DOI: 10.1016/j.epsl.2020.116574
论文题名: An evaluation of the C/N ratio of the mantle from natural CO2-rich gas analysis: Geochemical and cosmochemical implications
作者: Marty B. ; Almayrac M. ; Barry P.H. ; Bekaert D.V. ; Broadley M.W. ; Byrne D.J. ; Ballentine C.J. ; Caracausi A.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2020
卷: 551 语种: 英语
中文关键词: carbon nitrogen Earth mantle gases
英文关键词: Basalt
; Budget control
; Carbon
; Carbon dioxide
; Degassing
; Earth (planet)
; Geochemistry
; Inert gases
; Isotopes
; Radiogenic gases
; Silicates
; Structural geology
; Bulk silicate earth
; Carbon-to-nitrogen ratio
; Geochemical parameters
; Mantle source region
; Mid ocean ridge basalts
; Noble gas isotopes
; Oceanic basalts
; Volatile elements
; Molar ratio
; carbon
; carbon monoxide
; igneous geochemistry
; isotopic composition
; mantle chemistry
; mantle source
; mid-ocean ridge basalt
; nitrogen
英文摘要: The terrestrial carbon to nitrogen ratio is a key geochemical parameter that can provide information on the nature of Earth's precursors, accretion/differentiation processes of our planet, as well as on the volatile budget of Earth. In principle, this ratio can be determined from the analysis of volatile elements trapped in mantle-derived rocks like mid-ocean ridge basalts (MORB), corrected for fractional degassing during eruption. However, this correction is critical and previous attempts have adopted different approaches which led to contrasting C/N estimates for the bulk silicate Earth (BSE) (Marty and Zimmermann, 1999; Bergin et al., 2015). Here we consider the analysis of CO2-rich gases worldwide for which a mantle origin has been determined using noble gas isotopes in order to evaluate the C/N ratio of the mantle source regions. These gases experienced little fractionation due to degassing, as indicated by radiogenic H4e/40Ar⁎ values (where 4He and 40Ar* are produced by the decay of U+Th, and 40K isotopes, respectively) close to the mantle production/accumulation values. The C/N and C/3He ratios of gases investigated here are within the range of values previously observed in oceanic basalts. They point to an elevated mantle C/N ratio (∼350-470, molar) higher than those of potential cosmochemical accretionary endmembers. For example, the BSE C/N and A36r/N ratios (160-220 and 75×10−7, respectively) are higher than those of CM-CI chondrites but within the range of CV-CO groups. This similarity suggests that the Earth accreted from evolved planetary precursors depleted in volatile and moderately volatile elements. Hence the high C/N composition of the BSE may be an inherited feature rather than the result of terrestrial differentiation. The C/N and A36r/N ratios of the surface (atmosphere plus crust) and of the mantle cannot be easily linked to any known chondritic composition. However, these compositions are consistent with early sequestration of carbon into the mantle (but not N and noble gases), permitting the establishment of clement temperatures at the surface of our planet. © 2020 The Authors Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/165148
Appears in Collections: 气候变化与战略
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作者单位: Université de Lorraine, CNRS, CRPG, Nancy, F-54000, France; Marine Chemistry and Geochemistry Dept., Woods Hole Oceanographic Institution, Woods Hole, MA 02543, United States; Department of Earth Sciences, University of Oxford, Oxford, OX1 3AN, United Kingdom; Instituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, Palermo, 90146, Italy
Recommended Citation:
Marty B.,Almayrac M.,Barry P.H.,et al. An evaluation of the C/N ratio of the mantle from natural CO2-rich gas analysis: Geochemical and cosmochemical implications[J]. Earth and Planetary Science Letters,2020-01-01,551