crustmantle

Crustmantle is a nonstandard term used occasionally in geology to describe the shallow region directly beneath Earth's crust, or more loosely, the boundary zone between crust and mantle. In mainstream geology, the official boundary is the Mohorovičić discontinuity (Moho). When used, "crustmantle" often refers to the uppermost mantle that lies beneath the crust or to a composite zone including the crust and the immediate underlying mantle in simplified models.

Continental crust sits atop the crustmantle region and ranges in thickness from roughly 25 to 70 kilometers, while oceanic crust is thinner, commonly about 5 to 10 kilometers. Beneath the crust, the lithospheric mantle comprises rigid rocks that extend down to the asthenosphere, where rocks become weak and ductile. The Moho marks a sharp increase in seismic velocity, separating crustal rocks from the mantle.

Compositionally, crustal rocks are granitic to granodioritic in continents and basaltic/gabbroic in oceans; the upper mantle is dominated by ultramafic peridotite. Physical properties differ: crust is generally less dense and more buoyant than the underlying mantle, influencing isostatic balance and tectonic behavior.

Geophysically, the crustmantle concept is relevant to models of lithosphere structure, plate tectonics, and crust–mantle differentiation. It is distinct from the lithosphere–asthenosphere boundary (LAB), which lies deeper and marks a transition to weak, ductile mantle material.