1. April 17
Plate Tectonics
Allen

2. Plate Tectonics Earth’s crust is cracked and fragmented
Fragments called plates
The Earth’s mantle is very hot and fluid, so the plates move atop the mantle

3. Earth’s Crust Two kinds of crust exist
Granitic (felsic) and basaltic (mafic)

4. Earth’s Crust
Think of the Earth as completely covered with a layer of thin, dense basalt rock with chunks of thicker, less dense granite here and there
The granite chunks are the continents riding on the basalt like wood floats on water

5. Plate Boundaries--where tectonic plates meet and interact
Where can you find this image?

6. Plate Boundaries
Three types
Convergent
Divergent
Transform

7. Divergent Boundaries Where plates are moving apart
Cracks in the crust are filled by upwelling molten rock
Give one example of a divergent boundary:

8. Divergent Boundaries
Divergent boundaries on continents are called rifts
Example: the African Rift Valley
Splitting Africa in two
Divergent boundaries under oceans form mid-ocean ridges

9. Divergent Boundaries
Several plates are pulling apart beneath the Atlantic ocean forming the Mid-Atlantic Ridge
Diverging ocean plates cause sea floor spreading
Where new sea floor is constantly being added

11. EAST AFRICAN RIFT VALLEY – CONTINENTAL RIFT

12. In Afar, Ethiopia, a 40-mile magmatic rift that opened up 1 year ago

13. April 17
Spreading Center
Allen

14. Mid-ocean ridges (rifts) normally form where tectonic plates are
(1) converging (3) stationary
(2) diverging (4) sliding past each other
The motion of the convection currents in the mantle beneath the Atlantic Ocean appears to be mainly making this ocean basin
(1) deeper (3) wider
(2) shallower (4) narrower

16. Convergent Boundaries
Where plates are coming together
Here for example
What is the name of this boundary?

17. Convergent Boundaries
Where mountains form
Where earthquakes occur (and sometimes volcanoes)
Several plates are colliding with the Pacific Plate creating the Pacific Ring of Fire
An area that experiences lots of earthquake and volcanic activity

18. Pacific Ring of Fire

19. Convergent Boundary Types
Ocean-Ocean
Continental-Continental
Ocean-Continental

20. Convergent Boundaries
Oceanic crust - Oceanic Crust
older, denser crust subducts forming ocean trench
Oceanic Crust – Continental Crust
denser oceanic crust subducts forming ocean trench
Continental Crust – Continental Crust
resists subduction - folding, faulting, and mountain building

21. Ocean-Ocean Convergence
Forms ocean trenches
Deepest places on Earth
Name one ocean-ocean boundary

22. Oceanic Crust – Oceanic Crust
Older, denser oceanic crust is SUBDUCTED
VOLCANIC ISLAND ARC FORMED – ALEUTIAN ISLANDS

23. Ocean-Continental Convergence
Site of subduction zones
Denser ocean plate slides beneath the less dense continental plate
Example: the Pacific Northwestern U.S.
Creates many of the Earth’s volcanic mountain chains as the ocean plate dives down, melts and is forced back to the surface
Name one ocean-continental boundary

25. Oceanic-Continental Convergent Boundary - SUBDUCTION
April 17
DENSER OCEANIC CRUST GOES DOWN INTO MANTLE
Allen

26. Continental-Continental Convergence
How non-volcanic mountains are formed
Example: the Appalachian chain and the Himalayas
Rising of land due to plate collisions is called uplift
Name one continental-continental boundary

27. Continental Crust – Continental Crust Convergent Boundary NO SUBDUCTION - COLLISION ZONE

29. Collision of India and Asia
April 17
Collision of India and Asia
Allen

31. TRANSFORM PLATE BOUNDARIES
Transform Fault Boundaries
TRANSFORM PLATE BOUNDARIES
At a transform fault boundary, plates grind past each other without creating or destroying the lithosphere.
SHALLOW EARTHQUAKES
 Transform faults
• Most join two segments of a mid-ocean ridge.
• At the time of formation, they roughly parallel the direction of plate movement.

32. Transform Fault Boundary AT MID-OCEAN RIDGES
April 17
Transform Fault Boundary AT MID-OCEAN RIDGES
Allen

33. So, what causes plates to move?
Convection currents: drag and move the lithospheric plates above the asthenosphere
(three sources of heat produce the convection currents):
Leftover heat from earth’s formation
Decay of Radioactive elements
Plate friction

34. Convection Cells

35. Convection Currents in the mantle drag and pull the lithospheric plates above them

36. Mid-Atlantic Ridge As the plates pull apart new ocean floor is added
What 2 continents are moving away from each other as a result of the mid-Atlantic Ridge?

37. Convection Currents
It is theorized convection currents within the Mantle cause plates to move around
There are other theories about what causes plates to move!

39. Evidence for Plate Tectonics
 Ocean Drilling
The data on the ages of seafloor sediment confirmed what the seafloor spreading hypothesis predicted.
The youngest oceanic crust is at the ridge crest, and the oldest oceanic crust is at the continental margins.

40. Which graph best represents the geologic age of the surface bedrock on the ocean bottom?

41. More Evidence for Plate Tectonics
 Earthquake Patterns
Scientists found a close link between deep-focus earthquakes and ocean trenches.
The absence of deep-focus earthquakes along the oceanic ridge system was shown to be consistent with the new theory.

42. Convergent plate (subduction) boundaries have deeper earthquakes Divergent plate boundaries and collision zones have shallow earthquakes

43. April 17
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f07_58_pg196.jpg
f07_58_pg196
Allen

44. SUMMARY 3 PLATE BOUNDARIES
DIVERGING
CONVERGING (SUBDUCTION ZONE)
Oceanic Crust – Continental Crust
Oceanic Crust - Oceanic Crust
CONVERGING (COLLISION ZONE)
Continental Crust – Continental Crust
TRANSFORM

45. Boundaries: Diverging

46. Boundaries: Converging SUBDUCTION

47. CONVERGING –- COLLISION ZONE
No subduction – continental crust less dense - buoyant

48. Boundaries: Transform

51. Due to plate tectonics the world is constantly changing