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| Titel |
Redox and speciation mapping of rock thin sections using high spatial resolution full-field imaging technique |
| VerfasserIn |
V. de Andrade, J. Susini, M. Salomé, O. Beraldin, T. Heymes, E. Lewin |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250028264
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| Zusammenfassung |
| Because of their complex genesis, natural rocks are the most often heterogeneous systems,
with various scale-level heterogeneities for both chemistry and structure. In the last decade,
the dramatic improvements of hyperspectral imaging techniques provided new tools for
accurate material characterisation. Most of these micro- and nano- analytical techniques
rely on scanning instruments, which offer high spatial resolution but suffer from
long acquisition times imposing practical limits on the field of view. Conversely,
full-field imaging techniques rely on a fast parallel acquisition but have limited
resolution.
Although soft X-ray full-field microscopes based on Fresnel zone plates are commonly
used for high resolution imaging, its combination with spectroscopy is challenging and
2D chemical mapping still difficult. For harder X-rays, lensless X-ray microscope
based on simple propagation geometry is easier and can be readily used for 2D
spectro-microscopy.
A full-field experimental setup was optimized at the ESRF-ID21 beamline to image iron
redox and speciation distributions in rocks thin sections. The setup comprises a Si111 or
Si220 (ÎE = 0.4 eV) monochromator, a special sample stage and a sensitive camera
associated with a brand new GGG:Eu light conversion scintillator and high magnification
visible light optics. The pixel size ranges from 1.6 to 0.16 μm according to the optic
used.
This instrument was used to analyse phyllosilicates and oxides of metamorphic sediments
coming from the Aspromonte nappes-pile in Calabria. Iron chemical state distributions were
derived - from images of 1000 à 2000 à 30 μm3 rock thin sections - by subtraction of
absorption images above and below the Fe K-edge. Using an automatic stitching
reconstruction, a wide field image (4Ã3 mm2 with a 1 μm2 resolution for a total of about 12
millions pixels) of Fetotal elemental distribution was produced. Moreover, μ-XANES
analyses (more than 1 million individual μ-XANES spectra) were performed from 7100 to
7280 eV with an energy resolution of 0.3 eV. This spectral resolution allows fine pre-edge
features to be clearly observed. A redox mapping was then derived from these full-field
μ-XANES acquisitions. It highlights different mineral generations that crystallized at
different redox conditions. Redox mapping has also been coupled with electron
μ-probe analyses in order to calculate accurately the P-T path of the studied rock. |
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