Dynamics of mantle convection with realistic rheology

"Convection in rocky or icy planetary mantles controls the long-term evolution of the terrestrial planets and many of the moons in the solar system. The style of mantle convection is intimately linked to planetary habitability: it determines whether surface material participates in the global-scale dynamics (as on Earth) or remains isolated (as on Venus) and also determines the viability of magnetic field generation in the liquid core. The rich and complex dynamics exhibited by the terrestrial planets arise since the physical properties that characterise mantle material are enormously sensitive to small changes in temperature, pressure and composition. The nonlinear feedbacks between transport properties (e.g. thermal conductivity and viscosity) and flow dynamics are most prevalent in the upper and lower regions of the mantle, the so-called boundary layers, and it is the behaviour in these regions that is largely responsible for the diversity of planetary behaviour and evolution. The overall aim of this project is to quantitatively analyse the boundary layer dynamics of mantle convection using computer simulations that couple fluid dynamics with state-of-the-art transport properties obtained from mineral physics.

Boundary layers are thin regions at the top and bottom of a convecting system where temperature, composition and flow change dramatically in order to meet externally-imposed conditions. These regions are thought to control the efficiency of heat transfer into and out of the mantle and therefore dictate the long-term thermal evolution of terrestrial planets. There have been extensive efforts to build physical models of heat transfer in mantle boundary layers using results from numerical simulations of varying complexity, but the results are extremely varied and lead to dramatically different predictions when applied to planets. The discrepancy centres on the treatment of material properties, specifically thermal conductivity and viscosity. Most studies that focus on boundary layer dynamics assume that these properties vary with depth and/or with temperature. However, the reality is that mantle properties will depend strongly on chemical composition as well as the stable mineral phase at a given location. These dependencies are now being revealed by mineral physics calculations constrained by seismic observations of deep Earth structure. The time is ripe to use this information in fluid dynamical models to elucidate the role of realistic material properties in determining the dynamics and evolution of mantle convection.

You will undertake numerical simulations of mantle convection with spatially-varying thermal conductivity and viscosity. You will use these models to quantify heat transfer and flow dynamics with a view to developing simplified models of the fundamental physics. The first stage is to begin with 2D models and simple parameterizations of the material properties since this is the configuration used by most previous studies. Using the 2D model you will systematically add more complex dependencies between material and thermodynamic properties, approaching the predictions made by mineral physics calculations. This understanding will permit a numerical study of the 3D case where statistical measures of boundary layer behaviour can be compared with observations of the Earth, and boundary layer heat-flux can be used to explore the long-term evolution of the terrestrial planets"

http://www.nercdtp.leeds.ac.uk/projects/index.php?id=509