[SCG69-P03] Deformation experiments of chlorite at high pressures and temperatures: A preliminary study
Keywords:chlorite, high pressure, shear instability, intermediate-depth earthquakes
Uniaxial deformation experiments were conducted at 5 GPa, 230-800℃ using Deformation-DIA apparatuses at SPring-8 (BL04B1). Monochromatic X-rays (60 keV) were used as an incident beam to observe compression behavior, dehydration reaction, and deformation behaviors with recording AEs. The starting material is natural clinochlore from Brazil. We put a powder and a stacking of disk-shaped single crystals (c plane is perpendicular to the compression axis) in tandem in a hBN capsule. Au foils are placed at the upper and lower edges of the sample as a strain marker. Deformation experiments were carried out with a constant anvil displacement rate of 200 μm/h and a temperature ramping rate of 0.1K/s.
In the experiment at 5 GPa, the d004 spacing in clinochlore decreased during compression at room temperature and increased with heating. It decreased when the deformation started at 230℃, then increased again above ~500℃. Both powdered and single-crystal samples exhibited similar changes in values of d004. AEs were detected during cold compression, heating, and deformation, whereas no AEs were observed above ~400℃ including during dehydration. These AE activities may be related to the changes in the d004 spacing, although we did not observe the abrupt changes implying the structural transition. The strain rate and the final strain in the powdered sample (7.2e-5/s and 37%) were about 8-9 times larger than those of the disk-shaped single crystal sample (8.5e-6/s and 5%), suggesting the large difference in the deformation mechanism during the uniaxial compression. This may also cause the difference in AE activities, which will be discussed after the quantitative determination of AE locations. We are also planning to conduct shear deformation experiments, in which the c-plane of clinochlore is parallel to the shear plane, to investigate deformation-induced structural changes in the stacking layer and shear instability.