differentiate between high temperature serpentinization (>250–3008C) occurring at the axis (i.e., Chenaillet, similar to serpentinites from magmatically poor mid-ocean ridges), from lower temperature serpentinization (<200–2508C), likely occurring off axis and possibly during obduction (i.e., Pindos and Oman). At both settings, serpentinization can result in significant hydrogen release

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Redistribution of Iron and Titanium in High‐Pressure Ultramafic Rocks

Crossley

Evans

Reddy

et al. 2017

Geochem Geophys Geosyst

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The redox state of iron in high‐pressure serpentinites, which host a significant proportion of Fe3+ in subduction zones, can be used to provide an insight into iron cycling and constrain the composition of subduction zone fluids. In this study, we use oxide and silicate mineral textures, interpretation of mineral parageneses, mineral composition data, and whole rock geochemistry of high‐pressure retrogressed ultramafic rocks from the Zermatt‐Saas Zone to constrain the distribution of iron and titanium, and iron oxidation state. These data provide an insight on the oxidation state and composition of fluids at depth in subduction zones. Oxide minerals host the bulk of iron, particularly Fe3+. The increase in mode of magnetite and observation of magnetite within antigorite veins in the investigated ultramafic samples during initial retrogression is most consistent with oxidation of existing iron within the samples during the infiltration of an oxidizing fluid since it is difficult to reconcile addition of Fe3+ with the known limited solubility of this species. However, high Ti contents are not typical of serpentinites and also cannot be accounted for by simple mixing of a depleted mantle protolith with the nearby Allalin gabbro. Titanium‐rich phases coincide with prograde metamorphism and initial exhumation, implying the early seafloor and/or prograde addition and late mobilization of Ti. If Ti addition has occurred, then the introduction of Fe3+, also generally considered to be immobile, cannot be disregarded. We explore possible transport vectors for Ti and Fe through mineral texture analysis.

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Evolution of Fe redox state in serpentine during subduction

Cited by 94 publications

References 84 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)

Magnetic signatures of serpentinization at ophiolite complexes

Redistribution of Iron and Titanium in High‐Pressure Ultramafic Rocks

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