The Structure of the Earth and Plate margins (Crust (Continental Crust…
The Structure of the Earth and Plate margins
Formed at mid-ocean ridges through a process of partial melting - the extrusive and intrusive solidification of basaltic magmas, resulting in a uniform, layered, ocean crust
Younger - 200 million years old
Granite - formed through many cycles of partial melting of oceanic crust , resulting in the differentiation and "recycling" of the denser crust, producing rock that is composed of less dense material
Destructive plate margins - thrown up in orogeny
Older - 4.3 billion years old
Outer Core (5500°)
Inner Core (5500°)
Magma (semi-molten rock) near the outer core is heated.
Magma warms, expands, and becomes less dense.
Less dense magma starts to rise towards the crust.
Magma nears the crust and begins to cool (600-800°C).
Cooling magma becomes denser + starts to sink.
Rising +falling creates circular currents within the mantle.
The friction with the crust above makes the crust move.
What is a plate boundary?
Plate boundaries are locations where two tectonic plates meet - they are divisions of the earth's crust.
What is a subduction zone?
The subduction zone is an area on a plate tectonic boundary where two plates converge and one plate (oceanic) is thrust beneath the other (continental). There is a deep ocean trench where the oceanic (subducted) plate bends downwards.
How do oceanic plates form?
Oceanic plates are formed from mantle material at mid-ocean ridges.
Young oceanic lithosphere is hot + buoyant (low density) when it forms at a MOR.
But as it spreads away from the ridge, it cools + contracts (becomes denser) and is able to sink into the hot underlying mantle.
What is a mid-ocean ridge?
A 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 e.g. The Mid-Atlantic Ridge
A series of volcanic islands may develop e.g. Iceland ----- Tristan de Cunha