subcrust

The term "subcrust" refers to the layer of the Earth's interior that lies beneath the crust. It is not a distinct layer with a clear boundary, but rather a transition zone between the crust and the mantle. The subcrust is characterized by a gradual increase in temperature and pressure with depth, and it is composed of rocks that are more mafic (rich in magnesium and iron) than those found in the crust.

The thickness of the subcrust varies depending on the tectonic setting. In oceanic regions, it is relatively thin, typically ranging from a few kilometers to about 10 kilometers. In continental regions, it can be significantly thicker, sometimes exceeding 30 kilometers. The subcrust is important for understanding the dynamics of plate tectonics, as it plays a role in the generation and movement of magma, as well as the recycling of crustal material back into the mantle.

The subcrust is not directly observable, and its properties are inferred from seismic data and other geophysical techniques. It is known to be less rigid than the crust above it, and it is capable of flowing over geological timescales. This flow is thought to be driven by the convection of the mantle, which causes the subcrust to deform and contribute to the overall dynamics of the Earth's interior.