Snapshots of magma chemistry recorded in magmas and crystal cargoes reflect combinations of processes that operate in the magma source (e.g. metasomatism and tapping of various mantle components) and during differentiation in the crust (e.g. fractional crystallization, crustal assimilation, mixing/mingling, replenishment of magma reservoirs and chambers, and crustal melting). The fundamental questions addressed by this session concern the principal controls on primary, parental and derivative magma compositions as witnessed by the crystalline components of magmas, isotopic records, and experiments that replicate natural systems. We therefore welcome contributions focusing on the generation and differentiation of magmas in the mantle and crust with particular emphasis on crystal-scale studies, experimental petrology, thermodynamic and geochemical modelling, and layered intrusions.