5:15 PM - 6:45 PM
[SSS05-P16] Geological study of strain release mechanism at plate boundary fault
Keywords:MBT, Bedding plane slip, Shear plane, Microstructure observation, Frictional heating
The purpose of our research is to understand the geological phenomena that occur at plate boundaries as a result of plate subduction. For this purpose, I conducted a geological survey at the hanging wall side of MBT (main boundary thrust), which developed by the collision of the Indian and Asian continents. And more the microstructures of the collected rock samples were observed. The studied area is the MBT exposed at Sabathu, Himachal Pradesh, India.
The important result of the geological survey reveals the numerous traces of slip on the bedding plane. And the duplex structures developed parallel to the bedding plane are also observed. The slip direction and the maximum main compression axis, which are obtained from the slip line direction and the kink bands, are usually nearly parallel to the dip direction of the MBT. These results strongly suggest that the bedding plane slip occurs predominantly during plate subduction.
The slip lines, often accompanied by fine grained quartz veins, are commonly often observed on the slip surface. The microstructural observation indicates that the quartz veins come from the quartz grains composed of the sandstone. This result strongly suggests that the quartz grains were deformed plastically due to frictional heating caused by bedding plane slip. The crystallographic orientation of the quartz grains in the veins was measured by EBSD. And more, the recrystallized quartz grains of the veins were estimated by the EBSD mapping. From these data, the strain rate of the quartz grains, namely bedding plane slip was determined. The results are 10-10~10-13 /s and 10-5~10-7 /s.
This study suggests that some of the strain caused by plate subduction is likely to be released by the bedding plane slip and the frictional heat generated by the slip.
The important result of the geological survey reveals the numerous traces of slip on the bedding plane. And the duplex structures developed parallel to the bedding plane are also observed. The slip direction and the maximum main compression axis, which are obtained from the slip line direction and the kink bands, are usually nearly parallel to the dip direction of the MBT. These results strongly suggest that the bedding plane slip occurs predominantly during plate subduction.
The slip lines, often accompanied by fine grained quartz veins, are commonly often observed on the slip surface. The microstructural observation indicates that the quartz veins come from the quartz grains composed of the sandstone. This result strongly suggests that the quartz grains were deformed plastically due to frictional heating caused by bedding plane slip. The crystallographic orientation of the quartz grains in the veins was measured by EBSD. And more, the recrystallized quartz grains of the veins were estimated by the EBSD mapping. From these data, the strain rate of the quartz grains, namely bedding plane slip was determined. The results are 10-10~10-13 /s and 10-5~10-7 /s.
This study suggests that some of the strain caused by plate subduction is likely to be released by the bedding plane slip and the frictional heat generated by the slip.