Plate Tectonics: Theory & Boundaries

1. Plate Tectonics Chapter 3, part 2

2. Last Time • Expanding Earth • Contracting Earth • Continental drift hypothesis • Sea floor spreading

3. What drives plate movement? • Late 1900’s: Plate tectonics • Crust: cold, rigid • Mantle: hotter, behaves plastically

4. What drives plate movement? • Ultimately: heat transported from core and mantle to surface • Heat transported by convection • Core is ~5,000°C and surface is ~0°C • Mantle convection creates a conveyor belt in mantle • Crust dragged along on top

5. Plate movement with convection • Where mantle rises: rifting • Where mantle dives: subduction zones

6. Theory of plate tectonics • Crust made of rigid plates • Ocean plates: thin and dense • Continental: thicker, less dense • Plates are moving on top of mantle

7. Theory of plate tectonics • Crust made of rigid plates • Ocean plates: thin and dense • Continental: thicker, less dense • Plates are moving on top of mantle • Plates separate and collide

8. Types of plate boundaries • Divergent: plates move apart • Convergent: plates collide • Transform: plates slide by each other

9. Divergent Plate boundaries • A.k.a. spreading ridges

10. Evidence of divergent plate boundary in oceans • Pillow lavas of basalt along mid-Atlantic ridge

11. Beginning of continental rifting

12. Mid-stage of rifting

13. Ultimate goal of rifting

14. Ultimate goal of rifting

15. Modern divergent plate boundaries

16. Convergent plate margins • 2 plates meet head on

17. Ocean-ocean convergence • One plate dives down (subducts) below other plate • Volcanoes form above subduction zone • Basalts • Volcanic island arc

18. Ocean-ocean convergence • One plate dives down (subducts) below other plate • Volcanoes form above subduction zone • Basalts • Volcanic island arc • Aleutians, Japan etc.

19. Convergent plate boundaries • Ocean-continent convergence • Ocean plate subducts below continent

20. Ocean-continent convergent margin • Melting forms volcanoes above subduction zone • Forms rhyolites, andesites

21. Ocean-continent convergent margin • Melting forms volcanoes above subduction zone • Forms rhyolites, andesites • Cascades, Andes

22. Continent-continent convergence • Neither plate wants to subduct • Lots of metamorphic rocks, lots of folds, high mountains

23. Continent-continent convergence • Neither plate wants to subduct • Lots of metamorphic rocks, lots of folds, high mountains • Himalaya, Alps

24. How to recognize ancient subduction zone? • Volcanic rocks, andesites • Deformed ocean sedimentary rocks

25. Transform plate margin • 2 plates slide past each other

26. Transform boundary and earthquakes • The division between two blocks is called a fault • Strain builds up in rocks due to friction • Rocks rupture releasing strain in the form of earthquake energy

27. Transform boundary and earthquakes • The division between two blocks is called a fault • Strain builds up in rocks due to friction • Rocks rupture releasing strain in the form of earthquake energy

28. Transform boundary on ocean floor

29. Transform boundary on ocean floor

30. Transform plate boundary:San Andreas fault

31. San AndreasFault

32. How to recognize ancient transform boundaries • Broken, ruptured rock • Adjacent rock units that shouldn’t be next to each other

33. How are plate movements determined? • Satellite/GPS • Age of ocean floor, distance from spreading ridge • Distance= rate x time

34. 3 main types of plate boundaries

35. Plate tectonics • Controls where mountains are built • Controls where earthquakes are • Controls biologic world (climate, geographic barriers)

36. Plate tectonics homework 3 PM Friday • Scavenger hunt by 3 PM Wednesday • Potential test question today • Name • Question from tectonics or rocks lectures you want to see on the first test.

37. Where are earthquakes? • Transform boundaries • Subduction zones • Areas of active mountain building

38. Where are areas of active mountain building? • Collision zones between plates • Volcanoes, earthquakes, deformed rocks