Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
, 102 (28), 9751-3

Iron-rich Silicates in the Earth's D'' Layer

Affiliations

Iron-rich Silicates in the Earth's D'' Layer

Wendy L Mao et al. Proc Natl Acad Sci U S A.

Abstract

High-pressure experiments and theoretical calculations demonstrate that an iron-rich ferromagnesian silicate phase can be synthesized at the pressure-temperature conditions near the core-mantle boundary. The iron-rich phase is up to 20% denser than any known silicate at the core-mantle boundary. The high mean atomic number of the silicate greatly reduces the seismic velocity and provides an explanation to the low-velocity and ultra-low-velocity zones. Formation of this previously undescribed phase from reaction between the silicate mantle and the iron core may be responsible for the unusual geophysical and geochemical signatures observed at the base of the lower mantle.

Figures

Fig. 1.
Fig. 1.
X-ray diffraction patterns. Patterns are shown for Fs20 at 147 GPa (λ = 0.3888 Å) (a), Fs40 at 141 GPa (λ = 0.4233 Å) (b), Fs60 at 124 GPa (λ = 0.4008 Å) (c), and Fs80 at 138 GPa (λ = 0.4057 Å) (d). ppv peaks are additionally marked with *. Re oxide peaks are marked with †. Pressures were determined from the equation of state of Pt (28). (e) The crystal structure of ppv is shown with silicon octahedrons in blue and iron and magnesium cations in orange.
Fig. 2.
Fig. 2.
Enthalpy of ppv with respect to the silicate perovskite phase of the same composition (the zero horizontal line) in the MgSiO3–FeSiO3 system.
Fig. 3.
Fig. 3.
Density of the ppv phase as a function of x. For comparison, results are corrected to the same pressure at 130 GPa using the theoretical bulk modulus and elastic constants (11, 29). Density is shown with comparison to Fs12 silicate perovskite (× symbol shown with 1% error bar) (21) and the α-PbO2-type (dotted line) and CaCl2-type (dashed line) SiO2 phases (30).

Similar articles

See all similar articles

Cited by 6 articles

See all "Cited by" articles

LinkOut - more resources

Feedback