Considerable geochemical and petrographic evidence suggests that magma mixing phenomena are important in producing the chemical heterogeneity commonly observed in plutonic and volcanic rocks on a variety of scales in both space and time. Simulations of time-dependent, variable viscosity, double-diffusive convection have been carried out to quantitatively investigate the mixing dynamics of magma in melt-dominated magma bodies. Two distinct measures of the ''goodness of mixing'' are used to quantify magma mixing: (1) the linear scale of segregation (L) which corresponds to the length scale of a typical compositional anomaly; and (2) the intensity of segregation (I) which is a measure of the deviation of compositional anomalies from the mean. Nondimensionalization of the governing conservation equations shows that the style and time scale of mixing depend on the flux Rayleigh number (Rq=αgqd4/k&kgr;vm), the buoyancy ratio (Rr=βDk/α1d), the Lewis number (Le=&kgr;/D), the silicic to mafic melt viscosity ratio (vr=vs/vm), and the aspect ratio (A=w/d) of the chamber. Simulations of magma mixing were carried out by solving the conservation equations for parameter ranges 1050), crystal distributions within convecting magma bodies will be different from those predicted assuming steady state velocity fields. Flow reversals cause significant temporal variation in the heat supplied to the roof of the chamber; these may be important in explaining episodic phases of hydrothermal alteration. In sill-like magma bodies (A>2), multiple cells of distinct composition may persist for geologically significant time periods. Finally, our simulations show that the dynamics of double-diffusive convection can impart complex patterns of composition through time and space in magma bodies. ¿ American Geophysical Union 1989