| Description |
Synchrotron x-ray diffraction is used to analyze two sedimentary rock samples of different composition. Sample D1592 is made up of predominantly clay phases, and sample D1691 is mainly composed of calcite and quartz. Samples are loaded into a custom assembly specially made for this experiment that allows for lower pressure to be generated in a deformation DIA (D-DIA). Sample D1592 was deformed at a strain rate of 1.4E-3s-1 until 10% strain then increased to 2.6E-3s-1. Sample D1691 was deformed at a constant strain rate of 4.7E-3s-1. Synchrotron x-ray diffraction was used to track texture and lattice strain evolution and radiography was used to measure macrostrain and determine onset of failure. Sample D1592 displayed strongest texture before differential stress was applied to the sample due to the high phase percentages of illite-smectite (52%) and illite-mica (10%). Sample D1691 expressed mostly random textures in the quartz and calcite phases. Reorientation of clay phases in sample D1592, initially parallel to the compressional axis, was observed as texture randomized during compression, then began to reorient orthogonal to the compression axis. During initial quasi hydrostatic loading of sample D1592, fractures were oriented sub-vertically at an average angle of 13o. After decompression the average fracture angle was 27o and fractures were oriented sub-horizontally consistent with the pole figures. Sample D1691 had an average fracture angle of 21o after extension. Differential stress drops were used to identify failure of the sample due to fracturing and relate it to fracture sets on the radiography images. A brittle iv to ductile transition was observed in sample D1592 due to the high confining stresses and strain values, which reached up to 27%. Brittle deformation dominated sample D1691 partly due to lower confining stresses, but also a large volume proportion of calcite (60%) and quartz (19%) phases. Lower fracture angles were observed for higher amounts of clay content and clay preferred orientation, whereas higher angles were observed for low clay content or more random clay orientations. |
