The effect of pressure on grain-growth kinetics in olivine aggregates

Abstract:

Effects of pressure on grain-growth kinetics of olivine were investigated up to 10 GPa and at 1773 K under the water-poor conditions. The results are interpreted using a relation (dⁿ-d₀ⁿ)/t = k₀exp(-(E^*+PV^*)/RT) to obtain the activation volume, V^* = 4.8±1.3 cm³/mol for n = 2 or V^* = 5.0±1.3 cm³/mol for n = 3. The small activation volume means that grain-growth kinetics in pure olivine aggregates is fast even in the dry deep upper mantle. The present results are applied to the absorption-band model of seismic wave attenuation. We suggest that the absorption-band model alone is insufficient to explain the recent seismic observations showing a peak in shear attenuation right below the lithosphere-asthenosphere boundary in the central Pacific mantle. The present results are also applied to the elastically-accommodated grain-boundary sliding (EAGBS). We suggest that the deep upper mantle is likely to be relaxed by EAGBS, which implies that the shear velocity of the deep upper mantle can be several percent smaller than that inferred from single crystal elasticity.