Table S1: Compositions of glass and mineral standards Standard Formula d18OVSMOW* San Carlos Olivine Mg1.86Fe0.14SiO4 5.35 Orthopyroxene Mg0.87Fe0.13SiO3 9.2 Albite glass Na0.98K0.02AlSi3O8 10.8 Anorthite glass CaAl2Si2O8 8.3 Orthoclase glass KAlSi3O8 10.3 Silica glass SiO2 10.8 Hydrous albite glass (1 wt. %) (NaAlSi3O8)0.87(H2O)0.13 5.1 Hydrous albite glass (3 wt. %) (NaAlSi3O8)0.69(H2O)0.31 4.7 Hydrous albite glass (7 wt. %) (NaAlSi3O8)0.48(H2O)0.52 3.1 * Measured by laser fluorination of ~ 2mg aliquots at the University of Wisconsin