Why Do Divergent and Convergent Boundaries Produce Different Types of Igneous Rocks?
Igneous rocks are formed when magma or lava cools and solidifies. The type of igneous rock that is formed depends on the composition of the magma or lava, the temperature at which it cools, and the pressure under which it cools.
Divergent boundaries are places where two tectonic plates are moving away from each other. At divergent boundaries, magma rises from the mantle and fills the gap between the plates. As the magma cools, it forms new oceanic crust.
Convergent boundaries are places where two tectonic plates are moving towards each other. At convergent boundaries, one plate is usually subducting beneath the other. As the subducting plate descends into the mantle, it melts and forms magma. The magma rises through the overlying plate and erupts onto the surface.
Types of Igneous Rocks
The type of igneous rock that is formed depends on the composition of the magma or lava. There are three main types of igneous rocks:
- Felsic rocks are light-colored and have a high silica content. Felsic rocks are formed from magma that is rich in silica, potassium, and sodium.
- Mafic rocks are dark-colored and have a low silica content. Mafic rocks are formed from magma that is rich in iron, magnesium, and calcium.
- Ultramafic rocks are very dark-colored and have a very low silica content. Ultramafic rocks are formed from magma that is rich in magnesium and iron.
Divergent Boundaries
At divergent boundaries, the magma that forms new oceanic crust is typically felsic. This is because the mantle beneath divergent boundaries is relatively hot and contains a lot of silica. The felsic magma cools slowly, forming large crystals. The resulting igneous rock is called granite.
Convergent Boundaries
At convergent boundaries, the magma that forms is typically mafic or ultramafic. This is because the mantle beneath convergent boundaries is relatively cool and contains a lot of iron and magnesium. The mafic or ultramafic magma cools quickly, forming small crystals. The resulting igneous rock is called basalt.
Conclusion
The type of igneous rock that is formed depends on the composition of the magma or lava, the temperature at which it cools, and the pressure under which it cools. Divergent boundaries produce felsic igneous rocks, such as granite, while convergent boundaries produce mafic or ultramafic igneous rocks, such as basalt.
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