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E437: Microstructural proxies for igneous and metamorphic timescales (Lead Supervisor: Marian Holness, Earth Sciences)

Supervisors: Marian Holness (Earth Sciences), Emilie Ringe (Earth Sciences & Materials Science and Metallurgy

Importance of the area of research:

The shape of mineral grains in dolerites and gabbros has recently been shown to provide invaluable information on solidification rate. Grain shape can also be used to determine the extent to which magma bodies convected during crystallisation. These new results are opening up new horizons in the use of microstructure in developing our understanding of igneous processes but we are still in the very early stages of exploring this underexploited source of information. The project is aimed at developing this exciting field by expanding our understanding of how we can decode microstructures to constrain timescales in both igneous and metamorphic rocks.

Project summary:

The factors controlling grain shapes in solidifying magma are well known, but we do not yet have a quantitative understanding of the dependence of these factors on the magmatic environment which is essential if we are to use microstructural analysis to decode rock history. Similarly, it is well known that the shape of grains in undeformed metamorphic rocks is dependent on the relative rates of reaction and textural equilibration, as well as their place within the (purely qualitative) crystalloblastic series (a progression from euhedral (e.g. staurolite) to anhedral (e.g. quartz) shapes), but we have no quantitative understanding of these controls. The project is aimed at understanding the fundamental controls on grain shape during crystallisation in both igneous and metamorphic rocks. The approach will use a combination of detailed experimental work and analysis of natural examples.

What the student will do:

The student will undertake detailed microstructural examination of a wide range of rocks, including a comparison of contact and regionally metamorphosed rocks and detailed analysis of microstructural variation across suites of intrusions of varying size. Field work will be undertaken to collect suitable sample suites which will allow us to isolate variables such as temperature and heating/cooling rates. Experiments will be undertaken using heating stages mounted on an optical microscope, directly observing mineral growth from silicate melts for comparison with natural examples.;Analysis will involve the extensive use of electron microscopy techniques, including scanning electron microscopy and scanning transmission electron microscopy for the determination of crystal shape, to be correlated with growth environment and corroborated with analytical growth models based on Wulff and kinetic Wulff constructions. Electron diffraction approaches will be used for the determination of crystalline orientation, and electron-energy loss and energy dispersive x-ray spectroscopy for the analysis of composition at the macro and nanoscale.

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:

Holness, M.B. 2014. The effect of crystallization time on plagioclase grain shape in dolerites. Contributions to Mineralogy and Petrology, vol. 168, pp. 1076. DOI 10.1007/s00410-014-1076-5

Ringe, E., Van Duyne, R.P., & Marks, L.D. 2013. Kinetic and Thermodynamic Modified Wulff Constructions for Twinned Nanoparticles. The Journal of Physical Chemistry C, vol. 117, pp.15859-15870

Rivers, T. & Fyson, W.K. 1977. Shape, size and orientation of muscovite crystals in a schist of variable metamorphic grade. Canadian Journal of Earth Sciences, vol. 14, pp 185-195.

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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