The Impact of Double Subduction on Plate Velocity and Euler Pole Shifts: Insights From Spherical Subduction Models

Abstract

Same‐dip double subduction (SDDS), in which two parallel slabs dip in the same direction, has been linked to accelerated plate motion in both modern and ancient convergent systems, such as the Late Cretaceous Africa–Eurasia system. Yet a systematic framework for quantifying how SDDS alters plate kinematics in a large‐scale spherical geometry is lacking. Here, we use 3‐D spherical geodynamic models to investigate plate velocity changes and corresponding Euler pole shifts caused by the insertion of a second (rear) subduction zone. Across a wide range of rheological and geometric parameters, SDDS consistently increases the velocity of the subducting plate, especially behind the rear trench, redirects subducting‐plate motion toward the rear slab, and produces pronounced Euler pole shifts of up to 33 ° ${}^{\circ}$ (∼3,600 km). We complement the numerical models with a torque‐balance analysis, which shows that these dramatic plate velocity changes arise from two primary effects: (a) additional slab pull exerted by the added slab and (b) a reduction in the effective subducting‐plate area contributing to basal‐drag resistance. This plate‐area reduction is the dominant contributor to Euler pole displacement, with enhanced slab pull providing a secondary but reinforcing effect. We characterize the impact of an extensive set of model parameters: plate and mantle rheology primarily modify velocity magnitudes, while geometric factors that modify plate and trench geometry govern the relative velocity differences (e.g., Euler pole shifts) between the single‐ and double‐subduction geometries. Our spherical subduction modeling provides a generalized geodynamic framework for interpreting plate‐motion reorganizations associated with intra‐oceanic subduction initiation and termination.