Assisted by laser ablation (LA) inductively coupled plasma mass spectrometry (ICPMS) analytical techniques, calcite is now accepted as an important U–Pb dating mineral for application to various issues in geology. However, appropriate calcite reference materials with homogeneous composition and structure remain lacking due to limited research work on such reference materials. This study successfully identifies a new natural megacryst calcite reference material, TARIM, for in situ U–Pb isotope measurement by LA-ICPMS analysis. Electronic probe microanalysis (EPMA) shows TARIM to be a homogenous low-Mg calcite. LA-ICPMS trace elemental analyses and mapping results suggest that TARIM is relatively homogenous with U content (mean value = 0.48 μg g⁻¹) appropriate for U–Pb isotopic dating. U–Pb analysis using isotope dilution-thermal ionization mass spectrometry methods (ID-TIMS) yielded a lower intercept age of 208.5 ± 0.6 Ma (2S, mean squared weighted deviation (MSWD) = 1.04). A total of 515 LA-ICPMS U–Pb isotope analyses on random calcite pieces show consistent ages with a lower intercept age of 208.0 ± 0.4/3.2 Ma (2S, MSWD = 3.0), overlapping with the ID-TIMS age. We propose that TARIM calcite can be applied as a reference material for matrix-matched calibration or as a monitoring standard for calcite LA-ICPMS U–Pb dating.

In situLu–Hf geochronology is useful for constraining the evolution of geological systems.

The Chakabeishan (CKBS) deposit is the first pegmatite-type Li-Be deposit discovered in the eastern North Qaidam Tectonic Belt (NQTB) of Tibetan Plateau. The correct understanding of its petrogenesis and the precise determination of its formation age are of great significance for further regional prospecting and the discovery of new economically valuable rare-metal deposits. Therefore, a systematic study of texture, major-element composition, and U-Pb dating of columbite-tantalite group minerals (CGMs) in the spodumene pegmatite dyke from the CKBS deposit was undertaken. Three types of CGMs were identified, including concentric oscillatory ferrocolumbite (CGMs-1), homogeneous ferrocolumbite (CGMs-2), and irregular ferrotantalite (minor manganocolumbite) with abundant early ferrocolumbite replacement remnants (CGMs-3). The zoning patterns and chemical compositions in the CGMs record the complex evolutionary history of their host pegmatite from the magmatic stage (CGMs-1, disequilibrium crystallization) to the magmatic-hydrothermal transition stage (CGMs-2, equilibrium crystallization) and then to the late metasomatic stage (CGMs-3, replacement/re-equilibrium). CGMs U-Pb dating results suggest that the spodumene pegmatite dyke (No.15) emplaced at 230.1 ± 2.6 Ma. Subsequently, it experienced fluid metasomatism at 221 ± 5.3 Ma. Based on the new age data and published geochronological data, it can be concluded that the spodumene pegmatite dykes in the CKBS deposit formed in an oceanic subduction-related setting, representing a new metallogenic event in western China. Except for the CKBS deposit, a large number of rare-metal pegmatite dykes have also been discovered in the eastern NQTB, indicating that the eastern NQTB may be an important potential rare-metal metallogenic belt that should be explored in detail and arouse painstaking attention.

Columbite–tantalite is predominantly found in rare-metal granites and pegmatites, alkaline and carbonatitic rocks, and columbite–tantalite-bearing peraluminous granites. It is recognized as a potentially valuable mineral for use in U–Pb isotopic dating. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) can be used in the U–Pb dating of columbite–tantalite. LA-ICP-MS requires matrix-matched reference materials for isotopic fractionation/mass bias correction. Some columbite–tantalite reference materials contain common Pb. However, columbite–tantalite reference materials with low contents of common Pb are scarce. Thus, in this study, we proposed a new potential reference material, OXF, with a low common Pb content for use in LA-ICP-MS U–Pb dating of columbite–tantalite. LA-ICP-MS analysis revealed that the average U, Th, and Pb concentrations in OXF are 428 ± 156 ppm (2s), 6.3 ± 2.5 ppm (2s), and 20.0 ± 10.0 ppm (2s), respectively, with a total weight of 336.6 g. Chemical abrasion isotope dilution thermal ionization mass spectrometry (CA-ID-TIMS) revealed that the weighted mean ²⁰⁶Pb/²³⁸U age of OXF is 262.85 ± 0.64 Ma (MSWD = 1.8, 2s). The LA-ICP-MS U–Pb ages of the four laboratories in the China University of Geosciences (Wuhan) (CUGW), the China University of Geosciences (Beijing) (CUGB), Wuhan Sample Solution Analytical Technology Co. Ltd, China (WHSS), and the Institute of Geology and Geophysics, Chinese Academy of Sciences (IGGCAS) were determined. The ²⁰⁶Pb/²³⁸U ages of the CUGW, the CUGB, WHSS, and the IGGCAS were 262.71 ± 0.33 Ma (2s, n = 151), 263.3 ± 2.3 Ma (2s, n = 46), 263.5 ± 1.3 Ma (2s, n = 42) and 264.3 ± 2.4 Ma (2s, n = 25), respectively. The weighted mean ²⁰⁶Pb/²³⁸U age of the four laboratories obtained using LA-ICP-MS and by combining the U–Pb data obtained from the laboratories was 262.83 ± 0.29 Ma (2s, n = 358), which aligns with its value obtained using CA-ID-TIMS after allowing for analytical uncertainties. OXF demonstrated homogeneous U–Pb ages with minimal Pb contributions, indicating its potential for serving as a primary reference material in LA-ICP-MS calibrations.

Apatite, an important mineral widely distributed in various geological environments, can be used for in situ U–Pb dating and Sr–Nd isotope analyses. The LA-ICPMS U–Pb dating and Sr–Nd isotopic determinations require suitable matrix-matched reference materials. Current apatite standards are rare and have some defects. Most natural apatite references display high and variable common Pb, which may be the most difficult issue in microbeam determination. We provided a gem-quality apatite MAP-3, subjected to detailed major- and trace element composition, U–Pb dating, and Sr–Nd isotopic analyses to assess its homogeneity of chemical composition and suitability as a reference material for microbeam U–Pb dating and Nd isotope analyses. Through comprehensive analyses, we show that the MAP-3 apatite is free of mineral inclusions and is uniform at the level of analytical precision of major- and trace element, U–Pb isotopic, and Nd isotopic ratios despite compositional zones from CL images. The MAP-3 apatite has ID-TIMS determined mean isotopic ratio values of 0.13222 ± 0.00016 for ²⁰⁶Pb^/238U, 1.2084 ± 0.0030 for ²⁰⁷Pb^/235U, and 0.0663 ± 0.0001 for ²⁰⁷Pb^/206Pb and the weighted mean ²⁰⁶Pb^/238U ages of 800.5 ± 0.9 Ma (2 s, MSWD = 1.5, n = 11). The ¹⁴³Nd/¹⁴⁴Nd isotopic results determined by (ID)-TIMS are 0.511248 ± 0.000006 (2 s, MSWD = 4.2, n = 11) with moderate Nd contents of ∼1532 ppm. U–Pb age and Nd isotopic compositions obtained by LA-(Q, SF-SC, MC)-ICPMS analysis are reproducible and agree with the values of TIMS, which indicates that MAP-3 apatite has the potential to be a primary reference material for microbeam determination of U–Pb ages and Nd isotope analyses. To validate the effectiveness of the potential, we dated some apatite reference materials of known age and two geological apatites. The results demonstrated the high-quality U–Pb dating reference materials used with MAP-3 apatite.

Zircon U–Pb dating by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) is a widely used analytical method in the field of geology. However, the U–Pb dating of zircons with complex interior structures has always been a challenge in laser in situ analysis. To address this issue, we introduce a novel method, termed reverse depth profiling, for LA-ICPMS U–Pb dating of such zircons. This method combines the traditional LA-ICPMS method with depth profiling, analyzing the over-polished zircon from core to rim. We applied this method to zircons from the Himalayan leucogranites in Dinggye and garnet-bearing granitic gneiss in Yadong. The method allows the successful dating of zircon rims as narrow as only 0.6 μm. Characterized by high sample analysis efficiency, superior vertical spatial resolution, and optimal data utilization, this method enhances the success rate of U–Pb dating of structurally complex zircons. Valid geochronological information on the inherited cores and magmatic/metamorphic rims of zircons can be obtained by this method, which has great potential for unraveling complex magmatic and metamorphic events in tectonically active regions in geological history.