Terrane Collision-Induced Subduction Initiation: Mode Selection and Implications for Western Pacific Subduction System

In the regime of plate tectonics, the subduction of an oceanic plate generally terminates with the collision and accretion of continental terranes. Then, a new subduction zone may form in the neighboring oceanic plates, which is defined as the terrane collision-induced subduction initiation (SI). Based on the analyses of the western Pacific subduction system in the Cenozoic, three types of collision-induced SI have been observed: subduction polarity reversal, subduction transference and far-field subduction. However, the dynamics and controlling factors of SI mode selection after terrane collision are not clear. In this study, a multi-terrane collision model has been conducted with variable rheological strength of continental terranes and different convergence velocities. The model results indicate that the relative strength of the terranes controls the SI mode selection, with the new subduction zone tending to form beneath weaker terranes. In addition, the higher convergence velocity can facilitate the collision-induced SI. An analytical study of force balance has been further conducted, which provides a mechanical explanation for the numerical prediction of a weak overriding terrane as a favorable SI site. The numerical models and force balance analyses are further compared with the natural cases in the western Pacific subduction system. This indicates that subduction polarity reversal is the most favorable mode after terrane collision in the western Pacific, possibly due to the weakness of overriding plate during the preceding subduction-induced fluid/melt activity. This comprehensive study provides systematic constraints for the dynamics of collision-induced subduction jump, especially for the western Pacific subduction zones in the Cenozoic. The Earth's rocky surface is composed of both oceanic and continental crusts. The oceanic plate is denser and can sink into the Earth's interior as a subducting slab. A specific subduction process terminates when the whole oceanic plate is consumed and the neighboring continental blocks collide together. Then, the continued convergence may lead to the formation of a new subduction zone in the neighboring oceanic plate; however, the localization of new subduction zone varies. In the western Pacific subduction system in the Cenozoic, a new subduction zone may form in three different positions of the overriding and subducting plates. The mode selection of the new subduction zone formation plays an important role in Earth's plate tectonic evolution; however, its mechanism is not clear. In this study, systematic numerical models and force balance analyses have been conducted, which indicate that the relative strength of the continental blocks controls the position of new subduction zone formation, which favors the formation beneath weaker blocks. This prediction is further confirmed by the natural cases in the western Pacific system. This comprehensive study improves our understanding of the formation of new subduction zones as well as the more general subduction dynamics and plate tectonics. Terrane collision may lead to three different modes of subduction jump: polarity reversal, transference, and far-field subduction The collision-induced subduction initiation prefers to occur beneath the rheologically weak overriding terrane Subduction polarity reversal is the dominant mode in the western Pacific due to the widely distributed rheologically weak island arc