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Modes of deformation of rocks presentation

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how the rock deform

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Modes of deformation of rocks presentation

  1. 1. Modes Of Deformation Of Rocks
  2. 2. Deformation • when an object is changed temporarily or permanently due to applied force.
  3. 3. Deformation of rocks • Within the Earth rocks are continually being subjected to forces that tend to bend them, twist them, or fracture them. When rocks bend, twist or fracture we say that they deform (change shape or size). The forces that cause deformation of rock are referred to as stresses (Force/unit area). So, to understand rock deformation we must first explore these forces or stresses.
  4. 4. Stress and Strain • Stress is a force applied over an area. One type of stress that we are all used to is a uniform stress, called pressure. A uniform stress is a stress wherein the forces act equally from all directions. In the Earth the pressure due to the weight of overlying rocks is a uniform stress, and is sometimes referred to as confining stress.
  5. 5. Stress and Strain • If stress is not equal from all directions then we say that the stress is a differential stress. Three kinds of differential stress occur.
  6. 6. Strain • When rocks deform they are said to strain. A strain is a change in size, shape, or volume of a material.
  7. 7. STRENGTH . the ability of an object to resist deformation • compressive strength • tensile strength • shear strength
  8. 8. FACTORS AFFECTING on ROCK DEFORMATION • Pressure • Temperature • Strain rate • Rock composition
  9. 9. Pressure • 1 Rocks near the surface, where pressures are low, usually behave like brittle solids. Called brittle deformation. 2 At depth, where pressures are high, rocks show ductile behavior. Called ductile deformation.
  10. 10. Temperature Rocks deform permanently in two ways: brittle deformation and ductile deformation. 1 Rocks near the surface, where temperatures are low, usually behave like brittle solids. 2 At depth, where temperatures are high, rocks show ductile behavior.
  11. 11. Strain Rate  High Strain Rate forms a Brittle Deformation.  Low Strain Rate forms a Ductile Deformation.
  12. 12. Composition  Hard composition of rocks (like granite) caused Brittle Deformation.  Soft composition of rocks (like marble) caused Ductile Deformation
  13. 13. TYPES OF DEFORMATION • 1 ELASTIC DEFORMATION • STRESS is applied, released and rock returns to • original shape and volume. • Material is not DEFORMED. • If stressed to a point where the material doesn’t resume • original shape and volume, the rock is deformed. • Point at which this occurs is the ELASTIC LIMIT. • Pressure and temperature when stress is applied also • determine how rocks deform at the elastic limit.
  14. 14. 2 PLASTIC or DUCTILE DEFORMATION Rocks subjected to stress at temperature and pressure tend to , resulting from. An irreversible change in shape and/or volume occurs without the rock breaking. Rocks go beyond the elastic limit. Atoms move about and adjust without the bonds breaking. Atoms move from areas of high stress to those with low stress.
  15. 15. Kinds of differential stress • Tensional stress (or extensional stress), which stretches rock; • Compression stress, which squeezes rock; and • Shear stress, which result in slippage and translation.
  16. 16. Stages of Deformation • When a rock is subjected to increasing stress it passes through 3 successive stages of deformation. • Elastic Deformation • Ductile Deformation • Fracture
  17. 17. Ductile Deformation • -- wherein the strain is irreversible. • it is when something breaks from its original shape and cannot return to its original position.
  18. 18. Elastic Deformation • -- wherein the strain is reversible. The temporary change in length, volume, or shape produced in an elastic substance by a stress that is less than the elastic limit of the substance.
  19. 19. Fracture geologic,fault rock stress exceeding the rock strength,
  20. 20. •Thank you