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Plate tectonics

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  • 1. Kaustubh J. Sane HJD Institute of Technical Education & Research
  • 2.  Theory of plate tectonics  Types of plates  Causes of plate motion  Importance of plate tectonics
  • 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.  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. 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.  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. Click here for a hyperlink to an animation of convection Be sure to click the play button!
  • 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. • 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. Can you explain this diagram!?
  • 11. The place where two plates move apart or diverge is called a divergent boundary.
  • 12. This is a model of sea floor spreading at a divergent boundary called a mid ocean ridge.
  • 13. Did you know that the Earth’s longest mountain range is underwater and is called the mid-ocean ridge? : www.ocean.udel.edu 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.  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. • 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. • 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. Also the way the Appalachian Mountains formed
  • 18. from: http://www.geo.lsa.umich.edu/~crlb/COURSES/270 Continental crust to continental crust collision India-Asia (Himalayas) Before collision After collision
  • 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. A transform boundary is a place where two plates slip past each other, moving in opposite directions.
  • 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)

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