1. Folding, Faulting, and Mountains
Folding – Mount Kidd, Alberta, Canada – Figure 17.2 in text
GLY 2010 – Summer Lecture 13

2. Stress
Stress is a force that is capable of greatly deforming rocks, and may result in folding or faulting of rock, and even to the building of mountains

3. Types of Stress There are three types of stress Compression Tension
Shear
Each type is discussed on next slides

4. Compression Opposing forces directed inward along a single line
Compression shortens an object along the axis of compression, and thickens it in the directions perpendicular to the stress direction
After
Before

5. Tension
Tension is the result of divergence, pulling an object in opposite directions along a common axis
Tension lengthens an object along the axis of tension, and thins it in the perpendicular directions
After
Before

6. Tensional Cracking
Tension can produce cracks in the direction perpendicular to the axis of tension
Cracking develops

7. Tension Crack Pictures
Left photo: Ground failure along North Deschutes Parkway showing lateral spread toward Capitol Lake, which is to the right of the photograph; view is to the north. (N47.040° W °; 03/01/2001)
Source:
Right Photo: Lateral spreading of railroad embankment extending from Marathon Park (looking northeast).
(N ° W °; 02/28/2001)
Photo Source:
Nisqually Earthquake, 2/28/01, in Washington caused tension cracking.

8. Shear
Opposing stress is created by two plates moving in opposite directions

9. Responses to Stress There are three responses to stress Elastic
Plastic
Rupture

10. Elastic Substances Behave elastically, stretch without breaking
Snap back to their original position, when stress is removed
Elastic limit: a limit beyond which substances cannot be stretched without breaking
Example: Rubber band

11. Plastic Substances Slow deformation without breaking
Plastically deformed substances do not return to their original shape when the stress is removed
Rate of deformation is important - Stress applied quickly will cause rupture
Rocks subjected to stress at high confining (load) pressures, and moderate to high temperatures, may deform plastically
Example: Silly putty
Movie from:
Silly George, by Vern Hart
Time-lapse slumping of
silly putty. Notice
movement in upper left corner.

12. Plastic Deformation The rate of plastic deformation makes a difference
Silly putty breaks if pulled rapidly, stretches if pulled slowly
Movie: ddx.avi, converted from ddx.avi

13. Rupture
Elastic substances stretched beyond the elastic limit, or plastic substances deformed quickly, will rupture
Rupture is called brittle failure

14. Deformation Rocks subjected to stress may: Deform by folding
Rupture, with subsequent movement along the plane of rupture - this is called faulting
Fold, then rupture

15. Folding Folds may be described in terms of two parameters: Axial Plane
Limbs
Axial Plane
Limb
Limb

16. Anticline
If the fold is convex upward, it is called an anticline

17. Anticlinal Fold
Rainbow Gap, Virginia
Photo: Henry Johnson

18. Atlas Mountains Anticline
One of the best exposures of a complexly folded mountain belt anywhere occurs in the Atlas Mountain system of northwest Africa

19. Domes
Domes are anticlines that curve in three dimensions, like an upside down bowl
Figure shows the Black Hills, South Dakota
Diagram of dome – Figure 17.6, text

20. Eroded Dome, Sinclair, Wyoming

21. Syncline
If the fold is convex downward, it is called a syncline

22. Syncline Photo
Photo: Duncan Heron
Synclinal fold exposed by roadcut

23. Anticline-Syncline Pair
Anticline-Syncline pair in Devonian Old Red Sandstone. SW Wales, UK
Note the different fold shapes

24. Basins Basins are syncline that curve in three dimensions, like a bowl
Diagram: Figure 17.7 in text

25. Overturned Folds
Overturned fold in lower center of picture

26. Recumbent Folds
Recumbent folds are defined as folds with horizontal (<10° dip) axial surfaces
Photo: Ron Perkins
Photo # st036th.gif

27. Fold Diagram Diagram shows the major types of folds
Figure 17.3 in text
Diagram shows the major types of folds

28. Plunging Folds
The axes of the folds may be tilted, creating a series of plunging folds
Figure 17.4 in text

29. Folding Animation
From Chapter 17, FoldingV2_PC.ppt

30. Joints Three joint sets (left photo)
Video: Joints_&_Dikes,_Thunder_Hole,_Acadia.wmv from author
Three joint sets (left photo)
Joints and dikes, Acadia National Park video (right)

31. (Click picture to remove block)
Faults
A fault is a fracture along which definite movement has occurred
(Click picture to remove block)

32. Strike and Dip
The strike is any horizontal line drawn on an inclined surface.
Strike-slip faulting is the result of shear forces.
The strike-dip symbol, used on geologic maps, is shown - the long direction points in the horizontal direction, and the shorter side shows dip direction

33. Strike-slip Direction
Strike-slip faults are further described as "right-lateral" or "left-lateral" depending if the block opposite the viewer moved to the right or left, respectively

34. Strike Slip Fault Photo: Arthur G. Sylvester.
San Jacinto fault, Anza, Southern California

35. Right-Lateral Strike Slip
Block is displaced to the right, looking across the fault
Image: Source:

36. Strike Slip Faults Right Lateral
Near Coos Bay, Oregon

37. Left-Lateral Strike Slip
Block is displaced to the left, looking across the fault
Image: Source:

38. Strike Slip Faults - Left Lateral
Near Lillooet, British Columbia

39. Dip-slip Faults
Dip direction is always perpendicular to the strike line

40. Fault Terminology
Foot Wall and Hanging Wall are borrowed from mining terminology
Ore veins are often deposited along faults

41. Normal Fault Normal faulting results from tensional forces
Hanging wall moves down relative to the footwall (here, to the right)
Places younger rocks on top of older
Image: Source:

42. Sevier Normal Fault
Figure 17.8 in text

43. Death Valley Normal Faults
photo:

44. Reverse Fault Reverse faulting results from compressional forces
Hanging wall moves up relative to the footwall (here, to the left)
Places older rocks on top of younger
Source:

45. Reverse Fault Reverse faults and associated fold
Near Klamath Falls, OR.
Reverse faults and associated fold

46. Thrust Fault Thrust faults are low angle reverse faults
They sometimes move large distances (tens of kilometers)
Image: Source:

47. Lewis Overthrust Photo: http://www.uoregon.edu/~millerm/Lewis1.html
Lewis Thrust fault. As viewed from Marias Pass, Glacier National Park, Montana. Looking N.
Green arrow points to fault. There, Precambrian rocks of the Belt Supergroup lie directly on top Cretaceous shale and sandstone.

48. Explanation of Lewis Overthrust
Image: chfsketch.jpg
Chief Mountain was moved about forty kilometers and isolated by erosion
Chief Mountain is much older (Precambrian) than the rock upon which it rests (Cretaceous)

49. Chief Mountain Older rock above younger, typical of thrust faults
Glacier National Park, Montana

50. Oblique Slip
Image: Source:
Oblique-slip is a combination of vertical and horizontal movement

51. Horst and Graben
Occur when there is offset along high-angle normal faults, so that one block (the graben) drops relative to the blocks (horsts) on either side. Tensional forces create these structures

52. San Andreas/Garlock Faults From Space

53. San Andreas Fault
Pacific plate, left
North America, right

54. San Andreas Offsetting Fence

55. Fault Animations
From Chapter 17, FaultsV2_PC.ppt

56. Fault Diagram Summary
Figure 17.9 in text

57. Orogenesis
Tectonic forces often create mountains, a process called orogenesis
There are several types of mountains
Folded
Faulted
Upwarped
Volcanic

58. Orogenesis by Folding
Plate collisions involving continental plates can produce high mountains
Examples:
Himalayas (India, Tibet, China)
Alps (Europe)
Urals (Europe/Asia boundary)
Appalachians

59. High peaks in the Himalayas
Himalayan Mountains
Mt. Everest
High peaks in the Himalayas

60. Owens Valley and the Sierra Nevada Range

61. Orogenesis by Upwarping
Formed when a large region of the earth’s crust is bent into a broad, regional uplift with little apparent deformation of the rocks
Upwarping may be due to local vertical motion, rather than plate tectonic forces - often far from plate boundaries

62. Custer State Park, Black Hills, South Dakota

63. Volcanic Mountains

64. (Click picture to restore block)
Faults
A fault is a fracture along which definite movement has occurred
(Click picture to restore block)