1. Basalt:
* This is the most abundant type of volcanic rock found at divergent plate boundaries.
* It is a dark-colored, fine-grained, extrusive igneous rock.
* It is formed from the rapid cooling of mafic lava, rich in magnesium and iron.
* Basalt is typically associated with mid-ocean ridges, where new oceanic crust is created.
2. Gabbro:
* This is the intrusive equivalent of basalt.
* It is a dark-colored, coarse-grained, igneous rock.
* It forms when magma cools slowly beneath the Earth's surface.
* Gabbro is often found in association with basalt at mid-ocean ridges.
3. Peridotite:
* This is a dark-colored, coarse-grained, igneous rock that is found in the upper mantle.
* It is the source rock for basalt and gabbro.
* Peridotite is rarely found on the surface, but it can be exposed at divergent plate boundaries where the oceanic crust is thin.
4. Tholeiitic basalt:
* This is a specific type of basalt characterized by a high content of silica and iron.
* It is often found in the initial stages of ocean spreading, when the magma is relatively rich in iron.
5. Alkali basalt:
* This is a type of basalt with a high content of sodium and potassium.
* It is typically found in areas where the magma is more evolved, often associated with hotspot volcanoes.
Why these rocks?
The types of rocks found at divergent plate boundaries are a result of the specific conditions found there:
* Low pressure: The pressure at divergent plate boundaries is relatively low, allowing the magma to rise to the surface easily.
* High temperature: The magma is also very hot, leading to rapid cooling and the formation of fine-grained rocks like basalt.
* Mafic composition: The magma at divergent plate boundaries is typically mafic in composition, meaning it is rich in magnesium and iron. This leads to the formation of basalt and gabbro.
In addition to these primary rock types, other rocks like rhyolite and andesite can also be found in small quantities, especially in areas where there is more complex interaction between plates.
