Volume changes during diagenesis and metamorphism: where are they?


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


  • External Supervisors: Jeremy Elvins (British Gypsum)
    Giancarlo Molli (Uni. Pisa)
  • Contact:

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

  • CASE Partner:

Application deadline: 10 January 2020

Introduction:

When a chemical environment induces growth of new minerals, they may in theory have different volumes to the existing minerals. When volume change is manifest, it can deform the surroundings and create or alter fluid flow pathways. This has implications for CO2 sequestration in metamorphic rock, for example when CO2 is added to peridotite it may induce fracturing and that would assist in further sequestration. It has implications for the weathering and degradation of concrete, where growth of new minerals in confined spaces can lead to unwelcome fracturing.  It has implications for engineering projects especially when gypsum is generated from anhydrite beneath a building. 

However there are geological settings where the volume change is not at all obvious. Gypsum forming from anhydrite is a particularly good example since a 60% solid volume increase is to be expected. The circumstances under which volume change occurs, creating stress and deformation, or doesn’t occur, indicating large-scale transport of dissolved material, are not understood. 

The environmental challenge is to understand the interplay between stress, fluid flow and chemical change; it is relevant for assessing the opportunities and hazards described above, and others.

Project Summary:

Geological investigation of where anhydrite is turning into gypsum with consequent deformation in Fauld mine, Staffs. Here, layer of anhydrite become bulbous diapirs where they transform to gypsum. Deformation is driven by a combination of volume change and gravitational instability as gypsum is less dense than the adjacent anhydrite and interleaved mudstone layers. In contrast, investigation of where anhydrite is turning into gypsum without apparent volume change, at localities in Italy. Microstructural work to look for evidence of volume change and deformation on all scales. Development of overview of controls on the new mineral formation processes.

References:

Bedford, J., Fusseis, F., Leclere, H., Wheeler, J. & Faulkner, D. 2017. A new 4D view on the evolution of metamorphic dehydration reactions Scientific Reports 7, Art. No. 6881.

Hildyard, R. C., Prior, D. J., Mariani, E. & Faulkner, D. R. 2009. Crystallographic preferred orientation (CPO) of gypsum measured by electron backscatter diffraction (EBSD). Journal Of Microscopy-Oxford 236(3), 159-164.

Hildyard, R. C., Prior, D. J., Mariani, E. & Faulkner, D. 2011. Characterisation of microstructures and interpretation of flow mechanisms in naturally deformed fine-grained anhydrite by means of EBSD analysis. In: Deformation Mechanisms, Rheology & Tectonics: Microstructures, Mechanics & Anisotropy (edited by Prior, D. J., Rutter, E. H. & Tatham, D.) 360. The Geological Society, 237-255.

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.

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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