The oxygen fugacity of magmas partially governs the chemical evolution, degassing behavior, and economic potential of volcanic systems. Fe XANES analyses of volcanic glass is among the most important precise tools used to characterize magmatic oxygen fugacity. In recent years this technique has led to a number of exciting discoveries about how oxygen fugacity evolves during the life of a volcanic system. However, these discoveries are underlain by a cri5cal assump5on: that the valence state of iron
in volcanic glass is the same as the valence state of iron in high-temperature silicate melt. In this talk, I test whether sulfur and iron exchange electrons during the rapid cooling of silicate melts, altering iron valence state from its high temperature value. As a natural test case, I study the glassy margins of two pillow basalts erupted on the sea-floor, and will describe S and Fe XANES analyses along transects from the rapidly quenched rim of the pillows down into the slowly-quenched crystal-rich interiors. I will
discuss the implications of these results both for prior work and for future studies.

*Refreshments: 12-12:30 PM, ES&T Atrium