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DOI	10.1016/j.epsl.2021.117013
	Timescales of impact melt sheet crystallization and the precise age of the Morokweng impact structure, South Africa
	Kenny G.G.; Harrigan C.O.; Schmitz M.D.; Crowley J.L.; Wall C.J.; Andreoli M.A.G.; Gibson R.L.; Maier W.D.
发表日期	2021
ISSN	0012821X
卷号	567
英文摘要	Impact cratering was a fundamental geological process in the early Solar System and, thus, constraining the timescales over which large impact structures cool is critical to understanding the thermal evolution and habitability of early planetary crusts. Additionally, impacts can induce mass extinctions and establishing the precise timing of the largest impacts on Earth can shed light on their role in such events. Here we report a high-precision zircon U–Pb geochronology study of the Morokweng impact structure, South Africa, which appears to have a maximum present-day diameter of ∼80 km. Our work provides (i) constraints on the cooling of large impact melt sheets, and (ii) a high-precision age for one of Earth's largest impact events, previously proposed to have overlapped the ca. 145 Ma Jurassic–Cretaceous (J–K) boundary. High-precision U–Pb geochronology was performed on unshocked, melt-grown zircon from five samples from a borehole through approximately 800 m of preserved impact melt rock. Weighted mean 206Pb/238U dates for the upper four samples are indistinguishable, with relative uncertainties (internal errors) of better than 20 ka, whereas the lowermost sample is distinguishably younger than the others. Thermal modeling suggests that the four indistinguishable dates are consistent with in situ conductive cooling of melt at this location within 30 kyr of the impact. The younger date from the lowest sample cannot be explained by in situ conductive cooling in line with the overlying samples, but the date is within the ∼65 kyr timeframe for melt-present conditions in footwall rocks below the impact melt sheet that is indicated by our thermal model. The Morokweng impact event is here constrained to 146.06 ± 0.16 Ma (2σ; full external uncertainty), which precedes current estimates of the age of the J–K boundary by several million years. © 2021 The Author(s)
关键词	baddeleyite high-precision geochronology impact melting Jurassic–Cretaceous boundary thermal modeling zircon
英文关键词	Cooling; Geochronology; Uncertainty analysis; Zircon; Baddeleyite; High-precision; High-precision geochronology; Impact melt; Impact melting; Impact structures; Jurassic-Cretaceous boundary; Melt sheet; Thermal model; Time-scales; Thermoanalysis; age determination; baddeleyite; crystallization; impact structure; melt inclusion; temperature anomaly; timescale; uranium-lead dating; zircon; South Africa
语种	英语
来源期刊	Earth and Planetary Science Letters
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/203161
作者单位	Department of Geosciences, Swedish Museum of Natural History, Stockholm, SE-104 05, Sweden; Isotope Geology Laboratory, Department of Geosciences, Boise State University, 1910 University Drive, Boise, ID 83725, United States; School of Geosciences, University of the Witwatersrand (WITS), Johannesburg, South Africa; School of Earth and Ocean Sciences, Cardiff University, Park Place, Cardiff, CF10 3AT, United Kingdom
推荐引用方式 GB/T 7714	Kenny G.G.,Harrigan C.O.,Schmitz M.D.,et al. Timescales of impact melt sheet crystallization and the precise age of the Morokweng impact structure, South Africa[J],2021,567.
APA	Kenny G.G..,Harrigan C.O..,Schmitz M.D..,Crowley J.L..,Wall C.J..,...&Maier W.D..(2021).Timescales of impact melt sheet crystallization and the precise age of the Morokweng impact structure, South Africa.Earth and Planetary Science Letters,567.
MLA	Kenny G.G.,et al."Timescales of impact melt sheet crystallization and the precise age of the Morokweng impact structure, South Africa".Earth and Planetary Science Letters 567(2021).