Multicomponent Diffusion and Speciation Reactions of Major Melt Components, High Field Strength Elements, and Ligands in Haplogranite Melt

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London & DewersEAR-0124179Three projects will assess or utilize mass transport by diffusion in silicate melts to better understand the properties of granitic liquids. In Project I, we will complete a self-consistent thermodynamic, kinetic, and transport model for the crystallization of water-bearing granite melts under near- and far-from-equilibrium conditions. The mathematical algorithms are now mostly developed, and we have recently completed a large number of experiments that provide constraints on the kinetics of crystallization in the granite system. Project II addresses a simple but intriguing question, namely how do granitic melts become homogeneous by diffusion through the melt (i.e., once eutectic grain-boundary contacts are lost)? Preliminary experiments indicate that rapid diffusion of alkalis promotes the attainment of an equilibrium proportion of alkali feldspar components throughout the melt, and that mixing then occurs between this alkali feldspar component and silica derived from the melting of quartz. Project III will address longstanding presumptions about the relationships among ore-forming metals (e.g., Nb, Ta, Sn, W, Zr, Hf, and REE) and potential ligands (halogens F, and Cl, and oxyanions of H, B, P). Not only will the case for speciation be tested, but the stoichiometry of the probable melt species, along with their diffusion coefficients, will be derived. The results of Project III will elucidate the extent to which anions other than oxygen enhance or decrease the solubility of ore-forming metals in melt.