Iron-rich silicates in the Earth's D'' layer

Area of Science:

• Geophysics
• Mineral Physics
• High-Pressure Science

Background:

• The Earth's core-mantle boundary (CMB) exhibits complex seismic features, including low-velocity and ultra-low-velocity zones.
• Understanding the mineralogy and physical properties at the CMB is crucial for interpreting deep Earth dynamics.

Purpose of the Study:

• To investigate the potential formation and properties of iron-rich silicate phases under core-mantle boundary conditions.
• To explain the observed seismic anomalies attributed to these deep Earth regions.

Main Methods:

• High-pressure, high-temperature experimental synthesis of silicate phases.
• Theoretical calculations and computational modeling of material properties.
• Analysis of seismic velocity reductions and density variations.

Main Results:

• An iron-rich ferromagnesian silicate phase was successfully synthesized at CMB pressure-temperature conditions.
• This new silicate phase is up to 20% denser than known silicates at the CMB.
• The high mean atomic number of this phase significantly reduces seismic velocity, explaining low-velocity zones.

Conclusions:

• The newly discovered iron-rich silicate phase provides a plausible explanation for seismic velocity anomalies at the base of the lower mantle.
• Its formation via reaction between the silicate mantle and the iron core may account for observed geophysical and geochemical signatures.
• This finding advances our understanding of deep Earth composition and processes at the core-mantle boundary.