1. Global Tectonics II- Origin of an Idea

4. Divergent Plate Boundaries –Plates moving apart Convergent Plate Boundaries –Plates moving toward one another Transform Plate Boundaries –Plates move laterally past each other

5. Cascadia Suduction Zone-local Plate Tectonics

6. Continental Drift Predecessor to modern plate tectonics Shape and “fit” of the continents was the initial evidence –Snider-Pelligrini (1858) –Taylor (1908) –Wegner (1915)

7. Continental drift maps by Wegner (1915)

8. Continental Drift Alfred Wegener (1880-1930) –Proposed all of the continents were once part of a large supercontinent - Pangaea –Based on: Similarities in shorelines Distinctive rock and fossil groups found in Africa & South America

10. Evidence for Continental Drift Paleontological –Similarity of fossils on opposite sides of the Atlantic and Indian Oceans

11. Paleontological evidence

12. Evidence for Continental Drift Rock type & structures –Distinct rock type and geologic structures on both sides of the Atlantic Ocean

13. Rock type & structure evidence

14. Evidence for Continental Drift Glaciation –Late Paleozoic glaciation Covered large portions of the southern continents Distinct glacial deposit

15. Reconstruction from glacial deposits

16. Evidence for Continental Drift Paleoclimate –Evidence of extreme changes in climate as compared to the present

17. Paleoclimate evidence

18. Development of Plate Tectonic Theory Original evidence for continental drift was from continental rocks Technological advances in the 1950’s and 1960’s allowed investigation of the sea floor Geophysics & paleomagnetism provided new data

19. Geology of the Ocean Floor Topography of the ocean basins –Basins are divided by a large ridge system –Ridge system continuous around the entire globe –Central rift valley within the ridge

21. Paleomagnetism –Fe rich minerals magnetized by Earth’s magnetic field present at time of formation. Polar wandering –Earth’s north magnetic pole has (apparently) moved through time

22. Reconstruction from paleomagnetic data

23. Magnetic reversals –Earth’s magnetic field polarity has reversed through time

24. Magnetic polarity stripes in ocean crust parallel ridges –Symmetrical on either side of the ridge –Polarity chrons give age of seafloor Increases away from ridge Rates of plate motion may be calculated

25. Patterns of magnetic reversals

26. Age of the sea floor

27. Global Distribution of Earthquakes

28. Major tectonic boundaries

29. Divergent Plate Boundaries –Plates moving apart Convergent Plate Boundaries –Plates moving toward one another Transform Plate Boundaries –Plates move laterally past each other

30. Divergent plate margins

31. Convergent plate boundaries

32. Rates of Plate Motion Two ways to look at plate motion –Relative velocity – the movement of one plate relative to another –Absolute velocity – compares plate movement to a fixed position Rates vary from 1 to 20 cm/yr

33. Rates of plate motion around the world

34. Tectonic Mechanisms Convection of heat from the core and mantle drives tectonics –Convection cells bring new material to the surface –Old crust is pushed away from ridges –Subduction carries cool crust back into the mantle

35. Models of plate tectonic motion