Microstructure and transport properties of pyrolite melt at mantle conditions

The microstructure and transport properties of silicate melts are key physical parameters for elucidating geodynamic processes during the evolution of the early magma ocean. Here, we systematically investigate the equation of state, microscopic structure and transport properties of pyrolite melt over 2000-3500 K and 0-60 GPa by molecular dynamics simulations. The calculated results show pressure induced increases in the average Si-O and Al-O coordination numbers, accompanied by the replacement of SiO₄tetrahedra by higher coordination polyhedra such as SiO₅and SiO₆. The fraction of non-bridging oxygen decreases, whereas the abundances of bridging oxygen and tricluster oxygen increase, indicating that the pyrolite melt network gradually evolves toward denser and more highly polymerized configurations. The density-pressure relationships derived from the third-order Birch-Murnaghan equation are consistent with existing theoretical results. The viscosities of pyrolite melts at 2000-3500 K are ∼10^-3-10^-1Pa·s and increase monotonically with pressure along all isotherms. These findings provide important insights into the formation and evolution of the Earth and establish a framework for interpreting the geodynamic processes of other terrestrial planets.