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1. Viscous anisotropy of textured olivine aggregates, Part 1: Measurement of the magnitude and evolution of anisotropy

   https://doi.org/10.1016/j.epsl.2016.04.008  

   Hansen, Lars N.; Warren, Jessica M.; Zimmerman, Mark E.; Kohlstedt, David L. (July 2016, Earth and Planetary Science Letters)
2. Effects of pressure on diffusion creep in wet olivine aggregates

   https://doi.org/10.1016/j.pepi.2022.106840  

   Silber, Reynold E.; Girard, Jennifer; Karato, Shun-ichiro (March 2022, Physics of the Earth and Planetary Interiors)
3. Global Analysis of Experimental Data on the Rheology of Olivine Aggregates

   https://doi.org/10.1029/2018JB016558  

   Jain, Chhavi; Korenaga, Jun; Karato, Shun‐ichiro (January 2019, Journal of Geophysical Research: Solid Earth)

   Abstract Following the reanalysis of individual experimental runs of some widely cited studies (Jain et al., 2018,https://doi.org/10.1002/2017JB014847), we revisit the global data analysis of Korenaga and Karato (2008,https://doi.org/10.1029/2007JB005100) with a significantly improved version of their Markov chain Monte Carlo inversion. Their algorithm, previously corrected by Mullet et al. () to minimize potential parameter bias, is further modified here to estimate more efficiently interrun biases in global data sets. Using the refined Markov chain Monte Carlo inversion technique, we simultaneously analyze experimental data on the deformation of olivine aggregates compiled from different studies. Realistic composite rheological models, including both diffusion and dislocation creep, are adopted, and the role of dislocation‐accommodated grain boundary sliding is also investigated. Furthermore, the influence of interrun biases on inversion results is studied using experimental and synthetic data. Our analysis shows that existing data can tightly constrain the grain‐size exponent for diffusion creep at ∼2, which is different from the value commonly assumed (p= 3). Different data sets and model assumptions, however, yield nonoverlapping estimates on other flow‐law parameters, and the flow‐law parameters for grain boundary sliding are poorly resolved in most cases. We thus provide a few plausible candidate flow‐law models for olivine rheology to facilitate future geodynamic modeling. The availability of more data that explore a wider range of experimental conditions, especially higher pressures, is essential to improve our understanding of upper mantle rheology. 

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4. Laboratory investigation of mechanisms for phase mixing in olivine + ferropericlase aggregates

   https://doi.org/10.1098/rsta.2017.0417  

   Wiesman, Harison S.; Zimmerman, Mark E.; Kohlstedt, David L. (October 2018, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences)
5. Rheological Weakening of Olivine + Orthopyroxene Aggregates Due to Phase Mixing: Effects of Orthopyroxene Volume Fraction

   https://doi.org/10.1029/2020JB019888  

   Tasaka, Miki; Zimmerman, Mark E.; Kohlstedt, David L. (September 2020, Journal of Geophysical Research: Solid Earth)

   Abstract To understand the effects of secondary minerals on changes in the mechanical properties of upper mantle rocks due to phase mixing, we conducted high‐strain torsion experiments on aggregates of iron‐rich olivine + orthopyroxene (opx) with opx volume fractions off_opx = 0.15, 0.26, and 0.35. For samples with larger amounts of opx,f_opx = 0.26 and 0.35, the value of the stress exponent decreases with increasing strain fromn ≈ 3 for γ ≲ 5 ton ≈ 2 for 5 ≲ γ ≲ 25, indicating that the deformation mechanism changes as strain increases. In contrast, for samples withf_opx = 0.15, the stress exponent is constant atn ≈ 3.3 for 1 ≲ γ ≲ 25, suggesting that no change in deformation mechanism occurs with increasing strain for samples with smaller amounts of opx. The microstructures of samples with larger amounts of opx provide insight into the change in deformation mechanism derived from the mechanical data. Elongated grains align subparallel to the shear direction for samples of all three compositions deformed to lower strains. However, strain weakening with grain size reduction and the formation of a thoroughly mixed, fine‐grained texture only develops in samples withf_opx = 0.26 and 0.35 deformed to higher strains of γ ≳ 16. These mechanical and associated microstructural properties imply that rheological weakening due to phase mixing only occurs in the samples with largerf_opx, which is an important constraint for understanding strain localization in the upper mantle of Earth. 

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