1. Plate Tectonics and Plate Boundaries
Lithosphere (with oceanic and continental crust) floats on the Asthenosphere

2. Lithosphere Plates
Plates consist of continent AND adjoining ocean crust.
Broken into 7 major plates (several minor)
Ocean crust is thinnest (few km)
Continental crust is thickest (up to km)
Plates move as a unit relative to each other.
Move slowly: 2-10 cm/year. 2 6 1 4 7 3 5

3. Oceanic Crust is made of one type of rock: igneous basalt
7 km (5 miles ) thin
Composed of dark, igneous rock
Basalt (black, ocean basin)
3.0 g/ml density
180 million years young (or less)

4. Continental Crust Cold, brittle, fractures (earthquakes)
Averages km (25 miles ) thick
Can exceed 70 km (40 mi) in mountains!
Rock types:
Upper crust is mostly light, silicate rocks such as granite rock
Up to 4 billion years old!
2.7 g/ml density

5. Plate Boundaries
What 3 directions/ways are plates moving (relative to each other)?
(there are more scenarios for the convergent boundaries that are not being shown)
. The plate edges (boundaries) are being
_________toward,
__________away or
__________past each other.
pushed
(convergent)
pulled
(divergent)
slide
(transform)
Which boundary causes earthquakes? Volcanoes? Mountains?

6. Lithospheric plates moving away from each other
Plate Boundaries:
Divergent Boundaries
Lithospheric plates moving away from each other

7. Ocean ridges are a continuous underwater volcanic mountain chain that runs for 43,000 miles, covering 20% of earth’s surface!

8. Textbook pages 712 and 713 for boundary map
Volcanoes (shield) and some earthquakes may be present
On your ocean floor map draw RED arrows at divergent boundaries to indicate the direction of plate motion

9. Divergent plate boundary lines
Continental Rifting
Divergent plate boundary lines

10. Divergent Boundary: continental
Rifting at a divergent boundary

11. Continental Rifting East coast of Africa is “rifting” away from the continent, as the Arabian Peninsula has already done. The Red Sea (a linear sea) is widening, and a new ocean will form.

12. A 13 ft. wide fissure formed after the Sept
A 13 ft. wide fissure formed after the Sept. 14th 2005 earthquake in Ethiopia, Africa. It will continue to split at a rate of 0.8 inches a year eventually forming a new ocean basin.

13. Iceland sits on the mid-Atlantic Ridge Iceland is the only location where a mid-ocean ridge rises above the water

14. Thingvellir in Iceland,
where the North American and Eurasian tectonic plates move apart

15. Quiet eruptions at divergent boundaries: shield volcanoes
Iceland or Hawaii

16. Divergent Boundary: oceanic
spreading centers / rift valleys
mid-ocean ridges
molten magma forces up through rift
igneous basalt rock
new ocean floor created! (2-20 cm/yr)
Hydrothermal vents, pillow lava

17. Divergent: Sea-floor spreading: magma from the upper mantle forces its way up through the thin ocean crust at a ridge. (CONVECTION) This cools and spreads the sea floor apart and makes NEW ocean crust: RIDGE PUSH
Rift valley
More of a gravitational sliding than a true ridge push
Ridges can be HUNDREDS of km wide and HUNDREDS of meters high

18. Sea-Floor Spreading Model Final Outcome

19. Most scientist believe that the nebular hypothesis states that our earth formed 4.6 billion years ago…

20. oldest rock in the Atlantic Ocean
Yet the
oldest rock in the Atlantic Ocean
is only
200
million
years old
????
Using core samples, they dated the ocean floor rocks (basalt). It’s youngest where new rock is forming on the ridges

21. Directions and rates of plate motions
Figure 7.28
What direction is (has) the Pacific plate (been) moving?

22. Volcanic islands and seamounts in Hawaii
Oldest island
north
Northwest
Youngest island

23. Hotspots are where a mantle plum rises to the surface

24. As the Pacific plate moves northwest, a new volcanic island forms over the hotspot.
How Hot Spots form and "move"
Hot Spots and How Hawaii has changed

25. Changing ocean sizes:
If the Atlantic Ocean is spreading and growing larger, is the Pacific Ocean getting smaller?
Yes, the Pacific is getting smaller, it’s subducting under the continents, being melted and recycled.

26. If ....the sea floor is spreading at the ocean ridges
And.... new sea floor is made all the time…
Then..... is the earth growing LARGER???
No, it’s not growing larger,
it has stayed the same size for millions of years.
So where did the old ocean floor go????

27. The old ocean floor is being RECYCLED
The old ocean floor is being RECYCLED! Its subducting under the continent crust –back into the mantle and re-melting