Rotated Transtensional Basins Formed During Back-Arc Spreading in Japan: Simultaneous Rapid Tectonic Rotation and Basin Subsidence

Previous models of strike-slip basins do not consider the rotation of the basin itself; however, we show that the Tanakura transtensional basin in Japan was rotated and propose that this basin rotation was related to rifting caused by back-arc spreading. The Tanakura Basin was formed by displacement along the Tanakura Fault Zone, one of the major active transform faults during the opening of the Sea of Japan. We carried out paleomagnetic analyses and U-Pb dating of the Neogene Tanakura Basin fill rocks. We present a revised, high-precision stratigraphic record for the Neogene Tanakura Basin fill sequence shows that verticalaxis counter-clockwise rotation occurred between similar to 17.2 and similar to 16.6 Ma. Comparison with paleomagnetic data from adjacent areas shows that rotation was restricted to the basin. In addition, the timing of basin rotation corresponds to the rifting phase of the Tanakura Basin, suggesting that rapid basin subsidence owing to rifting and rapid basin rotation owing to strike-slip faulting occurred simultaneously. The Tanakura Basin has the characteristics of both rift and transtensional basins that have experienced rotation. This study reveals the detailed relationships between the development and rotation of the Tanakura Basin: rifting-related subsidence accompanied by basin rotation. Rifting owing to back-arc spreading may have been accompanied by tectonic basin rotation in Northeast Japan, leading to variations in the magnitude and age of rotation, as the rifting occurred at different times in different locations.