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Plate Tectonics

Plate Tectonics. Plate Tectonics. Tectonics : bending and breaking of the lithosphere Plate tectonic theory explains volcanism, seismic activity, continental movement, folding and faulting. Lithosphere : 15 plates. See pp 438-439. Lithospheric plates rest on soft, plastic asthenosphere.

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Plate Tectonics

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  1. Plate Tectonics

  2. Plate Tectonics • Tectonics : bending and breaking of the lithosphere • Plate tectonic theory • explains volcanism, seismic activity, continental movement, folding and faulting

  3. Lithosphere : 15 plates See pp 438-439

  4. Lithospheric plates rest on soft, plastic asthenosphere. • Allows plates to move away from, towards and against one another. • Plate boundaries • Oceanic and continental crust at boundaries

  5. Types of Plate Boundaries: 1. Divergent (Spreading) 2.Convergent 3.Transform

  6. 1. Divergent (Spreading) Boundaries: • plates pull apart a) at oceanic/oceanic crust boundaries (most common) * mid-oceanic ridges (“sea-floor spreading”) on ocean floor b) at continental/continental crust boundaries * rift valleys on land

  7. a) oceanic/oceanic crust boundary

  8. P 426

  9. P 429

  10. a. oceanic/oceanic crust boundary sea-floor spreading: as plates beneath oceans spread, magma wells up from mantle and solidifies as new ocean floor resulting ridge of igneous rock: mid-oceanic ridge (axial rift) (See undersea topography pp. 430 – 431)

  11. b) continental/continental crust boundary • cause continental rupture • rift valleys form • narrow sea may form • new oceans may form • Examples: East African Rift Valley, Iceland rift valley, Red Sea

  12. East African Rift Valley

  13. Iceland

  14. 2. Convergent Boundaries a) at oceanic/continental crust boundary b) at continental/continental crust boundary c) at oceanic/oceanic crust boundary

  15. a) oceanic/continental • Oceanic crust is thinner and denser; it plunges into the soft asthenosphere beneath continent in a process called subduction. • Ocean floor trench forms at subduction zone • On land, a chain of volcanic mountains parallels the subduction zone • Earthquakes • examples: Andes, Cascade Range

  16. Andes

  17. Pacific “Ring of Fire”

  18. b) continental/continental • Plates collide; crustal rocks fold, break, become fused in a suture • mountain chains • Example: Himalayas

  19. c) oceanic/oceanic • Subduction of one plate beneath another • submarine trench and island arc (chain of volcanic islands) • Example: Aleutians

  20. Aleutian Trench

  21. 3. Transform Boundaries • 2 plates move past one another in opposite directions laterally; plates “stick” as they move; tremendous strain builds up and is released in earthquakes • most transform boundaries occur along mid-oceanic ridges, parallel to direction of plate movement • Example: San Andreas Fault

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