Geodynamics

Description

Advertisement

There is strong evidence, including freeboard (Sandu et al., 2011), to suggest that Earth has had a significant and virtually constant ocean volume for a large part of its history. Given that water is cycled back into the mantle by subduction, and also back out by magmatism, questions include, how has it been able to keep such a constant level? Also, where are the major internal reservoirs of water in the mantle? Are they in the transition zone, between upper and lower mantle, or in the large low shear velocity provinces that appear as two large entities in the deepest mantle beneath Africa and the Pacific (Davies et al., 2012)?

Current models of the deep water cycle are basic. Modelling of mantle convection, melting and subduction processes has improved over the past decades, but these improvements have not been completely incorporated into deep water cycle models. Equally there are increasing constraints on the deep water (estimated to be as much as 5 oceans worth in the mantle!) from aspects of laboratory experiments, electrical conductivity and seismology. Clearly given the huge significance of water for most natural world phenomena from rheology of rocks to life itself a better understanding of how a planet can keep itself fit and healthy is critical.

This studentship is part of a large Consortium project which is part of a large NERC Directed Programme on Volatiles and Geodynamics. It will overlap in time with another Consortium Cardiff University project employing a Post-Doctoral Research Associate (PDRA). The PDRA will focus on the influence of water on the mantles rheology, and will do the more advanced code development. The PDRA will look at the lithophile element cycles, sulphur and constraints from electrical conductivity and seismology. There will be strong synergy.

Aspects that this studentship will investigate specifically include:

* What we can learn from tracking water, the noble gases and the stable isotope of 11B simultaneously.
* Look at constraints from freeboard and melt production

The student will start by investigating simple models parameterising the critical processes but incorporating more realistic processes and parameters than current models. This class of models will allow a wide range of possible Earth evolutionary paths to be investigated. The project will then advance to utilising leading edge mantle convection codes capable of simulating mantle convection in three-dimensional spherical geometry at Earth-like vigour (see figure below) using High Performance Computing (HPC). These have already been developed to allow the tracking of chemistry, including melting (Davies and van Heck, 2013). The models already track the heat-producing elements, the resulting daughter lead and noble gas isotopes, and the related stable primordial isotopes. The models also already track bulk composition allowing thermo-compositional convection. In these much more advanced and computationally expensive water tracking models the student will focus on the sub-set of the models found to be interesting from the first stage of the project. This will test how the geometry, rheology and buoyancy feedbacks, which cannot be addressed in the simple models, affect the evolution. The student will then constrain these models with the wide-ranging observations and look at their implications for the volatile cycles.

This project will lead to an improved understanding of the water cycle. Since this is so fundamental to the whole Directed Programme the student should benefit extensively from outputs from the whole Volatiles Directed programme.

Contents

Research 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 Geodynamics 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 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. The student will use 3D visualisation exists within the research group 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 water, the lithophile and noble gas elements). The supervisory team has expertise in all these fields.

Requirements

Residency: Full awards (fees plus maintenance stipend) are open to UK Nationals and EU students who can satisfy UK residency requirements. To be eligible for the full award, EU Nationals must have been in the UK for at least 3 years prior to the start of the course for which they are seeking funding, including for the purposes of full-time education. EU Nationals who do not meet the above residency requirement are eligible for a fees only award, provided that they have been ordinarily resident in the EU for at least 3 years prior to the start of their proposed programme of study.

Academic criteria: Applicants for a studentship must have obtained, or be about to obtain, a 2.1 degree or higher in a relevant subject. Applications are particularly welcome from applicants with a good first degree or Masters qualification in Earth Sciences or related fields.