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Cambridge NERC Doctoral Training Partnerships

Graduate Research Opportunities

Lead Supervisor: Helen Williams, Earth Sciences  

Co-Supervisor:  Oliver Shorttle, Earth Sciences

Importance of the area of research concerned: 
The tectonic recycling of surface material by subduction is widely considered to contribute to the mineralogical and chemical enrichment of ocean island basalt (OIB) source regions (e.g. Jackson et al., 2007 and references therein). However, the impact of tectonic recycling on the spatial and temporal distribution of volatile elements such as carbon and sulfur within the mantle is poorly known. A major contributor to this uncertainty is because these elements are lost during magmatic degassing, making the reconstruction of their concentrations in primary mantle-derived melts challenging. While recent studies have demonstrated the potential of chalcophile trace elements (e.g. Jenner et al., 2012), melt inclusions and novel stable isotopes (e.g. Andersen et al., 2015) to unravelling this complexity, no study has as yet combined these different approaches, and secular variations in volatile recycling remain almost completely unexplored.
Project summary : 
This project will explore carbon and sulfur cycling and mantle source region heterogeneity using a combination of novel stable isotope and geochemical tracers. Through this it will be possible to explore the interplay between partial melting processes, mantle chemical and mineralogical heterogeneity and volatile element cycling. Key ocean island localities will be targeted, which possess abundant evidence for recycled components in their source regions. The study will also extend its reach back over Earth history by considering komatiites, with this project's analyses contributing important new results to the debate about the origin (thermal vs. compositional) of these enigmatic high-degree melts.
What will the student do?: 
This project presents an exciting chance for a student to combine multiple state-of-the-art microanalytical, trace element and isotopic techniques and apply these to a fundamental problem in Earth Sciences: that of volatile cycling between the Earth's surface and deep interior. The student will focus on well-characterised archive oceanic basalt samples from a range of localities including the main geochemical domains of the Iceland plume as well as larger volume mantle melts as represented by picrites and komatiites. The student will use then use their trace element, isotopic and volatile element data to explore the links between tectonic recycling and mantle source region heterogeneity, longevity and volatile contents.
Andersen et al., (2015) The terrestrial uranium isotope cycle. Nature 517 p 356-359
Jackson et al., (2007) The return of subducted continental crust in Samoan lavas. Nature 448, 684-687
Jenner et al., (2012) Chalcophile element systematics in volcanic glasses from the northwestern Lau Basin. Geophysics, Geochemistry, Geosystems 13, 6
You can find out about applying for this project on the Department of Earth Sciences page.