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Plate margins

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AQA A2 tectonics powerpoint on the types of plate margin

AQA A2 tectonics powerpoint on the types of plate margin

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  • 1. Types of plate margin
    • There are 2 types of crust:
    • Continental crust which is older, thicker and less dense than…
    • Oceanic crust which is younger, thinner and denser
    • There are 3 directions of movement between plates:
    • Converging: where 2 plates are moving towards each other
    • Diverging: where 2 plates are moving away from each other
    • Passive: where 2 plates are moving side by side
    • There are 6 different combinations of types of crust and directions of movement:
    • Destructive – where oceanic and continental crust converge
    • Destructive – where oceanic and oceanic crust converge
    • Destructive (Collision) – where continental and continental crust converge
    • Constructive – where 2 plates diverge under the ocean
    • Constructive – where continental crust is diverging
    • Conservative – where 2 plates move parallel to each other
    • Each of the 6 combinations above create different tectonic hazards and produce different landforms.
  • 2.
    • Description
    • denser oceanic crust is subducted
    • friction and heat cause partial melting of the crust
    • this magma is less dense than the mantle and rises / forces its way through fissures in the lithosphere
    • Landforms
    • deep ocean trenches such as the Peru-Chile trench
    • Fold mountains from rock scraped off the descending plate and folding of the continental crust
    • Hazards
    • Violent volcanoes (composite cone) – due to viscous acidic lavas which block the vents in the volcanoes
    • Powerful earthquakes
    1. Destructive boundary - Continental / oceanic convergence
  • 3.
    • Description
    • 2 plates with oceanic crust collide
    • the densest crust will be subducted
    • Landforms
    • Deep ocean trenches e.g. the Marianas trench
    • Island arcs as volcanoes rise out of the sea e.g. Caribbean, Philippines, Japan, Indonesia
    • Hazards
    • Violent earthquakes and volcanoes
    2. Destructive boundary - Oceanic / oceanic convergence
  • 4.
    • Description
    • Subduction of oceanic crust brings 2 continental masses together
    • Both have a similar density so can’t be subducted
    • Sedimentary rocks scraped off the old sea floor are compressed together to form young fold mountains
    • Landforms
    • Young fold mountains such as the Himalayas (created in the last 40 million years) These are still growing despite erosion
    • Hazards
    • Earthquakes as powerful as at destructive margins
    3. Collision boundary - Continental / continental convergence
  • 5.
    • Description
    • plates are moving away from each other causing the crust to weaken and hot magma to force upwards creating a ridge
    • in the centre of the ridge, the crust can subside into to magma below creating a valley
    • the fissures (splits) in the crust provide a route for the more fluid lavas to escape if these continue submarine volcanoes form
    • Landforms
    • Mid-ocean ridges
    • Volcanic islands e.g. Iceland, Surtsey
    • Hazards
    • Volcanoes that erupt with basic (runny) lava – more frequent & less violent eruptions
    • Shallow focus earthquakes
    4. Constructive boundary – sub-marine divergence
  • 6.
    • Description
    • occurs where spreading occurs beneath the continents
    • the up-welling magma leads to fracturing and rifting
    • central sections collapse to form rift valleys
    • volcanoes form where magma forces its way through fissures
    • Landforms
    • Rift valleys such as East African Rift valley – these can widen and eventually get flooded by the sea e.g the Red Sea
    • Volcanoes such as Mt Kilimanjaro & Mt Kenya
    • Hazards
    • Volcanoes
    • Shallow focus earthquakes
    4. Rifting – continental divergence
  • 7.
    • Description
    • plates are moving parallel to each other, no collision or subduction occurs
    • movement is erratic as plates stick together, pressure builds up and is released in a sudden movement
    • Landforms
    • Fault lines such as the San Andreas and Hayward faults
    • Hazards
    • No volcanoes
    • Earthquakes as powerful as at destructive margins
    4. Conservative boundary – passive movement