1. EARTH SCIENCE Prentice Hall EARTH SCIENCE Tarbuck Lutgens 

2. Earth’s Major Roles 9.2 Plate Tectonics  Plate tectonics – The theory that explains how large pieces of the lithosphere called plates move and change shape. A plate is one of numerous rigid sections of the lithosphere that move as a unit over the material of the asthenosphere.

3. Types of Plate Boundaries 9.2 Plate Tectonics  Divergent boundaries (also called spreading centers) are the place where two plates move apart.  Convergent boundaries form where two plates move together.  Transform fault boundaries are where two plates grind past each other.

4. Three Types of Plate Boundaries

5. Spreading Center

6. Divergent Boundaries 9.3 Actions at Plate Boundaries  Continental Rifts When spreading centers develop within a continent, the landmass may split into two or more smaller segments, forming a rift. Rift – where two plates are splitting apart.

7. Continental - Continental Place where continental plates are splitting. Landform created “rift valley”

8. East African Rift Valley Continental - Continental

9. East African Rift Valley

10. Oceanic – Oceanic Location where oceanic crusts move away from each other. Landform created is mid-ocean ridge.

11. Mid-Atlantic Ridge oceanic to oceanic

12. ICELAND IS SPLITTING due to Mid-Atlantic Ridge

13. On the back of your paper, write the following definition Boundaries 9.3 Actions at Plate Boundaries  A subduction zone occurs when one oceanic plate is forced down into the mantle beneath a second plate.

14. Convergent Boundaries 9.3 Actions at Plate Boundaries Denser oceanic slab sinks into the asthenosphere.  Oceanic-Continental Pockets of magma develop and rise. Continental volcanic arcs form in part by volcanic activity caused by the subduction of oceanic lithosphere beneath a continent. Examples include the Andes, Cascades, and the Sierra Nevadas.

15. Oceanic-Continental Convergent Boundary

16. Continental – oceanic Andes

17. Continental – Oceanic Cascade Mountains (Mt. St. Helens)

18. Convergent Boundaries 9.3 Actions at Plate Boundaries Two oceanic slabs converge and the more dense one descends beneath the other.  Oceanic-Oceanic This kind of boundary often forms volcanoes on the ocean floor. Volcanic island arcs form as volcanoes emerge from the sea.

19. Oceanic-Oceanic Convergent Boundary

21. Convergent Boundaries 9.3 Actions at Plate Boundaries When subducting plates contain continental material, two continents collide.  Continental-Continental This kind of boundary can produce new mountain ranges, such as the Himalayas.

22. Continental-Continental Convergent Boundary

23. Collision of India and Asia

24. Continental – Continental Himalayas (Mount Everest)

25. Transform Fault Boundaries 9.3 Actions at Plate Boundaries  At a transform fault boundary, plates grind past each other without destroying the lithosphere.

26. Transform Fault Boundary

27. San Andreas Fault

28. ON THE BACK: Evidence for Plate Tectonics 9.4 Testing Plate Tectonics Earthquake Patterns Scientists found a close link between deep-focus earthquakes and ocean trenches. The absence of deep-focus earthquakes along the oceanic ridge system was shown to be consistent with the new theory.

29. Evidence for Plate Tectonics 9.4 Testing Plate Tectonics  Hot Spots A hot spot is a concentration of heat in the mantle capable of producing magma, which rises to Earth’s surface; The Pacific plate moves over a hot spot, producing the Hawaiian Islands. Hot spot evidence supports that the plates move over the Earth’s surface.

30. Hot Spot

31. Causes of Plate Motion 9.5 Mechanisms of Plate Motion  Scientists generally agree that convection occurring in the mantle is the basic driving force for plate movement. Convective flow is the motion of matter resulting from changes in temperature.

32. Causes of Plate Motion 9.5 Mechanisms of Plate Motion  Slab-Pull and Ridge-Push Ridge-push causes oceanic lithosphere to slide down the sides of the oceanic ridge under the pull of gravity. It may contribute to plate motion. Slab-pull is a mechanism that contributes to plate motion in which cool, dense oceanic crust sinks into the mantle and “pulls” the trailing lithosphere along. It is thought to be the primary downward arm of convective flow in the mantle.

33. Causes of Plate Motion 9.5 Mechanisms of Plate Motion  Mantle Convection The unequal distribution of heat within Earth causes the thermal convection in the mantle that ultimately drives plate motion. Mantle plumes are masses of hotter-than- normal mantle material that ascend toward the surface, where they may lead to igneous activity.

34. Mantle Convection Models