HR: 11:50h
AN: T21F-07    [PDF]
TI: Diamond Formation in Core Segregation Experiments : a key for Estimating the Carbon Content of Planetary Cores
AU: Siebert, J
EM: sieb2001@hotmail.com
AF: Laboratoire Geomateriaux, Universite de Marne la Vallee. Cite Descartes. Champs-sur-Marne, Marne la Vallee, 77454 France
AU: * Guyot, F
EM: guyot@lmcp.jussieu.fr
AF: LMCP-IPGP, 4 place Jussieu, Paris, 75005 France
AU: Malavergne, V
EM: malaverg@univ-mlv.fr
AF: Laboratoire Geomateriaux, Universite de Marne la Vallee. Cite Descartes. Champs-sur-Marne, Marne la Vallee, 77454 France
AU: Chaussidon, M
EM: chocho@crpg.cnrs-nancy.fr
AF: CRPG, 15 rue ND des Pauvres, Vandoeuvre, 54501 France
AB: High-pressure experiments were performed in a multi-anvil press at 1700 $\deg$C and pressures between 10 and 25 GPa on assemblages of iron carbonate (siderite) and silicon. The relative proportions of the two phases were varied in order to investigate different conditions of oxygen fugacities in the run products. The relevance of the investigated experimental conditions to core formation models is discussed. Samples were studied by Raman spectroscopy, electron microscopy, ion and nuclear microprobes. In all samples, siderite was reduced to (Fe,Si) metallic alloy and to diamond whereas silicon was partially oxidized to stishovite. The diamonds formed are euhedral crystals with characterisitc sizes of 20 micrometers. The carbon content in the metal phase equilibrated with those diamonds (diamond saturation) has been measured by ion microprobe to be of 1.5 wt %. This number would be an upper bound for the carbon content of planetary cores formed under such conditions. This suggests that the carbon content in the Earth's core is low when compared to the cosmic abundance of this element, but large enough for the inner core to be constituted of iron carbide (see Wood et al 1993, Earth and Planetary Science Letters, 117, 593-607). Moreover, this study brings new constraints on the relative position of silicon-stishovite and carbon-carbonate buffers at high pressure and provides experimental evidence of diamond formation from reduction of carbonates by reaction with Fe-Si alloys.
DE: 1015 Composition of the core
DE: 3630 Experimental mineralogy and petrology
DE: 3924 High-pressure behavior
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 8147 Planetary interiors (5430, 5724)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting