Onset of Double Subduction Controls Plate Motion Reorganization

Abstract

Face-to-face double subduction systems, in which two oceanic plates are subducted toward each other, are common elements of plate tectonics. Two subduction zones in such systems are typically uneven in age and their subduction dynamics vary both temporarily and spatially and remain enigmatic. Here we use 2D geodynamic numerical modeling to show that plate motion partitioning in these subduction systems is dynamically unstable and strongly varies in time. As the result of this instability, the waxing younger subduction zone may gradually absorb the plate convergence from the waning older one. Consequently, the trench of the older subduction zone may stop retreating and its subduction rate notably decreases. The stress state of the overriding plate and the mantle flow field between the two simultaneously active trenches reflect this dynamical transition from older subduction to younger subduction activity. Our results allow us to classify several different characteristic trench migration and overriding plate motion patterns between older and younger subduction, which provide a reference to interpret the past and predict the future evolution of several key double subduction regions found in modern Earth.