A Paleozoic age for the Tunnunik impact structure

Abstract

We report paleomagnetic directions from the target rocks of the Tunnunik impact structure, as well as from lithic impact breccia dikes that formed during the impact event. The target sedimentary rocks have been remagnetized after impact‐related tilting during a reverse polarity interval. Their magnetization is unblocked up to 350 °C. The diabase dikes intruding into these sediments retained their original magnetization which unblocks above 400 °C. The impact breccia records a paleomagnetic direction similar to that of the overprints in the target sedimentary rocks. The comparison of the resulting virtual geomagnetic pole for the Tunnunik impact structure with the apparent polar wander path for Laurentia combined with biostratigraphic constraints from the target sedimentary rocks is most consistent with an impact age in the Late Ordovician or Silurian, around 430–450 Ma, soon after the deposition of the youngest impacted sedimentary rocks. Our results from the overprinted sedimentary rocks and diabase dikes imply that the postimpact temperature of the studied rocks was about 350 °C.

In situ U–Pb analysis of shocked zircon from the Charlevoix impact structure, Québec, Canada

“…Many, if not all, of these impact structures predominantly clustered across Northern Europe and North America may be potentially related to the~470 Ma L chondrite breakup event in space (Schmitz et al 2001(Schmitz et al , 2008Korochantseva et al 2007;Swindle et al 2014). The Brent, Carswell, Couture, East Clearwater Lake, La Moinerie, Pilot, Slate Islands, and Tunnunik impact structures in Canada; the Ames, Calvin, Decorah, Glasford, Glover Bluff, and Rock Elm impact structures in the United States; the Granby, Hummeln, Lockne, M alingen, and Tv€ aren impact structures in Sweden; the K€ ardla impact structure and the Osmussaar impact breccia in Estonia; the Ilyinets impact structure in Ukraine; and the Lawn Hill impact structure in Australia are of demonstrated, or at least likely, Ordovician age (e.g., Pesonen et al 2004;Alwmark et al 2010Alwmark et al , 2015Alwmark et al , 2017Schmieder et al 2015a;Darlington et al 2016;French et al 2018;Lepaulard et al 2019;McGregor et al 2019). A number of additional structures of suspected impact origin have Ordovician ages (see, e.g., table 3 of Schmieder et al Fig.…”

“…Plot showing number of confirmed terrestrial impact structures (n = 199) versus best-estimate impact age. Most crater ages were taken from the Earth Impact Database (2018); however, others were sourced from the literature (Pesonen et al 2004;Alwmark et al 2010Alwmark et al , 2015Alwmark et al , 2017Jourdan et al 2012;Schmieder et al 2015a and references therein; Darlington et al 2016;Meier and Holm-Alwmark 2017;Erickson et al 2019;Holm-Alwmark et al 2019;Lepaulard et al 2019;McGregor et al 2019). A reported age of, e.g., "<1400 Ma" was counted as "700 AE 700 Ma."…”

Geophysical signature of the Tunnunik impact structure, Northwest Territories, Canada

“…Indeed, using paleomagnetism, Lepaulard et al. () estimated that this impact event occurred 430–450 Ma ago.…”

“…Magnetic parameters used to constrain the model are described in Lepaulard et al. (): the remanent magnetization intensity was obtained from measurements with a Superconducting Quantum Interference Devices (SQUID) 760R (2G Entreprises) magnetometer while the magnetic susceptibility was measured with an AGICO Kappabridge MFK1.…”

“…Paleomagnetic analyses of these dykes have provided an age for the impact event of 440 ± 10 Ma (Lepaulard et al. ). The present topography decreases from about 200 m altitude in the southeast corner to the sea level of the Richard Collinson Inlet in the northwest.…”