Warm-up:

1. Warm-up: • What are the two types of crust? • What’s the difference?

2. Plate Boundaries Plate boundaries occur where two crustal plates meet. There are three types of plate boundaries: • Divergent plate boundaries (constructive margins) occur where two plates move apart. • Convergent plate boundaries (destructive margins) occur where two plates collide. • Transform fault boundaries occur where plates slide past one another

3. Divergent Plate Boundaries Divergent plate boundaries (constructive margins) occur where two plates move apart. The mantle material up-wells to create new seafloor. Oceanic ridges develop along well-developed boundaries. Along ridges, seafloor spreading creates new seafloor.

4. Divergent boundaries are located along oceanic ridges. Figure 7.11

5. Distribution of the Oceanic Ridge System

6. Figure 7.10 (left)

7. The East African rift is a divergent boundary on land • Continental rifts form at spreading centers within a continent. Figure 7.13

8. Figure 7.13 (top right)

9. Continental rifting

10. Convergent Plate Boundaries Convergent plate boundaries (destructive margins) occur when plates collide, an ocean trench forms, and lithosphere is subducted into the mantle.

11. Convergent Plate Boundaries Oceanic - continental convergence occurs when a denser oceanic slab sinks into the asthenosphere. Pockets of magma develop and rise and a continental volcanic arc forms.

12. An Oceanic - Continental Convergent Plate Boundary Figure 7.15 A

13. Convergent Plate Boundaries Examples of oceanic – continental convergence include: the Andes Mountains of South America.

14. Convergent Plate Boundaries Examples of oceanic – continental convergence include: the Cascade Mountains of Washington and Oregon.

15. Convergent Plate Boundaries Examples of oceanic – continental convergence include: the Sierra Nevada Mountains of California.

16. Convergent Plate Boundaries Oceanic - oceanic convergence occurs when two oceanic slabs converge and one descends beneath the other. This often forms volcanoes on the ocean floor. A volcanic island arc forms as volcanoes emerge from the sea.

17. Convergent Plate Boundaries Examples of oceanic – oceanic convergence include: • the Aleutian Islands.

18. Convergent Plate Boundaries Examples of oceanic – oceanic convergence include: • the Mariana Islands.

19. Convergent Plate Boundaries Examples of oceanic – oceanic convergence include: • the Tonga Islands.

20. Convergent Plate Boundaries Continental - Continental Convergence When two continental plates converge, they collide. One continental plate subducts under the other. This can produce buckling of the upper plate and new mountain ranges form, such as the Himalayas

21. The Collision of India and Asia Produced the Himalayas

22. Transform Plate Boundaries Transform plates slide past one another. No new crust is created or destroyed. Transform faults are created. Most transform faults join two segments of a mid-ocean ridge. These faults and ridges aid the movement of oceanic crustal material.

23. California’s Fault Issue