Terrane collision-induced subduction initiation: Mode selection and implications for western Pacific subduction system

In the regime of plate tectonics, 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 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 the mechanical explanation for the numerical prediction of 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. It 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.