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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

How the mantle controls plate-tectonics could be constrained if we knew the way the mantle flowed. This flow though is very poorly understood. Progress can be made since mantle seismic studies can now resolve seismic anisotropy (seismic wave speeds dependent on direction of propagation). This anisotropy reflects mantle texture and is generated by its flow. This project will further develop tools that allow textures and seismic anisotropy to be predicted directly from models of mantle circulation, and apply it to derive some of the first direct rigorous constraints on global mantle flow.

The project will utilise a parallel global mantle convection code which has been adapted to undertake mantle circulation simulations, i.e. allowing the flow to be relevant to the actual Earth rather than a generic silicate planet. This code has been further adapted to predict the evolution of mantle texture throughout. The project will incorporate the standard methods of converting texture to seismic velocity, and then will compare the model predictions with the observed seismic anisotropy measurements, allowing tests of the mantle flow field. The project will focus on the uppermost mantle where there are better constraints on both the texture development in olivine and seismic observations.

The mantle circulation modelling will be undertaken at Cardiff University while University of Bristol will guide the seismic testing.  This studentship will run alongside a joint NERC Cardiff/Bristol project investigating thermo-compositional mantle circulation models using waveform seismology with a focus on the deepest mantle. There is also a strong international team of project partners who will be active co-supervisors. The simulations will be run on multi-thousand core supercomputers. Specifically examples of the exciting and significant hypotheses this studentship will address include - the asthenosphere drives the plates, there is significant return flow from subduction to ridge, upwelling plumes form the asthenosphere, and mantle flow accommodates slab roll-back.

This project will suit a student who has an interest in using computational methods to answer real world problems by testing the predictions of hypotheses produced by sophisticated modelling tools with large data-sets. While training will be provided, ideally candidates should have a strong background in at least one of the required facets, be it Earth Sciences (e.g. seismology, geodynamics) and/or Numerical Modelling / Computing (e.g. programming, numerical methods, running simulations on clusters).

Fing 1a   Fig 1b

Fig 1. (A) Mantle flow and (B) radial velocity flow. Such flows produce the mantle textures which seismology can detect through anisotropy.

Training

This is a very interdisciplinary project bringing together fluid dynamics (applied to the mantle), mineral physics (especially texture development) and seismology (especially seismic anisotropy). The supervisory team has expertise in all these fields. The student will academically be trained in mantle studies broadly but especially mantle dynamics and seismology, with focus on mantle flow and seismic anisotropy. 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.  The student will have access to Programming courses in LEARN at Cardiff University, and Python at University of Bristol, if required, and to courses on Numerical Methods for Fluid Mechanics in the School of Mathematics 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, visualisation of large data sets. The student will also get the opportunity to learn to process seismic data and run waveform models, with a focus on the measurement of seismic anisotropy.  These skills are highly transferrable from basin modelling to general computing and fluid mechanics, and will provide an ideal background for further research in either academic or industrial context.

Through this studentship the student will use many leading edge facilities. These include the local Cardiff cluster (Raven) [free at the point of use] 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. Both supervisors have extensive experience with this. The student will need access to 3D visualisation which again can be provided at no cost at Cardiff in the Helix suite.

Background Reading

Davies DR, Goes S, Davies JH, et al., Reconciling dynamic and seismic models of Earth's lower mantle Earth Planet Sci. Lett. doi:10.1016/j.epsl.2012.08.016, 2012.

A Walker, A Forte, J Wookey, et al., Elastic anisotropy of D″ predicted from global models of mantle flow, Geochem. Geophys. Geosys, doi:10.1029/2011GC003732, 2011

Contact Details

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