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.

Picture1

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.

W17_mosaic c

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.

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