TY - JOUR

T1 - Confocal μ-XANES as a tool to analyze Fe oxidation state in heterogeneous samples

T2 - the case of melt inclusions in olivine from the Hekla volcano

AU - Botcharnikov, Roman

AU - Wilke, Max

AU - Garrevoet, Jan

AU - Portnyagin, Maxim

AU - Klimm, Kevin

AU - Buhre, Stephan

AU - Krasheninnikov, Stepan

AU - Almeev, Renat

AU - Moune, Severine

AU - Falkenberg, Gerald

N1 - Funding Information: This research has been supported by the Deutsches Elektronen-Synchrotron (grant nos. I-20160716 and I-20170875), the Deutsche Forschungsgemeinschaft (grant no. Bo2941/4) and Johannes Gutenberg-Universität Mainz (JGU TeMaS Research Platform).This open-access publication was funded by Johannes Gutenberg University Mainz.

PY - 2024/2/12

Y1 - 2024/2/12

N2 - 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.

AB - 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.

UR - http://www.scopus.com/inward/record.url?scp=85185832730&partnerID=8YFLogxK

U2 - 10.5194/ejm-36-195-2024

DO - 10.5194/ejm-36-195-2024

M3 - Article

AN - SCOPUS:85185832730

VL - 36

SP - 195

EP - 208

JO - European journal of mineralogy

JF - European journal of mineralogy

SN - 0935-1221

IS - 1

ER -