Unit 4 Tectionic activity- Plates

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Convergent plate boundary

  • Two plates moving towards each other
    • pressure between plates can build and form earthquakes when plates slip 
  • Due to decending convection currenta in the mantel 
  • Denser oceanic crust gets subducted beneath the less dense continental crust
  • Plate melts around 100km in the asthenosphere 
  • Melted material is less dense so rises through weaknesses in faults and plate boundaries- creating volcanoes
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Divergent plate boundary

  • Pplates move away from each
  • This is due to two convection currents diverginf beneath the surface 
  • Pressure from rising magma can lead to doming of the surface and form ridges 
  • As the plates move apart faults are produced which magma can rise through
  • Rising magma cools and solidifies producing new crust
  • Most earthquakes are low magnitude and shallow due to the constant release of pressure

Example: Creation of Caribbean islands

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Conservative// Transform plate boundary

  • No magma is released 
  • No new crust is formed
  • Can produce both shallow earthquakes and high magnitude earthquakes 
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Slab and pull theory

  • Ridges at diverging plate boundaries have a higher elevation, gravity aids in pulls the plates apart creating a divergent plate boundary.
  • New lithosphere moves away from the divergent boundary and cools becoming more dense causing it to sink (subduction zone)
  • As it melts it rises due to it being less dense creating mountains on continental crust.
  • Sinking oceanic plate explains the slab pull theory, as it sinks it continues to pull the rest of the plate down into the asthenosphere. 
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