On the Grain Size Sensitivity of Olivine Rheology

Using the Markov chain Monte Carlo (MCMC) inversion technique of Mullet et al. (2015), we reassess the validity of the conventionally accepted values of the grain size exponent of diffusion creep in olivine aggregates. A systematic and comprehensive analysis of individual experimental runs taken from three widely cited studies reveals that these data do not tightly constrain the grain size exponent or any other flow law parameter for diffusion and dislocation creep. Our analysis indicates that large data uncertainties can cause inversion results to deviate significantly from true values because of the covariance between the grain size and stress exponents, and that even resolving a grain size exponent of 2 from 3 is difficult. The versatility of our MCMC inversion technique can, however, be exploited to improve this situation by identifying optimal conditions for future experimental studies. Because the uncertainties of the grain size and stress exponents are highly correlated, for example, increasing the range of grain size variation can help better constrain both exponents simultaneously.