The Topographic Signature of Mantle Pressure Build‐Up Beneath Subducting Plates: Insights From Spherical Subduction Models.

Subduction zones are associated with spatially heterogeneous pressure fields that, depending on location, push/pull on Earth's surface producing dynamic topography (DT). Despite this, subduction zones, and associated pressure fields, are typically over‐simplified within global mantle flow models. Here, I use subduction models within a global domain to probe mantle pressure build‐up beneath subducting plates (SPs) and the resulting DT. Positive pressure develops beneath the SP in most subduction models. This produces positive DT (≤450 m) and tilts the SP upwards toward the trench (≤0.25 m/km). As SP size increases, the pressure magnitude increases producing greater topography/tilting. At a global scale, I find potential evidence for the modeled tilting in published residual topography. I argue that the rigorous incorporation of subduction zones into mantle flow models, and hence the inclusion of this signal, is needed to continue to bring future DT predictions and observational estimates into closer alignment. Plain Language Summary: Over millions of years, the solid mantle behaves as a fluid and its movement causes Earth's outer surface to deform (producing "dynamic" topography). Computational models of this movement are now able to match the main features of observational estimates of dynamic topography (DT), but models and observations do not match in all regions. Here, I explore whether a component of this mismatch could be due to a simplified treatment of subduction zones (i.e., plate boundaries where one tectonic plate descends beneath another) in these models. I create and analyze subduction models to isolate the topographic signature of subduction, focusing on topography above the subducting oceanic plate. In the models, mantle material gets trapped beneath the plate, which pushes up on the surface and produces positive topography. This upwards‐push also tilts the plate up toward the subduction zone. On average, this plate tilt appears to be present within observational estimates of Earth's DT, but more detailed future work is needed to confirm this. Key Points: Positive dynamic pressure develops beneath subducting plates in subduction models within global domainsSlab dip is inversely correlated with the magnitude of this positive pressureThis pressure produces positive oceanic dynamic topography and tilts the plate upwards toward the trench [ABSTRACT FROM AUTHOR]