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Plate Tectonics    Chapter 9
Rigid Earth Theory
Rigid Earth Theory• It was once believed that Earth’s crust was  hard and brittle and could not bend
Rigid Earth Theory• It was once believed that Earth’s crust was  hard and brittle and could not bend
Rigid Earth Theory• It was once believed that Earth’s crust was  hard and brittle and could not bend• Plasticity
Rigid Earth Theory• It was once believed that Earth’s crust was  hard and brittle and could not bend• Plasticity  – We now...
Isostacy• “The maintenance of hydrostatic  equilibrium in the crust”  – hydrostatics—branch of physics related to the    p...
Isostacy
Isostacy• Addition or removal of crustal material causes a sinking  or rebounding of crust
Isostacy• Addition or removal of crustal material causes a sinking  or rebounding of crust   – Add or remove continental m...
Isostacy• Addition or removal of crustal material causes a sinking  or rebounding of crust   – Add or remove continental m...
Alfred Wegener andHis Continental Drift Theory
Alfred Wegener and        His Continental Drift Theory• German meteorologist, 1920s    “The present continents were    ori...
Alfred Wegener and         His Continental Drift Theory• German meteorologist, 1920s     “The present continents were     ...
Alfred Wegener and         His Continental Drift Theory• German meteorologist, 1920s     “The present continents were     ...
Wegener’s Lines of Evidence
Wegener’s Lines of Evidence• Similar geology (rocks and rock structures)…
Wegener’s Lines of Evidence• Similar geology (rocks and rock structures)…• …petrology (rock chemistry),
Wegener’s Lines of Evidence• Similar geology (rocks and rock structures)…• …petrology (rock chemistry),• …paleontology (fo...
Wegener’s Lines of Evidence•   Similar geology (rocks and rock structures)…•   …petrology (rock chemistry),•   …paleontolo...
Wegener’s Lines of Evidence• Similar geology (rocks and rock structures)…• …petrology (rock chemistry),• …paleontology (fo...
Wegener’s Lines of Evidence• Similar geology (rocks and rock structures)…• …petrology (rock chemistry),• …paleontology (fo...
Wegener’s Lines of Evidence• Similar geology (rocks and rock structures)…• …petrology (rock chemistry),• …paleontology (fo...
Wegener’s Lines of Evidence• Similar geology (rocks and rock structures)…• …petrology (rock chemistry),• …paleontology (fo...
…but no one bought it.
…but no one bought it.  Thecrust is  too rigid!
…but no one bought it.  The        So why don’t wecrust is      see the crust  too         ripping apart rigid!         ri...
…but no one bought it.  The            So why don’t wecrust is          see the crust  too             ripping apart rigid...
…but no one bought it.  The            So why don’t wecrust is          see the crust  too             ripping apart rigid...
…but no one bought it.  The               So why don’t wecrust is             see the crust  too                ripping ap...
Then along came OceanographerHarry Hess in the 1960s…
Then along came OceanographerHarry Hess in the 1960s…
The evidence continued to mount…
The evidence continued to mount…• Military seafloor mapping: Seafloor geology—  structure, chemistry, and age
The evidence continued to mount…• Military seafloor mapping: Seafloor geology—  structure, chemistry, and age  – Oceanic c...
The evidence continued to mount…• Military seafloor mapping: Seafloor geology—  structure, chemistry, and age  – Oceanic c...
The evidence continued to mount…• Military seafloor mapping: Seafloor geology—  structure, chemistry, and age  – Oceanic c...
The evidence continued to mount…• Military seafloor mapping: Seafloor geology—  structure, chemistry, and age  – Oceanic c...
The evidence continued to mount…• Military seafloor mapping: Seafloor geology—  structure, chemistry, and age   – Oceanic ...
The evidence continued to mount…• Military seafloor mapping: Seafloor geology—    structure, chemistry, and age    – Ocean...
The evidence continued to mount…• Military seafloor mapping: Seafloor geology—    structure, chemistry, and age    – Ocean...
The Theory of Plate TectonicsTectonic (crustal) plates• Pulling apart (spreading/diverging)• Slamming together and sinking...
Divergent Plate Boundaries• Spreading centers  – Crust pulling apart, magma rising to the surface
Convergent Plate Boundaries
Convergent Plate Boundaries• Subduction zones
Convergent Plate Boundaries• Subduction zones  – Crust being forced together
Convergent Plate Boundaries• Subduction zones  – Crust being forced together  – Lightest material rises (mountain-building...
Convergent Plate Boundaries• Subduction zones  – Crust being forced together  – Lightest material rises (mountain-building...
Convergent Plate Boundaries• Subduction zones  – Crust being forced together  – Lightest material rises (mountain-building...
Three Types of Subduction Zones
Three Types of Subduction Zones1. Continental crust meets oceanic crust
Three Types of Subduction Zones1. Continental crust meets oceanic crust  – Oceanic crust sinks
Three Types of Subduction Zones1. Continental crust meets oceanic crust  – Oceanic crust sinks  – Big trench offshore
Three Types of Subduction Zones1. Continental crust meets oceanic crust  – Oceanic crust sinks  – Big trench offshore  – V...
Three Types of Subduction Zones1. Continental crust meets oceanic crust  – Oceanic crust sinks  – Big trench offshore  – V...
Continental-Oceanic Subduction
Three Types of Subduction Zones
Three Types of Subduction Zones2. Oceanic crust meets oceanic crust
Three Types of Subduction Zones2. Oceanic crust meets oceanic crust  – The older and colder crust will probably sink
Three Types of Subduction Zones2. Oceanic crust meets oceanic crust  – The older and colder crust will probably sink  – Bi...
Three Types of Subduction Zones2. Oceanic crust meets oceanic crust  – The older and colder crust will probably sink  – Bi...
Three Types of Subduction Zones2. Oceanic crust meets oceanic crust  – The older and colder crust will probably sink  – Bi...
Oceanic-Oceanic Subduction
Three Types of Subduction Zones
Three Types of Subduction Zones3. Continental crust meets continental crust
Three Types of Subduction Zones3. Continental crust meets continental crust  – Too light to subduct
Three Types of Subduction Zones3. Continental crust meets continental crust  – Too light to subduct  – Mountain-building
Three Types of Subduction Zones3. Continental crust meets continental crust  – Too light to subduct  – Mountain-building  ...
Three Types of Subduction Zones3. Continental crust meets continental crust  – Too light to subduct  – Mountain-building  ...
Continental-Continental Subduction
Transform Fault Boundaries
Transform Fault Boundaries• Tectonic plates slide past one another
Transform Fault Boundaries• Tectonic plates slide past one another  – Earthquakes are less intense than subduction
Transform Fault Boundaries• Tectonic plates slide past one another  – Earthquakes are less intense than subduction  – No v...
Transform Fault Boundaries• Tectonic plates slide past one another  – Earthquakes are less intense than subduction  – No v...
“Hot spots”
“Hot spots”• Also called magma plumes
“Hot spots”• Also called magma plumes• Generally occur some distance from any  other type of plate boundary
“Hot spots”• Also called magma plumes• Generally occur some distance from any  other type of plate boundary• Unrelated to ...
“Hot spots”• Also called magma plumes• Generally occur some distance from any  other type of plate boundary• Unrelated to ...
“Hot spots”• Also called magma plumes• Generally occur some distance from any  other type of plate boundary• Unrelated to ...
Accreted Terranes• A moving continent may  pick up new land material  as lighter (felsic) material  scrapes off of a  subd...
Accreted Terranes• A moving continent may  pick up new land material  as lighter (felsic) material  scrapes off of a  subd...
Craton• These terranes were added to the original  material first formed from magma that rose  out of Earth’s earliest cru...
Continental Shields• More magma material was added to the  cratons, forming continents.   – Continental shields: Where the...
31
Topography• Right from the very beginning, the crust  was affected by stresses and strains that  caused crustal deformatio...
GEOG 100--Lecture 12--Plate Tectonics
GEOG 100--Lecture 12--Plate Tectonics
GEOG 100--Lecture 12--Plate Tectonics
GEOG 100--Lecture 12--Plate Tectonics
GEOG 100--Lecture 12--Plate Tectonics
GEOG 100--Lecture 12--Plate Tectonics
GEOG 100--Lecture 12--Plate Tectonics
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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

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