1. Chapter 9: Structures & Mountain Building
PowerPoint Presentation
Stan Hatfield . SW Illinois College
Ken Pinzke . SW Illinois College
Charles Henderson . University of Calgary
Tark Hamilton . Camosun College
Copyright (c) 2005 Pearson Education Canada, Inc.

3. Chapter 9: Structural Deformation
Forces
Origin
Nomenclature

5. Structural Geology: A Study of Earth’s Architecture
Earth is a dynamic planet. Some rock units in the Canadian Rockies have been thrust for over 100 kilometres
Structural geologists study the architecture and processes responsible for deformation of Earth’s crust
A working knowledge of rock structures is essential to our economic well-being for hazards & resources
Copyright (c) 2005 Pearson Education Canada Inc.

6. Caledonides formed Late Paleozoic with the closing of Iapetus Ocean, forming Pangea

7. Deformation Deformation involves
Stress - force applied to a given area
Types of stress (differential stress that is applied unequally in different directions)
Compressional stress – shortens a rock body
Tensional stress – tends to elongate or pull apart a rock unit
Shear stress – produces a motion similar to the slippage that occurs between individual playing cards when the top of the stack is moved relative to the bottom
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8. Compression (convergence) Tension (uplift) Shear (lateral rotation)

10. Deformation How Rocks Deform
Rocks subjected to stresses greater than their own strength begin to deform usually by folding, flowing, or fracturing
Weaker rocks deform more easily (lithology, bedding)
Fluids and Heat affect lower strength
Pressure increases rock strength
General characteristics of rock deformation
Elastic deformation – the rock returns to nearly its original size and shape when the stress is removed
Once the elastic limit (strength) of a rock is surpassed, it either flows slowly (ductile deformation) or fractures quickly (brittle deformation)
This depends on Strain Rate and Time/Duration
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11. Deformed Lacustrine Strata, {Normal Fault} Palmdale, CA

12. Increasing Confining Pressure/Depth Brittle Ductile
S max
S min
S int

13. Shear reorients Foliation

14. Strike: intersection of dipping rock layer with horizontal surface & contact direction on map (azimuth relative to north) Dip: Angle below horizontal

15. Folds
During crustal deformation rocks are often bent into a series of wave-like undulations called folds
Characteristics of folds
Most folds result from compressional stresses which shorten & thicken the crust: mountain belts
Parts of a fold
Limbs – refers to the two sides of a fold
Axis – a line drawn down the points of maximum curvature of each layer
Axial plane – an imaginary surface that divides a fold more or less symmetrically
Asymmetry points in the direction of crustal transport, roll over, vergence
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16. Strike & Dip Permits 3-D Visuals
Read the map symbols:
Visualize the Cross Sections

17. Folds Common types of folds Anticline – upfolded or arched rock layers
Oldest in the middle
Outwards directed, antithetic dips
Syncline – downfolds or troughs of rock layers
Youngest in the middle
Inwards directed, synthetic dips
Depending on their orientation, anticlines and synclines can be described as
Symmetrical, asymmetrical, recumbent (an overturned fold), or plunging
Antiform & Synform when age is unknown
Anticlinorium or Synclinorium for continental size
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18. Symmetric Anticline Opposing outwards dips Oldest beds in middle

19. Plunging Anticline Strike wraps around Nose points down plunge

20. East Verging Fold & Thrust Belt
 Vergence (transport) Direction 

21. Kink Folds, Sharp Axial Planes: Syncline Anticline

22. Plunging Folds: Tilted or Refolded Fold Belt

23. Doubly Plunging Anticline or Asymmetric Dome

24. Chevrons on flank of Monocline
Compression
Drape Fold
Reverse Fault in Basement

25. Folds Common types of folds Other types of folds
Monoclines – large, step-like folds in otherwise horizontal sedimentary strata
Other types of folds
Dome
Upwarped displacement of rocks
Circular or slightly elongated structure
Oldest rocks in centre, younger rocks on the flanks
Basin
Downwarped displacement of rocks
Youngest rocks in centre, older rocks on the flanks
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26. Salt, Intrusion
Or Central Uplift

27. Subsidence

28. Black Hills, SD Cretaceous (Laramide Orogeny) Deforms Mesozoic through Precambrian RocksMz Pc Pz

29. Late Paleozoic Michigan Basin

30. Faults
Faults are fractures in rocks along which appreciable displacement has taken place
Brittle/Shallow in the upper crust
Ductile/Deep in the lower crust
Sudden movements along faults are the cause of most earthquakes usually deeper than 5 km to about 660 km
Along faults, rock is often broken into breccia, pulverized into gouge or polished as slickenslides
Faults are classified by their relative orientation & movement which can be
Horizontal, vertical, or inclined
Strike Slip, Dip Slip or Oblique Slip
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31. Normal Fault (Tension)

32. Faults Types of Faults Dip-Slip Faults: (Normal, Reverse & Thrust)
Movement is mainly parallel to the dip of the fault surface
May form in either compression or tension
Normal faults thin the crust & miss out some strata
Reverse & Thrust Faults thicken the crust & double some strata
May produce long, low cliffs called fault scarps
Active if fault cuts to surface
Resequent if erosional & controlled by strata
Parts of a dip-slip fault include the hanging wall (rock surface above the fault) and the footwall (rock surface below the fault)
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33. Normal Fault: (Extension)

34. Normal Fault: (Extension)
Hanging Wall Falls
Section Thins

35. Faults Types of dip-slip faults Normal Faults
Hanging wall block moves down relative to the footwall block
Accommodate lengthening or extension of the crust
Many are small like landslides with displacements of a metre or so
Larger scale normal faults are associated with Mid Ocean Ridges, Rifts & Fault-block mountains, Horsts & Grabens
Reverse & Thrust Faults
Hanging wall block moves up relative to the footwall block
Accommodate shortening or compression of crust
Larger scale thrust faults are associated with edges of Fold & Thrust Mountain Belts
Copyright (c) 2005 Pearson Education Canada Inc.

36. Faults: Horst & Graben as in Rifts or Basin & Range
Diagrammatic sketch of downfaulted (graben) and upfaulted (horst) blocks.
Note that there are places where if you drilled there is missing stratigraphy due to extensional faulting.
Copyright (c) 2005 Pearson Education Canada Inc.

37. Development of a Normal Fault

38. Most Normal Faults “sole-out” and become Listric with depth.

39. Faults: Thrust & Reverse
Types of dip-slip faults
Reverse and Thrust Faults
Hanging wall block moves up relative to the footwall block
Reverse faults have dips greater than 45o and thrust faults have dips less than 45o
Most thrust faults have flat soles and arise from a common surface called a decollement
Accommodate shortening of the crust
Strong compressional forces
Common in mountain belts like the Alps and Rockies
An isolated outlying remnant of a thrust sheet is called a klippe (old rocks surrounded by younger rocks, Teeth point inwards)
Copyright (c) 2005 Pearson Education Canada Inc.

40. Reverse Fault: (Compression)
Hanging Wall Rises
Section Thickens
Angle > 15°

41. Thrust Fault: (Compression) Laramide Orogeny Rockies
Section thickens
Older over younger
Thrust Vergence direction

42. Crowsnest Mountain Klippe: Thrust Outlier
Paleozoic Limestone
Cretaceous Shales

45. Right Lateral Strike Slip Fault: Like Queen Charlotte & San Andreas

46. Columnar Joints: Thermal Cooling

47. Joints from from Decompression