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| Titel |
Hydrogen diffusion in Zircon |
| VerfasserIn |
Jannick Ingrin, Peipei Zhang |
| 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 |
250127290
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| Publikation (Nr.) |
 EGU/EGU2016-7148.pdf |
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| Zusammenfassung |
| Hydrogen mobility in gem quality zircon single crystals from Madagascar was investigated
through H-D exchange experiments. Thin slices were annealed in a horizontal furnace flushed
with a gas mixture of Ar/D2(10%) under ambient pressure between 900 ˚ C to 1150 ˚ C.
FTIR analyses were performed on oriented slices before and after each annealing run. H
diffusion along [100] and [010] follow the same diffusion law D = D0exp[-E /RT], with log
D0 = 2.24 ± 1.57 (in m2/s) and E = 374 ± 39 kJ/mol. H diffusion along [001]
follows a slightly more rapid diffusion law, with log D0 = 1.11 ± 0.22 (in m2/s) and
E = 334 ± 49 kJ/mol. H diffusion in zircon has much higher activation energy
and slower diffusivity than other NAMs below 1150 ˚ C even iron-poor garnets
which are known to be among the slowest (Blanchard and Ingrin, 2004; Kurka et al.
2005).
During H-D exchange zircon incorporates also deuterium. This hydration reaction
involves uranium reduction as it is shown from the exchange of U5+ and U4+ characteristic
bands in the near infrared region during annealing. It is the first time that a hydration reaction
U5+ + OH− = U4+ + O2− + 1/2H2, is experimentally reported. The kinetics of deuterium
incorporation is slightly slower than hydrogen diffusion, suggesting that the reaction is
limited by hydrogen mobility. Hydrogen isotopic memory of zircon is higher than other
NAMs. Zircons will be moderately retentive of H signatures at mid-crustal metamorphic
temperatures. At 500 ˚ C, a zircon with a radius of 300 μm would retain its H isotopic
signature over more than a million years. However, a zircon is unable to retain this
information for geologically significant times under high-grade metamorphism unless the
grain size is large enough.
Refrences
Blanchard, M. and Ingrin, J. (2004) Hydrogen diffusion in Dora Maira pyrope. Physics
and Chemistry of Minerals, 31, 593-605.
Kurka, A., Blanchard, M. and Ingrin, J. (2005) Kinetics of hydrogen extraction and
deuteration in grossular. Mineralogical Magazine, 69, 359-371. |
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