Search

BACKGROUND Mircobeam Lu-Hf isotopic analysis on minerals provides an important means to understand the microscopic process of magmatic activity and metamorphic reaction and to trace provenance of sediment, which greatly promotes the development of petrogeochemistry. Many methods were provided to obtain accurate and precise microbeam Lu-Hf isotopic data, and many mineral standards for microbeam Lu-Hf isotopic analysis were developed. OBJECTIVES To review and understand the microbeam methods for Lu-Hf isotopic analysis. METHODS Systematic compilations of published data of standards and discussion on the different methods for microbeam Lu-Hf isotopic analysis. RESULTS The development history of microbeam Lu-Hf isotopic analysis in the past 30 years is reviewed, and the influence of 176Yb and 176Lu isobars, REE oxides, and Ta-rich matrices on the precision and accuracy of Hf isotope measurement is systematically evaluated as well as the different correction strategies and programs provided in previous studies. In addition, a comprehensive compilation of the different Yb and Lu isotopic compositions reported in references and the different methods of microbeam Lu-Hf isotopic analyses on various Hf-rich minerals such as zircon, baddeleyite, zirconolite, zirkelite, calzirtite, eudialyte, rutile, cassiterite, and columbite-group minerals is made. The micro-drill/micro-saw sampling Lu-Hf isotopic analysis of Lu-rich minerals has played an important role in revealing the multi-stage orogenic process and the duration of mineral growth. The advent of laser ablation inductively coupled plasma triple quadrupole mass spectrometry (LA-ICP-Q-MS/MS) has increased the spatial resolution of Lu-Hf single-spot/isochron dating analysis of Lu-rich minerals to the micrometer scale. This method relies on the collision reaction of Hf and NH3 to realize the online separation of Hf from Lu, and achieves the purpose of synchronous measurement of 176Lu/177Hf and 176Hf/177Hf ratios, which is introduced in detail. CONCLUSIONS The new generation of tandem multi-collector sector field mass spectrometer with collision/reaction cell has high stability and sensitivity, which can be used to determine online separation of Hf from REEs, produce high-precision Hf isotope measurements for high Yb/Hf or Ta-rich minerals under high spatial resolution conditions, and significantly improve the precision and accuracy of microbeam Lu-Hf isotopic analysis. This deserves extensive attention in the future.

The bulk chemical compositions of extraterrestrial materials can provide critical information on the evolution and magmatism of planetary bodies. However, accurate measurements are challenging because these samples, particularly returned samples, are extremely limited and valuable. We demonstrate the practicality of chemical analysis using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) on highly diluted fused glass discs (lithium borate flux : sample = 100 : 1). Only 30 mg of sample is required to produce a lithium borate disc, which is one magnitude lower than previously used (>300 mg). We proposed a modified Jet sample cone (the orifice diameter enlarging from 1.1 mm to 1.2 mm) to improve the sensitivity by a factor of ∼4.5 compared to that of standard sample cone. The interferences from the lithium borate discs were evaluated systemically, and corrections are necessary for some elements (e.g., Si, Ca, Pb). The limits of detection for most elements are in the range of 0.1–1.0 μg g−1. The analytical precision is better than 30% (relative standard deviation) for elements with concentrations of >0.5 μg g−1. The accuracy is better than 15% (relative deviation), as demonstrated by analyses of BCR-2 and BHVO-1 rock powder reference materials. This innovative technique was applied to lunar samples collected by Chang'e-5 (CE-5) mission, and an independent dataset of 38 major and trace elements was obtained. We report the average chemical composition of the CE-5 lunar soil samples, which will be an important reference for future study. This method will be useful for other precious extraterrestrial samples (e.g., CE-6 lunar samples). [ABSTRACT FROM AUTHOR]

The Ti-in-zircon thermometer is widely used in geoscience for constraining the temperatures of geological settings. Precise and accurate determination of Ti contents (∼1–10 μg g−1) in zircon is a prerequisite for the application of this thermometer; however, traditional laser ablation–single quadrupole–inductively coupled plasma–mass spectrometry (LA–SQ–ICP–MS) analysis of Ti contents in zircon is challenging due to the low abundance of the interference-free isotope of 49Ti (isotope abundance: 5.51%), resulting in poor precision (>30%, 2RSD), in particular for the high spatial resolution (laser spot size <20 μm) analysis. We have developed a robust technique for determining low Ti contents in zircon using LA–ICP–MS/MS with NH3 as the reaction gas. Using an iCAP TQ ICP–MS/MS instrument (Thermo Scientific, USA), high-purity NH3 was a more effective reaction gas than the commonly used 1 : 9 NH3 : He mixture gas, and a three-fold improvement in sensitivity was achieved using an N2 flow rate of 5.0 mL min−1. The reaction products of Ti, Ca, and Zr with NH3 were identified over a mass range of 40 to 160 amu. The reaction product 48Ti(14N1H)(14N1H3)4 (a mass shift of +83, expressed as (48+83)Ti) was measured to separate 48Ti+ from 48Ca+ and 96Zr2+. Interfering ions 48Ca+ and 96Zr2+ have low reaction rates (∼0.0046% and ∼0.07%) at a mass shift of +83, and corrections are not required for glass reference materials and zircon samples. Five zircon reference materials with Ti contents of 2.5–5.0 μg g−1 were analysed, and the analytical precision was better than 10%. Compared with the single quadrupole (SQ) mode, our method is more robust for determining low Ti contents in zircon at high spatial resolutions (laser spot size <20 μm), making it useful for the analysis of complex zircon grains, e.g., metamorphic zircon. [ABSTRACT FROM AUTHOR]

Monazite is a LREE-rich accessory mineral in various igneous and metamorphic rocks; therefore, monazite geochronology has the potential to answer a range of important geological questions. We demonstrate the feasibility of in situ Lu–Hf dating by LA-ICP-MS/MS applied to monazite for the first time. Eight monazite samples were investigated, with ages of 2.65–0.27 Ga and Lu contents of 19–180 μg g−1. Although the isobaric interferences of 176Lu and 176Yb occur at extremely low reaction rates (reacted/unreacted fractions) for higher mass reaction products (+82 a.m.u), isobaric interference corrections are still needed for the monazite samples due to their high Lu/Hf and Yb/Hf ratios (mean 175Lu/177Hf = ∼24 000; mean 172Yb/177Hf = ∼52 000) when using an iCap TQ instrument. The RW-1, ELK, 44 069, and Maine 1 monazites yield relatively low common Hf contents, whereas the Vermillion, Namaqualand, 117 531, and Maine 2 monazites have high and variable common Hf contents. The results show that in situ monazite Lu–Hf dating by LA-ICP-MS/MS is feasible and can yield precise (0.40–2.96%, 2 relative standard error) and accurate (−0.40 to +1.99%, 2 relative deviation) ages that are comparable to those from the U–Th–Pb system. There are no systematic Lu–Hf age biases with respect of the U–Th–Pb ages and Lu and Hf contents. We report a data reduction scheme (DRS) and Visual Lu–Hf age plugin for Iolite software to process in situ Lu–Hf age data. Lu–Hf geochronology could provide independent age constraints for the monazite, which has previously been successfully dated using the U–Th–Pb system. [ABSTRACT FROM AUTHOR]

A new natural epidote reference material, PSV, sourced from Alchuri village, Shigar valley, Haramosh mountains, Gilgit, Pakistan, is characterized in this study for O and Sr isotope composition analysis by micro-beam analytical techniques. Comprehensive studies including thermal ionization mass spectrometry (TIMS), solution nebulization multi-collector inductively coupled plasma-mass spectrometry (SN-MC-ICP-MS), laser ablation multi-collector inductively coupled plasma-mass spectrometry (LA-MC-ICP-MS), secondary ion mass spectrometry (SIMS), and laser fluorination have been performed on PSV epidote to assess the homogeneity of O and Sr isotope compositions and provide recommended values for δ18O and the 87Sr/86Sr ratio. The mean δ18O value measured by the laser fluorination method is 12.58 ± 0.07‰ (2s, n = 12), recommended as the reference value for micro-beam analysis. Seventy SIMS analyses were performed on PSV epidote, resulting in a mean δ18O value of 19.67 ± 0.03‰ (2s, n = 70) obtained without external calibration utilizing matrix-matched reference materials. This finding emphasizes the necessity of employing external calibration with matrix-matched reference materials for accurate determination of oxygen isotope ratios in epidote utilizing the SIMS method. The mean 87Sr/86Sr ratio derived by TIMS and SN-MC-ICP-MS is 0.707672 ± 0.000013 (2s, n = 2) and 0.707679 ± 0.000007 (2s, n = 10), respectively. The in situ Sr isotopic analysis utilizing LA-MC-ICP-MS revealed homogeneous Sr isotopic compositions at a micro-scale of 40 to 85 μm. The weighted mean 87Sr/86Sr ratio was determined to be 0.70768 ± 0.00001 (2s, n = 336; MSWD = 2.0), which is in agreement with the solution value within the analytical uncertainty. In conclusion, despite the chemical composition variability, the PSV epidote exhibits reproducible O and Sr isotope compositions, making it a suitable reference material for in situ O–Sr isotope ratio analysis utilizing micro-beam methods. [ABSTRACT FROM AUTHOR]

Lu–Hf geochronology is useful for constraining the evolution of geological systems. In this study, the in situ LA-ICP-MS/MS Lu–Hf dating technique was successfully applied to Paleozoic-Precambrian xenotime, apatite and garnet. For an iCap TQ ICP-MS/MS instrument (Thermo Fisher, USA), high-purity NH3 was more effective in the reaction than the commonly used 1 : 9 NH3–He mixture, and an 80% improvement in sensitivity was achieved using an N2 flow rate of 4.0 mL min−1. Lutetium, Yb and Hf reaction products with NH3 were identified in the mass range from 175–300 amu. The reaction product of (176+82)Hf (expressed for 176Hf(14N1H)(14N1H2)(14N1H3)3, mass shift by +82) is measured for the separation of 176Hf from 176Lu and 176Yb. Isobaric interferences 176Lu and 176Yb have extremely low reaction rates of ∼0.0034% and ∼0.00036% (at mass shift +82), which are only required to be corrected for the samples (e.g., xenotime) with extremely high 175Lu/177Hf and 172Yb/177Hf ratios. A matrix-induced bias of 176Lu/177Hf ratios was observed between NIST SRM 610 and the samples, which required further correction using matrix-matched reference materials. For xenotime, the accuracy of the common-Hf corrected single-spot ages is generally better than 1.5%, comparable to those obtained by in situ U–Pb analysis. The precisions of common-Hf corrected single-spot ages were in a range of 1.5–8.1% and 9.2–36.0% for xenotime and apatite samples. For garnet, the analytical uncertainties of the isochron ages are in a range of 3.5–10%, which could be further improved using a sensitivity-enhanced instrument and/or enlarged sampling volume. Our study revealed that the xenotime reference materials can be used as calibrators for apatite Lu–Hf dating. The novel in situ Lu–Hf dating technique may be especially useful for determining the age of the samples with complex temporal records or lack of traditional U-rich accessory minerals (e.g., zircon). [ABSTRACT FROM AUTHOR]