Plate Tectonics

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Plate Tectonics
2013-12-13 12:26:33
Geography notes
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  1. What is plate tectonics?
    Plate tectonics is the theory explaining the motions of the Earth's lithosphere. Plates move on the mantle, fuelled by convection currents
  2. How do convection currents fuel the movement of plates
    Crust is divided into plates. Magma is heated it moves and rises towards the upper mantle. It flows sidewards, cools and sinks, bringing with it a plate. Circular movement-convection currents fuel the movement of the plates
  3. What is sea-floor spreading?
    • Ocean floors widen as new rock is formed where plates have split apart.
    • Convection currents fuel the separation of plates.
    • As they separate,magma rises and fills the opening made.It cools to form a new crust.
    • New ocean floor is formed
    • Older crust moves away from the centre
  4. Continental drift?
    • Suggests that continents are transported by convection currents.
    • Single landmass-Pangea 
    • Single ocean-Panthalassa
    • 200 million years ago, broke apart
    • Laurasia and Gondwanaland

  5. Subduction?
    • Continents collide when they are carried across the globe by convection currents.
    • Ocean floor is pulled down into the mantle by subduction. Oceanic plate heavier than continental ones. 
  6. Proof of continental drift?
    • Edges of continents fit together- S.America and Africa
    • Same fossils found in S America and Africa
    • Same kind of rocks in S America and Africa
    • Ice sheets and glacial deposits found in Oz, Africa and India are of same age
  7. Plate boundaries
    Rocks are either created or destroyed
    What are the three types of plate boundary?
    • Divergent (construction)
    • Convergent ( destruction)
    • Conservative (passive)
  8. Divergent (construction)
    • New rock is formed
    • Mid-ocean ridges
    • Plates separate and move away from each other
  9. Convergent (destruction)
    • Rock is changed or destroyed as plates collide
    • Oceanic-oceanic
    • Oceanic-continent
    • Continent-continent
  10. Conservative (passive)
    • Rock is neither created nor destroyed
    • Plates slide past each other
  11. Divergent plate boundaries
    Seafloor spreading results in 2 plates moving apart. eg Mid-Atlantic Ridge
    Plates split apart creating a rift valley East African Rift Valley
    Provides route for magma, creates new sea floor, cools and forms volcanic mts over time. Further eruptions, volcanoes apear above water and are known as volcanic islands eg Iceland
    North American plate and Eurasian plate
  12. Convergent plate boundaries

    Destructive.Plates collide and rock is changed or destroyed. Subduction occurs when a plate dips beneath another plate. Oceanic-oceanic. Oceanic-continent. Continent-Continent.
    • Oceanic-Oceanic plate boundary:
    • Heavier older plate subducts, deep sea trench may form. Subducted plate melts.  Volcanic activity occurs. Magma rises and forms islands eg island arc. Japan is an eg- Pacific Plate and Eurasian Plate. Earthquakes
  13. Convergent plate boundaries
    Heavier oceanic plate subducts, ocean trench is formed, oceanic plate melts. Magma creates volcanoes at continental plate. Continental plate is buckled, compression causes the plate to rise forming a mountain belt. FOLD MTS. Andes - Nazca and S American plate
    Faulting may occur- stress in earths crust. Earthquakes
  14. Convergent :Oceanic oceanic boundaries
  15. Convergent: Continent-continent
    Neither plate sinks. Lighter  plate will subduct (was previously a continental one)while the continental plate remains intact. Collision continues. Buckle and form fold mountains
    Indian and Eurasian - Himalayas
  16. Conservative plate boundaries
    Rock is neither created nor destroyed
    Plates slide past each other
    Fault line - transform faults
    The San Andreas Fault Line in Cali
    Pacific and N American
    Earthquake activity as they often get stuck , pressure builds up and releases causing earthquakes
  17. The position of Ireland
    850 million years ago, One section of Ire was part of NAmerican plate, other England and Wales
    400 million years ago, plates collided forming Ireland, sea closed
    380 mill Ireland moved to south of Equator, north above sea level, south submerged
    350 mill sea levels rose, formed limestone as Ireland was closed
    200 mill Ireland moved North
    Atlantic ocean was formed 65 mill years ago as American and Eurasian plates moved apart