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Earth Science, 10e

Earth Science, 10e. Edward J. Tarbuck & Frederick K. Lutgens . Plate Tectonics Chapter 7. Earth Science, 10e Stan Hatfield and Ken Pinzke Southwestern Illinois College. Continental drift: an idea before its time . Alfred Wegener First proposed hypothesis, 1915

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Earth Science, 10e

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  1. Earth Science, 10e Edward J. Tarbuck & Frederick K. Lutgens

  2. Plate TectonicsChapter 7 Earth Science, 10e Stan Hatfield and Ken Pinzke Southwestern Illinois College

  3. Continental drift: an idea before its time • Alfred Wegener • First proposed hypothesis, 1915 • Published The Origin of Continents and Oceans • Continental drift hypothesis • Supercontinent called Pangaea began breaking apart about 200 million years ago • Continents "drifted" to present positions • Continents "broke" through the ocean crust

  4. Pangaea approximately 200 million years ago

  5. Continental drift: an idea before its time • Wegener's continental drift hypothesis • Evidence used by Wegener • Fit of South America and Africa • Fossils match across the seas • Rock types and structures match • Ancient climates • Main objection to Wegener's proposal was its inability to provide a mechanism

  6. Wegener’s matching of mountain ranges on different continents

  7. Paleoclimatic evidence for Continental Drift

  8. Plate tectonics: the new paradigm • More encompassing than continental drift • Associated with Earth's rigid outer shell • Called the lithosphere • Consists of several plates • Plates are moving slowly • Largest plate is the Pacific plate • Plates are mostly beneath the ocean

  9. Plate tectonics: the new paradigm • Asthenosphere • Exists beneath the lithosphere • Hotter and weaker than lithosphere • Allows for motion of lithosphere • Plate boundaries • All major interactions among plates occur along their boundaries

  10. Convergent: Continental to Continental Convergent plate boundaries (destructive margins) • Definition:When subducting plates contain continental material, two continents collide • How they move: two continental plates push each other up • Landform Results: new mountain ranges • Example: Himalayas • Density: Same density so they both push each other up

  11. A continental-continental convergent plate boundary

  12. The collision of India and Asia produced the Himalayas (before)

  13. The collision of India and Asia produced the Himalayas (after)

  14. Convergent Plate Boundaries: Oceanic to Continental Convergent plate boundaries (destructive margins) • Oceanic-continental convergence • Definition: an oceanic plate and continental plate colliding • How they move:oceanic plate slides underneath continental plateDenser oceanic slab sinks into the asthenosphere • Land formations: Pockets of magma develop and rise, continental volcanic arcs form, chain of volcanic islands • Examplesinclude the Andes, Cascades, and the Sierra Nevadan system

  15. An oceanic-continental convergent plate boundary

  16. Convergent Plate Boundaries: Oceanic to Oceanic • Oceanic-oceanic convergence • Definition: Two oceanic slabs converge and one descends beneath the other • How they move: Often forms volcanoes on the ocean floor • Land formation results:Volcanic island arcs forms as volcanoes emerge from the sea • Examples: include the Aleutian, Mariana, and Tonga islands, • Density: same

  17. An oceanic-oceanic convergent plate boundary

  18. Divergent Plate Boundaries Divergent plate boundaries (constructive margins) • Definition: Two plates move apart • How they move: Mantle material upwells to create new seafloor • Landform Results: Ocean ridges and seafloor spreading • Oceanic ridges develop along well-developed boundaries • Along ridges, seafloor spreading creates new seafloor • Examples: Iceland, and East Africa • Density: Same density

  19. Divergent boundaries are located mainly along oceanic ridges

  20. The East African rift – a divergent boundary on land

  21. Transform Boundaries • Definition: Plates slide past one another, horizontally (side to side) • No new crust is created • No crust is destroyed • How they move: At the time of formation, they roughly parallel the direction of plate movement • Aid the movement of oceanic crustal material • Examples: San Andres fault in California • Density: Plates have the same density

  22. Plate tectonics: the new paradigm • Evidence for the plate tectonics model • Paleomagnetism • Probably the most persuasive evidence • Ancient magnetism preserved in rocks • Paleomagnetic records show • Polar wandering (evidence that continents moved) • Earth's magnetic field reversals • Recorded in rocks as they form at oceanic ridges

  23. Apparent polar-wandering paths for Eurasia and North America

  24. Paleomagnetic reversals recorded by basalt flows at mid-ocean ridges

  25. Plate tectonics: the new paradigm • Evidence for the plate tectonics model • Earthquake patterns • Associated with plate boundaries • Deep-focus earthquakes along trenches provide a method for tracking the plate's descent • Ocean drilling • Deep Sea Drilling Project (ship: Glomar Challenger)

  26. Distribution of earthquake foci at plate boundaries

  27. Earthquake foci in the vicinity of the Japan trench

  28. Plate tectonics: the new paradigm • Evidence for the plate tectonics model • Hot spots • Rising plumes of mantle material • Volcanoes can form over them • e.g., Hawaiian Island chain • Chains of volcanoes mark plate movement

  29. Plate tectonics: the new paradigm • Evidence for the plate tectonics model • Ocean drilling • Age of deepest sediments • Youngest are near the ridges • Older are at a distance from the ridge • Ocean basins are geologically young

  30. The Hawaiian Islands have formed over a stationary hot spot

  31. Plate tectonics: the new paradigm • Measuring plate motion • By using hot spot “tracks” like those of the Hawaiian Island - Emperor Seamount chain • Using space-age technology to directly measure the relative motion of plates • Very Long Baseline Interferometry (VLBI) • Global Positioning System (GPS)

  32. Directions and rates of plate motions

  33. Plate tectonics: the new paradigm • Driving mechanism of plate tectonics • No one model explains all facets of plate tectonics • Earth's heat is the driving force • Several models have been proposed • Slab-pull and slab-push model • Descending oceanic crust pulls the plate • Elevated ridge system pushes the plate

  34. Plate tectonics: the new paradigm • Driving mechanism of plate tectonics • Several models have been proposed • Plate-mantle convection • Mantle plumes extend from mantle-core boundary and cause convection within the mantle • Models • Layering at 660 kilometers • Whole-mantle convection • Deep-layer model

  35. Layering at 660 kilometers

  36. Whole-mantle convection

  37. Deep-layer model

  38. End of Chapter 7

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