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Si in the core? New high-pressure and high-temperature experimental data |
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| Authors: | Va?rie Malavergne Julien Siebert Fra?ois Guyot Laurent Gautron Tahar Hammouda Dan Frost |
| Institution: | 1 Universit? de Marne-La-Val?e, Laboratoire des ?omat?riaux and FRE CNRS 2455, Cit? Descartes, Champs-sur-Marne, 77454 Marne-La-Val?e ?dex, France 2 Institut de Physique du Globe de Paris, 4 place Jussieu, 75 252 Paris cedex 05, France 3 Laboratoire de mińralogie-cristallographie and UMR CNRS 7590, Case 115, 4 place Jussieu, 75 252 Paris cedex 05, France 4 Laboratoire Magma et Volcan, OPGC, Universit? Blaise Pascal—CNRS, 5 rue Kessler, 63038 Clermont-Ferrand cedex, France 5 UPR15 du CNRS, Physique des Liquides et Electrochimie, 4 Place Jussieu, 75252 Paris Cedex 05, France 6 Bayerisches Geoinstitut, Universi?t Bayreuth, D-95440, Bayreuth, Germany 7 Laboratoire de ?ochimie des Isotopes Stables, IPGP—Universit? Paris 7, 2, place Jussieu, Tour 54-64 -75252 Paris Cedex 05, France |
| Abstract: | High-pressure high-temperature experiments have been carried out up to 25 GPa and 2200°C in a multianvil press on assemblages made of silicates and iron-silicon alloys. At 20 GPa, silicon is extracted from the metal phase, forming stishovite reaction rims around metal grains. The silicon content in metal has been measured by analytical electron microscopy and electron microprobe. In contrast with earlier experiments, the present data were obtained by using silicon-rich metal alloys as starting materials instead of studying incorporation of silicon in initially silicon-free metal. As in most of previous studies carried out below 25 GPa, the silicon content in liquid metal increases with increasing pressure and with decreasing oxygen fugacity. The oxygen fugacity in most experiments was calculated by using two independent buffers: iron/?stite (IW) and SiO2/Si, allowing to link consistently the Fe contents in silicates, the Si contents in metal and the temperatures of the experiments. At oxygen fugacities 4 log units below IW, silicates are in equilibrium with Si-rich metallic alloys (up to 17 wt% of Si in metal at 20 GPa and 2200°C). Extrapolation to 2 log units below IW leads to less than 0.1 wt% Si in the metal phase. Presence of several wt% of silicon in the Earth’s core thus requires highly reduced initial materials that, if equilibrated at conditions relevant to small planets, should already contain significant amount of silicon dissolved in metal. |
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