Subduction development along extinct mid-ocean ridges versus weakened passive continental margins

Abstract

Where subduction zones develop is a fundamental issue in subduction dynamics. Intra-oceanic settings and continental margins are the main regions for subduction development, and various tectonic settings are further proposed based on these two categories, including extinct mid-ocean ridges and passive continental margins. Mid-ocean ridges often locate adjacent to passive continental margins since they formed in successive extension processes. However, it remains enigmatic how these two tectonic settings compete in terms of subduction initiation and development. Here, we use a 2-D numerical model to investigate how subduction develops in the tectonic setting where mid-ocean ridges and passive continental margins are juxtaposed. The results exhibit three oceanic plate subduction types: continental margin subduction, ridge-inversed subduction, and a transitional type featured by double subduction along ridges and margins. The physical parameters that influence the formation of the three types of subduction, including the geometry of weakened passive margins, the cooling age of extinct mid-ocean ridges, the direction and magnitude of convergence rates, and the ridge-margin distance, are systematically investigated. Small cooling ages, pushing from oceanic plates, short ridge-margin distances, and strong continental margins favor ridge-inversed subduction, while large cooling ages, pushing from overriding plates, long ridge-margin distances, and weakened continental margins facilitate continental margin subduction. We emphasize the importance of preexisting weakness along the passive margins, which primarily promote subduction development along margins. Our model results shed new light on the natural examples of subduction development along extinct mid-ocean ridges and weakened passive margins.