What is the relationship between oceanic crust and the mantle beneath it?

The oceanic crust and the underlying mantle are fundamentally linked through the processes of plate tectonics and Earth's internal thermal structure.

• Structural Boundary: The oceanic crust sits directly atop the mantle. The boundary separating these two layers is known as the Moho, where the velocity of seismic waves increases rapidly.
• Compositional Differences: While the oceanic crust is primarily composed of basalt and gabbro, the mantle is composed mostly of peridotite, a rock consisting largely of the mineral olivine.1
• Formation and Evolution: New oceanic crust is formed at spreading centres on oceanic ridges, where hot magma wells up from the underlying mantle. As this crust moves away from the ridge, both the crust and the upper mantle cool and contract, which influences the depth of the ocean floor.2
• Dynamic Interaction: The mantle undergoes thermal convection, which is a primary driver of plate movement. Subducted oceanic crust can penetrate deep into the mantle, and the chemical interaction between these subducted slabs and the mantle is essential to the geochemical composition of oceanic basalts.34