Table of Deformation Mechanisms and Processes

VIEPS/Mainz Microstructure Course  
| TOC | Lecture 1 2 3 4 a b   5 a b | Lab 1 a b c 2 a b c 3 a b 4 a b 5 a b | Glossary Table 1 2 3 4 5 Index |

 
NAME OF PROCESS(P) OR MECHANISM (M)  ATOMIC SCALE PROCESS DIAGNOSTIC MICRO- 
STRUCTURES
Grain Shape Foliation Crystallographic Preferred Orientation  RHEOLOGICAL IMPLICATIONS  COMMON MINERALS
Fracturing (M) Breaking of inter-atomic bonds  Gouge, breccias, boudinaged grains  +ve or -ve -ve (ie negative, is weakened by this mechanism)    Any, more at high stress & low T 
Frictional Sliding (M) Frictional sliding on surfaces  Gouges, breccias, pseudotachylites, domino grains  +ve or -ve -ve  Any, more at high stress & low T 
Diffusional Creep (M) Diffusional movement of vacancies and interstitials  New crystal void of pre-existing impurities (hard to prove in nature)  +ve ?  (Nabarro-Herring) or  (Coble creep)  Any, more at low stress & high T 
Dislocation Glide (M) Re-arrangement of inter-atomic bonds  Deformation lamellae, deformation bands, undulose extinction  +ve ++ve  also a hardening with finer grain size (Hall-Petch Law)  Any, more at low stress & high T 
Twinning (M) Re-arrangement of inter-atomic bonds and re-orientation of lattice site  Twins (sharp nosed, narrow, parallel to rational twin planes)  +ve +ve    Calcite especially at low T and low strain, plagioclase, quartz (but not visible), amphiboles 
Kinking (M) Dislocation glide on single slip system  Kink bands +ve  +ve   Micas, low T quartz, kyanite 
Grain Boundary Migration (P or M)  Atomic scale diffusional processes, possibly involving dissolution and precipitation  Irregular grain boundaries, pinning microstructures, orientation families, Lattice preferred orientations with strong point maxima, non-120°-triple junctions  +ve or -ve +ve  Produces low dislocation density material Q softer  Any, more at high T, especially quartz, olivine, fsp 
Rotation Recrystallisation (P)  Progressive addition of dislocations of same sign to sub-grain wall  Mortar texture or core and mantle texture, bi-modal grain size  -ve -ve  Change in grain size can strengthen or weaken material  Any, more at low stress & high T, especially quartz, fsp, olivine 
Recovery (P) Climb, mutual annihilation of dislocations of opposite signs, formation of subgrain walls  Polygonisation, foam textures, 120°-triple junctions  -ve +ve or -ve  Produces low dislocation density material Q softer  Any, more at high T
Climb (M) Diffusional addition or removal of atoms at dislocation line    +ve  0   Any, more at high T
Lattice Rotation (P) Dislocation glide and/or bulk rotation of grains  Crystallographic preferred orientations  0 +ve  Well developed fabrics may be stronger or weaker than random fabrics  Any, more at low stress & high T 
Bulk Rotation (M or P) Physical rotation of whole or part of mineral grains  Helical inclusion trails, bending of crystals, delta & sigma porphyroclasts  +ve +ve or -ve    Any 
Grain Boundary Sliding (M)  Dislocation movement on "clean" grain boundaries, shearing on "dirty" ones    0  0   Any
Diffusive Mass Transfer (M or P)  "Long range" diffusion of atoms  Veins, pressure shadows, porhyroblasts  +ve or -ve +ve    Any, especially quartz and calcite 
Phase Change (M or P) Changed crystal structure without change in bulk chemistry of mins  Phase boundaries in minerals  ? ?  Often associated with volume change  Quartz, calcite-aragonite, olivine