1. Summary Divergent Boundaries – Mid- Ocean Ridges (MOR) Separates 2 tectonic plates Tectonic plates move apart – extensional forces New oceanic crust generated - ~ 5 cm/yr Earthquakes – shallow, low energy

2. MOR - Ophiolite Complex

3. Pillow Basalts in the Ocean

4. Pillow Basalts on the Continents

5. Sheeted Dikes

6. Gabbro

7. Convergent Boundaries Plates come together Ocean-Ocean Convergence Ocean-Continent Convergence Continent-Continent Convergence

8. Subduction Zones Ocean-ocean collision or ocean-continent collision Density differences in crust forces one plate to descend under the other plate More dense plate descends Descends at an angle between 15 o to 75 o with an average of  45 o Subduction of plate creates a deep-ocean trench

9. Deep Ocean Trenches Range in depth between 8 – 12 km 100’s km wide and 1000’s km long

10. Additional Terminology Accretionary Wedge – sediment that has accumulated as sediment has been “scraped” of off the subducting plate Forearc – region lying between the trench and the magmatic arc Backarc – region lying behind the magmatic arc

11. Ocean-Continent Collision Ocean crust is more dense (3.0 g/cm3) than continental crust (2.8 g/cm3) Ocean Crust subducts Within the mantle, plate begins to melt Melt has basaltic to intermediate composition Hot melt (magma) is less dense (more buoyant) than surrounding material and rises Ascending magma incorporates continental crust – composition becomes intermediate to felsic Creates linear zone of igneous activity (volcanoes or intrusions-plutons) called a Continental (Magmatic) Arc

12. Ocean-Continent Example – Cascade Subduction Zone

13. Ocean-Continent Example – Peru-Chile Subduction Zone

14. Ocean-Ocean Convergent Zone

15. Ocean-Ocean Collision Similar to Ocean-Continent Convergent Zone except no influence of Continental Crust Magmas are basaltic to intermediate in composition Ascending magma creates linear Volcanic Island Arc

16. Continent-Continent Convergent Zone (Collision) Is preceded by Ocean-Continent Convergence Density between plates is similar – neither will subduct Crust buckles, fractures, shortens, thickens due to compressional stress Creates large mountains of folded and faulted rocks.

17. Migration of India & Collision Into Eurasia

18. Formation of the Himalayan Mts.

19. Mt. Everest

20. Ocean Evolution

21. Earthquakes & Convergent Boundaries Earthquake depth ranges from shallow ( 300 km) High magnitude (high energy) – 95% of all earthquake energy is released from convergent zone earthquakes Wide zone, but with a pattern

22. Transform Boundary

23. Transform Faults Plates slide past one another Crust is neither produced nor destroyed Facilitate plate movement Connect segments of MOR Transition zone between MOR and Subduction zone Transition/Connection between two Subduction zones

24. Transform Faults to Facilitate MOR Movement

25. Transform Faults Found in both ocean crust and continental crust Can create compressional structures (folds) and extensional structures (basins)

26. San Andreas Fault

27. Earthquakes are shallow, less than 10 km in depth Small magnitude (low energy) Common Narrow pattern along MOR Earthquakes and Transform Boundaries

28. Boundary Locations

29. Similarities-Differences of Boundaries Transform DivergentConvergent 1. Shallow Earthquakes 2. Intermediate Earthquakes 3. Deep Earthquakes 5. Crust generated 6. Crust destroyed 7. Compression Forces 8. Extension Forces 9. Volcanoes 10. Mountains

30. Hot Spots

31. Produced by rising plume of mantle material (mantle plume) They are stationary – plates move over the hotspots

32. Basalts produced by hot spots are chemically different from basalts produced at MOR

33. Hot Spot Example – Island Chains

34. Island Chain Formation

35. Hot Spot Under Hawaii Notice linear layout of islands Could determine plate movement rate for data Island continually being formed

36. Hot Spot Example – Continental Yellowstone

37. Continental Hot Spot Mechanics

38. Volcanism and Continental Hot Spots

39. Plate Tectonics – Driving Mechanisms Driven by the release of internal energy in the form of heat Proposed mechanisms –Convection cells –Differences in density and forces generated by plates

40. Forces Active on Plates Slab-pull – sinking of dense ocean crust pulls the plate Ridge-push – gravity pulls plate of of the MOR Basal drag – resistance of plate from underlying asthenosphere Mantel resistance – subducting plate is resisted in the asthenosphere and mesosphere Friction – resistance along transform faults and between converging plates