1. Four Basic Concepts of the Theory of Plate Tectonics

2. The entire theory can be reduced to
Four basic concepts
really only three, since the fourth is the third turned inside out and
sdrawkcab!
backwards!

3. Concept 1: Plates are formed from the lithosphere
Layers Defined by Physical Properties
Lithosphere
rigid (breaks when stress is applied)
forms the plates.
Asthenosphere
plastic (flows when stress applied)
allows the plates to glide horizontally.

5. Layers Defined by Composition
Crust
continental: thicker, less dense.
oceanic: thinner, denser.
Mantle

6. Model showing Earth’s inferred internal structure.

7. Concept 2: Plates move in one of three ways relative to each other.
Divergent motion
Convergent motion
Transform motion
It’s as simple as putting your hands side by side, palms down.
Pull them apart.
Move them toward one another.
Slide one hand past the other.
Descriptions of each type follow.

8. Divergent Boundary

9. Convergent boundary

10. Transform Boundary

11. Plates and continents are not the same!

12. Concept 3: Most internally-driven geologic activity occurs at or near plate boundaries.
Divergent boundary
Description
Associated geologic phenomena
Examples

13. Most divergent boundaries are located along the crests
of oceanic ridges

14. Rising magma forces the crust apart
As the crust is pulled apart, large slabs of rock sink producing a rift zone.

15. Eventually, an expansive ocean basin and ridge system are created.
Further spreading generates a narrow sea.
Eventually, an expansive ocean basin and ridge system are created.

16. East African rift valleys and associated features.

17. Convergent boundary Description
Associated geologic phenomena: details depend on type (below)

18. Convergent boundary (continued)
Variations: there are only three ways that two entities can relate to each other….if the entities are ocean lithosphere and continental lithosphere, what are these three combinations?
Answer:
ocean to continent
ocean to ocean
continent to continent

19. Convergent boundary (continued)
The details of geologic phenomena depend on the specific type of convergent boundary.
Ocean to continent:
Explosive volcanoes
Earthquakes from shallow to deepest.
Folded/faulted mountain building

20. earthquakes from shallow to deepest. no folded/faulted mountains.
Convergent boundary (continued)
Ocean to ocean:
explosive volcanoes
earthquakes from shallow to deepest.
no folded/faulted mountains.

21. continent to continent: no volcanism
Convergent boundary (continued)
continent to continent:
no volcanism
earthquakes of variable depth but scattered.
folded/faulted mountain building

22. Ocean - continent convergent boundary

23. Cascade volcanoes form near a ocean - continent
convergent boundary.

24. Ocean - ocean convergent boundary

25. Continent - continent convergent boundary

26. Head-on collision of India and Asia produced the Himalayas Mountains.

27. Test yourself: Which types of plate boundaries are suggested by oceanic ridges? By trenches?

28. Which types of plate boundaries are suggested by only shallow-focus earthquakes? By deep-focus quakes?

29. Transform boundary
Description
Associated geologic phenomena
Examples

30. Transform fault boundary, in this
case offsetting a divergent boundary.

31. Some West Coast transform faults.

32. Concept 4: Interiors of plates are relatively quiet geologically
Exceptions exist, including…
Intra-plate earthquakes
Hot spots
Volcanic activity
Evidence for plate motion

33. Hot Spot Tracks...
Magma rises from mantle through the lithosphere and erupts to form a volcano.
Volcanic activity only occurs at the site above the hot spot.

34. Hawaiian Islands: older to northwest, younger to southeast

35. Hot Spot Tracks...
As the plate moves over the hot spot the volcano moves off the hot spot and goes extinct.

36. Of course, externally-driven geological activity occurs away from plate boundaries!
Weathering
Erosion by streams
by glaciers
by wind
directly by gravity
Deposition of sediment (delta, floodplain, etc.
Flooding
Storms

37. How this applies to your class:
Understanding where earthquakes occur most commonly is closely related to knowledge of plate tectonic theory. Also, knowing the particular type of plate boundary will help you understand if an earthquake is likely to be shallow and if it might be very large.

38. How this applies to your class:
Understanding where volcanic eruptions occur and knowing about the specific type of eruption and hence specific volcanic hazards is closely related to knowledge of plate boundaries.

39. How this applies to your class:
Understanding where some mineral deposits are formed is related to plate tectonics.

40. How this applies to your class:
Recognize that geologic hazards related to surface processes
differential solar heating and wind
gravity
can occur any place conditions are favorable for them, including in the middle of a lithospheric plate!

41. The End