Hydrogen concentration analyses using SIMS and FTIR: Comparison and calibration for nominally anhydrous minerals

Abstract

[1] We report analyses of hydrogen abundance in experimentally annealed and natural mantle minerals using FTIR and use these data to establish calibration lines for measurement of H 2 O concentrations in olivine, pyroxenes, garnet, amphibole and mica by secondary ion mass spectrometry (SIMS). We have reduced the detection limit for H 2 O analysis by SIMS to 2-4 ppm H 2 O (by weight) through careful attention to sample preparation and vacuum quality. The accuracy of the SIMS calibrations depends on the choice of FTIR extinction coefficients; however, all of the calibrations reported here are shown to be consistent with measurements on standards whose H 2 O abundance has been determined independently via manometry or nuclear reaction analysis. The resulting calibrations are accurate to 10-30% at the 95% confidence limit, with improvements possible through the use of higher-H 2 O standards. Using our SIMS calibration, we determined hydrogen concentrations in coexisting olivine, orthopyroxene, and glass from a single melting experiment at 2 GPa and 1380°C. Olivine/melt and orthopyroxene/melt partition coefficients are equal to 0.0020 ± 0.0002 and 0.0245 ± 0.0015, respectively, and the orthopyroxene/olivine coefficient is 12 ± 4 (2s uncertainties).

Expanding the application of the Eu‐oxybarometer to the lherzolitic shergottites and nakhlites: Implications for the oxidation state heterogeneity of the Martian interior

“…Therefore, this cumulate package represents depleted Martian mantle, a composition comparable in incompatible element composition to terrestrial depleted mantle (i.e., the MORB source [Sun and McDonough 1989] The addition of a reasonable amount of initial water (0.05 wt%) to the Martian magma ocean does not affect the majority of the crystallization sequence perceptibly. The early crystallizing minerals are all nominally anhydrous, meaning that though they can contain petrologically significant amounts of OH (as much as 1000-1500 ppm for olivine and orthopyroxene) (Koga et al 2003;Bell et al 2004;Aubaud et al 2004;Bolfan-Casanova and Keppler 2000), the effect on the overall water content of the melt is small. It is in the late stages of crystallization that the amount of water becomes significant (Fig.…”

NanoSIMS results from olivine-hosted melt embayments: Magma ascent rate during explosive basaltic eruptions

“…It is worth noting that H + diffusion by the redox mechanism in olivine is on the same order of magnitude as H 2 O diffusion in andesitic melt, which raises the question whether any H 2 O-loss occurred through the olivine instead of exclusively through the melt in the embayment. However, diffusive equilibration through the olivine is also a function of its partition coefficient (Qin et al, 1992), which is very low in olivine (Kd H2O ol/liq = 0.001; Aubaud et al 2004;Koga et al 2003), and so equilibration will be much more efficient through the melt embayment to the bubble. Moreover, significant diffusive equilibration (> 10%) was only observed for relatively small melt inclusions in the Fuego samples (< 30 μm radius; Lloyd et al, 2013); the larger relative volume of the melt embayments (equivalent to a 100-200 μm diameter inclusion) would only experience 1-2% equilibration through the olivine over 10-30 minutes, based on the calculations in Lloyd et al (2013, their Fig.…”

Understanding the origin and evolution of water in the Moon through lunar sample studies

“…However, a major challenge in making accurate and precise measurements of H 2 O contents at such low abundances with an instrument such as SIMS is the quantification of background hydrogen. Methods used to reduce extraneous contribution of H during measurements include bakingout of the instrument, mounting samples and analytical standards in a hydrogen-free medium, and storing samples in a vacuum oven/desiccator prior to analysis [149,150]. As a result, indium metal is now routinely used as a mounting medium for the standards used to calibrate against unknowns [149,150].…”