GEOLOGY CMU Bill Palmer

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GEOLOGYCMUBill Palmer

• Lecture 12
• Geologic Structure

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GEOLOGY-Geologic Structure

• DEFORMATION
• JOINTS
• FOLDS
• FAULTS
• FOLIATION
• MOUNTAINS

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GEOLOGY-Geologic Structure

• Mountains occur in belts-rows of peaks-linear
  ranges
• These are orogens (mountain formation)
• Orogeny is a mountain building event
• limited lifetime-ends with erosion of mountain

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GEOLOGY-Geologic Structure
Mt. Everest-(Chomolungma) Highest point on
Earth-29,028 feet
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GEOLOGY-Geologic Structure

• Rock layers get deformed due to strain
• Brittle Deformation-Like dropping a plate on the
  tile floor and it cracks, breaks, and shatters.
• Ductile Deformation-Like dropping a ball of dough
  onto the tile floor and it goes plop. The dough
  changes shape without breaking.

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GEOLOGY-Geologic Structure

• How rock layers deform depends on several factors
• Temperature
• Pressure
• Deformation rate
• Composition

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GEOLOGY-Geologic Structure

• Causes of deformation of rock layers
• Compression-occurs when a rock body is squeezed
• Tension-occurs when a rock body is pulled apart
• Shear Stress-occurs when one side of a rock body
  moves sideways past the other side
• Pressure-is a special condition that occurs when
  a push occurs on all sides of a rock body

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GEOLOGY-Geologic Structure

• JOINTS- are natural cracks in rocks
• Joints develop in response to stress in rock
  bodies
• Caves may be develop along joints
• Minerals may be deposited in joints
• Joints may affect engineering projects (dont
  build a nuclear power plant on a joint)

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GEOLOGY-Geologic Structure
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GEOLOGY-Geologic Structure

• FAULTS-joints along which there has been movement
  (in any direction). Types
• Dip-slip
• Thrust faults
• Reverse faults
• Strike-slip
• Oblique-slip

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GEOLOGY-Geologic Structure

• Dip-slip Fault-Sliding occurs up or down the
  slope of the fault.
• Normal-The hanging wall moves down the slope
• Reverse-The hanging wall moves up the slope

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GEOLOGY-Geologic Structure
Dip-Slip Fault
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GEOLOGY-Geologic Structure

• Strike-slip Fault-One block slides past another
  horizontally.
• Left Lateral-face the fault and the block on
  the far side appears to have moved left.
• Right Lateral- face the fault and the block on
  the far side appears to have moved right.

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GEOLOGY-Geologic Structure
Strike-Slip Fault
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GEOLOGY-Geologic Structure

• Oblique-slip Fault-Up and down movement and
  lateral movement.

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GEOLOGY-Geologic Structure
Oblique-Slip Fault
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GEOLOGY-Geologic Structure

• Faults have displacement-The amount of movement
  along the fault face.
• Fault scarp-A visible fault surface above the
  ground-varies from a few feet in height to
  mountain height (Tetons)

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GEOLOGY-Geologic Structure
Fault Scarp (six feet)
Fault Scarp 1,000s ft Grand Tetons
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GEOLOGY-Geologic Structure

• FOLDS-occur when stress bend a rock body
• Anticline-Arch like shape
• Called a plunging fold if it is not horizontal

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GEOLOGY-Geologic Structure
Anticline
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GEOLOGY-Geologic Structure

• FOLDS-occur when stress bend a rock body
• Syncline-Trough-like shape

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GEOLOGY-Geologic Structure

• Anticlines and Synclines usually occur together

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GEOLOGY-Geologic Structure

• FOLDS-occur when stress bend a rock body
• Dome-Upside down bowl shape

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GEOLOGY-Geologic Structure
Dome-The top of the dome erodes leaving a pattern
of concentric circles
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GEOLOGY-Geologic Structure

• FOLDS-occur when stress bends a rock body
• Basin-Right side up bowl shape

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GEOLOGY-Geologic Structure
Basin Oil Field-Montana
Basin
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GEOLOGY-Geologic Structure

• Foliation-pressure cause the particles of the
  rock to change shape and orient themselves in the
  same direction.

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GEOLOGY-Geologic Structure
Foliation
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GEOLOGY-Geologic Structure

• All of the bending, folding, faulting can occur
  to the same rock body creating a complex puzzle
  for the geologist.
• Weathering and erosion can exposed the structure
  and give clues to what has happened.

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GEOLOGY-Geologic Structure Wrap-ups

• 1. What is Orogeny?
• 2. What are the four forces that cause rock
  bodies to deform?
• 3. What is a joint (geologically speaking, that
  is)?
• 4. What are the three main types of geologic
  faults?
• 5. What is a Fault Scarp?

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GEOLOGY-Geologic Structure Wrap-ups

• Define the following and sketch
• 6. Anticline
• 7. Syncline
• 8. Dome
• 9. Basin
• 10. Foliation