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Time for a thread: I want to show you what I do with Raman spectroscopy and thin sections. It’s a big fancy machine with lasers, and is incredibly useful for a wide variety of purposes! #thinsectionthursday #erc #geology #truedepths @MineralogyPavia 1/11
My work is on metamorphic rocks from the Alps, where I study inclusions in garnet to understand the conditions where these inclusions were “trapped”, and what it tells us about subduction and the formation of mountain ranges. 2/11
Certain inclusions trapped in garnet at depth and then brought to the surface, will become strained because of the difference in elastic properties of these minerals. Example pic: strained coesite in garnet. The garnet locally has strain-induced birefringence. 3/11
I won’t go into detail about how Raman works, but what it comes down to is that you shoot a laser at a substance and measure a spectrum, which is unique for that substance – and we can also learn more from certain peaks in those spectra. 4/11
Before I can start my lab work, the machine needs to be calibrated, first with elemental silicon (very shiny!), and then I measure a reference crystal of zircon as a standard, as I will be measuring zircon inclusions today. 5/11
This is the thin section I’m currently working on. It’s not very impressive, but this piece of quartzite contains many small garnets with tons of useful inclusions! It’s actually a thick section (250 microns) so stresses and strains are preserved. 6/11
I keep track of the garnets and inclusions in QGIS, which is a neat way of linking a dataset to a scan of the thin section. There are over 1000 garnets in this section, and 30 zircon inclusions that are good enough for Raman analysis. 7/11
When zircon is elastically strained, certain peaks in its Raman spectrum will shift to a different position. Essentially, higher strains will result in larger peak position changes. This also works with quartz in garnet. Pics: Raman spectroscopy at work. 8/11
Here we see two Raman spectra from the reference zircon (red) and a strained zircon inclusion in garnet (red). You can see that some peaks not at the same position, relative to the x-axis. 9/11
Using Raman in this way to understand the pressure and temperature conditions in metamorphic rocks during garnet growth is called elastic geothermobarometry. We at @MineralogyPavia are working hard on developing and applying this method. 10/11 @teoalvarounipv
A bit of advertising to finish: for more information on this research, go visit http://www.mineralogylab.com where you can find updates and publications on this topic. 11/11 #erc #truedepths
