Sorcha McMahon – 3rd year PhD student
“New insights into deep mantle melts and the carbonatite-meliliitite connection”
1) The Twitter challenge: Your PhD in 140 characters
Investigating how strange igneous rocks called carbonatites may have formed, using both natural samples and high-pressure experiments
2) How are you pushing the frontiers of science?
There are two main aims of my PhD. The first part has been to characterise some unusual carbonate-rich volcanic deposits in the Calatrava Volcanic Province, central Spain. This region was only quite recently discovered as carbonatite-bearing and the varied products can be used to provide insights into the mantle beneath continental rift settings. The second aspect of my research lies in experimental petrology, investigating carbonate melting at mantle conditions, and has wider applicability to processes involved in carbonatite formation. I’m specifically investigating the synthetic CMAS (CaO-MgO-Al2O3-SiO2) system with the addition of potassium (K2O) and carbon dioxide (CO2).
3) What part of your work do you enjoy the most?
The best part of my PhD is the variety – the combination of looking at natural samples and running experiments means that there is very little time to be bored! Although it can be very frustrating (and a little soul-destroying when things go wrong), I am happiest in the lab. Preparing piston cylinder experiments involves a lot of making and fiddling with small parts, and the process often feels like an art project.
4) What’s the most challenging aspect?
Staying motivated and not panicking! The experimental aspect of my research is both highly rewarding but very challenging at times. There are many opportunities for things to break and explode, and after investing so much time preparing parts, dismantling a failed experiment can be very disheartening.
The piston cylinder: it’s a love-hate relationship. This piece of equipment is used to simulate the conditions beneath the Earth’s surface, at pressures and temperatures equivalent to ~100 km depth and 1000 – 1400oC. Credit: Charly Stamper
5) Favourite piece of equipment
Like Charly, I am a big fan of the Scanning Electron Microscope (SEM). There isn’t one aspect of my research that hasn’t involved using this piece of equipment to take images of either natural carbonatites or my experimental products.
But before I can look at my experiments, I have to run them! The piston cylinder apparatus is my weapon of choice, and I would say we have quite a love/hate relationship. I use the piston cylinder to recreate pressure and temperature conditions in the Earth, equivalent to ~100 km depth and 1000 – 1400oC.
6) Best travel perk of the job
Before starting my PhD I had the pleasure of spending a week in Calatrava to carry out fieldwork with former student Emma and my supervisors, including the late Professor Ken Bailey. It was a great experience to observe these carbonatites and associated silicate rocks in a range of volcanic deposits, and be shown them by a world’s leading expert. The huge amount of mantle material, indicating direct and rapid eruption from the mantle, remains one of the most memorable and impressive features of this province.
FInca La Nava (left), a matrix-supported carbonatite tuff in which country rock fragments, juvenile silicate lapilli and mantle debris are set within an igneous carbonate matrix. Direct and rapid eruption from the mantle is indicated by an abundance of large mantle xenoliths (centre), and phlogopite and amphibole (right) xenocrysts. Credit: Sorcha McMahon
