青藏高原中部羌塘地体南部晚始新世二辉石长英岩（2020-2025）

本项目针对青藏高原中部羌塘地体南部的晚始新世二辉石长英岩，委托桂林理工大学、中国地质科学院及中国科学院地质与地球物理研究所，利用LA-ICP-MS、MC-ICP-MS和Rigaku ZSX100e X射线荧光光谱仪，开展了锆石U-Pb定年、全岩Sr-Nd同位素、锆石Hf-O同位素以及全岩主微量元素的分析。

1. 锆石U-Pb定年
锆石U-Pb数据通过ICPMSDataCal软件对原始数据进行离线处理。Pb校正采用Andersen（2002）的方法。不确定度评估、谐和图绘制及年龄加权平均计算使用Isoplot（Excel™版）完成。

2. 锆石Lu-Hf同位素分析
Lu-Hf同位素分析在束斑直径44 μm、激光频率6 Hz、能量密度10 J·cm⁻²的条件下进行。剥蚀物质由氦气载送，并掺入少量氮气以提高信号稳定性。采用¹⁷⁹Hf/¹⁷⁷Hf = 0.7325、¹⁷⁶Lu/¹⁷⁵Lu = 0.02655、¹⁷²Yb/¹⁷³Yb = 0.5886，并以 βYb = 0.8725 × βHf 对¹⁷⁶Hf/¹⁷⁷Hf进行质量分馏校正。每分析5个样品插入2个GJ-1及1个蓬莱（Penglai）锆石标样，全程监控仪器状态。

3. 全岩Sr-Nd同位素分析
全岩Sr-Nd同位素分析在桂林理工大学完成。约100 mg粉末样品采用HF-HNO₃（体积比1:3）混合酸于120°C、PFA罐中密闭消解7天。Sr和Nd分别经阳离子交换柱与HDEHP萃淋树脂分离纯化。同位素组成采用MC-ICP-MS测定，质量分馏分别以⁸⁶Sr/⁸⁸Sr = 0.1194和¹⁴⁶Nd/¹⁴⁴Nd = 0.7219进行校正。⁸⁷Rb/⁸⁶Sr和¹⁴⁷Sm/¹⁴⁴Nd比值根据ICP-MS测得的相应元素含量计算获得。

4. 矿物原位主微量元素分析

背散射图像与主量元素：在中国冶金地质总局山东测试中心，使用JEOL JXA‑8230型电子探针（EPMA）获取矿物的背散射电子（BSE）图像及原位主量元素（wt.%）数据。分析条件为加速电压15 kV、束流10 nA、束斑直径2 μm，以相应硅酸盐及氧化物标样进行校准。

原位微量元素：在桂林理工大学利用LA-ICP-MS同步测定单斜辉石（Cpx）、斜方辉石（Opx）、斜长石及基质玻璃的主微量元素含量。激光频率为8 Hz，能量密度0.01–0.03 mJ，束斑尺寸44 × 44 μm。以NIST 612为外标，采用ICPMSDataCal程序进行数据校正。分析过程中穿插测定USGS标样BCR‑2、BHVO‑1及BCR‑01，数据质量优于5%，分析流程详见Liu等（2008）。

This project targets the late Eocene two-pyroxene felsic rocks from the southern Qiangtang terrane, central Tibetan Plateau. We commissioned Guilin University of Technology, Chinese Academy of Geological Sciences, and the Institute of Geology and Geophysics, Chinese Academy of Sciences to conduct analytical works including zircon U-Pb geochronology, whole-rock Sr-Nd isotopes, zircon Hf-O isotopes, and whole-rock major and trace element analyses, using LA-ICP-MS, MC-ICP-MS, and Rigaku ZSX100e X-ray fluorescence spectrometer.

1. Zircon U-Pb Geochronology
Zircon U-Pb raw data were processed offline using ICPMSDataCal software. Pb correction was performed following the method of Andersen (2002). Uncertainty estimation, concordia diagram plotting, and weighted average age calculation were completed using Isoplot (Excel™ edition).

2. Zircon Lu-Hf Isotope Analysis
Lu-Hf isotope analyses were conducted with a beam diameter of 44 μm, laser frequency of 6 Hz, and energy density of 10 J·cm⁻². The ablated material was carried by helium gas, with a small amount of nitrogen added to improve signal stability. Mass fractionation correction for ¹⁷⁶Hf/¹⁷⁷Hf was performed using ¹⁷⁹Hf/¹⁷⁷Hf = 0.7325, ¹⁷⁶Lu/¹⁷⁵Lu = 0.02655, ¹⁷²Yb/¹⁷³Yb = 0.5886, and βYb = 0.8725 × βHf. Two GJ-1 and one Penglai zircon standard samples were inserted after every 5 analyzed samples to monitor the instrument status throughout the analytical process.

3. Whole-Rock Sr-Nd Isotope Analysis
Whole-rock Sr-Nd isotope analyses were completed at Guilin University of Technology. Approximately 100 mg of powdered sample was digested in a PFA vessel with a mixed acid of HF-HNO₃ (volume ratio 1:3) at 120°C for 7 days under sealed conditions. Sr and Nd were separated and purified using cation exchange columns and HDEHP extraction chromatography resin, respectively. Isotopic compositions were determined by MC-ICP-MS, with mass fractionation corrected using ⁸⁶Sr/⁸⁸Sr = 0.1194 and ¹⁴⁶Nd/¹⁴⁴Nd = 0.7219, respectively. The ⁸⁷Rb/⁸⁶Sr and ¹⁴⁷Sm/¹⁴⁴Nd ratios were calculated based on the corresponding element contents measured by ICP-MS.

4. In-situ Major and Trace Element Analyses of Minerals
- Backscattered Electron Images and Major Element Data: Backscattered electron (BSE) images and in-situ major element (wt.%) data of minerals were obtained using a JEOL JXA-8230 electron probe microanalyzer (EPMA) at the Shandong Testing Center of China Metallurgical Geology Bureau. The analytical conditions were accelerating voltage of 15 kV, beam current of 10 nA, and beam diameter of 2 μm, with calibration using corresponding silicate and oxide standards.
- In-situ Trace Element Analysis: In-situ major and trace element contents of clinopyroxene (Cpx), orthopyroxene (Opx), plagioclase, and matrix glass were synchronously determined by LA-ICP-MS at Guilin University of Technology. The laser parameters were frequency of 8 Hz, energy density of 0.01–0.03 mJ, and beam size of 44 × 44 μm. NIST 612 was used as the external standard, and data correction was performed using ICPMSDataCal software. USGS reference materials BCR-2, BHVO-1, and BCR-01 were inserted during the analytical process, with analytical precision better than 5%. The detailed analytical procedure is referred to Liu et al. (2008).