Lasering rocks in Norway

Jordy De Vries
Sunday 10 September 2017

Rocks won’t come to you, so you’ll have to go to them: one of my reaons for studying Geology! My Laidlaw project concerns an area in Norway, so I spent ten days studying the rocks over there. This involved lasering them with a novel spectrometer, which formed the crux of my project.

When continents collide, the immense resulting forces thrust rock bodies onto each other. These rock slivers, ‘nappes’, can get stacked into huge ‘imbricates’ (figure 1). The creation of such intricate structures is often linked to the presence of a weak layer, e.g. a muddy horizon that acts as a “grease”.For my Laidlaw project, I studied such an area, the Porsa Imbricate Stack in Northern Norway, where stacking seems to be enabled by the abundant graphitic slates.

fig. 1 – cross-section of the Porsa Imbricate Stack, note all the tiny slivers on the left!

Graphite (e.g. your pencil lead) is essentially organic matter that became crystalline under exposure to high temperatures, deep in the Earth. This process, graphitisation, is gradual and irreversible, which makes graphitisation an indicator of the maximum temperature a rock experienced (fig 2)

fig. 2 – diagram of graphitisation (2)

This is were the laser gun comes in. By measuring the ‘Raman’ backscattering of the laser hitting the rock, you get a spectrum that tells you the rock’s graphitisation grade (fig 3). Normally, one would have to collect many samples and analyse the rocks at home, but this new handheld device allows you to measure the spectra right in the field.

fig 3. example of an Raman spectrum. The area & height ratios of the peaks will change, depending on the temperature the rock was exposed to.

However, this involves having software that quickly analyses the spectra for you. This, I came to realise over the latter course of my project, is far from a wee two-week task! Especially obtaining an accurate spectrum-temperature correlation turned to out to be difficult. Each Raman set-up gives a different “signature” to the theoretical spectra, which makes it impossible to take a correlation from another paper (that uses different equipment) without incurring some level of error (1). I did manage to create a functioning, accurate fitter, but until we manage to obtain calibration data on our samples, the data can only interpreted as relative, not absolute temperatures. Sadly though, I won’t be able to obtain those constraints before the end of the summer: the lab technician is on holiday, the convential laser in the chemistry building is about to move away and my supervisor left to the States for fieldwork…

Thus, whilst I’m currently trying to finish the report and poster, it will be another while before our laser gun is completely fit for work. I’m very keen to keep working on this though; hopefully fourth year will leave me at least a bit of time for that. Research projects like this often make little impact, but I’m excited that this project might just slightly contribute to enhancing our “old-fashioned” field trip equipment (hammer, hand lens, compass) with compact analytical devices as this one.

Overall, the Laidlaw internship has been very rewarding and enjoyable, but there also were harder moments every now and then. Especially after a month of dissertation field work in June, keeping myself motivated in Norway sometimes was difficult. The overall research question, furthermore, is becoming larger and more difficult, the more I look into it; it’s quite a challenge to keep the report’s synthesis neatly framed.

Part of the excitement of Laidlaw lied in that somebody apparently deemed you ready to do academic research! Whilst of course I still feel pretty unknowledgeable compared to my supervisor and all the other staff in the department, I do feel I gained confidence throughout my internship. I really enjoyed completely submerging myself into my research topic and learning more and more about it, something I’ll definitely look for when planning out my future.

Lastly, I’d like to express my gratitude towards my supervisor Tim Raub for his time, patience, guidance and sharing his inspiring thoughts, Catriona and Eilidh for organising such thought-provoking, inspiring events and Lord Laidlaw for offering me this invaluable opportunity.

the “office” in Norway, bathing in the midnight sun

The field area on a sunny day

A nicely folded volcanic rock in the mapping area.

Example of the graphitic slates in the mapping area, with some quartz veins running through them.

1: Kjøll, H.J. (2015) Structural Evolution of the Porsa Imbricate Stack (Finnmark, Northern Norway) [master’s thesis: NTNU]
2: Gao, Fengge. (2002). The future prospect of polymer nanocomposites in reinforcement application. e-Polymer. 2. T_004.

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