Chapter 8, Section 2 Objectives : 1. Summarize the theory of plate tectonics.

1. Chapter 8, Section 2 Objectives: 1. Summarize the theory of plate tectonics. 2. Compare the characteristic geologic activities that occur along the three types of plate boundaries. 3. Explain the possible role of convection currents in plate movement.

2. Theory of Plate Tectonics: describes continental movement and proposes a possible explanation of why and how continents move. • From Greek word tektonikos, meaning construction • Tectonics: the study of the formation of features in the Earth’s crust • Earth’s surface consists of a number of rigid, but moving pieces called plates

3. 2 Types of Earth’s crust • Oceanic Crust:material on the ocean floor. • Continental Crust: makes up the continental landmasses.

4. Lithosphere: made up of the crust and the rigid upper mantle. • Forms the thin outer shell of the Earth • Rigid but broken into plates that move with respect to one another • Asthenosphere: a layer of plastic rock • Solid rock that slowly flows (like putty) • Layer within the mantle that the lithospheric plates rest on

5. According to the Theory of Plate Tectonics: • Lithosphere is broken into separate plates • Plates ride on denser asthenosphere • Most plates composed of both continental and oceanic crust • To date about 30 lithospheric plates have been identified

6. Plate Boundaries: • Place where one plate is moving relative to another plate • 3 types • Each associated with a characteristic type of geological activity • Differs according to the way the plates move in relation to each other

7. Kinds of Plate Boundaries…

8. Transform Fault Boundries:plates are grinding past one another • Move in a series of sudden spurts of activity • Earthquakes • Ex: San Andreas fault

9. Example: San Andreas Fault

11. Divergent boundaries: where two lithospheric plates are moving apart (spreading centers) • As plates move apart, molten rock rises and fills space between plates • cools and hardens creating new oceanic crust • Most divergent boundaries are found on the ocean floor

12. Mid-Atlantic Ridge Spreading Center New ocean floor is being created

13. Rift Valley: narrow valley formed as the plates separate.

14. Convergent Boundary: the place where one plate directly collides with another plate. • 3 types of convergent boundries

15. Oceanic crust collides with continental crust: since oceanic crust is denser it is forced under the continental crust (subducted) • Subduction Zone: region along a plate boundary where one plate moves under another

16. Deep Ocean Trench: usually forms along a subduction zone. • Oceanic crust moves down • Melts and becomes part of the mantle material • Some magma rises through the continental crust • Produces volcanic mountains

17. Continental crust collides with continental crust:neither plate is subducted • Colliding edges are crumpled and uplifted • Produces large mountain ranges • Himalayas

21. Oceanic crust collides with oceanic crust • Island Arc is formed when: • One plate is subducted, forming a trench • Subducted plate melts • Molten rock rises to surface along trench • Forms volcanic islands

22. Convection:the transfer of heat through the movement of heated fluid material. • Convection Current:the cycle of warm less dense material rising and cooler denser material sinking

23. Let’s go to this website and review! CLICK HERE>>> http://www.pbs.org/wgbh/aso/tryit/tectonics/# Click on Plate Tectonics Activity (with a yellow arrow) when you get there!

24. Here it is – all in one big picture… Can you pick out the types of Plate Boundaries?

25. Were you right?