Modeling diffusion creep in the upper mantle and associated grain size evolution

Decades of seismic anisotropy observations and geodynamic modeling yield generally consistent results in the flow of Earth's mantle. Yet, regional inconsistency indicates an incomplete understanding of the mantle flow. Notably, assumptions in many geodynamic models likely underestimated the contribution of diffusion creep to the development of mantle anisotropy. A growing amount of experimental and geological observations show that the processes of diffusion creep can align olivine crystals, indicating the importance of correctly modeling diffusion creep.

The rate of diffusion creep is highly dependent on grain size, which is not well-constrained by the extrapolation of various experimental parameterizations. The choice of grain size parameterizations control the importance of diffusion creep in the upper mantle. To avoid subjective choices of parameterization, we compare our model results against rock records to place a constraint on the parameterization. Our preferred model indicates a flow law transition into the diffusion creep regime in the upper mantle, which will be used to interpret the implication for seismic anisotropy.