Diffusion Creep and Grain Growth in Forsterite +20 vol% Enstatite Aggregates: 1. High-Resolution Experiments and Their Data Analyses

We conducted uniaxial compression and grain growth experiments on fine-grained (~1 μm) forsterite +20 vol% enstatite aggregates. Based on analyses of the sensitivity of the strain rate as a function of stress, we find power law creep at low stress, Newtonian creep at intermediate stress, and again power law creep at high stress, which correspond to interface-controlled diffusion creep, grain boundary diffusion (Coble) creep, and a dislocation-controlled process, respectively. The creep rate of these samples is well expressed by a combination of strain rates of these three mechanisms where interface-controlled and Coble creep rates are combined as series-sequential processes, while the rate of the dislocation process is added with them as a parallel-concurrent process. Mechanical data collected continuously during the application of a constant load but while slowly changing temperature were decomposed into data for every 1 °C, which allowed consideration of >600 mechanical data points from 1054 to 1370 °C. The data were analyzed using Bayesian statistics implementing a Markov chain Monte Carlo method imposed on the above constitutive equation, resulting in the best fit flow law parameters for interface-controlled and Coble creep. Samples were annealed for 500 hr at various temperatures. A comparison of the final grain sizes as a function of temperature on an Arrhenius plot resulted in an activation energy for grain growth similar to that observed for grain boundary diffusion during Coble creep of these materials.