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This project is eligible for support from Cardiff Universtiy through the School of Earth & Ocean Sciences.

To apply, please visit the Cardiff University Postgraduate Research portal: http://www.cardiff.ac.uk/for/prospective/postgraduate/applying.html

Description

Mantle convection drives plate tectonics and as a result is critical in controlling geological evolution of Earth’s surface. However how it controls plate tectonics is not understood. In particular the role of composition in mantle dynamics mantle is very controversial. This studentship will develop improved understanding of this critical process by testing thermo-compositional models of mantle dynamics.

There are a large number of hypotheses in mantle chemical geodynamics, some with distinctive names! These include: piles, marble cake, varying depth of subduction, recycling, phase change layering, plum pudding, and deep abyssal layer. This studentship will test these hypotheses quantitatively by undertaking supercomputing simulations on multi-thousand core systems to predict the evolution of mantle chemistry, and compare these melt geochemistry predictions with observations held in international databases.

The simulations will utilise a spherical global mantle convection model in which melting and recycling have recently been implemented. In particular the model allows (i) variation in bulk composition which allows thermo-compositional convection; (ii) tracks heat producing elements U,Th,K through the melting processing allowing spatially variable heating, (iii) tracks the radioactive and stable daughters of the heat producing elements (Pb,Ar,He), allowing predictions to be compared with observations, (iv) and in addition to the mixing mantle reservoir it also includes a continent and atmosphere reservoirs. This world-leading tool will allow this proliferation of hypotheses to be tested by using predictions of geophysical and geochemical data, for example the size of the inner core, Pb-Pb isotopes, He3/He4 ratios, Argon40 in the atmosphere, uppermost mantle temperature etc. As a specific example can a layer/pile stay stable at the base of a vigorously convecting mantle over geological time especially if it contains heat-producing elements which will make the layer hotter and more buoyant? Other specific questions that will be considered include can recycled basalt act like a barrier in mid-mantle and is there a primordial or replenished isolated geochemical reservoir at the base of the mantle.

We are looking for a student with a strong physical sciences background and ideally some experience with computational modelling. The student will be expected to attend international conferences. The mantle convection modelling will be led from Cardiff University while University of Bristol will guide the geochemistry testing, with support from Dr. Porcelli, University of Oxford, an expert in noble gases.

F1a   F1b

Fig 1. (A) Cross-section showing bulk composition, and (B) hot isosurfaces showing strong plumes.

Training

The student will academically be trained in mantle studies broadly but especially mantle dynamics and geochemistry within the strong respective research groups. This will include being offered a place on a Level M course on Mantle dynamics, evolution and structure being developed at the School of Earth and Ocean Sciences at Cardiff University.

Technically the student will be trained in running mantle circulation models on large parallel clusters. This will include introduction to parallel computing, high performance programming, and visualisation of large data sets. The student will have access to Programming course in LEARN at Cardiff University, if required, and to courses on Numerical Methods for Fluid Mechanics in the School of Mathematics at Cardiff University.

The student will also get the opportunity to learn about mantle geochemistry including the data, their interpretation and the methods of data collection, with training on analytical models of cycling and looking at volatile data.

The student will use the local Cardiff cluster (Raven) and Archer – RCUK/NERC National Supercomputer. Access on Archer will be requested as part of core funding for the Geophysics and Mineral Physics NERC consortium for which the supervisor has extensive experience.  The student will need access to 3D visualisation which can be provided at no cost at Cardiff in the Helix suite.

This is a very interdisciplinary project bringing together fluid dynamics (applied to the mantle), and geochemistry (applied especially to the lithophile and noble gas elements). The supervisory team has expertise in all these fields.

Background Reading

Davies DR, Goes S, Davies JH, et al., Reconciling dynamic and seismic models of Earth's lower mantle Earth Planet Sci. Lett., 353, 253-269, 2012.

Porcelli D & T Elliott, The evolution of He isotopes in the convecting mantle and the preservation of high 3He/4He ratios, Earth Planet Sci. Lett., 269, 175-85, 2008.

Contact Details

Dr J Huw Davies - daviesjh2@cardiff.ac.uk