DOI: 10.1016/j.epsl.2021.117013
论文题名: Timescales of impact melt sheet crystallization and the precise age of the Morokweng impact structure, South Africa
作者: 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.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2021
卷: 567 语种: 英语
中文关键词: 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
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) Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/165539
Appears in Collections: 气候变化与战略
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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
Recommended Citation:
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]. Earth and Planetary Science Letters,2021-01-01,567