The term emplacement used in the context of petrology and structure means the attainment of the present position of a particular intrusive mass of rock. It is most commonly used in association with intrusive igneous rocks, but it is also used in relation to the modes of emplacement of material (other than magma) infilling volcanic necks and breccia pipes, as well as to salt domes and other intrusive sediments. Emplacement may also be used in connection with the conversion in situ of crustal rocks into rocks of igneous aspect (feldspathization-granitization), but this use of the term is excluded from this description.
Magmas move in the crust owing to the influence of gravity, tectonic forces, or pressures from within the magmas themselves. Their movement necessitates displacements of the surrounding crustal rocks and accordingly their mode of emplacement is often controlled by structures within these rocks.