Flux melting

Flux melting occurs when water released from a subducting slab lowers the melting temperature of mantle rock above it, producing magma.

Subduction zone: A region where one tectonic plate descends beneath another into the mantle. The descending plate supplies water that drives melting in the overlying mantle.
Oceanic crust: The basaltic and gabbroic outer layer of oceanic plates. Its hydrated rocks can release water as the crust descends into hotter mantle.
Decompression melting: Melting caused when hot rock rises and pressure falls faster than it cools. Unlike flux melting, it lowers pressure rather than adding water to initiate melting.
Volcanic arc: A chain of volcanoes formed above a subduction zone on an overriding plate. Arc volcanoes commonly erupt magmas generated by melting in the mantle wedge.
Mantle wedge: The wedge-shaped mantle region between a subducting plate and the overriding plate. This is the mantle region hydrated and melted above the slab.
Hydrothermal alteration: Chemical and mineralogical change caused by hot, circulating aqueous fluids in rock. Seafloor alteration stores water in minerals later carried down by the slab.
Heat-transfer melting: Melting caused when hot material transfers heat into cooler surrounding rock. This mechanism adds thermal energy, whereas flux melting mainly changes the solidus.
Island arc: A curved chain of volcanic islands built above an oceanic subduction zone. Its magmas provide a clear setting for studying slab-fluid-driven melting.
Aqueous fluid: A water-rich fluid capable of dissolving and transporting chemical components through rock. Fluids released from the slab carry water into the mantle wedge.
Metamorphic dehydration: The release of water as pressure and temperature transform hydrous minerals into less hydrated assemblages. Dehydration reactions in the slab deliver water to the overlying mantle.

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