Transcript Lesson 11 - Subduction Boundary Volcanism

Plate Boundary Volcanism
 Volcanoes are associated with two of the three
types of plate boundaries, these being convergent
and divergent boundaries. Very little volcanic
activity is seen at transform fault boundaries.
 Volcanism associated with plate tectonic
activity are found in three areas on Earth;
1) Ridges (or spreading centers)
Reference:
2) Subduction zones
3) Interior of tectonic plates.
Tarbuck and Lutgens
Pages 232 - 235
Subduction Zone Volcanism
 At trenches, ocean floor bends and moves downward
into the upper mantle. At depths of 100 km partial
melting of the ocean crust and mantle takes place.
 Basaltic and andesitic magmas are produced at
subduction zones.
 After great quantities of magma are produced, the
molten rock moves upward toward the surface
because it is less dense than the surrounding rock.
 Ocean – Ocean convergent boundaries and
Ocean – Continent convergent boundaries
have this type of volcanism.
Subduction Zone Volcanism
1) Ocean – Ocean Volcanism
 Ocean crust subducts beneath ocean crust.
 Basaltic magmas are produced and burns upward
toward the surface forming a chain of volcanoes called
a “volcanic island arc” parallel to the trench.
 Examples include; Islands of Japan.
Ocean Plate
Asthenosphere
Ocean Plate
Subduction Zone Volcanism
2) Ocean – Continent Volcanism
 Ocean crust subducts beneath continental crust.
 Andesitic and Granitic magmas burns upward into the
continental crust adding to mountain systems.
 This type of volcanism is very explosive and is mainly
found surrounding the Pacific Ocean.
 Examples include; volcanoes in the Andes mountains.
Ocean Plate
Asthenosphere
Continental Plate
Subduction Zone Volcanism
2) Ocean – Continent Volcanism
 At a depths of 100 km, the subducting ocean crust starts
to melt. This generates magmas that are thick and
contains large amounts of gases. As a result, subduction
eruptions at ocean-continent boundaries are very
explosive and produce composite volcanic cones.
 most of the world’s volcanoes are of this type and border
the Pacific Ocean, called the Pacific Ring of Fire.
Ocean Plate
Asthenosphere
Continental Plate
Sample Problem
With the aid of a diagram describe the volcanic features
formed at a ocean-ocean convergent boundary.
Answer:
At an ocean-ocean convergent boundary, one oceanic plate subducts
beneath another and melts when it descends into the mantle at
approximately 100km depth. This molten material moves up through the
oceanic plate located above and erupts onto the ocean floor. This forms a
chain of volcanic islands parallel to the trench called a “volcanic island
arc.”
Ocean Plate
Asthenosphere
Ocean Plate