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A Two-Step K-Ar Experiment on Mars: Dating the Diagenetic Formation of Jarosite from Amazonian Groundwaters

Martin, P. E.; Farley, K. A.; Baker, M. B.; Malespin, C. A.; Schwenzer, S. P.; Cohen, B. A.; Mahaffy, P. R.; McAdam, A. C.; Ming, D. W.; Vasconcelos, P. M. and Navarro-González, R. (2017). A Two-Step K-Ar Experiment on Mars: Dating the Diagenetic Formation of Jarosite from Amazonian Groundwaters. Journal of Geophysical Research: Planets, 122(12) pp. 2803–2818.

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Following K-Ar dating of a mudstone and a sandstone, a third sample has been dated by the Curiosity rover exploring Gale Crater. The Mojave 2 mudstone, which contains relatively abundant jarosite, yielded a young K-Ar bulk age of 2.57 ± 0.39 Ga (1σ precision). A two-step heating experiment was implemented in an effort to resolve the K-Ar ages of primary and secondary mineralogical components within the sample. This technique involves measurement of 40Ar released in low-temperature (500°C) and high-temperature (930°C) steps, and a model of the potassium distribution within the mineralogical components of the sample. Using this method, the high-temperature step yields a K-Ar model age of 4.07 ± 0.63 Ga associated with detrital plagioclase, compatible with the age obtained on the Cumberland mudstone by Curiosity. The low-temperature step, associated with jarosite mixed with K-bearing evaporites and/or phyllosilicates, gave a youthful K-Ar model age of 2.12 ± 0.36 Ga. The interpretation of this result is complicated by the potential for argon loss after mineral formation. Comparison with the results on Cumberland and previously published constraints on argon retentivity of the individual phases likely to be present suggests that the formation age of the secondary materials, correcting for plausible extents of argon loss, is still less than 3 Ga, suggesting post-3 Ga aqueous processes occurred in the sediments in Gale Crater. Such a result is inconsistent with K-bearing mineral formation in Gale Lake and instead suggests postdepositional fluid flow at a time after surface fluvial activity on Mars is thought to have largely ceased.

Item Type: Journal Item
Copyright Holders: 2017 American Geophysical Union
ISSN: 2169-9100
Project Funding Details:
Funded Project NameProject IDFunding Body
Support for Mars Science Laboratory OperationsST/P002110/1UKSA UK Space Agency
Keywords: K-Ar dating; jarosite; Mars; Mars Science Laboratory; Curiosity; alteration; habitability
Academic Unit/School: Faculty of Science, Technology, Engineering and Mathematics (STEM) > Environment, Earth and Ecosystem Sciences
Faculty of Science, Technology, Engineering and Mathematics (STEM)
Research Group: Space
Item ID: 53023
Depositing User: Susanne Schwenzer
Date Deposited: 29 Jan 2018 09:46
Last Modified: 01 Jun 2019 22:43
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