TY - JOUR A1 - Tutu, Anthony Osei A1 - Steinberger, Bernhard A1 - Sobolev, Stephan Vladimir A1 - Rogozhina, Irina A1 - Popov, Anton A. T1 - Effects of upper mantle heterogeneities on the lithospheric stress field and dynamic topography JF - Solid earth N2 - 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 3-D lithosphere–asthenosphere 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 (WSM2016) and the observation-based residual topography. We derive the upper mantle thermal structure from either a heat flow model combined with a seafloor 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. The modeled stress field directions, using only the mantle heterogeneities below 300 km, are not perturbed much when the effects of lithosphere and crust above 300 km are added. In contrast, modeled stress magnitudes and dynamic topography are 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 good correlation of 0.51 in continents, but this correction leads to no significant improvement of the fit between the WSM2016 and the resulting lithosphere stresses. In continental regions with abundant heat flow data, TM1 results in relatively small angular misfits. For example, in western Europe the misfit between the modeled and observation-based stress is 18.3°. Our findings emphasize that the relative contributions coming from shallow and deep mantle dynamic forces are quite different for the lithospheric stress field and dynamic topography. Y1 - 2018 U6 - https://doi.org/10.5194/se-9-649-2018 SN - 1869-9510 SN - 1869-9529 VL - 9 IS - 3 SP - 649 EP - 668 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Tutu, Anthony Osei A1 - Sobolev, Stephan Vladimir A1 - Steinberger, Bernhard A1 - Popov, A. A. A1 - Rogozhina, Irina T1 - Evaluating the Influence of Plate Boundary Friction and Mantle Viscosity on Plate Velocities JF - Geochemistry, geophysics, geosystems N2 - Lithospheric plates move over the low-viscosity asthenosphere balancing several forces, which generate plate motions. We use a global 3-D lithosphere-asthenosphere model (SLIM3D) with visco-elasto-plastic rheology coupled to a spectral model of mantle flow at 300 km depth to quantify the influence of intra-plate friction and asthenospheric viscosity on plate velocities. We account for the brittle-ductile deformation at plate boundaries (yield stress) using a plate boundary friction coefficient to predict the present-day plate motion and net rotation of the lithospheric plates. Previous modeling studies have suggested that small friction coefficients (mu < 0.1, yield stress similar to 100 MPa) can lead to plate tectonics in models of mantle convection. Here we show that in order to match the observed present-day plate motion and net rotation, the frictional parameter must be less than 0.05. We obtain a good fit with the magnitude and orientation of the observed plate velocities (NUVEL-1A) in a no-net-rotation (NNR) reference frame with mu < 0.05 and a minimum asthenosphere viscosity of similar to 5 . 10(19) Pas to 10(20) Pas. Our estimates of net rotation (NR) of the lith-osphere suggest that amplitudes similar to 0.1-0.2 (degrees/Ma), similar to most observation-based estimates, can be obtained with asthenosphere viscosity cutoff values of similar to 10(19) Pas to 5 . 10(19) Pas and friction coefficients mu < 0.05. Y1 - 2018 U6 - https://doi.org/10.1002/2017GC007112 SN - 1525-2027 VL - 19 IS - 3 SP - 642 EP - 666 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Mulyukova, Elvira A1 - Steinberger, Bernhard A1 - Dabrowski, Marcin A1 - Sobolev, Stephan Vladimir T1 - Survival of LLSVPs for billions of years in a vigorously convecting mantle: Replenishment and destruction of chemical anomaly JF - Journal of geophysical research : Solid earth N2 - We study segregation of the subducted oceanic crust (OC) at the core-mantle boundary and its ability to accumulate and form large thermochemical piles (such as the seismically observed Large Low Shear Velocity Provinces (LLSVPs)). Our high-resolution numerical simulations of thermochemical mantle convection suggest that the longevity of LLSVPs for up to three billion years, and possibly longer, can be ensured by a balance in the rate of segregation of high-density OC material to the core-mantle boundary (CMB) and the rate of its entrainment away from the CMB by mantle upwellings. For a range of parameters tested in this study, a large-scale compositional anomaly forms at the CMB, similar in shape and size to the LLSVPs. Neutrally buoyant thermochemical piles formed by mechanical stirringwhere thermally induced negative density anomaly is balanced by the presence of a fraction of dense anomalous materialbest resemble the geometry of LLSVPs. Such neutrally buoyant piles tend to emerge and survive for at least 3Gyr in simulations with quite different parameters. We conclude that for a plausible range of values of density anomaly of OC material in the lower mantleit is likely that it segregates to the CMB, gets mechanically mixed with the ambient material, and forms neutrally buoyant large-scale compositional anomalies similar in shape to the LLSVPs. KW - LLSVPs KW - thermochemical modeling KW - segregating oceanic crust KW - mantle convection Y1 - 2015 U6 - https://doi.org/10.1002/2014JB011688 SN - 2169-9313 SN - 2169-9356 VL - 120 IS - 5 SP - 3824 EP - 3847 PB - American Geophysical Union CY - Washington ER -