Intramolecular fractionation of hydrogen isotopes in silicate quenched melts

Abstract

The interplay between the chemical composition and the molecular structure of silicate melts was central to the evolution of the Earth's crust, mantle and core. This interplay also affects geochemical records such as the partitioning of isotopes between minerals, melts and fluids in the Earth's interior. For instance, large 2H/1H fractionations between silicate melts and aqueous fluids have been observed at high temperature and pressure. Such behaviour may be promoted by the occurrence of 2H/1H intramolecular fractionation within the molecular structure of silicate melts. New Raman spectroscopy and 1H and 2H Nuclear Magnetic Resonance (NMR) spectroscopy data reveal the source of such 2H/1H intramolecular isotopic fractionation, showing that 1H and 2H fractionate between the silicate tetrahedral units. Such a process might affect other isotopic systems (e.g., N, C, or S) where the isotopes interact with the melt silicate network.