Implications for plastic flow in the deep mantle from modelling dislocations in MgSiO3 minerals

Area of Science:

• Geophysics
• Mineral Physics
• Materials Science

Background:

• Mantle convection, driven by heat transport, governs Earth's interior dynamics.
• High-temperature creep of MgSiO3 perovskite dominates deep mantle flow.
• The mechanical properties of MgSiO3 perovskite and its post-perovskite phase are crucial for understanding the lowermost mantle but remain largely unknown.

Purpose of the Study:

• To investigate the mechanical properties of MgSiO3 perovskite and post-perovskite phases under high pressure.
• To understand the role of dislocations in the plastic deformation of these minerals.
• To explore the implications for seismic anisotropy in the Earth's lowermost mantle.

Main Methods:

• Development of dislocation core models based on the Peierls-Nabarro framework.
• Modeling of MgSiO3 perovskite at 100 GPa and post-perovskite at 120 GPa.
• Analysis of plastic deformation influenced by unit cell distortions and dislocation core dissociation.

Main Results:

• Plastic deformation in perovskite is significantly affected by orthorhombic unit cell distortions.
• In silicate post-perovskite, dislocations relax through core dissociation.
• These findings provide insights into the mechanical behavior of minerals in the deep Earth.

Conclusions:

• The study provides a novel approach to modeling dislocation behavior in high-pressure mantle minerals.
• The proposed models offer explanations for seismic anisotropy observed in the lowermost mantle.
• Understanding these dislocation dynamics is essential for accurate geodynamic models of the Earth's interior.