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E444: Enigma at the roots of whole-mantle plumes (Lead Supervisor: Sanne Cottaar, Earth Sciences)

Supervisor: Sanne Cottaar (Earth Sciences)  

Importance of the area of research:

Over the past decades, strong heterogeneity has been discovered right above the boundary between the core and the mantle. Studies have identified the scattered occurrence of patches of extremely slow velocities. These patches are suggested to be tens of kilometres thick and hundreds of kilometres across and have been named Ultra-Low Velocity Zones (ULVZs). In the past five years, unusually large ULVZs have specifically been found beneath the major volcanic hotspots of Hawaii, Iceland and Samoa. The ULVZs could represent high-density roots to broad whole-mantle upwellings that cause (mid-plate) volcanism at the surface and fix volcanic hotspots in space. Potentially, the ULVZs are an explanation to anomalous geochemical signatures in the basalts at these hotspots. Some propose ULVZs contain partial molten material, reflecting the high temperatures close to the core-mantle boundary and beneath volcanic hotspots.

Project summary:

Seismology provides the most direct observations on the composition and dynamics of the deep Earth. In terms of ULVZs, studies have mostly been able to constrain the shear wave velocity reduction. To understand the nature and composition of these zones, complimentary constraints on P wave velocity and density need to be constrained.  The goal of this project is to apply new techniques to map these additional constraints.

What the student will do:

The student will work on synthetic data to test new techniques to resolve P-wave velocity and density structure of ULVZs. These will then be applied to real data, initially for data sampling Hawaii, but other ULVZs can be explored later. The student will also model thermo-chemical scenarios of ULVZs. Depending on interest, the student is encouraged to work with others in the department to assess dynamical and geochemical implications of the new constraints.

Please contact the lead supervisor directly for further information relating to what the successful applicant will be expected to do, training to be provided, and any specific educational background requirements.

References:

Cottaar, S. & Romanowicz, B. 2012. An unusually large ULVZ at the base of the mantle near Hawaii. Earth Planetary Science Letters, 355, pp.213-222. DOI: 10.1016/j.epsl.2012.09.005

Li, M., McNamara, A. K., Garnero, E. J. & Yu, S. (2017) ‘Compositionally-distinct ultra-low velocity zones on Earth's core-mantle boundary.', Nature comm. Nature Publishing Group, 8(1), p. 177. DOI: 10.1038/s41467-017-00219-x

Yuan, K. & Romanowicz, B. (2017) ‘Seismic evidence for partial melting at the root of major hot spot plumes', Science, 357(6349). DOI: 10.1126/science.aan0760

Follow this link to find out about applying for this project.

Other projects available from the Lead Supervisor can be viewed here.

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