DOI: 10.1016/j.epsl.2020.116356
论文题名: Evaporative loss of moderately volatile metals from the superheated 1949 Ma Sudbury impact melt sheet inferred from stable Zn isotopes
作者: Kamber B.S. ; Schoenberg R.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2020
卷: 544 语种: 英语
中文关键词: evaporative metal loss
; impact fractionation
; moderately volatile metals
; stable Zn isotopes
; super-heated melt sheet
英文关键词: Binary alloys
; Cesium alloys
; Isotopes
; Lead alloys
; Rubidium alloys
; Silicates
; Stratigraphy
; Structural geology
; Zinc
; Chemical Fractionation
; Fractionation factors
; Isotope compositions
; Isotope fractionation
; Isotopic signatures
; Terrestrial accretion
; Volatile elements
; Volatile inventory
; Zinc alloys
; chemostratigraphy
; concentration (composition)
; evaporation
; isotopic composition
; isotopic fractionation
; isotopic ratio
; sedimentation
; silicate melt
; uncertainty analysis
; volatile element
; zinc
; Canada
; Ontario [Canada]
; Sudbury
英文摘要: The retention of moderately volatile elements on the growing Earth remains a major uncertainty in models of terrestrial accretion. Large impactors were the main carriers of accreted material but their mutual energetic collisions and impacts onto the Earth also caused chemical fractionation for which limited experimental data exist. The objective of this work was to study several moderately volatile elements in the third-largest impact basin preserved on Earth at Sudbury, Ontario. We conducted a new chemostratigraphic transect (n=41) of Zn isotope ratios and concentrations by analysing melt sheet and basin fill samples. The data were compared to common Pb, Cs, Cd and Sb concentration systematics. Within the crystallised melt sheet there are strong trends in the extent of moderately volatile element deficits, Zn isotope composition (δ66/64ZnJMC-L from 0.18 to 0.47‰) and initial Pb isotope composition. The combined evidence suggests that these trends reflect footwall contamination of a melt sheet that had experienced evaporative Zn-loss of up to 75–80%. Accounting for plausible isotopic signatures of target rocks, the maximum mass-dependent Zn isotope fractionation ε was 0.29 ± 0.04‰ (1 s.d.), which translates to modest fractionation factors α=0.99986 to 0.99975. This is comparable to melt fallout-glass and fused sands from nuclear detonation sites. We attribute the observed Zn loss and isotope fractionation to the formation of the impact melt. The rapid formation of a solid lid of breccias upon seawater ingress may have prevented stronger evaporative loss and isotope fractionation. Within the crater fill, there is an up-stratigraphy increase in Zn isotope variability (δ66/64ZnJMC-L from 0.29 to 1.05‰). Combined with evidence for biogenic reduced C, this suggests sedimentation of authigenic particulates within an enclosed crater sea. In the melt sheet, the Zn-Pb and Rb-Cs pairs experienced different extents of maximum evaporative loss (Pb up to 98.4% vs. Zn 78%; and Cs ∼90% vs. Rb ∼30%). The relative loss pattern could reflect evaporation from superheated silicate melt at ∼1,450 °C and 1 atm. Loss from super-liquidus melts formed by bolide impacts could have been a significant process shaping the Earth's volatile and moderately volatile inventory. © 2020 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/165067
Appears in Collections: 气候变化与战略
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作者单位: School of Earth and Atmospheric Sciences, Queensland University of Technology, Australia; Isotope Geochemistry, Department of Geosciences, Eberhard-Karls University of Tuebingen, Germany; Department of Geology, University of Johannesburg, South Africa
Recommended Citation:
Kamber B.S.,Schoenberg R.. Evaporative loss of moderately volatile metals from the superheated 1949 Ma Sudbury impact melt sheet inferred from stable Zn isotopes[J]. Earth and Planetary Science Letters,2020-01-01,544