1. Chapter 7
Plate Tectonics

2. Chap 7, Sec 3 (The Theory of Plate Tectonics)
Objectives:
Describe the three types of plate boundaries.
What is plate tectonics?
What are subduction zones?

3. Tech Terms:
plates – separate sections of the lithosphere.
plate tectonics – geological theory that states that pieces of Earth’s lithosphere are in constant, slow motion, driven by convection currents in the mantle.

5. faults – breaks in Earth’s crust where plate boundaries form.

6. 4. convergent boundary – the place where two plates come together, or collide. (the density of the plates dictates which one comes out on top).
Oceanic crust (basalt) is more dense
Continental crust (granite) is less dense

7. Subduction zones occur at convergent boundaries and create trenches

8. divergent boundary – the place where two plates move apart, or dive away (most occur at the mid-ocean ridge).
rift valley – develops on land, where two plates diverge.

10. 7. transform boundary –
a place where two
plates slide past
each other in
opposite directions.

11. Transform boundaries do not create landforms
Transform boundaries do not create landforms. They do, however, destroy land!

12. 8. deep ocean trench – this forms from subduction (the oceanic crust bends downward forming a deep underwater canyon on the ocean floor).

13. deep ocean trench close to home

14. 9. subduction – when the ocean floor sinks beneath a deep ocean trench and gets swallowed by the mantle.

15. Sea-floor spreading and subduction can change the size and shape of the oceans.
The Pacific Ocean, aka The Ring of Fire, has lots of subduction zones, thus it is getting smaller.
The Atlantic Ocean is expanding.