Bonus: Electron Probe Micro-Analysis (EPMA) - Mistastin Impact Melt

January 16, 2019

Hey everyone!

 

As I promised to be more consistent with my blogs, I am releasing a bonus one this week.

 

This blog was a last minute creation because I only finished collecting this data this morning. Instead of waiting another week I decided I would share with you guys what I am doing. 

 

I completed electron probe micro-analysis (EPMA) collecting geochemical data from Mistastin impact melt samples. EPMA measures the elemental composition of minerals by exciting their electrons. This is achieved using a high-energy beam of electrons striking the surface of samples such as thin sections. The data can be energy dispersive spectroscopy (EDS) or wave dispersive spectroscopy (WDS). EDS measures the energy difference between electron shells in elements while WDS analyses characteristic X-ray wavelengths of the elements to obtain quantitative results. The X-rays must follow Bragg's Law (2dsinϴ = nλ, https://serc.carleton.edu/research_education/geochemsheets/wds.html).

 

My focus is the geochemistry of the melt matrix because it represents the composition of the impact melt, and is one of its chemical properties (one of focus points of my research). I am also looking at the physical properties of the impact melt rocks. These include vesicularity, crystallinity, and viscosity. The data was not collected as points but as areas to incorporate the entire matrix chemistry. If I used point analysis I will only obtain chemical data representing a small part of the matrix. The data is energy dispersive spectroscopy, and most sampling areas were restricted to areas in the sample where there are no clasts and large vesicles. There are some exceptions where the vesicles are very small and cover a large portion of the sample. An example of the area sampling is below, which shows how the areas do not incorporate clasts, cracks in the thin sections, and large vesicles.

 

 

 

The samples analysed include clast-rich melt rocks, clast-poor melt rocks, vesicular melt, and impact melt-bearing breccias. The next blog will contain a more detailed description of the samples and a map showing their locations at the Mistastin Lake impact structure in Labrador, Canada.

 

This is a very short blog but it was quickly written just to give you guys more information on what is to come in the coming weeks!

 

See you all next time! 

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