Summary: Structural Geology | 9780521516648 | Haakon Fossen

Read the summary and the most important questions on Structural Geology | 9780521516648 | Haakon Fossen

• 1 lecture 1

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• Kinematic criteria to determine the sense and direction of movement in brittle rocks 

  1 fault drag (sleur) reliable criterion as long as outcrop face is at high angle to the fault and layers and the slip vector is at small angle to the fault. 

  2 . secondary faults/structures

  3. slickensides with slickenlines or slickolites (less reliable) 

       

• 4 Stress

• 4.1 Definitions, magnitudes and units

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• What is pressure, in geology?

  Pressure (p) is limited to media with no (or little) shear resistance, such as fluids.

• What are the two types of forces?

  1. Body forces: affect entire volume of rock (outside and inside)
     -define 3D fields, e.g. gravity or magnetic forces
  2. Surface forces: acts across the contact area between two bodies
     -very important during deformation

• 4.2 Stress on a surface

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• What is shear stress?

  A stress vector that acts parallel to surface.

• 4.3 Stress at a point

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• Stress ellipsoid and its orientation

  • Tells us everything about the state of stress at a given point in a rock, or in a rock volume (in which stress is homogenous) 
  • Has three axes: the principle stresses, are poles to the principle planes of stress:
    σ1 is the longest, in the direction of maximum stress
    σ3 is the shortest, normal to the plane with the least surface stress (traction)

• 5 lecture faults

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• What is the significance of faults?

  • Faults make movements in the earth possible and are hence important for plate tectonics.

  • Knowledge of faults is needed to understand maps and sections.

  • Faults are important for topography and morphology of the earth’s surface.

  • Faults control the permeability of rocks and are of importance for the migration of fluids

  • Faults are important for oil and gas fields and ore deposits

• 6 Folds

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• Fold axes (plooias):

  straight line that when moved parallel to itself, generates the form of the fold

  Axial surface (assenvlak):

  to itself, generates the form of the fold

• Buckling, bending, passive folding

  plaatjes

• Active Folding (flexural folding)

  • layering has mechanical significance

  i.e. layers have different mechanical

  properties.

  • presence of layers with different

  competency affect the strain pattern

  • dynamic conditions for active folding

• 8 Fracture and Brittle deformation

• 8.1 Brittle deformation mechanisms

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• What is the brittle regime?

  where physical conditions promote brittle deformation mechanisms

  •  as frictional sliding along grain contacts, 
  • grain rotation, 
  • grain fraction