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Mica exhibits a relatively high Rb/Sr ratio and possesses a closure temperature for the Rb-Sr isotope system that is higher than the ore-forming temperature range of low- to medium-temperature deposits. Consequently, utilizing the laser ablation (LA) technique for in situ Rb-Sr dating in mica constitutes a significant methodology for resolving the mineralization chronology of low- to medium-temperature hydrothermal ore deposits. In this study, we employed a combination of a triple quadrupole inductively coupled plasma mass spectrometer (ICP-MS/MS) and 193 nm LA system with SF6 as the reaction gas to achieve interference removal of 87Rb+ on 87Sr+. We then developed an in situ Rb-Sr dating method for mica. In addition, an investigation was conducted to identify the factors that could influence the analytical accuracy of the method. Subsequently, we applied the developed method to carry out in situ Rb-Sr dating for the ZBH-25 biotite, a national primary reference material (GBW04439) for K-Ar dating, and yielded a younger age (ca. 12%, relative standard deviation, RSD) than the reference K-Ar age when using NIST SRM 610 as the reference material for external calibration. This finding indicated that in the process of determining Rb-Sr ages for mica by LA-ICP-MS/MS, there are significant matrix effects between the NIST SRM 610 and the mica samples, resulting in inaccurate Rb-Sr ages. In response to this issue, a two-step calibration method is proposed here. Based on external calibration using NIST SRM 610, ZBH-25 biotite is employed as a second external reference material to perform a second calibration of the sample data to correct the matrix effect between the glass standards and the natural mica samples, thereby improving the accuracy of Rb-Sr dating by LA-ICP-MS/MS. Using the proposed method, in situ Rb-Sr dating by LA-ICP-MS/MS was performed on mica samples from monzonite exposed in Mt. Dromedary, New South Wales, Australia, porphyritic granodiorite in Fangshan pluton and albionite granite in the Gyirong area of Tibet. The obtained Rb-Sr age results show agreement with the recommended values within the analytical uncertainty, which serves to validate the accuracy and effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Titanium (Ti) isotopes are emerging as a power tool for studying magmatic processes on the Earth and other planets. Pioneering studies carried out bulk-rock Ti isotopic measurements by conventional solution nebulization multi-collector inductively coupled plasma mass spectrometry (SN-MC-ICP-MS) and in situ Ti isotopic analysis via secondary ionization mass spectrometry (SIMS), which sacrificed spatial resolution and had relatively low analytical precision, respectively. In this work, a novel and robust method for in situ Ti isotopic analysis of titanium-bearing minerals (i.e., rutile and ilmenite) was presented, based on a femtosecond laser ablation multi-collector inductively coupled plasma mass spectrometer (fs-LA-MC-ICP-MS). Very stable isotopic signals can be ensured after careful optimization of the parameters of fs-LA (e.g., fluence, spot size, and frequency), and thus a high analytical precision has been obtained for Alfa-Ti (an ultrapure Ti metal rod) under a high spatial resolution of spot diameter = 30 μm. The within run and external reproducibility for δ49/47Ti (49Ti/47Ti isotopic ratio, reported as δ49/47Ti notation, in parts in 103) measurement on Alfa-Ti are 0.05‰ (2SE, internal precision of within-spot analysis) and 0.07‰ (2SD, external reproducibility of spot-to-spot analysis), respectively. A series of titanium-bearing minerals, including five potential rutile U–Pb chronological standards and four potential ilmenite Fe isotope standards, were assessed for Ti isotopic homogeneity on a 30 μm-scale and precision of the measurement. The most homogeneous minerals were subsequently used to comprehensively evaluate the analytical accuracy and potential matrix effect. Our results show that in situ Ti isotopic analysis is susceptible to matrix effects when using fs-LA and accurate δ49/47TiOL-Ti values (calibrated against the OL-Ti reference material developed in the Origins Laboratory of the University of Chicago) can be obtained when a matrix-matched reference material is used as a bracketing standard. Therefore, well characterized matrix-matched reference materials are necessary for in situ Ti isotopic analysis. KNW rutile and PZH12-15 ilmenite characterized in this study show potential as suitable reference materials for micro-beam Ti isotopic analysis. [ABSTRACT FROM AUTHOR]

To meet the rapid development of zircon U-Pb geochronology and Hf-O isotope geochemistry, it is imperative to develop well-characterized zircon reference materials for microbeam analysis. Here, zircon KV01 separated from the Kaap Valley pluton, South Africa is introduced as a potential Archean reference material for microbeam U-Pb age and Hf-O isotope determination. SIMS and LA-ICP-MS U-Pb isotopic measurements gave grand mean 207Pb/206Pb ages of 3233±16 Ma (2s, n=90) and 3230±26 Ma (2s, n=52), which are consistent with reported CA-ID-TIMS results. Slight heterogeneity of oxygen isotopes is revealed by SIMS analyses that yielded a relatively large δ18O range of 4.61–6.51‰. Among them, the zircon grains with clear oscillatory zones give a grand mean δ18O value of 6.17±0.33‰ (2s), which is suggested to record the primary O isotopic compositions. The homogeneity in the Hf isotopic compositions of KV01 zircon was checked by the laser ablation and solution MC-ICP-MS methods. They yielded consistent results with a recommended 176Hf/177Hf ratio of 0.280810±0.000013 (2s). The results reported here demonstrate that KV01 zircon could be a reliable reference material for microbeam 207Pb/206Pb age and Hf isotope determinations of ancient zircons, and be suitable as a quality monitor for SIMS oxygen isotopic analysis. [ABSTRACT FROM AUTHOR]

In this study, we report both 143Nd/144Nd and 147Sm/144Nd values in twelve minerals (apatite, titanite, monazite and eudialyte) based on analyses over 4 years using LA‐MC‐ICP‐MS. The positive correlation between the measured βSm and βNd (r2 = 0.9981) over this time in our laboratory demonstrates the excellent long‐term stability of the method. Compared with the normal method, Sm and Nd signal intensities were improved by a factor of 2.9 with the use of X skimmer and Jet sample cones in combination with the addition of nitrogen at 3–6 ml min−1 to the central gas flow. The enhancement of signal intensity benefits the accurate in situ determination of the Sm‐Nd isotopes of samples poor in these elements. 143Nd/144Nd values were also determined in two manganese nodules and GSMC Co‐rich crust with low mass fractions of Nd (94–293 μg g−1). Generally, most of the obtained Sm‐Nd isotopic compositions in these geological materials are consistent with published values. ‘External reproducibility’ (2s) of 143Nd/144Nd and 147Sm/144Nd was typically better than 0.06‰ and 2.5‰, respectively, demonstrating that the Durango, Otter Lake, NW‐1 and MAD apatites, the Khan, and OLT‐1 titanites, MGMH#117531 monazite and LV01 eudialyte are promising candidate reference materials for in situ Sm‐Nd isotopic determinations. The Trebilcock, Mae Klang and 44069 monazites are only suitable for in situ Nd isotopic determinations because of their heterogeneous Sm/Nd compositions. The heterogeneous Sm‐Nd composition of titanite BLR‐1 demonstrates that it is not a suitable reference material for in situ Sm‐Nd isotopic determinations. Deep‐sea samples (NOD‐A‐1 and NOD‐P‐1 manganese nodule, GSMC Co‐rich crust) with low mass fractions of Nd also show homogenous Nd isotopic compositions. Sm‐Nd isotopic ratios of a monazite (MQG‐22) from the North China Craton were measured as a case study and gave a 147Sm‐143Nd isochron age of 1792 ± 35 Ma (MSWD = 3.2) consistent with the published metamorphic age of the host metasedimentary rocks. The results for both candidate reference materials and geological samples demonstrate that the in situ LA‐MC‐ICP‐MS analytical protocol described is feasible and robust for research in geological evolution. [ABSTRACT FROM AUTHOR]

The hafnium isotopic analysis using laser ablation has been widely conducted on Hf-rich minerals (zircon/baddeleyite/calzirtite/eudialyte), however, little work has been reported on Hf-poor (<100 ppm) minerals. This work presents a detailed procedure of in situ hafnium isotopic analysis from rutile using laser ablation multiple collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS). The rutile U-Pb dating reference material JDX shows homogeneous hafnium isotopic ratios, with Hf/Hf=0.281795±0.000015 (2SD, n=33) and Lu/Hf=0.000018±0.000004 (2SD, n=17) that suggest the possibility of using JDX as a new reference material hafnium isotopic measurement. We also measure hafnium isotopic compositions of other rutile U-Pb dating reference material (R10, Sugluk-4 and PCA-S207) and the Hf/Hf values are similar to previously reported results, which confirms that we can acquire accurate and precise hafnium isotopic compositions using our developed analytical protocol. We analyzed hafnium isotopic compositions and U-Pb ages of rutile in high-temperature and ultrahigh-temperature granulites from various terrains of the Khondalite Belt from the North China Craton, combined with zircon results in the same area, suggesting that the metamorphic evolution history of the granulite is much more complicated than previously thought. [ABSTRACT FROM AUTHOR]

Titanite is an ideal mineral for U-Pb isotopic dating because of its relatively high U, Th and Pb contents. Here, we developed a technique for U-Pb dating of titanite using the 193 nm ArF laser-ablation system and Agilent 7500a Q-ICP-MS. Standards of titanite (BLR-1 and OLT-1) and zircon (91500 and GJ-1) were dated using single spot and line raster scan analytical methods. To check the matrix effect, titanite (BLR-1) and zircon (91500) standards were analyzed as the external standards. The weighted mean Pb/U ages of OLT-1 titanite are 1015±5 Ma (2 σ, n=24) and 1017±6 Ma (2 σ, n=24) by single spot and line raster scan analyses, respectively, using BLR-1 titanite as the external standard. These ages are consistent with its reference age of about 1014 Ma. However, using 91500 zircon as the external standard, the weighted mean Pb/U ages are 917±4 Ma (2 σ, n=24) and 927±5 Ma (2 σ, n=24) for BLR-1 titanite, and 891±4 Ma (2 σ, n=24) and 901±5 Ma (2 σ, n=24) for OLT-1 titanite by single spot and line raster scan analyses, respectively. It is evident that these ages are ∼12% younger than their reference values. Our results reveal that significant matrix effect does exist between different kinds of minerals during LA-ICPMS U-Pb age determination, whereas it is insignificant between same minerals. Therefore, same mineral must be used as the external standard for fractionation corrections during in situ LA-ICPMS U-Pb age analysis. In addition, we determined U-Pb ages for titanites from the Early Cretaceous Fangshan pluton, which indicates a rapid cooling history of this pluton. [ABSTRACT FROM AUTHOR]

Xenotime is an ideal mineral for U-Th-Pb isotopic dating because of its relatively high U and Th contents, but typically low concentration of common Pb. These characteristics, and the fact that it is widespread throughout various types of rocks, suggest that the U-Th-Pb dating of xenotime has broad applications. Studies of U-Pb dating on xenotime by ion microprobe (such as SHRIMP) have increased in recent years, whereas studies by laser ablation (LA)-ICP-MS are still rare. In this study, we developed a technique for U-Pb dating of xenotime using the 193 nm ArF laser-ablation system and Agilent 7500a Q-ICP-MS. To evaluate the reliability of our method, a xenotime standard, BS-1, was analyzed and calibrated against another xenotime standard, MG-1. The weighted mean Pb/U ages of 510.1 ± 5.2 Ma (2 σ, n = 21), 509.8 ± 4.3 Ma (2 σ, n = 21) and 510.0 ± 4.6 Ma (2 σ, n = 21) were obtained using beam diameters of 16, 24 and 32 μm, respectively. These ages are identical to those determined by ID-TIMS method (weighted mean Pb/U age of 508.8 ± 1.4 Ma), which supports the reliability of our LA-ICP-MS method. We also analyzed xenotimes in leucogranites from South Tibet and granites from Xihuashan in southern China, and obtained accurate and precise ages. Nevertheless, we observed systematic differences in Pb/U fractionation among xenotime, monazite and zircon. The matrix-effect resulted in either under-correction or over-correction of fractionation, and thus led to inaccurate ages. Thus, a matrix-matched material is required for U-Pb dating of xenotime by LA-ICP-MS. [ABSTRACT FROM AUTHOR]

Problems with REE oxide interferences during in-situ Hf isotope analysis in zirconium-bearing minerals can give rise to inaccuracies in the obtained dataset. In this study, we present an in-run 177Hf16O/177Hf measurement protocol pertaining to in-situ Hf isotope analysis by laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) as a routine method, allowing for a robust real-time method of monitoring the oxide formation rates and offering a method to monitor REE oxide interferences (e.g., Gd and Dy). For this purpose, we set up a static data collection mode to measure Hf isotopes and 177Hf16O signals concurrently in-run. By analyzing zirconium-bearing minerals characterized with a broad range of Dy/Hf and Gd/Hf ratios (e.g., zircon: typically, 0.0001–0.022 for Dy/Hf and 0.00002–0.013 for Gd/Hf; zirconolite: typically, >0.2 for Dy/Hf and > 0.4 for Gd/Hf; eudialyte: typically, >0.1 for Dy/Hf and > 0.1 for Gd/Hf), influences of oxide formation rate on 176Hf/177Hf ratios are investigated via the present in-run method. The level of oxide formation during the analysis is found to impact the measurement accuracy, especially for samples with higher REE/Hf ratios. Therefore, it is imperative that oxide ratios should be routinely monitored for daily in-situ Hf isotope analysis along with oxide formation rates. In addition, based on results of the present work, a higher REE/Hf zircon, like SA02 zircon, is strongly recommended as the primary refence material for routine in-situ analysis of Hf isotopic compositions in zircons to carefully test the accuracy of analysis for zircons. [Display omitted] • An in-run 177Hf16O/177Hf measurement protocol is presented allowing for a real-time monitoring of the oxide formation rate. • Using present method, analyses were done and results indicate detrimental effect of oxide rate of REEs on Hf isotope ratios. • A higher REE/Hf zircon is strongly recommended as the refence material for routine in-situ Hf isotope analysis in zircons. [ABSTRACT FROM AUTHOR]