The solution behavior of H2O in peralkaline aluminosilicate melts at high pressure with implications for properties of hydrous melts

Solution mechanisms of H2O were obtained by combining Raman and 29Si NMR spectroscopic data. Degree of melt depolymerization, NBO/T, increases with H2O content. The rate of NBO/T-change with H2O is negatively correlated with H2O and positively correlated with Al/(Al+Si). The main depolymerization reaction involves breakage of oxygen bridges in Q4-species to form Q2 species. Steric hindrance appears to restrict bonding of H+ with nonbridging oxygen in Q3 species. The presence of Al3+ does not affect the water solution mechanisms significantly.