Assessing the effect of weak tectonic plate boundaries in 3D global mantle circulation models

A key characteristic of plate tectonics is strain localization along narrow, weak boundaries between otherwise rigid tectonic plates. This localization enables efficient deformation, subduction, and plate motion, and plays a central role in the dynamic evolution of Earth. However, in mantle circulation models, plate velocities are often assimilated as surface boundary conditions without accounting for the rheological weakness of plate boundaries, relative to the surrounding lithosphere.

Weak plate boundaries can be reproduced via sophisticated strain weakening rheologies. While effective, this strategy makes the Stokes system nonlinear and incurs substantial computational cost.

Here, we exploit the fact that data assimilation implies that the locations of plate boundaries are known a priori and introduce specifically prescribed weak zones along plate boundaries in the models. These low-viscosity zones allow us to mimic the natural strain localization of Earth’s lithosphere, allowing deformation to focus at plate margins. We show that this approach can provide a computationally efficient and robust framework for bridging the gap between simplified convection models and the complex tectonic behavior of the real Earth.