1. Guided Notes on the Theory of Plate Tectonics
Chapter 17, Section 3

2. 1. State the theory of plate tectonics in its entirety
The earth’s crust and rigid upper mantle are broken into enormous slabs called plates. These plates move in different directions and at different speeds and this movement is caused by the Earth’s internal heat.

3. 2. What are the 3 types of movement that can occur at plate boundaries?
Plates can come together, or converge
Plates can move away from each other, or diverge
Plates can move horizontally past each other

4. 3. Divergent boundaries are places where 2 tectonic plates are moving apart. Most divergent boundaries are found on the seafloor, where they form ocean ridges.

5. 4. The process of seafloor spreading along a divergent boundary may cause an ocean basin to grow wider.

6. 5. A divergent boundary formed on a continent is called a rift valley, which is a long narrow depression in continental crust.

7. 6. Convergent boundaries are places where 2 tectonics plates are moving toward each other.

8. 3 Types of Convergent Boundaries
Continental-Continental
One continental plate converges with another continental plate. Neither plate is forced downward and a folded mountain range is formed.

9. 3 Types of Convergent Boundaries
2. Oceanic-Oceanic
Oceanic crust converges with oceanic crust. One plate is forced downward, resulting in a deep-sea trench and an island arc of volcanoes.

10. 3 Types of Convergent Boundaries
Oceanic-Continental
An oceanic plate converges with a continental plate and the oceanic plate is forced downward. A trench forms along with a volcanic mountain range on the edge of the continent

11. What is subduction?
Subduction is the process of one crustal plate descending beneath another.

12. Where does it occur?
Subduction occurs at a subduction zone, where one plate descends beneath another.

13. How does it happen?
If one oceanic plate becomes denser than another plate (because it is cooler), then it will descend below the other plate as they converge.

14. What forms as a result of it?
A deep-sea trench and an island arc of volcanoes form at subduction zones.

15. When subduction occurs between a continental and oceanic plate…
When an oceanic and continental plate converge, the oceanic plate is subducted because it is denser.
A trench is formed along the coast of the continent, along with a series of volcanoes along the edge of the continental plate.

16. 10. When two continental plates converge, the colliding edges of the continents are crumpled and uplifted to form a mountain range.

17. 11. A transform boundary is a place where two plates slide horizontally past each other.

18. 12. What happens to crust at a transform boundary?
Crust is only deformed or fractured. It is neither subducted or uplifted. Transform boundaries are characterized by long faults and shallow earthquakes.