1. The Earth’s Crust is in Motion
PLATE TECTONICS
The Earth’s Crust is in Motion

2. Relating Plate Tectonics to the Rock Cycle and other Processes

3. http://earthsci. terc. edu/content/investigations/es0602/es0602page01

5. Structure of the Earth
Earth’s Layers Overhead Transparency and Questions

7. 4 Main Layers of the Earth
Crust – Made up of two types: Oceanic and Continental. Contains mostly Silicon, Oxygen, and Aluminum
Mantle – Divided into upper and lower mantle; mostly Iron and magnesium
Outer Core – Liquid, mostly Iron and Nickel
Inner Core – Solid, Mostly Iron and Nickel

8. Layers of the Earth

10. Comparison of Earth’s Two Types of Crust
Oceanic
Continental
Thinner and more dense
Made up mostly of mafic (basaltic) igneous rocks basalt and gabbro
Thicker and less dense
Made up mostly of the felsic (granitic) igneous rocks granite and rhyolite

11. Theories Prior to Plate Tectonics
Continental Drift
Proposed by Alfred Wegener
Says that the continents have moved horizontally to their present location

12. Evidence for Continental Drift
Continents fit together
Fossils
Continents fit like a puzzle
Wegener called this large landmass Pangaea
Fossils of similar animals such as mesosaurus and plants like glossopteris were found on different continents.
(See fig. 2, p.273)

14. Movement of the Continents

15. Another View

16. Evidence for Continental Drift (continued)
Climate
Rock Type and Structure
Warm-weather fossils found in the Arctic
Evidence of glaciers found in present-day warm areas.
Same rock types and structures on different continents (example: Eastern U.S. and Western Europe

19. Why was Wegener’s Original Proposal of Continental Drift not Accepted?

20. Theories Prior to Plate Tectonics (continued)
Seafloor Spreading
Proposed by Harry Hess .
The theory states that hot, less dense material in the mantle is forced upward to the surface at the mid - ocean ridges.

21. Seafloor Spreading (continued)
As magma is forced upward at mid-ocean ridges, it flows in opposite directions away from the ridge.
As it moves away from the ridge, the magma cools, solidifies, gets thinner and becomes ______ dense.
Becoming more dense than the asthenosphere below it, the oceanic crust sinks downward at convergent boundaries, forming trenches

22. Evidence for Seafloor Spreading
Oceanic crust is younger than continental crust
Oceanic crust is million years old while continental crust is almost 4 billion years old.
Rocks are younger at the mid-ocean ridges and get increasingly older away from the ridge on both sides
Age of the Seafloor

23. Evidence for Seafloor Spreading (continued)
Magnetic Clues
Iron minerals in basaltic rocks align with the Earth’s magnetic field.
The magnetic field has reversed several times.
The reversal creates an alternating pattern of normal and reversed polarity that is the same on both sides of the ridge (see fig.7, p.278).

27. Theory of Plate Tectonics
(Unifying theory that explains many complex Earth systems);
This theory helps explain continental _______, seafloor ________, AND provides a cause (mechanism) for these movements of the crust.
The cause was what was lacking in the previous theories.

28. Theory of Plate Tectonics (cont.)
The theory of plate tectonics states that the Earth’s continental and oceanic crust is broken up into sections. These sections are called tectonic or lithospheric plates, and they move over the surface the Earth.
The larger plates and their boundaries can be seen in figure 9 on page 281.

31. Layers Related to Plate Tectonics
Lithosphere
Asthenosphere
Consists of the crust and rigid upper mantle
Broken into large pieces called tectonic plates.
Plastic-like part of the upper mantle.
Is beneath the lithosphere

32. Tectonic Plate Boundaries
As the tectonic (lithospheric) plates move along and above the asthenosphere, the plates meet at three types of boundaries:
3 Types of Boundaries
Divergent – plates move away from each other
Convergent – plates move toward each other
Transform – plates slide past each other horizontally

33. Divergent Boundaries
The tectonic plates are moving away from each other
Characteristics of a divergent boundary are:
- Shallow-focus Earthquakes
- Volcanoes since molten material of
the mantle is so close to the surface.
Examples of divergent boundaries are the Mid-Atlantic _______ and the East-African rift valley.

37. A plume of hot magma rises from deep within the mantle pushing up the crust and causing pressure forcing the continent to break and separate. Lava flows and earthquakes would be seen.

38. As the rift valley expands two continental plates have been constructed from the original one. The molten rock continues to push the crust apart creating new crust as it does.

39. As the rift valley expands, water collects forming a sea.

40. The sea floor continues to spread and the plates get bigger and bigger.

43. Convergent Boundaries
Plates move directly towards each other
There are three types of convergent boundaries:
Oceanic-to-Continental
Oceanic-to-Oceanic
Continental-to-Continental

44. Oceanic-to-Continental Convergent Boundaries
The more dense _______ crust subducts under the less dense ___________ crust.
Characteristics include:
- Trench at subduction zone
- Volcanoes
- Shallow- and deep-focus earthquakes
An example is the ______ mountains on the west coast of South America

47. Andes Mountains in South America

49. Oceanic-to-Oceanic Convergent Boundaries
An older, cooler, and _____ dense oceanic plate subducts under another oceanic plate
Characteristics include:
- Volcanic island arcs
- Earthquakes and volcanoes
- Ocean or sea on both sides of the boundary
Examples of this type of boundary are Japan and the Aleutian Islands in Alaska

52. Aleutian Island Chain, Alaska

53. Aleutian Mountains

54. Pavlof Volcano

55. Continental-to-Continental Convergent Boundary
This occurs when less –dense continental-crust plates collide.
Being less dense, these plates can only move upward during collision.
Characteristics include:
- Tall mountains
- Earthquakes (Shallow- and medium-focus)
- Absence of __________ since there is no
subduction.
The Himalaya mountains where _____ and ____ collided are an example.

56. Continental-to-Continental Convergent Boundary

57. Collision of India and Asia

58. Himalaya Mountains

59. Transform Plate Boundaries
At this boundary, the tectonic plates slide past each other with little or no vertical movement or subduction.
Characteristics of a transform boundary:
- Shallow-focus Earthquakes
- An Absence of volcanoes since there is
no subduction.
An example of a transform boundary is the ___ _______ fault in California

60. Transform Boundary Example

61. Diagram of Transform Boundary

62. Example of Transform Boundary

63. Plate Boundary Summary

64. Plate Boundary Summary

65. Other Characteristics Related to Plate Tectonics
Volcanoes and Earthquakes are concentrated along plate boundaries
An example is the “ring of ____” around the Pacific Ocean
(See figures 2 on page 301 and 5 on page 333)

67. Earthquakes are Also Concentrated Along Plate Boundaries

70. Other Characteristics of the Plate Tectonics Theory (continued)
An EXCEPTION to earthquakes and volcanoes being along plate boundaries is the occurrence of hot spots.
These occur where the mantle material is very close to the surface in isolated areas within a plate (See fig.8 on p.335)
An example of a hot spot is ________

72. Plate Moves over Hot Spot, Creating an Island Chain

73. Map of Island Chain Created by the Hawaiian Hot Spot

74. What Causes the Plates to Move?
The cause of tectonic (lithospheric) plate movement is __________ currents in the plastic-like mantle, or the _____________
There are different models made to explain these __________ currents
(See figure 12 on page 285)

77. Now, Repeat Everything

78. Comprehensive Review
(Also see links on volcano power point presentation)

79. Va. Tectonic landforms link