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Constructive Plate Margins
Where convection currents rise and then diverge, they can create high temperatures that cause updoming
of the crust and tensional forces that pull it apart.

There are two types of divergence:

In oceanic areas, seafloor spreading occurs on either side of mid-ocean ridges such as the Mid-…

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Case Study: The Great African Rift Valley
A rift is taking place right now and it is tearing the eastern side of Africa apart.

Uncertainty remains as to the exact causes of the Great African Rift Valley, but it is widely accepted that it
is a result of plumes of…

Page 3

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Destructive Plate Margins
Destructive plate margins are found where plates converge.
There are three types of converge margins:

Oceanic plate meeting continental plate
Oceanic plate meeting oceanic plate
Continental plate meeting continental plate




Oceanic Plate Meets Continental
Because oceanic crust is denser than continental crust, when plates collide the oceanic…

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Case Study: Peru-Chile Trench and the Andes
The Peru­Chile Trench is the longest ocean trench, marking the point at which the Nazca Plate meets
the South American Plate.

The Nazca Plate is primarily dense ocean crust and so is being subducted beneath the more buoyant
South American continental plate.

The…

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Oceanic Plate Meets Oceanic
When two oceanic plates collide, one plate subducts beneath the other.
The one that is subducted may be marginally denser or moving quicker.

This leads to the formation of a deep ocean trench and melting into the upper mantle.

The resulting rising magma from the Benioff…

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Case Study: Marianas Trench
The Marianas Trench and the associated Marianas Islands in the Western Pacific are an example of where
oceanic plate meets oceanic plate.

The Marianas Trench is located in the Pacific Ocean, East of the 14 Marianas Islands, near Japan.

It is the deepest part of the…

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Continental Plate Meets Continental
When two plates of continental crust move towards each other; neither is subducted due to the fact they
have similar densities. They have a lower density than the asthenosphere beneath them.

The colliding plates, and any sediments deposited between them, simply become uplifted and buckle to…

Page 8

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Conservative Plate Margins
When two plates slide past each other they form a conservative plate margin.

Along these margins crust is not being destroyed by subduction.
There is no melting of rock and therefore, no volcanic activity or formation of new crust.

Despite the absence of volcanic activity, these margins…

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Hot Spots
While most of the world's volcanoes are located along plate margins, there are notable exceptions.

Radioactive decay within the Earth's core generates very hot temperatures. If the decay is
concentrated, then hot spots will form around the core. These hot spots heat the lower mantle, creating
localised thermal…

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Case Study: Hawaii Hotspot
The current hotspot is underneath the southern end of the island of Hawaii.

As the Pacific plate moves slowly north-west at a rate of 5-10 cm per year, the next volcano in the chain is
forming on the sea floor just to the South of Hawaii,…

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