COMPOSITIONAL X-RAY MAPS OF METAMORPHIC AND MAGMATIC MINERALS

This paper deals with the applications of qualitative and quantitative x-ray compositional maps collected by either an energy-dispersive spe ctrometer (EDS) or a wavelength-dispersive spectrometer (WDS) on magma tic and metamorphic minerals. The data from qualitative elemental maps , represented by matrices of counts, are converted to a MS-DOS media f ormat and then processed by using an image analysis program. The digit al acquisition of quantitative EDS and WDS x-ray maps produces matrice s of spectra and peak counts, respectively, with known X, Y coordinate s. The matrices collected are converted to MS-DOS media-format and the n processed by a dedicated program which applies a quantitative matrix correction (ZAF/FLS for EDS and pure ZAF for WDS maps). The results o btained are comparable with conventional quantitative microprobe analy ses. 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 knowledg e of the P-T history of rock formation. In fact, it is possible to det ermine the type and shape of the chemical zoning and to evaluate the p roportion of each mineral involved in post-growth chemical diffusion p rocesses. The procedure described has been tested by collecting qualit ative and quantitative x-ray maps on metamorphic and magmatic minerals .