Physics
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufm.t21f..07s&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #T21F-07
Physics
1015 Composition Of The Core, 3630 Experimental Mineralogy And Petrology, 3924 High-Pressure Behavior, 8124 Earth'S Interior: Composition And State (Old 8105), 8147 Planetary Interiors (5430, 5724)
Scientific paper
High-pressure experiments were performed in a multi-anvil press at 1700 ° 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.
Chaussidon Marc
Guyot Francois
Malavergne Valã©Rie
Siebert Joachim
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