Structure and Deformation Folds and Faults Structure and Deformation The driving force for geologic deformation is Earth s internal heat engine Radioactive decay of U Th K Deformation Terms Stress Strain Compression stress Tension stress Shear stress Elastic strain Plastic strain Ductile strain Brittle strain Anticline Syncline Monocline Strike Dip Joint Fault Dip slip fault Strike slip fault Oblique slip fault Normal fault Reverse fault Thrust fault Left lateral Right lateral Stress and Strain Stress is an applied force Strain is the resultant deformation The rocks get deformed because the continents move Stress is an applied force Compressional pushed together Tensional pulled apart Shear tearing Isostatic hydrostatic Strain is deformation Elastic deformation is temporary Like an elastic band Plastic deformation is permanent Materials that undergo continuous plastic deformation are said to be ductile Materials that fracture are said to be brittle 1 Folds and Faults Stress applied to rocks can result in ductile behavior folding or brittle behavior faulting Even though rocks are usually brittle small stresses applied over long times can result in ductile behavior Folds in Sediments Folds An anticline is a concave downward fold arch A syncline is a concaveupward fold smile A monocline is a flexure Anticline Split Mountain Monocline Syncline 2 Monocline Strike and Dip Strike and dip are used to Recumbent Fold Yukon Strike and Dip describe the orientation of any planar feature such as bedding in sedimentary rocks Strike is the compass direction of the intersection of the plane with the horizontal Dip is the measured angle between the plane and the horizontal Rock Fractures A joint is a fracture in rock on which Joints in basalt Giant s Causeway Co Antrim Ireland there has been no movement A fault is a fracture in rock on which there has been movement Dip slip is movement in the direction of dip Strike slip is movement in the direction of strike Oblique slip is movement in both directions 3 Joints in basalt Grand Canyon Dip Slip Folds and Faults Faults Dip slip is movement of one block up or down the plane of the fault Normal fault upper block moves down Reverse fault upper block moves up Thrust fault low angle reverse fault Stress and Fault Movement Normal faults are tensional Reverse faults and thrust faults are compressional Strike Slip Faults A strike slip fault is the horizontal movement of the blocks relative to each other Left lateral the opposite block has moved to the left Right lateral The opposite block has moved to the right It doesn t matter which block you re on 4 Unconformities San Andreas Fault An unconformity is any break in the sedimentary geologic record A disconformity is a break with no deformation An angular unconformity is a break in which the lower beds have been tilted and eroded before sedimentation resumed RightLateral Angular Unconformity GCNP Deformation Terms Stress Strain Compression stress Tension stress Shear stress Elastic strain Plastic strain Ductile strain Brittle strain Anticline Syncline Monocline Strike Dip Joint Fault Dip slip fault Strike slip fault Oblique slip fault Normal fault Reverse fault Thrust fault Left lateral Right lateral Clicker A Normal Fault B Reverse Fault C Thrust Fault D Strike slip fault 5 Clicker 1 Clicker A Normal Fault B Reverse Fault C Thrust Fault A Normal Fault B Reverse Fault C Thrust Fault D Strike slip fault D Strike slip fault 2 Clicker 3 A Normal Fault B Reverse Fault C Thrust Fault D Strike slip fault Clicker A Normal Fault B Reverse Fault C Thrust Fault D Right lateral Strike slip Fault E Left lateral Strike slip Fault A Angular unconfomity B Disconformity C Thrust Fault D Right lateral Strike slip Fault E Left lateral Strike slip Fault A Anticline B Syncline C Monocline D Dome 6 Clicker Clicker 1 2 A B C D Anticline Syncline Monocline Reverse fault A B C D Anticline Syncline Monocline Reverse fault Clicker 3 A B C D Anticline Syncline Monocline Reverse fault 7
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