Deformation Mechanisms in Shear Zones

Shear zones are narrow regions of intense strain that accommodate displacement within the Earth’s crust and lithosphere. Deformation within these zones spans a continuum from brittle fracturing and grain‐size reduction at low temperatures and pressures to crystal-plastic flow and viscous creep at greater depths and higher temperatures. Key mechanisms include dislocation creep, in which lattice defects migrate under stress to permit crystal-plastic deformation; diffusion creep, involving atom‐scale mass transport along grain boundaries; dissolution–precipitation creep, where material dissolves from high‐stress sites and reprecipitates in low‐stress domains; and grain-boundary sliding, allowing grains to accommodate strain through intergranular slip. Reaction weakening and phase mixing often localise strain in polyphase rocks, with the development of fine-grained aggregates that promote grain-size-sensitive creep. In phyllosilicate-rich rocks, new defect types such as ripplocations permit layer-normal strain without brittle failure. Interactions among these mechanisms control the rheology of shear zones, influence seismic cycle behaviour, and determine the long-term strength profile of the crust. Understanding these processes is essential for models of earthquake nucleation, mountain-building, and resource distribution.

Research from Nature Portfolio

Recent studies have revealed a previously unrecognised deformation mechanism in layered phyllosilicates. High-resolution transmission electron microscopy has identified atomic‐scale bending defects—termed ripplocations—that accommodate layer-normal strain without inducing fractures. These defects form conjugate delamination arrays as elastic strain is relaxed, thereby providing a missing link in our understanding of how phyllosilicate layers deform at seismogenic depths. The discovery of ripplocations has important implications for the rheology of phyllosilicate-bearing faults and subduction interfaces, potentially altering estimates of fault strength and seismic hazard in clay-rich fault cores.

Deformation Mechanisms in Shear Zones publication trend

The graph below shows the total number of articles in deformation mechanisms in shear zones across all publications each year (not limited to Nature Index journals).

Technical terms

Shear zone: A narrow zone in the crust or lithosphere where deformation is highly localised and strain is concentrated.

Dislocation creep: Crystal-plastic deformation mechanism involving the movement of dislocations through a crystal lattice under stress.

Diffusion creep: Deformation by atom-scale diffusion along grain boundaries or through the crystal lattice, leading to shape change without dislocation movement.

Dissolution–precipitation creep: A stress-driven mechanism where mineral matter dissolves at high-stress grain contacts and reprecipitates in low-stress areas, enabling strain at low differential stress.

Grain-boundary sliding: Relative movement of adjacent grains along their boundaries, often accommodated by diffusion or dynamic recrystallisation.

Ripplocations: Atomic-scale bending defects within layered minerals that accommodate layer-normal strain without brittle fracture.

References

1. Grain boundary networks and shape preferred orientation – A fresh angle on pattern quantification with GBPaQ. Computers & Geosciences (2023).
2. Ripplocations provide a new mechanism for the deformation of phyllosilicates in the lithosphere. Nature Communications (2019).
3. Myrmekite and strain weakening in granitoid mylonites. Solid Earth (SE) (2018).