1. The Unifying Theory of Earth Science
Plate Tectonics
The Unifying Theory of Earth Science

2. Learning Targets:
Explain how mantle convection, ridge push, and slab pull drive the movement of lithospheric plates.
Identify and describe the 3 types of plate boundaries
Convergent
Divergent
Transform
Infer the relationship between the type of plate boundary and landforms, such as ocean trenches, mountain ranges, and mid-ocean ridges.

3. Plate Tectonics Continents are not moving Plates are moving
Continental Drift + Seafloor Spreading = Plate Tectonics
Continents are not moving
Plates are moving
Pieces of the lithosphere

4. Plate Movement
Mantle convection moves the plates

6. What is the primary force that drives seafloor spreading
What is the primary force that drives seafloor spreading? Mantle convection cells

7. Ridge push Because mid-ocean ridges lie at a higher elevation than the rest of the ocean floor, gravity causes the ridge to push on the lithosphere that lies farther from the ridge.

8. Slab Pull is a tectonic plate motion due to higher densities
Slab Pull is a tectonic plate motion due to higher densities. Plate motion is partly driven by the weight of cold, dense plates sinking into the mantle at trenches.

9. Plates
Monitoring for nuclear weapons tests led to a greater understanding of earthquakes and faults
Earthquakes are not random
Connect the dots to form plate boundaries
Earthquakes occur at plate boundaries

11. Plates
Most plates have some continental crust and oceanic crust
Move at 2-10 cm/year
Like fingernail growth
Move in jerks – Earthquakes
Lithospheric plates because both the crust and the top part of the mantle moves

13. Plate Boundaries 3 types of plate boundaries Divergent: moving apart
Convergent: moving together
Transform: moving past each other
The edges where two plates meet is known as a plate boundary.

14. Divergent Boundaries Mid-ocean ridges in oceans
Seafloor spreading
Continental rift on land
Breaks continents apart to make new oceans
Source of most of earth’s new rock
Which of the following describes two plates that are moving away from each other? Divergent plate boundary

15. Divergent Boundaries
Shallow earthquakes and a lot of volcanic activity
Magma rises to the surface in these places for two reasons
Crust is thin
There is a strong upwelling in the mantle beneath

18. Which of the following plate boundaries is the result of seafloor spreading? Divergent plate boundaries

21. Convergent Boundaries
Three types
Oceanic-oceanic collisions
Oceanic-continental collisions
Continental-continental collisions
Each type has unique but predictable consequences
Subduction Zones
Which of the following describes two plates that are moving towards each other? Convergent plate boundary

22. Oceanic-continental Convergence
Oceanic crust always sinks under the continental crust
Why?
Subduction: crust being pushed into the mantle
Oceanic crust is pushed into the mantle and melted
The process by which a dense piece of the Earth’s crust is forced back down into the mantle is called subduction.

24. Oceanic-Continental Subduction Zones
Very strong earthquakes
Volcanic activity on the continent
Line of volcanoes running parallel to the subduction zone: continental arc
The least dense minerals from the seafloor melt and are forced up onto the continent
Forms deep trenches

25. There is water in the rocks of the oceanic plate (because they are underwater), and as this plate moves further down into the subduction zone, much of the water contained in the plate is squeezed out when the plate begins to subduct. This addition of water to the mantle causes partial melting of the mantle, generating magma, which then rises, and which normally results in volcanoes. This normally happens at a certain depth, about 70 to 80 miles below the Earth's surface, and so volcanoes are formed fairly close to, but not right next to, the trench.
An oceanic trench is found where the denser plate is subducted underneath the other plate.

26. Oceanic-Oceanic Convergence
Denser plate gets subducted
Usually the older plate is more dense
Deep sea trenches
Very strong earthquakes
Volcanic activity on the top plate
Volcanoes form in a line: island arc

28. Continental-Continental Convergence
Continental crust is too thick and buoyant to be subducted
Gets pushed up to form mountains
This is how mountain ranges without volcanoes form
Which type of plate boundary convergence is responsible for mountain building in the absence of volcanic activity? Continental-continental convergence

30. Continental-Continental Convergence
Earthquakes
No volcanic activity
Why not?
What types of rocks form at this boundary?
Granite forms

32. Plate Boundary Review Divergent Convergent Transform
Mid-ocean ridges, continental rifts
Convergent
Oceanic-Oceanic, subduction
Oceanic-Continental, subduction
Continental-Continental, mountain building
Transform

33. Transform Plates move past one another Not as important geologically
No new rock
No rock is destroyed
Not as important geologically
Shallow earthquakes
No volcanoes
Which of the following describes two plates that are slipping past one another? Transform plate boundary

36. Intraplate Activity
Hotspots: volcanic activity in the middle of plates
Mantle is very hot in these places
Earthquakes and volcanoes can form anywhere

39. Plate Tectonics