Geostandards and Geoanalytical Research最新文献

Laser ablation multi-collector-inductively coupled plasma-mass spectrometry (LA-MC-ICP-MS) has become a valuable tool for the in situ measurement of the boron isotope composition of geological samples at high (tens to hundreds of μm) spatial resolution. That said, this application suffers from significant analytical challenges. We focus in this study on the underlying processes of two of the main causes for inaccuracies using this technique. We provide empirical evidence that not only Ca ions (Sadekov et al. 2019, Standish et al. 2019, Evans et al. 2021) but also Ar ions, that are reflected within the flight tube of the mass spectrometer, are the source for previously reported issues with spectral baselines. We also address the impact of plasma conditions on the instrumental mass fractionation as a source for matrix- and mass-load-related analytical biases. Comparing experimental data with the results of a dedicated release and diffusion model (RDM) we estimate that a close to complete (~ 97%) release of boron from the sample aerosol is needed to allow for consistently accurate LA boron isotope measurement results without the need for corrections.

Over the last few decades geo- and thermochronological techniques based on the accumulation of radiogenic ⁴He in minerals have gained popularity. Currently there is no mineral-based ⁴He reference material that allows routine screening of gas extraction and measurement procedures. The commonly-used mineral reference material for (U-Th)/He thermochronology have variable U and Th contents which result in variable ⁴He concentrations. Here we demonstrate that native platinum grains (RS-Pt) from placer deposits in the Santiago River, Ecuador, yield constant ⁴He contents and may be used as a reference material. Helium concentrations measured at the Scottish Universities Environmental Research Centre (n = 8) and Institute of Precambrian Geology and Geochronology RAS (n = 9) noble gas laboratories yield mean ⁴He concentrations that overlap at the 95% confidence level. The weighted mean ⁴He concentration is 215 ± 4 × 10¹¹ at g^-1 (2s) and mean ¹⁹⁰Pt-⁴He age is 39.6 ± 0.7 Ma (2s). Samples of the Santiago River Pt concentrate are available on request from the SUERC laboratory.

Uranium isotope ratios are reported for twenty-nine geological reference materials (RMs) including igneous, metamorphic and sedimentary rocks, as well as sediments. Measurements were conducted on a multi-collector inductively coupled plasma-mass spectrometer (MC-ICP-MS) using the ²³³U-²³⁶U double spike technique. These RMs possess a wide range of matrices with U mass fractions ranging from 0.11 μg g^-1 to 18.7 μg g^-1. The δ^234/238U values (relative to the n(²³⁴U)/n(²³⁸U) ratio at secular equilibrium) show minor fluctuations around the secular equilibrium value except for two Pleistocene speleothem RMs. The δ^238/235U values (relative to the value for NBL CRM 112a (NBS SRM 960)) of igneous rocks and metamorphic rocks are within the range of the continental crust value (-0.29 ± 0.03‰, 95% CI). The δ^238/235U value for sedimentary rock and sediment RMs spans a wide range of 0.98‰, suggesting significant ²³⁸U/²³⁵U isotopic fractionation in low temperature environments. The range of δ^238/235U RMs reported in this study (-0.63‰ to 0.35‰) exceeds that of previous RMs (-0.61‰ to 0.17‰), allowing inter-laboratory calibration of wider ranges of geological and environmental samples.

Columbite-tantalite LA-ICP-MS U-Pb dating is a fast and useful method to determine the age of rare-metal deposits and fingerprint the provenance of columbite-tantalite ore concentrates. Accurate LA-ICP-MS U-Pb dating requires matrix-matched reference materials. We analysed three columbite-tantalite samples (SN3, HND and RL2) from China using ID-TIMS and LA-ICP-MS to assess their potential as reference materials for in situ U-Pb dating. Coltan 139 and these three columbite-tantalite samples with variable compositions yielded internally consistent LA-ICP-MS U-Pb ages when using each other for calibration and the weighted mean ²⁰⁶Pb/²³⁸U ages are comparable to respective ID-TIMS ages. Composition-dependent U-Pb fractionation seems to be insignificant under the LA-ICP-MS conditions used. Sample SN3 has a low percentage of heterogeneity for ²⁰⁶Pb/²³⁸U ages (4%) with low common Pb contributions (f₂₀₆ < 1%) and shows a good potential in calibrating unknown samples as primary reference material for LA-ICP-MS analysis. Samples RL2 and HND have altered sections characterised by high LREE contents, flat LREE patterns and old ²⁰⁶Pb/²³⁸U apparent ages, and are not suited as reference materials. The low ²⁰⁷Pb/²⁰⁶Pb intercepts for samples RL2 and HND lack geological meaning but provide strong evidence that the disturbed U-Pb systematics with anomalous apparent ²⁰⁶Pb/²³⁸U ages is a secondary feature.

Here we present an analytical method for Zinc (Zn) isotopic measurements using “standard-sample bracketing” on a Nu Sapphire multi-collector inductively coupled plasma-mass spectrometer. The effects of Zn mass fraction and HNO₃ molarity mismatch between the standard and the sample, as well as the presence of matrix elements have been evaluated. Long-term reproducibility of better than ±0.03‰ for δ⁶⁶Zn (2s) was routinely obtained. Accurate measurements were achieved when C_Ni/C_Zn < 0.001, C_Ti/C_Zn < 0.03, C_Ba/C_Zn < 0.05, C_Na/C_Zn and C_Al/C_Zn < 0.5, C_Mg/C_Zn < 0.1, C_Fe/C_Zn < 5 and C_Cu/C_Zn as well as C_Cd/C_Zn < 10. High-precision Zn isotopic determination were performed on twenty-one widely available geological certified reference materials, with an overall range of ~ 0.62‰ (0.15 to 1.07‰), which is nearly twenty times the current analytical precision (0.03), and the results are in agreement with most previously published data within 2s. Among them, δ⁶⁶Zn_{JMC 3-0749L} of eleven geological certified reference materials are reported for the first time: 0.22 ± 0.03‰ (dolerite, DR-N), 0.23 ± 0.02‰ (gabbro, GSR-10), 0.20 ± 0.04‰ (microgabbro, PM-S), 0.15 ± 0.02‰ (andesite, GSR-2), 0.22 ± 0.08‰ (diorite, GSR-9), 0.19 ± 0.07‰ (syenite, GSR-7), 0.30 ± 0.06‰ (granite, GSR-1), 0.25 ± 0.00‰ (rhyolite, GSR-11), 0.37 ± 0.01‰ (shale, GSR-5), 0.21 ± 0.03‰ (limestone, GSR-6) and 0.20 ± 0.03‰ (hornblendite, GSR-15). The novel Zn isotopic data from these certified reference materials can be used for future interlaboratory comparisons.

The precision and accuracy of ⁴⁰Ar/³⁹Ar dates are ultimately linked to co-irradiated reference materials of known age. Here we provide new data from the SK01 sanidine, which was analysed in three different laboratories to evaluate it as a ⁴⁰Ar/³⁹Ar reference material. Aliquots of 5 mg, incrementally heated in two laboratories, yielded indistinguishable results with a weighted mean age of 27.58 ± 0.06 Ma (95% confidence level). Single-crystal step heating and single-crystal total fusion analyses of SK01 sanidine were undertaken in the third laboratory to further test the intracrystalline homogeneity. For the seven step-heating analyses, six crystals yielded nearly concordant age spectra with ⁴⁰Ar/³⁹Ar ages ranging from 26.853 ± 0.094 Ma to 26.963 ± 0.067 Ma, whereas one crystal gave an older age of 27.774 ± 0.071 Ma with a slightly discordant age spectrum. Twenty-three single-crystal total fusion analyses yielded ⁴⁰Ar/³⁹Ar ages ranging from 27.070 ± 0.108 Ma to 27.736 ± 0.062 Ma with a dispersion of ~ 3.8%. The older ages from single-crystal total fusion dates are interpreted to reflect an inherited or excess argon component in some crystals. This is an initial characterisation of the SK01 sanidine, and additional work needs to be conducted to further evaluate the age dispersion so that it can be utilised as a ⁴⁰Ar/³⁹Ar reference material.

This work presents Sm-Nd and Sr isotopic ratios of the BRP-1 (“Basalt Ribeirão Preto”) reference material (RM) based on repeated TIMS measurements over twelve years carried out by the LAGIR laboratory, Brazil. The BRP-1 RM was produced by the Brazilian Geological Survey from a ca. 130 Ma within-plate basalt, collected from a quarry near Ribeirão Preto city in the Paraná basin. Isotope ratios were measured using a TRITON mass spectrometer. Instrumental bias and fractionation corrections were performed based on repeated measurements of the certified RMs JNdi-1 and NIST SRM 987. The measured Nd and Sr isotopic ratios of BRP-1 are: ¹⁴³Nd/¹⁴⁴Nd = 0.512408 ± 0.000010 (2s), and ⁸⁷Sr/⁸⁶Sr = 0.706011 ± 0.000017 (2s). The mass fractions of Sm and Nd are 11.0 ± 0.2 and 51.9 ± 0.6 μg g^-1, respectively, showing no significant differences compared with the accepted values from the literature. No significant difference between measurements was observed, whether digesting samples in single or batch mode, using metal-jacketed PTFE bombs or PFA vials, or with or without the addition of a spike. The accuracy of these results was evaluated through the measurement of well-characterised USGS RMs, such as AGV-1, BCR-1, BHVO-1, G-2 and GSP-1.

Four natural chromite samples (LBS13-04, LBS13-06 and LBS13-13) from the Luobusa ophiolite (China) and 16SW2-6 from the Stillwater Complex (USA) were developed as reference materials for in situ element microanalysis. Approximately 8 g of chromite fragments with grain sizes of 0.5–1.5 mm from each chromite sample were separated under a binocular microscope and analysed by EPMA, XRF, LA-ICP-MS and solution nebulisation ICP-MS techniques for major and trace elements at six laboratories. The results show that the four chromite samples are homogeneous with respect to MgO, Al₂O₃, Cr₂O₃, FeO, Sc, Ti, V, Mn, Co, Ni, Zn and Ga. These samples are thus suitable to be used as reference materials for in situ microanalysis.

The in situ (U-Th-Sm)/He and U/Pb laser-ablation double-dating procedure is a valuable method that can provide a large dataset relatively efficiently in contrast with conventional bulk helium thermochronometry. In this study, we evaluate the potential age error associated with the double ablation procedure and report the in situ (U-Th-Sm)/He double-ablation dating of 249 zircons from the Fish Canyon Tuff locality. With LA-ICP-MS pseudo-depth profiling and 3D numerical modelling, we show that the concentric double-ablation procedure in minerals with U-Th-Sm zoning can generate a significant (U-Th-Sm)/He age error (positive or negative), resulting in over-scattering and/or an offset of the mean age. Pseudo-depth profiling is insufficient to predict the individual age error, partly because of the superimposed ablations. To evaluate the consequence of this inherent bias, we confront a synthetic age distribution to the error expected for U-Th-Sm zoned zircons analysed with double-ablation (U-Th-Sm)/He thermochronometry. As expected, a strong age bias causes the spreading of peak ages, downgrading the original signal. Yet, the throughput of the ablation-based method can allow intra- and inter-sample peak age identification and comparison, and the coupling of (U-Th-Sm)/He and U/Pb ages extends our ability to deconvolute a multimodal age spectrum.