Compositional X-Ray Maps of Metamorphic and Magmatic Minerals

Abstract

This paper deals with the applications of qualitative and quantitative x-ray compositional maps collected by either an energy-dispersive spectrometer (EDS) or a wavelength-dispersive spectrometer (WDS) on magmatic and metamorphic minerals.

The data from qualitative elemental maps, represented by matrices of counts, are converted to a MS-DOS media format and then processed by using an image analysis program.

The digital acquisition of quantitative EDS and WDS x-ray maps produces matrices of spectra and peak counts, respectively, with known X, Y coordinates. The matrices collected are converted to MS-DOS media-format and then processed by a dedicated program which applies a quantitative matrix correction (ZAF/FLS for EDS and pure ZAF for WDS maps). The results obtained are comparable with conventional quantitative microprobe analyses.

The final quantitative data are displayed as wt% oxide, cation or end-member two-dimensional compositional maps, either in a grey-scale or a false-colour, which can contribute significantly to the knowledge of the P-T history of rock formation. In fact, it is possible to determine the type and shape of the chemical zoning and to evaluate the proportion of each mineral involved in post-growth chemical diffusion processes.

The procedure described has been tested by collecting qualitative and quantitative x-ray maps on metamorphic and magmatic minerals.