Publication Type:Journal Article
Source:Journal of the Geological SocietyJournal of the Geological Society, Geological Society of London, London, United Kingdom, Volume 173, Number 1, p.59-75 (2016)
Keywords:Abitibi Belt, absolute age, Archean, Canada, Canadian Shield, dates, depth, eastern canada, excavations, gneisses, granites, Hadean, Huronian, ICP mass spectra, igneous rocks, impact craters, impact features, impacts, mass spectra, melting, Metamorphic rocks, nesosilicates, North America, Onaping Formation, Ontario, orthosilicates, plutonic rocks, Precambrian, proterozoic, recycling, silicates, spectra, Sudbury structure, superior province, U/Pb, upper Precambrian, zircon, zircon group
The Sudbury impact structure is one of only a few terrestrial impact craters capable of providing insight into large impact processes. However, despite more than a century of study, no consensus exists regarding its depths of excavation and melting. This study presents 3920 U-Pb zircon dates for target lithologies and the crater-fill as well as new Pb-isotope data for target lithologies in an attempt to further constrain these depths and understand the behaviour of zircon in large impacts. Only 1.5% of the crater-fill zircons have dates within uncertainty of the 1.85 Ga impact event, with most seeming to preserve their pre-impact U-Pb systematics. The preponderance of undisturbed zircon in the crater-fill suggests that this mineral is an effective means of tracing target lithologies in impact basins. A significant fraction of crater-fill zircon was dated between 2.50 and 2.61 Ga, which is negligible amongst known target lithologies, and therefore identifies previously unrecognized target rocks. The Pb-isotope systematics are compatible with the proposal that the 2.6 Ga rock represents typical mid- to lower-crustal basement and could have been an important contributor to the melt-sheet. The combined data argue against a shallow melting scenario. With regard to Hadean terrestrial zircon, the lesson from Sudbury is that zircon can be recycled through multiple large impact events and still preserve the age of the original crust.
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