Plate tectonic theory

• The 5 layers of the Earth:

  1 - Crust

  2 - Upper mantle

  3 - Mantle

  4 - Outer core

  5 - Inner core
• oceanic plate:

  • can subduct
  • not thick (7-10km thick)
  • made up of basaltic rock
  • high density
• continental plate:

  • can't subduct
  • low density
  • made up of granitic rock
  • very thick (25km-75km thick)
• destructive plate boundaries landforms:

  • young fold mountains
  • volcanoes
  • deep sea trench
  • Island Arches
• young fold mountains:

  • 10-25 million years old
  • plates move together, sediment pushed up into folds
  • example : Himalayas - collision boundary , Andes - subduction boundary
• deep sea trenches:

  • form at destructive subduction plate
  • 50-100km wide
  • example : Marianas trench , Pacific plate subducted under Philippine plate
• Island Arches:

  • destructive subduction boundary
  • descending plate melts , material rises to surface as photons of magma
  • Example : Marianas Island Arc
• Constructive plate boundary landforms:

  • Rift valleys
  • ocean ridges
  • volcanoes
• rift valleys:

  • two contintental plates pulling apart
  • crust thins , heats and bulges , forming cracks
  • area of crust drops down between parallel faults = rift valleys
  • example : East Africa
• ocean ridges:

  • two oceanic plates pull apart
  • as pressure reduces , semi-molten magma of mantle melts , rises up to gap between plates = forms ridge
  • Ex: Mid-Atlantic ridge
• distribution of tectonic hazards is uneven
• earthquakes and volcanoes are examples of plate tectonic hazards
• hotspots:

  • hot mass of rising heat under a weakness in a plate
  • magma rise to the surface through this weakness
  • Hawaiian islands form as a result of a mid-pacific hotspot
• infra-plate volcanoes are volcanoes that take place away from margins of tectonic plates
• theory of plate tectonics :

  • slab pull
  • gravitational sliding
  • sea floor spreading
  • Wegener's continental drift
  • Holmes' hypothesis
• slab pull:

  ocean floor dragged down by gravity beneath continental crust , it subducts
• divergent plate boundary is another name for constructive plate boundaries
• convergent plate boundaries is another name for destructive plate boundaries
• destructive subduction plate boundaries

  • continental and oceanic plate meet
• destructive collision plate boundaries:

  • two continental plates meet
• volcanoes found at constructive plate margins along ocean ridge

  • found on destructive collusion boundaries or conservative boundaries (NO subduction)