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E405: Tracing mineralogical variations in the Earth's mantle: implications for accretion and the onset of tectonic recycling (Lead Supervisor: Helen Williams, Earth Sciences)

Supervisors: Helen Williams (Earth Sciences) and Oliver Shorttle (Earth Sciences/Institute of Astronomy

Importance of the area of research:

Mineralogical variations in the Earth's mantle provide a record of planetary geochemical and geodynamic evolution including the crystallization of a magma ocean in the Hadean, the extraction of the crust, the onset of plate tectonics and crustal recycling and the generation of mantle plumes.  This mineralogical heterogeneity also has implications for mantle melting and dynamics today, as well as the long-term survival and isolation of mantle reservoirs for billions of years (e.g. Rizo et al., 2016).  A major unsolved paradox is that magmas displaying evidence of derivation from pyroxenite source lithologies, created by the recycling and deep melting of slab material, also display primordial isotopic signatures consistent with derivation from ancient deep-seated mantle reservoirs isolated from the ambient convecting mantle (e.g. Mundl et al., 2017).

Project summary:

The principal issue this project will address is how new geochemical tools can be used to infer the source lithology of oceanic basalts and their equivalents and how this information can be linked with the Earth's long-term history of tectonic recycling and mantle differentiation.  Through this it will be possible to explore the impact of these processes on the chemical and dynamic evolution of the Earth's mantle over the last ~ 4 billion years.

What the student will do:

This project presents an exciting opportunity for the student to use a variety of state-of-the-art methods (e.g. Williams and Bizimis, 2014) to develop new tracers of mantle mineralogical variation. The project will use these tracers to determine relationships between mantle lithology and geochemical enrichment over geological time. The student will focus on oceanic basalts from a range of localities including the main geochemical domains of the Iceland plume and flood basalts as well as more ancient samples.  The student will then use these data to develop models of lithologically heterogeneous mantle mixing and melting.

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:

Mundl et al., 2017 Tungsten-182 heterogeneity in modern ocean island basalts. Science 356 66-69

Rizo et al., 2016 Preservation of Earth-forming events in the tungsten isotopic composition of modern flood basalts. Science 352, 809-812

Williams, H.M. and Bizimis, M., 2014. Iron isotope tracing of mantle heterogeneity within the source regions of oceanic basalts. EPSL 404, 396- 407.

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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