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Which rock types make up the layers of oceanic crust?
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oceanic crust
A cross section of Earth's outer layers, from the crust through the lower mantle.
Oceanic crust is primarily composed of basaltic rock types arranged in distinct layers beneath any overlying sediment. These layers include:1
- Topmost Layer: Consists of basaltic lavas, which appear as either pillow lavas or sheet flows.1
- Sheeted Dikes: Located below the lavas, this layer serves as the plumbing system for transporting magma to the surface. These dikes are also basaltic in composition.1
- Gabbro Layers: The lower sections of the crust are composed of gabbros, which are essentially coarser-grained versions of basalt.1
- The upper gabbro layer is isotropic (uniform) and may contain pods of plagiogranite, a rock richer in silica.1
- The lower gabbro layer has a stratified, cumulate structure, representing the floor or sides of ancient magma chambers.1
While the oceanic crust sits atop the mantle—which is composed mostly of peridotite—the crust itself is defined by its basaltic, iron- and magnesium-rich composition.12