Title :

Effect of deformation on helium storage and diffusion in polycrystalline forsterite

Author(s) :

Delon, Rémi [Auteur]
Demouchy, Sylvie [Auteur]
Marrocchi, Yves [Auteur]
Bouhifd, Mohamed Ali [Auteur]
Gasc, Julien [Auteur]
Cordier, Patrick [Auteur]
Unité Matériaux et Transformations - UMR 8207 [UMET]
Unité Matériaux et Transformations (UMET) - UMR 8207
Koizumi, Sanae [Auteur]
Burnard, Pete G. [Auteur]

Journal title :

Geochimica et Cosmochimica Acta

Abbreviated title :

Geochim. Cosmochim. Acta

Volume number :

273

Pages :

226-243

Publisher :

Elsevier BV

Publication date :

2020-03

ISSN :

0016-7037

English keyword(s) :

Helium
Diffusion
Storage
Deformation
Dislocation
Forsterite

HAL domain(s) :

Planète et Univers [physics]/Sciences de la Terre
Physique [physics]/Matière Condensée [cond-mat]/Science des matériaux [cond-mat.mtrl-sci]

English abstract : [en]

Although recent studies have investigated He behavior in undeformed mantle minerals, the effect of defects generated by plastic deformation on He storage and transport remains unconstrained. For this purpose, synthetic ...
Show more >Although recent studies have investigated He behavior in undeformed mantle minerals, the effect of defects generated by plastic deformation on He storage and transport remains unconstrained. For this purpose, synthetic dense aggregates of fine-grained iron-free forsterite were deformed under 300 MPa confining pressure at 950, 1050, and 1200 °C using a Paterson press. Three deformed samples and one undeformed sample were then doped with He under static high-pressure (1.00 ± 0.02 GPa) and high-temperature (1120 ± 20 °C) conditions for 24 h in a piston cylinder. Uraninite was used as a source of noble gases. The samples were subsequently analyzed using a cycled step heating protocol coupled with noble gas mass spectrometry to investigate He storage and diffusion in the deformed polycrystalline forsterite aggregates. Results show complex diffusive behaviors that cannot be fitted by a single linear regression. Nevertheless, individual step heating cycles can be fitted by several linear regressions determined by a F-test, suggesting that diffusivities follow Arrhenius law within the given temperature ranges. Our results highlight the complex diffusive behavior of He in deformed forsterite aggregates, which is due to the competition between several diffusion mechanisms related to different He storage sites (Mg vacancies, interstitial sites, dislocations, and grain boundaries). Diffusion parameters (activation energy Ea and pre-exponential factor D0) for He diffusion in grain boundaries were refined from literature data (Ea = 36 ± 9 kJ·mol−1 and D0 = 10−10.57 ± 0.58 m2·s−1), and those of He diffusion in interstitials (Ea = 89 ± 7 kJ·mol−1 and D0 = 10−8.95 ± 1.16 m2·s−1) and Mg vacancies (Ea = 173 ± 14 kJ·mol−1 and D0 = 10−5.07 ± 1.25 m2·s−1) were defined from our results and literature data. Furthermore, we determined Ea = 56 ± 1 kJ·mol−1 and D0 = 10−9.97 ± 0.37 m2·s−1 for He diffusion along dislocations. These results suggest that a maximum He fraction of only 1.2% can be stored along dislocations in mantle minerals, which is negligible compared to 22% in grain boundaries as reported by previous studies. This implies that bulk lattice diffusivities are barely affected by the presence of dislocations, whereas the proportion of He stored in grain boundaries can significantly enhance the bulk diffusivities of mantle rocks. Thus, deformation processes can significantly increase He storage capacity by decreasing grain size (i.e., via dynamic recrystallization), but will not sufficiently increase the dislocation density to induce a change in He storage and mobility within the crystallographic lattice. Furthermore, rapid redistribution of He between the mineral lattice and grain boundaries could enhance the bulk He concentrations of deformed peridotites upon equilibration with nearby undeformed (or less-deformed) peridotites.Show less >

Language :

Anglais

Peer reviewed article :

Oui

Audience :

Internationale

Popular science :

Non

ANR Project :

Incorporation et diffusion des gaz rares dans les joints de grain.

Administrative institution(s) :

Université de Lille
CNRS
INRA
ENSCL

Collections :

• Unité Matériaux et Transformations (UMET) - UMR 8207

Research team(s) :

Plasticité

Submission date :

2020-02-06T12:29:21Z
2020-02-26T12:16:50Z