Time-resolved in Situ Stress and Strain Measurements Using a CdTe Photon-counting Detector: A Technical Development for Experiments on Time-dependent Rheological Properties of Rocks at High Pressures and Temperatures

To understand the processes of time-dependent phenomena such as transient creep and brittle failure, a WidePIX CdTe photon-counting detector was installed at the BL04B1, SPring-8. The detector enables the exposure time to be shortened for acquiring high-energy two-dimensional X-ray diffraction patterns of minerals. In situ triaxial deformation experiments on olivine aggregates were conducted at pressures 1-3 GPa and temperatures 760-1150 K using a deformation-DIA apparatus, installed at BL04B1, SPring-8. Two-dimensional X-ray diffraction patterns (40 s of exposure time for each image) and radiographic images (2 s for each) were alternately acquired by adjusting the sizes of the incident slit and operating a CdTe detector equipped with a CMOS camera using a high-energy monochromatic X-ray beam (energy ∼60 keV). Pressure and differential stress were determined from the d-spacing of olivine. Strain at a deforming sample was evaluated from the distance between platinum strain markers, which were placed at both ends of the sample. Yield of the deforming sample was clearly recognized at strains of less than 0.05 and apparent steady-state strength was achieved at strains of ∼0.1 or higher. The CdTe detector combined with a CMOS camera is a powerful tool for understanding the process controlling the time-dependent rheological phenomena such as transient creep and brittle failure at high pressures.