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Plate Tectonics

Plate Tectonics. It’s a pretty zany idea What brought it about? Geologic observations made by Wegener and first suggested in 1915 Why is it important?. Types of Evidence for Continental Drift. Geographic Evidence. Fossil Evidence. Types of Evidence for Continental Drift.

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Plate Tectonics

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  1. Plate Tectonics • It’s a pretty zany idea • What brought it about? • Geologic observations made by Wegener and first suggested in 1915 • Why is it important?

  2. Types of Evidence for Continental Drift Geographic Evidence Fossil Evidence

  3. Types of Evidence for Continental Drift Evidence from Glacial Deposits Evidence from Coal Deposits

  4. Magnetic Evidence The Earth’s magnetic field can be: Normal: Compass points North Reversed: Compass points South The direction of the magnetic field is recorded by rocks as they form Patterns of reversal are nearly mirror image

  5. AnimationFrom Smith and PunSea Floor Spreading andSea Floor Magnetism skip

  6. Whole Ocean Magnetics

  7. How Plates Behave (Bean pot analogy) Smith and PunPlate Motions Through Time

  8. The Plates The plates are essentially RIGID pieces of the Earth’s crust They move due to convection of the mantle They can contain both OCEANIC and CONTINENTAL crust Passive Margin Active Margin (Plate Boundary)

  9. Thick Pine Thin Pine Thin Oak H T D Isostacy D=kT Depth below waterline H=(1-k)T Height above waterline k= rB/rW Fraction of block below water line

  10. Where does continental crust come from?

  11. Continental Crust

  12. Three Basic Types of Plate Boundaries • Divergent - plates moving away from one another (Tension) • Convergent - plates moving toward one another (Compression) • Transform - plates moving past one another (Shear) ! Most plates include con/divergent and transform components !

  13. Smith and PunCorrelating Processes and Plate Boundaries

  14. Smith and PunSea Floor Spreading and Sea Floor MagnetizationMotion at Divergent Boundaries skip

  15. Formation of Oceanic Crust Sediments Pillow lavas Sheeted dikes Gabbro Peridotite (Mantle rock)

  16. Life at Midocean Ridges

  17. midocean RIDGES Cooler More Dense Lower Hotter Less Dense Higher Cooler More Dense Lower

  18. Smith and PunForming a Divergent BoundaryANIMATION20 - Plate Divergence

  19. Smith and PunMotion at Convergent Boundaries

  20. Convergent Boundaries • Oceanic crust is denser and “rides lower” than continental crust • Expect different things to happen • Ocean-Continent Collisions • Continent Continent Collisions Trenches Mountains

  21. Animations • Subduction • Animation 20- Ocean-Continent • Animation 20- Continent-Continent

  22. Transform Boundaries • San Andreas Fault in California • Animation 20-Transform Boundaries • Transform Faults in Midocean Ridges • Motion at a transform plate boundary

  23. The Complex Nature of Plate Boundaries

  24. Hotspots • Smith and Pun: Hotspots and Plumes

  25. What drives the plates?

  26. What drives the plates, really?

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