Abstract
The longitudinal sound velocity (VP) and the density (ρ) of wüstite, FeO, were measured at pressures of up to 112.3 GPa and temperatures of up to 1700 K using both inelastic X-ray scattering and X-ray diffraction combined with a laser-heated diamond-anvil cell. The linear relationship between VP and ρ, Birch’s law, for wüstite can be expressed as VP = 1.55 (1) × ρ [g/cm3] − 2.03 (8) [km/s] at 300 K and VP = 1.61 (1) × ρ [kg/m3] − 2.82 (10) [km/s] at 1700 K. The sound velocity of wüstite is significantly lower than that of bridgmanite and ferropericlase under lower mantle conditions. In other words, the existence of wüstite in the lower mantle can efficiently decrease the seismic velocity. Considering its slow velocity and several mechanisms for the formation of FeO-rich regions at the core–mantle boundary, we confirm earlier suggestions indicating that wüstite enrichment at the bottom of the Earth’s mantle may contribute to the formation of denser ultra-low velocity zones.
Highlights
Wüstite, FeO, is one of the most important oxides in the interior of the Earth because it is an endmember of ferropericlase, (Mg,Fe)O, which is the second most dominant phase in the Earth’s lower mantle
The density of wüstite was calculated using the unit cell volume obtained via X-ray diffraction (XRD) at the same conditions as the inelastic X-ray scattering (IXS) measurements
The IXS spectra are characterized by an elastic contribution centered at zero energy and inelastic contributions from the longitudinal acoustic (LA) mode of wüstite and the transverse acoustic (TA) mode from the diamond anvil
Summary
FeO, is one of the most important oxides in the interior of the Earth because it is an endmember of ferropericlase, (Mg,Fe)O, which is the second most dominant phase in the Earth’s lower mantle. Knowledge of the elasticity of wüstite under lower mantle conditions will allow a better understanding of ULVZs. Sound velocity measurements of ferropericlase (e.g., Jackson et al 2006; Lin et al 2006) and magnesiowüstite (e.g., Wicks et al 2010, 2017) have been reported. For sound velocity measurements at high pressure, the combination of a diamond-anvil cell (DAC) and inelastic X-ray scattering (IXS) is a powerful technique (e.g., Badro et al 2007).
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