气候变化领域集成服务门户(CCPortal): Kinetic carbon isotope fractionation links graphite and diamond precipitation to reduced fluid sources

CCPortal

DOI	10.1016/j.epsl.2019.115848
	Kinetic carbon isotope fractionation links graphite and diamond precipitation to reduced fluid sources
	Kueter N.; Schmidt M.W.; Lilley M.D.; Bernasconi S.M.
发表日期	2020
ISSN	0012821X
卷号	529
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)
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
语种	英语
来源期刊	Earth and Planetary Science Letters
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/202710
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
推荐引用方式 GB/T 7714	Kueter N.,Schmidt M.W.,Lilley M.D.,et al. Kinetic carbon isotope fractionation links graphite and diamond precipitation to reduced fluid sources[J],2020,529.
APA	Kueter N.,Schmidt M.W.,Lilley M.D.,&Bernasconi S.M..(2020).Kinetic carbon isotope fractionation links graphite and diamond precipitation to reduced fluid sources.Earth and Planetary Science Letters,529.
MLA	Kueter N.,et al."Kinetic carbon isotope fractionation links graphite and diamond precipitation to reduced fluid sources".Earth and Planetary Science Letters 529(2020).