Thermochronology of Alkali Feldspar and Muscovite at T > 150 °C Using the ⁴⁰Ar/³⁹Ar Method: A Review

Spikings, Richard A. and Popov, Daniil V. (2021). Thermochronology of Alkali Feldspar and Muscovite at T > 150 °C Using the ⁴⁰Ar/³⁹Ar Method: A Review. Minerals, 11(9), article no. 1025.

DOI: https://doi.org/10.3390/min11091025

Abstract

The ⁴⁰Ar/³⁹Ar method applied to K-feldspars and muscovite has been often used to construct continuous thermal history paths between ~150–600 °C, which are usually applied to structural and tectonic questions in many varied geological settings. However, other authors contest the use of ⁴⁰Ar/³⁹Ar thermochronology because they argue that the assumptions are rarely valid. Here we review and evaluate the key assumptions, which are that (i) ⁴⁰Ar is dominantly redistributed in K-feldspars and muscovite by thermally-driven volume diffusion, and (ii) laboratory experiments (high temperatures and short time scales) can accurately recover intrinsic diffusion parameters that apply to geological settings (lower temperatures over longer time scales). Studies do not entirely negate the application of diffusion theory to recover thermal histories, although they reveal the paramount importance of first accounting for fluid interaction and secondary reaction products via a detailed textural study of single crystals. Furthermore, an expanding database of experimental evidence shows that laboratory step-heating can induce structural and textural changes, and thus extreme caution must be made when extrapolating laboratory derived rate loss constants to the geological past. We conclude with a set of recommendations that include minimum sample characterisation prior to degassing, an assessment of mineralogical transformations during degassing and the use of in situ dating.

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• Item ORO ID
• 79079
• Item Type
• Journal Item
• ISSN
• 2075-163X
• Project Funding Details

• Funded Project Name	Project ID	Funding Body
  Early Postdoctoral Mobility fellowship	P2GEP2_191478	Swiss National Science Foundation

• Keywords
• 40Ar/39Ar; thermochronology; diffusion; K-feldspar; muscovite; in situ dating
• Academic Unit or School
• Faculty of Science, Technology, Engineering and Mathematics (STEM) > Environment, Earth and Ecosystem Sciences
  Faculty of Science, Technology, Engineering and Mathematics (STEM)
• Copyright Holders
• © 2021 The Authors.
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