Skip to Main content Skip to Navigation
Conference papers

Effect of deformation on 40Ar/39Ar dating in granitic rocks: an experimental approach

Alexane Legeay 1, 2 Stéphane Scaillet 1, 2 Jacques Précigout 1, 2 Romain Augier 1 Holger Stünitz 1, 2 Florian Duval 1
2 Géodynamique - UMR7327
INSU - CNRS - Institut national des sciences de l'Univers, UO - Université d'Orléans : UMR7327, BRGM - Bureau de Recherches Géologiques et Minières (BRGM), ISTO - Institut des Sciences de la Terre d'Orléans - UMR7327 : UMR7327
Abstract : Although the effect of temperature for argon retentivity is a well-known process in the realm of the Dodsonian closure theory, the role of deformation for Ar diffusion remains very elusive. To address this issue, we performed deformation experiments followed by 40Ar/39Ar dating on white mica within a Hercynian microgranite (Carnac, France). A set of 8 mm diameter and 15 mm long cores were first extracted, and then deformed as-is using a solid-medium Griggs-type apparatus at a pressure of 1.2 GPa and a temperature of 650 • C. Coaxial deformation has been applied for different amounts of shortening between 15% and 35%. Each experiment was doubled by a clone experiment performed in the same pressure-temperature-time conditions, but without deformation (hot pressing) to constrain the influence of temperature alone. 40Ar/39Ar dating was then applied on muscovite using in-situ UV laser ablation at the University of Orléans (ISTO). While 40Ar/39Ar ages on the starting material distribute between 285.7 ± 4.0 to 319.0 ± 5.6 Ma, a deformed sample shows a younger and more extended distribution from 205.8 ± 3.59 to 308.3 ± 5.13 Ma, with a heterogeneous spatial distribution that depends on the size of grains and location of ablation spot (core vs. rim). These observations are reproducible for 20 and 30% shortening. Such an argon loss is also observed with respect to the hot-pressed sample, suggesting that deformation promotes significant rejuvenation of 40Ar/39Ar ages. Although our data acquisition is still ongoing, our findings may have strong implications for the interpretation of geological processes based on mica ages from equivalent natural settings.
Document type :
Conference papers
Complete list of metadatas

https://hal-insu.archives-ouvertes.fr/insu-02301731
Contributor : Nathalie Pothier <>
Submitted on : Monday, September 30, 2019 - 4:21:02 PM
Last modification on : Wednesday, September 23, 2020 - 4:36:05 AM

Identifiers

  • HAL Id : insu-02301731, version 1

Collections

Citation

Alexane Legeay, Stéphane Scaillet, Jacques Précigout, Romain Augier, Holger Stünitz, et al.. Effect of deformation on 40Ar/39Ar dating in granitic rocks: an experimental approach. EGU General Assembly 2019, Apr 2019, Vienne, Austria. pp.2019 - 15550. ⟨insu-02301731⟩

Share

Metrics

Record views

50

Files downloads

8