Plate Tectonics

1. Plate Tectonics Chapter 3

2. Plate Tectonics In 1855, Antonio Snider published a sketch showing how the two continents could fit together, jigsaw-puzzle fashion In 1912, Alfred Wegener published the concept of continental drift Continental drift is just one aspect of a broader theory known as plate tectonics, which has evolved over the last several decades Tectonics is the study of large-scale movement and deformation of the earth’s outer layers Plate tectonics relates such deformation to the existence and movement of rigid “plates” over a weak or partly molten layer in the earth’s upper mantle

3. Figure 3.6

4. Continental Drift and Plate Tectonics • Jigsaw-puzzle fit of continents observed a few centuries ago • Mechanism to describe how continental masses moved was not easily visualized for decades • Later half of 20th century the concept of continental drift was incorporated into a broader concept of Plate Tectonics • Mechanisms and processes of continent scale movement detailed • Evidence based on physics, chemistry, mathematics, and geology used to explain how rigid plates move relative to each other

5. Figure 3.1

6. Figures 3.2 a and b

7. Rock Response to Plate Tectonics • Stress –force applied on a rock • Compressive stress – squeeze or compress an object • Tensile stress – pull or stretch an object • Shearing stress – different parts of an object move in different directions or at different rates • Strain – results from stress; is the change in shape or size of an object because of the stress it experienced

8. Strain • Temporary or permanent • Elastic deformation – temporary strain, object recovers original size and shape once the stress is removed • Elastic limit – strain that becomes permanent in an object once limit of recoverable strain has been exceeded • Plastic deformation occurs in materials once elastic limit has been exceeded • Brittle deformation occurs at the limit of strength of the material, a rupture or a break occurs

9. Figure 3.3

10. Lithosphere and Asthenosphere • Earth’s crust and upper most mantle are solid and compose the lithosphere • Stresses cause brittle and elastic deformation • Beneath the lithosphere is a plastic layer called the asthenosphere • Lithospheric plates can move over this plastic layer; plate tectonics plausible • Boundaries of the plates are active with earthquake and some with volcanic activity

11. Figure 3.4

12. Evidence for Plate Tectonics • Earthquakes and volcanoes • Sea Floor topography • Trenches • Ridges • Paleomagnetism • Magnetic patterns imprinted on oceanic crust • Curie temperature • Magnetic reversals • Magnetic polar wandering curves • Sea Floor Spreading • Age of the sea floor • Other evidence • Fit of continents, GPS data, and more …

13. Figure 3.5

14. Figure 3.7

15. Figures 3.8 a and b

16. Figure 3.9

17. Figure 3.10

18. Other Evidence for Plate Tectonics • Distribution of rocks representing ancient deserts, sea shores, tropical areas, glaciated areas, swamps, and equatorial regions • Location of fossils that were originally restricted in their distribution but now separated by oceans and on separate continents • Fit of continents reveal super continent of Pangaea • Recognition of plate boundaries

19. Figure 3.13

20. Figure 3.14

21. Figure 3.6

22. Figures 3.15 a, b, and c

23. Plate Boundaries • Divergent Plate Boundary • Lithospheric plates move apart; form oceanic ridges • Upwelling of asthenosphere injects magma forming oceanic ridges and new oceanic crust • Forces plates apart • Sea floor spreading occurs • Transform Boundaries – short segments of a ridge • Transform faults offset ridge • San Andreas Fault – transform fault under continental crust

24. Figures 3.16 a and b

25. Plate Boundaries • Convergent Plate Boundaries • Lithospheric plates move toward each other • Higher density oceanic crust overridden by low density continental crust • Subduction zone forms and produces a trench • Subduction of older oceanic crust balances the spreading seafloor equation • Subduction zones are active geologic places • Volcanism • Earthquakes • Island arc formation

26. Figures 3.18 a, b, and c

27. Figure 3.19

28. Tectonics • Convection cells operate in mantle • Upwelling of heat and magma occurs at divergent plate boundaries • New oceanic crust formed • Oceanic crust pushed away from spreading centers • Hot spots located independent of plate boundaries • High heat flow radiate from them • Volcanic activity associated with them • Hawaiian Islands • Yellowstone

29. Figure 3.20

30. Figure 3.21

31. Figure 3.22

32. Figure 3.23