igneous petrology Igneous petrology is the study of igneous rocks—those that are formed from magma. As a branch of geology, igneous petrology is closely related to volcanology, tectonophysics, and petrology in general. The modern study of igneous rocks uses a num ...

and

volcanology Volcanology (also spelled vulcanology) is the study of volcanoes, lava, magma and related geology, geological, geophysical and geochemistry, geochemical phenomena (volcanism). The term ''volcanology'' is derived from the Latin language, Latin ...

, flux melting occurs when water and other volatile components are introduced to hot solid rock, depressing the solidus. In engineering and metallurgy, flux is a substance, such as salt, that produces a low melting point ( liquidus) mixture with a metal oxide. In the same way, the addition of water and other volatile compounds to rocks composed of

silicate minerals Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, the crystalline forms of silica (silicon dio ...

lowers the melting temperature ( solidus) of those rocks. In subduction zones, the ultramafic rock of the

upper mantle The upper mantle of Earth is a very thick layer of rock inside the planet, which begins just beneath the crust (geology), crust (at about under the oceans and about under the continents) and ends at the top of the lower mantle (Earth), lower man ...

is melted by the addition of volatiles from the subducting plate. The subducting

oceanic crust Oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramaf ...

carries water and other volatiles into the mantle, primarily in the form of hydrous minerals which form as a result of the interaction of oceanic crust and seawater. Bound in the subducting crust, these volatiles are released by metamorphic dewatering into the overlying mantle wedge. The partial melting triggered by the incorporation of volatiles produces mafic

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma (sometimes colloquially but incorrectly referred to as ''lava'') is found beneath the surface of the Earth, and evidence of magmatism has also ...

which rises and differentiates forming the

igneous Igneous rock ( ), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rocks are formed through the cooling and solidification of magma or lava. The magma can be derived from partial ...

and

volcanic rock Volcanic rocks (often shortened to volcanics in scientific contexts) are rocks formed from lava erupted from a volcano. Like all rock types, the concept of volcanic rock is artificial, and in nature volcanic rocks grade into hypabyssal and me ...

s of the overlying

volcanic arc A volcanic arc (also known as a magmatic arc) is a belt of volcanoes formed above a subducting oceanic tectonic plate, with the belt arranged in an arc shape as seen from above. Volcanic arcs typically parallel an oceanic trench, with the arc ...

.Wallace, Paul J., ''Volatiles in subduction zone magmas: concentrations and fluxes based on melt inclusion and volcanic gas data,'' Journal of Volcanology and Geothermal Research 140 (2005) pp. 217– 240

References

Petrology Plate tectonics {{petrology-stub