Micro-XANES with synchrotron radiation:: a complementary tool of micro-PIXE and micro-SXRF for the determination of oxidation state of elements.: Application to geological materials

Micro-PIXE and micro-Synchrotron X-ray fluorescence (SXRF) are powerful techniques dedicated to the study of trace elements in different matrices. However they do not give access to the chemical states of elements. By combining micro-X-Ray Absorption Near Edge Structure (XANES)and micro-SXRF using synchrotron radiation, the point analysis of an element and its proportion in different chemical states become possible. Moreover the shape and fine structures of the edge give information concerning its local structure (inter-atomic distances and coordination number). After a short presentation of both the experimental and the basic principles of mu-XANES, the study of iron oxidation states will be given to illustrate the case of geological samples. Such a study at a micrometer scale on coexisting minerals remains a fundamental god in geochemistry. Particularly in glass inclusions trapped in volcanic minerals, this information enables one to infer the physical and chemical conditions which control the evolution of the magmas. A practical method of quantification has been employed and theoretical simulations are in development simultaneously. First results as well as the capabilities of the method are presented. (C) 1999 Elsevier Science B.V. All rights reserved.