Upper mantle

The upper mantle is the part of Earth’s mantle from the crust–mantle boundary to about 660 kilometers depth. It includes the rigid mantle lithosphere and the weaker asthenosphere.

Asthenosphere: A mechanically weak, slowly deforming region of the upper mantle beneath the lithosphere. Its low strength lets tectonic plates move over the mantle.
Mohorovičić discontinuity: The seismic boundary between Earth’s crust and mantle, commonly called the Moho. The upper mantle begins beneath this crust–mantle boundary.
Seismic tomography: A method that uses seismic-wave observations to image variations inside Earth. It maps upper-mantle temperature and structure from variations in wave speed.
Earth's heat budget: The accounting of heat stored within Earth and released through its surface. Uncertainty in upper-mantle temperature and heat transport affects estimates of Earth’s internal heat loss.
Mantle convection: The slow circulation of solid mantle driven by heat loss and buoyancy. Convection transports heat through the upper mantle and helps drive plate motion.
Lithosphere: Earth’s rigid outer shell, comprising the crust and the mechanically strong uppermost mantle. Its mantle portion is the upper mantle’s stiff outer layer.
Mid-ocean ridge: An underwater mountain chain where tectonic plates diverge and new oceanic crust forms. Rising upper-mantle material partially melts beneath these spreading centers.
Mantle water: Water incorporated in mantle minerals or present in small amounts within mantle rock. Its abundance can alter upper-mantle melting, viscosity, and seismic properties.
Mantle melting: The production of magma when mantle rock partially melts as pressure, temperature, or composition changes. Partial melting of upper-mantle rock produces much of Earth’s basaltic magma.
Lower mantle: The mantle region below about 660 kilometers, extending to the core–mantle boundary. It lies beneath the upper mantle, separated from it by a major mineral transition.

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