HR: 1340h
AN: MR43A-0873    [Abstracts]
TI: Trace Element Partitioning Between Metal and Melt at High Pressure
AU: * Campbell, A J
EM: a-campbell@uchicago.edu
AF: University of Chicago, Dept. of the Geophysical Sciences, 5734 S. Ellis Ave., Chicago, IL 60637 United States
AU: Moses, M
EM: mmoses@rohan.sdsu.edu
AF: San Diego State University, Dept. of Geological Sciences, 5500 Campanile Dr., San Diego, CA 92182 United States
AU: Fei, Y
EM: y.fei@gl.ciw.edu
AF: Carnegie Institution of Washington, Geophysical Laboratory, 5251 Broad Branch Rd., N. W., Washington, DC 20015 United States
AB: Fractionations between siderophile trace elements are produced during crystallization of solid metal from a molten planetary core. It has been proposed (e.g., Brandon et al., 2003) that fractionations of Re/Os and Pt/Os produced during crystallization of Earth's inner core are recorded in rocks whose source regions lie at the core-mantle boundary. However, the possible effects of pressure, temperature, composition, and metal crystal structure on metal-melt partitioning have not been fully evaluated experimentally. Accordingly, we have begun to measure the partitioning of major and trace siderophile elements between Fe-rich metal and metal-sulfide melt at high pressures and temperatures using laser ablation ICP-MS of multi-anvil press samples. The starting materials included iron meteorite powder (having natural abundances of PGEs at the $/sim$10 ppm level) and troilite. In some cases Ru powder was also added to the starting material to promote transformation of the Fe-rich metal to the hcp structure, as described by Campbell et al. (2003). The powders were loaded into an MgO or BN sample capsule in a 10/5 multi-anvil press assembly, and pressurized to 14.5 GPa. The sample chamber thickness was held to $<$0.4 mm to minimize the temperature gradient experienced by the samples. Melting was achieved at temperatures of 975 C or above, and run durations were 6 to 24 hours. The recovered run products were polished and examined by SEM or electron microprobe before LA-ICP-MS analysis. Laser ablation spot sizes ranged from 15 to 50 microns, depending on the available grain size. Partition coefficients (D) were determined for Co, Ni, Ru, Re, Os, Ir, and Pt. Errors on the D values were based on the reproduceability of at least 3 measurements in each phase, and were $<$10% for major elements and $<$25% for trace elements. The effects of temperature and composition were evaluated and implications on the chemistry of the core will be discussed. Brandon A. D. et al. (2003) EPSL 206:411-426. Campbell A. J. et al. (2003) Fall AGU Meeting.
DE: 3630 Experimental mineralogy and petrology
DE: 3924 High-pressure behavior
DE: 1065 Trace elements (3670)
DE: 1015 Composition of the core
SC: Mineral and Rock Physics [MR]
MN: 2004 AGU Fall Meeting