scholarly journals Technical note: Lithium isotopes in dolostone as a palaeo-environmental proxy – an experimental approach

2019 ◽  
Vol 15 (2) ◽  
pp. 635-646 ◽  
Author(s):  
Holly L. Taylor ◽  
Isaac J. Kell Duivestein ◽  
Juraj Farkas ◽  
Martin Dietzel ◽  
Anthony Dosseto
Keyword(s):  
Isotope Fractionation ◽  
Isotope Composition ◽  
Relative Proportion ◽  
Significant Proportion ◽  
Technical Note ◽  
Fractionation Factor ◽  
Calcium Carbonates ◽  
Marine Carbonates ◽  
Li Isotope ◽  
Environmental Proxy

Abstract. Lithium (Li) isotopes in marine carbonates have considerable potential as a proxy to constrain past changes in silicate weathering fluxes and improve our understanding of Earth's climate. To date the majority of Li isotope studies on marine carbonates have focussed on calcium carbonates. The determination of the Li isotope fractionation between dolomite and a dolomitizing fluid would allow us to extend investigations to deep times (i.e. Precambrian) when dolostones were the most abundant marine carbonate archives. Dolostones often contain a significant proportion of detrital silicate material, which dominates the Li budget; thus, pretreatment needs to be designed so that only the isotope composition of the carbonate-associated Li is measured. This study aims to serve two main goals: (1) to determine the Li isotope fractionation between Ca–Mg carbonates and solution, and (2) to develop a method for leaching the carbonate-associated Li out of dolostone while not affecting the Li contained within the detrital portion of the rock. We synthesized Ca–Mg carbonates at high temperatures (150 to 220 ∘C) and measured the Li isotope composition (δ7Li) of the precipitated solids and their respective reactive solutions. The relationship of the Li isotope fractionation factor with temperature was obtained: 103ln⁡αprec-sol=-(2.56±0.27)106(1)/T2+(5.8±1.3) Competitive nucleation and growth between dolomite and magnesite were observed during the experiments; however, there was no notable effect of their relative proportion on the apparent Li isotope fractionation. We found that Li isotope fractionation between the precipitated solid and solution is higher for Ca–Mg carbonates than for Ca carbonates. If the temperature of a precipitating solution is known or can be estimated independently, the above equation could be used in conjunction with the Li isotope composition of dolostones to derive the composition of the solution and hence make inferences about the past Li cycle. In addition, we also conducted leaching experiments on a Neoproterozoic dolostone and a Holocene coral. Results show that leaching with 0.05 M hydrochloric acid (HCl) or 0.5 % acetic acid (HAc) at room temperature for 60 min releases Li from the carbonate fraction without a significant contribution of Li from the siliciclastic detrital component. These experimental and analytical developments provide a basis for the use of Li isotopes in dolostones as a palaeo-environmental proxy, which will contribute to further advance our understanding of the evolution of Earth's surface environments.

scholarly journals Lithium isotopes in dolostone as a palaeo-environmental proxy – An experimental approach

2018 ◽  
Author(s):  
Holly L. Taylor ◽  
Isaac J. Kell Duivestein ◽  
Juraj Farkaš ◽  
Martin Dietzel ◽  
Anthony Dosseto
Keyword(s):  
Isotope Fractionation ◽  
Isotope Composition ◽  
Relative Proportion ◽  
Seawater Temperature ◽  
Significant Proportion ◽  
Treatment Needs ◽  
Fractionation Factor ◽  
Marine Carbonates ◽  
Li Isotope ◽  
Environmental Proxy

Abstract. Lithium (Li) isotopes in marine carbonates have considerable potential as a proxy to constrain past changes in silicate weathering fluxes and improve our understanding of Earth’s climate. To date the majority of Li isotope studies on marine carbonates have focussed on calcium carbonates. Determination of the Li isotope fractionation between dolomite and a dolomitizing fluid, would allow us to extend investigations to deep times (i.e., Precambrian) when dolostones were the most abundant marine carbonate archives. Dolostones often contain a significant proportion of detrital silicate material, which dominates the Li budget, thus pre-treatment needs to be designed so that only the isotope composition of the carbonate-associated Li is measured. This study aims to serve two main goals: (1) determining the Li isotope fractionation between Ca-Mg carbonates and solution and (2) to develop a method for leaching the carbonate-associated Li out of dolostone while not affecting that contained within the detrital portion of the rock. We synthesized Ca-Mg carbonates at high temperature (150 to 220 °C) and measured the Li isotope composition (δ7Li) of precipitated solids and their respective reactive solutions. The relationship of the Li isotope fractionation factor with temperature was obtained: 103lnαprec-sol = −(2.56 ± 0.27) × 106T2 + (5.8 ± 1.3) Competitive nucleation and growth between dolomite and magnesite were observed during the experiments, however, without notable effect of their relative proportion on the apparent Li isotope fractionation. We found that Li isotope fractionation between precipitated solid and solution is much greater for Ca-Mg carbonates than for Ca carbonates. If the seawater temperature can be estimated independently, the above equation could be used in conjunction with the Li isotope composition of dolostones to derive those of the precipitating solutions and hence make inferrals about the past oceanic Li cycle. In addition, we also conducted leaching experiments on a Neoproterozoic dolostone and a Holocene coral. Results show that leaching with 0.05M HCl or 0.5 % acetic acid at room temperature for 60 min releases Li from the carbonate fraction without significant contribution of Li from the siliciclastic detrital component. These experimental and analytical developments provide a basis for the use of Li isotopes in dolostones as a palaeo-environmental proxy, which will contribute to further advance our understanding of the evolution of Earth’s surface environments.

scholarly journals Bromine Isotope Variations in Magmatic and Hydrothermal Sodalite and Tugtupite and the Estimation of Br Isotope Fractionation between Melt and Sodalite

Minerals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 370
Author(s):  
Hans G. M. Eggenkamp ◽  
Michael A. W. Marks ◽  
Pascale Louvat ◽  
Gregor Markl
Keyword(s):  
Late Stage ◽  
Isotope Fractionation ◽  
Isotope Composition ◽  
Fractionation Factor ◽  
Data Set ◽  
Geothermal Fluids ◽  
A Value ◽  
Isotope Fractionation Factor ◽  
Very High ◽  
Fractionation Factors

We determined the bromine isotope compositions of magmatic and hydrothermal sodalite (Na8Al6Si6O24Cl2) and tugtupite (Na8Al2Be2Si8O24Cl2) from the Ilímaussaq intrusion in South Greenland, in order to constrain the Br isotope composition of the melt and hydrothermal fluids from which these minerals were formed. Early formed magmatic sodalite has high Br contents (138 ± 10 µg/g, n = 5) and low δ81Br values (+0.23 ± 0.07‰). Late stage hydrothermal sodalite has lower Br contents (53±10 µg/g, n = 5) and higher δ81Br values (+0.36 ± 0.08‰). Tugtupite that forms at even later stages shows the lowest Br contents (26 ± 2 µg/g, n = 2) and the highest δ81Br values (+0.71 ± 0.17‰). One hydrothermal sodalite has a Br concentration of 48 ± 9 µg/g and an exceptionally high δ81Br of 0.82 ± 0.12‰, very similar to the δ81Br of tugtupites. We suggest that this may be a very late stage sodalite that possibly formed under Be deficient conditions. The data set suggests that sodalite crystallises with a negative Br isotope fractionation factor, which means that the sodalite has a more negative δ81Br than the melt, of −0.3 to −0.4‰ from the melt. This leads to a value of +0.5 to +0.6‰ relative to SMOB for the melt from which sodalite crystallises. This value is similar to a recently published δ81Br value of +0.7‰ for very deep geothermal fluids with very high R/Ra He isotope ratios, presumably derived from the mantle. During crystallisation of later stage hydrothermal sodalite and the Be mineral tugtupite, δ81Br of the residual fluids (both melt and hydrothermal fluid) increases as light 79Br crystallises in the sodalite and tugtupite. This results in increasing δ81Br values of later stage minerals that crystallise with comparable fractionation factors from a fluid with increasingly higher δ81Br values.

scholarly journals Lithium Behaviour and Isotope Fractionation During Fluid–Rock Interactions in Variscan Oceanic Suture Zones: Limousin Ophiolite and Ile de Groix High-pressure Terrane (France)

2019 ◽  
Vol 60 (10) ◽  
pp. 1963-1990 ◽  
Author(s):  
Afifé El Korh ◽  
Etienne Deloule ◽  
Béatrice Luais ◽  
Marie-Christine Boiron ◽  
Luc Bastian ◽  
...  
Keyword(s):  
High Pressure ◽  
Hydrothermal Alteration ◽  
Isotope Fractionation ◽  
Isotope Composition ◽  
Oceanic Lithosphere ◽  
Ultrahigh Pressure ◽  
Fluid Composition ◽  
Lithium Isotope ◽  
Early Stages ◽  
Li Isotope

Abstract Ophiolites and high-pressure/low-temperature (HP–LT) terranes are important sites for the study of geochemical cycling in ancient oceanic lithosphere. We have analysed Li abundances and isotope composition in a series of ultrabasic and basic rocks from the Variscan Limousin ophiolite, as well as in basic and pelitic rocks from the Ile de Groix HP–LT terrane. Both bulk and in situ analyses are employed to evaluate Li mobility and isotope fractionation in the oceanic lithosphere during fluid–rock interactions related to seafloor and sub-seafloor hydrothermal alteration, subduction and exhumation processes. In the Limousin ophiolite, early stages of high-temperature (high-T) hydrothermal alteration of oceanic ultrabasic rocks produced serpentine with low Li abundances (0·9–4·6 ppm) and low δ7Li (–8·9‰). The δ7Li increase from –2·2 to +4·2‰ in the following generations of serpentine during late-stage hydrothermal alteration results from changes in the fluid composition and temperature conditions. Therefore, even if dehydrating subducted serpentinites generate high amounts of fluids during subduction, abyssal serpentinites do not constitute an important source of Li for Li-rich metabasic rocks. In the associated amphibolites, hornblende displays typical Li contents (3·1–8·2 ppm) and isotopic compositions (+3·5 to +12·5‰) similar to hydrothermally altered sheeted dykes and gabbros. In contrast, the low Li abundances and extremely high δ7Li values recorded by omphacite and pargasitic amphibole in the ultrahigh-pressure (UHP) zoisite-eclogite from the Limousin probably reflect interaction with a heavy-Li sediment-derived fluid. The HP–LT metabasites of the Ile de Groix record different Li behaviour, with high Li abundances and low δ7Li. They contain Li abundances significantly higher than fresh mid-ocean ridge basalts (MORB) (16–124 ppm), indicating a metasomatic overprint by fluids derived from the neighbouring Li-rich mica-schist (15–52 ppm) in addition to seawater during the early stages of subduction. Lithium is mainly hosted by (1) glaucophane and omphacite in blueschists and eclogites, (2) chlorite and albite in retrograde greenschists, and (3) phengite and chlorite in mica-schists. The metabasites have δ7Li values of –4·8 to +3·2‰ that are generally lower than those of fresh and altered MORB. The intercalated mica-schists display δ7Li values ranging from –1·7 to +0·2‰ that are typical of subducted sediments. The δ7Li decrease from blueschists to eclogites from +1·8 to –4·8‰, as well as the rimward δ7Li decrease in glaucophane from MORB-like δ7Li values to negative values in blueschists (core: –2·4 to +8·8‰; rims: –7·1 to +2·2‰), reveals that significant fluid-induced Li isotope fractionation occurred at the transition from the lawsonite-blueschist facies to the epidote-blueschist facies, and may be triggered by prograde lawsonite breakdown. In eclogites, the low δ7Li measured in whole-rocks (–4·8 to –2·5‰), omphacite (–22·4 to +3·3‰) and glaucophane (–6·9 to +1·4‰) indicates that Li isotope kinetic fractionation had stronger effects under eclogite-facies conditions. The δ7Li increase toward positive values in the most retrogressed greenschist samples suggests Li mineral–fluid isotopic exchange during rehydration reactions and interaction with a Li-heavy fluid that is probably derived from the dehydrating metabasites. Thus, lithium isotope fractionation in the HP–LT rocks of the Ile de Groix highlights migration of heavy-Li fluids along the oceanic crust–mantle interface in the subduction zone.

scholarly journals Isotope Fractionation of Toluene: A Perspective to Characterise MicrobialIn SituDegradation

2002 ◽  
Vol 2 ◽  
pp. 1227-1234 ◽  
Author(s):  
H.H. Richnow ◽  
A. Vieth ◽  
M. Kastner ◽  
M. Gehre ◽  
R.U. Meckenstock
Keyword(s):  
Groundwater Flow ◽  
Carbon Isotope ◽  
Organic Contaminants ◽  
Isotope Fractionation ◽  
Isotope Composition ◽  
Flow Path ◽  
Groundwater Hydrology ◽  
Ground Water Flow ◽  
Fractionation Factor

A concept to assessin situbiodegradation of organic contaminants in aquifers is presented. The alteration of the carbon isotope composition of contaminants along the groundwater flow path indicates microbial degradation processes and can be used as an indicator forin situbiodegradation. The Rayleigh equation was applied to calculate the percentage of thein situbiodegradation (B[%]) using the change in the isotopic composition of contaminants (Rt/R0) along the ground water flow path and a kinetic carbon isotope fractionation factor (αC) derived from defined biodegradation experiments in the laboratory. When the groundwater hydrology is known and a representative source concentration (C0) for a groundwater flow path can be determined, the extent ofin situbiodegradation can be quantified.

scholarly journals Measurement on Diffusion Coefficients and Isotope Fractionation Factors by a Through-Diffusion Experiment

Minerals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 208
Author(s):  
Takuma Hasegawa ◽  
Kotaro Nakata ◽  
Rhys Gwynne
Keyword(s):  
Groundwater Flow ◽  
Diffusion Coefficients ◽  
Isotope Fractionation ◽  
Free Water ◽  
Effective Porosity ◽  
Diffusion Experiment ◽  
Fractionation Factor ◽  
Through Diffusion ◽  
Geological Formations ◽  
Fractionation Factors

For radioactive waste disposal, it is important that local groundwater flow is slow as groundwater flow is the main transport medium for radioactive nuclides in geological formations. When the groundwater flow is very slow, diffusion is the dominant transport mechanism (diffusion-dominant domain). Key pieces of evidence indicating a diffusion-dominant domain are the separation of components and the fractionation of isotopes by diffusion. To prove this, it is necessary to investigate the different diffusion coefficients for each component and the related stable isotope fractionation factors. Thus, in this study, through-diffusion and effective-porosity experiments were conducted on selected artificial materials and natural rocks. We also undertook measurements relating to the isotope fractionation factors of Cl and Br isotopes for natural samples. For natural rock samples, the diffusion coefficients of water isotopes (HDO and H218O) were three to four times higher than those of monovalent anions (Cl−, Br- and NO3−), and the isotope fractionation factor of 37Cl (1.0017–1.0021) was slightly higher than that of free water. It was experimentally confirmed that the isotope fractionation factor of 81Br was approximately 1.0007–1.0010, which is equivalent to that of free water. The enrichment factor of 81Br was almost half that of 37Cl. The effective porosity ratios of HDO and Cl were slightly different, but the difference was not significant compared to the ratio of their diffusion coefficients. As a result, component separation was dominated by diffusion. For artificial samples, the diffusion coefficients and effective porosities of HDO and Cl were almost the same; it was thus difficult to assess the component separation by diffusion. However, isotope fractionation of Cl and Br was confirmed using a through-diffusion experiment. The results show that HDO and Cl separation and isotope fractionation of Cl and Br can be expected in diffusion-dominant domains in geological formations.

scholarly journals Chlorine isotope composition in chlorofluorocarbons CFC-11, CFC-12 and CFC-113 in firn, stratospheric and tropospheric air

2015 ◽  
Vol 15 (12) ◽  
pp. 6867-6877 ◽  
Author(s):  
S. J. Allin ◽  
J. C. Laube ◽  
E. Witrant ◽  
J. Kaiser ◽  
E. McKenna ◽  
...  
Keyword(s):  
Isotope Fractionation ◽  
Isotope Composition ◽  
Stratospheric Ozone ◽  
Standard Uncertainty ◽  
Gas Chromatography Mass Spectrometry ◽  
Sources And Sinks ◽  
Chlorine Isotope ◽  
Tropospheric Measurements ◽  
Single Detector

Abstract. The stratospheric degradation of chlorofluorocarbons (CFCs) releases chlorine, which is a major contributor to the destruction of stratospheric ozone (O3). A recent study reported strong chlorine isotope fractionation during the breakdown of the most abundant CFC (CFC-12, CCl2F2, Laube et al., 2010a), similar to effects seen in nitrous oxide (N2O). Using air archives to obtain a long-term record of chlorine isotope ratios in CFCs could help to identify and quantify their sources and sinks. We analyse the three most abundant CFCs and show that CFC-11 (CCl3F) and CFC-113 (CClF2CCl2F) exhibit significant stratospheric chlorine isotope fractionation, in common with CFC-12. The apparent isotope fractionation (ϵapp) for mid- and high-latitude stratospheric samples are respectively −2.4 (0.5) and −2.3 (0.4) ‰ for CFC-11, −12.2 (1.6) and −6.8 (0.8) ‰ for CFC-12 and −3.5 (1.5) and −3.3 (1.2) ‰ for CFC-113, where the number in parentheses is the numerical value of the standard uncertainty expressed in per mil. Assuming a constant isotope composition of emissions, we calculate the expected trends in the tropospheric isotope signature of these gases based on their stratospheric 37Cl enrichment and stratosphere–troposphere exchange. We compare these projections to the long-term δ (37Cl) trends of all three CFCs, measured on background tropospheric samples from the Cape Grim air archive (Tasmania, 1978–2010) and tropospheric firn air samples from Greenland (North Greenland Eemian Ice Drilling (NEEM) site) and Antarctica (Fletcher Promontory site). From 1970 to the present day, projected trends agree with tropospheric measurements, suggesting that within analytical uncertainties, a constant average emission isotope delta (δ) is a compatible scenario. The measurement uncertainty is too high to determine whether the average emission isotope δ has been affected by changes in CFC manufacturing processes or not. Our study increases the suite of trace gases amenable to direct isotope ratio measurements in small air volumes (approximately 200 mL), using a single-detector gas chromatography–mass spectrometry (GC–MS) system.

scholarly journals Chlorine isotope composition in chlorofluorocarbons CFC-11, CFC-12 and CFC-113 in firn, stratospheric and tropospheric air

2014 ◽  
Vol 14 (23) ◽  
pp. 31813-31841
Author(s):  
S. J. Allin ◽  
J. C. Laube ◽  
E. Witrant ◽  
J. Kaiser ◽  
E. McKenna ◽  
...  
Keyword(s):  
Isotope Fractionation ◽  
Isotope Composition ◽  
Stratospheric Ozone ◽  
Isotope Ratios ◽  
Gas Chromatography Mass Spectrometry ◽  
Chlorine Isotope ◽  
Site Model ◽  
Tropospheric Measurements ◽  
Single Detector

Abstract. The stratospheric degradation of chlorofluorocarbons (CFCs) releases chlorine, which is a major contributor to the destruction of stratospheric ozone (O3). A recent study reported strong chlorine isotope fractionation during the breakdown of the most abundant CFC (CFC-12, CCl2F2), similar to effects seen in nitrous oxide (N2O). Using air archives to obtain a long-term record of chlorine isotope ratios in CFCs could help to identify and quantify their sources and sinks. We analyse the three most abundant CFCs and show that CFC-11 (CCl3F) and CFC-113 (CClF2CCl2F) exhibit significant stratospheric chlorine isotope fractionation, in common with CFC-12. The apparent isotope fractionation (ϵapp) for mid- and high-latitude stratospheric samples are (−2.4 ± 0.5) and (−2.3 ± 0.4)‰ for CFC-11, (−12.2 ± 1.6) and (−6.8 ± 0.8)‰ for CFC-12 and (−3.5 ± 1.5) and (−3.3 ± 1.2)‰ for CFC-113, respectively. Assuming a constant source isotope composition, we estimate the expected trends in the tropospheric isotope signature of these gases due to their stratospheric 37Cl enrichment and stratosphere–troposphere exchange. We compare these model results to the long-term δ(37Cl) trends of all three CFCs, measured on background tropospheric samples from the Cape Grim air archive (Tasmania, 1978–2010) and tropospheric firn air samples from Greenland (NEEM site) and Antarctica (Fletcher Promontory site). Model trends agree with tropospheric measurements within analytical uncertainties. From 1970 to the present-day, we find no evidence for variations in chlorine isotope ratios associated with changes in CFC manufacturing processes. Our study increases the suite of trace gases amenable to direct isotope ratio measurements in small air volumes, using a single-detector gas chromatography-mass spectrometry system.

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