17:15 〜 19:15
[SCG62-P18] Effects of quartz deformation lamellae on strain hardening revealed by HR-EBSD
キーワード：変形ラメラ、歪硬化、低温塑性変形、HR-EBSD、GND密度、石英
The strength of the crust is greatest in the brittle-plastic transition zone, which has been linked to the occurrence of large inland earthquakes. This zone corresponds to the depth range where plastic deformation of quartz begins. However, at relatively low temperatures, dislocation movement is restricted, and recovery is limited. Consequently, dislocation density within the crystal is expected to increase with strain, leading to strain hardening. Therefore, understanding the strain-hardening process associated with low-temperature plastic deformation in quartz is crucial. To investigate this strain-hardening process, we focused on the potential role of deformation lamellae of quartz. These lamellae form in the early stages of deformation and have been identified as kink bands through crystallographic analysis [1]. The formation of kink bands has been suggested to influence dislocation movement by increasing the number of interfaces that can potentially act as barriers to dislocation glide, thereby contributing to strain hardening. Therefore, it is essential to crystallographically investigate the details of the interfaces formed by the deformation lamellae and assess their influence on dislocation motion.
We analyzed the crystallographic relationships of quartz deformation lamellae and the distribution of geometrically necessary dislocations (GNDs) using high-angular resolution electron backscatter diffraction (HR-EBSD). The analysed samples are quartz veins from the Chichibu Belt (Akaragi Pass) in the central Shikoku Mountains [1]. The peak metamorphic temperature of the pelitic schist containing the quartz veins is estimated to have been 290°C by Raman spectroscopic thermometry of carbonaceous materials [2]. The EBSD mapping was performed at an accelerating voltage of 20 kV with a step size of 0.75–1 µm. In the HR-EBSD method, the cross-correlation processing of the Kikuchi band images has the dual benefit of improving the angular resolution to about 0.005° and also enabling the mapping of elastic strains [3]. These rotations and elastic strains can respectively be used to calculate GND densities of each dislocation type and residual stresses.
The observed deformation lamellae are characterized by straight structures with widths ranging from 1-20 µm, exhibiting kink bands. The deformation lamellae exhibit misorientation of 4–12° relative to the surrounding matrix. These are formed primarily by dislocations on slip systems with Burgers vectors, such as basal edge dislocations or screw dislocations. Additionally, chessboard-like structures are present and are formed by subgrain boundaries with misorientations of approximately 10° due to dislocations with Burgers vectors and 0.5–2° due to dislocations with Burgers vectors. The GND densities, considering all types of dislocation, are on the order of 1013 m-2 within the matrix, whereas they increase to approximately 1015 m-2 around the lamellae. This difference suggests that dislocation motion is impeded by the deformation lamellae due to dislocation storage and enhanced dislocation interactions. Furthermore, local residual stresses formed by deformation lamellae were estimated to be around 1.5 GPa.
Moving forward, we aim to quantitatively assess the extent to which deformation lamellae contribute to strain hardening. This will be achieved using the slip-transmission method, which enables the investigation of dislocation transmission across the lamellae.
References
[1] O. Nishikawa and T. Takeshita, 1999, Tectonophysics, 301, 21-34.
[2] S. Endo and S. R. Wallis, 2017, J. Metamorph. Geol., 35, 695-716.
[3] D. Wallis et al., 2019, J. Geophys. Res. Solid Earth, 124, 6337-6358.
We analyzed the crystallographic relationships of quartz deformation lamellae and the distribution of geometrically necessary dislocations (GNDs) using high-angular resolution electron backscatter diffraction (HR-EBSD). The analysed samples are quartz veins from the Chichibu Belt (Akaragi Pass) in the central Shikoku Mountains [1]. The peak metamorphic temperature of the pelitic schist containing the quartz veins is estimated to have been 290°C by Raman spectroscopic thermometry of carbonaceous materials [2]. The EBSD mapping was performed at an accelerating voltage of 20 kV with a step size of 0.75–1 µm. In the HR-EBSD method, the cross-correlation processing of the Kikuchi band images has the dual benefit of improving the angular resolution to about 0.005° and also enabling the mapping of elastic strains [3]. These rotations and elastic strains can respectively be used to calculate GND densities of each dislocation type and residual stresses.
The observed deformation lamellae are characterized by straight structures with widths ranging from 1-20 µm, exhibiting kink bands. The deformation lamellae exhibit misorientation of 4–12° relative to the surrounding matrix. These are formed primarily by dislocations on slip systems with Burgers vectors, such as basal edge dislocations or screw dislocations. Additionally, chessboard-like structures are present and are formed by subgrain boundaries with misorientations of approximately 10° due to dislocations with Burgers vectors and 0.5–2° due to dislocations with Burgers vectors. The GND densities, considering all types of dislocation, are on the order of 1013 m-2 within the matrix, whereas they increase to approximately 1015 m-2 around the lamellae. This difference suggests that dislocation motion is impeded by the deformation lamellae due to dislocation storage and enhanced dislocation interactions. Furthermore, local residual stresses formed by deformation lamellae were estimated to be around 1.5 GPa.
Moving forward, we aim to quantitatively assess the extent to which deformation lamellae contribute to strain hardening. This will be achieved using the slip-transmission method, which enables the investigation of dislocation transmission across the lamellae.
References
[1] O. Nishikawa and T. Takeshita, 1999, Tectonophysics, 301, 21-34.
[2] S. Endo and S. R. Wallis, 2017, J. Metamorph. Geol., 35, 695-716.
[3] D. Wallis et al., 2019, J. Geophys. Res. Solid Earth, 124, 6337-6358.