Crustal

Crustal is an adjective referring to the Earth's crust or, more broadly, to the outermost solid shell of a planetary body. In geology, crustal rocks, structures, and processes are those associated with the crust. Earth's crust is divided into continental crust and oceanic crust.

Continental crust is thick and less dense, averaging about 30 to 50 kilometers, with granitic and felsic rocks. Oceanic crust is thinner and more dense, averaging about 5 to 10 kilometers, composed mainly of basaltic rocks. The boundary between crust and mantle is the Mohorovičić discontinuity, or Moho, whose depth varies from roughly 5 to 10 kilometers beneath oceans to tens of kilometers beneath continents.

Crustal growth and modification occur through magmatic differentiation, tectonic accretion, sedimentation, and metamorphism. Tectonic forces bend, fault, and deform the crust, creating orogenic belts, rifts, and plate boundaries. Oceanic crust is continually formed at mid-ocean ridges and recycled back into the mantle at subduction zones.

Crustal structure is studied with seismology, seismic reflection and refraction, gravity, and magnetics. Understanding crustal properties informs earthquake and volcanic risk, mineral and groundwater resources, and landscape development.

In planetary geology, the term crustal describes outer shells of other bodies, where thickness and composition vary with formation history and tectonics.