10:45 AM - 12:15 PM
[SGL23-P04] Fault rock analysis in the Southern Fossa Magna Multiple Collision Zone
Keywords:Kanagawa prefecture, fault rock, Foliated cataclasite
The Southern Fossa Magna area is known as the site where the Izu-Ogasawara arc on the Philippine Sea plate collides with the Honshu arc, and is proposed as a multiple collision zone between island arcs (Amano, 1986). The main geology consists of volcanic rocks, which are collision masses originating from the oceanic plate, and sedimentary rocks from the Neogene period onward that fill in between the volcanic rocks. The Ashigara Group, which is distributed in the western part of Kanagawa Prefecture and the eastern part of Shizuoka Prefecture, is a trough-filling deposit of the Pliocene to Pleistocene age (Imanaga, 1999). It has been reported that conglomerates of the Ashigara Group Shiozawa Formation, which is distributed near the Tanzawasachi district in Kanagawa Prefecture, have been deformed as cataclysite by faulting (Kobayashi and Kokawa, 2014). Deformation of conglomerates in collision zones has also been reported from the Hamashidake Formation of the Fuji River Group in the lower reaches of the Fuji River in eastern Shizuoka Prefecture (Suzuki and Kobayashi, 2019), which may have recorded events associated with collision. Therefore, in this study, various analyses were conducted on deformed conglomerates developed within the Shiozawa Formation.
The deformed conglomerates in the Shiozawa Formation were found to be more deformed toward the upper part of the formation. Since cataclasite deformation is usually accelerated by increasing pressure and temperature toward deeper underground (Sibson, 1983; C Passchier and R Trouw, 1995), the fact that deformation is more pronounced in the upper layers where pressure decreases suggests that local temperature increase or pressure increase may be responsible for the deformation. On the other hand, the deformation of the Shiozawa Formation is not so remarkable. On the other hand, it is reported that the depth of deposition of the Shiozawa Formation is less than 1 km (Arai and Ito, 1997). Therefore, the formation of the cataclysite at such a shallow depth is a very unique geologic body.
The temperature of formation of clay minerals was used to estimate the thermal conditions of the Shiozawa Formation by XRD analysis. In addition, Raman spectroscopy was performed using charcoal in sedimentary rocks to determine the temperature environment from two viewpoints. The results show no clear difference in the temperature environment between the conglomerate with significant deformation and the conglomerate that is not deformed. The clay minerals are mainly rich in smectite, which indicates a relatively low temperature environment. The depth of cataclasite formation was estimated to be shallow, since smectite is formed more significantly in oxidizing environments. Raman spectroscopy was based on Koukethu et al (2014) to determine the degree of crystallinity of the carbonates. The results of both XRD analysis and Raman spectroscopy indicate that there is no clear temperature variation within the formation, and the entire formation is assumed to be under uniform temperature conditions. Based on the above, it is concluded that the Shiozawa Formation has been successively formed at shallow depths and at low temperatures (around 150 to 200c) throughout the formation.
In this study, the temperature and environment for the diagenesis of cataclasite formation in the Shiozawa Formation were determined. The future direction of the analysis is to focus on the discussion of the pressure surface. As specific methods, comparison of deformation conditions by the Rf-dia method and estimation of internal strain of quartz by the X-ray powder diffraction method are in mind.
The deformed conglomerates in the Shiozawa Formation were found to be more deformed toward the upper part of the formation. Since cataclasite deformation is usually accelerated by increasing pressure and temperature toward deeper underground (Sibson, 1983; C Passchier and R Trouw, 1995), the fact that deformation is more pronounced in the upper layers where pressure decreases suggests that local temperature increase or pressure increase may be responsible for the deformation. On the other hand, the deformation of the Shiozawa Formation is not so remarkable. On the other hand, it is reported that the depth of deposition of the Shiozawa Formation is less than 1 km (Arai and Ito, 1997). Therefore, the formation of the cataclysite at such a shallow depth is a very unique geologic body.
The temperature of formation of clay minerals was used to estimate the thermal conditions of the Shiozawa Formation by XRD analysis. In addition, Raman spectroscopy was performed using charcoal in sedimentary rocks to determine the temperature environment from two viewpoints. The results show no clear difference in the temperature environment between the conglomerate with significant deformation and the conglomerate that is not deformed. The clay minerals are mainly rich in smectite, which indicates a relatively low temperature environment. The depth of cataclasite formation was estimated to be shallow, since smectite is formed more significantly in oxidizing environments. Raman spectroscopy was based on Koukethu et al (2014) to determine the degree of crystallinity of the carbonates. The results of both XRD analysis and Raman spectroscopy indicate that there is no clear temperature variation within the formation, and the entire formation is assumed to be under uniform temperature conditions. Based on the above, it is concluded that the Shiozawa Formation has been successively formed at shallow depths and at low temperatures (around 150 to 200c) throughout the formation.
In this study, the temperature and environment for the diagenesis of cataclasite formation in the Shiozawa Formation were determined. The future direction of the analysis is to focus on the discussion of the pressure surface. As specific methods, comparison of deformation conditions by the Rf-dia method and estimation of internal strain of quartz by the X-ray powder diffraction method are in mind.