Impact of Aseismic Ridges on Subduction Systems: Insights From Analog Modeling

The influence of aseismic ridges on subduction kinematics and dynamics, and on the deformation of the overriding plate, remains a topic of debate. This study presents laboratory‐based geodynamic models that simulate the process of aseismic ridge subduction below an overriding plate. The analog experiments show that, depending on its size, subduction of an aseismic ridge can impact on the kinematics of subduction, overriding plate deformation and, to a lower extent, on the geometry of the slab and that of the trench. Specifically, it can cause a reduction of the subducting plate and trench retreat velocities, decreases overriding plate extension and even drives local forearc shortening for the widest ridge, increases the slab dip angle next to the aseismic ridge, but decreases the dip angle at the aseismic ridge in case the ridge is thick and wide, and produces a local perturbation (indentation) of the trench geometry. The magnitude of the described modifications relies to a comparable extent on aseismic ridge width and thickness. The effects of aseismic ridge subduction observed in our models compare to those of the Louisville Seamount Chain, the Cocos Ridge, and the d'Entrecasteaux Ridge system in nature and provide an explanation for the local deformation observed at these subduction zones. Plain Language Summary Subduction zones are locations where one tectonic plate sinks (subducts) beneath another plate. Beyond that simple definition, substantial differences have been documented for the current subduction systems around the globe. However, the factors controlling the different observed variables are still uncertain. One of these factors is the presence of submarine ridges on subducting oceanic plates, as these are relatively light features that reduce the bulk density of the sinking plates. What is the role of those ridges on the subduction process? We addressed this question by constructing laboratory models of subduction zones with aseismic ridges. Our experiments show that relatively large ridges allow subducting oceanic plates to sink more slowly into the Earth's mantle and remain relatively shallow. Nevertheless, these ridges cannot account for the extremely low angle at which some regions of the Nazca plate subduct below South America (the controversial “flat regions”). The margin of the overlying continental or oceanic plate is modified, developing a curvature in front of the ridges. Finally, the subduction of large ridges leads to local horizo