We combined the split cylinder technique with microfabrication technology to observe strain heterogeneities that were produced during high-pressure transient creep of Carrara marble. Samples were patterned with a custom-designed grid of markers spaced 10 µm apart and containing an embedded coordinate system. The microscale strain measurement (MSSM) technique described here allowed us to analyze the local strain distribution with unprecedented detail over large regions. The description of the strain field is a function of the area over which strain is being computed. The scale at which the strain field can be considered homogeneous can provide insight into the deformation processes taking place. At 400–500°C, when twinning production is prolific, we observe highly strained bands that span several grains. One possible cause for the multigrain bands is the need to relieve strain incompatibilities that result when twins impinge on neighboring grains. At 600–700°C, the strain fields are still quite heterogeneous, and local strain varies substantially within grains and near grain boundaries, but the multigrain slip bands are not present. Deformation is concentrated in much smaller areas within grains and along some grain boundaries. The disappearance of the multigrain slip bands occurs when the deformation conditions allow additional slip systems to be activated. At 600°C, when the total strain is varied from 0.11 to 0.36, the spatial scale of the heterogeneity does not vary, but there are increases in the standard deviation of the distribution of local strains normalized by the total strain; thus, we conclude that the microstructure does not achieve a steady state in this strain interval.
Bibliographical noteFunding Information:
All data necessary to evaluate and build upon this work are included in the figures and tables; the data can also be obtained in electronic form by contacting the authors. Funding was provided by NSF through grant EAR1451022. We thank Derek Hirst for help with sample preparation, as well as Kurt Broderick and Dennis Ward for their help at the MIT Microsystems Technology Laboratories. Fabrice Barou and David Mainprice are gratefully acknowledged for their help acquiring the EBSD data shown in Figure, as well as for their insightful comments on this work. A. Q.-T. thanks Mark Zimmerman, David Kohlstedt, and the members of the Rock and Mineral Physics Laboratory at the University of Minnesota for their hospitality. We benefited from enriching discussions with Matej Pec, William B. Durham, Ricardo A. Lebensohn, Guilhem Martin, and Taylor Perron and thoughtful reviews from Holger Stunitz, Chris Spiers, and Hans de Bresser.
©2016. American Geophysical Union. All Rights Reserved.
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- experimental rock deformation
- image analysis
- strain heterogeneity