Pressure dependence of olivine grain growth at upper mantle conditions

The grain size of olivine influences mass and heat flux in Earth's upper mantle. We performed annealing experiments on synthetic olivine-pyroxene aggregates (6-13 vol.%) at 1-12 GPa and 1323-1793 K. Grain-size analysis via EBSD reveal an activation volume of $4.8 \times 10^{-6}\mathrm{m}^3/\mathrm{mol}$, matching silicon grain-boundary diffusion values. This suggests pressure-driven reduction in olivine growth rates may offset temperature effects at depth, enabling grain-size-sensitive creep at shallower mantle depths than previously modeled.