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E418: Olivine dislocation microstructure: a new archive of magmatic processes (Lead Supervisor: Emilie Ringe, Earth Sciences & Materials Science and Metallurgy)

Supervisors: Emilie Ringe (Earth Sciences & Materials Science and Metallurgy), John Maclannen (Earth Sciences) and Oliver Shorttle (Earth Sciences/Institute of Astronomy)

Importance of the area of research:

How magmas move through volcanic plumbing systems fundamentally determines their hazard to human populations.  As magma rises through Earth's crust it evolves in composition by cooling and crystallising, with olivine being one of the first crystal phases to grow. These early formed crystals of olivine contain a valuable record of a magma's storage and transport history leading up to, and in some cases even beyond, its eventual eruption.  An often-exploited archive of these processes carried in olivine crystals is the small pockets of melt they trap as inclusions, and in particular the carbon and water content these retain.  However, our recent work has shown the susceptibility of these inclusions to cracking and through this mechanism the loss of their volatiles.  What's more, the melt inclusion record and other petrological tools typically applied to olivines are almost entirely blind to the stress history the olivine has experienced.  This leaves us ignorant about key stages in a magma's life, with growing evidence that magmas may spend long periods in crystalline mushes. To address these issues this project will develop magmatic olivine microstructure as a new petrological tool.

Project summary:

This project will focus on adding a new tool to the igneous petrologist's toolkit: the dislocation microstructure of olivine crystals.  Whilst olivine is frequently used as a key petrological archive, a detailed assessment of its growth and deformation history is rarely considered.  However, development of these microstructural observations will profoundly improve our understanding of the migration of magma beneath volcanoes.  Therefore, this project will focus on making novel observations of olivine dislocation structure using a range of optical, electron microscopy and spectroscopy techniques.  Observations will be carried out on natural olivines, to survey the diversity of textures produced according to magmatic history, and on olivines synthesised under controlled conditions.  With these results we will have a new resource to interrogate magmatic processes from eruptive products.

What the student will do:

This project will comprise three parts: 1) During fieldwork in Iceland the student will collect new samples from recent eruptions with detailed geophysical and geochemical characterisation.  The remarkable detail with which these eruptions have been studied will enable the new microstructural observations to be placed in context with classical petrological and geochemical tools.  2) A synthetic suite of olivine crystals will be synthesised in high temperature experiments.  These will form a reference set of crystals with uniform microstructural characteristics.  3) A suite of observational techniques will be employed on natural and synthetic olivines.  A key aim of these is to identify the optimum analytical strategy for incorporating olivine microstructural analyses into a typical workflow of geochemical and petrological characterisation. Optical and electron spectroscopy, including hyperspectral and correlated approaches developed by the lead supervisor, will be explored and referenced to the classical method of dislocation ornamentation to evaluate these new, non-destructive approaches.

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:

Maclennan, J. 2017. Bubble formation and decrepitation control the CO2 content of olivine-hosted melt inclusions. Geochemistry Geophysics Geosystems, vol. 18, pp.597-616, DOI: 10.1002/2016GC006633.

Sakyi, P.A., Tanaka, R., Kobayashi, K. & Nakamura E. 2012. Inherited Pb isotopic records in olivine antecryst-hosted melt inclusions from Hawaiian lavas. Geochimica et Cosmochimica Acta, vol. 95, pp.169-195, DOI: 10.1016/j.gca.2012.07.025.

Kohlstedt, D.L., Goetze, C., Durham, W.B. & Vander Sande J. 1976. New technique for decorating dislocations in olivine. Science, vol. 191, pp. 1045-1046.

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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