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A Level Physical Geography > Plate Tectonics > Flashcards

Flashcards in Plate Tectonics Deck (11)
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State the two types of crust, what are the made out of?

Oceanic crust - basaltic rock formed from silica and magnesium (sima)
Continental crust- granite rocks formed from silica and aluminium (sial)


What is the lithosphere?

Curst and upper mantle


Give four pieces of evidence for plate tectonics

1) similar fossils found on either side of oceans - mesosaurus ( and S.America)
2) similar landforms and rock patterns e.g. Appalachian mountains fit with mountains in western Scotland
3) jigsaw fit of Africa and south America
4) paleomagnetism - every 72 million years magnetic field flips, rocks have striated patterns of metallic minerals facing north and south along the atlantic ocean shows sea floor spreading


Give three ways in which the tectonic plates move

Convection currents - radioactive decay in the mantle produces convection currents that exert a force on the tectonic plates
Slab pull - destructive margin mass of sinking plate pulls the rest of it down
Ridge push at a constructive boundary new crust formed which cools and condenses gravity cools and pulls denser rock down


What is sea floor spreading?

Magma rises where plates diverge
Fills the gap and forms new crust
New crust is dragged apart
Sea floor gets wider creating ridges


What is another name for a constructive plate margin? What landforms occur in oceanic areas? What about continental areas?

Divergent margin
Two plates move towards each other
In oceanic areas ocean ridges will form with transform faults parallel to the margin - magma leaks out solidifies
In continental areas - rift valleys will form e.g. Great African rift valley, stretching from Mozambique to the red sea,
Often volcanoes will be found within them e.g. Mt kenya


What occurs at a oceanic vs continental destructive margin?

Denser oceanic plate subducts underneath the lighter continental plate
Forms an ocean trench
Continental land mass rises = mountains
Oceanic crust melts in the benioff zone due to friction and mantle heat
Pressure can build up and plates can suddenly move past each other = earthquake


What happens at an oceanic vs oceanic destructive margin?

Denser of two plates subducts
Earthquakes and volcanoes
Underwater volcanoes and island arcs


What happens at a continental vs continental plate

Two plates collide
Fold mountains occur
No subduction therefore no volcanoes


Why can earthquakes be bad at conservative margins?

Because the tend to have a very shallow focus


What is a magma plume? How does it form Hawaii and other similar landforms

Vertical column of extremely hot magma
Volcanoes form above plumes
Plumes are stationary but crust moves over them
Hence volcanoes form in rows
Those that get further from the plume become dormant