Study of Fe-S-Si immiscible system at high pressure and high temperature: implications for planetary cores

Details Study of Fe-S-Si immiscible system at high pressure and high temperature: implications for planetary cores Study of Fe-S-Si immiscible system at high pressure and high temperature: implications for planetary cores

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmmr43b1872m&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #MR43B-1872

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[1015] Geochemistry / Composition Of The Core

Scientific paper

Even if it is not really quantified, there is a general agreement on the fact that the Earth's core is an alloy of Fe with 5-15 % of light elements. The list of the light elements that are sufficiently abundant in cosmochemical models, siderophile and not too volatile under proto Earth's conditions is not very long: S, Si, O, C and H. The nature and proportion of these elements are important not only because it is necessary to power the geodynamo (Alfè et al., Earth Planet. Sc. Lett. 195, 91-98 2002), but also because it has large influences on the global geochemical balance (Rubie et al., Nature 429, 58-61 2004), and on segregation processes during Earth’s differentiation (Terasaki et al., Earth Planet. Sc. Lett. 232, 379-392 2005). Fe-S-Si immiscibility has been investigated using in situ X-ray methods at high pressure and high temperature (Morard et al., J. Geophys. Res. 113, B10205 2008). On one hand, in order to prove that quench textures represent the high temperature-high pressure state, we performed X-ray radiography experiments using multi anvil apparatus at Spring8 facility. On the other hand, we studied the liquid structure by in situ X-ray diffraction in order to bring crucial information to understand the cause of the immiscibility at low pressure and the reason of the closure of the gap at high pressure. Hard sphere models have been applied to the high pressure Fe-S liquid diffraction signal, and compressibility data has been extracted. The closure of miscibility gap in the Fe-S-Si system has been studied from 4 GPa to 12 GPa up to 2200 K, highlighting a stable immiscible zone up to 4 GPa. The evolution of Fe-S-Si miscibility gap is linked with the change in the local order in Fe and Fe-S liquids. Earth’s core composition, derived from chondritic models, needs to be inherited from processes at higher pressure than 4 GPa. Planetesimal differentiation would be affected by immiscibility up to size similar to the Moon.

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