1. Plate Tectonics

2. Plate Tectonics The Continental Drift Hypothesis
Plate Tectonics – Overview
Divergent Boundaries
Convergent Boundaries
Transform Boundaries
Testing the Theory of Plate Tectonics
Measuring Plate Motion
What Makes Plates Move?

3. The Continental Drift Hypothesis
GEOL131: Plate Tectonics
The Continental Drift Hypothesis

4. Alfred Wegener (1880-1930) German paleoclimatologist
GEOL131: Plate Tectonics: Continental Drift
Alfred Wegener ( )
German paleoclimatologist
Studied evidence for ancient climates
Traveled extensively, collected thousands of samples
Published continental drift ideas in 1915
Died during expedition to Greenland in 1930

5. Pangaea “All lands” 200 million years ago
GEOL131: Plate Tectonics: Continental Drift
Pangaea
“All lands”
200 million years ago

6. Wegener’s Evidence The “continental jigsaw puzzle”
GEOL131: Plate Tectonics: Continental Drift
Wegener’s Evidence
The “continental jigsaw puzzle”
Trans-oceanic fossil matching
Trans-oceanic rock matching
Ancient climates

7. Wegener’s Evidence: Continental Jigsaw
GEOL131: Plate Tectonics: Continental Drift
Wegener’s Evidence: Continental Jigsaw

8. Wegener’s Evidence: Matching Fossils
GEOL131: Plate Tectonics: Continental Drift
Wegener’s Evidence: Matching Fossils

9. Wegener’s Evidence: Matching Fossils
GEOL131: Plate Tectonics: Continental Drift
Wegener’s Evidence: Matching Fossils

10. Wegener’s Evidence: Matching Rocks
GEOL131: Plate Tectonics: Continental Drift
Wegener’s Evidence: Matching Rocks
Pangaea
Present

11. Wegener’s Evidence: Ancient Climates
GEOL131: Plate Tectonics: Continental Drift
Wegener’s Evidence: Ancient Climates
Pangaea
Present

12. Reaction to Wegener’s Ideas
GEOL131: Plate Tectonics: Continental Drift
Reaction to Wegener’s Ideas
Other scientists were highly critical
Major problem: no good explanation for how continents could move
Wegener proposed
Moon’s gravity moved continents
Continents pushed through ocean crust like icebreaker ships

13. Reaction to Wegener’s Ideas
GEOL131: Plate Tectonics: Continental Drift
Reaction to Wegener’s Ideas
Moon’s gravity too weak
Ocean crust too dense and strong
Most scientists concluded continental drift was incorrect

14. Plate Tectonics: Overview
GEOL131: Plate Tectonics
Plate Tectonics: Overview

15. Earth’s Layers: Two schemes
GEOL131: Plate Tectonics: Plate Tectonics Overview
Earth’s Layers: Two schemes
Based on composition
Crust, mantle, core
Based on seismic wave behavior
Lithosphere, asthenosphere, mesosphere, outer core, inner core
Lithosphere, asthenosphere most important for plate tectonics

16. Earth’s Layers: Two schemes
GEOL131: Plate Tectonics: Plate Tectonics Overview
Earth’s Layers: Two schemes
Asthenosphere

17. Lithospheric Plates Rigid, brittle Continents are “embedded” in them
GEOL131: Plate Tectonics: Plate Tectonics Overview
Lithospheric Plates
Rigid, brittle
Continents are “embedded” in them

18. Why is plate tectonic theory successful?
GEOL131: Plate Tectonics: Plate Tectonics Overview
Why is plate tectonic theory successful?
Provides plausible explanation for how continents move
Doesn’t require them to “plow” through ocean crust

19. Two types of lithosphere
GEOL131: Plate Tectonics: Plate Tectonics Overview
Two types of lithosphere
Oceanic
Thin, dense, able to subduct into mantle
“asphalt”
Continental
Thick, low density, buoyant, does not subduct
“styrofoam”

20. GEOL131: Plate Tectonics: Plate Tectonics Overview
Plate Motion

21. Plate Boundaries: Divergent
GEOL131: Plate Tectonics
Plate Boundaries: Divergent

22. Plates separate at divergent boundaries
GEOL131: Plate Tectonics: Divergent Boundaries
Plates separate at divergent boundaries
New crust created by undersea volcanism

23. Creation of Divergent Boundaries
GEOL131: Plate Tectonics: Divergent Boundaries
Creation of Divergent Boundaries
1. Continental lithosphere pushed up by upwelling magma
2. Lithosphere stretched & thinned, forming a continental rift

24. Creation of Divergent Boundaries
GEOL131: Plate Tectonics: Divergent Boundaries
Creation of Divergent Boundaries
3. Ocean water floods rift, creating narrow seaway
4. Seaway continues to widen as plates separate

25. Creation of Divergent Boundaries
GEOL131: Plate Tectonics: Divergent Boundaries
Creation of Divergent Boundaries
Stage 1: Yellowstone NP - Continental lithosphere being pushed up by magma below

26. Creation of Divergent Boundaries
GEOL131: Plate Tectonics: Divergent Boundaries
Creation of Divergent Boundaries
Stage 3: Red Sea and Gulf of Aden- Narrow seaways
Stage 2: East African Rift - Lithosphere being stretched and thinned

27. Creation of Divergent Boundaries
GEOL131: Plate Tectonics: Divergent Boundaries
Creation of Divergent Boundaries
Stage 4: Atlantic Ocean – wide ocean basin with divergent boundary at center

28. Plate Boundaries: Convergent
GEOL131: Plate Tectonics
Plate Boundaries: Convergent

29. Plates come together at convergent boundaries
GEOL131: Plate Tectonics: Convergent Boundaries
Plates come together at convergent boundaries
Three types, based on lithosphere involved
Oceanic-oceanic
Oceanic-continental
Continental-continental

30. Oceanic-oceanic boundaries
GEOL131: Plate Tectonics: Convergent Boundaries
Oceanic-oceanic boundaries

31. Oceanic-continental boundaries
GEOL131: Plate Tectonics: Convergent Boundaries
Oceanic-continental boundaries

32. Continental-continental boundaries
GEOL131: Plate Tectonics: Convergent Boundaries
Continental-continental boundaries
A.k.a. “continental collision zones”
Example: India and Asia

33. GEOL131: Plate Tectonics: Convergent Boundaries
India-Asia Collision: Example of a continent-continent convergent boundary

34. Plate Boundaries: Transform
GEOL131: Plate Tectonics
Plate Boundaries: Transform

35. Plates slide past each other at transform boundaries
GEOL131: Plate Tectonics: Transform Boundaries
Plates slide past each other at transform boundaries

36. San Andreas Fault: A transform boundary
GEOL131: Plate Tectonics: Transform Boundaries
San Andreas Fault: A transform boundary
Los Angeles is moving northwest
San Francisco is moving southeast

37. San Andreas Fault: A transform boundary
GEOL131: Plate Tectonics: Transform Boundaries
San Andreas Fault: A transform boundary

38. Testing the Plate Tectonic Theory
GEOL131: Plate Tectonics
Testing the Plate Tectonic Theory

39. Much evidence comes from ocean drilling
GEOL131: Plate Tectonics: Testing the Plate Tectonic Theory
Much evidence comes from ocean drilling
Research ships drill into ocean sediments and rock
Drill cores are collected that show cross-section of ocean floor at that location

40. Major Lines of Evidence
GEOL131: Plate Tectonics: Testing the Plate Tectonic Theory
Major Lines of Evidence
Sediment thicknesses
Ocean crust ages
Hot spot tracks
Apparent polar wandering
Paleomagnetic striping

41. Sediment Thickness and Crustal Age
GEOL131: Plate Tectonics: Testing the Plate Tectonic Theory
Sediment Thickness and Crustal Age
Both increase away from oceanic ridges

42. GEOL131: Plate Tectonics: Testing the Plate Tectonic Theory
Hot Spot Tracks

43. Apparent Polar Wandering
GEOL131: Plate Tectonics: Testing the Plate Tectonic Theory
Apparent Polar Wandering
Earth has a magnetic field
Some minerals are magnetic
These minerals act like compass needles
They record where magnetic poles were located at the time the minerals formed

44. Apparent Polar Wandering
GEOL131: Plate Tectonics: Testing the Plate Tectonic Theory
Apparent Polar Wandering
Rocks in North America and Eurasia seem to show that magnetic poles have moved thousands of miles
Continents have moved, not the poles

45. Paleomagnetic Striping
GEOL131: Plate Tectonics: Testing the Plate Tectonic Theory
Paleomagnetic Striping
Earth’s magnetic field has reversed many times
Normal polarity: North magnetic pole near north geographic pole
Reversed polarity: N. magnetic near S. geographic
Magnetic field polarities over the last 4 million years. Periods of normal polarity shown in white.

46. Paleomagnetic Striping
GEOL131: Plate Tectonics: Testing the Plate Tectonic Theory
Paleomagnetic Striping
Oceanic crustal rocks record the polarity in effect at the time they formed
Symmetrical “stripe” pattern of normal and reversed polarity created in ocean crust

47. GEOL131: Plate Tectonics
What Makes Plates Move?

48. Three mechanisms: slab pull, ridge push, mantle drag
GEOL131: Plate Tectonics: What Makes Plates Move?
Three mechanisms: slab pull, ridge push, mantle drag * * *

49. GEOL131: Plate Tectonics
End of Chapter