The Open UniversitySkip to content

Compositional controls on 40Ar/39Ar ages of zoned mica from a rare-element pegmatite

Smith, S. R.; Kelley, S. P.; Tindle, A. G and Breaks, F. W. (2005). Compositional controls on 40Ar/39Ar ages of zoned mica from a rare-element pegmatite. Contributions to Mineralogy and Petrology, 149(5) pp. 613–626.

Full text available as:
Full text not publicly available (Version of Record)
Due to publisher licensing restrictions, this file is not available for public download
DOI (Digital Object Identifier) Link:
Google Scholar: Look up in Google Scholar


A high spatial resolution Ar–Ar dating study of compositionally zoned micas using UV laser extraction has been used to investigate the effect of composition and compositional boundaries upon argon diffusion in mica. The crystals are characterised by muscovite cores and Li–F–Rb–Cs-rich lepidolite rims produced by the interaction of a residual melt-vapour phase with the original muscovite during the late stages of pegmatite crystallisation. Single crystals exhibit dramatic intra-grain age variations, with a maximum range of 2,880–2,117 Ma. Backscattered electron images combined with UV-laser analyses reveal that apparent ages younger than 2,600 Ma are directly associated with the compositionally distinct rims, suggesting that Ar diffusion was faster in the lepidolite than in muscovite. Although it is not possible to be fully quantitative using the present data, it seems that argon diffusion rates in lepidolite are similar to those in biotite. Major rearrangements of the crystal structure needed to accommodate high concentrations of lithium, fluorine and large interlayer cations (Rb+, Cs+) in muscovite account for lower argon retentivity of the crystal rims. In most cases the age profiles show no disturbance at the compositional boundary, despite the transition from a di-octahedral to tri-octahedral mica, indicating that in general the boundaries do not act as fast diffusion pathways. However, in some cases there is a clear drop in ages at the compositional boundary, which acts as an effective sub-grain boundary. The difference between the two types may be related to the internal structure of the compositional boundaries or their degree of contact with the grain boundary network of the rock.

Item Type: Journal Item
Copyright Holders: 2005 Springer
ISSN: 0010-7999
Academic Unit/School: Faculty of Science, Technology, Engineering and Mathematics (STEM) > Environment, Earth and Ecosystem Sciences
Faculty of Science, Technology, Engineering and Mathematics (STEM)
Institute of Educational Technology (IET)
Item ID: 14938
Depositing User: Elizabeth Lomas
Date Deposited: 05 Mar 2009 17:01
Last Modified: 15 Dec 2019 03:42
Share this page:


Altmetrics from Altmetric

Citations from Dimensions

Actions (login may be required)

Policies | Disclaimer

© The Open University   contact the OU