Types of volcanism associated with plate margins
Types of volcanism associated with plate margins
There are two types of plate margin. When there is a boundary between two diverging tectonic plates, such as between the North American and Eurasian plates, it is known as a constructive plate margin. This is because it recognises the importance of magma rising up from the mantle to create new crustal rock. The boundary between two converging plates is known as a destructive plate margin, as it is responsible for more violent seismic activity, volcanoes and high mountain ranges.
Destructive Plate Margins
Destructive plate margins can either result in collision zones or subduction zones. When a plate of oceanic lithosphere comes into contact with a continental plate the oceanic plate is subducted beneath the continental plate due to the higher density of the oceanic crust. This can sometimes form what is known as a volcanic arc. As the slab descends it encounters progressively greater temperatures and pressures, causing it to release water into the overlying mantle wedge. This lowers the melting temperature of said mantle and causes it to partially melt; producing magma. This is known as flux melting. The magma then rises upward as lava due to its greater buoyancy to form a linear belt of volcanoes parallel to the trench. Approximately 90% of the earth’s volcanoes are formed this way. The average densities of the oceanic and continental crusts are 2.9g/cm3 and 2.7g/cm3 respectively. Subduction happens very slowly, at rates of approximately 2-8 centimetres a year.
Along these subduction zones are increasing depths of earthquake foci. These inclined planes are known as Wadati-Benioff zones. They range from 300 to 700km deep; it is not possible for any earthquake foci to exist lower than this as the temperature is too high for faults to occur as the rock is no longer brittle but ductile.
These arc volcanoes on the continental crust erupt mainly andesitic magma. This is an example of ‘intermediate’ magma which
There are two types of plate margin. When there is a boundary between two diverging tectonic plates, such as between the North American and Eurasian plates, it is known as a constructive plate margin. This is because it recognises the importance of magma rising up from the mantle to create new crustal rock. The boundary between two converging plates is known as a destructive plate margin, as it is responsible for more violent seismic activity, volcanoes and high mountain ranges.
Destructive Plate Margins
Destructive plate margins can either result in collision zones or subduction zones. When a plate of oceanic lithosphere comes into contact with a continental plate the oceanic plate is subducted beneath the continental plate due to the higher density of the oceanic crust. This can sometimes form what is known as a volcanic arc. As the slab descends it encounters progressively greater temperatures and pressures, causing it to release water into the overlying mantle wedge. This lowers the melting temperature of said mantle and causes it to partially melt; producing magma. This is known as flux melting. The magma then rises upward as lava due to its greater buoyancy to form a linear belt of volcanoes parallel to the trench. Approximately 90% of the earth’s volcanoes are formed this way. The average densities of the oceanic and continental crusts are 2.9g/cm3 and 2.7g/cm3 respectively. Subduction happens very slowly, at rates of approximately 2-8 centimetres a year.
Along these subduction zones are increasing depths of earthquake foci. These inclined planes are known as Wadati-Benioff zones. They range from 300 to 700km deep; it is not possible for any earthquake foci to exist lower than this as the temperature is too high for faults to occur as the rock is no longer brittle but ductile.
These arc volcanoes on the continental crust erupt mainly andesitic magma. This is an example of ‘intermediate’ magma which