Earth's Tectonic Plates and Plate Boundaries

1. http://www.geophysics.rice.edu/plateboundary/ Where are the Earth’s tectonic plates and their boundaries? What happens at plate boundaries? How do Earth scientists classify plate boundaries?

2. Part 1. • Identify the patterns of your area of expertise – volcanology, seismology, geography, geochronology - AT PLATE BOUNDARIES • Describe what you observe – do not interpret what you see, just describe the patterns • Use descriptive terms: Wide or narrow, straight or curved, symmetric or not symmetric, deep or shallow, ridge or valley, active or inactive • Identify 3-5 boundary types; color each on your transparency; define in words

3. Part 2. • 10 min • 10 min • Bring together areas of expertise – volcanology, seismology, geography, geochronology • Correlate your data sets; what collective patterns emerge? • Identify 3-5 boundary types; color each on a master transparency; define in words

4. Part 3. • Describe the different types of boundaries • What patterns were related in the different data sets?

5. What skills did you use in undertaking this activity? • Historical use … • How might you use it in your classroom? • What might you modify?

6. Plate BoundariesWhere Stuff Happens

7. Plate Tectonics Theory • The upper mechanical layer of Earth (lithosphere) is divided into rigid plates that move away, toward, and along each other • Most (!) geologic action occurs at plate boundaries in DISTINCT patterns

8. Compositional Crust - 2 Mantle Core Physical / Mechanical Lithosphere Asthenosphere Mesosphere

9. Crust(Compositional) • Two types of crust: • Continental • 30% of crust • Granites and Diorites - rich in silicates and feldspars (lighter materials) • 40 Km thick • Oldest is 3.8 billion years (90% solar system age; missing ~700 m.y.) • 4.4 billion year old zircons in Western Australia • Oceanic crust • Basalt - Mg, Fe (heavier materials - relatively) • 5-10 Km thick • 200 Ma oldest; 100 Ma average • Ophiolites

10. Lithosphere / Asthenosphere(Mechanical) • Lithosphere • PLATES in Plate Tectonics • Upper 200 km • Crust and upper mantle • Rigid • Asthenosphere • 200 km to ~700 Km • Upper mantle • Hi temperatures / high pressure: little strength; ductile / plastic - NOT A LIQUID! • Plates moving on this • Magma generation • Mesosphere • Also hot; strong due to pressure

11. 3 Basic Boundary Interactions 5 to 6 Basic Boundary Types

16. 1. Divergent Boundaries • Volcanic activity in fissures, some volcanos • Shallow earthquakes, on plate boundary • Young crust, symmetrical around boundary • Ridge • Rocks? Mid- Atlantic Ridge North American Plate Eurasian Plate

18. Nazca Plate South American Plate Antarctic Plate

20. Andes Mountains

22. 2. Convergent Boundaries (a) Ocean-continent convergence • Volcanos tight, parallel boundary, landward • Shallow to deep earthquakes • Age varies on one side of the boundary; not symmetrical • Trench, mountain chain • Rocks? Andes Mountains Peru-Chile Trench South American Plate Nazca Plate

23. Foreshadowing … Many on Earth Relatively small … but mighty …

28. 2. Convergent Boundaries (b) Ocean-ocean convergence • Volcanos tightly spaced, parallel boundary, arc • Shallow to deep earthquakes • Age varies on one side of the boundary; not symmetrical • Trench, volcanic island chain • Rocks? Mariana Islands Marianas Trench Philippine Plate Pacific Plate

30. Eurasian Plate Indian Plate

31. Himalaya Mountains

32. Tibetan Plateau Mt. Everest Himalayan Mtns.

33. 2. Convergent Boundaries (c) Continent-continent convergence • Volcanos rare, dispersed • Shallow (to medium) dispersed earthquakes • No age data • High mountain chain • Rocks? Himalayan Mountains Tibetan Plateau Indian-Australian Plate Eurasian Plate

37. 3. Transform-Fault Boundaries • Volcanos dispersed, most on one side • Earthquakes complex, shallow (to medium) on both sides • Age data not symmetrical, one side of boundary • Complex topography, wide mountains and basins • Rocks? Pacific Plate North American Plate

38. Plate Tectonics • The upper mechanical layer of Earth (lithosphere) is divided into rigid plates that move away, toward, and along each other • Most (!) geologic action occurs at plate boundaries in DISTINCT patterns

39. What’s Driving Plate Tectonics on Earth?

40. Mantle • 85% volume of Earth • Density - 3.3 - 5.5 g/cm3 • Probably material such as Peridotite (lots of heavy olivine - Fe, Mg) • Solid; high pressure  slow, creeping, viscous movement - convection • Samples from kimberlites, xenoliths in volcanic eruptions, basalt composition; lab experiments

41. Core • 15% of Earth’s volume / ~half of diameter of Earth • Outer core • Molten • Density of pure iron or nickel/iron; ~2x density of mantle • Convection … Earth’s magnetic field • Inner core • Solid (very hot, but higher pressure than outer core) • Density of nickel/iron (~13 g/cm3) • Conducts heat - cooling • ~ Size of Moon (~70% of Moon)

42. Earth’s Magnetic Field • Magnetic dipole … a bar magnet tilted ~11 degrees • Generated by eddies in the conductive liquid of the outer core – currents create magnetic fields • Changes over time – north magnetic pole wanders, north and south reverse • Rather important to life … really important to geology

44. What’s Driving Plate Tectonics on Earth?

46. How Did Earth (and other planets) Get Layers?