HR: 0800h
AN: V41F-1524    [Abstracts]
TI: Experimental Investigation of High-Temperature Iron Isotope Fractionation in the Iron-Iron Sulfide System
AU: * Homburg, J M
EM: jhomburg@rice.edu
AF: Department of Earth Science, Rice University, 6100 Main St. MS#126, Houston, TX 77005 United States
AU: Gaetani, G A
EM: ggaetani@whoi.edu
AF: Department of Geology and Geophysics, Woods Hole Oceanographic Institution, 360 Woods Hole Road MS #8, Woods Hole, MA 02543 United States
AU: Sims, K W
EM: ksims@whoi.edu
AF: Department of Geology and Geophysics, Woods Hole Oceanographic Institution, 266 Woods Hole Road MS#23, Woods Hole, MA 02543 United States
AB: Several recent studies have suggested that isotopes of Fe and other mid-weight elements can be fractionated at high temperatures. Reduction-oxidation reactions have been proposed as a mechanism by which these fractionations are produced. Specifically in studies of iron meteorites that contain iron sulfide, the sulfidation reaction associated with the formation of troilite has been invoked in order to explain the Fe isotope fractionations reported in these samples (Williams et al., Eos, Transactions, American Geophysical Union, vol.85, no.47, 2004). We carried out a series of experiments in order to examine the plausibility of the sulfidation reaction as a mechanism for generating high-temperature Fe isotope fractionation. Experiments were carried out using a solid-medium piston-cylinder device in which a homogenized powder comprised of high-purity Fe metal and sulfur was packed into a fused-quartz capsule and equilibrated at high temperature and pressure conditions (1000°C, 10 kb) for varying lengths of time (6 to 168 hours). The experiments produced two equilibrium phases: solid Fe metal and solid Fe sulfide (troilite). Electron microprobe analyses of the charges indicate that both phases are pure and homogeneous with Fe metal representing the iron phase and stoichiometric troilite representing the iron sulfide phase. Analysis of the Fe isotopic composition of the experimentally produced phases was carried out using laser ablation-multi collector-inductively coupled plasma-mass spectrometer (LA-MC-ICP-MS) on the Thermo Finnigan Neptune. Results indicate that no systematic fractionation occurred in the experiments, within the analytical resolution of the measurements (external reproducibility approximately 500 ppm). While the iron sulfide displayed a systematically light isotopic composition (-0.30 δ^57/54Fe to -0.07 δ^57/54Fe) relative to IRMM-014, it was not always lighter then the corresponding metal phase (-0.47 δ^57/54Fe to 0.32 δ^57/54Fe).
DE: 1015 Composition of the core
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1060 Planetary geochemistry (5405, 5410, 5704, 5709, 6005, 6008)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005