Upwelling

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Molten rock may collect and solidify in magma chambers deep in the Earth. Alternatively magma may rise, only to cool at a shallower depth within the Earth, or it may reach the surface, where it may be extruded as lava or erupt explosively.

Within magma chambers, crystals of denser minerals that solidify early can sink to the base of the melt, while lighter minerals may float to the top of the melt. These processes of fractional crystallization can produce layered igneous rocks called cumulates [i]. As minerals crystallize out of the melt, the composition of the liquid phase of the melt is altered in a process called magmatic differentiation. Similarly, as a rising magma melts minerals out of the walls of the chamber, the melt's composition may change.

Magmatic mixing involves adjacent magma bodies that have developed transient subsurface communications before they solidify at depth or erupt at the surface. (I created the image before being put in mind of this phenomenon.)