9632591 Newton It is proposed to continue an investigation of the thermodynamic properties of concentrated electrolyte solutions and their interaction with rock-forming minerals and melts under deep-earth conditions. Previous work has identified an important property of possible deep crust/upper mantle fluids, namely a low H2O activity and yet high alkali mobility of concentrated brines owing to pressure-induced ionic dissociation. This property of brines could have important implications for melting at crustal levels. The main objectives of the current study are to describe the activity-concentration relationships of such fluids, to determine the melting capability for various silicate assemblages in the presence of these brines, and to constrain partition coefficient of alkalis and oxygen isotopes between minerals and silicate melts under crustal conditions.
