Inter-mineral Fe isotope variations in mantle-derived rocks and implications for the Fe geochemical cycle

Beard, Brian L.; Johnson, Clark M.

doi:10.1016/j.gca.2004.04.023

Cited by 121 publications

(94 citation statements)

References 43 publications

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“…Craddock et al (2013) estimated the average Fe isotope composition of the terrestrial mantle to be 0.025 ± 0.025‰ (95% CL), based on analyses of abyssal peridotites. However, large Fe isotope variations from −0.54 to +0.16‰ have been identified in bulk mantle xenoliths (Beard and Johnson 2004;Weyer and Ionov 2007;Zhao et al 2010;Poitrasson et al 2013;Su et al 2015). In the following discussion, we will address how processes in subduction zones could induce Fe isotope mantle heterogeneities.…”

Section: Fe Isotope Fractionation During Retrograde Greenschist Faciesmentioning

confidence: 99%

“…8). According to Beard and Johnson (2004), fluid released during dehydration of the altered oceanic crust may serve as metasomatic agents and produced isotopically variable mantle composition through selective Fe transfer from the crust. 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.…”

Section: Implications For the Mantle Fe Isotopic Compositionmentioning

confidence: 99%

“…In magmatic rocks, fractionation may result from: (1) variable degrees of partial melting (Williams et al 2005;Weyer and Ionov 2007;Dauphas et al 2009;Teng et al 2013); (2) fractional crystallisation (e.g. Teng et al 2008Teng et al , 2013Schuessler et al 2009;Sossi et al 2012;Liu et al 2014); and/or (3) fluid-and melt-induced mantle metasomatism (Beard and Johnson 2004;Zhao et al 2010;Poitrasson et al 2013). Variations of oxygen fugacity and redox conditions in the mantle also play a role in Fe isotope fractionation, as they affect mantle melting processes (Williams et al 2004(Williams et al , 2005Dauphas et al 2009;Teng et al 2013).…”

Section: Introductionmentioning

confidence: 99%

“…Studies on orogenic eclogites (Beard and Johnson 2004) and eclogite xenoliths from kimberlite pipes (Williams et al 2009) have revealed that eclogites may conserve mantlelike δ 56 Fe values. On the contrary, Fe isotope fractionation is currently undetermined in metabasalts of blueschist and eclogite facies that were formed during subduction zone metamorphism and have recorded various stages of fluidrock interactions.…”

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: Fe Isotope Fractionation During Retrograde Greenschist Faciesmentioning

confidence: 99%

Section: Implications For the Mantle Fe Isotopic Compositionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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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“…Iron isotope analysis is emerging as a tracer for biogeochemical Fe cycling in aquatic environments (Anbar and Rouxel, 2007) as post-sedimentary precipitated Fe (oxyhydr)oxides as well as pore water Fe 2+ are known to be significantly enriched in light Fe isotopes compared to terrigenous Fe minerals (Severmann et al, 2006;Staubwasser et al, 2006Staubwasser et al, , 2013 Fe: 0.28% (Taylor et al, 1992). The terminology and general isotopic fractionation reactions have been reviewed by Anbar (2004 (Beard and Johnson, 2004). For instance, the oxidation of electron donors and reduction of a metal used by microbes to obtain energy, namely microbial dissimilatory iron reduction (DIR), preferentially releases light Fe isotopes into solution (e.g., Beard et al, 1999Beard et al, , 2003Crosby et al, 2007 (Severmann et al, 2006;Staubwasser et al, 2006).…”

Section: Introductionmentioning

confidence: 99%

Iron assimilation by the clam Laternula elliptica: Do stable isotopes (δ56Fe) help to decipher the sources?

et al. 2015

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Chromium isotope signature during continental crust subduction recorded in metamorphic rocks

Shen

Liu

Qin

et al. 2015

Geochem Geophys Geosyst

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The chromium isotope compositions of 27 metamorphic mafic rocks with varying metamorphic degrees from eastern China were systematically measured to investigate the Cr isotope behavior during continental crust subduction. The Cr isotope compositions of all samples studied were Bulk Silicate Earth (BSE) like, with d 53 Cr NIST979 of greenschists, amphibolites, and eclogites ranging from 20.06& to 20.17&, 20.05& to 20.27&, and 20.01& to 20.24&, respectively. The lack of resolvable isotopic variability among the metamorphic rocks from different metamorphic zones indicated that no systematic Cr isotope fractionation was associated with the degree of metamorphism. However, the Cr isotopic variability among homologous samples may have reflected effects induced by metamorphic dehydration with a change of redox state, rather than protolith heterogeneity (i.e., magma differentiation). In addition, the differences in d 53 Cr (D 53 Cr Cpx-Gt ) between coexisting clinopyroxene (Cpx) and garnet (Gt) from two garnet pyroxenites were 0.06& and 0.34&, respectively, indicating that significant inter-mineral Cr isotope disequilibria could occur during metamorphism. To provide a basis for comparison with metamorphic rocks and to provide further constraints on the potential Cr isotope heterogeneity in the mantle and in the protolith of some metamorphic rocks, we analyzed mantle-derived chromites and the associated peridotites from Luobusa, and we obtained the following general order: chromite-free peridotites (20.21& to 20.11&) < chromite-bearing peridotite (20.07&) < chromite (20.06&). These findings imply potential mantle heterogeneity as a result of partial melting or fractional crystallization associated with chromite. Key Points:It is the first time to investigate Cr isotopic behaviors during subduction We obtain the limited Cr isotopic fractionation during metamorphic dehydration There are potential Cr isotopic fractionations between hightemperature minerals (2015), Chromium isotope signature during continental crust subduction recorded in metamorphic rocks, Geochem. PUBLICATIONSDue to the high compatibility of chromium during magma activity, ultramafic and mafic rocks are the major reservoirs of Cr in Bulk Silicate Earth (BSE) [Faure, 1991]. Schoenberg et al. [2008] first studied the Cr isotope compositions of a variety of mantle-derived rocks, including mantle xenoliths, ultramafic rocks, cumulates, and oceanic and continental basalts. The Cr isotope composition (d 53 Cr NIST979 ) of the investigated samples was in a limited range of 20.21& to 20.02& with an average value of 20.12 6 0.10& (2SD), implying that mantle-derived rocks have relatively homogenous Cr isotope compositions. Farka s et al. [2013] observed that the global igneous chromites have slightly heavier Cr isotope compositions with an average d 53 Cr NIST 979 value of 20.08 6 0.13& (2SD) compared with the BSE reported by Schoenberg et al. [2008] and then inferred that chromite-bearing mantle might be isotopically heavier than mantle without chromites. This phe...

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Inter-mineral Fe isotope variations in mantle-derived rocks and implications for the Fe geochemical cycle

Cited by 121 publications

References 43 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)

Iron assimilation by the clam Laternula elliptica: Do stable isotopes (δ56Fe) help to decipher the sources?

Chromium isotope signature during continental crust subduction recorded in metamorphic rocks

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