Stress-induced amorphization triggers deformation in the lithospheric mantle

Area of Science:

• Geophysics
• Materials Science
• Mineral Physics

Background:

• The mechanical properties of olivine-rich rocks are crucial for understanding the lithosphere-asthenosphere coupling.
• Crystal defect motion governs plastic flow in crystalline materials, but olivine requires additional deformation mechanisms due to limited slip systems.
• Grain-boundary sliding is a proposed mechanism for olivine deformation, yet its microstructural basis and theoretical integration remain unclear.

Purpose of the Study:

• To identify and characterize the deformation mechanism at grain boundaries in olivine-rich rocks.
• To provide a theoretical framework for incorporating grain boundary mechanics into polycrystalline plasticity models.
• To explain the onset of ductility and plastic flow in olivine-rich materials.

Main Methods:

• Experimental investigation of forsterite (an olivine-rich mineral) under stress.
• Microstructural analysis focusing on grain boundaries.
• Theoretical modeling of polycrystalline plasticity.

Main Results:

• Amorphization occurs at grain boundaries in forsterite under stress.
• The development of amorphous layers at grain boundaries activates grain-boundary mobility, leading to ductility.
• This mechanism is particularly relevant at the lithosphere-asthenosphere boundary where olivine approaches its glass transition temperature.

Conclusions:

• A novel mechanism of stress-induced amorphization at grain boundaries governs the ductility of olivine-rich rocks.
• This process facilitates plastic flow in deep Earth environments, especially at the brittle-plastic transition and the lithosphere-asthenosphere boundary.
• The findings provide a new theoretical basis for understanding large-scale geological deformation.