Mantle Structure Assessed from Tomography Models Coupled with Thermodynamic Constraints

Abstract:

The origin of the seismic velocity anomalies imaged by tomography models is still under debate. Could it be mainly thermal? Which part is due to compositional differences? One of the main recent scientific advances is the design of new higher-resolution tomography models. The amplitude of the velocity anomalies from these new models is much larger than the amplitude of the previous generation of tomography models. Another major scientific advance is the assembly of thermodynamic databases, which allow a more realistic interpretation of tomography models. When we couple the new tomography models with thermodynamic constraints and assume a purely thermal origin for the seismic velocity variations, we obtain lateral temperature variations on the order of ±1000K. This unrealistic range forces us to consider the effect of compositional variation on seismic velocities. Within this study we explore a wide range of mantle compositions and derive for each of them the physical properties, such as the seismic velocities, densities and temperatures. We provide a range of possible mantle structures, with different partitioning between thermal and chemical origin, in agreement with the observed seismic velocities and the thermodynamic constraints.