Redox State of Volatiles and Their Relationships with Iron in Silicate Melts

The question of how degassing of H-C-O-S-Cl fluids may change Fe 3+ /ΣFe ratio and redox conditions in silicate melts has been widely addressed via the experiments and studies of natural systems. After a brief summary of the solubility data and the possible role of the volatile species (CO 2 , H 2 O, S, Cl) on the redox of magmas during their decompression, the review focuses on the behavior of water and sulfur redox during magma degassing, the relationships between these two species with iron in silicate melts through experimental petrology, geochemical investigations, and modeling of natural systems using cutting-edge methods to determine the redox of S and Fe.