1. The Theory of Tectonic Plates
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 (lower mantle).
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
Divergent
Transform

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
Continental-oceanic
Oceanic-oceanic

8. Convergent Boundary Continental-Continental
The two continental plates
come together
Buckle
Thicken
Push continental
crust upward

9. Convergent Boundary Continental-Oceanic
Dense oceanic crust sinks below the continental crust and sinks into the asthenosphere.
This is a subduction zone.
Sub means below (submarine, subway)
Old ocean crust is pushed below the asthenosphere and gets re-melted and recycled.

10. Convergent Boundary Oceanic-Oceanic
One oceanic plate sinks below the other.
Another subduction zone

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

13. 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.

14. 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

15. 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