40Ar/39Ar systematics of melt lithologies and target rocks from the Gow Lake impact structure, Canada

Pickersgill, A. , Mark, D., Lee, M. and Osinski, G. (2020) 40Ar/39Ar systematics of melt lithologies and target rocks from the Gow Lake impact structure, Canada. Geochimica et Cosmochimica Acta, 274, pp. 317-332. (doi: 10.1016/j.gca.2020.01.025)

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Abstract

The age of the Gow Lake impact structure (Saskatchewan, Canada) is poorly constrained, with previous estimates ranging from 100 to 250 Ma. Using a combination of step-heating and UV laser in situ 40Ar/39Ar analyses we have sought to understand the 40Ar/39Ar systematics of this small impact crater and obtain a more precise and accurate age. This structure is challenging for 40Ar/39Ar geochronology due to its small size (∼5 km diameter), the silicic composition of the target rock, and the large difference in age between the impact event and the target rock (∼1.2 Ga). These factors can serve to inhibit argon mobility in impact melts, leading to retention of ‘extraneous’ 40Ar and anomalously older measured ages. We mitigated the undesirable effects of extraneous 40Ar retention by analysing small volume aliquots of impact glass using step-heating and even smaller volumes via the UV laser in situ 40Ar/39Ar technique. Although primary hydration of impact-generated glasses enhanced the diffusivity of 40Ar inherited from silica-rich melts, data still had to be corrected for extraneous 40Ar by using isotope correlation plots to define the initial trapped 40Ar/36Ar components. Our inverse isochron age of 196.8 ± 9.6/9.9 Ma (2σ, analytical/external precision) demonstrates that the Gow Lake event occurred within uncertainty of the Triassic-Jurassic boundary, but there is no evidence that it was part of an impact cluster.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Pickersgill, Dr Annemarie and Mark, Professor Darren and Lee, Professor Martin
Authors: Pickersgill, A., Mark, D., Lee, M., and Osinski, G.
College/School:College of Science and Engineering > School of Geographical and Earth Sciences
Journal Name:Geochimica et Cosmochimica Acta
Publisher:Elsevier
ISSN:0016-7037
ISSN (Online):1872-9533
Published Online:21 January 2020
Copyright Holders:Copyright © 2020 The Authors
First Published:First published in Geochimica et Cosmochimica Acta 274:317-332
Publisher Policy:Reproduced under a Creative Commons License

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
172314A journey from the solar nebula to planetary bodies: cycling of heat, water and organicsMartin LeeScience and Technology Facilities Council (STFC)ST/N000846/1GES - Earth Sciences