folds and faults supplemental review and exercises this is a plunging anticline

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  • Slide 1
  • Folds and Faults Supplemental Review and Exercises This is a plunging anticline
  • Slide 2
  • Deformation of Rocks When rocks have been deformed, folding or faulting may result When rocks have been deformed, folding or faulting may result How the deformation manifests its self is dependent on: How the deformation manifests its self is dependent on: Temperature Pressure Rock type Rocks under high pressure, warm, and flexible are more likely to fold Rocks under high pressure, warm, and flexible are more likely to fold Rocks under low pressure, cold, and brittle are more likely to break or fault Rocks under low pressure, cold, and brittle are more likely to break or fault
  • Slide 3
  • Driving force of deformation Plate Tectonics: Plate Tectonics: The lithosphere is broken into plates free to move around on the Earths asthenosphere These plates are free to move with respect to each other, either slipping along one another, colliding, or pulling apart Forming three different plate boundaries which can result in various types of faulting and or folding.
  • Slide 4
  • The Plates http://observe.arc.nasa.gov/nasa/earth/tectonics/Tectonics2.html
  • Slide 5
  • The Plate Boundary Types http://observe.arc.nasa.gov/nasa/earth/tectonics/Tectonics3.html Divergent Plate Boundary: plates move away from each other resulting in extension (tensional forces) Divergent Plate Boundary: plates move away from each other resulting in extension (tensional forces) Convergent Plate Boundary: plates move toward each other resulting in shortening (compress ional forces) Convergent Plate Boundary: plates move toward each other resulting in shortening (compress ional forces) Transform Plate Boundary: plates slide past each other results in lateral movement (shear forces) Transform Plate Boundary: plates slide past each other results in lateral movement (shear forces)
  • Slide 6
  • Convergent Boundaries Folding Folding Anticlines: Arch shaped structure Synclines: Basin like structure Faulting Faulting Reverse Faults (shortening) Vertical movements
  • Slide 7
  • Divergent Boundaries Normal Faults (Extension) vertical movements Normal Faults (Extension) vertical movements Tension
  • Slide 8
  • Transform Boundaries Strike Slip Faults lateral movement and shear forces Strike Slip Faults lateral movement and shear forces Shear
  • Slide 9
  • More on folds and inclined beds. The axis of the fold divides it in half, separating the fold into two limbs the limbs of the fold have the same strike for a non-plunging fold but opposite dips The axis of the fold divides it in half, separating the fold into two limbs the limbs of the fold have the same strike for a non-plunging fold but opposite dips Describe orientation of the beds of rocks using strike and dip Describe orientation of the beds of rocks using strike and dip Strike: the trend of a rock with respect to north, typically parallel to bed contacts and axis of fold Dip: the inclination of the rock away from the horizontal down slope in a direction perpendicular to strike.
  • Slide 10
  • Strike and Dip Symbol The strike and dip symbol resembles a T. However the strike line is longer than the dip line. The strike and dip symbol resembles a T. However the strike line is longer than the dip line. Click to insert strike and dip symbols on the below images. You may want to think of the dip symbol as having an arrow on the end pointing in the direction the rocks are dipping downward
  • Slide 11
  • Rules for Strike and Dip Older rocks dip in the direction of younger rocks Older rocks dip in the direction of younger rocks For an anticline, dips point away from each other on opposite sides of the axis of the fold For an anticline, dips point away from each other on opposite sides of the axis of the fold For a syncline, dips point toward each other on opposite sides of the axis of the fold For a syncline, dips point toward each other on opposite sides of the axis of the fold
  • Slide 12
  • Age of the rock units play a role in interpretation. Age is important for determining dip, and fold type. Age is important for determining dip, and fold type. Use the geologic time scale as follows: Use the geologic time scale as follows: Q Quaternary (youngest) T Tertiary K - Cretaceous J - Jurassic T R - Triassic P - Permian lP - Pennsylvanian M - Mississippian D - Devonian S - Silurian O - Ordovician - Cambrian P Pre Cambrian NOTE: the law of superposition indicates that in undeformed rocks, younger rocks are on top of older rocks at a single point in a vertical succession
  • Slide 13
  • Looking at the Structures Geologic Maps Geologic Maps Cross-Sections Cross-Sections Block Diagrams Block Diagrams
  • Slide 14
  • Geologic Maps Geologic maps of course provide geologic information as related to rock type, age, and structure Geologic maps of course provide geologic information as related to rock type, age, and structure Rock ages are described on the maps using the symbols previously discussed Rock ages are described on the maps using the symbols previously discussed Different rock types and ages are depicted as different colors on the map with the contacts between the units represented by a line. Different rock types and ages are depicted as different colors on the map with the contacts between the units represented by a line. The map symbols and configuration of the units provide structural information such as fold or fault type. The map symbols and configuration of the units provide structural information such as fold or fault type. Geologic maps show the features as seen in map view what things look like on the surface as if you were flying or walking over an area Geologic maps show the features as seen in map view what things look like on the surface as if you were flying or walking over an area.
  • Slide 15
  • Geologic Cross-Sections Provide information regarding the vertical configuration of the units Provide information regarding the vertical configuration of the units Similar to a topographic profile, but providing subsurface information. Similar to a topographic profile, but providing subsurface information. A slice of the earth/feature to provide a side view, so what you would see if cut a vertical slice, like cutting a cake in half and seeing the layers inside A slice of the earth/feature to provide a side view, so what you would see if cut a vertical slice, like cutting a cake in half and seeing the layers inside
  • Slide 16
  • Block Diagrams Incorporate the information from the map view and the cross-sectional view to show both the surface and subsurface Incorporate the information from the map view and the cross-sectional view to show both the surface and subsurface Seeing a block of the earth illustrated how it would look if you could cut a piece out like using a cookie cutter and see the top and the sides allow you to get an idea of the feature in a three dimensional aspect Seeing a block of the earth illustrated how it would look if you could cut a piece out like using a cookie cutter and see the top and the sides allow you to get an idea of the feature in a three dimensional aspect
  • Slide 17
  • Map View and Cross Sectional View to a Block Diagram The diagrams above are all illustrating the same features just from in different views and or dimensions
  • Slide 18
  • The Anticline Anticline: an arch like structure with older beds near its center that are flanked by younger rock Anticline: an arch like structure with older beds near its center that are flanked by younger rock Cross-sectional View Erosion Map View Click to add Strike And dip
  • Slide 19
  • The Syncline Syncline: a basin like structure with younger beds near its center that are flanked by older beds Syncline: a basin like structure with younger beds near its center that are flanked by older beds Cross-sectional View Erosion Map View Click to add Strike And dip
  • Slide 20
  • Plunging Folds (Map View) In map view, non plunging folds have straight contact lines while plunging folds contact lines curve around axial trace. In map view, non plunging folds have straight contact lines while plunging folds contact lines curve around axial trace. For a plunging anticline the bed contacts converge around the fold axis in the direction the fold plunges and for a syncline the bed contacts diverge in the direction of dip around the fold axis For a plunging anticline the bed contacts converge around the fold axis in the direction the fold plunges and for a syncline the bed contacts diverge in the direction of dip around the fold axis
  • Slide 21
  • Three Types of Faults Normal Fault: any fault where the hanging wall has moved down with respect to its footwall. Results in elongation of rocks on the surface due to tensional forces such as along a divergent plate boundary. Reverse Fault: any fault where the hanging wall moves up with respect to its footwall. Results in shortening due to compressional forces such as along a convergent plate boundary Strike Slip Fault: any fault where adjacent fault blocks move parallel to the strike or trend of the fault surface. Results in lateral movement due to shear forces such as along transform boundaries.
  • Slide 22
  • Hanging VS Foot Wall If a tunnel was placed along the fault plane, a persons feet would be on the foot wall and their head by the hanging wall for a normal

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