123 / 2023-04-14 13:40:18

Grain growth kinetics of bridgmanite and lower mantle rheology

grain growth;,bridgmanite,lower mantle,rheology

高压物理与材料科学 > 高压地球科学-I

The absence of seismic anisotropy in most regions of the lower mantle implies that the dominant creep mechanism in the lower mantle may be diffusion creep. Since the diffusion-creep rate is inversely proportional to the 2~3 power of grain size, the knowledge of grain growth kinetics of lower mantle minerals is crucial for investigating lower-mantle dynamics. Here we measured the grain growth rate of bridgmanite, the dominant mineral in the lower mantle, as a function of pressure, temperature, and fraction of coexisting ferropericlase under lower mantle conditions by multi-anvil experiments. Our results indicate that the grain growth of bridgmanite is significantly suppressed by ferropericlase. Pure bridgmanite rocks have more than one order of magnitude higher viscosity than bridgmanite + ferropericlase aggregates with pyrolitic composition, which interprets the viscosity variation in the lower mantle inferred from geoid analysis [1].

  

[1] Rudolph, M., Lekic, V., Lithgow-Bertelloni, C., Viscosity jump in Earth’s mid-mantle. Science 350, 1349-1352 (2015).