Double subduction-induced orogeny in Northeast Japan and ancient margins

Double subduction zones manifest in three distinct configurations: divergent double subduction (e.g., the Molucca Sea and Mediterranean subduction zones); convergent double subduction, characterized by regions with subduction zones dipping in opposite directions (e.g., the Caribbean Plate and Southeast Asia); and same-dip double subduction (SDDS). The SDDS system includes both ancient and active examples, such as the Mesozoic Neothetyan arc system and the late Cenozoic Nankai-Ryukyu/Izu-Bonin-Marianas SDDS. Recent studies have underscored the significant geodynamic effects of SDDS initiation, particularly its role in accelerating major plate motions. Investigations of the Ryukyu/Izu-Bonin-Marianas SDDS, where the Pacific Plate subducts beneath the Philippine Sea Plate, which in turn subducts beneath the Eurasian Plate along the Ryukyu-Nankai Trench, suggest that this system triggers steepening of the Pacific slab and advances the trench. These findings open exciting new possibilities for understanding active margin dynamics and the scale at which double subduction influences tectonics. While most SDDS research has concentrated on the direct effects within the zone of double plate convergence, the broader implications of SDDS on adjacent plate margin tectonics remain largely unexplored. To address this, we examine the geological evolution of Northeast Japan in connection with the fusion of the Philippine Sea Plate and the initiation of the Ryukyu/Izu-Bonin-Marianas SDDS, comparing this reconstructed evolution with new 3-D geodynamic models. Our results indicate that this SDDS system, pulling the Pacific trench westward, drives northward trench propagation and plate margin compression that affect both the Northeastern Japan arc and backarc regions. Therefore, the initiation of the Ryukyu/Izu-Bonin-Marianas SDDS around 10-5 Ma accounts for the puzzling origin of plate kinematics that facilitated non-collisional orogeny and backarc subduction initiation in Northeast Japan from 6-3.5 Ma. The orogenic effects of SDDS initiation reveal a novel mechanism by which subduction zones achieve the critical plate kinematic conditions necessary for non-collisional mountain building. These results not only provide valuable insights into the seismotectonic dynamics of Northeast Japan, a region known for its catastrophic megathrust and intraplate earthquakes, but also enhance our understanding of plate margin tectonics in relation to many proposed ancient SDDS systems.