Trench-parallel mid-ocean ridge subduction driven by along-strike transmission of slab pull

Abstract Trench-parallel mid-ocean ridge (MOR) subduction is observed and/or predicted on the present Earth and during geological history. Slab break-off normally occurs after such a MOR subduction, leading to an absence of local slab pull. The driving force of such MOR subduction is a puzzling issue. We realize that the MOR is generally dislocated by transform faults, which means that the MOR does not enter the trench simultaneously along strike. In this case, the slab pull does not vanish simultaneously along the entire subduction zone. Consequently, the trench-parallel MOR subduction may be driven by along-strike transmission of neighboring slab pull. We tested this idea using a series of 3-D, high-resolution numerical models. The results indicate that the transform fault (TF) and fracture zone (FZ) should not be too weak in order for the lateral transmission of slab pull. Such rheological strength of a TF/FZ is consistent with observation-based inferences and rheological analyses. In addition, the thermal structure and strength of oceanic plates neighboring the MOR also affect the MOR subduction: faster spreading MOR in a younger plate leads to easier subduction. Based on the model results and geological constraints, we propose a self-driven MOR subduction model, which highlights the role of along-strike transmission of slab pull during diachronic entry of MOR into the trench.