Strain localization by diffusion creep of Bridgmanite-Ferropericlase mixture: Application of self-consistent method

In this study, we investigate the finite deformation of a polycrystalline mixture of bridgmanite (Br) and ferropericlase (Fp) by diffusion creep at the lower mantle-like temperature and pressure by using the self-consistent approach. We explore the influence of volume fraction of Fp, viscosity contrast, and strain dependence (effect of shape change) under both axial (coaxial deformation) and simple shear (non-coaxial deformation). Our present study shows: i) the strength (viscosity) contrast between Fp and Br increases with strain since the viscosity of Fp significantly decreases as Fp grain elongates, and (ii) deformation starts from nearly homogeneous strain to finally nearly homogeneous stress under simple shear whereas deformation behavior remains nearly homogeneous strain under axial deformation. A more substantial creep rate partitioning occurs in simple shear than in axial deformation. These results imply that strain localization via diffusion creep might occur in the lower mantle, particularly in regions where the simple shear is dominated (i.e., in the boundary layers (e.g., the D″ layer)).