Plate Tectonics: A Scientific Revolution Unfolds Chapter 7

1. Plate Tectonics: A Scientific Revolution UnfoldsChapter 7

2. What evidence was used to support the continental drift hypothesis? What was one of the main objections to the continental drift hypothesis? What is the theory of plate tectonics? In what major way does the plate tectonics theory depart from the continental drift hypothesis? Focus on Concepts

3. What are the three types of plate boundaries? Where does new lithosphere form? How do mountain systems such as the Himalayas form? What type of plate motion occurs along a transform fault boundary? Focus on Concepts

4. What evidence is used to support the plate tectonics theory? What are the major driving forces for plate tectonics? What models have been proposed to explain the driving mechanism for plate motion? Focus on Concepts

5. 7.1From Continental drift to Plate Tectonics

6. The collision of India and Asia produced the Himalayas

7. K7 in Pakistan’s Karakoram (Himalayas)

8. 7.2Continental Drift: An idea before its time

9. Alfred Wegener • Pangaea • Continental Drift Hypothesis

10. Eduard Suess Gondwana

11. Began in early Mesozoic (~200 mya) • Evidence • Continental jigsaw puzzle • Fossil distribution • Rock types & geologic features • Ancient climates Continental Drift Hypothesis

12. Continental Jigsaw Puzzle

13. Continental Jigsaw Puzzle

14. Evidence

16. Fossil Distribution

17. Fossil Distribution

18. Beardmore Glacier Location of the fossil site at the Oliver Bluffs on the Beardmore Glacier

19. There are rock formations (such as mountain ranges) on different continents that match up beautifully when the continents are put back together. Rock Types & Geologic Features

20. Rock Types & Geologic Features

21. Paleoclimatic data Extreme global cooling? Wegener’s explanation Ancient Climates

22. Glacial Striations

23. Post-Drift Ice Sheets

24. Pre-Drift Ice Sheet

25. 7.3The Great Debate

26. What mechanism allows movement? Not all evidence supported the hypothesis. Some thought the idea was intriguing or an answer to a previously unexplained phenomena. Objections to the Continental Drift Hypothesis

27. Objections to the Continental Drift Hypothesis

28. 7.4Plate Tectonics

29. 1968; more encompassing than CDH Lithosphere broken into plates, slide over asthenosphere Plate tectonics theory

30. Earth’s Major tectonic Plates

31. LARGE – 94% of Earth’s S.A. • North American • South American • Pacific • African • Eurasian • Australian-Indian • Antarctic Earth’s Major tectonic Plates

32. INTERMEDIATE – mostly oceanic • Caribbean • Nazca • Phillipine • Arabian • Cocos • Scotia • Juan de Fuca Earth’s Major tectonic Plates

33. Divergent (constructive) Convergent (destructive) Transform (conservative) Plate Boundaries

34. Plate Boundaries

35. Plate Boundaries

36. 7.5Divergent Boundaries

37. Plate boundaries • Types of plate boundaries • Transform fault boundaries • Plates slide past one another • No new crust is created or destroyed • Transform faults • Most join two segments of a mid-ocean ridge • Aid the movement of oceanic crustal material Plate tectonics: the new paradigm

38. Evidence from ocean drilling • Some of the most convincing evidence confirming seafloor spreading has come from drilling directly into ocean-floor sediment • Age of deepest sediments • Thickness of ocean-floor sediments verifies seafloor spreading Testing the plate tectonics model

39. Hot spots and mantle plumes • Caused by rising plumes of mantle material • Volcanoes can form over them (Hawaiian Island chain) • Mantle plumes • Long-lived structures • Some originate at great depth, perhaps at the mantle-core boundary Testing the plate tectonics model

40. The Hawaiian Islands have formed over a hot spot

41. Evidence for the plate tectonics model • Paleomagnetism • Probably the most persuasive evidence • Ancient magnetism preserved in rocks • Paleomagnetic records show • Polar wandering (evidence that continents moved) • Earth’s magnetic field reversals • Recorded in rocks as they form at oceanic ridges Testing the plate tectonics model

42. Polar wandering paths for Eurasia and North America

43. Paleomagneticreversals Recorded by basalt flows

44. Measuring plate motion • By using hot spot “tracks” like those of the Hawaiian Island – Emperor Seamount chain • Using space-age technology to directly measure the relative motion of plates • Very Long Baseline Interferometry (VLBI) • Global Positioning System (GPS) Measuring plate motion

45. Directions and rates of plate motions

46. Driving mechanism of plate tectonics • No one model explains all facets of plate tectonics • Earth’s heat is the driving force • Several models have been proposed • Slab-pull and ridge-push model • Descending oceanic crust pulls the plate • Elevated ridge system pushes the plate What drives plate motion

47. Several mechanisms contribute to plate motion

48. Several models have been proposed • Plate-mantle convection • Mantle plumes extend from mantle-core boundary and cause convection within the mantle • Models • Layering at 660 kilometers • Whole-mantle convection What drives plate motion

49. Layering at 660 km

50. Whole-mantle convection