HR: 0800h
AN: V31D-0680    [Abstracts]
TI: Diffusion experiments with natural alkaline melts: estimation of diffusion coefficients for a multicomponent system
AU: * Teixido, F
EM: fteixido@ija.csic.es
AF: Dept. of Earth and Environmental Sc., Theresienstr. 41/III, Munich, 80333, Germany
AU: * Teixido, F
EM: fteixido@ija.csic.es
AF: CSIC, Inst. of Earth Sciences Jaume Almera, C/Lluis i Sabaris s/n, Barcelona, 08028, Spain
AU: De Campos, C P
EM: campos@min.uni-muenchen.de
AF: Dept. of Earth and Environmental Sc., Theresienstr. 41/III, Munich, 80333, Germany
AU: Costa, F
EM: fcosta@ija.csic.es
AF: CSIC, Inst. of Earth Sciences Jaume Almera, C/Lluis i Sabaris s/n, Barcelona, 08028, Spain
AU: Dingwell, D B
EM: Dingwell@lmu.de
AF: Dept. of Earth and Environmental Sc., Theresienstr. 41/III, Munich, 80333, Germany
AU: Marti, J
EM: joan.marti@ija.csic.es
AF: CSIC, Inst. of Earth Sciences Jaume Almera, C/Lluis i Sabaris s/n, Barcelona, 08028, Spain
AB: Magma mixing is known to be interplay between convection and diffusion. Widespread evidence for magma mixing in the Canary Islands, Spain, motivated this work on the diffusion component of this process. We performed a time series of diffusion experiments at 1350°C using alkaline melts from volcanic products from this province. The two end-members are: 1) an alkali basalt (43% SiO2; η=4.412 Pa·s) and 2) a phonolite (59% SiO2; η=1000 Pa·s). For every experiment, a 3 mm thick disk of alkali basaltic glass and a 6 mm thick disk of phonolitic glass were loaded in a 5mm diameter Pt open capsule. They were arranged in a buoyantly stable geometry, where the denser material is placed at the bottom (alkali basalt, ρ=2.73g/cm3) and the lighter material at the top (phonolite, ρ=2.36 g/cm3). We run experiments during 4, 25, 49 and 125 hours at 1350°C at atmospheric conditions. This temperature, well above the liquidus of the system, has been kept constant during the whole experimental runs, with a negligible thermal gradient (< 2°C). No forced convection was applied so that the diffusion process takes over and the compositional gradient becomes the only parameter enhancing the mixing process. Microprobe analyses were performed along longitudinal lines from sections of the resulting products. In order to fit a curve to the experimental data, the diffusion equation is solved using the finite difference method. The conspicuous asymmetry of the diffusion profiles suggests that the D-value is strongly compositional dependent. A better fit can be obtained when the curve is splitted in two and different D-values are calculated for each end- member. Our first estimation of the diffusion coefficients for the major elements will be shown in this work.
DE: 1012 Reactions and phase equilibria (3612, 8412)
DE: 3630 Experimental mineralogy and petrology
DE: 8439 Physics and chemistry of magma bodies
DE: 8445 Experimental volcanism
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting