John Seach, Volcano Live


Basalt is the most common extrusive rock on earth.  It is mostly extruded as lava flows.
There are 4 types of Basalt according to thier zone of formation.

Ocean Floor Basalt
Magma is produced by plate spreading resulting in adiabatic decompression melting of the peridotite mantle.
Ocean Island Basalt
These basalts are caused by adiabatic decompression of mantle plumes. They are oceanic hot spot volcanoes.
Examples are: Hawaii, Azore, Canary Islands, Easter Island, Reunion.
Island Arc Basalt
These basalts are formed above subduction zones by decompression melting of the mantle due to the addition of volatiles.
Examples: Ambrym, Lopevi, Tinakula.
Continental Basalt
These are formed in Rift Valleys by adiabatic melting within mantle plumes due to plate spreading.
Examples: East African Rift Valley, Baikal Rift (Siberia), Rio Grande Rift (USA).


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