DOI: 10.1016/j.epsl.2019.115848
论文题名: Kinetic carbon isotope fractionation links graphite and diamond precipitation to reduced fluid sources
作者: Kueter N. ; Schmidt M.W. ; Lilley M.D. ; Bernasconi S.M.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2020
卷: 529 语种: 英语
中文关键词: carbon isotopes
; diamond
; graphite
; kinetic isotope fractionation
; methane
英文关键词: Diamonds
; Diffusion in liquids
; Graphite
; Kinetics
; Methane
; Carbon isotope composition
; Carbon isotope fractionation
; Carbon isotopes
; Equilibrium fractionations
; Fractionation factors
; Kinetic isotope fractionation
; Positive correlations
; Time-series experiments
; Isotopes
; carbon isotope
; diamond
; experimental mineralogy
; graphite
; isotopic fractionation
; methane
; precipitation (chemistry)
; reaction kinetics
; time series
英文摘要: At high temperatures, isotope partitioning is often assumed to proceed under equilibrium and trends in the carbon isotope composition within graphite and diamond are used to deduce the redox state of their fluid source. However, kinetic isotope fractionation modifies fluid- or melt-precipitated mineral compositions when growth rates exceed rates of diffusive mixing. As carbon self-diffusion in graphite and diamond is exceptionally slow, this fractionation should be preserved. We have hence performed time series experiments that precipitate graphitic carbon through progressive oxidization of an initially CH4-dominated fluid. Stearic acid was thermally decomposed at 800 °C and 2 kbar, yielding a reduced COH-fluid together with elemental carbon. Progressive hydrogen loss from the capsule caused CH4 to dissociate with time and elemental carbon to continuously precipitate. The newly formed C0, aggregating in globules, is constantly depleted by −6.2±0.3‰ in 13C relative to the methane, which defines a temperature dependent kinetic graphite-methane 13C/12C fractionation factor. Equilibrium fractionation would instead yield graphite heavier than the methane. In dynamic environments, kinetic isotope fractionation may control the carbon isotope composition of graphite or diamond, and, extended to nitrogen, could explain the positive correlation of δ13C and δ15N sometimes observed in coherent diamond growth zones. 13C enrichment trends in diamonds are then consistent with reduced deep fluids oxidizing upon their rise into the subcontinental lithosphere, methane constituting the main source of carbon. © 2019 The Author(s) Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/165088
Appears in Collections: 气候变化与战略
There are no files associated with this item.
作者单位: Department of Earth Sciences, ETH Zurich, Sonneggstrasse 5, Zurich, 8092, Switzerland; School of Oceanography, University of Washington, 1503 NE Boat Street, Seattle, WA 98195-7940, United States
Recommended Citation:
Kueter N.,Schmidt M.W.,Lilley M.D.,et al. Kinetic carbon isotope fractionation links graphite and diamond precipitation to reduced fluid sources[J]. Earth and Planetary Science Letters,2020-01-01,529