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The Rise and Fall of the Lower Mantle: Modelling Thermal Conductivity in Earth’s Interior


Project Description

Introduction

The Earth’s lower mantle is convecting, with cold slabs subducting and hot plumes rising. Surface expressions of this large-scale convection include earthquakes, volcanism, oceanic trenches, mid-ocean ridges and island arc chains. The key role of heat transport means that thermal conductivity is a fundamental parameter in controlling mantle processes. In addition, as the thermal conductivity of the mantle mediates heat-loss from the core, it will also have significant implications for the thermoevolution of the Earth (Lay et al., 2008) and magnetic field generation (Gubbins et al. 2011).

The importance of constraining the thermal conductivity of the mantle is reflected in the number of recent experimental investigations of major mantle phases (e.g. Ohta et al., 2012). While these are of some interest, technical limitations mean that measurements are restricted to temperatures far below those in the deep Earth and long extrapolations must be made to estimate values at mantle conditions. Theoretical calculations offer an invaluable alternative and have been used to determine the thermal conductivity of major mantle phases at high temperature (e.g. Amman et al., 2014; Stackhouse et al., 2015).

To date, almost all studies of the thermal conductivity of the lower mantle have focused on the pure magnesium end-members of major mantle phases (i.e. MgSiO3 bridgmanite and MgO periclase), which comprise the bulk of the mantle. However, most interesting processes in the mantle (e.g. subduction and mantle upwelling), involve regions that are expected to differ in composition from the bulk (e.g. subducting slabs, large low shear velocity provinces (LLSVP) and ultra-low velocity zones (ULVZs)). The aim of this project is to determine the thermal conductivity of these regions, by performing atomistic simulations. The results will provide constraints on two important mantle processes (subduction of slabs, plume generation) and be integrated with previous results to construct a complete model of the thermal conductivity of the mantle, for use in mantle dynamics models.

Proposed work

Lattice thermal conductivity will be calculated from non-equilibrium molecular dynamics simulations and Green-Kubo calculations, making use of the ab initio code VASP and the classical code LAMMPS. In addition, part of the project will involve looking into new methods.
The Leeds Earth Modeling Apparatus (LEMA) will be used to predict the implications of the calculated lattice thermal conductivity values on heat-flow in the lower mantle.

Training Environment

You will be trained in the application of atomistic simulations and high performance computing. In particular, you will be taught to perform density functional theory calculations, a method that is used widely in chemistry, physics, and materials science research. Alongside the transferable skills in communication and management this can open a range of career pathways. These skills will be developed by a mixture of hands on experience, attending external training courses, and taking part in the Leeds – York NERC doctoral training partnership programme. You will become a member of the University of Leeds Deep Earth Research Group, benefiting from interactions with other staff and students who have a range of interests and expertise.

Requirements

You will have a good first degree in the physical sciences (e.g. physics, chemistry, geophysics or related subject). The ideal candidate will also have experience of basic scientific programming and computation possibly derived from the completion of an undergraduate research project in the area. Experience performing atomistic simulations would be an advantage.

References

Ammann, M.W., Walker, A.M., Stackhouse, S., Wookey, J., Forte, A.M., Brodholt, J. and Dobson, D.P. 2014. Variation of thermal conductivity and heat flux at the Earth’s core mantle boundary. Earth Planet. Sci. Lett. 390, 175-185.

Gubbins, D., Sreenivasan, B., Mound, J. and Rost, S. 2011. Melting of the Earth’s inner core. Nature 473, 361-363.

Lay, T., Hernlund, J. and Buffet, B.A. 2008. Core-mantle boundary heat-flow. Nat. Geosci. 1, 25-32.

Ohta, K., Yagi, T., Taketoshi, N., Hirose, K., Komabayashi, T., Baba, T., Ohishi, Y. and Hernlund, J. 2012. Lattice thermal conductivity of MgSiO3 perovskite and post- perovskite at the core–mantle boundary. Earth Planet. Sci. Lett. 349, 109–115.

Stackhouse, S., Stixrude, L. and Karki, B.B., 2015. First-principles calculations of the lattice thermal conductivity of the lower mantle. Earth and Planet. Sci. Lett. 427, 11-17.

How good is research at University of Leeds in Earth Systems and Environmental Sciences?

FTE Category A staff submitted: 79.20

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