EPMA, RAMAN AND XANES APPLIED FOR THE STUDY OF OXIDATION PROCESSES IN GLASS

摘要

Quantifying the oxidation state of Fe and S in silicate melts is an important aspect of volcanology and igneous petrology as the ratios can be used as proxies for oxygen fugacity, a fundamental thermodynamic parameter that provides information on the chemical history of melt from the magma chamber to the Earth's surface. In practice, analyses of these elements are performed on quenched volcanic melt forming the matrix between crystals or as trapped inclusions. As a result, microanalytical techniques are required due to their small volume and multiple techniques are applied to the same small region to extract the full information required to understand volcanic and magmatic processes. This can be problematic as glasses are often unstable under the electron and photon beams used to analyse them. It is, therefore, important to understand the compositional and structural changes to the glass during analysis to ensure accurate measurements and that subsequent complimentary analyses are not compromised. Here we look at the most common techniques currently used for measuring the oxidation state of Fe and S in silicate glass and how these glasses respond to electron and photon beam irradiation.