1. The Theory of Plate Tectonics

2. Plate Tectonics
Plate tectonics is the theory that the Earth’s lithosphere is divided into tectonic plates that move around the top of the asthenosphere.
Plate boundaries – a place where tectonic plates touch: collide, separate, or slide past each other.

3. Three types of plate boundary
Convergent
Divergent
Transform

4. Convergent Boundaries
Convergent boundaries - the boundary formed by the collision of two lithospheric plates.
There are three styles/types of convergent plate boundaries
Continent-continent boundaries
Continent-oceanic boundaries
Ocean-ocean boundaries

5. Continent-Continent Collision
Continent-Continent Collision - when the two plates collide, they buckle and thicken, which pushes the continental crust upward
Forms mountains, e.g. European Alps, Himalayas

6. Himalayas

7. Continent-Oceanic Crust Collision
Continent-Oceanic Crust Collision - the denser oceanic crust sinks below the continental crust where it is remelted and recycled
Called subduction zone; can form volcanoes

8. Subduction

9. Ocean-Ocean Plate Collision
Ocean- Ocean Plate Collision - when two oceanic plates collide, one runs over the other which causes it to sink into the mantle forming a subduction zone.
The subducting plate is bent downward to form a very deep depression in the ocean floor called a trench.
The worlds deepest parts of the ocean are found along trenches.

10. Age of Oceanic Crust
Courtesy of

11. Divergent Boundaries - The boundary between two tectonic plates moving away from each other
As the plates move apart, magma rises to fill the gap; can cause volcanic activity
Mid-ocean ridges are the most common type

12. Iceland
Iceland has a divergent plate boundary running through its middle

13. Transform Boundaries
Two tectonic plates slide past each other horizontally
Above: View of the San Andreas transform fault

15. San Andreas Fault, CA