2:30 PM - 2:45 PM
[SGL23-04] Paleo-stress indicated by sandstone dikes intruding into the Miocene Hokusetsu Subgroup in eastern Aichi Prefecture
Keywords:Sandstone dike, Paleo-stress, Miocene, Hokusetsu Subgroup
Based on the geological structure of sedimentary basins formed in Southwest Japan during the opening of the Sea of Japan, it is considered that Southwest Japan was under widespread extensional stress during the formation of these sedimentary basins. In the Hokusetsu Subgroup, which is one of the basins, analysis of faults in the northern part of the sedimentary basin (Shidara Basin) suggests that the area was under NW-SE extensional stress during sedimentation (Fournier et al., 1995). However, the exact timing of this tensile field and whether the entire Shidara Basin was in a tensile field during deposition have not been clarified.
In the area around the Median Tectonic Line (MTL) in the southeastern part of the Shidara Basin, sandstone dikes trending NE-SW are intruded into the Shimoda Formation of the lower Hokusetsu Subgroup (Irizuki and Takahashi, 1997; Yabuta et al., 2024). The source of these sandstone dikes has been identified as the Umedaira Sandstone Member of the upper part of the Shimoda Formation (Yabuta et al., 2024). The direction of stress at the time of intrusion can be estimated from the direction of the dikes, including clastic dikes (e.g., Yamaji, 2012), and it is thought that it is also possible to estimate the paleo-stress in the Hokusetsu Subgroup using sandstone dikes. The aim of this study is to clarify the attitude and form of these sandstone dikes in detail and to estimate the paleo-stress at the time of intrusion.
First, we conducted field surveys in the southeastern part of the Hokusetsu Subgroup basin to clarify the attitude and form of sandstone dikes in the area. Next, we applied a stress analysis method using the mixed Bingham distribution method (Yamaji and Sato, 2011) to a planar sandstone injectites. We used GArcmB (Yamaji, 2016), stress analysis software that uses the mixed Bingham distribution method, to analyze the stress of the dikes.
The results of the field survey show that the sandstone dikes in the study area are basically planar dikes with clear boundaries with the host rock, and the width of the dikes is 1 to 80 cm. These sandstone dikes form parallel dikes with a NE–SW strike and a nearly vertical dip and are parallel to the MTL in the study area. The sandstone dikes are concentrated in an area about 2 km north-west of the MTL and extend in a NE–SW direction for about 2 km parallel to the MTL. They are also distributed 3.5 km north-west of the MTL. On the other hand, it was found that the attitude and form of the sandstone dikes differs depending on the distance from the source bed, the Umedaira Sandstone Member. Near the Umedaira Sandstone Member (around Sd-3), sandstone dikes dip at middle angular in addition to vertical, and intrusion surfaces show unclear boundaries or curved. In addition to these dikes, composite injections of dikes and sills are also observed. Stress analysis was carried out using a total of 51 intrusion surface attitude data obtained from these injectites, and as a result, stress indicating NW–SE direction extension was measured, as well as stress that differed from this. We will discuss the paleo-stress at the time these sand injectites were formed, including the differences in intrusion morphology according to distance from the source.
[Reference]
Fournier, M., Jolivet, L. and Fabbri, O., 1995, Neogene stress field in SW Japan and mechanism of deformation during the Sea of Japan opening. Journal of Geophysical Research: Solid Earth, 100, no. B12, 24295-24314.
Irizuki, T., and Takahashi, T., 1997, Forecast of clastic veins in the Shidara Group in the eastern part of the Horaiji Mountains. Bulletin of the Houraijisan Museum of Natural History, 26, 23–29.
Yabuta, S., Takeuchi, M., Asahara, Y. and Li, Q., 2024, Clarification of the source sandstone of sandstone dikes based on the occurrence of sandstone dikes intruding into the Miocene Hokusetsu Subgroup and detrital zircon U–Pb ages of sandstone dikes. 131st Ann. Meet. Geol. Soc. Japan, Abstr., T15-P-18.
Yamaji, A., 2012, A historical review of the methods for inferring paleostresses from dike orientations. J. Geol. Soc. Japan, 118, 335–350.
Yamaji, A., 2016, Generic algorithm for fitting a mixed Bing-ham distribution to 3D orientations: a tool for the statistical and paleostress analyses of fracture orientations. Isl. Arc, 25, 72–83.
Yamaji, A. and Sato, K., 2011, Clustering of fracture orientations using a mixed Bingham distribution and its application to paleostress analysis from dike or vein orientations. J. Struct. Geol., 33, 1148–1157.
In the area around the Median Tectonic Line (MTL) in the southeastern part of the Shidara Basin, sandstone dikes trending NE-SW are intruded into the Shimoda Formation of the lower Hokusetsu Subgroup (Irizuki and Takahashi, 1997; Yabuta et al., 2024). The source of these sandstone dikes has been identified as the Umedaira Sandstone Member of the upper part of the Shimoda Formation (Yabuta et al., 2024). The direction of stress at the time of intrusion can be estimated from the direction of the dikes, including clastic dikes (e.g., Yamaji, 2012), and it is thought that it is also possible to estimate the paleo-stress in the Hokusetsu Subgroup using sandstone dikes. The aim of this study is to clarify the attitude and form of these sandstone dikes in detail and to estimate the paleo-stress at the time of intrusion.
First, we conducted field surveys in the southeastern part of the Hokusetsu Subgroup basin to clarify the attitude and form of sandstone dikes in the area. Next, we applied a stress analysis method using the mixed Bingham distribution method (Yamaji and Sato, 2011) to a planar sandstone injectites. We used GArcmB (Yamaji, 2016), stress analysis software that uses the mixed Bingham distribution method, to analyze the stress of the dikes.
The results of the field survey show that the sandstone dikes in the study area are basically planar dikes with clear boundaries with the host rock, and the width of the dikes is 1 to 80 cm. These sandstone dikes form parallel dikes with a NE–SW strike and a nearly vertical dip and are parallel to the MTL in the study area. The sandstone dikes are concentrated in an area about 2 km north-west of the MTL and extend in a NE–SW direction for about 2 km parallel to the MTL. They are also distributed 3.5 km north-west of the MTL. On the other hand, it was found that the attitude and form of the sandstone dikes differs depending on the distance from the source bed, the Umedaira Sandstone Member. Near the Umedaira Sandstone Member (around Sd-3), sandstone dikes dip at middle angular in addition to vertical, and intrusion surfaces show unclear boundaries or curved. In addition to these dikes, composite injections of dikes and sills are also observed. Stress analysis was carried out using a total of 51 intrusion surface attitude data obtained from these injectites, and as a result, stress indicating NW–SE direction extension was measured, as well as stress that differed from this. We will discuss the paleo-stress at the time these sand injectites were formed, including the differences in intrusion morphology according to distance from the source.
[Reference]
Fournier, M., Jolivet, L. and Fabbri, O., 1995, Neogene stress field in SW Japan and mechanism of deformation during the Sea of Japan opening. Journal of Geophysical Research: Solid Earth, 100, no. B12, 24295-24314.
Irizuki, T., and Takahashi, T., 1997, Forecast of clastic veins in the Shidara Group in the eastern part of the Horaiji Mountains. Bulletin of the Houraijisan Museum of Natural History, 26, 23–29.
Yabuta, S., Takeuchi, M., Asahara, Y. and Li, Q., 2024, Clarification of the source sandstone of sandstone dikes based on the occurrence of sandstone dikes intruding into the Miocene Hokusetsu Subgroup and detrital zircon U–Pb ages of sandstone dikes. 131st Ann. Meet. Geol. Soc. Japan, Abstr., T15-P-18.
Yamaji, A., 2012, A historical review of the methods for inferring paleostresses from dike orientations. J. Geol. Soc. Japan, 118, 335–350.
Yamaji, A., 2016, Generic algorithm for fitting a mixed Bing-ham distribution to 3D orientations: a tool for the statistical and paleostress analyses of fracture orientations. Isl. Arc, 25, 72–83.
Yamaji, A. and Sato, K., 2011, Clustering of fracture orientations using a mixed Bingham distribution and its application to paleostress analysis from dike or vein orientations. J. Struct. Geol., 33, 1148–1157.