Uranium–lead zircon systematics in the Sudbury impact crater-fill: implications for target lithologies and crater evolution

Abstract

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. Supplementary materials: Sample information, trace element and Pb-isotope data for granitoid and gneiss feldspar, Pb modelling parameters, U–Pb zircon data, concordia diagrams and airborne radiometric images are available at http://www.geolsoc.org.uk/SUP18881 .

Protracted volcanism after large impacts: Evidence from the Sudbury impact basin

“…The Sandcherry Member and the Contact Unit of the Dowling Member are described as breccias, whereas the Lower, Middle, and Upper Units of the Dowling Member are described as tuffs, progressively finer‐grained up stratigraphy. Zircon data are from Petrus et al [] (square) and Pb concentrations in matrix separates are from O ' Sullivan et al [] (triangle).…”

“…Field, petrographic, and compositional data make it possible to reconstruct the origin of the 1.5 km thick, petrologically complex Onaping Formation with unprecedented detail. In this section we discuss our findings in the context of previous models [ Ames , ; Ames et al ., ; Mungall et al ., ; Grieve et al ., ; Petrus et al ., , ; O'Sullivan et al ., ] before developing a new working model in section 5.4 (Figure ).…”

“…Recently published zircon ages and volatile metal chemostratigraphy (Figure ) provide additional support for our proposal. Petrus et al [] demonstrated that the zircon U/Pb age distribution between the Sandcherry and Dowling Members differs markedly. Whereas the Sandcherry Member zircon age distribution is uniform across the basin, the Dowling Member zircon age distribution is different between the South and North Ranges.…”

Investigating the shock histories of lunar meteorites Miller Range 090034, 090070, and 090075 using petrography, geochemistry, and micro‐FTIR spectroscopy

“…; Petrus et al. ; Darling et al. ), optical effects (e.g., mechanical twinning, mosaicism; French , ; Rubin et al.…”

U-Pb memory behavior in Chicxulub's peak ring — Applying U-Pb depth profiling to shocked zircon

“…Only with robust high-resolution chronology will we be able to answer fundamental questions about impactinduced environmental change, extinction events, and the impact cratering flux through geologic time (e.g., French, 1998;Bland, 2005;Schulte et al, 2010). Further, inherited target rock ages obtained from target rocks and impactities can hold fundamental information about the pre-impact thermal history of the target area including the identification of previous unknown target materials, evaluating the origin of impactites, times of high impact flux, and the cratering process itself (e.g., Compston et al, 1987;Krogh et al, 1993a, Krogh et al, 1993bAbbott et al, 2012;Petrus et al, 2016).…”