Theory of Plate Tectonics

2. Theory of Plate Tectonics Plate Tectonics Plate Boundaries Causes of Plate Tectonics

3. Plate Tectonics

4. What is Plate Tectonics • The Earth’s crust and upper mantle are broken into sections called plates • Plates move around on top of the mantle like rafts

5. What is a plate? • The Earth’s crust and upper mantle are broken into sections called plates A plate is a massive, irregularly shaped slab of solid rock, generally composed of both continental and oceanic lithosphere.

7. What is the Lithosphere? • The crust and part of the upper mantle = lithosphere • 100 km thick • Less dense than the material below it so it “floats”

8. History of Plate Tectonics…Theory #1 • Continental Drift Theory states that parts of the Earth's crust slowly drift atop a liquid core • Continental Drift was proposed by Alfred Wegener in 1915.

9. Evidence to Support Wegener’s theory • Fit of the continents • Fossil evidence (Mesosaurus (animal) and Glossopteris (plant) • Rock type and structures • Paleoclimatic evidence

10. Theory #2 Seafloor Spreading • is a process that occurs at midocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge. Seafloor spreading helps explain continental drift in the theory of plate tectonics.

12. Magnetic Reversals • The north pole and south pole reverse throughout geologic history meaning the compass needle points the opposite direction. • Magnetic minerals line up with the poles

13. Accepted Theory: Theory of Plate Tectonics? • Plate Tectonics is a theory that explains the formation of mountains and volcanoes as well as the cause of earthquakes by movement of cold rigid slabs of lithosphere by way of mantle convection.

14. What is the Asthenoshere? • The plastic layer below the lithosphere = asthenosphere • The plates of the lithosphere float on the asthenosphere

15. 2 Types of Plates • Ocean plates - plates below the oceans • Continental plates - plates below the continents

16. Mantle Convection • Hot magma in the Earth moves toward the surface, cools, then sinks again. • Creates convectioncurrents beneath the plates that cause the plates to move.

18. Questions... • What is the theory of plate tectonics? • What is the lithosphere? • What is the asthenosphere? • What is the connection between the two? • What are the two types of plates?

19. Plate Boundaries

20. Divergent Boundaries • Boundary between two plates that are moving apart or rifting   • RIFTING causesSEAFLOOR SPREADING

21. Features of Divergent Boundaries • Mid-ocean ridges • rift valleys • fissure volcanoes

25. Convergent Boundaries • Boundaries between two plates that are colliding   • There are 3 types…

26. Type 1 • Ocean plate colliding with a less dense continental plate • Subduction Zone: where the less dense plate slides under the more dense plate • VOLCANOES occur at subduction zones

28. Andes Mountains, South America

29. Type 2 • Ocean plate colliding with another ocean plate • The less dense plate slides under the more dense plate creating a subduction zone called a TRENCH

31. Aleutian Islands, Alaska

32. Type 3 • A continental plate colliding with another continental plate • Have Collision Zones: • a place where folded and thrust faulted mountains form.

35. Transform Fault Boundaries • Boundary between two plates that are sliding past each other • EARTHQUAKES along faults

37. San Andreas Fault, CA

38. Questions... • What are the three types of boundaries? • What direction do plates go for each? • Which boundary has a subduction zone…what occurs at a subduction zone?