Diamond Formation in Core Segregation Experiments: a key for Estimating the Carbon Content of Planetary Cores

摘要: 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 …