1. Ch. 17 Crustal Deformation and Mountain Building

2. Chapter 17 Opening Figure

3. Rock Deformation
Rock deformation refers to changes in the shape, volume, or orientation of a rock due to changes in temperature and pressure over time.

4. Rock Deformation due to Stress
Stress is strictly defined as force per unit area, and is used to describe all forces that deform rocks
Compressional stress (squeezes and shortens)
Tensional stress (elongates)
Shear stress (causes splaying, e.g. deck of cards).

5. Elastic deformation
We’ve already talked about elastic deformation, which is temporary. The rock will return to original shape and form after stress is removed.
What happens if the elastic limit is surpassed?

6. Brittle Deformation: Rocks behave like a brittle solid and fracture
near surface conditions
relatively low pressures and temperatures
result is faulting

7. Ductile deformation: solid state flow of rocks that results in permanent deformation without fracture
conditions at depth
relatively high pressures and temperatures
result is folding

8. Factors in Rock Deformation
Pressure
Temperature
Rock composition
Time rock is exposed to pressure and temperature

9. Synclines and Anticlines
An anticline is a structure in which the strata (layers) in the middle are older than those of the limbs (sides).
Anticlines are formed by upfolding or arching of rock layers.
A syncline (“sin makes you smile”) is a structure in which the strata in the middle are younger than those of the limbs.
Synclines are formed by downfolding of rock layers.

10. Synclines and Anticlines
These two types of folds are most often found in adjacent to one another.
Both are examples of ductile deformation.
Both are commonly due to horizontal compressional stress.

11. Syncline: See the smile?
Anticline
Syncline: See the smile?
Chapter 17, Figure 17.4

12. Syncline, anticline, syncline (the right syncline is cut by a vertical fault)
Chapter 17, Figure 17.2a

13. Overturned Fold

14. Plunging Folds
Synclines and anticlines are “plunging” when their axis is no longer parallel to the land surface, due to a perpendicular component of stress.

15. Plunging folds vs non-plunging folds

17. Monocline
A monocline is a large, steplike fold in otherwise horizontal sedimentary strata
Monoclines are associated with the reactivation of faults of faults in the basement rock below the sediments.

18. The San Rafael Swell in Utah, is an example of a monocline

19. Brittle Deformation: Faults
Faults- fractures in rocks along which there is (or has been) displacement.

20. Dip-Slip Faults
Movement primarily along the inclination (dip) of fault plane (i.e. up/down)
Parts of a dip-slip fault
Hanging wall – the rock above the fault surface
Footwall – the rock below the fault surface

21. Normal Dip-Slip Fault
Hanging wall block moves down due to gravity (that’s the normal part
Associated with fault-block mountains
Prevalent at spreading centers
Caused by tensional forces.

23. Fault block mountain range produced by normal faulting
Horst (high)– uplifted block, Graben (grave) – downdropped block
Horst and Graben Topography: results from a series of normal faults in an extensional environment.
Dip of normal faults decrease with depth.
Nearly horizontal detachment fault separates brittle deformation above with ductile deformation below.

24. Basin and Range Geographic Province, (Nevada and parts of California, Utah)

25. Reverse Dip-slip Faults and Thrust Fault
Hanging wall block moves up (this is the reverse of normal!)
Caused by strong compressional stresses
Reverse fault - dips greater than 45º
Thrust fault - dips less than 45º

27. Thrust fault – low angle reverse fault

28. Thrust Fault in Nevada

29. What kind of fault, normal or reverse?

30. Strike-Slip Faults: Dominant displacement is horizontal and parallel to the trend, or strike

32. Strike-slip vs. Transform
Strike-slip faults
Dominant displacement is horizontal and parallel to the trend, or strike
Often associated with tranform-fault boundaries, BUT
Not all strike-slip faults are transform!

33. Strike-slip vs. Transform
Transform fault
Strike-slip fault that links spreading centers lithosphere
Considered a plate boundary if large enough
All transform faults are strike-slip, as they move parallel to strike.

34. Strike-slip faults are classified as right-lateral or left lateral
Strike-slip faults are classified as right-lateral or left lateral. Which is the San Andreas?

35. Right-lateral or Left lateral?

36. San Andreas Fault System

37. San Andreas Fault System

39. From E to W, San Andreas, San Jacinto, Elsinore Faults

40. Peninsular Ranges Batholith and Transverse Ranges

41. Extension in the Basin and Range

42. Figure 17.20

43. Joints Fractures along which no appreciable displacement has occurred
Most are formed when rocks in the outer-most crust are deformed

44. Figure 17.11

45. Orogenesis (Mountain Building)

46. Orogenesis Processes that collectively produce a mountain belt
Occurs due to plate movements and often (not always!) at plate boundaries.

47. Orogenesis at Convergent Boundaries
Island Arcs (Oceanic-oceanic crust convergence )
Subduction zone forms
Volcanic arc forms
Often associated with deep ocean trench

48. Volcanic Island Arc

49. Orogenesis at Convergent Boundaries
Andean-type orogenesis (Oceanic-continental crust convergence )
Subduction zone forms
Continental volcanic arc forms
Accretionary wedge* forms seaward of arc
*Large mass of sediments scraped from subducting oceanic plate which attaches to to the overiding block

50. Andean-Type Orogenesis

51. Andean-Type Orogenesis

52. Andean-Type Orogenesis

53. Andean-type orogenesis
Active Examples-Volcanic Arcs
Andes (accretionary wedge under water?)
Cascades – active volcanoes, slightly inland from non-volcanic coastal mountains, the Olympus Range.
Inactive Example:
Sierra Nevada Range (magma chamber of volcanic arc) and California's Coast Ranges (accretionary wedge)

54. Orogenesis at convergent boundaries
Accretion of Exotic Terranes
Small crustal fragments collide with and accrete to continental margins
Accreted crustal blocks are called terranes (note spelling). Terrane refers to any landmass that has a geologic history distinct from that of an adjoining landmass
Much of western North America is composed of exotic terranes.

55. Accretion of Exotic Terranes

56. Accretion of Exotic Terranes

57. Accretion of Exotic Terranes

58. Accreted Terranes in the Western United States
Source material include:
island arc material (igneous parent rock)
submarine deposits (sedimentary parent rock)
Ancient ocean floor (igneous parent rock)
displaced continental (igneous parent rock)

60. Orogenesis at Convergent Boundaries
Collisional Mountain Belt: Two plates with continental crust converge
Characterized by shortening and thickening of continental crust

61. Formation of Himalayas

62. Formation of Himalayas

63. Chapter 17, Figure 17.22

64. Collisional Mountain Ranges
Active Example
Himalayan Mountains and the Tibetan Plateau
Inactive Example
Appalachians (collision of N. America and Africa)

65. Figure 17.19a,b

66. Figure 17.19b,c

67. Figure 17.19c,d

68. Chapter 17, Figure 17.24
Landsat Image of Valley and Ridge Province, with location map on right.

69. Orogenesis not associated with Convergence – Fault Block Mountains
Associated with Normal Faulting
Basin and Range Province
Teton Range, Wyoming

70. Isostasy
The earth’s lithosphere can be thought of as “floating” in gravitational balance upon the denser, deformable rocks in the asthenosphere.
To support more weight (i.e mountains) above, means you need to displace more material below.

71. Isostasy
Horizontal compressional forces cause shortening and thickening of crust, in both directions.

72. Isostatic Adjustment
As weight is removed from the top by erosion, the crust “rebounds” upward.
The processes of erosion and isostatic uplifting will continue until mountain block reaches normal thickness.
Eroded sediments cause adjacent areas to subside.

73. Chapter 17, Figure 17.27

74. Normal Fault
FAULT SCARP

75. Reverse Fault