High precision water quantification by Raman spectroscopy: Applications to volcanic and extraterrestrial samples

Volcanic petrology is a promising field to quantify processes that occur during eruptions, but it currently relies on very expensive and complex analytical techniques. Of particular importance is the development of precise, high spatial resolution techniques to measure volatile species (e.g., H 2 O, CO 2 , S) in volcanic glasses for understanding magmatic storage and eruptive potential. H 2 O controls the chemical and physical properties of magmas, impacting crystallization, viscosity, and buoyancy, and plays a significant role in the development of terrestrial planets. The predominant tools used to measure volatiles in volcanic glasses (as recorded in melt inclusions; MIs) typically require extensive and time-consuming sample preparation, and instrumentation is often not available in the timeframe of ongoing volcanic eruptions. Confocal Raman spectroscopy provides an alternative method that has been used successfully in recent years to quantify H 2 O contents of volcanic glasses and MIs with high spatial resolution, minimal sample preparation, and high throughput, such that samples can be analyzed within hours to days following sample collection. Here, we present high-precision calibrations for measuring dissolved H 2 O in silicate glasses by Raman spectroscopy using a high-energy 473-nm (blue) excitation source. To understand how this calibration compares to those derived from other microanalytical techniques, we analyzed reference glasses commonly used in different laboratories to calibrate volatile species. We then applied this calibration to exposed terrestrial MIs, melt embayments, and unexposed terrestrial and Martian MIs. The development of a method to measure water concentrations in unexposed MIs is critical for applications where preservation of rare samples is essential.