Articles | Volume 8, issue 4
Method article
10 Jul 2017
Method article |  | 10 Jul 2017

Microscale and nanoscale strain mapping techniques applied to creep of rocks

Alejandra Quintanilla-Terminel, Mark E. Zimmerman, Brian Evans, and David L. Kohlstedt

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, TTm, 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.

Short summary
Modeling natural deformation requires a good understanding of how the microscale and mesoscale properties of rocks affect bulk deformation. However, describing strain accommodation at a range of scales during rock deformation is an experimental challenge. We developed a novel technique that allows us to map strain down to the microscale. This technique was successfully applied to high-pressure, high-temperature deformation experiments and could be applied to a wide variety of geomaterials.