Macquarie’s Geophysics and Geodynamics Group

 

Available PhD Projects

Imaging the small-scale dynamics of the upper mantle

Imaging the small-scale dynamics of the upper mantleThe concept of small-scale convection currents (SSC) from about 100-400 km below the Earth’s surface is a model proposed to explain intraplate volcanism and uplift of topography in continental interiors, which are believed to be triggered either by edge-driven convection or by another model involving Rayleigh-Taylor (gravity) instability of a thicken lithosphere. So far, most of evidence for small-scale upper mantle convection is derived purely from isotropic seismic tomographic models with low velocity and high velocity anomalies interpreted as the upwelling and downwelling limbs of small-scale upper mantle convections, respectively. However, isotropic seismic velocities can only reveal information about the temperature and composition of upper mantle rocks. High velocity anomalies interpreted as downwelling drips could be simply residues of eroded lithosphere and low velocity anomalies could reflect compositional and thermal anomalies rather than downwelling or upwelling upper-mantle rocks. The direct evidence for small-scale convection must come from studies of seismic anisotropy, which provides direct constraints on deformation and flow related to SSC within the Earth’s interior. The PhD candidate will develop and apply innovative methods to map seismic anisotropy in the upper mantle in order to understand the nature of small-scale convection and its roles in shaping intraplate geological phenomena. Understanding SSC could help to fill the gap in the plate tectonic paradigm left by its inability to resolve the mechanisms responsible for intraplate geological activity such as volcanism, mountain building and earthquakes. Direct observational evidence for SSC will provide fundamental constraints on the use of dynamic modelling to understand the origin and evolution of intraplate geological features.

Desirable background: Geophysics, Physics

Supervisors: Yingjie Yang and Juan Carlos Afonso

Geophysically constrained mantle flow simulations.

Geophysically constrained mantle flow simulations.Mantle flow within the Earth complicates the interpretation of geophysical and geodynamic observables as well as evolutionary models of the lithosphere. The problem of discriminating between dynamic versus thermochemical contributions to absolute elevation (topography) is an example of this. Valid models of the thermochemical structure of the Earth’s interior must be consistent with all geophysical and geodynamic observations. Our group has recently developed a fully non-linear probabilistic method to invert geophysical and geodynamic observations to provide realistic estimates of the temperature and compositional structures of the Earth’s interior. This requires solving the “mantle flow problem” or “Stokes flow” millions of times in cluster machines. The candidate will work in developing super-fast Stokes solvers for geophysical and geodynamic applications based on Reduced Basis techiques. The candidate will collaborate closely with members of the CCFS group at Macquarie as well as with international collaborators (Prof. Gianluigi Rozza) through research stays in Europe.

Desirable background: Geophysics, Physics, Applied Mathematics, Engineering

Supervisors: Juan Carlos Afonso and Gianluigi Rozza

Inversion of multiple geophysical datasets for the composition and thermal structure of the Earth.

Geophysically constrained mantle flow simulations.One of the main challenges concerning the Earth’s upper mantle is the determination of its present-day thermal and compositional structure. This information represents the basis for any evolutionary model of the Earth, as well as for understanding the relationships between geophysical observables (e.g. electrical conductivity, seismic velocity, etc) and the physical state of the Earth’s interior. This project builds on recent advances in the improvement and integration of geophysical, petrological, mineral physics, and geochemical data into self-consistent models of the Earth’s mantle as well as on the development of high-resolution tomographic techniques. The candidate will deal with multi-parameter inversion techniques and state-of-the-art geophysical modelling tools to advance/develop recent interdisciplinary methods to map compositional and thermal anomalies in the upper mantle. Through this project the candidate will interact closely with renowned scientists in the CCFS group as well as with international collaborators through research stays in Ireland, UK and/or USA.

Desirable background: Geophysics, Physics

Supervisors: Juan Carlos Afonso and Yingjie Yang

Many others!!!

Geophysically constrained mantle flow simulations.Send us an email!!!!