Structural, redox and isotopic behaviors of iron in geological silicate glasses: A NRIXS study of Lamb-Mössbauer factors and force constants

We report a combined conventional Mössbauer and synchrotron Nuclear Resonant Inelastic X-ray Scattering (NRIXS) study of series basalt, andesite, dacite, rhyolite glasses at temperatures ranging from 5 to 1223 K. These were synthesized under controlled oxygen fugacities span wide range Fe3+/Fetot ratios. As expected theory, we find that in these glasses, the inverse Lamb-Mössbauer factor (the recoil-free fraction) correlates linearly with fraction spectrum can be ascribed Fe3+. Extrapolating linear relationships pure Fe3+ Fe2+ endmembers yields ratio for factors C 1.203 ± 0.017 (1σ), no clear dependence on chemical composition glass. show materials studied follow harmonic approximation up K olivine 773 basaltic glass, allowing us extrapolate temperature. The temperature-dependence is well approximated by formula C=1.203±0.033T/300 over temperature 50–750 This calibration used correct previous redox determinations. investigate how iron state influence mean force constant key driver Fe isotopic fractionation during magma generation differentiation. previously documented Dauphas et al. (2014), correlation between bond strength secondarily modulated coordination effects more alkali-rich felsic magmas. New data simplified glass compositions reveal network modifiers, notably Na, seem exert an important control strengths. refined improve calibrations geological using XANES spectroscopy. reevaluate MORBs based published data. 0.087±0.005