Slab dip angle variation controlled by evolving lateral pressure gradients

The dip angle of subducting slabs is one of the key factors controlling mantle flow and upper-plate tectonic evolution. In the extreme case, flat subduction forms when the dip angle of the slab is less than 15°. Although this scenario accounts for only about 10% of the present-day global subduction system, it has profound geological significance for continental tectonic evolution, magmatic activities, and mantle–crust interactions. Previous studies have proposed multiple mechanisms influencing the evolution of slab dip, with the proposed controlling factors including the properties of the overriding plate, the buoyancy of the subducting slab, and plate convergence rates; however, a unified dynamical understanding has not yet been established. Based on a global geodynamical model with data assimilation that systematically simulates subduction evolution over the past 200 Ma, we quantitatively investigate the relationship between slab dip and its dynamical origin. We select representative subduction systems in East Asia, South America, and North America to analyze the evolution of slab dip over time from subduction initiation to termination.

The results reveal a new mechanism controlling slab dip angle: dynamic pressure in the mantle wedge. As subduction proceeds, the dynamic pressure in the mantle wedge generally decreases, leading to an increasing pressure difference across the subducting slab; this directly reduces the slab dip angle over time, as confirmed from all subduction zones considered. More tests show that the lateral pressure difference also fluctuates with time, with the slab dip angle demonstrating the same variation, further confirming their causal relationship. We conclude that this lateral force represents an important new mechanism driving changes in slab dip.