M3 L3: Rock Behaviors Under Stress

• DEFORMATION OF CRUST

  - Layers of sediments caused by accumulation; compacted into rock strata.

  - Deformation is a change in shape and position, and/or volume in response to stress: force or pressure.
• ● Conditions of Deformation of Rocks

  1. Rock material must be able to deform under pressure and heat.

  2. Pressure must not exceed a rock’s internal strength or else fracturing occurs.

  3. Deformation must be applied slowly. Millions of years.

  4. Due to high mineral content, high temperature makes rock elastic. Higher temp = more elastic.
• Kinds of Stress

  ● Uniform

  ● Differential

  ○ Tension

  ○ Compression

  ○ Shear
• ● Uniform: The force acts equally in all directions. Also called confining stress or confining pressure.
• ● Differential: Stress that acts with different magnitudes in different directions.
• ○ Tension: forced apart by tensional stress, which leads to stretching and breaking; divergent borders.
• ○ Compression: pressed together causing the rock to fold or break; convergent borders.
• ○ Shear: pressures pass each other in oppositional directions, causing slippage and translation; transform plate borders.
• GEOLOGIC STRUCTURES

  ● Folds

  ● Faulting
• ● Folds

  ○ Bending of ductile rocks because of their plasticky behavior.

  ○ Response to compressional force. Most visible in rocks that contain layering

  ○ A fold has anticlines and synclines forming ridges and valleys – the ridges are “up” folds and the valleys are “down” folds.
• ● Faulting

  ○ Planar surface in which the rocks have broken and slid/shifted into opposite directions.

  ○ Faults form in rocks when the stresses overcome the internal strength of the rock resulting in a fracture