DOI: 10.1016/j.epsl.2018.03.010
Scopus记录号: 2-s2.0-85043458917
论文题名: Uranium isotope ratios of Muonionalusta troilite and complications for the absolute age of the IVA iron meteorite core
作者: Brennecka G.A. ; Amelin Y. ; Kleine T.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2018
卷: 490 起始页码: 1
结束页码: 10
语种: 英语
英文关键词: 238U/235U
; chronology
; fractionation
; IVA
; Muonionalusta
; uranium
Scopus关键词: Cooling
; Coremaking
; Fractionation
; Iron
; Isotopes
; Lead
; Meteorites
; Silicates
; Solar system
; Uranium
; chronology
; Isotopic composition
; Isotopic variations
; Muonionalusta
; Proto-planetary bodies
; Short-lived radionuclides
; Uranium isotope ratios
; ^238U/^235U
; Core samples
; accuracy assessment
; iron meteorite
; isotopic fractionation
; isotopic ratio
; precision
; radionuclide
; uranium isotope
英文摘要: The crystallization ages of planetary crustal material (given by basaltic meteorites) and planetary cores (given by iron meteorites) provide fiducial marks for the progress of planetary formation, and thus, the absolute ages of these objects fundamentally direct our knowledge and understanding of planet formation and evolution. The lone precise absolute age of planetary core material was previously obtained on troilite inclusions from the IVA iron meteorite Muonionalusta. This previously reported Pb–Pb age of 4565.3 ± 0.1 Ma—assuming a 238U/235U =137.88—only post-dated the start of the Solar System by approximately 2–3 million years, and mandated fast cooling of planetary core material. Since an accurate Pb–Pb age requires a known 238U/235U of the sample, we have measured both 238U/235U and Pb isotopic compositions of troilite inclusions from Muonionalusta. The measured 238U/235U of the samples range from ∼137.84 to as low as ∼137.22, however based on Pb and U systematics, terrestrial contamination appears pervasive and has affected samples to various extents for Pb and U. The cause of the relative 235U excess in one sample does not appear to be from terrestrial contamination or the decay of short-lived 247Cm, but is more likely from fractionation of U isotopes during metal–silicate separation during core formation, exacerbated by the extreme U depletion in the planetary core. Due to limited Pb isotopic variation and terrestrial disturbance, no samples of this study produced useful age information; however the clear divergence from the previously assumed 238U/235U of any troilite in Muonionalusta introduces substantial uncertainty to the previously reported absolute age of the sample without knowledge of the 238U/235U of the sample. Uncertainties associated with U isotope heterogeneity do not allow for definition of a robust age of solidification and cooling for the IVA core. However, one sample of this work—paired with previous work using short-lived radionuclides—suggests that the cooling age of the IVA core may be significantly younger than previously thought. This work indicates the metallic cores of protoplanetary bodies solidified no earlier than the first ∼5–10 million years of the Solar System. © 2018 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/109948
Appears in Collections: 影响、适应和脆弱性 气候变化事实与影响
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作者单位: Institut für Planetologie, University of Münster, Wilhelm-Klemm-Str. 10, Münster, 48149, Germany; Research School of Earth Sciences, The Australian National University, Canberra ACT, 0200, Australia
Recommended Citation:
Brennecka G.A.,Amelin Y.,Kleine T.. Uranium isotope ratios of Muonionalusta troilite and complications for the absolute age of the IVA iron meteorite core[J]. Earth and Planetary Science Letters,2018-01-01,490