Rheological Weakening of Olivine + Orthopyroxene Aggregates Due To Phase Mixing: Part 2. Microstructural Development

Miki Tasaka; Mark E Zimmerman; David L Kohlstedt; Holger Stünitz; Renée Heilbronner

doi:10.1002/2017JB014311

Rheological Weakening of Olivine + Orthopyroxene Aggregates Due To Phase Mixing: Part 2. Microstructural Development

Miki Tasaka, Mark E Zimmerman, David L Kohlstedt, Holger Stünitz, Renée Heilbronner

Earth and Environmental Sciences-Twin Cities

Research output: Contribution to journal › Article › peer-review

39 Scopus citations

Abstract

To understand the processes involved in phase mixing during deformation and the resulting changes in rheological behavior, we conducted torsion experiments on samples of iron-rich olivine plus orthopyroxene. The experiments were conducted at a temperature, T, of 1200°C and a confining pressure, P, of 300 MPa using a gas-medium deformation apparatus. Samples composed of olivine plus 26% orthopyroxene were deformed to outer radius shear strains up to γ ≈ 26. In samples deformed to lower strains of γ ≲ 4, elongated olivine and pyroxene grains form a compositional layering. Already by this strain, mixtures of small equant grains of olivine and pyroxene begin to develop and continue to evolve with increasing strain. The ratios of olivine to pyroxene grain size in deformed samples follow the Zener relationship, indicating that pyroxene grains effectively pin the grain boundaries of olivine and inhibit grain growth. Due to the reduction in grain size, the dominant deformation mechanism changes as a function of strain. The microstructural development forming more thoroughly mixed, fine-grained olivine-pyroxene aggregates can be explained by the difference in diffusivity among Me (Fe or Mg), O, and Si, with transport of MeO significantly faster than that of SiO₂. These mechanical and associated microstructural properties provide important constraints for understanding rheological weakening and strain localization in upper mantle rocks.

Original language	English (US)
Pages (from-to)	7597-7612
Number of pages	16
Journal	Journal of Geophysical Research: Solid Earth
Volume	122
Issue number	10
DOIs	https://doi.org/10.1002/2017JB014311
State	Published - Oct 2017

Bibliographical note

Funding Information:
We thank A. Dillman, J. Tielke, M. Pec, C. Qi, C. Meyers, and Z. Michels for helpful discussions and technical assistance, T. Hiraga and M. Morishige for valuable discussions, A. van der Handt for assistance of electron microprobe analyses, and B. Richter and N. Seaton for assistance of EBSD analysis. We thank L. Hansen for providing the original EBSD data in Hansen et al. (). The manuscript was significantly improved by insightful comments from two reviewers, R. Cooper and L. Hansen, and an Editor, M. Walter. This study was supported by a JSPS Research Fellowship for Young Scientists (26-4879) and the Japan Society for the Promotion of Science (16K17832) to M. T., a NASA grant (NNX15AL53G) to D. L. K., and a NSF grant (EAR-1345060) and a NASA grant (NNX11AF58G) to M. E. Z. Parts of this work were carried out in the Characterization Facility, University of Minnesota, which is a member of the NSF-funded Materials Research Facilities Network (www.mrfn.org) via the MRSEC program. Electron microprobe analyses were carried out at the Electron Microprobe Laboratory, Department of Earth Sciences, University of Minnesota, Twin Cities, and some of the EBSD work at the Department of Geosciences of the University of Tromso, Norway. Data used in this paper are available in the main text and supporting information.

Funding Information:
We thank A. Dillman, J. Tielke, M. Pec, C. Qi, C. Meyers, and Z. Michels for helpful discussions and technical assis tance, T. Hiraga and M. Morishige for valuable discussions, A. van der Handt for assistance of electron microprobe analyses, and B. Richter and N. Seaton for assistance of EBSD analysis. We thank L. Hansen for providing the origi nal EBSD data in Hansen et al. (2012). The manuscript was significantly improved by insightful comments from two reviewers, R. Cooper and L. Hansen, and an Editor, M. Walter. This study was supported by a JSPS Research Fellowship for Young Scientists (26-4879) and the Japan Society for the Promotion of Science (16K17832) to M. T., a NASA grant (NNX15AL53G) to D. L. K., and a NSF grant (EAR-1345060) and a NASA grant (NNX11AF58G) to M. E. Z. Parts of this work were carried out in the Characterization Facility, University of Minnesota, which is a member of the NSF-funded Materials Research Facilities Network (www.mrfn. org) via the MRSEC program. Electron microprobe analyses were carried out at the Electron Microprobe Laboratory, Department of Earth Sciences, University of Minnesota, Twin Cities, and some of the EBSD work at the Department of Geosciences of the University of Tromso, Norway. Data used in this paper are available in the main text and supporting information.

Publisher Copyright:
©2017. American Geophysical Union. All Rights Reserved.

Keywords

Zener pinning
deformation
olivine
phase mixing
pyroxene

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title = "Rheological Weakening of Olivine + Orthopyroxene Aggregates Due To Phase Mixing: Part 2. Microstructural Development",

abstract = "To understand the processes involved in phase mixing during deformation and the resulting changes in rheological behavior, we conducted torsion experiments on samples of iron-rich olivine plus orthopyroxene. The experiments were conducted at a temperature, T, of 1200°C and a confining pressure, P, of 300 MPa using a gas-medium deformation apparatus. Samples composed of olivine plus 26% orthopyroxene were deformed to outer radius shear strains up to γ ≈ 26. In samples deformed to lower strains of γ ≲ 4, elongated olivine and pyroxene grains form a compositional layering. Already by this strain, mixtures of small equant grains of olivine and pyroxene begin to develop and continue to evolve with increasing strain. The ratios of olivine to pyroxene grain size in deformed samples follow the Zener relationship, indicating that pyroxene grains effectively pin the grain boundaries of olivine and inhibit grain growth. Due to the reduction in grain size, the dominant deformation mechanism changes as a function of strain. The microstructural development forming more thoroughly mixed, fine-grained olivine-pyroxene aggregates can be explained by the difference in diffusivity among Me (Fe or Mg), O, and Si, with transport of MeO significantly faster than that of SiO2. These mechanical and associated microstructural properties provide important constraints for understanding rheological weakening and strain localization in upper mantle rocks.",

keywords = "Zener pinning, deformation, olivine, phase mixing, pyroxene",

author = "Miki Tasaka and Zimmerman, {Mark E} and Kohlstedt, {David L} and Holger St{\"u}nitz and Ren{\'e}e Heilbronner",

note = "Funding Information: We thank A. Dillman, J. Tielke, M. Pec, C. Qi, C. Meyers, and Z. Michels for helpful discussions and technical assistance, T. Hiraga and M. Morishige for valuable discussions, A. van der Handt for assistance of electron microprobe analyses, and B. Richter and N. Seaton for assistance of EBSD analysis. We thank L. Hansen for providing the original EBSD data in Hansen et al. (). The manuscript was significantly improved by insightful comments from two reviewers, R. Cooper and L. Hansen, and an Editor, M. Walter. This study was supported by a JSPS Research Fellowship for Young Scientists (26-4879) and the Japan Society for the Promotion of Science (16K17832) to M. T., a NASA grant (NNX15AL53G) to D. L. K., and a NSF grant (EAR-1345060) and a NASA grant (NNX11AF58G) to M. E. Z. Parts of this work were carried out in the Characterization Facility, University of Minnesota, which is a member of the NSF-funded Materials Research Facilities Network (www.mrfn.org) via the MRSEC program. Electron microprobe analyses were carried out at the Electron Microprobe Laboratory, Department of Earth Sciences, University of Minnesota, Twin Cities, and some of the EBSD work at the Department of Geosciences of the University of Tromso, Norway. Data used in this paper are available in the main text and supporting information. Funding Information: We thank A. Dillman, J. Tielke, M. Pec, C. Qi, C. Meyers, and Z. Michels for helpful discussions and technical assis tance, T. Hiraga and M. Morishige for valuable discussions, A. van der Handt for assistance of electron microprobe analyses, and B. Richter and N. Seaton for assistance of EBSD analysis. We thank L. Hansen for providing the origi nal EBSD data in Hansen et al. (2012). The manuscript was significantly improved by insightful comments from two reviewers, R. Cooper and L. Hansen, and an Editor, M. Walter. This study was supported by a JSPS Research Fellowship for Young Scientists (26-4879) and the Japan Society for the Promotion of Science (16K17832) to M. T., a NASA grant (NNX15AL53G) to D. L. K., and a NSF grant (EAR-1345060) and a NASA grant (NNX11AF58G) to M. E. Z. Parts of this work were carried out in the Characterization Facility, University of Minnesota, which is a member of the NSF-funded Materials Research Facilities Network (www.mrfn. org) via the MRSEC program. Electron microprobe analyses were carried out at the Electron Microprobe Laboratory, Department of Earth Sciences, University of Minnesota, Twin Cities, and some of the EBSD work at the Department of Geosciences of the University of Tromso, Norway. Data used in this paper are available in the main text and supporting information. Publisher Copyright: {\textcopyright}2017. American Geophysical Union. All Rights Reserved.",

year = "2017",

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AU - Tasaka, Miki

AU - Zimmerman, Mark E

AU - Kohlstedt, David L

AU - Stünitz, Holger

AU - Heilbronner, Renée

N1 - Funding Information: We thank A. Dillman, J. Tielke, M. Pec, C. Qi, C. Meyers, and Z. Michels for helpful discussions and technical assistance, T. Hiraga and M. Morishige for valuable discussions, A. van der Handt for assistance of electron microprobe analyses, and B. Richter and N. Seaton for assistance of EBSD analysis. We thank L. Hansen for providing the original EBSD data in Hansen et al. (). The manuscript was significantly improved by insightful comments from two reviewers, R. Cooper and L. Hansen, and an Editor, M. Walter. This study was supported by a JSPS Research Fellowship for Young Scientists (26-4879) and the Japan Society for the Promotion of Science (16K17832) to M. T., a NASA grant (NNX15AL53G) to D. L. K., and a NSF grant (EAR-1345060) and a NASA grant (NNX11AF58G) to M. E. Z. Parts of this work were carried out in the Characterization Facility, University of Minnesota, which is a member of the NSF-funded Materials Research Facilities Network (www.mrfn.org) via the MRSEC program. Electron microprobe analyses were carried out at the Electron Microprobe Laboratory, Department of Earth Sciences, University of Minnesota, Twin Cities, and some of the EBSD work at the Department of Geosciences of the University of Tromso, Norway. Data used in this paper are available in the main text and supporting information. Funding Information: We thank A. Dillman, J. Tielke, M. Pec, C. Qi, C. Meyers, and Z. Michels for helpful discussions and technical assis tance, T. Hiraga and M. Morishige for valuable discussions, A. van der Handt for assistance of electron microprobe analyses, and B. Richter and N. Seaton for assistance of EBSD analysis. We thank L. Hansen for providing the origi nal EBSD data in Hansen et al. (2012). The manuscript was significantly improved by insightful comments from two reviewers, R. Cooper and L. Hansen, and an Editor, M. Walter. This study was supported by a JSPS Research Fellowship for Young Scientists (26-4879) and the Japan Society for the Promotion of Science (16K17832) to M. T., a NASA grant (NNX15AL53G) to D. L. K., and a NSF grant (EAR-1345060) and a NASA grant (NNX11AF58G) to M. E. Z. Parts of this work were carried out in the Characterization Facility, University of Minnesota, which is a member of the NSF-funded Materials Research Facilities Network (www.mrfn. org) via the MRSEC program. Electron microprobe analyses were carried out at the Electron Microprobe Laboratory, Department of Earth Sciences, University of Minnesota, Twin Cities, and some of the EBSD work at the Department of Geosciences of the University of Tromso, Norway. Data used in this paper are available in the main text and supporting information. Publisher Copyright: ©2017. American Geophysical Union. All Rights Reserved.

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N2 - To understand the processes involved in phase mixing during deformation and the resulting changes in rheological behavior, we conducted torsion experiments on samples of iron-rich olivine plus orthopyroxene. The experiments were conducted at a temperature, T, of 1200°C and a confining pressure, P, of 300 MPa using a gas-medium deformation apparatus. Samples composed of olivine plus 26% orthopyroxene were deformed to outer radius shear strains up to γ ≈ 26. In samples deformed to lower strains of γ ≲ 4, elongated olivine and pyroxene grains form a compositional layering. Already by this strain, mixtures of small equant grains of olivine and pyroxene begin to develop and continue to evolve with increasing strain. The ratios of olivine to pyroxene grain size in deformed samples follow the Zener relationship, indicating that pyroxene grains effectively pin the grain boundaries of olivine and inhibit grain growth. Due to the reduction in grain size, the dominant deformation mechanism changes as a function of strain. The microstructural development forming more thoroughly mixed, fine-grained olivine-pyroxene aggregates can be explained by the difference in diffusivity among Me (Fe or Mg), O, and Si, with transport of MeO significantly faster than that of SiO2. These mechanical and associated microstructural properties provide important constraints for understanding rheological weakening and strain localization in upper mantle rocks.

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KW - phase mixing

KW - pyroxene

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