Geologic Structures by WNudkeoO

VIEWS: 20 PAGES: 4

									                           Geologic Structures
1. Evidence of Crustal Deformation
  •   Mountains
       – Folded
       – Horst and graben
  •   Non-horizontal strata (rock layers)
  •   Regional warping
  •   Faults
       – Normal
       – Thrust/reverse

2. What are we talking about?
  • Topography – the shape of the land surface.
      –   Hills?
      –   Valleys?
      –   Flat?
      –   Rolling?
  • Rock structure – the shape of the rock UNDER the land surface.
      –   Fold?
      –   Basin? Dome?
      –   Plunging fold?



3. How to Deform the Earth’s Crust
  • Stress – a force per unit area.
  • Strain – a change in volume or shape as a result of an applied stress.

4. How Rocks Deform
  • Elastic – will recover original shape after the stress is reduced or removed;

5. How Rocks Deform
     Ductile – bends while under stress but does not return to original shape after the
      stress is reduced or removed;

6. How Rocks Deform
      • Brittle – fracture occurs when material is stressed beyond the elastic limit.

7. Elastic Rock

8. Ductile Rock

9. Brittle Rock

10. Dip and Strike
11. Dip and Strike
12. Dip and Strike
• ‘Dip and strike’ is a way of describing the orientation and position of tilted rock
  layers.
   – Strike is a compass direction
   – Dip is an angle

13. Dip and Strike

14. Folds
  •   Tilted rock layers are a result of folding.

  •   Folding occurs when rocks are subjected to compressive stress.

  •   Folding has taken place at depth and/or slowly, and as a result, the rocks have
      behaved in a ductile fashion.

  •   Folding can take place on a very large or very small scale.

15. Anticline and Syncline

16. Fold Terminology

17. Folds
  •   Notice that the presence of a syncline doesn’t necessarily mean that there is a
      topographic valley (and vice versa).

18. Fold Shapes

19. Overturned Fold

20. Recumbent Fold

21. Basin

22. Dome

23. Non-Plunging and Plunging Folds

24. Plunging Folds

25. Plunging Anticlines and Synclines

26. Joint
27. Faults
  • A fracture along which there is movement.

  • Without the movement it is ‘just’ a joint.

28. Types of Faults
   • Dip-slip faults (Normal, thrust, reverse)
      – Occur as a result of compressive or tensional stress

   • Strike-slip faults
      – Occur as a result of shear stress

29. Dip-Slip Faults

30. Normal Faulting

31. Reverse and Thrust Faults

32. Strike-Slip Fault

33. Strike-Slip Faults
   • Straddle the road – which direction did the block on the other side of the fault
      move?

34. Does This Look Familiar?

35. What kind of faulting?

36. What kind of faulting?

37. Interpreting Geologic Maps
  • There are many types of maps.
  • Examples:
      –   Topographic: elevations
      –   Political: political boundaries and features
      –   Thematic: map any particular subject
      –   Geologic: map rock types and structures
38. A Picture is Worth A Thousand Words
  • The patterns we see on geologic maps tell us a lot about the underlying structure,
    the resistance of the rock to erosion, the angle of dip, etc.
  • The ‘trick’ is knowing how to read them.
  • Just keep in mind that a geologic map does NOT map the surface topography.

39. Geologic Map Symbols

40. Horizontal Strata

41. Inclined Strata

42. Structural Dome

43. Structural Basin

44. Plunging Folds

45. Normal and Thrust Faults

46. Strike-Slip Faults

47. Intrusive Rocks

48. Surficial Deposits

49. Michigan Basin

								
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