Deformation and Anisotropy of Upper Mantle Materials

The mechanical behaviour of Earth’s upper mantle is governed by the deformation of peridotite, dominated by the mineral olivine, under high‐temperature and high‐pressure conditions. Deformation processes such as dislocation creep, diffusion creep and grain‐boundary sliding control the way mantle rocks accommodate stress over geological timescales. Crystallographic preferred orientations develop as minerals deform, producing anisotropy in seismic wave speeds and viscosity. Such anisotropy influences plate motions, mantle convection patterns and the localisation of strain into shear zones. Grain size, temperature, pressure, fluid presence and mineral phase assemblage all modify creep mechanisms and the evolution of fabric. Recent advances combine field observations of exhumed mantle peridotites, laboratory experiments on synthetic aggregates and theoretical models of dislocation dynamics. Together, these studies reveal how feedbacks between microstructural evolution, fluid circulation and regional tectonics govern the strength and anisotropic fabric of the upper mantle, with implications for interpreting seismic anisotropy, understanding fault mechanics at depth, and modelling large‐scale geodynamic processes.

Research from Nature Portfolio

Recent studies have demonstrated that fluid-assisted dissolution–precipitation creep can dramatically reduce grain size and localise strain in oceanic transform faults. Analysis of ultramafic mylonites reveals that fluid-mediated grain-scale reactions weaken the mantle at lower stresses than predicted by dislocation creep alone, providing a key mechanism for fault initiation and maintenance in the lower oceanic lithosphere.

Microstructural investigations of olivine crystals in volcanic mush piles show that pressure and strain produce distorted lattice fabrics analogous to those in deformed mantle peridotites. Electron backscatter diffraction data from melt-rich reservoirs indicate differential stresses of several megapascals, constraining the thickness and dynamics of crystal-rich accumulations beneath active volcanic systems.

Deformation and Anisotropy of Upper Mantle Materials publication trend

The graph below shows the total number of articles in deformation and anisotropy of upper mantle materials across all publications each year (not limited to Nature Index journals).

Technical terms

Anisotropy: Directional dependence of a material’s physical properties, such as viscosity or seismic wave speed.

Dislocation creep: Deformation mechanism in crystalline materials involving movement of dislocations through the crystal lattice under stress.

Diffusion creep: Grain-size-sensitive deformation controlled by atomic diffusion along grain boundaries and through the crystal lattice.

Grain-boundary sliding: Relative motion between adjacent mineral grains accommodating strain, often coupled with diffusion or dislocation processes.

Shear zone: Localised region of intense deformation in the upper mantle where strain is accommodated by ductile or brittle processes.

Crystallographic preferred orientation (CPO): Alignment of mineral crystals in a rock, leading to anisotropy in its mechanical and seismic properties.

References

1. Fluid-assisted grain size reduction leads to strain localization in oceanic transform faults. Nature Communications (2023).
2. Microstructural constraints on magmatic mushes under Kīlauea Volcano, Hawaiʻi. Nature Communications (2020).
3. Ductile Deformation of the Lithospheric Mantle. Annual Review of Earth and Planetary Sciences (2023).
4. Dislocation theory of steady and transient creep of crystalline solids: Predictions for olivine. Proceedings of the National Academy of Sciences of the United States of America (2023).
5. Low‐Temperature Plasticity in Olivine: Grain Size, Strain Hardening, and the Strength of the Lithosphere. Journal of Geophysical Research: Solid Earth (2019).
6. The Effect of Secondary‐Phase Fraction on the Deformation of Olivine + Ferropericlase Aggregates: 1. Microstructural Evolution. Journal of Geophysical Research: Solid Earth (2023).