The Open UniversitySkip to content
 

Ar–Ar dating of authigenic K-feldspar: Quantitative modelling of radiogenic argon-loss through subgrain boundary networks

Mark, D. F.; Kelley, S. P.; Lee, M. R.; Parnell, J.; Sherlock, S. C. and Brown, D. J. (2008). Ar–Ar dating of authigenic K-feldspar: Quantitative modelling of radiogenic argon-loss through subgrain boundary networks. Geochimica et Cosmochimica Acta, 72(11) pp. 2695–2710.

Full text available as:
[img]
Preview
PDF (Not Set) - Requires a PDF viewer such as GSview, Xpdf or Adobe Acrobat Reader
Download (9Mb)
DOI (Digital Object Identifier) Link: http://dx.doi.org/10.1016/j.gca.2008.03.018
Google Scholar: Look up in Google Scholar

Abstract

We have analysed two distinct generations of authigenic K-feldspar in Fucoid Bed sandstones from An-t-Sron and Skiag Bridge, NW Highlands, Scotland, which have experienced post-growth heating to levels in excess of the predicted Ar-closure temperature. Authigenic K-feldspars show microtextural similarities to patch perthites; that is subgrains separated by dislocation-rich boundary networks that potentially act as fast diffusion pathways for radiogenic argon.

The two generations of authigenic K-feldspar in the Fucoid Bed sandstones can be distinguished by different microtextural zones, bulk mineral compositions, fluid-inclusion populations, and inferred temperatures and chemistries of parent fluids. Ar–Ar age data obtained using high-resolution ultraviolet laser ablation, show that the first cementing generation is Ordovician and the second cementing generation is Silurian.

Modelling of Ar diffusion using subgrain size as the effective diffusion dimension and a simplified tectono–thermal thrust model assuming transient heating of the Fucoid Beds is inconsistent with observed data. Removal of heat from the thrust zone through rapid flushing of heated fluids rather than transient heating can be invoked to explain the observed Ar–Ar ages for both generations of cement. Alternatively, Ar-diffusion modelling using overgrowth thickness as the effective diffusion dimension instead of subgrain size also yields models that are consistent with both the Fucoid Bed palaeothermal maxima and determined Ar–Ar age ages for the two generations of K-feldspar cement. Based on this alternate explanation, we propose a theoretical microtextural model that highlights fundamental differences between the microtextures of deuterically formed patch perthites and authigenic K-feldspars, explaining the apparent robustness of authigenic K-feldspar with respect to Ar-retention.

Item Type: Journal Article
ISSN: 0016-7037
Keywords: Authigenic K-feldspar; Ar diffusion; FIB-TEM; Ar-Ar; subgrain; microtexture
Academic Unit/Department: Science > Environment, Earth and Ecosystems
Interdisciplinary Research Centre: Centre for Earth, Planetary, Space and Astronomical Research (CEPSAR)
Item ID: 10571
Depositing User: Simon Kelley
Date Deposited: 29 May 2008
Last Modified: 25 Jan 2011 00:49
URI: http://oro.open.ac.uk/id/eprint/10571
Share this page:

Actions (login may be required)

View Item
Report issue / request change

Policies | Disclaimer

© The Open University   + 44 (0)870 333 4340   general-enquiries@open.ac.uk