HR: 15:04h
AN: MR23D-08    [Abstracts]
TI: Oxygen Fugacity Buffers at Conditions of the Deep Earth
AU: * Campbell, A J
EM: ajc@umd.edu
AF: University of Maryland, Dept. of Geology, College Park, MD 20742, United States
AU: Danielson, L R
EM: lisa.r.danielson1@jsc.nasa.gov
AF: Johnson Space Center, NASA, Houston, TX 77058, United States
AU: Righter, K
EM: kevin.righter-1@jsc.nasa.gov
AF: Johnson Space Center, NASA, Houston, TX 77058, United States
AU: Seagle, C T
EM: seagle@uchicago.edu
AF: University of Chicago, Dept. of the Geophysical Sciences, Chicago, IL 60637, United States
AU: Wang, Y
EM: wang@cars.uchicago.edu
AF: University of Chicago, Center for Advanced Radiation Sources, Chicago, IL 60637, United States
AU: Prakapenka, V B
EM: prakapenka@cars.uchicago.edu
AF: University of Chicago, Center for Advanced Radiation Sources, Chicago, IL 60637, United States
AB: Oxygen fugacity, a proxy for the chemical potential of oxygen, not only drives redox reactions, element partitioning and structural phase transitions, but also controls some transport and rheological properties, especially in minerals like silicates and oxides in which oxygen vacancies can play a large role. Therefore, the importance of oxygen fugacity in the deep Earth can hardly be overstated. In this study we have constructed oxygen fugacity buffers for the metal-oxide systems Fe-FeO, Ni-NiO, and Re-ReO2 at high pressures and temperatures, extending to the conditions of the lower mantle. Pressure-volume-temperature relations for the Fe-FeO, Ni-NiO, and Re-ReO2 metal-oxide pairs were measured by synchrotron X-ray diffraction in both a multi-anvil press and a laser heated diamond anvil cell. Simultaneous measurement of both the metal and its oxide provided a measure of the volume difference between the two phases that is more precise than comparisons between independently determined equations of state. This allows more precise evaluation of the thermodynamics of the metal-oxide system, including oxygen fugacity buffer curves at high pressure. Nonstoichiometric effects in wustite were eliminated by high-PT equilibration with Fe, allowing the equation of state of stoichiometric FeO to be measured. We show that the differences (in log fO2 units) between the IW and NNO buffers, and also between the IW and RRO buffers, decrease significantly with increasing pressure. These results can augment our understanding of metal-silicate partitioning at high pressures, for example, and form a basis for further investigations into the redox state of the deep Earth.
DE: 1011 Thermodynamics (0766, 3611, 8411)
DE: 3630 Experimental mineralogy and petrology
DE: 3919 Equations of state
DE: 3924 High-pressure behavior
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting