Chemical interdiffusion of dacite and rhyolite: anhydrous measurements at 1 atm and 10 kbar,application of transition state theory,and diffusion in zoned magma chambers |
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| Authors: | Don R Baker |
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| Institution: | 1. Department of Geology and Center for Glass Science and Technology, Rensselaer Polytechnic Institute, 12180-13590, Troy, NY, USA
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| Abstract: | Chemical diffusivity measurements have been made on anhydrous metaluminous diffusion couples of dacite and rhyolite at 1 atm,
1200°–1400° C, and 10 kbar, 1300°–1600° C, and on anhydrous peraluminous and peralkaline dacite-rhyolite diffusion couples
at 10 kbar, 1300°–1600° C. Chemical diffusivities for Si, Al, Fe, Mg, and Ca were measured in all experiments on the metaluminous
diffusion couples using Boltzmann-Matano analysis, and Si diffusivities were measured on the other diffusion couples. Two
10 kbar metaluminous experiments were analyzed with the X-ray microprobe and diffusivities of Sr, Y, Zr and Nb were measured.
Si diffusivity displays a weak negative correlation with SiO2 content over the range of 65%–75% SiO2. At a given SiO2 content chemical diffusivities of all non-alkali elements are usually within less than an order of magnitude of Si chemical
diffusivity and are controlled by partitioning along the diffusion profile so as to maintain local equilibrium at each point
along the profile. Alkali chemical diffusivities were not measured but can be estimated from the experiments to be orders
of magnitude higher than non-alkali chemical diffusivities. Data were fit to Arrhenius equations for diffusivities measured
at 65, 70 and 75% SiO2. At 1 atm the Arrhenius equation for non-alkalies at 70% SiO2 in the metaluminous system is:
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