1. CHAPTER 2 Plate Tectonics and the Ocean Floor (I)
Instructor: Dr. Dong at ECC

2. Layered Earth
Fig. 1.14

3. Fig. 1.15

4. Asthenosphere Upper mantle Plastic—deforms by flowing
High viscosity—flows slowly

5. Plate tectonics explains:
Global distribution of
Volcanoes
Earthquakes
Faults
Mountain belts
Features of seafloor
Evolution of continents and oceans

6. Exe. 2-1 How many layers in the earth structure?
2. What is the plate tectonic?

7. Hypothesis: Continental drift
Wegener proposed one large continent (1912)
Pangaea
Surrounded by single large ocean
Panthalassa
About 200 million years ago

8. Fig. 2.2

9. Evidence for continental drift
Puzzle-like fit of continents
Edward Bullard fit continents at 2000m water depth
Fig. 2.3

10. Evidence for continental drift
Matching sequences of rocks and mountain chains
Similar age, rock types, structures

11. Figure 2.4a

12. Figure 2.4b

13. Evidence for continental drift
Glacial ages and other climate evidence
Ancient glaciation in modern tropical regions
Direction of glacial flow
Distribution of organisms
Same land animals distributed in different continents (e.g., South America and Africa)

14. Fig. 2.5

15. Fig. 2.6

16. Objections to continental drift
Continents cannot “plow” through ocean crust
Gravitational forces associated with tides too small

17. Exe. 2-2 List evidences to support the continental drift
Why was the continental drift a hypothesis?

18. Evidence for plate tectonics
Earth’s magnetic field
Paleomagnetism
Magnetic alignment (N or S)
Magnetic inclination (magnetic dip)
Latitude

19. Fig. 2.7

20. Apparent polar wandering
Pangaea
Fig. 2.8

21. Magnetic polarity reversals
Fig. 2.9

22. How is earth’s magnetic field used for the tectonic plate?
Exe
How is earth’s magnetic field
used for the tectonic plate?

23. Sea floor spreading Harry Hess (1962)
Mid-ocean ridge site of new ocean crust
Oceanic trench site of crust destruction (subduction)
Fig. 2.10

24. Evidence to support sea floor spreading

25. Earth’s magnetic polarity as sea floor created
1. Parallel magnetic anomalies record changes in
Earth’s magnetic polarity as sea floor created
Fig. 2.11

26. 2. Age of ocean floor increases away from crest of mid-ocean ridge
Fig. 2.12

27. 3. Global distribution of earthquakes
Fig. 2.13

28. Evidence to support sea floor spreading
Parallel magnetic anomalies record changes in Earth’s magnetic polarity as sea floor created
Age of ocean floor increases away from crest of mid-ocean ridge
Most large earthquakes occur along plate margins

29. Fig. 2.10

30. Plate tectonics theory
Lithospheric plates “float” on the asthenosphere
Large scale geologic features occur at plate boundaries
Two major tectonic forces
Slab pull
Slab suction

31. Exe
List evidences to support plate tectonic theory.