5:15 PM - 6:45 PM
[SCG41-P01] Middle Miocene or younger dextral faulting along the Tanakura Fault Zone, Japan: Constraints from the structural and geochronological analyses
★Invited Papers
Keywords:Tanakura Fault Zone, Opening of the Sea of Japan, zircon, apatite, radiometric Dating, cataclasite
The Tanakura Fault Zone (TFZ) was one of the main strike-slip faults associated with the formation and spreading of back-arc basins related to the opening of the Sea of Japan. Constraining the history of the TFZ during this period is important for understanding the separation and migration of the Japanese islands from the Asian continent. In this study, we examine the activity of the TFZ since the Miocene using data obtained from field investigations along the TFZ, structural and provenance analysis of deformed Miocene conglomerate, and thermal history modeling using zircon and apatite radiometric dating for the cataclasite.
The results of the investigation and analyses suggest the following: 1) The deformed conglomerate along the fault show apparently deformed ductilely shapes, but they were formed by the combined processes of weathering, compaction, and cataclastic deformation related to dextral faulting along the Tanakura Western Marginal Fault (TWMF). The deformed gravels are composed of crushed clasts and grains, and thermal analyses indicates that they were not underwent later heating. Elongation of the clasts by cataclastic deformation is recognized at locations where a P foliation (P shear) has developed in response to dextral faulting along the TWMF. 2) Cataclasite samples contain Paleozoic zircons, suggesting that some of the clasts were derived from the Paleozoic Hitachi Metamorphic Rocks. The analyzed cataclasite sample site and the Hitachi Metamorphic Rocks are far from each other. Since they must have been adjacent to each other at the time of the deposition of the conglomerate. It is likely that the Tanakura Fault Zone (especially the Tanakura Eastern Marginal Fault (TEMF)) underwent right lateral displacement after the formation of the Miocene conglomerate. 3) Fault outcrop observations indicate subhorizontal dextral movement on the TWMF. Based on all of the above data obtained in the study, both the TWMF and the TEMF must have undergone right lateral movement after the deposition of the Miocene conglomerate (i.e., after 16–15 Ma).
The results of the investigation and analyses suggest the following: 1) The deformed conglomerate along the fault show apparently deformed ductilely shapes, but they were formed by the combined processes of weathering, compaction, and cataclastic deformation related to dextral faulting along the Tanakura Western Marginal Fault (TWMF). The deformed gravels are composed of crushed clasts and grains, and thermal analyses indicates that they were not underwent later heating. Elongation of the clasts by cataclastic deformation is recognized at locations where a P foliation (P shear) has developed in response to dextral faulting along the TWMF. 2) Cataclasite samples contain Paleozoic zircons, suggesting that some of the clasts were derived from the Paleozoic Hitachi Metamorphic Rocks. The analyzed cataclasite sample site and the Hitachi Metamorphic Rocks are far from each other. Since they must have been adjacent to each other at the time of the deposition of the conglomerate. It is likely that the Tanakura Fault Zone (especially the Tanakura Eastern Marginal Fault (TEMF)) underwent right lateral displacement after the formation of the Miocene conglomerate. 3) Fault outcrop observations indicate subhorizontal dextral movement on the TWMF. Based on all of the above data obtained in the study, both the TWMF and the TEMF must have undergone right lateral movement after the deposition of the Miocene conglomerate (i.e., after 16–15 Ma).