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Iron-rich silicates in the Earth's D'' layer
Wendy L Mao1, Yue Meng, Guoyin Shen
1Department of the Geophysical Sciences and Chicago Center for Cosmochemistry, University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637, USA. wmao@uchicago.edu
Summary
A novel iron-rich silicate phase synthesized near the core-mantle boundary explains seismic anomalies. This dense phase, formed from mantle-core reactions, offers insights into deep Earth processes and signatures at the lower mantle base.
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.