固体地球物理研究生学术报告第十期(一）

Si and O diffusion in both stishovite and CaCl2-type silica are simulated using first-principles calculations. Diffusion in both phases show weak anisotropies. Si diffuses along a,b-axis directly while migrating through 2 equivalentjumps for c-axis. The migration enthalpy of Si in sitshovite fordirections is slightly lower than that of bridgmanite. After the phase transition, Si diffusion in CaCl2-type silica is enhanced with both temperature and pressure because of the negative activation volumes. Our results show O migrate along the SiO6 octahedra edges and diffusion of O is 2~3 orders of magnitute faster than that of Si. The effective diffusion of CaCl2-type silica is assessed to be at least one order of magnitude faster than that of bridgmanite. The rheological weaker CaCl2-type silica significantly reduce the MORB viscosity and facilitate the segregation of subducted oceanic crust with increasing depth during the slab heating.