Effects of upper mantle heterogeneities on lithospheric stress field and dynamic topography

Abstract

Abstract. The orientation and tectonic regime of the observed crustal/lithospheric stress field contribute to our knowledge of different deformation processes occurring within the Earth's crust and lithosphere. In this study, we analyze the influence of the thermal and density structure of the upper mantle on the lithospheric stress field and topography. We use a 3D lithosphereasthenosphere numerical model with power-law rheology, coupled to a spectral mantle flow code at 300 km depth. Our results are validated against the World Stress Map 2016 and the observation-based residual topography. We derive the upper mantle 5 thermal structure from either a heat flow model combined with a sea floor age model (TM1) or a global S-wave velocity model (TM2). We show that lateral density heterogeneities in the upper 300 km have a limited influence on the modeled horizontal stress field as opposed to the resulting dynamic topography that appears more sensitive to such heterogeneities. There is hardly any difference between the stress orientation patterns predicted with and without consideration of the heterogeneities in the upper mantle density structure across North America, Australia, and North Africa. In contrast, we find that the dynamic 10 topography is to a greater extent controlled by the upper mantle density structure. After correction for the chemical depletion of continents, the TM2 model leads to a much better fit with the observed residual topography giving a correlation of 0.51 in continents, but this correction leads to no significant improvement in the resulting lithosphere stresses. In continental regions with abundant heat flow data such as, for instant, Western Europe, TM1 results in relatively a small angular misfits of 18.30

On the amplitude of dynamic topography at spherical harmonic degree two

“…However, this improvement comes at the expense of deteriorating fits to the geoid. Finally, in the scenario including LVV above 300 km (Osei Tutu et al, 2017; Osei Tutu et al), we consider plastic yielding with friction coefficient 0.5 in plate interiors and yield stresses that are reduced along plate boundaries, with friction coefficient 0.03, such that the surface velocity field becomes approximately plate-like. We set a minimum viscosity cutoff 10 18 Pa s within the asthenosphere and maximum viscosity of 10 24 Pa s in the lithosphere.…”

“…(b) Predicted dynamic topography using a purely radial viscosity profile with density anomalies generated from SL2013sv tomography model above 200 km and TX2011 below (Schaeffer and Lebedev, 2013;Grand, 2002). (c) Version that also includes the effect of lateral viscosity variations above 300 km (Osei Tutu et al, 2017). All maps are expanded to maximum spherical harmonic degree lmax = 31.…”

Controls on Asymmetric Rift Dynamics: Numerical Modeling of Strain Localization and Fault Evolution in the Kenya Rift

“…Our models neither represent magmatic processes like diking and underplating, nor surface processes, dynamic topography, plume‐related lithosphere erosion, or 3D effects. Since deeply sourced dynamic topography is excluded from the model, about 1–2 km elevation has to be added when comparing the model results to topography in nature (Faccenna et al., 2019; Moucha & Forte, 2011; Osei Tutu et al., 2018). Another limitation is the uncertainty in radiogenic heat, that has a big impact on deformation patterns and wide or narrow rifting styles (Jaupart et al., 2016), mainly because it affects the thicknesses of the viscous and brittle layers in the upper and lower crust.…”

Evaluating the Influence of Plate Boundary Friction and Mantle Viscosity on Plate Velocities

“…At each time step we calculate the net rotation of the lithosphere and plate velocities in the no-net-rotation reference frame. This study's modeling technique is also complemented with the calculation of the lithosphere stress field and dynamic surface topography (Osei Tutu et al, 2017), which are used to evaluate the influence of the crustal and upper mantle heterogeneities on the observed lithosphere stress field and the corresponding topography beneath air.…”