1. The Theory of Plate Tectonics
Chapter 7 Section 3

2. The Theory of Plate Tectonics
The Earth’s lithosphere (crust and upper mantle) is divided into tectonic plates.
These plates move on top of the asthenosphere.
We know that these plates move in different ways.

3. Tectonic Plates

4. Tectonic Plate Boundaries
A boundary is a place where tectonic plates touch.
There are 3 types of tectonic plate boundaries:
Convergent- move toward each other
Divergent- move away from each other
Transform- move past each other

5. The numbers on the map represent the rate at which plates are moving in centimeters.

6. Plate Movement

7. Convergent Boundary
When two plates collide, or move toward each other, the boundary is called convergent
There are 3 types of convergent boundaries, depending on what type of crust comes together.
Continental-continental-mountains form
Continental-oceanic- subduction zone-volcanoes
Oceanic-oceanic- subduction zone- volcanoes- old crust is recycled by subduction

8. What forms at a Convergent Boundary?
1. Continental meets continental MOUNTAIN RANGES form

9. What forms at a Convergent Boundary?
Dense oceanic crust sinks below the continental crust and sinks into the asthenosphere.
This is a subduction zone.
A VOLCANO forms

10. What forms at a Convergent Boundary?
One oceanic plate sinks below another oceanic plate.
Another subduction zone
A VOLCANO

11. What forms at a Divergent Boundary
Two tectonic plates move away from each other.
On the sea floor at the mid-ocean ridge this is called sea floor spreading.
As the plates move apart, magma rises to fill the gaps.
The magma is cooled and forms new ocean floor.
The volcanic country of Iceland, which straddles the Mid-Atlantic Ridge, offers scientists a natural laboratory for studying on land the processes also occurring along the submerged parts of a spreading ridge. Iceland is splitting along the spreading center between the North American and Eurasian Plates, as North America moves westward relative to Eurasia.

12. Divergent- mid ocean ridges form here, plates, move apart.

13. Mid Ocean Ridge- Atlantic Ocean

14. Divergent Boundary Sea Floor Spreading On-land exposure of the
Mid-Atlantic Ridge in Iceland.
Sea Floor Spreading

15. What forms at a Transform Boundary?
Two tectonic plates move past one another.
Their edges are jagged and irregular.
As they grind together and jerk, they slide past each other creating earthquakes.

16. Transform Boundary

17. Possible Causes of Plate Movement
Convection Currents: hot rock deep in the Earth rises, cooler rock sinks. This movement of magma causes plates to move
Ridge push
Slab pull

18. Tracking Tectonic Plate Movement
Plates move very slowly, centimeters to inches a year.
GPS, Global Positioning System, measures the rate of movement.
Radio signals beam continuously from satellites to the Earth.
By recording the time it takes for the Ground station to move a given distance, scientists can measure the speed at which plates move.
Plate Boundary Animation

19. KNOW FOR TEST-
Ridge push- the process that results when magma rises at a mid-ocean ridge and pushes oceanic plates in two different directions away from the ridge.
Slab pull- the process that results when a dense oceanic plate sinks beneath a more buoyant plate along a subduction zone, pulling the rest of the plate that trails behind it.
A change in Earth’s magnetic field is called a magnetic reversal.
The magnetic pattern of ocean floor rocks on one side of an ocean ridge is a mirror image of that of the other side.