10:45 AM - 11:00 AM
[SCG50-07] The evolving structure and material of normal fault in Yonaguni Island, Okinawa prefecture, Japan
Keywords:The Okinawa Trough, Fault core, Damage zone, Vitrinite reflectance, Clay mineral, Yaeyama Group
Map-scale normal faults which trending NE-SW, NW-SE, and E-W directions are widely recognized in Yonaguni Island, the westernmost island of Japan, and these faults clearly displaces the ground surface which is composed of upper Pleistocene coral reef deposits (the Ryukyu Group). Since Yonaguni Island is surrounded by various tectonic elements such as the subducting Philippine sea plate (the Ryukyu trough), the spreading back-arc basin (the Okinawa trough), and the arc-continent
collision zone (Taiwan), it is important to know how and when these faults are created to understanding the tectonic process and crustal evolution of island arc. Thus, we have analyzed fault zone structure and paleo-thermal structure in the eastern coast of the island.
In the eastern coast of the island, one of the NE-SW trending faults is widely exposed along the shoreline. The fault zone strikes ENE-WSW direction and dipping 60 degree to the north. In the outcrop, the Ryukyu Group and the Yaeyama Group (middle Miocene) are distributed in the hanging wall and footwall, respectively, suggesting about 70 m normal offset after the deposition of the Ryukyu Group. ~3 m wide fault gouge and fault breccia zone is recognized between the hanging wall and footwall. Also ~40 m wide damage zone is developed in the footwall of the fault. In this presentation, we will discuss the temporal evolution of structure and material of the fault zone.
collision zone (Taiwan), it is important to know how and when these faults are created to understanding the tectonic process and crustal evolution of island arc. Thus, we have analyzed fault zone structure and paleo-thermal structure in the eastern coast of the island.
In the eastern coast of the island, one of the NE-SW trending faults is widely exposed along the shoreline. The fault zone strikes ENE-WSW direction and dipping 60 degree to the north. In the outcrop, the Ryukyu Group and the Yaeyama Group (middle Miocene) are distributed in the hanging wall and footwall, respectively, suggesting about 70 m normal offset after the deposition of the Ryukyu Group. ~3 m wide fault gouge and fault breccia zone is recognized between the hanging wall and footwall. Also ~40 m wide damage zone is developed in the footwall of the fault. In this presentation, we will discuss the temporal evolution of structure and material of the fault zone.