Decompression melting

Decompression melting occurs when hot rock rises and loses pressure, allowing some minerals to melt without added heat. It generates much of the magma at mid-ocean ridges and beneath volcanic regions.

Solidus: The temperature-pressure boundary below which a material is entirely solid. Rising rock begins to melt when its path crosses the solidus.
Mid-ocean ridge: An underwater mountain chain where tectonic plates separate and new oceanic crust forms. Mantle rises beneath ridges, melts as pressure drops, and feeds new seafloor.
Earth's mantle: The thick silicate-rock layer between Earth's crust and core. Decompression melting mainly occurs as mantle material rises toward the surface.
Flux melting: Melting caused when added substances, especially water, lower a rock's melting temperature. Unlike decompression melting, flux melting is driven chiefly by added volatiles.
Adiabatic process: A thermodynamic process in which a system exchanges no heat with its surroundings. Mantle rock can rise and cool slightly while pressure falls, without gaining heat.
Oceanic crust: The thin, dense outer layer of Earth beneath the oceans. Its basaltic rocks largely crystallize from melts generated beneath spreading ridges.
Peridotite: A coarse-grained ultramafic rock composed chiefly of olivine and pyroxene. Peridotite is the common mantle source rock that partially melts during ascent.
Heat-transfer melting: Melting caused when hot material transfers heat to cooler surrounding rock. It adds heat to the source, unlike pressure-release melting.
Partial melting: The melting of only some minerals or components in a rock. Pressure release usually melts only part of the rising mantle rock.
Iceland: A volcanic island in the North Atlantic situated across the Mid-Atlantic Ridge. Ridge-related decompression melting feeds Iceland's abundant volcanism.

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