Interpreting in situ x-ray diffraction data from high pressure deformation experiments using elastic plastic self-consistent models: an example using quartz

We present synchrotron x-ray diffraction observations from a deformation experiment on fine-grained polycrystalline quartz using the newly developed deformation DIA apparatus. During deformation experiments we were able to observe the elastic strain of the (100), (101) and (112) lattice reflections. The elastic strains are typically converted into stresses and interpreted in terms of the differential stress supported by the specimen. Consistently with results from others obtained using this technique to deform monomineralic polycrystals, our results show substantial variations in stress levels between grain populations. Rather than averaging the lattice reflection stresses or choosing a single reflection to determine the macroscopic stress supported by the specimen, we explore the use of elastic-plastic self-consistent (EPSC) models. We are able to match the measured differential elastic lattice strains with an EPSC model in which basal and prism \langle

a\rangle slips are activated. An interesting outcome of the EPSC model is the prediction that the macroscopic stress experienced by the sample should be greater than the stress calculated from any of the reflections that we observed. This observation serves as a caution against using reflection stresses as a proxy for the macroscopic stress in in situ deformation experiments.