High-resolution mantle flow models reveal importance of plate boundary geometry and slab pull forces on generating tectonic plate motions

Plate tectonics can explain several geological and geophysical phenomena on Earth, and a number of mantle flow models have been developed to investigate the underlying plate tectonic forces. However, these models have come to contradictory conclusions on the balance between the resisting and driving forces. Additionally, they have used the same simplified model to represent the geometry of the plates, and therefore the impact of plate boundary geometry on surface deformation remains unknown.

To address these issues, we have developed high-resolution global instantaneous mantle convection models based on recent geophysical constraints with a heterogeneous density and viscosity distribution and weak plate boundaries prescribed using different plate boundary configurations. We find a good fit to the observed GPS data for models with plate boundaries that are 3 to 4 orders of magnitude weaker than the surrounding lithosphere and low asthenospheric viscosities between 5×10¹⁷ and 5×10¹⁸ Pa s for all plate boundary configurations. We also find that the model with plate boundaries defined by the Global Earthquake Model (GEM, Pagani et al., 2018)—featuring open plate boundaries with discrete lithospheric-depth weak zones in the oceans and distributed crustal faults within continents—achieves the best fit to the observed GPS data with a directional correlation of 95.1% and a global point-wise velocity residual of 1.87 cm/year. These results show that Earth’s plate boundaries are not uniform and better described by more discrete plate boundaries within the oceans and distributed faults within continents.

Our models also quantify the contributions to the plate driving forces originating from heterogeneities in the upper mantle and the lower mantle, respectively, finding that the slab-pull in the top 300 km alone contributes ~70% of the total plate speeds. Noting the importance of slab pull as a major plate driving force, we further investigate the influence of subduction zone and slab geometry on surface plate motions and their fit to GPS data. Specifically, our models compare a simplified slab structure to a more detailed representation of slabs based on the Slab2 database (Hayes et al., 2018), and reaffirm that a realistic slab geometry is a crucial factor in the transmission of slab pull forces to the plate.