Micro-XANES with synchrotron radiation: a complementary tool of micro-PIXEand 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 tec hniques dedicated to the study of trace elements in different matrices. How ever they do not give access to the chemical states of elements. By combini ng micro-X-Ray Absorption Near Edge Structure (XANES)and micro-SXRF using s ynchrotron radiation, the point analysis of an element and its proportion i n different chemical states become possible. Moreover the shape and fine st ructures of the edge give information concerning its local structure (inter -atomic distances and coordination number). After a short presentation of b oth the experimental and the basic principles of mu-XANES, the study of iro n oxidation states will be given to illustrate the case of geological sampl es. Such a study at a micrometer scale on coexisting minerals remains a fun damental god in geochemistry. Particularly in glass inclusions trapped in v olcanic minerals, this information enables one to infer the physical and ch emical conditions which control the evolution of the magmas. A practical me thod of quantification has been employed and theoretical simulations are in development simultaneously. First results as well as the capabilities of t he method are presented. (C) 1999 Elsevier Science B.V. All rights reserved .