The lower oceanic crust is primarily made of gabbro.
Here's a more detailed breakdown:
The oceanic crust is generally divided into three layers:
- Layer 1: Sediments
- Layer 2: Pillow basalts and sheeted dikes
- Layer 3: Gabbro
Gabbro, a coarse-grained, mafic intrusive igneous rock, comprises the majority of the lower oceanic crust. Mafic rocks, like gabbro, are rich in magnesium and iron.
Essentially, as magma rises from the Earth's mantle at mid-ocean ridges, it cools and solidifies. The upper portions cool quickly, forming the basaltic pillow lavas and sheeted dikes. However, deeper down, the magma cools more slowly, allowing larger crystals to grow, resulting in the formation of gabbro. This gradual cooling process creates the layered structure of the oceanic crust.
In summary, while other minerals are present in smaller quantities, gabbro is the dominant rock type of the lower oceanic crust.
