Rheological controls on the plate-mantle system using Earth-like mantle models

Earth’s interior plays an important role in the long-term evolution of the surface, climate and biosphere. Rheology is the cornerstone of mantle convection and tectonics, and constraining mantle viscosity has been a priority in the geodynamic community. In this study, we employ fully self-consistent and three-dimensional Earth-like mantle convection models^[1]. The mantle rheology is temperature-, pressure- and stress-dependent. Plate-like behaviour in global mantle models can be obtained using a pseudo-plastic rheology^[2]. Rheology in some of our models also depends on phase and creep mechanism. As in previous work^[3], this is implemented by using laboratory values for activation energy and activation volume for the upper mantle and an analytical fit to experimental data for the lower mantle. The novelty of this work lies in employing a composite rheology with “realistic” rheological parameters in a fully three-dimensional geometry. Using these more realistic models, we aim to improve our understanding of mantle rheology in the context of self-consistent generation of plate-like behaviour. To achieve this, slab sinking rates will be computed that can be compared to estimates based on tomography^[4], which is a relatively new source of constraint^[5]. The tectonic mode depends on the plastic yield stress. In turn, the yield stress parameter space for a plate-like regime depends on whether continents, phase-dependent rheology and dislocation creep are considered. Thus, the yield stress and reference viscosity parameter spaces must first be explored for each rheological model. Generally, we observe that lower yield stresses lead to higher surface mobilities. On top of high surface mobility (deformation), plate-like behaviour asks for localisation of deformation in narrow zones. Plateness is a widely used measure for this, which we find to be high for models with sufficiently low yield stresses. Furthermore, preliminary results show that models with phase-dependent rheology are more likely to be in a plate-like regime compared to models without a viscosity jump between the upper and lower mantle. Lastly, we hypothesise that the slab sinking speed may be highly sensitive to rheology and may be affected by the presence of continents.

 

^[1] Tackley, P. J. (2008). Modelling compressible mantle convection with large viscosity contrasts in a three-dimensional spherical shell using the yin-yang grid. Physics of the Earth and Planetary Interiors, 171(1–4), Article 1–4.

^[2] Moresi, L., & Solomatov, V. (1998). Mantle convection with a brittle lithosphere: Thoughts on the global tectonic styles of the Earth and Venus. Geophysical Journal International, 133(3), 669–682.

^[3] Tackley, P. J., Ammann, M., Brodholt, J. P., Dobson, D. P., & Valencia, D. (2013). Mantle dynamics in super-Earths: Post-perovskite rheology and self-regulation of viscosity. Icarus, 225(1), 50–61.

^[4] Van der Meer, D. G., Van Hinsbergen, D. J., & Spakman, W. (2018). Atlas of the underworld: Slab remnants in the mantle, their sinking history, and a new outlook on lower mantle viscosity. Tectonophysics, 723, 309-448.

^[5] Van Der Wiel, E., Van Hinsbergen, D. J. J., Thieulot, C., & Spakman, W. (2024). Linking rates of slab sinking to long-term lower mantle flow and mixing. Earth and Planetary Science Letters, 625, 118471.