XANES study of the oxidation state of Cr in lower mantle phases: Periclase and magnesium silicate perovskite

Eeckhout, S. G.; Bolfan-Casanova, Nathalie; McCammon, Catherine; Klemme, Stephan; Amiguet, Élodie

doi:10.2138/am.2007.2318

Cited by 31 publications

(33 citation statements)

References 39 publications

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“…The energy of the shoulder component coincides with that of the standard sample of CrF 2 . A similar spectral profile was reported on synthetic Cr -bearing ferropericlase and periclase samples that contained Cr 2+ in their structure (Eeckhout et al, 2007). The results of the present study strongly suggest that the natural ferropericlase inclusions in diamonds that originated from the lower mantle contain Cr 2+ in their structure.…”

Section: Resultssupporting

confidence: 87%

“…They suggested that the XANES spectra of Cr -bearing silicate glasses quenched from melts could be represented as a function of their oxygen fugacity. Recently, Eeckhout et al (2007) reported that the Cr 2+ concentrations are closely related to the relative area of the absorption edge shoulder observed in the XANES spectra of Cr -bearing enstatite (Cr 2+ in Mg 0.90 Cr 0.10 SiO 3 ) and chromite (Cr 3+ in FeCr 2 O 4 ). These two calibration lines reported by the two research groups are very similar and result in the same Cr 2+ concentration within the experimental error.…”

Section: Resultsmentioning

confidence: 99%

“…However, minerals formed under extremely reduced conditions, for example, lunar olivine, can contain Cr 2+ in their structure (Sutton et al, 1993). Eeckhout et al (2007) ) to occur. Thus, the presence of Cr 2+ in a mineral could be an indicator of the reduced environment.…”

Section: Introductionmentioning

confidence: 99%

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Divalent chromium in ferropericlase inclusions in lower-mantle diamonds revealed by micro-XANES measurements

Одаке

Fukura

Arakawa

et al. 2008

Journal of Mineralogical and Petrological Sciences

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Chromium K -edge X -ray absorption near -edge structure (XANES) spectra of natural ferropericlase were measured using an X -ray microbeam from a synchrotron radiation source to estimate the valence state of Cr. Measured samples were inclusions collected from lower -mantle diamonds. The obtained results revealed that divalent chromium is present in the materials in the lower mantle and that the proportion of Cr 2+ in the total Cr content varied among the samples. The valence state of chromium in the inclusions in diamonds is a potential indicator of the redox conditions in the lower mantle.

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Section: Resultssupporting

confidence: 87%

Section: Resultsmentioning

confidence: 99%

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Divalent chromium in ferropericlase inclusions in lower-mantle diamonds revealed by micro-XANES measurements

Одаке

Fukura

Arakawa

et al. 2008

Journal of Mineralogical and Petrological Sciences

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“…It is noteworthy that the shoulder feature assigned to Cr 2+ was observed even under an f O 2 condition near the QMF buffer, under which most of Cr is thought to exit as a trivalent (Papike et al, 2005). As reported in Odake et al (2008), Cr 2+ /ΣCr was estimated from the obtained shoulder area in the derivative spectra using the calibration by Eeckhout et al (2007). The obtained ratios are listed in Table 2, and they are similar to each other within uncertainty.…”

Section: Cr-k Edge Xanes Spectrasupporting

confidence: 54%

“…A shoulder component at 5990 -6000 eV can be assigned to Cr 2+ in ferropericlase, and its relative intensity to the main peak varies with f O 2 (Eeckhout et al, 2007;Odake et al 2008). Therefore, the spectral shape, which includes the shoulder part, was expected to be a potential indicator of the redox state in the lower mantle.…”

Section: Cr-k Edge Xanes Spectramentioning

confidence: 99%

Oxygen fugacity and valence state of chromium in ferropericlase: Can Cr2+ be a redox indicator for the deep mantle?

Kagi

Одаке

Ishibashi

et al. 2013

Journal of Mineralogical and Petrological Sciences

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The valence state of chromium in ferropericlase inclusions within diamonds was expected to serve as a redox indicator applicable to the deep earth environment with an extremely reduced condition. In this study, Cr Kedge X -ray absorption near -edge structure (XANES) spectra and 57 Fe Mössbauer spectra were obtained for ferropericlase samples synthesized under controlled oxygen fugacity conditions of −7, −9, and −11 in log f O 2 . All the ferropericlase samples were shown to have almost identical Fe 3+ /Fe 2+ ratios; this observation is consistent with a phase diagram of ferropericlase reported previously. All the ferropericlase samples contained Cr 2+, and the Cr 2+ /ΣCr ratio was almost constant among the samples, within the experimental precision of XANES spectroscopic measurements. Divalent chromium ions are stabilized in ferropericlase by the crystallographic constraint, even under an oxidized condition. The present study proposes that there is room for reconsidering the presence of Cr 2+ in ferropericlase inclusions in diamonds as evidence of the extremely reduced condition of the lower mantle.

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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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XANES study of the oxidation state of Cr in lower mantle phases: Periclase and magnesium silicate perovskite

Cited by 31 publications

References 39 publications

Divalent chromium in ferropericlase inclusions in lower-mantle diamonds revealed by micro-XANES measurements

Divalent chromium in ferropericlase inclusions in lower-mantle diamonds revealed by micro-XANES measurements

Oxygen fugacity and valence state of chromium in ferropericlase: Can Cr2+ be a redox indicator for the deep mantle?

Chromium isotope signature during continental crust subduction recorded in metamorphic rocks

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