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E412: Solving a gneiss problem: the structure and origin of the Earth's oldest crust (Lead Supervisor: Owen Weller, Earth Sciences)

Supervisors: Owen Weller (Earth Sciences), Alex Copley (Earth Sciences) and Richard Taylor (Earth Sciences)

Importance of the area of research:

The Archean is one of the last great frontiers in our knowledge of the Earth. Plate tectonics is considered to have initiated during this time period, and large swathes of the continental crust formed, but fundamental questions remain regarding the timing, mechanisms and drivers of these changes [1]. These questions have implications throughout the Earth Sciences, from the evolution of life to the distribution of present-day tectonic structures and natural resources. This project will shed new light on these questions using an innovative approach that integrates structural, metamorphic and geochronological techniques with a new understanding of what controls the deformation of present-day mountain ranges [2,3].

Project summary:

This project will combine a recently-developed understanding of what controls present-day continental deformation, with field and laboratory studies of exhumed Archean rocks, in order to understand the tectonic processes that may have been occurring in the Archean. Specifically, we can use the information encoded in Archean gneissic rocks to investigate the distribution of rock strength during their formation, which will yield novel insights into the nature of tectonics in the early Earth. The key feature of this work is using the distribution of foliations in Archean rocks, and relating them to our mechanical understanding of present-day mountain ranges, where such fabrics are currently forming.

What the student will do:

The student will begin by conducting fieldwork in well-exposed Archean terranes. We will map the range of deformation structures, from the oldest gneissic fabrics through to overprinting shear zones, and collect samples for dating and pressure-temperature calculations. State-of-the-art analytical techniques will be used on the samples, including: electron backscatter diffraction microscopy to establish the origins of the observed foliations, phase equilibria modelling to determine pressure-temperature formation conditions, and laser ablation split stream geochronology to obtain temporal constraints (at Curtin University, Australia). The student will then integrate this analytical information with recently-developed dynamic models of continental deformation, to deduce in which tectonic settings the observed foliations could have formed. This work will therefore give new insights into how the continents formed and evolved, and when the active deformation of the lithosphere began to resemble modern-day plate tectonics. The methodology will be initially developed and tested on the Lewisian Complex of the northwest UK, and then applied to Arctic Canada and/or peninsular India.

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:

[1] Weller, O.M. & St-Onge, M.R. 2017. Record of modern-style plate tectonics in the Palaeoproterozoic Trans-Hudson orogen. Nature Geoscience, vol. 10, pp. 305-311, doi:10.1038/ngeo2904.

[2] Copley, A., Avouac, J.P. & Wernicke, B.P. 2011. Evidence for mechanical coupling and strong Indian lower crust beneath southern Tibet. Nature, vol. 472, pp. 79-81, doi:10.1038/nature09926.

[3] Copley, A. & Woodcock, N. 2016. Estimates of fault strength from the Variscan foreland of the northern UK. Earth and Planetary Science Letters, vol. 451, pp. 108-113, doi:10.1016/j.epsl.2016.07.024.

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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