Classroom presentations to accompany Understanding Earth , 3rd edition

1. Classroom presentations to accompany Understanding Earth, 3rd edition prepared by Peter Copeland and William Dupré University of Houston Chapter 20 Plate Tectonics: The Unifying Theory

2. Plate Tectonics:The Unifying Theory Peter W. Sloss, NOAA-NESDIS-NGDC

3. Fundamental concept of geoscience Integrates from many branches First suggested based on geology and paleontology Fully embraced after evidence from geophysics Plate Tectonics

4. Mosaic of Earth’s Plates Fig. 20.3 Peter W. Sloss, NOAA-NESDIS-NGDC

5. Group of rocks all moving in the same direction Can have both oceanic and continental crust or just one kind. Plates

6. • divergent: mid-ocean ridges • convergent: collision zones volcanic arcs • strike-slip: San Andreas fault Alpine fault, N.Z. Types of plate boundaries

7. Usually start within continents— grow to become ocean basin Divergent plate boundaries

8. • Central rift valley (width is inversely proportional to the rate of spreading) • Shallow-focus earthquakes • Almost exclusively basalt Features of Mid Ocean Ridges

9. • East Africa, Rio Grande rift • Beginning of ocean formation (may not get that far) • Rifting often begins at a triple junction (two spreading centers get together to form ocean basin, one left behind). • Rock types: basalt and sandstone Continental Rifts

10. Rifting and Seafloor Spreading Fig. 20.4a

11. Rifting and Seafloor Spreading Along the Mid-Atlantic Ridge Fig. 20.4a Peter W. Sloss, NOAA-NESDIS-NGDC

12. Inception of Rifting Within a Continent Fig. 20.4b

13. Inception of Rifting Along theEast African Rift System Fig. 20.4b Peter W. Sloss, NOAA-NESDIS-NGDC

14. Nile Delta Gulf of ‘Aqaba Gulf of Suez Red Sea Fig. 20.5a Earth Satellite Corp.

15. The Gulf of California Formed by Rifting of Baja California from Mainland Mexico Fig. 20.5b Worldsat International/Photo Researchers

16. “Fit” of the Continents Fig. 20.1

17. Anomalous Distribution of Fossils Fig. 20.2

18. New crust created at MOR—old crust destroyed (recycled) at subduction zones (i.e., the Earth is not expanding) Relative important densities: continental crust ≈ 2.8 g/cm3 oceanic crust ≈ 3.2 g/cm3 asthenosphere ≈ 3.3 g/cm3 Convergent boundaries

19. Three types: ocean–ocean Philippines ocean–continent Andes continent–continent Himalaya Convergent boundaries

20. Island arcs: • Tectonic belts of high seismic ????? • High heat flow arc of active volcanoes (andesitic) • Bordered by a submarine trench Ocean–Ocean

21. Ocean–Ocean Subduction Zone Fig. 20.6b

22. Continental arcs: • Active volcanoes (andesite to rhyolite) • Often accompanied by compression of upper crust Ocean–Continent

23. Ocean-ContinentSubduction Zone Fig. 20.6a

24. In ocean–continent boundaries convergence, collision convergence is taken up by subduction (± thrusting). Continent–continent boundaries, convergence is accommodated by • Folding (shortening and thickening) • Strike-slip faulting • Underthrusting (intracontinental subduction) Continent–Continent

25. Continent-Continent Collision Fig. 20.6c

26. • Product of the collision between India and Asia. • Collision began about 45 M yr. ago, continues today. • Before collision, southern Asia looked something like the Andes do today. Himalayas and Tibetan Plateau

27. Models • Underthrusting • Distributed shortening •Strike-slip faulting Himalayas and Tibetan Plateau

28. Spreading Centers Offset by Transform Boundary Fig. 20.7

29. Plate tectonics repeats itself: rifting, sea- floor spreading, subduction, collision, rifting, … Plate tectonics (or something like it) seems to have been active since the beginning of Earth’s history. Wilson cycle

30. Examples of Plate Boundaries O-C convergent O-O divergent C-C divergent O-O divergent O-O convergent O-O divergent O-C convergent Fig. 20.8a,b

31. Ocean–Continent Convergent Boundaries Fig. 20.8c

32. Continent–Continent Convergent Boundary Fig. 20.d

33. Mostly obtained from magnetic anomalies on seafloor Fast spreading: 10 cm/year Slow spreading: 3 cm/year Rates of plate motion

34. Magnetic Anomalies Fig. 20.9

35. Formation of Magnetic Anomalies Fig. 20.10

36. Age of Seafloor Crust Fig. 20.11 R. Dietmar Muller, 1997

37. Relative Velocity and Direction of Plate Movement Fig. 20.12 Data from C. Demets, R.G> Gordon, D.F. Argus, and S. Sten, Model Nuvel-1, 1990

38. Opening of the Atlantic by Plate Motion Fig. 20.13 After Phillips & Forsyth, 1972

39. Each plate tectonic environment produces a distinctive group of rocks. By studying the rock record of an area, we can understand the tectonic history of the region. Rock assemblages and plate tectonics

40. Idealized Ophiolite Suite Deep-sea sediments Pillow basalt Gabbro Peridotite Fig. 20.14

41. Model for Forming Oceanic Crust at Mid-ocean Ridges Fig. 20.15

42. Precambrian Ophiolite Suite Pillow basalt Fig. 20.16 M. St. Onge/Geological Survey of Canada

43. Volcanic and Nonmarine sediments are deposited in rift valleys Fig. 20.17a

44. Cooling and subsidence of rifted margin allows sediments to be deposited Fig. 20.17b

45. Carbonate platform develops Fig. 20.17c

46. Continental margin continues to grow supplied from erosion of the continent Fig. 20.17d

47. Parts of an Ocean–Ocean Convergent Plate Boundary Fig. 20.18

48. Parts of an Ocean–ContinentConvergent Plate Boundary Fig. 20.19

49. Continued Subduction Fig. 20.20a

50. Continent– Continent Collision Fig. 20.20b