Roman Botcharnikov, Max Wilke, J. Garrevoet, Maxim Portnyagin, Kevin Klimm, Stephan Buhre, S. Krasheninnikov, R. Almeev, Severine Moune, Gerald Falkenberg
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引用次数: 0
Abstract
Abstract. Here we present a confocal Fe K-edge μ-XANES method (where XANES stands for X-ray absorption near-edge spectroscopy) for the analysis of Fe oxidation state in heterogeneous and one-side-polished samples. The new technique allows for an analysis of small volumes with high spatial 3D resolution of <100 µm3. The probed volume is restricted to that just beneath the surface of the exposed object. This protocol avoids contamination of the signal by the host material and minimizes self-absorption effects. This technique has been tested on a set of experimental glasses with a wide range of Fe3+ / ΣFe ratios. The method was applied to the analysis of natural melt inclusions trapped in forsteritic to fayalitic olivine crystals of the Hekla volcano, Iceland. Our measurements reveal changes in Fe3+ / ΣFe from 0.17 in basaltic up to 0.45 in dacitic melts, whereas the magnetite–ilmenite equilibrium shows redox conditions with Fe3+ / ΣFe ≤0.20 (close to FMQ, fayalite–magnetite–quartz redox equilibrium) along the entire range of Hekla melt compositions. This discrepancy indicates that the oxidized nature of glasses in the melt inclusions could be related to the post-entrapment process of diffusive hydrogen loss from inclusions and associated oxidation of Fe in the melt. The Fe3+ / ΣFe ratio in silicic melts is particularly susceptible to this process due to their low FeO content, and it should be critically evaluated before petrological interpretation.
期刊介绍:
EJM was founded to reach a large audience on an international scale and also for achieving closer cooperation of European countries in the publication of scientific results. The founding societies have set themselves the task of publishing a journal of the highest standard open to all scientists performing mineralogical research in the widest sense of the term, all over the world. Contributions will therefore be published primarily in English.
EJM publishes original papers, review articles and letters dealing with the mineralogical sciences s.l., primarily mineralogy, petrology, geochemistry, crystallography and ore deposits, but also biomineralogy, environmental, applied and technical mineralogy. Nevertheless, papers in any related field, including cultural heritage, will be considered.