Ductile Deformation Processes Chapter 9 in Van der Pluijm and Marshak

How can solid rock flow like taffy? Swiss Alps

Ice is a solid phase that flows when conditions are appropriate and there are forces acting on the material. “g”

Ductile deformation is permanent

Accomplished by these 3 mechanisms: Cataclastic flow Diffusional mass transfer Crystal plasticity

Mechanism is determined by: Temperature Stress Strain rate Grain size Composition Fluid content

Effect of Composition Slow Halite Gypsum Calcite Quartz Plag. Pyroxene Olivine

1) Cataclastic flow: small pieces sliding past each other

Cataclastic flow: Is it brittle or ductile? Ductile on large scale but brittle on small scale

2) Crystal Plasticity: The crystal changes shape by movement of lattice defects Point Defects are vacancies or impurities

Dislocations form in 2 ways: During crystal growth During deformation

By moving the dislocations, the crystal changes shape

Migrating defects change the lattice shape. Occurs under stress

Line defects in olivine

Twinning also changes the crystal shape

3) Diffusional Mass Transfer has three mechanisms: Grain boundary diffusion Volume diffusion Pressure solutionLow T High T

Grain boundary diffusion Atoms will diffuse along the edges of the grain to create shape changes (strain).

Volume diffusion Atoms will diffuse through the center of the grain to create shape changes (strain).

Pressure solution: Material is dissolved under stress Dissolved rock goes into veins

Deformed Marble

Mylonite