Modeling geoid and dynamic topography from tomography-based thermo-chemical mantle convection with temperature- and depth-dependent viscosity

Abstract

Mantle convection causes the most important contribution to the geoid and dynamic topography. With high resolution tomography models and numerical simulation methods solving the governing equations of mantle convection, the model geoid can fit well compared to observation. However, if wave speed variations are converted to density variations assuming both are due to temperature variation in the entire mantle, there is still a large discrepancy between the present dynamic topography predicted by mantle flow and that induced from observations: Especially large negative topography is predicted in cratons, contrary to observations. In order to improve the fit of model dynamic topography compared to observations, chemical density anomaly in earth’s lithosphere need to be included. In this study, we will combine these with lateral viscosity structure and study the effect on model dynamic topography and geoid, and investigate which density models would yield a good fit. In the sublithospheric mantle, under the assumption that the density anomalies are thermally induced from temperature variation in the mantle, we use temperature-dependent viscosity. We also include thermo-chemical density anomalies in the Large low-shear-velocity provinces (LLSVPs) in the lowermost mantle to compute their effect on the model geoid and dynamic topography. Our overall objective is a better constraint on the Earth’s interior structure, by achieving good fits of both dynamic topography and geoid to their observations, to provide as a good reference for the Earth’s study.