1. Plate Tectonics

2. Wegener’s Continental Drift
The proposition first published in 1912.
Continents can shift positions around the globe.
Continents were once joined together to form one landmass.
Supercontinent PANGAEA

3. Breakup of Pangaea

4. Breakup of Pangaea

5. Evidence for Wegener’s Continental Drift
Jigsaw Puzzle
Edges of Continents fit together like puzzle
Rock Layers
Similarities of rock layers and structures on opposing shores of Atlantic
Fossil Correlation
Glossopteris plant leaf fossils found in Southern Africa, Australia, South America, India, and Antarctica
Mesosaurus dinosaur fossils found in both South America and Southern Africa

6. Evidence for Wegener’s Continental Drift Jigsaw Puzzle

7. Evidence for Wegener’s Continental Drift Matching Mountain Ranges and Glaciers

8. Evidence for Wegener’s Continental Drift Fossil Correlation

9. Plate Tectonics Theory
Widely accepted theory for plate movement in scientific community.
Earth’s lithosphere is broken up into rigid sections called plates.
The movement and interaction of these plates cause major changes in Earth’s surface.
Plates can move horizontally and vertically.
Plates move due to floating on the asthenosphere.
Continents move as the plates they are attached to move.

10. Mantle Convection
Scientists generally agree that mantle convection is the basic driving force for plate movement.
Convective flow is the motion of matter resulting from changes in temperature.
Plate tectonics is a density driven process. The molten rock is less dense than the surrounding rock.

11. Mantle Convection

12. Mantle Convection

13. Mantle Convection Models

14. Convection and Tectonics
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15. Continents and the Plates to which they are attached

16. Tectonic Plates and Boundaries ESRT p. 5

17. Plate Tectonics Types of Plate Boundaries
 Divergent boundaries (also called spreading centers) are the place where two plates move apart.
 Convergent boundaries form where two plates move together.
 Transform fault boundaries are margins where two plates grind past each other without the production or destruction of the lithosphere.

18. Three Types of Plate Boundaries

19. Divergent Plate Boundaries – Spreading Centers
plates move apart
magma rises from below to fill gap and push plates away from each other
occurs at the mid-ocean ridges and at continental rifts
creates new basaltic ocean crust (dense) at the ridge
the oldest basaltic ocean crust is at the edge of the continents – see diagram

20. Spreading Center Divergent Boundary
Youngest Oceanic Crust
Oldest Oceanic Crust

21. Mid-Ocean Ridges
The mid-ocean ridge is a mountain range at the bottom of the ocean that is composed mainly of volcanoes and lava flows. See map p. 5 ESRT
The rocks created at the mid-ocean ridge have magnetic minerals that are aligned with Earth’s magnetic field.
Earth’s magnetic field reverses polarity on a cycle of thousands of years.

23. Testing Plate Tectonics
Evidence for Plate Tectonics
Testing Plate Tectonics
 The discovery of strips of alternating polarity, which lie as mirror images across the ocean ridges, is among the strongest evidence of seafloor spreading.

24. Polarity of the Ocean Crust

25. Magnetic Striping of the Ocean Floor

26. Actions at Plate Boundaries
Transform Fault Boundaries
Actions at Plate Boundaries
 At a transform fault boundary, plates grind past each other without destroying the lithosphere.
 Transform faults
• Most join two segments of a mid-ocean ridge.
• At the time of formation, they are roughly parallel to the direction of plate movement.
• They aid the movement of oceanic crustal material.

27. Transform Fault Boundary

28. Actions at Plate Boundaries
Convergent Boundaries
Actions at Plate Boundaries
 Oceanic-Oceanic
• Two oceanic slabs converge and one descends beneath the other.
• This kind of boundary often forms volcanoes on the ocean floor.
• Volcanic island arcs form as volcanoes emerge from the sea.
• Examples include the Aleutian, Mariana, and Tonga islands.

29. Oceanic-Oceanic Convergent Boundary

30. Actions at Plate Boundaries
Convergent Boundaries
Actions at Plate Boundaries
 Continental-Continental
• When subducting plates contain continental material, two continents collide.
• This kind of boundary can produce new mountain ranges, such as the Himalayas.

31. Continental-Continental Convergent Boundary

32. Collision of India and Asia

33. Actions at Plate Boundaries
Convergent Boundaries
Actions at Plate Boundaries
 A subduction zone occurs when one oceanic plate is forced down into the mantle beneath a second plate.
 Oceanic-Continental
• Denser oceanic slab sinks into the asthenosphere.
• Pockets of magma develop and rise.
• Continental volcanic arcs form in part by volcanic activity caused by the subduction of oceanic lithosphere beneath a continent.
• Examples include the Andes, Cascades, and the Sierra Nevadas.

34. Oceanic-Continental Convergent Boundary

35. Tectonic Settings and Volcanic Activity
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36. The Ring of Fire

37. Passive Continental Margin
5 main features
Coast – edge of continent
Continental Shelf – wide shallow extension of continent
Continental Slope – steepest gradient drop toward ocean floor
Continental Rise – collection of sediment from turbidity currents
Abyssal plain – ocean floor, flattest places on Earth

38. Passive Continental Margin – simple Trailing Edge of Continent

39. Passive Continental Margin – detailed Trailing Edge of Continent

40. Active Continental Margin Subduction Zone
Subduction is the sinking of the denser crust out of the two plates that are colliding. See map p. 5 ESRT
Ocean trenches are the deepest parts of the oceans.
created at subduction boundaries by bending down of the subducting plate and warping of the crust

41. Active Continental Margin Subduction Zone
Continental Volcanic Arcs form on the edge of the continental plate due a combination of factors:
Friction between plates
Subducting slab
Overriding slab
Increased temperature at depth
Lower density magma rises through denser solid rock

42. Active Continental Margin

43. Continental Margins of the US

44. Volcanoes
created at subduction boundaries due to the melting of the subducting plate at great depth
the rock becomes magma and rises because it is now less dense than the surrounding rock
continental volcanic arcs form on the edge of a continent that the plate is subducting beneath
Examples: Andes in South America, Cascades in United States
volcanic island arcs form on a plate boundary where an oceanic plate is colliding with another oceanic plate and the denser (older) plate is subducting below the less dense (younger) plate
Example: Mariana, Aleutian, and Tonga Islands

45. Anatomy of a “Typical” Volcano

46. Hot Spots are areas where intraplate volcanism occurs.
where a mass of hotter than normal mantle material called a mantle plume rises toward the surface
Examples: Hawaiian Islands, Yellowstone, Iceland, Canary Islands
See Tectonic Plates p. 5 ESRT

47. Hawaiian Hot Spot

48. Hot Spot Volcano Tracks
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