Hydrogen isotope fractionation <i>inside</i> silicate melts and glasses studied by <SUP>1</SUP>H and <SUP>2</SUP>H MAS NMR spectroscopy - Molecular insights into deuterium exchange at the melt-fluid interface

Hydrogen isotope ratios (D/H) measured on geological samples are used to trace the pathways of water in magmatic and hydrothermal systems. Interpreting respective isotope data relies thereby on the theoretical and empirical constraints on hydrogen isotope fractionation. This study revisits a recently discovered hydrogen isotope fractionation effect between alkali-rich and alkali-poor regions within hydrous alkali silicate melts (Wang et al., 2015). In a series of experiments conducted at variable P-T-X-H2O,X- D2O conditions, we studied this intramolecular isotope effect by H-1 and H-2 solid-state nuclear magnetic resonance (NMR) spectroscopy on quenched hydrous sodium tetrasilicate melts (Na(2)Os4SiO(2) with 1:1 H2O and D2O).