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| Titel |
Helium and neon diffusion in pure hematite (α-Fe2O3) crystal lattice |
| VerfasserIn |
Hilal Balout, Jérôme Roques, Cécile Gautheron, Laurent Tassan-Got |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250131605
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| Publikation (Nr.) |
 EGU/EGU2016-12033.pdf |
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| Zusammenfassung |
| Hematite (α-Fe2O3) has the corundum-type structure and is relatively present on Earth and
Mars surface associated to ore mineral precipitation or as a weathering phase. He and Ne
retention in such mineral has been intensively investigated experimentally because of the
potential use of (U−Th−Sm)/(He−Ne) chronometer and thermochronometer. Therefore, the
He/Ne diffusion in hematite crystal is an important issue for the interpretation of
(U−Th)/(He−Ne) thermochronometric ages.
For this purpose an accurate investigation of helium and neon diffusion in hematite crystal
lattice has been achieved by computational multi-scale approach. Different insertion sites and
diffusion pathways are first characterized where the spin polarized density functional theory
(sp−DFT) approach coupled to the nudged elastic band (NEB) method is used to
determine the migration energies between the insertion sites. Then, a statistical method,
based on transition state theory (TST), is used to compute the jump probability
between sites. The previous results are used as input data in a 3D random walk
simulation, which permits to determine the effective activation energy and diffusion
coefficient.
Using the He/Ne diffusion coefficients, the closure temperature Tc has been calculated. For
typical grain size of 100 microns, Tc will be of 116∘ C and 297∘ C for He and Ne atoms,
respectively. These results Show that He and Ne atoms are highly retained in the crystal
lattice at surface temperature.
The obtained diffusion coefficients confirm that He/Ne retentively power in hematite lattice is
very important, allowing a large range of different geological applications such the
measurement of hematite crystallization ages on Earth and Mars. |
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