Water and the Earth’s Crust: Using Hydrogen and Oxygen isotopes from rocks of the coast of Nova Scotia (Ian Cawood)

My 10-week summer project involved using a selection of rock samples from Nova Scotia, Canada to determine how they had originated and been emplaced onto the Earth’s surface where they are visible now today. The rock suite I was investigating are known as Appinites, these are igneous rocks that are rich in a mineral called amphibole. This mineral incorporates large amounts of water into its chemical structure and by studying the two components that make up water (Hydrogen and Oxygen) and their isotopic fractionation one can determine the origin of a crystallising magma and its interaction with water during its generation and intrusion into surrounding country rock. These elements have heavier and lighter isotopes that are preserved differently depending on the interaction of water, their mineral composition etc.

The first part of my labwork for this involved significant amounts of time spent characterising thin sections of my rock samples under a light microscope to assess their texture and mineralogy. This was key to further developing my skills which we have studied in lectures over the last few years and gave me a lot more confidence in interpreting the relationships of different minerals in respect to their crystallisation history (i.e. which mineral crystallised in which order). This in turn enabled me to understand the units I was analysing and determine appropriate samples that I could use for isotope analysis.

My work was largely split into 2 time blocks due to a significant amount of my summer being spent mapping rocks for my dissertation in the Pyrenees. Thus, when I returned from this work, my internship then took me to the Scottish Universities Environmental Research Centre (SUERC) located in East Kilbride (a short distance from Glasgow). Here first class scientific research facilities are housed. Working with Prof. Adrian Boyce and Alison McDonald I was able to record δ18O and δD values for my rock samples using some rather complicated geochemical techniques. Predominately my labwork focused on Silicate Laser Ablation using Chlorine Trifluoride as the reagent. An image of this machine is attached – this collected my samples into mass spectrometer tubes that were later analysed for the oxygen isotopic composition. A complex array of valves needed to be opened and closed at the right times in order to move the sample from one chamber to the next whilst removing excess gas from the chamber. When I first arrived the thought of using the machine seemed impossibly complicated, however after some guidance and many notes I was eventually able to understand the procedure.  A second image also shows the machine used to collect my hydrogen isotopes.

Working in the lab again was a fantastic experience to understand research environment relationships and workflow. It also encouraged me to think independently and utilise any available resources. A fantastic experience in both developing my leadership skills and my ability to act proactively and efficiently in an intense working environment.

I would like to thank Lord Laidlaw for the generous funding  provided to support this project.

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