Article
Map of the Earth's oceanic crust, with colours indicating the age of the crust. Lighter shades indicate younger age, and darker shades indicate older age. The lines represent tectonic plate boundaries. Continental and oceanic crust on the Earth's upper mantle
Oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramafic cumulates. The crust lies above the rigid uppermost layer of the mantle. The crust and the rigid upper mantle layer together constitute oceanic lithosphere.