Isotopic fractionation: A kinetic model for crystals growing from magmatic melts |
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| Authors: | A Jambon |
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| Institution: | Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, N.W., Washington, DC 20015, U.S.A. |
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| Abstract: | Recent experiments in the fields of crystal growth, crystal-melt element partitioning, and diffusion in magmatic melts make it possible to estimate disequilibrium partitioning for many species between liquid and crystals and to compute quantitative models which take into account partition coefficients, diffusivities and rates of crystal growth. A slight difference in the diffusivities of two isotopes should lead to selective depletion (or enrichment) in the crystals as they grow, resulting in varying isotopic ratios as crystallization proceeds. Reasonable hypotheses permit under general kinetic conditions an estimation of magnitude of possible effects. The resulting isotopic fractionation for major elements (like oxygen) may exceed the per ml level; for trace elements the effects may be more significant (5–10 per ml), especially in the case of low partition coefficients, but analytical difficulties are formidable at present. |
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