Abstract
Self-diffusion and viscosity coefficients of basaltic melts were computed over the pressure regime of the entire mantle by using first-principles molecular dynamics method. For model basalt, hydrous model basalt and mid-oceanic ridge basalt melts simulated in this study, the calculated temperature variations of transport coefficients at zero pressure closely follow the Arrhenian law with activation energies of 79 to 158 kJ/mol. The calculated results compare favorably with the available experimental data. The pressure variations of the diffusivity and viscosity coefficients deviate from the standard Arrhenius behavior and require an extended form of the Arrhenius relation. Increasing temperature has a tendency to subdue the pressure variations of the viscosity and diffusivities. The differences in viscosity of the basaltic melts with other silicate melts are small at pressures below 30 GPa, suggesting that the viscosity of major magma-forming silicate melts might not change much over that pressure regime. Using silicate melt viscosity, we also calculated critical dynamical parameters, such as Rayleigh ( approximately 3-12X10 (super 30) ) and Prandtl number (45-200) for a completely molten Earth.