How do dehydration reactions work?


  • Supervisors: Prof John Wheeler, University of Liverpool
    Dr. Betty Mariani, University of Liverpool
    Dr Dave Mcnamara, University of Liverpool

  • External Supervisors: Janos Urai (RWTH Aachen)

  • Contact:

    Prof. John Wheeler, University of Liverpool, johnwh@liverpool.ac.uk

  • CASE Partner:

Application deadline: 10 January 2020

Introduction:

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.

Project Summary:

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,

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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