Stirred not shaken; critical evaluation of a proposed Archean meteorite impact in West Greenland

1Chris Yakymchuk,2Christopher L.Kirkland,3Aaron J.Cavosie,4Kristoffer Szilas,5Julie Hollis,6Nicholas J.Gardiner,4Pedro Waterton,7Agnete Steenfelt,8LaureMartin
Earth and Planetary Science Letters 557, 116730 Link to Article [https://doi.org/10.1016/j.epsl.2020.116730]
1Department of Earth and Environmental Sciences, University of Waterloo, Canada
2Timescales of Mineral Systems Group, Centre for Exploration Targeting – Curtin Node, School of Earth and Planetary Sciences, Curtin University, Perth, Australia
3Space Science and Technology Centre, School of Earth and Planetary Sciences, Curtin University, Perth, Australia
4Department of Geosciences and Natural Resource Management, University of Copenhagen, Øster Voldgade 10, 1350 Copenhagen K, Denmark
5Department of Geology, Ministry of Mineral Resources, Government of Greenland, P.O. Box 930, 3900 Nuuk, Greenland
6School of Earth and Environmental Sciences, University of St Andrews, St Andrews, KY16 9AL, United Kingdom
7The Geological Survey of Denmark and Greenland, Øster Voldgade 10, 1350 Copenhagen K, Denmark
8Centre for Microscopy, Characterisation & Analysis, The University of Western Australia, Perth, Western Australia 6009, Australia
Copyright Elsevier

Large meteorite impacts have a profound effect on the Earth’s geosphere, atmosphere, hydrosphere and biosphere. It is widely accepted that the early Earth was subject to intense bombardment from 4.5 to 3.8 Ga, yet evidence for subsequent bolide impacts during the Archean Eon (4.0 to 2.5 Ga) is sparse. However, understanding the timing and magnitude of these early events is important, as they may have triggered significant change points to global geochemical cycles. The Maniitsoq region of southern West Greenland has been proposed to record a ∼3.0 Ga meteorite impact, which, if confirmed, would be the oldest and only known impact structure to have survived from the Archean. Such an ancient structure would provide the first insight into the style, setting, and possible environmental effects of impact bombardment continuing into the late Archean. Here, using field mapping, geochronology, isotope geochemistry, and electron backscatter diffraction mapping of 5,587 zircon grains from the Maniitsoq region (rock and fluvial sediment samples), we test the hypothesis that the Maniitsoq structure represents Earth’s earliest known impact structure. Our comprehensive survey shows that previously proposed impact-related geological features, ranging from microscopic structures at the mineral scale to macroscopic structures at the terrane scale, as well as the age and geochemistry of the rocks in the Maniitsoq region, can be explained through endogenic (non-impact) processes. Despite the higher impact flux, intact craters from the Archean Eon remain elusive on Earth.

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