In:
Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 109, No. 26 ( 2012-06-26), p. 10239-10244
Abstract:
Compressional wave velocity-density ( V P - ρ ) relations of candidate Fe alloys at relevant pressure-temperature conditions of the Earth’s core are critically needed to evaluate the composition, seismic signatures, and geodynamics of the planet’s remotest region. Specifically, comparison between seismic V P - ρ profiles of the core and candidate Fe alloys provides first-order information on the amount and type of potential light elements—including H, C, O, Si, and/or S—needed to compensate the density deficit of the core. To address this issue, here we have surveyed and analyzed the literature results in conjunction with newly measured V P - ρ results of hexagonal closest-packed (hcp) Fe and hcp-Fe 0.85 Si 0.15 alloy using in situ high-energy resolution inelastic X-ray scattering and X-ray diffraction. The nature of the Fe-Si alloy where Si is readily soluble in Fe represents an ideal solid-solution case to better understand the light-element alloying effects. Our results show that high temperature significantly decreases the V P of hcp-Fe at high pressures, and the Fe-Si alloy exhibits similar high-pressure V P - ρ behavior to hcp-Fe via a constant density offset. These V P - ρ data at a given temperature can be better described by an empirical power-law function with a concave behavior at higher densities than with a linear approximation. Our new datasets, together with literature results, allow us to build new V P - ρ models of Fe alloys in order to determine the chemical composition of the core. Our models show that the V P - ρ profile of Fe with 8 wt % Si at 6,000 K matches well with the Preliminary Reference Earth Model of the inner core.
Type of Medium:
Online Resource
ISSN:
0027-8424
,
1091-6490
DOI:
10.1073/pnas.1207086109
Language:
English
Publisher:
Proceedings of the National Academy of Sciences
Publication Date:
2012
detail.hit.zdb_id:
209104-5
detail.hit.zdb_id:
1461794-8
SSG:
11
SSG:
12
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