1. Plate Tectonics

3. Types of Plate Boundaries Divergent Convergent Transform

4. Divergent Convergent Transform Fault Plates move apart, resulting in upwelling of material from the Mantle to create new sea floor. Plates move together, causing one of the slabs of lithosphere to be consumed into the Mantle as it decends beneath the overriding plate. Plates slide past each other, without creating or destroying lithosphere.

5. Fig.4.28 W. W. Norton. Modified from Cox and Hardt, 1986. Each plate is bounded by a combination of these types of boundaries.

7. Transform Divergent Convergent

8. We can’t observe these different types of plate boundaries evolving over time, because the time scale is too great, but: We can see these different types of plate boundaries in different stages of development by going to different locations on the Earth.

10. Divergent Plate Boundaries Most divergent plate boundaries are situated at the crests of mid-ocean ridges.

11. Sea Floor Spreading As plates move away from the ridge axis, the gaps are filled with molten rock that oozes up from the hot asthenosphere.

12. Atlantic Ocean Floor The material cools slowly to produce new sea floor, and injections of magma add new crust between the diverging plates.

13. Atlantic Ocean Floor This mechanism has produced the floor of the Atlantic Ocean during the past 165 million years.

14. Some spreading centers are much younger than the mid-Atlantic ridge. The Red Sea is the site of a recently formed divergent plate boundary.

15. Here the Arabian peninsula separated from Africa (about 20 million years ago) and began to move toward the northeast. The Red Sea might resemble the way the Atlantic ocean looked in its infancy.

17. Development of a Spreading Center When a spreading center develops within a continent, the landmass splits into smaller segments as Wegener proposed for the breakup of Pangaea.

18. Development of a Spreading Center Fragmentation of a continent is initiated by an upward movement of hot rock from below. This causes upwarping of the crust above the hot rising material.

19. Crustal stretching associated with this doming generates tensional cracks. Large downfaulted valleys are generated by this process. The East African Rift Valleys are an example of this type of feature. Rift Valley

20. East African Rift Valleys If this spreading process continues, the rift valley will become wider and deeper, and eventually be transformed into an ocean.

21. Fig. 11.34 U.S. Geological Survey

23. Fig. 11.33 W. W. Norton

24. Development of a Spreading Center

26. Convergent Plate Boundaries

29. Oceanic - Continental Oceanic - Oceanic Continental - Continental

30. The Earth’s Crust

31. Oceanic - Continental Convergent Plate Boundary

34. Types of Plate Boundaries Divergent Convergent Transform