Publication Date:
2014-03-16
Description:
Earth's core is an iron-rich alloy containing several weight percent of light element(s), possibly including silicon. Therefore the high pressure-temperature equations of state of iron–silicon alloys can provide understanding of the properties of Earth's core. We performed X-ray diffraction experiments using laser-heated diamond anvil cells to achieve simultaneous high pressures and temperatures, up to ~200 GPa for Fe–9wt%Si alloy and ~145 GPa for stoichiometric FeSi. We determined equations of state of the D0 3 , hcp + B2, and hcp phases of Fe–9Si, and the B20 and B2 phases of FeSi. We also calculated equations of state of Fe, Fe 11 Si, Fe 5 Si, Fe 3 Si, and FeSi using ab initio methods, finding that iron and silicon atoms have similar volumes at high pressures. By comparing our experimentally-determined equations of state to the observed core density deficit, we find that the maximum amount of silicon in the outer core is ~11 wt%, while the maximum amount in the inner core is 6–8 wt%, for a purely Fe–Si–Ni core. Bulk sound speeds predicted from our equations of state also match those of the inner and outer core for similar ranges of compositions. We find a compositional contrast between the inner and outer core of 3.5–5.6 wt% silicon, depending on the seismological model used. Theoretical and experimental equations of state agree at high pressures. We find a good match to the observed density, density profile, and sound speed of the Earth's core, suggesting that silicon is a viable candidate for the dominant light element.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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