Hydrogen and oxygen isotopes of water from inclusions in minerals: design of a new crushing system and on-line continuous-flow isotope ratio mass spectrometric analysis (original) (raw)
Related papers
Chemical Geology, 2001
A general-purpose, on-line, continuous flow method for determination of d D and d 18 O values of water and hydrous minerals is described. Minor modifications of commercially available equipment allow for analyses of water and solid samples, fluid inclusions and in situ hydrogen isotope determinations of hydrous minerals using a laser. The technique involves reduction of H O or solid hydrous samples by reaction with glassy carbon at high temperatures. H and CO are 2 2 produced by reaction with the carbon at 14508C in a helium carrier gas. Product gases are separated in a gas chromatograph and analyzed in a mass spectrometer configured to make hydrogen isotope analyses in continuous flow mode. Ž. Sample size is as small as 0.1 ml of water or equivalent from hydrous phases for both hydrogen and oxygen isotope ratio determinations. Waters are injected through a heated septa into the He stream; solid materials are wrapped in silver foil and dropped into the furnace using an autosampler. Using standard correction procedures, results obtained with this method Ž. are identical to those obtained conventionally with a precision for water samples of "2‰ 1s for hydrogen and "0.2‰ Ž. 1s for oxygen. Saline waters can be analyzed without any additional preparation. Reproducibility of d D values from hydrous silicates is also "2‰ The d 18 O values of 'dehydration' water evolved from biotite during heating is variable and irreproducible. Total time of analysis is less than 2 min for a single hydrogen isotope analysis. Sample size can be reduced an order of magnitude by using a low He-flow rate, a narrow-bore reduction column, a capillary GC column and a more efficient open split. With the high sensitivity design, in situ measurements can be made on hydrous minerals using a CO laser for sample heating. Stable isotope determinations of fluid inclusions can be made by 2 decrepitating samples in the He-stream.
Rapid Communications in Mass Spectrometry, 2020
Online oxygen (δ 18 O) and hydrogen (δ 2 H) isotope analysis of fluid inclusion water entrapped in minerals is widely applied in paleo-fluid studies. In the state of the art of fluid inclusion isotope research, however, there is a scarcity of reported inter-technique comparisons to account for possible analytical offsets. Along with improving analytical precisions and sample size limitations, interlaboratory comparisons can lead to a more robust application of fluid inclusion isotope records. Methods: Mineral samples-including speleothem, travertine, and vein materialwere analyzed on two newly setup systems for fluid inclusion isotope analysis to provide an inter-platform comparison. One setup uses a crusher unit connected online to a continuous-flow pyrolysis furnace and an isotope ratio mass spectrometry (IRMS) instrument. In the other setup, a crusher unit is lined up with a cavity ringdown spectroscopy (CRDS) system, and water samples are analyzed on a continuous standard water background to achieve precisions on water injections better than 0.1‰ for δ 18 O values and 0.4‰ for δ 2 H values for amounts down to 0.2 μL. Results: Fluid inclusion isotope analyses on the IRMS setup have an average 1σ reproducibility of 0.4‰ and 2.0‰ for δ 18 O and δ 2 H values, respectively. The CRDS setup has a better 1σ reproducibility (0.3‰ for δ 18 O values and 1.1‰ for δ 2 H values) and also a more rapid sample throughput (<30 min per sample). Fluid inclusion isotope analyses are reproducible at these uncertainties for water amounts down to 0.1 μL on both setups. Fluid inclusion isotope data show no systematic offsets between the setups. Conclusions: The close match in fluid inclusion isotope results between the two setups demonstrates the high accuracy of the presented continuous-flow techniques for fluid inclusion isotope analysis. Ideally, experiments such as the one presented in this study will lead to further interlaboratory comparison efforts and the selection of suitable reference materials for fluid inclusion isotopes studies.
Geochemistry, Geophysics, Geosystems
18 O and D of fluid inclusions in carbonates provide insights into temperatures and fluid chemical compositions prevailing during the carbonate precipitation, however various analytical restrictions limit a wider application of this proxy. This paper presents a new fluid inclusions isotopic analytical line coupled to an online cavity ring-down spectrometer that increased the analytical productivity up to ten carbonate samples per working day. This efficiency allowed for the first time to assess the reliability a large set of water samples with size ranging from 0.1 to 1 µL. Good reproducibility (± 0.5 ‰ for 18 O and ± 2 ‰ D; 1) is obtained for water quantity superior or equal to 0.3 L and no evidence of memory effect is found. The line is further tested using two types of natural carbonates: (1) modern speleothems samples from caves for which 18 O and D values of drip water were measured and (2) diagenetic carbonates for which the 18 O of the parent water were independently back-calculated from carbonate clumped isotope 47 measurements. Speleothem fluid inclusion values despite falling close to the Global Meteoritic Water Line are not always representative of the isotopic composition of the parent drip water. Results on diagenetic cements show that the 18 O water values measured in fluid inclusions agree, within 1 %, with the 18 O water independently derived from 47 measurements. Overall, this study confirms the reliability and accuracy of the developed analytical line for carbonate fluid inclusion analyses with a good reproducibility obtained for water quantity above 0.3 L.
Hydrogen and oxygen isotope standards for the analysis of water inclusions in halite
Geostandards and Geoanalytical Research
Fluid inclusions represent a unique opportunity for a straightforward determination of the chemical and isotopic composition of fluids that composed the hydrosphere and atmosphere over Earth's history. The production of reference materials in the laboratory is needed to monitor and to validate the determination of hydrogen and oxygen isotope compositions of water inclusions. We propose a protocol leading to the experimental synthesis of halite crystals that contain water inclusions whose dD and d 18 O values can be related to those of surrounding evaporating waters where the crystals grew. Corrections to isotopic measurements were performed by applying an orthogonal projection of the raw data to the water evaporation trajectory line whose slope can be predicted by taking into account the parameters developed in the linear resistance model of . Several hundreds of grams of halite reference material can be produced rapidly (within 2 d) at a low cost and can be stored within a vacuum desiccator at ambient temperature over several months or years. The described method is especially useful for the analysis of anhydrous salts and the interpretation of isotopic fractionations that operate within the surficial water cycle.
Hydrogen and Oxygen Isotope Reference Materials for the Analysis of Water Inclusions in Halite
Geostandards and Geoanalytical Research, 2011
Fluid inclusions represent a unique opportunity for a straightforward determination of the chemical and isotopic composition of fluids that composed the hydrosphere and atmosphere over Earth's history. The production of reference materials in the laboratory is needed to monitor and to validate the determination of hydrogen and oxygen isotope compositions of water inclusions. We propose a protocol leading to the experimental synthesis of halite crystals that contain water inclusions whose dD and d18O values can be related to those ...
Quaternary International, 2016
The issue of diagenetic alteration of carbonate deposits in caves (speleothems) has gained increasing importance in recent years, as this process has serious consequences for speleothembased paleoclimate studies. In this study stable hydrogen and oxygen isotope data of water trapped in fluid inclusions were collected for recently forming stalagmites and flowstones in order to determine how dripwater compositions are reflected and preserved in the inclusion water compositions. Hydrogen isotope compositions were found to reflect dripwater values, whereas the oxygen isotope data were increasingly shifted from the local dripwater compositions with the time elapsed after deposition. The δ 18 O data are correlated with X-Ray diffraction full width at half maximum values (related to crystal domain size and lattice strain), suggesting that the oxygen isotope shift is related to recrystallization of calcite. Transmission electron microscope analyses detected the presence of nanocrystalline (<50 nm) calcite, whose crystallization to coarser-grained calcite crystals (>200 nm) may have induced re-equilibration between the carbonate and the trapped inclusion water. The Ostwald ripening process provides an explanation for unexpectedly low oxygen isotope compositions in the inclusion water. The detected diagenetic alteration and its isotopic effects should be taken into consideration during sampling strategies and data evaluation as speleothems containing nanocrystalline calcite during their deposition are prone to late-stage oxygen isotope water-carbonate re-equilibration, which may shift the oxygen isotope composition of the inclusion water to more depleted values while the hydrogen isotope composition remains intact.
Applied Geochemistry, 2000
Fluid inclusion studies combined with the isotope geochemistry of several generations of fracture calcite from the Olkiluoto research site, Finland, has been used to better understand the past thermal and¯uid history in the crystalline rock environment. Typically, fracture mineral investigations use O and C isotopes from calcite and an estimate of the isotopic composition of the water that precipitated the calcite to perform d 18 O geothermometry calculations to estimate past temperature conditions. By combining¯uid inclusion information with calcite isotopes, one can directly measure the temperature at which the calcite formed and can better determine past¯uid compositions. Isotopic, petrologic and¯uid inclusion studies at the Olkiluoto research site in Finland were undertaken as part of an investigation within the Finnish nuclear waste disposal program. The study revealed that four¯uids were recorded by fracture calcites. From petrologic evidence, the ®rst¯uid precipitated crystalline calcite at 151±2258C with a d 13 C signature of À21 to À13.9-PDB and a d 18 O signature of 12.3±13.0-SMOW. These closed fracture ®llings were found at depths greater than 500 m and were formed from a high temperature, low salinity, Na±Cl¯uid of possible meteoric water altered by exchange with wallrock or dilute basinal origin. The next uid precipitated crystalline calcite with clay at 92±2108C with a d 13 C signature of À2.6 to +3.8-PDB and a d 18 O signature of 19.4±20.7-SMOW. These closed fracture ®llings were found at depths less than 500 m and were formed from a moderate to high temperature, low to moderate salinity, Na±Cl¯uid, likely of magmatic origin. The last group of calcites to form, record the presence of two distinct¯uid types. The platy (a) calcite formed at 95± 2388C with a d 13 C signature of À12.2 to À3.8-PDB and a d 18 O signature of 14.9±19.6-SMOW, from a high temperature, low salinity, Na±Cl¯uid of possible magmatic origin. The platy (b) calcite formed at 67±988C with a d 13 C signature of À13.0 to À6.2-PDB and a d 18 O signature of 15.1±20.1-SMOW, from a low temperature, high salinity, Ca±Na±Cl¯uid of possible basinal brine origin. The two calcites are related through a mixing between the two end members. The source of the¯uids for the platy grey (a) calcites could be the olivine diabase dykes and sills that cut through the site. The source of¯uids for the platy (b) calcites could be the Jotnian arkosic sandstone formations in the northern part of the site. At the Olkiluoto site, d 18 O geothermometry does not agree with¯uid inclusion data. The original source of the water that forms the calcite has the largest eect on the isotopic signature of the calcites formed. Large isotopic shifts are seen in any water by mineral precipitation during cooling under Applied Geochemistry 15 0883-2927/00/$ -see front matter 7 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 8 8 3 -2 9 2 7 ( 0 0 ) 0 0 0 0 7 -X www.elsevier.com/locate/apgeochem * Corresponding
Hydrology and Earth System Sciences
A method to measure the δ<sup>2</sup>H and δ<sup>18</sup>O composition of pore waters in saturated and unsaturated geologic core samples using direct vapour equilibration and laser spectrometry (DVE–LS) was first described in 2008, and has since been rapidly adopted. Here, we describe a number of important methodological improvements and limitations encountered in routine application of DVE–LS over several years. Generally, good comparative agreement, as well as accuracy, is obtained between core pore water isotopic data obtained using DVE–LS and that measured on water squeezed from the same core. In complex hydrogeologic settings, high-resolution DVE–LS depth profiles provide greater spatial resolution of isotopic profiles compared to long-screened or nested piezometers. When fluid is used during drilling and coring (e.g. water rotary or wet sonic drill methods), spiking the drill fluid with <sup>2</sup>H can be conducted to identify core contami...
The recovery and isotopic measurement of water from fluid inclusions in speleothems
Geochimica et Cosmochimica Acta, 2001
The isotopic composition of speleothems is a useful palaeoclimatic indicator, but its value would be enhanced if information on the composition of the parent dripwaters could be recovered from fluid inclusions in the speleothem calcite. To develop a robust method for extracting and measuring oxygen and hydrogen isotopic composition of fluid inclusions we have used anhydrous Iceland Spar and microlitre glass capillaries of water as an analogue system. Crushing the capillary and calcite together in a high vacuum cell we have investigated the adsorbtive and isotopic behaviour of water when exposed to clean fracture surfaces. Significant water adsorption occurs at room temperature, accompanied by large negative isotopic shifts of both oxygen and hydrogen in the recovered free water at H 2 O/CaCO 3 mass ratios Ͻ10 mg g Ϫ1 . Cryogenic pumping fails to achieve total desorption. The degree of depletion is inversely related to the water/calcite ratio, fractionation of hydrogen isotopes exceeding Ϫ20‰, and oxygen isotopes Ϫ10‰, at ratios typically observed in natural speleothems. Heating the crushed calcite at 150°C for 60 min. totally desorbs the water and allows retrieval of the correct isotopic composition. Application of these methods to a British Late Holocene speleothem yields ␦ 18 O and ␦ 2 H compositions for the inclusion water which are closely comparable with the modern cave dripwaters and local precipitation. The results show that isotopic compositions can be recovered from inclusion samples of Ͻ1L (equivalent to approximately 1g of calcite) with precisions that are useful for palaeoclimatic research, Ϯ0.4‰ for ␦ 18 O and Ϯ3‰ for ␦ 2 H. Greater precision than this will require replicate analysis for each speleothem growth increment.