Structural Geology Geology 3321 Geology for Engineers

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					           Structural Geology

               Geology 3321

        Geology for Engineers
                  Kate C. Miller




                Introduction
• Study of rocks and how they’ve been
  deformed
• Description of position, shape, attitude
• Microscopic --> large geometric forms (km)




         Types of Deformation
• Elastic - no rock
  record
                                        Plastic
• Plastic - bending,        σ
  folding                                         Rupture
• Brittle Rupture -                Elastic
  fracture, fault                            ε




                                                            1
   Measuring Attitude of Rocks
• Dip - Angle of bed with the horizontal
• Strike - Bearing (compass direction) of line
  of intersection between horizontal plane and
  the inclined bed




                    Folds
• Formed by plastic deformation under
  compression
• Terms
  n   Anticline
  n   Syncline
  n   Limb
  n   Axial plane
  n   Plunge




      Types of Folds (Anticlines)
• Symmetric
• Asymmetric
  n   Overturned
  n   Recumbent
• Monocline




                                                 2
               3D - Structures
• Plunging Folds
  n   Oldest beds in the center of the anticline
  n   Nose points in direction of plunge
• Domes and Basins




        Types of Rock Fractures
• Fractures - narrow planar openings in rock
• Joints - Fractures w/ no movement parallel
  to fracture surface. Often occur in sets
• Shear Zones - fractures along which a small
  amount (cms) of movement has occurred
• Faults - fractures along which large
  amounts (m - kms) of movement has
  occurred.




               Types of Faults
• Terminology
  n   Footwall
  n   Hanging Wall
  n   Strike and Dip
• Normal Fault
• Reverse Fault
• Strike Slip Fault




                                                   3
            Faults and Stresses
• Maximum principal stress (σ1)
  n   Normal faults - vertical
  n   Reverse faults - horizontal
  n   Faults form at 30 - 60 deg. From the maximum
      principal stress




                     Faults




                      Folds




                                                     4
Strike and Dip




                 Anticlines
                         &
                 Synclines




Plunging Folds




                              5
Asymmetric Fold




Overturned Folds




Recumbent Folds




                   6
              Monocline




           Domes and Basins




             Normal Fault        σ1

Footwall


                Hanging
                 Wall

                          Normal Fault




                                         7
            Reverse Fault
Footwall


              Hanging
                                 σ1
               Wall

                        Reverse Fault




           Strike-slip Fault




                                        σ1




                                             8