1. PLATE TECTONICS Hypothesis: Earth’s Lithosphere moves on top of Aesthenosphere due to Mantle Convection Evidence of Lithospheric (Plate) motions (Tectonics) Driving Mechanism of Plate Tectonics

2. EVIDENCE OF LARGE-SCALE HORIZONTAL MOTIONS OF THE CRUST AND UPPER MANTLE: Contributions of Land-based Geologists ( observed from 1600’s to present ) Fit of coastlines, especially South America and Africa Identical species of land-dwelling fossils on different continents Alignments of rare minerals and fossils with other continents Linear patterns of mountain ranges, volcanoes, and earthquakes

3. Reconstructions of Continents at Various Times in the Past by Alfred Wegener

4. Fossil Relationships of Rare or Limited Species

5. EVIDENCE OF A DYNAMIC EARTH

6. Evidence from Ocean-based Data ( 1950-present ) “Young” Age of Seafloor (<200 m.y.) relative to Continents (up to 4.5 b.y.) Discovery of 40,000 km long Mid Ocean Ridges (MOR) Age of seafloor increases symmetrically away from MOR crest

7. Age of Seafloor

8. Topography of the Mid Ocean Ridge: N. Atlantic New seafloor comes to the Surface at MOR At MIMOR’s

9. MAGNETIC ANOMALIES Earth’s magnetic field periodically reverses its polarity: on average about every 400,000 years, but range is 10,000 yrs to millions of yrs Fe-rich minerals crystallizing in molten rock align with Earth’s magnetic field and point to N magnetic pole Magnetic signature is “locked in” as rock solidifies Subsequent pole reversals do not change the mineral alignment in solid rock

10. Seafloor-Spreading at Mid-Ocean Ridges a Divergent Plate Boundary Age of seafloor in m.y. 5 4 3 2 1 0 0 1 2 3 4 5

11. Earthquake Evidence Quakes form linear zones Usually associated with volcanoes Deepest quakes reach 700km –implies brittle failure occurring In some areas, there is an inclined plane of seismicity, marking the contact between a subducting plate and the overriding plate

12. Earthquakes define Plate Boundaries

13. Andean-type Convergent Plate Boundary Subduction Zone: where 2 plates collide, one sinks, or subducts. Evidence for subduction comes from inclined plane of seismicity, Called a Wadati-Benioff Zone

14. Earthquake Epicenters for central South America Color change from yellow to dark blue represents increasing depth

17. Driving Mechanism of the Plates: Convection in the Mantle

18. How Convection Works

19. Large convection currents in the aesthenosphere transfer heat to the surface, where plumes of less dense magma break apart the plates at the spreading centers, creating divergent plate boundaries. As the plates move away from the spreading centers, they cool, and the higher density basalt rocks that make up ocean crust get consumed at subduction zones. The crust is recycled back into the aesthenosphere.

20. IC OC MANTLE MOR SUBDUCTION ZONE CONVECTION CELLS in the EARTH

21. THREE TYPES OF PLATE BOUNDARIES

22. Transform Plate Boundary: San Andreas Fault

23. Japan-Sea Type Convergent Plate Boundary

24. Andean-type Convergent Plate Boundary

25. Himalayan-type Convergent Plate Boundary

26. Indian Plate Collides with Asian Plate SN

27. OBSERVATION: Because ocean plates are denser than continental plates, when these two types of plates converge, the ocean plates are subducted beneath the continental plates. The collision of plates is accompanied by earthquakes and volcanoes.

28. Hot Spot Beneath Pacific Plate Creates the Hawaiian Islands Not all volcanic activity occurs at plate boundaries

29. Plate Boundary Type SUMMARY TABLE: Process---Feature---Plate Boundary Type Divergent PlateSeafloor Spreading---Mid Ocean Ridges and Continental Rifts---Divergent PlateBoundaries Convergent Plate BoundariesSubduction---Subduction Zones--- Convergent Plate Boundaries Transform Plate BoundariesShear---Strike-slip Faults---Transform Plate Boundaries