Cumulates successions are closely linked to the phase relations of the crystallising magma. A closed system crystallisation will produce a succession of cumulates with progressively lower temperature mineral assemblages during crystallisation. The animation below shows a situation where minerals are separated from the fractionating magma (by deposition or crystallisation) on the floor of an intrusion generating a layered succession of cumulates. The composition of the magma is illustrated with the light red colour.
The geology of layered intrusions is tightly tied in with phase relations.
Most layered intrusions formed from basaltic magmas that undergo significant
fractionation during their crystallisation. The phase diagram above was
used by Irvine (1970) to explain layering successions in the Muskox intrusion
in northern Canada.