Experiments establishing the effect of pressure on the Fe 3+ /ΣFe ratio of andesitic silicate melts buffered by coexisting Ru and RuO 2 were performed from 100 kPa to 7 GPa and 1400-1750°C. Fe 3+ /ΣFe ratios were determined by room temperature Mössbauer spectroscopy, but corrected for the effects of recoilless fraction. Fe 3+ /ΣFe ratios in quenched glasses decrease with increasing pressure consistent with previous results between 100 kPa and 3 GPa (O'Neill et al., 2006), but show only small pressure effects above 5 GPa. Ratios also decrease with increasing temperature. Mössbauer hyperfine parameters indicate mean coordination of Fe 3+ ions of ~5 in glasses, with no dependence on the pressure from which the glasses were quenched, but show an increase with pressure in mean coordination of Fe 2+ ions, from ~5 to ~6. XANES spectra on these glasses show variations in pre-edge intensities and centroid positions that are systematic with Fe 3+ /ΣFe, but are displaced from those established from otherwise identical andesitic glasses quenched at 100 kPa (Zhang et al. 2016). These systematics permit construction of a new XANES calibration curve relating pre-edge sub-peak intensities to Fe 3+ /ΣFe applicable to high pressure glasses. Consistent with

11Andesitic glasses equilibrated at 1350 °C over a range of oxygen fugacities 12 (log fO 2 from -8.63 to -0.68) were examined with Fe K-edge X-ray absorption 13 near-edge structure (XANES) and Mössbauer spectra. XANES spectral features 14 were then calibrated as a function of Mössbauer-derived Fe 3+ /∑Fe ratios. 15Additionally, both methods help characterize the local structure of iron ions in 16 andesitic glasses. Fe 3+ /∑Fe ratios were determined from Mössbauer spectra 17 collected at room temperature but corrected with recoilless fractions obtained 18 from previously reported Mössbauer data collected on one of the glasses from 19 47-293 K. An empirical model was derived for the correlation between the pre-20 edge centroid energy and Fe 3+ /∑Fe ratio for andesitic glasses. This trend is 21 intermediate between those previously determined for rhyolitic and basaltic 22 glasses, but the distinction from basaltic compositions may be owing chiefly to 23