1. Plate Tectonics

2. Rigid, rocky outer surface of the Earth
Definition
Tectonic:
Plate:
Rigid, rocky outer surface of the Earth
To build or destroy
The processes by which the rocky plates of the planet move and interact with each other

3. Internal Structure of the Earth
lithosphere
plates
mantle
inner core
hot dense rock
solid iron
outer core
liquid iron

4. Lithospheric Plates Continental: Oceanic: thick, light, mostly granite
thin, heavy, mostly lava flows
Asthenosphere
Weak, plastic upper mantle

5. Lithospheric Plates

6. Diverging Plate Boundaries
Where plates pull apart from each other
Stretching & thinning
High heat flow
(New Crust Created)

7. Diverging Plate Boundaries
Key landform: mid-oceanic ridges
volcanic mt. ranges
axial valley
1000’s miles long
1-2 miles tall

8. Converging Plate Boundaries
Where plates collide
Subduction zone: collision between oceanic and continental lithosphere
(Crust Destroyed)

9. trenches & volcanic arcs
Subduction zones
Key landforms:
trenches & volcanic arcs

10. Transform Plate Boundaries
Where plates slide side by side
Key landform: faults
(Crust neither destroyed or created)

11. thermal convection / convection currents plate sinks and subducts
Driving Force
thermal convection / convection currents
pushes up at ridges
plates spread away
hot rock
cold rock
plate sinks and subducts

12. Geologic activity at plate margins
Volcanism: C, D
Earthquakes: C, D, T
Rock Deformation: C, D, T

13. Evidence: shape of continents
The margins of some continents look like they could fit together
First proposed by Alfred Wegner

14. Fossil Evidence

15. Nonrandom occurrence of volcanic activity
Evidence: volcanoes
Nonrandom occurrence of volcanic activity

16. Evidence: earthquakes
Nonrandom occurrence of earthquakes
Shallow at diverging margins
deep at converging margins

17. Stationary upwellings of heat away from plate margins
Evidence: hot spots
Stationary upwellings of heat away from plate margins

18. Evidence: hot spots
As plates move, the volcanoes are carried away from the hot spot
Only volcanoes near the hot spot are are active
Can determine direction and speed of the plate motion

19. Evidence: age of seafloor rocks
Youngest rocks are found at the mid oceanic ridges
Oldest rock are found farthest from the ridge

20. Evidence: paleomagnetism
Earth has a strong magnetic field
Iron rich volcanic rocks record Earth’s magnetic field at the time they form

21. seafloor paleomagnetic record
Bands of alternating polarity
Symmetrical about the mid oceanic ridges

22. seafloor paleomagnetic record
lava forming at the ridges picks up the current magnetism, then gets pushed out of the way as newer lava forms
Records of the growth and spreading of the seafloor

23. seafloor paleomagnetic record
The alternating polarity represents complete reversals of Earth’s magnetic field

24. continental paleomagnetic record
The location of magnetic poles on separate continents appear to wander with time
If the poles haven’t moved significantly, then the continents did
Use overlapping poles to reconstruct the past positions of the continents

25. Plate Tectonics in the PNW
Cascadia subduction zone

26. Plate Tectonics in the PNW
Cascades volcanic arc

27. Plate Tectonics in the PNW
Juan de Fuca & Gorda mid ocean ridges

28. Plate Tectonics in the PNW
Blanco & Medocino fracture zones

29. Plate Tectonics in the PNW
“exotic terranes
islands carried by the plates
Attached to the North America continent

30. seafloor paleomagnetic record
Bands of alternating polarity
Symmetrical about the mid oceanic ridges

31. Evidence: paleo-environments

32. Evidence: distribution of mountains

33. Importance of Plate Tectonics