Sinking slabs and rising mantle plumes; modelling the implications of the lower-mantle spin transition

Over half a century ago, it was predicted that increasing pressure within Earth’s deep interior may cause the collapse of atomic orbitals of iron (Fe2+) and, just over 10 years ago, this phenomenon was confirmed by experimental and theoretical mineral physics. This electronic spin transition within the Earth may only recently have been robustly detected using seismology. However, the spin transition of iron in lower mantle minerals, such as ferropericlase (Fp), is thought to have a profound effect on the mantle’s thermo-elastic properties which implies a significant impact on mantle dynamics.

The transition that is thought to occur between approximately 1000 - 2200 km depth, which is a range that contains sinking slabs of oceanic lithosphere and rising plumes of hot, buoyant material, and potentially also the tops of two large antipodal provinces (LLSVPs) along the core-mantle boundary. Some studies have suggested that the change in spin in Fp may alter the nature of upwellings and cause slabs to increase their spread along the core-mantle boundary; whereas others suggest minimal effects.

This MSc project would be made in close collaboration with multiple CEED team members (Earth Modelling, Dynamic Earth and Deep Earth). The Masters student would run state-of-the-art numerical models and analyse output using a community-leading, spherical mantle convection code (StagYY) to explore a limited suite of parameters, including thermal and chemical density contrasts, and evaluate effects on both slab and plume dynamics. A particular focus would be to predict changes in the speeds of sinking slabs and rising plumes on a global scale, which would be compared back to global sinking rates estimated from seismic and geologic studies.

Project organisation:

  • Literature review and required course work
  • Familiarization with using the geodynamic code StagYY and the post-processing code StagLab
  • Running a selected series of numerical simulations
  • Post-processing and visualization of the model data
  • Geodynamic interpretation of the model results in conjunction with observables from seismic tomography and previous studies

Recommended skills:

  • Basic knowledge of computer programming in order to use the remote super-computer, setup the model runs, and handle the resulting data sets
  • Basic knowledge of mantle convection dynamics
  • Learning outcomes:
  • Computer programming
  • State-of-the-art numeric geodynamic modelling
  • Post-processing and visualising large datasets
  • Quantitative and qualitative geophysical analysis
  • Broad understanding of multi-scale mantle convection and the integration of multiple datasets

This skillset, including scientific writing and critical thinking, is highly valuable for a career in both industry and academia.

Figure 1 Mantle convection model.

 

Published Dec. 12, 2018 11:08 AM - Last modified Dec. 12, 2018 11:08 AM