Earthquakes, volcanoes and mountains result from the dynamic Earth, driven by mantle convection. This fundamental process that underlies all these very important phenomena is very poorly understood. The great advances in imaging the mantle’s seismic structure over the past few years (e.g. Figure 1a) provide powerful constraints on the dynamics. Mantle convection modellers can now utilise these constraints using mantle circulation models (MCMs). These MCMs predict the internal thermal and compositional structure. By using advanced mineralogy the present-day predictions of temperature and composition can be converted to seismic structure which can be compared with the seismic models, both their radial and lateral (Figure 1) structures.
Project Aims and Methods
The project aims to constrain the mantle’s dynamics, composition and thermal structure.
The student will do this by utilising mantle circulation models (MCMs) (Price et al, 2019; van Heck et al. 2016; Barry et al., 2016; Price and Davies, 2018), which are numerical mantle convection models driven with a surface velocity boundary condition provided by plate motion history (e.g. Müller et al., 2019). These are global spherical models which must be investigated using high performance computing. The resulting present-day composition and thermal structure predicted by the MCMs can be converted to a seismic structure (Figure 1 b and c) by using thermodynamic mineralogy databases (e.g. Stixrude and Lithgow-Bertelloni, 2011) which give a rigorous framework for incorporating all the relevant mineralogy research. In particular the student will look at the combination of both lateral and radial seismic variations. Radial seismic models (Cobden et al., 2009) are very well constrained but have not been explained within the context of global dynamic models. Equally, while lateral variations in seismic tomography studies have been compared with the outputs of MCMs (e.g. Davies et al., 2012) they did not also consider radial models. Further constraints will be provided by observations such as the topography of mantle seismic discontinuities at around 410 and 660 km depth (Cammarano and Romanowicz, 2007). There is flexibility in deciding which parameters and variations to investigate in the MCMs; and also which seismic data and mineralogy databases to bring to bear. These give the student the chance to design large elements of the project and choose the research direction.
This is a very timely project, given the recent advances in MCMs (thermo-composition), mineralogical experiments and computational toolkits (e.g. ENKI), and seismic studies, and will have a big impact in Earth sciences.
The candidate would ideally have a background either in the methods of modelling or deep Earth processes. The student would also need to have a desire to develop numerical modelling skills and relish the prospect of interacting with high performance computing, and multiple disciplines (modelling, mineralogy, seismology). The student could therefore come from a broad range of discipline backgrounds, including for example geophysics, mathematics, physics, engineering, geology, or computing.
The student will learn about the fields of mantle dynamics, mineralogy and seismology. As regards high-level skills, this project will provide ample opportunities to develop computing, programming, numerical modelling and high performance computing skills, e.g. running simulations on the National Supercomputer ARCHER 2. The student will also have access to a very wide range of University and DTP provisioned courses which will further enhance research and transferable skills. The student would be expected to attend at least one international conference, e.g. AGU in San Francisco; and at least one international workshop, e.g. CIDER, at Santa Barbara; and visit expert colleagues in the UK and overseas.
How to apply:
You should apply to the Doctor of Philosophy in Earth and Ocean Sciences with a start date of October 2020, including:
an upload of your CV
a personal statement/covering letter
two references (applicants are recommended to have a third academic referee, if the two academic referees are within the same department/school)
current academic transcripts.
In the research proposal section of your application, please specify the project title and supervisors of this project and copy the project description in the text box provided. In the funding section, please select ’I will be applying for a scholarship/grant’ and specify that you are applying for advertised funding from NERC GW4+ DTP.
If you wish to apply for more than one project please email [email protected]
The deadline for applications is 16:00 on 6 January 2020.
Shortlisting for interview will be conducted by 31 January 2020.
Shortlisted candidates will then be invited to an institutional interview. Interviews will be held in Cardiff University between 10 February and 21 February 2020.
Davies et al., Reconciling dynamic and seismic models of Earth's lower mantle: the dominant role of thermal heterogeneity. Earth and Planetary Science Letters, 353-54 , pp. 253-269, 2012;
Barry, T, Davies JH, et al. Whole-mantle convection with tectonics plates preserves long-term global patterns of upper mantle geochemistry, Scientific Reports, 7, 1870, 2017
Cammarano, F and Romanowicz B, Insights into the nature of the transition zone from physically constrained inversion of long-period seismic data, Proc. Nat. Acad. Sci. 104, 9139-9144, 2007.
Cobden et al., Thermochemical interpretation of 1-D seismic data for the lower mantle: The significance of nonadiabatic thermal gradients and compositional heterogeneity, J. Geophys. Res., 114, B11309, 2009.
Müller et al., A global plate model including lithospheric deformation along major rifts and orogens since the Triassic, Tectonics, 38, https://doi.org/10.1029/2018TC005462, 2019.
Price M, Davies JH and Panton J, Controls on the deep-water cycle within three-dimensional mantle convection models, Geoch. Geophys. Geosys., 20, https://doi.org/10.1029/2018GC008158, 2019
Price, MG and JH Davies, Profiling the robustness, efficiency and limits of the forward-adjoint method for 3D mantle convection modelling, Geophysical Journal International, 212, 1450-1462, 2018.
Stixrude and Lithgow-Bertelloni, Thermodynamics of mantle minerals – II. Phase equilibria, Geophys J Int, 184, 1180-1213, 2011.
van Heck, HJ, JH Davies, T Elliott, and D Porcelli, Global scale modelling of melting and isotopic evolution of Earth’s mantle, Geosci. Model Dev., 9, 1399-1411, doi:10.5194/gmd-9-1399-2016, 2016