Fluids trapped inside fluid inclusions in quartz from the multiphase Starav monzogranite in Etive, Argyll, were extracted under vacuum and quantitative data for H2O and CO2 were obtained manometrically. Na and K were determined on an aqueous leach from the decrepitated grains. A bivariate diagram of H2O/CO2 versus Na/K discriminates between magma pulses and mirrors the whole-rock trace-element chemistry. This work shows that compositional variations of fluids in quartz from a weakly mineralised granitoid intrusion are sensitive indicators of its magmatic history and identify subtle changes in its mineralogical composition.

The primary focus of this review is on P-T conditions, mineralogical indicators of melt or fluid composition and textural evolution; lesser treatment is given to pegmatite sources or to pegmatite-wallrock interactions. Investigations of stable and radiogenic isotopes have revealed that the source materials for pegmatites are likely to be more heterogeneous or varied than previously thought, especially for peraluminous pegmatites, but that overall pegmatites bear a clear intrusive relationship with their hosts, as opposed to an origin in situ. The P-T conditions of crystallisation of some lithium-rich pegmatites have been constrained by lithium aluminosilicate stability relations in combination with stable isotope or fluid inclusion methods. Experimental studies have elucidated the effects of components such as Li, B, P and F, which are common in some classes of pegmatites, to liquidus relations in the hydrous haplogranite system. Experimentation has also provided corroboration of an old concept of pegmatite crystallisation—that pegmatites owe their distinctive textures and mineral/chemical zonation to relatively rapid crystallisation of melt from the margins inwards at conditions far from the equilibrium (i.e. from supercooled liquids). The origin of aplites, whether alone, layered, or paired with pegmatites, remains an active area of research. Studies of fluid inclusions, crystal-vapour equilibria and wallrock alteration have helped to define the timing and compositions of vapour phases in pegmatites and to aid in the economic evaluation of deposits.