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F olds and Faults

F olds and Faults. Field Geology. Fold: Layer of deformed rock. Fig 11.1. Fault: A fracture with relative movement of rocks on both sides of it, parallel to the fracture. Fig. 11.2.

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F olds and Faults

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  1. Folds and Faults

  2. Field Geology

  3. Fold: Layer of deformed rock Fig 11.1

  4. Fault: A fracture with relative movement of rocks on both sides of it, parallel to the fracture. Fig. 11.2

  5. Geology is a quantitative science.How do you precisely, quantitatively describe the orientation of faults and folds in the field?

  6. Strike and Dip • Strike: Compass direction of a rock layer as it intersects with a horizontal surface. • Dip: The amount of tilt. The angle at which a bed is inclined from the horizontal. The direction a drop of water travel when dropped on a rock layer. Fig. 11.4

  7. Fig. 11.3

  8. How do rocks get deformed? Fig. 11.6

  9. How do rocks deform? • Brittle material: Undergoes little deformation until it breaks suddenly. Example: Candy cane. • Ductile material: Undergoes smooth and continuous deformation. Does not spring back to its original shape once deforming force is released. Example: Caramel.

  10. Ductile rocks fold. Fig. 11.6

  11. Brittle rocks fault. Fig. 11.6

  12. Brittle deformation Ductile deformation Fig. 11.7

  13. The same rock can undergo brittle and ductile deformation? • Rocks are more ductile: • The higher the pressure (the deeper they are in the Earth). • The higher the temperature (the deeper they are in the Earth). • The faster the deforming force is applied. Quick shove = break; slow push = bend.

  14. Faults

  15. Two types of fractures • Joints: (We’ve seen these before.) A crack along which there has been little appreciable movement. A nondisplaced fracture. • Faults: A fracture with relative motion of the rocks on either side of it.

  16. JOINTS Fig. 11.9

  17. Fig. 11.11

  18. San Andreas Fault • A strike-slip fault in California • Right-lateral Fig. 11.10

  19. Reverse faulting in Nevada Fig. 11.12

  20. Mid-ocean ridges are normal faults. Fig. 11.13

  21. SCARP Fig. 11.14

  22. Folds

  23. Fig. 11.15

  24. Types of folds • Anticline: Upfolds or arches. • Synclines: Downfolds or troughs. Fig. 11.16

  25. Fold terms • Axial plane: Imaginary surface that divides the two halves (limbs) of a fold. • Horizontal folds and plunging folds. Fig. 11.16

  26. Fig. 11.16

  27. Fig. 11.16

  28. Fig. 11.16

  29. Fig. 11.16

  30. Fig. 11.16

  31. Plunging synclines or plunging anticlines are located where a fold dies out or seems to plunge into the ground. Fig. 11.17

  32. Fig. 11.18

  33. Dome: Broad circular or oval structure made of rock layers. An anticlinal structure. Fig. 11.19

  34. Fig. 11.19

  35. Domes and basins • Domes can be formed by • Intrusions of buoyant material (e.g., hot igneous rock or salt) • Successive periods of compressive deformation in different directions. • Basin: Bowl-shaped depression. Synclinal structure. Can be formed by • Subsidence and cooling of hot crust. • Stretching of crust.

  36. Putting it together: Field observations Fig. 11.20

  37. Fig. 11.21

  38. Fig. 11.21

  39. Fig. 11.22

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