Tracing fluid pathways in rocks and minerals

– NanoSIMS engineer no. 1: This is Wednesday, but already feels like a Friday. Why does it feel like a Friday?

– NanoSIMS engeneer no. 2: That’s because she made us work so hard this week…

– Me: Sorry guys, I have to keep my supervisor happy.

Of course, that was a half-joke. But we worked quite intensively during the last 1.5 weeks at the NanoSIMS facility in Perth. You do not want to waste time when a use of machine costs several thousand dollars a day.

NanoSIMS is a  high resolution ion-microprobe (NanoSIMS), which allows a detailed nano-scale mapping of various elements and isotopes. It can be used for rocks, metals and even biological samples. The samples I mapped come from experiments, where feldspar-rich rocks were reacted with an ¹⁸O-enriched fluid. Naturally most of the oxygen in minerals occur in a ¹⁶O form, so when we add ¹⁸O to the fluid, we are able to track the exact extent of the fluid-rock interaction, even if it is not reflected by chemical changes in the rock. Very exciting results and we were really pushing the capabilities of what this machine can do.

Overview Backscatter electron (BSE) image. The brightness of the colour reflects the atomic weight of the area. Thus the minerals containing heavier elements appear brighter.

A mosaic of images showing the distribution of 18O. Preliminary, barely processed data. There is more heterogeneity in the pink area, not reflected due to the colour scale. Little 18O = blue, a lot of 18O = red, and then pink.

“The importance of resolution” or “Why I want a field emission gun on my SEM”

Results from some recent experiments:

First look with our regular Scanning Electron Microscope (SEM) (not too bad piece of an equipment)
– “Hmm… pretty nice”

Well, I had a suspicion there is something more than what it looks like, so we brought the samples to an SEM with a field emission gun:
– “Wow! Just wow!”

The images show a Ca-rich plagioclase (lower, homogenous part in the picture), which was reacted with a Na-Si rich fluid and produced a complex reaction structures (upper, heterogenous part). The middle part that looks like a butterfly actually consist of tiny micrometer-sized garnet (grossular) grains.

Also note how homogenous the area in the red circle looks under a regular SEM, while the SEM with a field emission gun reveals that it is actually a very fine intergrowth between 2 different minerals.

A nerdy evening

I saw this guy at “Physics in the Pub” variety night yesterday. He was singing about why Pluto is no longer a planet. Unfortunately only the end of it got preserved for the history:

A little bit of google-stalking, and turns out he is a science communicator for Australian National University, Dr. Phil Dooley, and have quite a few other masterpieces on his youtube channel. Here is a song about the IPCC report on climate change. Good stuff (see from 2:30):

Field trips of 2013-2015. Part I: Fiordland (New Zealand)

I just realised that during the past 2 years I have not posted anything about the field trips I have been involved in. Well, that does not capture a life of a geology student very accurately. Besides of being a lab rat (which I enjoy, do not doubt it), I have also had my fair share of opportunities to see the sun, feel the rock and encounter few outdoor adventures, while either doing fieldwork for my own project or helping with undergraduate tutoring. So here you go: a story in 3 parts featuring Fiordland (New Zealand), Alice Springs (C-Australia) and Kiama coast (SE Australia). 

Milford Sound in Fiordland was the initially planned main field area for my project. The outcrops in Pembroke valley expose lower crustal rocks cut by a complicated network of several types of veins and shear zones. The idea was to compare the rheological properties of rocks in the “dry” and the fluid-affected shear zones, but even before the field trip I found in the samples from previous expeditions, that the shear zones in this setting feature a presence of melt, instead of a hydrous fluid. Ultimately we made a decision to work on samples from another area instead,  but I got to tag along for this field trip anyway. It was a week long camping in a distant wilderness, including a helicopter ride and beautiful outcrops.

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Nuclear experiments

The last 4 days I have been doing neutron diffraction experiments at Australian Nuclear Science and Technology Organisation (ANSTO). It has been quite an experience, a very cool one actually. I have been wearing a portable radiation dose monitor, taking almost hourly full body radiation scans every day and operating a neutron beam. However, so far it looks that the most dangerous thing about this place is not the radiation but an aggressive bird who decided to nest in front of the main entrance. Some of the scientists have already suffered terrible attacks.

Check out the live broadcast from my experiment (available for the next 24 h) – http://www.nbi.ansto.gov.au/wombat/status/#. We are measuring the rates of the mineral reaction where KBr crystal is replaced by KCl. The ultimate goal is to check if this reaction is faster for deformed crystals.

The diffraction peak for my KBr sample is around the unit 230 on the x-axis. The peak of KCl is just a little bit on the right side from the KBr peak. During the experiment, the signal of KBr becomes weaker but the signal of KCl intensifies due to the growth of KCl.

If you do not see the peaks, I am either changing the sample or obtaining terrible data.

PhD life: last week’s highlights

This is a new project which I decided to experiment a bit with in this blog. The rule is to take one picture every day of something from my daily activities to show my non-academic friends what the hell I really do at University all the time.

Last week was actually quite busy. I am working on finishing my first paper, hopefully till the end of the year, doing experiments with salt crystals in a high temperature oven, shopping minerals for other set of experiments and on top of all that I got in a  bicycle accident on my way to Uni.

It is actually a funny story how the accident happened because it was caused by a bicycle helmet. There is a law in Australia that every cyclist has to wear a helmet, which I find ridiculous and do not want to comply with.  So I rode without the helmet the whole last year until 2 weeks ago got stopped by a police and almost fined. Since then I started to wear it on the main roads and took it off on quite streets. So on Thursday I was peacefully driving to the Uni with this bloody annoying thing on my head. Then near the campus area I started to take it off. While doing this the only option was to hold the steering wheel with the left hand. The bike was going down the hill. The front wheel started to turn. I lost control. Hit the kerb of the sidewalk. Fall. Then – blood, blackout, ambulance, etc… All of this only because of a helmet : ) Anyway I am fine now. Some pretty deep scratches but nothing that can not heal.  

Middle crust challenge

The conference I mentioned earlier went pretty well. It was a small one, just for PhD students at our department but also a great opportunity to meet some numerical modellers from our centre and hear their perspective on my project.

The field study I work on is about the rock deformation in the Earth’s middle crust. Middle crust is an important rheological layer which has been quite challenging to describe numerically. While we have good approximations on the rock strength in the upper and lower crust, there are no generally accepted models for the middle crust. It is mainly due to the very complicated interaction between mechanical and chemical processes at these depths which results in a fluctuating strength of the rock.

However, I think  it is possible to identify and to a certain degree quantify the processes in middle crust using data from field studies and experiments. The question is if we have numerical tools, powerful enough to model them. And it actually looks quite promising. At this very moment my genious housemate  and colleague (let’s call him Benat)  is working on an advanced numerical code which could allow to solve this. Let’s see see what we can do.

Check out my mindblowing talk: