Research highlight

Plate tectonics is a phenomenon unique to our planet, and complex life would not exist without it. Significant scientific efforts have been made over the past two decades to better understand this phenomenon to give us a first-order understanding of the plates' different driving and resisting forces. Since then, advancements in numerical techniques and the availability of extensive observational data have enabled the development of more sophisticated models, providing deeper insights into plate tectonics and the associated surface expressions. Some key questions include: what is the impact of plate boundary geometry on surface deformation? How do differing slab structures govern plate motions? What are the relative effects of surface topography, upper-mantle structure, and lower-mantle structure on stresses along plate boundaries?

To address these questions, we are developing self-consistent global mantle flow models that incorporate non-linear material properties and realistic plate boundary geometry with adaptive mesh with a minimum cell size of approximately 8 km (Figure 1). We use ASPECT that interfaces with Geodynamic World Builder and allows us to prescribe complex geometries in our models. Our models integrate heterogeneity from the surface to the core-mantle boundary across several geoscience disciplines, including observed surface topography, variations in crustal and lithospheric thickness, plate boundaries and crustal faults from the Global Earthquake Model (Pagani et al., 2018), sub-lithospheric mantle structures from a global tomography model, and subducted slab geometries based on the Slab2 model (Hayes et al., 2018).

Due to the inherent uncertainties, we vary mantle rheology parameters to optimize the fit to observed plate deformation and to quantify the relative importance of mantle-driving forces. In our first series of models (Saxena et al., 2023), we investigate the influence of different plate boundary models on the observed plate motions. Our findings (Figure 2) indicate that the Earth’s plate boundaries are not uniform; they are better characterized by discrete shear zones in oceanic regions and distributed faults within continental areas. This emphasizes the essential role of plate boundary geometry in determining the direction and speed of plate motions. In our current model series, we include well-resolved slab structures from the Slab2 model. We find that a low-viscosity mid-mantle layer (660–1000 km depth) is required for slabs to effectively transfer slab pull forces to the surface plates and resolve the present-day plate motions. Currently, we are investigating the influence of surface topographic variations in our best-fitting model, allowing us to compute an Earth-like stress state.

Our models give us a realistic approximation to the present-day physical state of the Earth’s mantle and can be used as global constraints for regional studies of plate boundary dynamics and surface processes or as a starting guess for backward integration to understand the thermal and geological evolution of the Earth.

Contributed by: Arushi Saxena, University of California Davis

References

Bird, P. (2003). An updated digital model of plate boundaries. Geochemistry, Geophysics, Geosystems, 4 (3).

Hayes, Gavin P., Ginevra L. Moore, Daniel E. Portner, Mike Hearne, Hanna Flamme, Maria Furtney, and Gregory M. Smoczyk. "Slab2, a comprehensive subduction zone geometry model." Science 362, no. 6410, 2018. DOI: https://doi.org/10.1126/science.aat4723

Saxena, Arushi, Juliane Dannberg, Rene Gassmöller, Menno Fraters, Timo Heister, and Richard Styron. "High‐resolution mantle flow models reveal importance of plate boundary geometry and slab pull forces on generating tectonic plate motions." Journal of Geophysical Research: Solid Earth 128, no. 8, 2023. DOI: https://doi.org/10.1029/2022JB025877

Pagani, M., Garcia-Pelaez, J., Gee, R., Johnson, K., Poggi, V., Styron, R., . . . Monelli, D. Global earthquake model (GEM) seismic hazard map. Creative Commons Attribution-Non Commercial-Share Alike 4.0 International License (CC BY-NC-SA), 2018.