Trace element partitioning and melt structure: An experimental study at 1 atm pressure |
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| Authors: | Bjørn O Mysen David Virgo |
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| Institution: | Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20008, U.S.A. |
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| Abstract: | Diopside-melt and forsterite-melt rare earth (REE) and Ni partition coefficients have been determined as a function of bulk compositions of the melt. Available Raman spectroscopic data have been used to determine the structures of the melts coexisting with diopside and forsterite. The compositional dependence of the partition coefficients is then related to the structural changes of the melt.The melts in all experiments have a ratio of nonbridging oxygens to tetrahedral cations () between 1 and 0. The quenched melts consist of structural units that have, on the average, 2 (chain), 1 (sheet) and 0 (three-dimensional network) nonbridging oxygens per tetrahedral cation. The proportions of these structural units in the melts, as well as the overall , change as a function of the bulk composition of the melt.It has been found that Ce, Sm, Tm and Ni crystal-liquid partition coefficients () decrease linearly with increasing . The values of the individual REE crystal-liquid trace element partition coefficients have different functional relations to , so that the degree of light REE enrichment of the melts would depend on their .The solution mechanisms of minor oxides such as CO2, H2O, TiO2, P2O5 and Fe2O3 in silicate melts are known. These data have been recast as changes of of the melts with regard to the type of oxide and its concentration in the melt. From such data the dependence of crystal-liquid partition coefficients on concentration and type of minor oxide in melt solution has been calculated. |
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