Crystal Chemistry of Some Silicates and Carbonates

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Diffusion of Al and Si in network structures is greatly enhanced at pressures greater than 10 kbar in the presence of hydrogen, and the rate of the order-disorder reaction in feldspar is accelerated enough that structural state equilibration of some compositions was achieved, in the absence of water, at temperatures as low as 650oC. Further, direct anhydrous oxygen isotopic exchange between carbonates and silicates can be carried out. Hydrogen activated high-pressure diffusional enhancement will be pursued in this project in several directions: a)Reaction mechanisms. b) Structural state equilibration. c) Equilibrium oxygen isotope fractionation factors between CaCO3 and quartz, albite, anorthite, grossular will be further refined, and extended to magnetite, layer structures and amphiboles. d) The hydrothermal melting relations of KAlSi3O8 at high pressures will be investigated. Speeding up these diffusional mechanisms by the presence of hydrogen will permit us to determine, in laboratory time scales, natural reactions that occur in geologic time.