4 4 Deformation


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4 4 Deformation

  1. 1. Chapter 4 Plate Tectonics 4-4 Deforming the Earth’s Crust
  2. 2. Essential Questions/Learning Goals: <ul><li>How does stress affect the Earth’s crust? </li></ul><ul><li>Describe the three major types of folds. </li></ul>
  3. 3. Science Terms: <ul><li>Compression </li></ul><ul><li>Tension </li></ul><ul><li>Folding </li></ul>
  4. 4. Section Introduction: <ul><li>What is stress? </li></ul><ul><ul><li>The amount of force per unit of area on a substance. </li></ul></ul>
  5. 5. Deformation <ul><li>What is deformation? </li></ul><ul><ul><li>Changes in a rock’s shape due to stress </li></ul></ul><ul><ul><ul><li>De = “undo” </li></ul></ul></ul><ul><ul><ul><li>Form = “shape” </li></ul></ul></ul><ul><ul><ul><li>– tion = “process of” </li></ul></ul></ul>
  6. 6. Compression <ul><li>What is compression? </li></ul><ul><ul><li>Stress that squeezes rocks together </li></ul></ul><ul><li>What kind of boundary has compression? </li></ul><ul><ul><li>Convergent boundaries. </li></ul></ul>
  7. 7. Tension <ul><li>What is tension? </li></ul><ul><ul><li>Stress that stretches rocks. </li></ul></ul><ul><li>What kind of boundary has tension? </li></ul><ul><ul><li>Divergent </li></ul></ul>
  8. 8. Folding <ul><li>What are folds? </li></ul><ul><ul><li>Bends in rocks due to stress. </li></ul></ul>
  9. 9. Types of Folds <ul><li>The two most common types of folds are: </li></ul><ul><ul><li>Anticlines: </li></ul></ul><ul><ul><ul><li>Upward folds (arches) </li></ul></ul></ul><ul><ul><li>Synclines: </li></ul></ul><ul><ul><ul><li>Downward folds (troughs) </li></ul></ul></ul>
  10. 11. What is a monocline fold? <ul><li>A fold that has both ends of the fold still horizontal. </li></ul><ul><li>There is a middle portion that bends downwards. </li></ul>
  11. 12. Monocline fold
  12. 13. How big are folds? <ul><li>Folds can be as large as mountains </li></ul><ul><li>Or </li></ul><ul><li>As small as centimeters </li></ul>
  13. 15. Faulting <ul><li>Essential Question: </li></ul><ul><ul><li>How are the three types of faults different from each other? </li></ul></ul><ul><li>Science Term </li></ul><ul><ul><li>Fault </li></ul></ul>
  14. 16. What is a Fault? <ul><li>A break in rocks where one rock slide past the other </li></ul>
  15. 17. Fault Illustration
  16. 18. <ul><li>What are the pieces of broken rock on each side of the fault called? </li></ul><ul><ul><li>Fault blocks. </li></ul></ul><ul><li>Two types: </li></ul><ul><ul><li>Footwall </li></ul></ul><ul><ul><li>Hanging wall </li></ul></ul>
  17. 19. Footwall <ul><li>The block of rock beneath the fault </li></ul><ul><ul><li>You can climb up the footwall </li></ul></ul>
  18. 20. Hanging Wall <ul><li>The block of wall above the fault. </li></ul><ul><ul><ul><li>You could stand underneath a hanging wall. </li></ul></ul></ul>
  19. 21. Normal Faults <ul><li>How do the fault blocks move in a Normal Fault? </li></ul><ul><ul><li>The hanging wall slides down the foot wall </li></ul></ul><ul><li>What kind of stress makes a Normal Fault? </li></ul><ul><ul><li>Tension </li></ul></ul><ul><li>What kind of boundary are you likely to find a Normal Fault at? </li></ul><ul><ul><li>Divergent Boundary </li></ul></ul>
  20. 23. Reverse Faults <ul><li>How do the fault blocks move in a Reverse Fault? </li></ul><ul><ul><li>The hanging wall slides up the footwall </li></ul></ul><ul><li>What kind of stress makes a Reverse Fault? </li></ul><ul><ul><li>Compression </li></ul></ul><ul><ul><li>What kind of boundary are you likely to find a Reverse Fault at? </li></ul></ul><ul><ul><ul><li>Convergent </li></ul></ul></ul>
  21. 25. Telling the Difference Between Faults <ul><li>How can you tell the difference between a normal fault and a reverse fault? </li></ul><ul><ul><li>If you look at the rock layers, you can tell how the hanging wall and footwall have moved. </li></ul></ul>
  22. 26. Strike Slip Faults <ul><li>How do the fault blocks move in a strike slip fault? </li></ul><ul><ul><li>The blocks grind and slide past each other horizontally </li></ul></ul><ul><ul><li>Example of a strike slip fault </li></ul></ul><ul><ul><ul><li>San Andreas Fault </li></ul></ul></ul>
  23. 29. Plate Tectonics and Mountain Building <ul><li>What kinds of mountains are built by Plate Tectonics? </li></ul><ul><ul><li>Folded mountains </li></ul></ul><ul><ul><li>Fault-block mountains </li></ul></ul><ul><ul><li>Volcanic mountains </li></ul></ul>
  24. 30. Folded Mountains <ul><li>How are these mountains formed? </li></ul><ul><ul><li>Plates colliding at a… </li></ul></ul><ul><ul><ul><li>Convergent boundary </li></ul></ul></ul><ul><ul><li>Examples: </li></ul></ul><ul><ul><ul><li>Appalachian, Alps, Himalayas. </li></ul></ul></ul>
  25. 31. Fault-Block Mountains <ul><li>How are these mountains formed? </li></ul><ul><ul><li>Tension pulling huge blocks of rocks apart. </li></ul></ul><ul><ul><ul><li>Gravity causes the hanging wall to slide down the footwall </li></ul></ul></ul><ul><ul><ul><ul><li>Normal faulting </li></ul></ul></ul></ul>
  26. 32. Fault-Block Mountains <ul><li>Shape? </li></ul><ul><ul><li>Can be very jagged and sharp looking. </li></ul></ul><ul><li>Example: </li></ul><ul><ul><li>Tetons in Wyoming </li></ul></ul>
  27. 33. Volcanic Mountains <ul><li>How are these mountains formed? </li></ul><ul><ul><li>When plates collide and one is… </li></ul></ul><ul><ul><ul><li>Subducted </li></ul></ul></ul><ul><ul><li>The melted crust rises to form volcanic mountains </li></ul></ul>
  28. 34. Volcanic Mountains <ul><li>Where are most volcanic mountains formed? </li></ul><ul><ul><li>At plate boundaries such as…. </li></ul></ul><ul><ul><ul><li>Subduction zones </li></ul></ul></ul>
  29. 36. What is the Ring of Fire ? <ul><li>It is the plate boundaries that are found around the Pacific Ocean </li></ul>
  30. 39. Uplift and Subsidence <ul><li>What type of motion occurs in the crust in uplift and subsidence? </li></ul><ul><ul><li>Vertical movement </li></ul></ul><ul><li>Uplift? </li></ul><ul><ul><li>Upward movement of blocks of rock </li></ul></ul><ul><ul><ul><li>May or may not be deformed by stress </li></ul></ul></ul><ul><li>Subsidence? </li></ul><ul><ul><li>Downward movement of blocks of rock </li></ul></ul><ul><ul><ul><li>Usually are not deformed by stress. </li></ul></ul></ul>
  31. 40. Uplifting of Depressed Rocks <ul><li>Rocks that have been pushed down by the weight of glaciers will rise upwards after the glacier has melted away. </li></ul><ul><li>This is called… </li></ul><ul><ul><li>Rebound </li></ul></ul><ul><li>Does deformation occur? </li></ul><ul><ul><li>No. </li></ul></ul>
  32. 42. Subsidence of Cooler Rocks <ul><li>As rocks cool, they take up less… </li></ul><ul><ul><li>Space or volume </li></ul></ul><ul><li>What does this mean for the height of mountains? </li></ul><ul><ul><li>They shrink! </li></ul></ul>
  33. 43. Subsidence of Cooler Rocks <ul><li>Where does this occur? </li></ul><ul><ul><li>Mid ocean ridges. </li></ul></ul><ul><ul><ul><li>As the rocks get further from the MOR, the rocks cool and become more dense causing the ridges to become lower. </li></ul></ul></ul>
  34. 44. Tectonic Letdown <ul><li>What happens to the crust when you stretch it? </li></ul><ul><ul><li>It will sink lower </li></ul></ul><ul><ul><li>This creates a… </li></ul></ul><ul><ul><ul><li>Rift zone </li></ul></ul></ul>
  35. 45. Tectonic Letdown <ul><li>What kind of boundary does this occur at? </li></ul><ul><ul><li>A divergent boundary </li></ul></ul><ul><li>What kind of fault occurs here? </li></ul><ul><ul><li>Normal faults. </li></ul></ul>