Chapter 11notes


Published on

Published in: Technology, Health & Medicine
  • Be the first to comment

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

Chapter 11notes

  1. 1. Chapter 11 Mountain Building
  2. 2. Rock Deformation <ul><li>It is theorized that all continents were once mountainous masses and grow by adding mountains to their edges. </li></ul><ul><li>If this is so, then how do mountains grow in the middle of continents? </li></ul>
  3. 3. Factors Affecting Deformation <ul><li>Every rock has a point at which it will bend and/or break. </li></ul><ul><li>Deformation is the term that refers to all changes in the original shape and/or size of a rock body. </li></ul><ul><li>Most deformation occurs at plate margins. </li></ul>
  4. 4. <ul><li>Stress is the force per unit area acting on a solid. Under great stress, rocks tend to deform usually by: </li></ul><ul><li>Folding </li></ul><ul><li>Faulting </li></ul><ul><li>Flowing </li></ul><ul><li>Fracturing </li></ul>
  5. 5. <ul><li>The change in shape or volume of a body of rock as a result of stress is called strain . </li></ul><ul><li>Rocks can be bent into folds if stress is applied gradually and not going beyond the breaking point. </li></ul><ul><li>We already know that rocks under stress have elastic properties and will go back to their original shape and size when the force is removed. (elastic rebound) </li></ul>
  6. 6. <ul><li>Once the elastic limit or strength of a rock is surpassed, it either flows or fractures . </li></ul>
  7. 7. <ul><li>The factors that influence the strength of a rock and how it will deform include: </li></ul><ul><li>Temperature </li></ul><ul><li>Confining pressure </li></ul><ul><li>Rock type </li></ul><ul><li>Time </li></ul>
  8. 8. Temperature and Pressure <ul><li>Rocks deform permanently two ways: </li></ul><ul><li>Brittle deformation </li></ul><ul><li>Ductile deformation </li></ul>
  9. 9. <ul><li>Rocks near the surface, where temperatures and confining pressures are low, usually behave like brittle solids and fracture once their strength is exceeded. </li></ul><ul><li>This type of deformation is called brittle failure or brittle deformation . </li></ul><ul><li>Examples: china, bones, pencils, glass </li></ul>
  10. 10. <ul><li>At depth, where temperatures and confining pressures are high, rocks show ductile behavior. </li></ul><ul><li>Ductile deformation is a type of solid-state flow that produces a change is size and shape of an object without fracturing the object. </li></ul><ul><li>Examples: modeling clay, bee’s wax, caramel candy, and most metals </li></ul>
  11. 11. Question ???????????? <ul><li>Placing a penny on a railroad track and having a train run over it, causing the penny to flatten out is an example of? </li></ul><ul><li>ductile deformation </li></ul>
  12. 12. Rock Type <ul><li>The mineral composition and texture of a rock also affect how it will deform. </li></ul><ul><li>Granite and basalt contain minerals with strong internal molecular bonds will fracture . </li></ul><ul><li>Sedimentary rocks that are weakly cemented or metamorphic rocks that are foliated are more likely to deform by ductile flow . </li></ul>
  13. 13. <ul><li>Rocks that exhibit ductile flow may include: </li></ul><ul><li>Soft </li></ul><ul><li>Halite (rock salt) </li></ul><ul><li>Gypsum </li></ul><ul><li>Shale </li></ul><ul><li>Intermediate strength </li></ul><ul><li>Limestone </li></ul><ul><li>Schist </li></ul><ul><li>Marble </li></ul>
  14. 14. Time <ul><li>Natural stress applied over a long period of time will fold rocks. </li></ul><ul><li>Forces that are unable to deform rock when first applied may cause rock to flow if the force is maintained over a long period of time . </li></ul>
  15. 15. Types of Stresses <ul><li>Three types of stresses rocks undergo include: </li></ul><ul><li>Tensional forces – rocks being pulled in opposite directions </li></ul><ul><li>Compressional force – rocks are squeezed and shortened </li></ul><ul><li>Shear stress – when a body of rock is distorted </li></ul>
  16. 16. Stresses
  17. 17. Folds <ul><li>During mountain building, flat lying rocks (both sedimentary and igneous) are bent in wave-like ripples called folds . </li></ul>
  18. 18. <ul><li>There are three types of folds: </li></ul><ul><li>Anticline – an upward fold (arch) </li></ul><ul><li>Syncline – a downward fold (trough) </li></ul><ul><li>Monocline – closely associated with faults, monoclines are large step–like folds in otherwise horizontal layers of sedimentary strata. </li></ul><ul><li>Prominent features of the Colorado Plateau which coves Colorado, New Mexico, Utah, and Arizona. </li></ul>
  19. 19. Anticline and Syncline Process
  20. 21. Circular Anticline
  21. 22. Syncline
  22. 25. <ul><li>Joints – fractures in rock strata where no movement has taken place </li></ul><ul><li>So faults are…………… </li></ul>
  23. 27. Three types of faults <ul><li>Normal – caused by tensional stress </li></ul><ul><li>Reverse (or thrust) – caused by compressional stress </li></ul><ul><li>Strike-slip – commonly caused by shear stress – San Andreas Fault </li></ul>
  24. 28. Normal
  25. 29. Reverse or Thrust
  26. 30. Strike-Slip
  27. 31. What type of fault? <ul><li>Strike-slip </li></ul>
  28. 32. What type of fault? <ul><li>Normal </li></ul>
  29. 33. What type of fault? <ul><li>Reverse or Thrust </li></ul>
  30. 36. Thrust fault
  31. 37. Types of Mountains <ul><li>The collective processes that produce a mountain belt are called orogenesis . </li></ul><ul><li>The dominant processes that have formed them classify mountains. </li></ul>
  32. 38. Folded Mountains <ul><li>Mountains formed primarily by folding are called folded mountains . </li></ul><ul><li>Thrust faults are also important in the formation of folded mountains. </li></ul><ul><li>These mountains are called fold and thrust belts . </li></ul><ul><li>Examples: Appalachian Mountains, the northern Rocky Mountains, and the Alps of Europe </li></ul>
  33. 40. Fault-Block Mountains <ul><li>Large-scale normal faults are associated with structures called fault-block mountains. </li></ul><ul><li>These mountains form when large blocks of crust are uplifted and tilted along normal faults .  </li></ul><ul><li>Examples: Teton Range of Wyoming and the Sierra Nevada Range of California. </li></ul>
  34. 42. <ul><li>Normal faulting occurs when tensional stresses cause the crust to be stretched or extended. </li></ul><ul><li>As the crust is stretched, a block called a graben , which is bounded by normal faults, drops down. </li></ul><ul><li>Graben is German for ditch or trench. </li></ul><ul><li>Grabens produce an elongated valley bordered by relatively uplifted structures called horsts . </li></ul><ul><li>Examples: Basin and Range Province of Nevada, Utah, and California. </li></ul>
  35. 45. Rift or Grabben
  36. 46. <ul><li>Graben or Rift </li></ul><ul><li>example is: Death Valley 250 ft. below sea level </li></ul>Dead Sea is 1200 ft below sea level
  37. 47. Domes and Basins <ul><li>These mountains are produced by broad upwarping in the basement rock deforming the overlying sedimentary strata. </li></ul><ul><li>A dome is when upwarping produces a circular or elongated structure or dome . </li></ul>
  38. 48. <ul><li>How are these domes uncovered? </li></ul><ul><li>Erosion strips away the highest portion of the sedimentary beds exposing older igneous and metamorphic rocks in the center. </li></ul><ul><li>The oldest rocks form the core of these mountains.  </li></ul><ul><li>Example: Black Hills </li></ul>
  39. 49. <ul><li>Downwarped structures having a circular shape are called basins . </li></ul><ul><li>These structures have gently sloping bed similar to saucers. </li></ul><ul><li>Basins are thought to be formed by the accumulation of sediment, whose weight caused the crust to subside . </li></ul><ul><li>Example: Basins of Michigan & Illinois </li></ul><ul><li>In the case of a basin the oldest rocks are found in the center with the youngest rocks on the flanks. </li></ul>
  40. 51. Mountain Formation <ul><li>Just how old are mountains? </li></ul><ul><li>Appalachians are 100s of million of years old </li></ul><ul><li>Himalayas are about 45 million years old… Just a youngster! </li></ul>
  41. 52. Mountain Building at Convergent Boundaries <ul><li>Most mountain building occurs at convergent plate boundaries. </li></ul><ul><li>Colliding plates provide the compressional forces that fold, fault, and metamorphose the thick layers of sediment deposited on the edges of landmasses. </li></ul>
  42. 53. Ocean-Ocean Convergence <ul><li>Converging oceanic plates result in subduction that creates magma leading to the growth of a volcanic island arc once it grows above sea level. </li></ul><ul><li>Examples: Aleutian Islands in Alaska, Japan, </li></ul><ul><li>Ocean-ocean convergence mainly produces volcanic mountains. </li></ul>
  43. 57. Ocean-Continental Convergence <ul><li>Example: West coast of South America – the Andes Mountains </li></ul><ul><li>This produces a continental volcanic arc . </li></ul><ul><li>During subduction, sediment scraped from the subducting plate is stuck against the landward side of the trench. </li></ul><ul><li>This accumulation of sediment and metamorphic rock is called an accretionary wedge . </li></ul>
  44. 58. <ul><li>Ocean-continent convergence produces mountains in two roughly parallel belts. </li></ul><ul><li>The continental volcanic arc develops on the continental block and the accretion wedge is on the seaward belt. </li></ul><ul><li>The types of mountains formed by ocean-continent convergence are volcanic mountains and folded mountains . </li></ul>
  45. 60. Continent-Continent Convergence <ul><li>A convergent boundary between two plates carrying continental crust, a collision between the continental fragments will result and form folded mountains .   </li></ul><ul><li>Example: Himalayan Mountains and the Tibetan Plateau, European continent collided with Asia producing the Ural Mountains in Russia. </li></ul>
  46. 62. Mountain Building at Divergent Boundaries <ul><li>These mountains are usually formed on the ocean floor </li></ul><ul><li>Example: Mid-ocean ridges that extend 65,000 kilometers. </li></ul><ul><li>The mountains that form along ocean ridges at divergent plate boundaries are fault-block type mountains. </li></ul>
  47. 64. Non-Boundary Mountains <ul><li>Example: Hawaiian Islands </li></ul><ul><li>Continental Accretion </li></ul><ul><li>Accretion is when small crustal fragments collide and merge with continental margins. </li></ul>
  48. 66. <ul><li>Terrane – is any coastal fragment that has a geological history distinct from that of the adjoining terranes. </li></ul><ul><li>Some may be no larger than volcanic islands, while other are immense, such as the entire Indian subcontinent. </li></ul><ul><li>Some may have been microcontinents similar to present day Madagascar. </li></ul><ul><li>Many others were island arcs like Japan and the Philippines. </li></ul>
  49. 67. <ul><li>All these materials add to the continent width and thickness displacing other fragments further inland. </li></ul>
  50. 69. Mountains of Accretion <ul><li>Example: Mountains in western North America and western Canada contain rock, fossils, and structures different from the surrounding area. </li></ul><ul><li>These materials have been accreted (added to) the western margin of North America. </li></ul>
  51. 70. Principle of Isostasy <ul><li>This is a gradual up and down motion of materials that make up the interior of continents away from continental margins. </li></ul><ul><li>Earth’s crust floats on top of denser more flexible rocks in the mantle. </li></ul><ul><li>The concept of a floating crust in gravitational balance is isostasy . </li></ul>
  52. 71. <ul><li>Mountain belts float on top of more dense crustal roots that extend into the mantle. </li></ul><ul><li>The denser mantle supports the mountains from below. </li></ul>
  53. 72. <ul><li>If more material were added to the top of the mountains the combined block would sink until a new isostatic balance was reached. </li></ul><ul><li>However, the top of the combined block would be higher than before and the bottom would be lower. </li></ul><ul><li>This process of establishing a new level of gravitational equilibrium is called isostatic adjustment . </li></ul>
  54. 75. Isostatic Adjustment of Mountains <ul><li>Continental ice sheets provided evidence of crustal subsidence followed by rebound. </li></ul><ul><li>The weight of 3 kilometers of ice depressed Earth’s crust by hundreds of meters. </li></ul><ul><li>In 8000 years since the last ice sheets melted, uplift of as much as 330 meters has occurred in Canada’s Hudson Bay region. </li></ul>
  55. 76. <ul><li>Most mountain building causes the crust to shorten and thicken. </li></ul><ul><li>Because of isostasy, deformed and thickened crust will undergo regional uplift both during mountain building and for a long period afterward. </li></ul><ul><li>As the crust rises (rebounds) the processes of erosion increases and the deformed rock layers are carved into mountains. </li></ul>
  56. 77. <ul><li>Erosion removes material from the summit reducing the load causing the crust to rise. This will continue until the mountain block reaches its “normal” thickness. </li></ul>