ACADEMY: A new methodology for modal abundances, density and bulk composition of micrometer-sized assemblages by advanced electron microscopy: application to chondrites

Data analysis of a matrix of primitive chondrite

This is a demo of the data analysis procedure applied in this methodology

See Zanetta et al., 2019

ACADEMY (Analyzing the Composition, the modal Abundance and the Density using Electron MicroscopY) is a method developped for the analysis of fine grained material exhibiting sub-micrometric grains. This complete petrological description is based on the combination of the advantages giving by two conventional and easily accessible techniques (SEM and EPMA) and the development of data treatment procedures, in order to improve the characterization of natural samples with micrometer-sized assemblages. This method aims to produce quantitative chemical maps with improved spatial resolution in combining the EDX spectrum, density and proxy EPMA analysis for each pixel. The method includes the following main steps:

• To decrease the volume of interaction and reach a higher spatial resolution, the hyperspectral maps are acquired with a lower accelerating voltage than conventional SEM-EDX working conditions.
• Complementary deconvolution procedures are added to the thresholding methods allowing us to obtain the quantitative mineralogy. These supplementary procedures allow us to deal with the problem of extreme mixing and of compositional variation existing in some mineral phases due to solid solutions.
• Quantitative chemical compositions of each phase are obtained by coupling SEM-EDX datasets with EMP point analyses in order to gain in spectral resolution.
• Lastly, the density of the material is locally determined based on the modeling of the EDX hyperspectral signal. This thorough methodological development leads to a complete petrological description of the sample with an improved spatial resolution and permits a better calculation of the bulk composition in volume percent by the combination of the chemistry, the modal mineralogy and the density.

This methodology is expected to have broad applications in Earth and Planetary materials.

To see the demo please click on the "demo.ipynb" file or download the whole file and open it in a jupyter notebook window.