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1.
Determination of the Absolute Hydrogen Isotopic Ratio of V-SMOW and SLAP   总被引：1，自引：0，他引：1  
By mixing 1H2O and 2H2O, both with accurately known purity, samples were prepared with 2H/1H ratios close to those of the international isotopic water standards: V-SMOW and SLAP. A mass spectrometrical comparison of these calibration samples with the actual water standards revealed:
2H/1H of V-SMOW = (155.95 ± 0.08) × 10−6
2H/1H of SLAP = (89.12 ± 0.07) × 10−6
δ2HV-SMOW(SLAP) =−428.5 ± 0.5 %  相似文献   

2.
We report a new approach to conduct fast and accurate lithium isotope ratio measurements by MC-ICP mass spectrometry after wet chemical sample preparation. In contrast to most previously published methods our MC-ICP-MS set-up did not use a desolvating system to achieve appropriate ion beam intensities and, therefore, was less affected by matrix-induced shifts of the instrumental mass bias. As the total lithium background and build-up in the sample introduction system was low, previous sample residues could be washed out by an extended uptake of the new sample. Elimination of a nitric acid rinse step increased the sample throughput by a factor of two and allowed the instrumental mass bias drift to be tracked more precisely. δ7Li values of powdered silicate rock reference materials and seawater obtained in this study revealed good accuracy and an overall analytical uncertainty of typically 0.5‰ (2s). On the basis of a comparison between our lithium isotope data and compiled literature data, we recommend preliminary average δ7Li values for seawater (+30.8‰) and several silicate rock reference materials (BHVO-1: +5.0‰; JA-1: +5.6‰; JB-2: +4.8‰). The compilation of published δ7Li values for seawater suggests that the observed large lithium isotope differences are due to inter-method and/or interlaboratory bias. Most recently published δ7Li values for seawater show little variation and confirm a constant lithium isotope composition (at the sub ‰ level) of seawater in well mixed ocean basins.  相似文献   

3.
The high sensitivity, minimal oxide formation and single internal standard capability of high resolution inductively coupled plasma-mass spectrometry (HR-ICP-MS) is demonstrated in the direct determination of Sc, Y and REE in the international reference materials: basalts (BCR-1, BHVO-1, BIR-1, DNC-1), andesite (AGV-1) andultramafics (UB-N, PCC-1 and DTS-1). Time consuming ion exchange separation or preconcentration were found to be unnecessary. Smooth chondrite normalized plots of the REE in PCC-1 and DTS-1 were obtained in the range 0.8-50 ng g-1 (0.01-0.1x chondrite). Method precision was found to be digestion dependent with an average external repeatability of 2-4% for the basalts, AGV-1 and UB-N, and 10% for PCC-1 and DTS-1. The mass peak due to 45Sc was completely resolved from 29Si16O and 28Si16O1H spectral interferences using medium resolution, which casts doubt on the accuracy of Sc determinations using quadrupole ICP-MS. Literature values for Y in rock reference materials were found to be approximately 9% high after HR-ICP-MS and XRF analysis.  相似文献   

4.
A new method has been developed for the simultaneous determination of Pb abundance and Pb isotopic composition with high precision and accuracy for small test portion masses by thermal ionisation mass spectrometry. In this method, a 205pb-204pb double spike is added to samples prior to the chemical separation of Pb, and the isotopic composition of the spike-sample mixture is determined rigorously by the double spike technique using a 207Pb-204Pb spike. The isotopic composition and concentration of Pb in the sample are then obtained by utilising the principle of isotope dilution. Using this technique, replicate determinations of Pb from NIST SRM 981 and GSJ JP-1 (peridotite; 0.07 μg g−1 Pb) were performed. The measured concentration and isotopic data were identical, within uncertainty, to published data or to data that were determined independently in this study. The application of this method to U-Pb dating and the determination of the "initial" Pb isotopic composition was also tested. Lead isotopic compositions and the concentrations of Pb, Th and U were determined for a single batch of samples, through the addition of 205pb-204pb, 230Th and 235U spikes to samples prior to chemical separation. Also in these experiments, we confirmed that this routine gives accurate data for Pb, Th and U concentrations and Pb isotopic compositions.  相似文献   

5.
The fluorine concentration in seventy-one reference samples of geological interest has been determined using fast-neutron activation analysis. The reaction involved [19F(n, α) 16N] uses accelerator-derived neutrons produced by bombarding a Be target with 3 MeV deuterons. The gamma radiation associated with the decay of 16N (t1/2 = 7.13 s) is counted and for the irradiation conditions used there are no serious interferences. The advantages of this technique over other schemes of fluorine determination are its simple procedure for sample preparation, speed, high sensitivity and non-destructiveness. A comparison of the data obtained with those in the literature is highly favourable.  相似文献   

6.
For studies of mass-dependent fractionation of calcium isotopes in natural materials, the 48Ca/42Ca ratio is a superior choice to the conventionally measured 44Ca/40Ca ratio for two important reasons. These are (1) mass-dependent fractionation can be determined free from the effects of inherited or ingrown radiogenic 40Ca and (2) this ratio increases the spread of measured isotopic masses by 50%, resulting in statistically better resolution of fractionation, assuming similar precision. A third, though strictly technical, advantage is the inherent ability of a mass spectrometer to measure ratios close to unity (48Ca/42Ca) more precisely than very small or large ratios (44Ca/40Ca). However, because of the very low natural abundance of both 48Ca and 42Ca, their ratio has been very difficult to measure, the only attempt so far being on a high mass resolution MC-ICP-MS with a precision of 0.33%. We report here determination of the 48Ca/42Ca ratio by the more commonly available and user-friendly multi-collector TIMS using a 43Ca-46Ca double-spike, with a significantly better precision of 0.18% (2s). The 48Ca/40Ca or 44Ca/40Ca ratio can also be measured in the same mass spectrometer run to provide complementary information on any radiogenic component.  相似文献   

7.
We have measured 87Sr/86Sr and 143 Nd/144 Nd isotope ratios in different batches and aliquots of the new US Geological Survey (USGS) reference materials (RMs) BCR-2, BHVO-2, AGV-2 and GSP-2 and the original USGS RMs BCR-1, BHVO-1, AGV-1 and GSP-1 by thermal ionisation mass spectrometry. In addition, we also analysed the eight Max-Planck-Institut-Dingwell (MPI-DING) reference glasses. Nearly all isotope ratios obtained in the different aliquots and batches agree within uncertainty limits indicating excellent homogeneity of the USGS powders and the MPI-DING glasses. With the exception of GSP-2, the new USGS RMs are also indistinguishable from the ratios found in the original USGS RMs (87Sr/86Sr: 0.704960, 0.704958 (BCR-1, -2), 0.703436, 0.703435 (BHVO-1, -2), 0.703931, 0.703931 (AGV-1, -2); 143 Nd/144 Nd: 0.512629, 0.512633 (BCR-1, -2), 0.512957, 0.512957 (BHVO-1, -2); 0.512758, 0.512755 (AGV-1, -2)). This means that for normalisation purposes in Sr and Nd isotope geochemistry BCR-2, BHVO-2 and AGV-2 can well replace BCR-1, BHVO-1 and AGV-1 respectively.  相似文献   

8.
Determinations of the absolute age of cleavage formation can provide fundamental information about the evolution of orogenic belts. However, when applied to cleavages in slates and phyllites, conventional dating methods are complicated by problems related to mineral separation and the presence of multiple cleavage generations. In situ high-spatial-resolution 40Ar/39Ar laser microprobe geochronology and microstructural observations indicate that the age of cleavage formation in slates and phyllites can be constrained by analysing zones of tightly packed cleavage domains. Three regionally developed cleavages (S2, S3, and S4) are present in the northern Taconic Allochthon of Vermont and New York. Representative samples were studied from a variety of localities where these cleavages, which are defined by white micas, are well developed. In the suite of samples, only S3 and S4 are expressed as domains that are sufficiently wide and spatially isolated in thin section to permit quantitative 40Ar/39Ar geochronology. Mean 40Ar/39Ar laser microprobe ages for these domains are 370.7 ± 1.0 Myr for S3 and 345.5 ± 1.7 Myr for S4. Because estimates of the Ar closure temperature for white micas are substantially higher than the inferred growth temperatures of the micas defining S3 and S4, these values are interpreted as periods since cleavage formation. This interpretation is consistent with independent geochronological constraints on the age of the Acadian orogeny in the region.  相似文献   

9.
An igneous zircon reference material (OG1) was characterised for U-Pb isotopes by ID-TIMS, and utilised to evaluate SIMS (SHRIMP) instrumental mass fractionation (IMF) of radiogenic Pb isotopes (207Pb*/206Pb*). The TIMS 207Pb*/206Pb* reference value for OG1 was 0.29907 ± 0.00011 (95% confidence limit), 3465.4 ± 0.6 Ma. The high 207Pb* (∼ 30 μg g−1), negligible common Pb, and isotopic homogeneity permitted precise (± 1–2‰) 207Pb*/206Pb* measurements within the analytical sessions. External reproducibility of mean 207Pb*/206Pb* ratios between sessions was demonstrated for one instrument, yielding a mean IMF of +0.87 ± 0.49‰. The mean 207Pb*/206Pb* ratios between instruments were dispersed beyond uncertainties, with session IMF values from +3.6 ± 1.7‰ to −2.4 ± 1.3‰, and a grand mean IMF value (twenty-six sessions) of +0.70 ± 0.52‰, indicating a tendency towards elevated 207Pb*/206Pb*. The specific causes of variability in IMF are unclear, but generally reflect subtle differences in analytical conditions. The common practice in SIMS of assuming that IMF for Pb+ is insignificant could result in systematic age biases and underestimated uncertainties, of critical importance for precise correlation of Precambrian events. Nevertheless, a zircon RM such as OG1 can be readily incorporated into routine dating to improve 207Pb*/206Pb* accuracy and external reproducibility.  相似文献   

10.
Direct absolute dating of the Penninic Frontal Thrust tectonic motion is achieved using the 40Ar/39Ar technique in the Pelvoux Crystalline Massif (Western Alps). The dated phengites were formed syn-kinematically in shear zones. They underline the brittle-ductile stretching lineation, pressure-shadow fibres and slickensides consistent with underthrusting of the European continental slab below the propagating Penninic Thrust. Chlorite–phengite thermobarometry yields 10–15 km and T ∼280 °C, while 40Ar/39Ar phengite ages mainly range between 34 and 30 Ma, with one younger age at 27 Ma. This Early Oligocene age range matches a major tectonic rearrangement of the Alpine chain. Preservation of prograde 40Ar/39Ar ages is ascribed to passive exhumation of the Pelvoux shear zone network, sandwiched between more external thrusts and the Penninic Front reactivated as an E-dipping detachment fault. Partial resetting in the Low Temperature part of argon spectra below 24 Ma is ascribed to brittle deformation and alteration of phengites.  相似文献   

11.
Application of Laser Ablation ICP-MS to U-Th-Pb Dating of Monazite   总被引：2，自引：1，他引：2  
Recent advances in laser ablation ICP-MS techniques allow accurate U-Th-Pb age dating of monazites that are as young as several tens of million years to a precision better than 2%. Accuracy of the age determinations has been improved by true real-time mass bias correction via nebulisation of a solution containing enriched 233U and natural Tl isotopes. The Tl-U tracer solution eliminates possible effects of variable sample matrices on the precision and accuracy of measured isotopic ratios. Mass bias corrections based on measured 205Tl/233U ratios in the tracer solution allow direct measurement of 235U in monazite. Combined with high-sensitivity laser ablation ICP-MS measurements, direct measurement of 235U particularly improves the precision of U-Pb dating of young monazites. Correction for laser-induced Pb/U and Pb/Th elemental fractionation is based on a mathematical treatment of time resolved count-rate data that is independent of laser ablation characteristics, does not require external standardisation and allows variable laser pit size or raster patterns for each measurement. The new procedures make the LA ICP-MS technique more flexible for in situ U-Th-Pb analysis.  相似文献   

12.
A precise and simple method for the determination of lithium concentrations in small amounts of silicate sample was developed by applying isotope dilution-inductively coupled plasma-mass spectrometry (ID-ICP-MS). Samples plus a Li spike were digested with HF-HClO4, dried and diluted with HNO3, and measured by ICP-MS. No matrix effects were observed for 7Li/6Li in rock solutions with a dilution factor (DF) of 97 at an ICP power of 1.7 kW. By this method, the determination of 0.5 μg g-1 Li in a silicate sample of 1 mg can be made with a blank correction of < 1%. Lithium contents of ultrabasic to acidic silicate reference materials (JP-1, JB-2, JB-3, JA-1, JA-2, JA-3, JR-1 and JR-2 from the Geological Survey of Japan, and PCC-1 from the US Geological Survey) and chondrites (three different Allende and one Murchison sample) of 8 to 81 mg were determined. The relative standard deviation (RSD) was typically < 1.7%. Lithium contents of these samples were further determined by isotope dilution-thermal ionisation mass spectrometry (ID-TIMS). The relative differences between ID-ICP-MS and ID-TIMS were typically < 2%, indicating the high accuracy of ID-ICP-MS developed in this study.  相似文献   

13.
A Nordic colloquium on accelerators and dating was held in Uppsala on March 11th to 12th, 1983, and arranged by the Tandem Accelerator Laboratory and the Institute of Physics. Its aims were: to report on the accelerator technique using ion counting instead of decay counting, to discuss the advantages and possible disadvantages of the new technique, to discuss the dating possibilities using 10Be, 26A1, 36CI etc. besides 14C, and to organize a Nordic committee to establish cooperation. About 80 participants representing the five Nordic countries attended the meeting. Survey lectures were given by Jürg Beer, Berne and Robert Hedges, Oxford.  相似文献   

14.
A direct method for the determination of lead isotopic ratios by laser ablation-inductively coupled plasma-quadrupole mass spectrometry (LA-ICP-QMS) is presented. Samples of lake sediments were ground and pressed as pellets before being analysed. Mass bias was corrected by analysing an external calibration sample manufactured with pure silica doped with NIST SRM 981 solution. The efficiency of the mass bias correction was checked by comparing the ICP-MS data with lead isotopic ratios determined by thermal ionisation mass spectrometry (TIMS). The average long term reproducibilities were 0.40%, 0.40%, 0.20% and 0.30% (RSD) respectively for the 206Pb/204Pb, 207Pb/204Pb, 206Pb/207Pb and 208Pb/206Pb ratios. The method was applied to the study of lake sediment samples, in order to determine the amount and origin of historical contamination by lead.  相似文献   

15.
The geochemistry of Re-Os and the recent use of Re as a non-traditional stable isotope both need accurate and precise quantification of 187Re/185Re ratios. This paper reports rhenium isotopic data obtained from the analysis of a standard solution and geological samples by MC-ICP-MS. We show that measured isotopic ratios are modified by matrix effects that cannot be accounted for by the standard solution bracketing technique. The bias resulting from measurements on a spiked (185Re-enriched) sample is shown to alter the apparent Re concentration by several percent. When spiking samples and calibrators with tungsten, simultaneous measurement of tungsten and rhenium isotopes compensates for the matrix-induced modification of mass bias. Rhenium and tungsten are shown to have different fractionation factors. This may be due to the fact that the two elements fractionate in a different but systematic way, or that the reference isotopic ratios used for elemental Re and W are incoherent with one another. The consistency of fractionation through time can be used to obtain an empirical relationship between W and Re measured ratios from a standard solution to obtain a sample's fractionation-corrected 187Re/185Re spiked ratio on samples containing pg g−1 levels of Re, even if some matrix capable of affecting mass bias remains in the final solution.  相似文献   

16.
This paper reviews the deglaciation history and palaeoclimate from 22 to 9.5 14Cka BP in the Andfjord-Vagsfjord area. Eight main glacial events are recorded: The Egga-I (>22 14Cka BP), the Bjerka, the Egga-II (>14.6 14Cka BP), the Flesen (14.5 14Cka BP), the D (13.8–13.2 14Cka BP), the Skarpnes (12.2 14Cka BP), the Tromsø–Lyngen (10.7–10.3 14C ka BP) and the Stordal (10.0–9.5 14Cka BP). Onset of the final deglaciation occurred about 14.6 14Cka BP. Most of the western part of the Fennoscandian and Barents Sea Ice Sheets receded from the outer continental shelf 15–14 14Cka BP. The delivery and melting of icebergs at this time to the Norwegian-Greenland Sea resulted in a low oxygen isotope event recorded in a number of cores in the region. Atlantic water intruded the area 13.2 14Cka BP, and an atmospheric warming commenced 12.9/12.8 14Cka BP. A marked glacial recession occurred before the Skarpnes event. During Allerød time, the glaciers retreated to the fjord heads or even farther inland. The Fennoscandian outlet glaciers readvanced (locally more than 40 km), reached their Younger Dryas outer limit after 10.7 14Cka BP and retreated from this position before about 10.3 14Cka BP.  相似文献   

17.
In 140 metres of Maastrichtian White Chalk (nannofossil chalk) exposed near Hemmoor, NW Germany, values of 87Sr/86Sr increase from 0.707760 in the Belemnella sumensis Zone (Lower Maastrichtian) at the base of the section (-54.5 m; referred to 0 m at a prominent marl, M900) to 0.707821 in the Belemnella baltica/danica Zone (Upper Maastrichtian) at the top of the section (+84.5 m). A plateau in 87Sr/86Sr occurs between -5m and +50m in the section, probably as a result of a very high rate of sedimentation in this interval. A belemnite and associated nannofossil chalk have similar 87Sr/86Sr values, suggesting that there has been little diagenetic alteration of the 87Sr/86Sr ratios in the chalk, which therefore preserves its original 87Sr/86Sr. Comparison of 87Sr/86Sr and nannofossil zonations for sequences at Bidart, France, and DSDP Sites reveals discordance and so possible diachronism of the basal boundaries of nannofossil Zones CC25B and CC25C.  相似文献   

18.
Abstract. The Re-Os isotopic compositions of sulfide ores were analyzed for the Gacun, a volcanogenic massive sulfide deposit in southwestern China, to constrain the timing of mineralization. Sulfide ores from the deposit have a wide range of Re and Os concentrations, varying from 80.2 to 1543.2 ppb and from 0.307 to 8.83 ppb, respectively, and yielded a limited field of high 187Re/188Os and high 187Os/188Os ratios, ranging from 1452 to 3309 and from 5.77 to 13.24, respectively. All sulfide samples yielded an isochron with an age of 217±28 Ma and an initial 187Os/188Os ratio of around 0.52±0.73. The Re-Os isochron age agrees with ages previously constrained by the other isotopic dating of the host rocks and fossil strata for the deposit. The rhythmic variation in 187Os/188Os and 187Re/188Os ratios within massive sulfide zone records a complicated process for ore-forming fluids episodically vented into the brine pool on the Mesozoic seafloor.  相似文献   

19.
40Ar/39Ar geochronological and palaeomagnetic dating methods applied to fault breccias in western Norway have isolated two brittle reactivation episodes of the syn-post-Caledonian, extensional Nordfjord-Sogn Detachment. These events, of latest Permian and latest Jurassic–Early Cretaceous ages, demonstrate temporal relationships between development of chemical remanent magnetism and partial resetting of Ar isotopic systems during distinct breccia-forming episodes. A third event of Carboniferous age was also identified in the breccias with the 40Ar/39Ar technique and is a relict unroofing signature inherited from the fault wall-rocks. These brittle faults are significant time markers and become relevant to interpretations of offshore seismic data which attempt to place ages on faults that have undergone multiple reactivation episodes.  相似文献   

20.
The carbon (δ13 C) and oxygen (δ18O) isotopic composistion in mollusc shells in mainly determined by the isotopic composition of water and dissolved bicarbonate. The δ18O values of water show a good correlation with the salinity of the Baltic. This correlation served as a basis for reconstructing palaeosalinity and for stratifying the marine sediments according to the δ18O values of the carbonate skeletons of subfossil shells. The δ13C values in shells are mainly determined by the isotopic composition of land-originating bicarbonate, especially in the carbonate skeleton of Lymnaea balthica , which inhabits the immediate coastal zone. According to the δ18O data, salinity in the investigated area (the coastal area of W and NW Estonia) was highest (about 9–11%) during the Littorina stage. The Limnae a stage had, in general, a salinity similar to the contemporary one, but during some phases possibly exceeding it by 2–3%.  相似文献   

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