The Effect of Secondary-Phase Fraction on the Deformation of Olivine + Ferropericlase Aggregates: 2. Mechanical Behavior

Harison Wiesman, Mark E Zimmerman, David L. Kohlstedt

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Abstract

To study the mechanical behavior of polymineralic rocks, we performed deformation experiments on two-phase aggregates of olivine (Ol) + ferropericlase (Per) with periclase fractions (fPer) between 0.1 and 0.8. Each sample was deformed in torsion at T = 1523 K, P = 300 MPa at a constant strain rate to a final shear strain of γ = 6 to 7. The stress-strain data and calculated values of the stress exponent, n, indicate that Ol in our samples deformed by dislocation-accommodated sliding along grain interfaces while Per deformed via dislocation creep. At shear strains of γ < 1, the strengths of samples with fPer > 0.5 match model predictions for both phases deforming at the same stress, the lower-strength bound for two-phase materials, while the strengths of samples with fPer < 0.5 are greater than predicted by models for both phases deforming at the same strain rate, the upper-strength bound. These observations suggest a transition from a weak-phase supported to a strong-phase supported regime with decreasing fPer. Above γ = 4, however, the strength of all two-phase samples is greater than those predicted by either the uniform-stress or the uniform-strain rate bound. We hypothesize that the high strengths in the Ol + Per system are due to the presence of phase boundaries in two-phase samples, for which deformation is rate limited by dislocation motion along interfacial boundaries. This observation contrasts with the mechanical behavior of samples consisting of Ol + pyroxene, which are weaker, possibly due to impurities at phase boundaries.

Original languageEnglish (US)
Article numbere2022JB025724
JournalJournal of Geophysical Research: Solid Earth
Volume128
Issue number4
DOIs
StatePublished - Apr 2023

Bibliographical note

Funding Information:
We would like to thank Amanda Dillman, Lars Hansen, Leïla Hashim, Cameron Meyers, Zachary Michels, Chao Qi, and Amy Ryan for many invaluable discussions. The authors are also grateful to Anette van der Handt for her expertise and help with electron microprobe analyses. This manuscript was improved by thoughtful comments and reviews from Takehiko Hiraga and David Bercovici. This research was funded by NSF Grants EAR‐1755498 (M.E.Z.) and EAR‐1755805 (D.L.K.). Parts of this work were carried out in the Characterization Facility, University of Minnesota, which receives partial support from the NSF through the MRSEC (Award DMR‐2011401) and the NNCI (Award ECCS‐2025124) programs. Electron microprobe analyses were carried out at the Electron Microprobe Laboratory, University of Minnesota, Department of Earth and Environmental Sciences, University of Minnesota‐Twin Cities.

Funding Information:
We would like to thank Amanda Dillman, Lars Hansen, Leïla Hashim, Cameron Meyers, Zachary Michels, Chao Qi, and Amy Ryan for many invaluable discussions. The authors are also grateful to Anette van der Handt for her expertise and help with electron microprobe analyses. This manuscript was improved by thoughtful comments and reviews from Takehiko Hiraga and David Bercovici. This research was funded by NSF Grants EAR-1755498 (M.E.Z.) and EAR-1755805 (D.L.K.). Parts of this work were carried out in the Characterization Facility, University of Minnesota, which receives partial support from the NSF through the MRSEC (Award DMR-2011401) and the NNCI (Award ECCS-2025124) programs. Electron microprobe analyses were carried out at the Electron Microprobe Laboratory, University of Minnesota, Department of Earth and Environmental Sciences, University of Minnesota-Twin Cities.

Publisher Copyright:
© 2023. The Authors.

Keywords

  • olivine
  • periclase
  • torsional deformation
  • two-phase flow

MRSEC Support

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