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How do dehydration reactions work?


Project Description

The aim of this project is to improve understanding of how porosity, permeability and fluid pressure evolve when hydrous minerals break down.

Porosity and permeability are fundamental rock properties since they allow the accommodation and flow of fluid in the Earth. Fluids may carry chemicals which form economic mineral deposits. Conversely they may contribute to hazards, as increased fluid pressures from dehydration reactions can help trigger earthquakes. There is feedback in such reactions: reaction may increase fluid pressure, but that then slows down further reaction. Ongoing deformation may have the same effects. Under other circumstances the permeability may develop quickly, fluids escape freely and fluid pressure remains low.

The project will investigate a reaction which is rare but extremely simple: the breakdown of AlO(OH), to corundum, Al2O3. The strategy here is that this will shed light on the fundamental interactions between reaction, deformation and fluid flow that are obscured in other more complex reactions. Structural relationships of rocks in various states of dehydration (on te island of Naxos) will be investigated on all scales from field to microstructure. The diaspore deposits are metamorphosed bauxites. The original bauxites contained pisoids (subspherical concentric structures) which will allow for quantitative strain analysis, in other words we can discover the actual amount of deformation that such rocks have undergone. Electron microscopy (Electron Backscatter Diffraction, EBSD) will be used in the metabauxites and surrounding marbles to determine how these rocks deformed. Numerical models of fluid flow, as developed by Wheeler, will be used to deepen understanding of the feedbacks.

To apply for this opportunity please visit: https://www.liverpool.ac.uk/study/postgraduate-research/how-to-apply/ and click the ‘Apply online’ button.

Funding Notes

Full funding (fees, stipend, research support budget) is provided by the University of Liverpool for 3.5 years for UK or EU citizens. Formal training is offered through partnership between the Universities of Liverpool and Manchester. Our training programme will provide all PhD students with an opportunity to collaborate with an academic or non-academic partner and participate in placements.

References

Ankit, K., Urai, J. L. & Nestler, B. 2015. Microstructural evolution in bitaxial crack-seal veins: A phase-field study. Journal of Geophysical Research-Solid Earth 120(5), 3096-3118.
Leclere, H., Faulkner, D., Llana-Funez, S., Bedford, J. & Wheeler, J. 2018. Reaction fronts, permeability and fluid pressure development during dehydration reactions. Earth And Planetary Science Letters 496, 227-237.
Llana-Funez, S., Wheeler, J. & Faulkner, D. R. 2012. Metamorphic reaction rate controlled by fluid pressure not confining pressure: implications of dehydration experiments with gypsum. Contributions To Mineralogy And Petrology 164, 69-79.
Prior, D. J., Mariani, E. & Wheeler, J. 2009. EBSD in the Earth Sciences: applications, common practice and challenges. In: Electron Backscatter Diffraction in Materials Science (edited by Schwartz, A. J., Kumar, M., Adams, B. L. & Field, D. P.). Springer, 345-357.
Urai, J. L. & Feenstra, A. 2001. Weakening associated with the diaspore-corundum dehydration reaction in metabauxites: an example from Naxos (Greece). Journal Of Structural Geology 23(6-7), 941-950.
Wheeler, J. 2018. The effects of stress on reactions in the Earth: sometimes rather mean, usually normal, always important. Journal Of Metamorphic Geology 36, 439-461.

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