HR: 14:40h
AN: V23B-05    [Abstracts]
TI: Electrochemically-Induced Redox Reactions in Basalt at High Pressure and Temperature: An Iron and Vanadium K-edge XANES Study
AU: * Kavner, A
EM: akavner@igpp.ucla.edu
AF: UCLA, 595 Charles Young Dr., E, Los Angeles, CA 90095 United States
AU: Walker, D
EM: dwalker@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory at Columbia University, 61 Rt. 9W, Palisades, NY 10964 United States
AU: Newville, M
EM: newville@cars.uchicago.edu
AF: Consortium for Advanced Radiation Sources, University of Chicago, Chicago, IL 60637 United States
AU: Sutton, S R
EM: sutton@cars.uchicago.edu
AF: Consortium for Advanced Radiation Sources, University of Chicago, Chicago, IL 60637 United States
AB: An applied electric field across a silicate sample at high pressures and temperatures in a piston cylinder apparatus can generate a wide range of oxidation states of polyvalent cations within a single experiment. If two or more polyvalent cations are included, this technique can be used to cross-calibrate oxybarometers within a single experiment. The redox state of Fe and V within a partially melted basaltic silicate was manipulated in situ in a piston-cylinder experiment with a DC power supply providing a source and sink of electrons to the sample. A 1V electrical potential differential was applied across vanadium-doped and Fe-bearing synthetic basalt samples for 24 hrs. at 20 kbar and 1400°C in a specially-designed piston cylinder sample assembly. Three experiments were performed: a control sample with no applied voltage, one with bottom cathode and top anode, and a third with top cathode and bottom anode. Synchrotron-based x-ray absorption near edge structure (XANES) spectroscopy was used to provide spot analysis of iron and vanadium oxidation states with 5μm x 5μm spatial resolution throughout the recovered samples. Systematic spatial changes of increasing oxidation states of V and Fe were observed approaching the anode. The differences in oxidation states were mapped to a corresponding local effective oxygen fugacity by comparison and extension of a calibration of vanadium oxidation states as a function of controlled oxygen fugacity from a previous study (Sutton et al., 2005, GCA, vol. 69, pp. 2333-2348). The vanadium mapping indicates that a 1V potential drop across the sample induces effective oxygen fugacity perturbations in excess of ten orders of magnitude. The presence of both Fe and V within the same sample provides a wide range of oxygen fugacity cross-calibration in these recovered samples. A relationship between oxygen fugacity and electrochemical driving force is derived. The experimental results are in good agreement with the derived relationship between applied electrochemical potential difference (the 1V in this experiment), and corresponding calculated oxygen fugacity.
DE: 0471 Oxidation/reduction reactions (4851)
DE: 1011 Thermodynamics (0766, 3611, 8411)
DE: 1065 Major and trace element geochemistry
DE: 3630 Experimental mineralogy and petrology
DE: 3954 X-ray, neutron, and electron spectroscopy and diffraction
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005