PLATE TECTONICS- earth structure

• Lithosphere plates:

  • Earth's crust and upper mantle
  • Factures into plates that move via the deeper rheid mantle
  • 20 plates in total
  • 13 major plates
• Divergent boundary:

  • plates moving apart
  • oceanic crust formation
• convergent boundary:

  • plates moving together
  • collision zones
• transform boundary:

  • lateral plate movement
  • shearing forces
• the crust:

  • OCEANIC - thin, basalt
  • CONTINENTAL - thick, granite
• the mantle:

  • olivine rich
  • high density
  • rheid
• geothermal gradient:

  • increasing temperature with depth
  • 30 degreesC per kilometre
• upper mantle:

  • cool
  • brittle deformation results in earthquakes
• Lower mantle:

  • hot and soft
  • not molten
  • flows instead of breaks
• the core:

  • iron and nickel composition
  • 2900 - 6371 kilometres
• outer core:

  • liquid state
• inner core:

  • solid due to high pressures
• Convection currents:

  • currents caused by expansion of matter as temperature rises
  • the material rises as it becomes hotter and buoyant
  • at shallower depths the material cools, becoming denser
  • material sinks down and expands again as it experiences hotter temperatures again
• the asthenosphere:


  • layer beneath the lithosphere
  • made of slow flowing mantle
  • lithospheric plates move with it
  • 700 km depth
  • high viscosity
• continental crust


  • 20-60 km (av. 35 km)
  • 3 billion years old
  • silica rich
  • 2.7 g/cm3 density
• oceanic crust:


  • 6 km thickness
  • 70 - 100 million years old (oldest is 1.8 billion)
  • 3.0 g.cm3 density
• subduction mechanism:


  • convergent movement
  • dense oceanic plate forced beneath lighter continental plate
• Mid-ocean ridge:


  • divergent boundaries
  • higher regions on the seafloor
  • hydrothermal vents and volcanoes
• plate tectonics:


  • the theory that the top layer of the Earth is fractured into rigid plates
• Wegener:


  • theory of continental drift