Hyperspectral μ-XANES mapping in the diamond-anvil cell: analytical procedure applied to the decomposition of (Mg,Fe)-ringwoodite at the upper/lower mantle boundary

Abstract : We propose a new analytical approach to extract information from μ-X-ray Absorption Spectroscopy (XAS) based mapping techniques, where each pixel of a map contains full XANES (X-ray Absorption Near Edge Structure) information. Data reduction is performed thanks to specifically developed software, XASMAP, which allows automatic normalization, linear combination fits, map reconstruction and spectrum extraction. We illustrate an example of application on data acquired in a laser heated diamond-anvil cell, devoted to the investigation of the behavior of iron during the decomposition of (Mg,Fe)-ringwoodite into perovskite and ferropericlase at conditions relevant to Earth upper/lower mantle boundary. The analysis of 1600 Fe K-edge XANES spectra allows the reconstruction of maps based on iron-speciation, but it also drives to iron-concentration maps in a complex mixture of three crystalline phases. This analytical procedure opens the way to in situ studies at extreme conditions of pressure and temperature for the geosciences, physics and chemistry communities.