Title: Metamorphic reactions in evaporites: dehydration and re-hydration reactions in the calcium-sulphate system.
Description:
My PhD is based in structural geology and experimental rock deformation. I’m interested in the relationship between the stress states applied to evaporitic rocks and their metamorphism between the phases of gypsum and bassanite. The metamorphism occurs due to applied cycles of dehydration (when we increase temperature) and re-hydration (when we decrease temperature) under a variety of stress states. This is relevant to understanding crustal processes facilitated by dehydration. For example, catastrophic tectonic movements like earthquakes are caused by brittle failure within the crust and earthquakes produced within subduction zones are often facilitated by the dehydration of subducting hydrous minerals (Llana-fúnez et al., 2007). Consequently, it is important to develop our knowledge on dehydration and re-hydration processes in hydrous minerals to give us a comprehensive understanding of the mechanisms driving intermediate-depth seismicity.
Evaporites, specifically gypsum (hydrated calcium sulphate, CaSO4·2H2O), are an excellent material to study the microstructural processes that promote, facilitate and are controlled by dehydration and re-hydration reactions. Gypsum dehydrates at 60°C (Kelley et al., 1941) making it feasible to conduct triaxial pressure experiments using gypsum whilst concurrently pushing it to dehydrate/ re-hydrate. Additionally, it is a useful analogue for other hydrous minerals which are considerably more difficult to conduct triaxial pressure experiments on, specifically serpentinite. Gypsum is an effective analogue for hydrous minerals like serpentine because it is a hydrous mineral which, in comparison, dehydrates quickly and at low temperatures. Gypsum therefore makes an ideal experimental analogue material for observing the nature of dehydration and re-hydration reactions. During my PhD I will analyse data gained from synchrotron 4D microtomography experiments to determine the links between the effects of mechanical loads applied to the gypsum sample and mineral transformations within the gypsum sample; such as nucleation rate, grain growth and reaction rate.
