Determination of the iron oxidation state in basaltic glasses using XANES at the K-edge

Wilke, Max; Partzsch, Georg M.; Bernhardt, Ralf; Lattard, Dominique

doi:10.1016/j.chemgeo.2005.03.004

Cited by 124 publications

(119 citation statements)

References 40 publications

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“…The effect of water as a chemical component at fixed P, T, and fO 2 is more nuanced. The study of (Baker and Rutherford, 1996) suggested that the Fe 3+ /Fe 2+ ratio increased with the addition of water; however, as discussed by Wilke et al (2005) and Gaillard et al (2001), the study of Baker and Rutherford was not at constant oxygen fugacity (fO 2 ). Experimental studies on rhyolite (Moore et al, 1995) and basalt (Botcharnikov et al, 2005) indicate that water, as a chemical component in a melt held at fixed T, P, and oxygen fugacity (fO 2 ), has no effect on the Fe 3+ /Fe 2+ ratio.…”

Section: Introductionmentioning

confidence: 76%

Spherulite crystallization induces Fe-redox redistribution in silicic melt

et al. 2009

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Rhyolitic obsidians from Krafla volcano, Iceland, record the interaction between mobile hydrous species liberated during crystal growth and the reduction of ferric iron in the silicate melt. We performed synchrotron µ-FTIR and µ-XANES measurements along a transect extending from a spherulite into optically distinct colorless and brown glass zones. Measurements show that the colorless glass is enriched in OH groups and depleted in ferric iron, while the brown glass shows the opposite relationship. The color shift between brown and clear glass is sharp, suggesting that the colorless glass zone was produced by a redox front that originated from the spherulite margin and moved through surrounding melt during crystallization. We conclude that the most likely reducing agent is hydrogen, produced by magnetite crystallization within the spherulite. The Krafla obsidians dramatically capture redox disequilibrium on the micoscale and highlight the importance of hydrous fluid liberation and late-stage crystallization to the redox signature of glassy lavas.

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Section: Introductionmentioning

confidence: 76%

Spherulite crystallization induces Fe-redox redistribution in silicic melt

et al. 2009

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“…The areaweighted average energy of the baseline-subtracted pre-edge feature (the centroid) shifts in energy as a function of Fe oxidation state in basaltic glass (13) (Fig. 2A).…”

mentioning

confidence: 99%

Water and the Oxidation State of Subduction Zone Magmas

Kelley

Cottrell

2009

Science

717

350

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Mantle oxygen fugacity exerts a primary control on mass exchange between Earth's surface and interior at subduction zones, but the major factors controlling mantle oxygen fugacity (such as volatiles and phase assemblages) and how tectonic cycles drive its secular evolution are still debated. We present integrated measurements of redox-sensitive ratios of oxidized iron to total iron (Fe 3+ /SFe), determined with Fe K-edge micro-x-ray absorption near-edge structure spectroscopy, and pre-eruptive magmatic H 2 O contents of a global sampling of primitive undegassed basaltic glasses and melt inclusions covering a range of plate tectonic settings. Magmatic Fe 3+ /SFe ratios increase toward subduction zones (at ridges, 0.13 to 0.17; at back arcs, 0.15 to 0.19; and at arcs, 0.18 to 0.32) and correlate linearly with H 2 O content and element tracers of slab-derived fluids. These observations indicate a direct link between mass transfer from the subducted plate and oxidation of the mantle wedge. P late tectonics leads to a two-way geochemical exchange between Earth's interior and exterior. This process is driven by the formation of new oceanic crust by mantle melting at mid-ocean ridges, hydration and oxidative alteration of oceanic crust as it transits the seafloor, and the subsequent return of hydrated oxidized oceanic crust to the deep Earth at subduction zones (Fig. 1A) (1, 2). How this exchange has affected the oxygen fugacity of the mantle spatially (3) and over time (2, 4, 5) remains unclear. Many lines of evidence point to oxidizing conditions in arc peridotites and magmas (1, 6), but a quantitative link between oxidation state and the subduction process, although intuitive, has not been established. Here we provide coupled measurements of the redox-sensitive Fe 3+ /SFe ratio and magmatic H 2 O concentrations at the same spatial resolution in a global suite of undegassed basaltic glasses, in order to determine the current oxidation condition of the mantle as a function of tectonic regime.The ratio of oxidized iron to total iron [Fe 3+

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“…However, these results are somewhat variable depending upon whether the Fe coordination has been determined using XANES-EXAFS or Mössbauer spectroscopy. In addition, the ability to distinguish true fi ve-fold Fe ( [5] Fe) using the pre-edge features as opposed to a mixture of four-and six-fold Fe remains diffi cult (Wilke et al 2004). EXAFS-XANES data generally involve fi tting of a pre-edge peak in the Fe K-edge XANES (Galoisy et al 2001, Petit et al 2001, Berry et al 2003, Wilke et al 2004, Farges et al 2004 or modeling of the XANES spectrum itself (Farges et al 2004), whereas the Mössbauer spectra are fi t using different procedures depending upon whether (or not) the characteristic line-broadening observed in glasses due to variations in site distributions has been accounted for (Rossano et al 1999).…”

Section: Ironmentioning

confidence: 99%

The Structure of Silicate Melts: A Glass Perspective

Henderson

2005

The Canadian Mineralogist

126

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Glasses are widely used as analogues for the study of silicate melts. Although they are solid materials, their structure is inherently complex and diffi cult to study. However, progress has been made in elucidating this structure, its relationship to composition, and how it behaves at high temperatures and pressures. Recent research has brought to light some new fi ndings with important implications for natural melts. These include the observation that the structure is dependent upon the type and size of alkali or alkaline-earth cations incorporated into the glass network, with Li behaving very differently than other alkali cations. In addition, the presence of more than one type of alkali cation can cause non-linear physical behavior. Elements such as Al, Ti and Fe, which play important roles in petrological phenomena, can exhibit coordination environments (e.g., 5-fold) or polyhedral arrangements (e.g., triclusters) that are not common in crystalline phases. Furthermore, polyamorphic phase-transitions may occur at high temperature and pressures; the application of new theoretical models like mean fi eld-constraint hypothesis suggests that several glass phenomena, and probably melt phenomena as well, may be related to stress-rigid to fl oppy transitions. The state of understanding of glass structure, although still rudimentary relative to crystalline materials, has grown exponentially over the last few decades, often with geological researchers at the forefront.Keywords: melts, structure, glasses, petrology, spectroscopy, behavior, model. SOMMAIREOn se sert couramment des verres pour étudier les bains fondus silicatés. Quoiqu'ils sont des matériaux solides, leur structure est naturellement complexe et diffi cile à étudier. Toutefois, des progrès ont été faits dans l'étude de cette structure, sa relation à la composition, et son comportement à températures et pressions élevées. Les projets de recherche récents font ressortir les implications importantes aux bains fondus naturels. A titre d'exemple, la structure dépendrait de la sorte et la taille d'ion alcalin ou alcalino-terreux qui se trouve incorporé dans le réseau du verre. Le Li se comporte de façon très différente des autres alcalins. De plus, la présence de plus d'une sorte d'alcalin peut causer des comportements physiques non-linéaires. Les élements tels Al, Ti et Fe, dont l'importance pétrologique est évidente, peuvent adopter une coordinence inhabituelle, cinq par exemple, et un arrangement polyédrique, des groupements par trois, par exemple, qui ne sont pas communs dans les phases cristallines. De plus, des transitions de phases polyamorphiques pourraient avoir lieu à températures et à pressions élevées. L'application de nouveaux modèles théoriques, par exemple le modèle de contrainte moyenne du champ, fait penser que plusieurs phénomènes impliquant les verres, et tout probablement les bains fondus, pourraient résulter de transitions de matériau rigide face aux contraintes à maté-riau déformable. Quoique les connaissances de la structure du ve...

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Determination of the iron oxidation state in basaltic glasses using XANES at the K-edge

Cited by 124 publications

References 40 publications

Spherulite crystallization induces Fe-redox redistribution in silicic melt

Spherulite crystallization induces Fe-redox redistribution in silicic melt

Water and the Oxidation State of Subduction Zone Magmas

The Structure of Silicate Melts: A Glass Perspective

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