1. Please label the
following layers.

2. Brain Bender
I am the layer of the earth that is responsible for moving the tectonic plates. The temperature differential between the top and bottom of my layer causes convection.
Which layer of the earth am I?

3. Plate Tectonics

4. What is causing plates to move?

5. Plate Tectonics
Plate Tectonics: A model of global tectonics that suggests that the outer layer of the Earth, the lithosphere, is composed of several rigid, large plates that move relative to one another by sliding on a weak layer, the asthenosphere in the upper mantle; continents and ocean basins are passive riders on these plates.
This is a unifying concept of geology developed after WWII and only accepted during the 1960s!

6. Some Specifics on Plates
Plates are composed of fragments of the lithosphere (crust and upper mantle)
Plates may include both continental and oceanic crust
Plates move in relation to each other at varied rates
No major tectonic movements within plates
Dynamic actions concentrated along plate boundaries

7. Plate Boundaries

9. Remember: Earth’s interior convection is mechanism for plate tectonics
Plate Boundaries
Three types of plate boundaries:
Convergent: plates collide, resulting in subduction and mountain building
Divergent: plates moving apart, resulting in new lithosphere produced at mid-oceanic ridge
Transform: two plates slide past one another
Remember: Earth’s interior convection is mechanism for plate tectonics

10. Convection in the Earth

11. Convergent Boundaries
Plates move together (converge)
One plate may be forced beneath another
Subduction: Process in which one lithospheric plate descends beneath another
Subduction Zone: Convergence of tectonic plates where one plate dives beneath another and is consumed in the mantle
3 possible scenarios:
Ocean to Ocean
Ocean to Continent
Continent to Continent

12. Convergent Boundaries

13. Ocean-Ocean Convergence
Oceanic plate meets oceanic plate
Denser plate forced under (Subduction)
Trench forms
Volcanism occurs in “Island Arc”
Wide earthquake zones
Examples: Japan, Philippines

14. Oceanic-Oceanic Convergence

15. Ocean-Continent Convergence
Dense oceanic plate subducts beneath continent = subduction zone
Melting produces magma = volcanism
Arc of volcanoes forms on continent (volcanic mountain belts)
Oceanic trench forms parallel to subduction zone
Earthquakes
Examples: Cascades, Andes

16. Oceanic-Continental Convergence

17. Name this specific type of boundary.

18. Australian/Pacific
boundary

19. Continent-Continent Convergence
2 continental plates meet
Both are low density
Neither can subduct (too buoyant)
So-they build upward (as mountains)
Shallow Earthquakes
Example: Himalayas (India vs. Asia)

20. Himalaya Mountains: India-Eurasia Collision
Subduction of oceanic crust under Eurasia led to the collision of India with Eurasia, creating the Himalaya Mountains

21. Continental-Continental Convergence

22. Divergent Plate Boundaries
Plates moving apart (extension)
Occur in 2 places:
Oceanic (Mid Ocean Ridges)
Terrestrial (Continental Rift Valleys)
Results in
Creation of new seafloors
Extensional stress and shallow earthquakes
Basaltic volcanism

23. Divergent Boundaries Continental Rift Continental divergent boundary.
Example: East African Rift Zone
Mid Ocean Ridge
Oceanic divergent boundary.
Example: Mid-Atlantic Ridge

24. Transform Boundary Oceanic or continental crust
Results in a shear zone between the plates.
Minimal mountain building
Minimal volcanic activity
Lots of seismic activity!
Example: San Andreas Fault, California

25. Transform Boundaries Strike-slip faults (no vertical motion)
Lateral motion (shear)
Plates slide alongside one another
Occur in 2 realms:
Continents (such as the San Andreas fault)
Mid ocean ridges where they offset ridge segments (fractures)

26. San Andreas Fault

27. Plate Boundaries Divergent plate boundary = mid-ocean ridges
Convergent plate boundaries = subduction zones
Transform plate boundaries, San Andreas fault

28. Plate Motion Plates move at variable speeds Max Velocity ~16-17 cm/yr
Min Velocity ~ .1 cm/yr
Average Velocity ~ 2.5 cm/yr

29. Hot Spots Long-lived structures in the mantle
Volcanic centers that originate from rising plumes of magma from the deep mantle, called mantle plumes
Mantle Plumes:
Long-lived structures in the mantle
Originate at great depth, perhaps near the core-mantle boundary
Results in
Intra-plate (middle of plate) volcanism
A chain of volcanoes forms as tectonic plates move over a stationary hot spot
The bend of a seamount chain over a hot spot records the change of plate motion

31. Mantle Mantle can behave as a solid or a fluid.
Temperature, pressure, and stress are factors in how the mantle behaves
Rapid stress causes the mantle to act as a solid
Solid mantle can fracture and break

32. Mantle Upper mantle is less fluid because it is cooler.
Crust and upper mantle form the fractured lithosphere
When plates move strain accumulates
Too much strain causes the plates to rebound like a snapped elastic
These movements are earthquakes

33. Importance of Plate Tectonics
The theory provides explanations for:
Earth’s major surface processes
The distribution of
Quakes
Volcanoes
Mountains