Abstract
Abstract. Usually several deformation mechanisms interact to accommodate plastic deformation. Quantifying the contribution of each to the total strain is necessary to bridge the gaps from observations of microstructures, to geomechanical descriptions, to extrapolating from laboratory data to field observations. Here, we describe the experimental and computational techniques involved in microscale strain mapping (MSSM), which allows strain produced during high-pressure, high-temperature deformation experiments to be tracked with high resolution. MSSM relies on the analysis of the relative displacement of initially regularly spaced markers after deformation. We present two lithography techniques used to pattern rock substrates at different scales: photolithography and electron-beam lithography. Further, we discuss the challenges of applying the MSSM technique to samples used in high-temperature and high-pressure experiments. We applied the MSSM technique to a study of strain partitioning during creep of Carrara marble and grain boundary sliding in San Carlos olivine, synthetic forsterite, and Solnhofen limestone at a confining pressure, Pc, of 300 MPa and homologous temperatures, T∕Tm, of 0.3 to 0.6. The MSSM technique works very well up to temperatures of 700 °C. The experimental developments described here show promising results for higher-temperature applications.
Highlights
During plastic deformation of a crystalline material, strain is accommodated by a variety of deformation mechanisms, including atomic diffusion, mechanical twinning, grain boundary sliding, and dislocation glide, climb, and cross slip, which may operate separately or in combination
We describe a technique for microscale strain measurement (MSSM), which permits strain mapping at micrometer and submicrometer scales, and discuss several observations of strain partitioning in rocks deformed at high pressures and temperatures
Patterning using photolithography and e-beam lithography can provide maps of strain calculated over spatial scales of 10–0.5 μm
Summary
During plastic deformation of a crystalline material, strain is accommodated by a variety of deformation mechanisms, including atomic diffusion, mechanical twinning, grain boundary sliding, and dislocation glide, climb, and cross slip, which may operate separately or in combination. Simplified flow laws are established by assuming specific micromechanical models corresponding to the prevalent mechanisms and using experimental data to fit the material constants in the theoretical flow laws (Ashby, 1972; Frost and Ashby, 1982) Such simplified flow laws are a useful first step for the extrapolation of laboratory results to larger-scale geomechanical problems, but it is possible that the relative activity of the various deformation processes might change significantly when extended to natural conditions of rate, mean pressure, chemical environment, and temperature. We describe a technique for microscale strain measurement (MSSM), which permits strain mapping at micrometer and submicrometer scales, and discuss several observations of strain partitioning in rocks deformed at high pressures and temperatures.
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