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THE STRUCTURE OF THE EARTH AND PLATE MARGINS (What is mid-ocean ridge? (Is…
THE STRUCTURE OF THE EARTH AND PLATE MARGINS
What is mid-ocean ridge?
Is a long, submarine ridge system situated in the middle of an ocean basin
It marks the sit of an upwelling of magma associated with sea floor spreading.
What is a subduction zone
Is an area on a tectonic pate boundary where two plates converge and one plate (oceanic) is trhust beneath the other (continental). There is a deep ocean trench where the oceanic (subducted) plate bends downwards.
What is a plate boundary
Are locations where " tectonics plates meet. They are divisions of the earth's crust.
Convection Currents
1.Magma(semi molten rock) near the outer core is heated.
2.Magma warms, expands, and becomes less dense.
3.Less dense magma start to rise towards the crust.
4.Magma nears the crust and begins to cool (600/800ºC)
5.Cooling magma becomes denser+ starts to sink.
6.Rising+ falling creates circular currents within the mantle.
7.The friction with the crust above makes the crust move.
How do oceanic plates form?
Are formed from mantle material at mid ocean ridges.
Young oceanic lithosphere is hot + low density.
But as it spreads away from the rigde, it cools + contracts (becomes denser) and is able to sink into the hot underlying mantle.
Crust
Oceanic crust
Denser
5Km thick
Younger (200 million years old)
Continental crust
Contains granite
Older (4.3 billion years old)
Less dense
Outer Core
Inner Core
Mantle