magmatisme

Magmatisme is the set of geologic processes responsible for the generation, transport, emplacement, and crystallization of magma, leading to the formation of igneous rocks. It includes magmas formed by partial melting of mantle or crustal rocks, and their evolution through fractional crystallization, assimilation of surrounding material, and mixing with other magmas.

Magma generation begins with partial melting of existing rocks in the mantle or crust, producing magmas with varying silica content. As magma ascends, it may accumulate in magma chambers where it cools and evolves by fractional crystallization, partitioning minerals and changing its composition. Assimilation of surrounding rock and mixing with other magmas can further modify the melt before it erupts at the surface or solidifies underground.

Magmatic rocks are broadly classified by their chemical composition and texture. Silicic or felsic magmas yield light-colored rocks such as granite and rhyolite; intermediate magmas produce diorite and andesite; mafic magmas form darker rocks like gabbro and basalt; ultramafic magmas are richer in magnesium and iron. Extrusive magmatism forms volcanic rocks from rapidly cooled lava (e.g., basalt, andesite, rhyolite, obsidian), while intrusive magmatism yields plutonic rocks that crystallize below the surface (e.g., granite, diorite, gabbro).

Geodynamic settings shape magmatism. Mid-ocean ridges predominantly generate basaltic magmatism; subduction zones produce a range from andesite to rhyolite in volcanic arcs; continental rifts and mantle plumes (hotspots) drive diverse magmatic activity. Magmatisme is central to crustal growth, mineral deposits, and volcanic hazards, reflecting the interplay between tectonics, melting, and rock differentiation.