Magmatism

Magmatism is a set of geological processes by which magma is formed, stored, transported, crystallized, and emplaced within Earth's crust and mantle. It encompasses partial melting of existing rocks, differentiation by fractional crystallization, assimilation of surrounding material, and magma mingling. The products range from mantle-derived basalts to granitic magmas, producing a wide array of igneous rocks.

Magma originates by melting reactions in the mantle and lower crust and is shaped by tectonic setting. Decompression melting occurs at mid-ocean ridges and continental rifts, while flux melting is driven by volatiles released from subducting slabs. Magmas vary in silica content and viscosity and may mix or fractionate before final solidification or eruption.

Magma is transported and stored as magma chambers, dikes, and sills within the crust. Intrusive magmatism yields plutonic rocks such as granites and diorites, formed by slow cooling, whereas extrusive magmatism produces volcanic rocks from rapidly erupted lava. Cooling rate, pressure, and water content control mineralogy and textures via crystallization sequences.

Surface expressions include effusive eruptions that build lava flows and domes and explosive eruptions that eject ash, pumice, and gases. Magmatism influences crustal growth, ore-forming hydrothermal systems, and geothermal energy resources, and it records tectonic histories and planetary processes beyond Earth.