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# GEOG 100--Lecture 12--Plate Tectonics

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• ### GEOG 100--Lecture 12--Plate Tectonics

1. 1. Plate Tectonics Chapter 9
2. 2. Rigid Earth Theory
3. 3. Rigid Earth Theory• It was once believed that Earth’s crust was hard and brittle and could not bend
4. 4. Rigid Earth Theory• It was once believed that Earth’s crust was hard and brittle and could not bend
5. 5. Rigid Earth Theory• It was once believed that Earth’s crust was hard and brittle and could not bend• Plasticity
6. 6. Rigid Earth Theory• It was once believed that Earth’s crust was hard and brittle and could not bend• Plasticity – We now know that Earth’s crust can bend (like a tough plastic) before breaking
7. 7. Isostacy• “The maintenance of hydrostatic equilibrium in the crust” – hydrostatics—branch of physics related to the pressure and equilibrium of liquids (hydro) • statics—bodies not active; at rest; in equilibrium; as opposed to dynamics
8. 8. Isostacy
9. 9. Isostacy• Addition or removal of crustal material causes a sinking or rebounding of crust
10. 10. Isostacy• Addition or removal of crustal material causes a sinking or rebounding of crust – Add or remove continental mass and the crust will sink or rise to accommodate the added/removed weight
11. 11. Isostacy• Addition or removal of crustal material causes a sinking or rebounding of crust – Add or remove continental mass and the crust will sink or rise to accommodate the added/removed weight • a glacier growing or remelting, crust eroding off the surface, sediment deposits, water bodies on land, esp. those created by dams
12. 12. Alfred Wegener andHis Continental Drift Theory
13. 13. Alfred Wegener and His Continental Drift Theory• German meteorologist, 1920s “The present continents were originally connected as one enormous landmass that has broken up and drifted apart over the last few 100 million years. The drifting continues….”
14. 14. Alfred Wegener and His Continental Drift Theory• German meteorologist, 1920s “The present continents were originally connected as one enormous landmass that has broken up and drifted apart over the last few 100 million years. The drifting continues….”• Pangaea (Gk. “whole land”)
15. 15. Alfred Wegener and His Continental Drift Theory• German meteorologist, 1920s “The present continents were originally connected as one enormous landmass that has broken up and drifted apart over the last few 100 million years. The drifting continues….”• Pangaea (Gk. “whole land”)
16. 16. Wegener’s Lines of Evidence
17. 17. Wegener’s Lines of Evidence• Similar geology (rocks and rock structures)…
18. 18. Wegener’s Lines of Evidence• Similar geology (rocks and rock structures)…• …petrology (rock chemistry),
19. 19. Wegener’s Lines of Evidence• Similar geology (rocks and rock structures)…• …petrology (rock chemistry),• …paleontology (fossilized plants and animals),
20. 20. Wegener’s Lines of Evidence• Similar geology (rocks and rock structures)…• …petrology (rock chemistry),• …paleontology (fossilized plants and animals),• …matching glacial features (U-shaped valleys, glacial deposits, etc.) on continents separated by oceans
21. 21. Wegener’s Lines of Evidence• Similar geology (rocks and rock structures)…• …petrology (rock chemistry),• …paleontology (fossilized plants and animals),• …matching glacial features (U-shaped valleys, glacial deposits, etc.) on continents separated by oceans• …continent shapes that seem to fit together,
22. 22. Wegener’s Lines of Evidence• Similar geology (rocks and rock structures)…• …petrology (rock chemistry),• …paleontology (fossilized plants and animals),• …matching glacial features (U-shaped valleys, glacial deposits, etc.) on continents separated by oceans• …continent shapes that seem to fit together,• …patterns in the locations of volcanoes
23. 23. Wegener’s Lines of Evidence• Similar geology (rocks and rock structures)…• …petrology (rock chemistry),• …paleontology (fossilized plants and animals),• …matching glacial features (U-shaped valleys, glacial deposits, etc.) on continents separated by oceans• …continent shapes that seem to fit together,• …patterns in the locations of volcanoes
24. 24. Wegener’s Lines of Evidence• Similar geology (rocks and rock structures)…• …petrology (rock chemistry),• …paleontology (fossilized plants and animals),• …matching glacial features (U-shaped valleys, glacial deposits, etc.) on continents separated by oceans• …continent shapes that seem to fit together,• …patterns in the locations of volcanoesEx.: S. America/Africa, Madagascar/India, Australia/Antarctica
25. 25. …but no one bought it.
26. 26. …but no one bought it. Thecrust is too rigid!
27. 27. …but no one bought it. The So why don’t wecrust is see the crust too ripping apart rigid! right now?
28. 28. …but no one bought it. The So why don’t wecrust is see the crust too ripping apart rigid! right now? What do you mean, “Thecontinents are ﬂoating???”
29. 29. …but no one bought it. The So why don’t wecrust is see the crust too ripping apart rigid! right now? And hey, what’s the What do you power source driving mean, “The these movements of allcontinents are the land masses, ﬂoating???” anyway???
30. 30. …but no one bought it. The So why don’t wecrust is see the crust too ripping apart rigid! right now? And hey, what’s the What do you power source driving mean, “The these movements of allcontinents are the land masses, ﬂoating???” anyway??? What a knucklehead.
31. 31. Then along came OceanographerHarry Hess in the 1960s…
32. 32. Then along came OceanographerHarry Hess in the 1960s…
33. 33. The evidence continued to mount…
34. 34. The evidence continued to mount…• Military seafloor mapping: Seafloor geology— structure, chemistry, and age
35. 35. The evidence continued to mount…• Military seafloor mapping: Seafloor geology— structure, chemistry, and age – Oceanic crust: only 100 m.y.o
36. 36. The evidence continued to mount…• Military seafloor mapping: Seafloor geology— structure, chemistry, and age – Oceanic crust: only 100 m.y.o – Continental crust: 4.1 b.y.o.
37. 37. The evidence continued to mount…• Military seafloor mapping: Seafloor geology— structure, chemistry, and age – Oceanic crust: only 100 m.y.o – Continental crust: 4.1 b.y.o.• Core sampling
38. 38. The evidence continued to mount…• Military seafloor mapping: Seafloor geology— structure, chemistry, and age – Oceanic crust: only 100 m.y.o – Continental crust: 4.1 b.y.o.• Core sampling• Seafloor sediment
39. 39. The evidence continued to mount…• Military seafloor mapping: Seafloor geology— structure, chemistry, and age – Oceanic crust: only 100 m.y.o – Continental crust: 4.1 b.y.o.• Core sampling• Seafloor sediment• Rigid Earth folks retired—paradigm shift to plasticity
40. 40. The evidence continued to mount…• Military seafloor mapping: Seafloor geology— structure, chemistry, and age – Oceanic crust: only 100 m.y.o – Continental crust: 4.1 b.y.o.• Core sampling• Seafloor sediment• Rigid Earth folks retired—paradigm shift to plasticity• Convection currents as mechanism/power source
41. 41. The evidence continued to mount…• Military seafloor mapping: Seafloor geology— structure, chemistry, and age – Oceanic crust: only 100 m.y.o – Continental crust: 4.1 b.y.o.• Core sampling• Seafloor sediment• Rigid Earth folks retired—paradigm shift to plasticity• Convection currents as mechanism/power source• Geologists, geophysicists, seismologists, oceanographers, physicists, and paleontologists all agree the theory fits the evidence gathered within their respective fields
42. 42. The Theory of Plate TectonicsTectonic (crustal) plates• Pulling apart (spreading/diverging)• Slamming together and sinking (subducting/converging)• Sliding laterally (sideways)
43. 43. Divergent Plate Boundaries• Spreading centers – Crust pulling apart, magma rising to the surface
44. 44. Convergent Plate Boundaries
45. 45. Convergent Plate Boundaries• Subduction zones
46. 46. Convergent Plate Boundaries• Subduction zones – Crust being forced together
47. 47. Convergent Plate Boundaries• Subduction zones – Crust being forced together – Lightest material rises (mountain-building) while the heaviest stuff sinks (pushed back into the mantle)
48. 48. Convergent Plate Boundaries• Subduction zones – Crust being forced together – Lightest material rises (mountain-building) while the heaviest stuff sinks (pushed back into the mantle) – Remelting (mostly from friction) creates volcanoes
49. 49. Convergent Plate Boundaries• Subduction zones – Crust being forced together – Lightest material rises (mountain-building) while the heaviest stuff sinks (pushed back into the mantle) – Remelting (mostly from friction) creates volcanoes – Intense, deep-focus earthquakes
50. 50. Three Types of Subduction Zones
51. 51. Three Types of Subduction Zones1. Continental crust meets oceanic crust
52. 52. Three Types of Subduction Zones1. Continental crust meets oceanic crust – Oceanic crust sinks
53. 53. Three Types of Subduction Zones1. Continental crust meets oceanic crust – Oceanic crust sinks – Big trench offshore
54. 54. Three Types of Subduction Zones1. Continental crust meets oceanic crust – Oceanic crust sinks – Big trench offshore – Volcanoes on the continental margin
55. 55. Three Types of Subduction Zones1. Continental crust meets oceanic crust – Oceanic crust sinks – Big trench offshore – Volcanoes on the continental margin – Big earthquakes (potential for tsunamis)
56. 56. Continental-Oceanic Subduction
57. 57. Three Types of Subduction Zones
58. 58. Three Types of Subduction Zones2. Oceanic crust meets oceanic crust
59. 59. Three Types of Subduction Zones2. Oceanic crust meets oceanic crust – The older and colder crust will probably sink
60. 60. Three Types of Subduction Zones2. Oceanic crust meets oceanic crust – The older and colder crust will probably sink – Big earthquakes and volcanic islands (called “island arcs”)
61. 61. Three Types of Subduction Zones2. Oceanic crust meets oceanic crust – The older and colder crust will probably sink – Big earthquakes and volcanic islands (called “island arcs”) – Deep ocean trench
62. 62. Three Types of Subduction Zones2. Oceanic crust meets oceanic crust – The older and colder crust will probably sink – Big earthquakes and volcanic islands (called “island arcs”) – Deep ocean trench – Potential for tsunamis
63. 63. Oceanic-Oceanic Subduction
64. 64. Three Types of Subduction Zones
65. 65. Three Types of Subduction Zones3. Continental crust meets continental crust
66. 66. Three Types of Subduction Zones3. Continental crust meets continental crust – Too light to subduct
67. 67. Three Types of Subduction Zones3. Continental crust meets continental crust – Too light to subduct – Mountain-building
68. 68. Three Types of Subduction Zones3. Continental crust meets continental crust – Too light to subduct – Mountain-building – Big earthquakes
69. 69. Three Types of Subduction Zones3. Continental crust meets continental crust – Too light to subduct – Mountain-building – Big earthquakes – Little if any volcanism (mostly intrusive)
70. 70. Continental-Continental Subduction
71. 71. Transform Fault Boundaries
72. 72. Transform Fault Boundaries• Tectonic plates slide past one another
73. 73. Transform Fault Boundaries• Tectonic plates slide past one another – Earthquakes are less intense than subduction
74. 74. Transform Fault Boundaries• Tectonic plates slide past one another – Earthquakes are less intense than subduction – No volcanoes
75. 75. Transform Fault Boundaries• Tectonic plates slide past one another – Earthquakes are less intense than subduction – No volcanoes – Little or no mountain-building
76. 76. “Hot spots”
77. 77. “Hot spots”• Also called magma plumes
78. 78. “Hot spots”• Also called magma plumes• Generally occur some distance from any other type of plate boundary
79. 79. “Hot spots”• Also called magma plumes• Generally occur some distance from any other type of plate boundary• Unrelated to convergent, divergent, or transform boundaries
80. 80. “Hot spots”• Also called magma plumes• Generally occur some distance from any other type of plate boundary• Unrelated to convergent, divergent, or transform boundaries• Anomalous (odd) “balloons” of rising magma
81. 81. “Hot spots”• Also called magma plumes• Generally occur some distance from any other type of plate boundary• Unrelated to convergent, divergent, or transform boundaries• Anomalous (odd) “balloons” of rising magma – Hot spot stays in one position as the moving, island-covered crustal plate rides away from it
82. 82. Accreted Terranes• A moving continent may pick up new land material as lighter (felsic) material scrapes off of a subducting plate
83. 83. Accreted Terranes• A moving continent may pick up new land material as lighter (felsic) material scrapes off of a subducting plate
84. 84. Craton• These terranes were added to the original material first formed from magma that rose out of Earth’s earliest crust – Craton--the name given to these ancient proto- continents cratons 29
85. 85. Continental Shields• More magma material was added to the cratons, forming continents. – Continental shields: Where the earliest continental material still exists intact and is exposed at the surface. 30
86. 86. 31
87. 87. Topography• Right from the very beginning, the crust was affected by stresses and strains that caused crustal deformations• Over time, the crust has continued to be folded, faulted, broken, eroded and further built upon, creating the topography, the ups and downs of land relief, that we see today 32