THERMOPHYSICAL CRITERION FOR MELT VITRIFI CATION IN MAGMATIC BODIES

The relationship between two characteristic times (one of which reflec ts the average cooling rate V-T of the melt from its equilibrium cryst allization temperature T-l to glass transition temperature T-g, and th e other, the frequency of the hopping of a liquid particle across the phase boundary) is used to obtain a relatively simple criterion for vi trification of a magmatic melt of the form V-T greater than or equal t o D-g(T-l-T-g)/lambda(2) where lambda is the distance between particle s and D-g is the diffusion coefficient at (T = T-g). T-g is evaluated from the critical value of the viscosity coefficient eta(g) = 10(13)P, and the diffusion coefficient D-g is calculated from the known correl ation relation D = b/eta(n). The temperature dependence of eta is dete rmined from the modified Arrhenius law, which shows the effect of the chemical composition of the liquid, including volatiles, on the value of eta. The criterion relation obtained agrees satisfactorily with the available experimental values of T-g and D-g in silicate and aluminos ilicate melts and can be applied to problems of magma solidification d ynamics to predict the thermal conditions under which structural zones form.