Plate tectonics


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Plate tectonics

  1. 1. Chapter 6Chapter 6 Earth’s Crust &Earth’s Crust & Plate TectonicsPlate Tectonics
  2. 2. The Earth’s Crust and Plate Tectonics The Earth’s Crust This is where we live! The Earth’s crust is made of: Continental Crust - thick (10-70km) - buoyant (less dense than oceanic crust) - mostly old Oceanic Crust - thin (~7 km) - dense (sinks under continental crust) - young
  3. 3. If you look at a map of the world, you may notice that some of the continents could fit together like pieces of a puzzle…
  4. 4. World Plates
  5. 5. Plate Tectonics • The Earth’s crust is divided into many major plates which are moved in various directions. • This plate motion causes them to collide, pull apart, or scrape against each other. • Each type of interaction causes a characteristic set of Earth structures or “tectonic” features. • The word, tectonic, refers to the deformation of the crust as a consequence of plate interaction.
  6. 6. What are tectonic plates made of? Plates are made of rigid lithosphere. The lithosphere is made up of the crust and the upper part of the mantle.
  7. 7. Pangaea Alfred Wegener proposed the Continental Drift Hypothesis in 1912, that stated Earth’s continents were once joined in a single landmass and gradually moved or drifted apart.
  8. 8. Theory of Plate Tectonics Fossils, Climate, & Geology • •
  9. 9. Evidence from the Sea Floor
  10. 10. Three types of plate boundary Divergent Convergent Transform
  11. 11. Divergent Boundaries Also called spreading ridges As plates move apart new material is erupted to fill the gap
  12. 12. Iceland has a divergent plate boundary running through its middle Divergent Boundaries
  13. 13. Where plates slide past each other Transform Boundaries
  14. 14. Convergent Boundaries • 2 plates that are pushing together • There are three types of convergent plate boundaries – Continent-continent collision – Continent-oceanic crust collision – Ocean-ocean collision
  15. 15. Continent-Continent Collision Forms mountains, e.g. European Alps, Himalayas
  16. 16. Himalayas
  17. 17. Oceanic-Continental Subduction • Oceanic lithosphere subducts underneath the continental lithosphere • Oceanic lithosphere heats and dehydrates as it subsides • The melt rises forming volcanism • Deep ocean trenches & Coastal mountains
  18. 18. Oceanic-Oceanic Plate Subduction • When two oceanic plates collide, one runs over the other which causes it to sink into the mantle forming a subduction zone. • Island arcs form • The subducting plate is bent downward to form a very deep depression in the ocean floor called a deep ocean trench. • The worlds deepest parts of the ocean are found along trenches. – E.g. The Mariana Trench is 11 km deep!
  19. 19. Convection Currents “Plates” of lithosphere are moved around by the underlying hot mantle convection cells
  20. 20. Magnetic Reversal• After molten lava emerges from a volcano, it solidifies to a rock. In most cases it is a black rock known as basalt, which is faintly magnetic (iron) • Its magnetization is permanently fixed like tiny compass needles pointing north & south. • Instruments can measure the magnetization of basalt. • Surprisingly, this procedure suggested that times existed when the magnetization had the opposite direction from today's. All sorts of explanation were proposed, but in the end the only one which passed all tests was that in the distant past, indeed, the magnetic polarity of the Earth was sometimes reversed.