Important concepts in deformational behavior of rocks:

• deformation path, kinematics.
• strain.
• stress.
• elastic vs. inelastic.
• brittle vs. ductile.
• homogenous vs. inhomogenous strain.

What are important factors in deformation behavior and what is their effect?

• temperature.
• confining pressure (pressure is when force equal from all directions), function of depth.
• deviatoric pressure (or "directed pressure", stress state).
• fluids.
• rock type.
• strain rate.

Types of brittle structures:

• extensional features:
  • veins.
  • joints.
  • crevices and crevasses (e.g. in earth slumps and glaciers).
• shear planes (faults): normal, thrust, reverse, wrench, oblique.
• fault breccia, gouge, striae and slickensides, and pseudotachylite.

Types of ductile structures:

• flexural slip folds.
• flow folds.
• refolded folds.
• fabrics: flattening planes, and elongation lineations.

Brittle-ductile transition in the crust:

• rule of thumb: at about half the melting T rocks become much weaker.
• at about 300 to 350 degrees Celsius expect rocks to become weaker.
• given typical geothermal gradient how deep would need to go to reach these temperatures?
• seismogenic zone: circa 15 km average depth but varies.

Migmatites: special rock a mixture of metamorphic rock and often irregular veins of melt (usually granitic) that occurs at deep levels in the crust, usually when the crust has been thickened beyond normal. Deforms very complexly.

© Harmon D. Maher Jr. May be reproduced for non-profit educational purposes with source acknowledgement. Otherwise please contact me.

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