Application of X-ray Fluorescence Spectrometry and Electron Microprobe in the Identification of Intermediate-Felsic Volcanic Rocks

Intermediate-felsic volcanic rock has porphyritic texture and the matrix is characterized by microlitic, cryptocrystalline and vitreous textures. There will be errors when identifying and classifying the rocks using only a polarizing microscope because it is difficult to accurately identify the mineral species and content due to the small grains of matrix mineral species and the limited magnification of the standard polarizing microscope. Identification of the intermediate-felsic volcanic rock by using combined X-ray Fluorescence Spectrometry, Electron Microprobe and the Polarizing Microscope is introduced in this article. Results show that the method cannot be used to accurately identify the microlitic and microcrystalline intermediate-felsic volcanic rocks which have similar matrix features because the Polarizing Microscope cannot accurately identify the contents of feldspar and quartz. X-ray Fluorescence Spectrometry was used to analyze the major elements of the rocks. The rocks were identified by standard minerals QAPF double triangle graphic classification, TAS diagram classification and Li's volcanic rock quantitative classification. There are errors among these three methods. Minerals were checked by Electron Microprobe. The results show that the QAPF double triangle graphic classification and the Li's volcanic rock quantitative classification give the same results as identification analysis under the microscope, but the TAS graphic classification results are different from the others. Therefore, multiple classification methods should be used when identifying intermediate-felsic volcanic rock, avoiding the errors caused by the single test method.