1. OF ROCKS [L17 P. 363-373 /IP-B] DEFORMATION OF ROCKS [L17 P. 363-373 /IP-B]

2. Deformation of rocks Folds and faults are geologic structures. Structural geology - the study of the forces that deform rocks (stress applied) and the effects of this force (strain).

3. Phil Dombrowski Fig. 10.1 Small-scale Folds

4. Small-scale Faults Tom Bean Fig. 10.2

5. Stress (force per unit area) Types of directed (or differential ) stresses include: Compression - shorten Extension - elongate Shear - distort shape

6. Differential stress

7. Strength Ability of an object to resist deformation (low pressure vs. high pressure)

8. Strain is any change in original shape or size of an object in response to stress acting on the object

9. Types of deformation Elastic Ductile (plastic) Brittle (rupture)

10. Elastic deformation Temporary change in shape or size that is recovered when the deforming force is removed Think “rubber band”

11. Ductile (plastic) deformation Permanent change in shape or size that is not recovered when the stress is removed Occurs by the slippage of atoms or small groups of atoms past each other in the deforming material, without loss of cohesion Think “deck of cards”

12. Brittle deformation (rupture) Loss of cohesion of a body under the influence of deforming stress Sucker breaks!!! Usually occurs along sub-planar surfaces that separate zones of coherent material

13. Typical stress and strain curve

14. Factors that affect deformation Temperature Pressure Strain rate Rock type The variation of these factors determines if a rock will fault or fold.

15. Effects of rock type on deformation Some rocks are stronger than others. competent: competent: rocks that deform only under great stresses incompetent: incompetent: rocks that deform under moderate to low stresses

16. Effects of deformation on rock type Effects of deformation on rock type Experimental Deformation of Marble M.S. Patterson Fig. 10.7 Brittle Deformation (Under low pressure) Ductile Deformation (Under high pressure)

17. Orientation of deformed rocks ATTITUDE ATTITUDE - way to describe the orientation of geologic structures. Strike Strike: (compass) bearing of a line defined by the intersection of the plane in question and the horizontal Dip Dip: acute angle between the plane and the horizontal, measured perpendicular to strike.

18. Fig. 10.4

20. Dipping Sedimentary Beds Chris Pellant Fig. 10.3

21. P.L. Kresan Cockscomb Ridge, S. Utah

22. Dip Strike P.L. Kresan

23. Tectonic Forces and Resulting Deformation Fig. 10.6

24. BRITTLE DEFORMATION A. Abrupt movement breaks or cracks strata B. 2 kinds of breaks: –1. JOINTS - NO movement of blocks –2. FAULTS - YES movement of blocks 1. Movement along STRIKE 2. Movement along DIP

25. Columns Formed by Joint- controlled Weathering Terry Englander Fig. 10.20

26. Joint-controlled Landscape, S.E. Utah

27. Faults Fractures in rocks created by earthquakes that have moved A. Dip-slip faults normal reverse thrust B. Strike-slip faults right lateral or left lateral

28. Hanging-wall and footwall

29. Dip-slip faults Motion of the fault blocks, parallel to the dip direction.

30. Classification of Faults hanging wall footwall cross section

31. Normal Fault footwall hanging wall cross section

33. Normal Dip-slip Fault

34. Reverse Fault footwall hanging wall cross section

36. Reverse Dip-slip Fault

37. Drape Fold over Reverse Fault, WY George Davis

38. Thrust Fault footwall hanging wall cross section Thrust faults are low-angle reverse faults.

39. Thrust fault

40. Keystone Thrust Fault, S. Nevada John S..Shelton Cambrian Limestone Jurassic Sandstone

41. Lewis Thrust, Sawtooth Range, Wyoming Kurt N. Coonstenius

42. French Thrust, Wyoming Cretaceous Shale Mississippian Limestone Kurt N. Coonstenius

43. Strike-slip faults Motion of the fault blocks is parallel to the strike direction. To determine the direction of strike, put toes on the fault line & look at the direction the opposite block moved.

44. Left-lateral Strike Slip Fault map view

45. Right-lateral Strike Slip Fault map view

47. Gudmundar E. Sigvaldason Strike- slip Fault

48. Rift Valley Formed by Extension Graben Horst

49. Wildrose Graben, Southern California

50. NASA/TSADO/Tom Stack

51. 1872 Fault Scarp, Southern California

52. 1988 Armenian Earthquake Fault Scarp Armando Cisternas

53. 1992 Landers Earthquake Fault Scarp

54. FOLDS PLASTIC DEFORMATION FOLDS anticline anticline: older rocks on the inside syncline syncline: older rocks on the outside (scale (scale - from mm to tens of km)

55. Fold Terminology Fig. 10.10

56. Symmetrical Isoclinal Asymmetrical Overturned Recumbent Fig. 15.22

57. Bill Evarts Axial plane Anticline Fig. 10.11

58. Breck Kent Asymmetric Folds

59. Phil Dombrowski Fig. 10.1 Overturned Folds

60. Overturned Syncline, Israel Geological Survey of Israel Fig. 10.13

61. Valley and Ridge Province of the Appalachian Mountains Fig. 10.19

62. Valley and Ridge Province P. L. Kresan

63. J. Shelton, Geology illustrated Fig. 10.15 Plunging Folds in the Valley and Ridge

64. Raplee Anticline, S.E. Utah

65. Raplee Anticline on the San Juan River, Utah

66. Domes and Basins Fig. 10.16

67. John S. Shelton Fig. 10.17 Sinclair Dome, Wyoming

68. Anticlines and Synclines Fig. 10.9

69. Geologic Map and Cross Section Fig. 10.5

70. Outcrops of Syncline Fig. 10.18

71. All pau