Plate tectonics


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Plate tectonics

  1. 1. Kaustubh J. Sane HJD Institute of Technical Education & Research
  2. 2.  Theory of plate tectonics  Types of plates  Causes of plate motion  Importance of plate tectonics
  3. 3.  Wegener’s continental drift hypothesis stated that the continents had once been joined to form a single supercontinent.  Wegener proposed that the supercontinent, Pangaea, began to break apart 200 million years ago and form the present landmasses.
  4. 4.  According to the plate tectonics theory, the uppermost mantle, along with the overlying crust, behaves as a strong, rigid layer. This layer is known as the lithosphere.  There are two types of lithosphere  Oceanic lithosphere  Continental lithosphere
  5. 5. Continental Crust  Thick (10-50 km)  Old (>200 m.y. and up to 3.5 b.y.)  Iron Poor (<1%) / Silica Rich (>70%)  Less Dense (~ 2.5 g/cm3)  High Rising (mostly above see level)  Formed at Convergent Plate Boundaries Oceanic Crust – Thin (<10 km) – Young (<200 my) – Iron Rich (~5%) / Silica Poor (~50%) – Dense (s.g. ~3 x H2O) – Low lying (5-11 km deep) – Formed at Divergent Plate Boundaries
  6. 6.  Types of plate boundaries  Depending on the motion of the plate they are grouped into 3 major types viz, 1. Divergent plate (constructive plate boundary) 2. Convergent plate ( destructive plate boundary) 3. Transform plate
  7. 7. Click here for a hyperlink to an animation of convection Be sure to click the play button!
  8. 8. o Plates are moving away from each other o Midocean ridges are created and new ocean floor plates are created. o The plate gives birth to new earth surface hence it is also called as constructive plate boundary. o As new material comes on surface mostly in sea and increases the sea floor hence it is called as sea floor spreading.
  9. 9. • Oceanic ridges are continuous elevated zones on the floor of all major ocean basins. The rifts at the crest of ridges represent divergent plate boundaries. • Rift valleys are deep faulted structures found along the axes of divergent plate boundaries. They can develop on the seafloor or on land.
  10. 10. Can you explain this diagram!?
  11. 11. The place where two plates move apart or diverge is called a divergent boundary.
  12. 12. This is a model of sea floor spreading at a divergent boundary called a mid ocean ridge.
  13. 13. Did you know that the Earth’s longest mountain range is underwater and is called the mid-ocean ridge? : The Mid-Ocean Ridge system, shown above snaking its way between the continents, is more than 56,000 kilometers (35,000 mi) long. It circles the earth like the stitching on a baseball!
  14. 14.  A subduction zone occurs when one oceanic plate is forced down into the mantle beneath a second plate  Oceanic-Continental • Denser oceanic slab sinks into the asthenosphere. • Pockets of magma develop and rise. • Continental volcanic arcs form in part by volcanic activity caused by the subduction of oceanic lithosphere beneath a continent. • Examples include the Andes, Cascades, and the Sierra Nevadas.
  15. 15. • Two oceanic slabs converge and one descends beneath the other.  Oceanic-Oceanic • This kind of boundary often forms volcanoes on the ocean floor. • Volcanic island arcs form as volcanoes emerge from the sea. • Examples include the Aleutian, Mariana, and Tonga islands.
  16. 16. • When subducting plates contain continental material, two continents collide.  Continental-Continental • This kind of boundary can produce new mountain ranges, such as the Himalayas.
  17. 17. Also the way the Appalachian Mountains formed
  18. 18. from: Continental crust to continental crust collision India-Asia (Himalayas) Before collision After collision
  19. 19.  At a transform fault boundary, plates grind past each other without destroying the lithosphere.  Transform faults • Most join two segments of a mid-ocean ridge. • At the time of formation, they roughly parallel the direction of plate movement. • They aid the movement of oceanic crustal material.
  20. 20. A transform boundary is a place where two plates slip past each other, moving in opposite directions.
  21. 21.  The plates may move in opposite directions or in the same directions but at different rates and frequent earthquakes are created (example: San Andreas Fault)