SUCCESSIONS OF THE MISSISSIPPIAN NANDUAN FORMATION IN THE “MIDDLE-UPPER DEVONIAN” AND THE “PERMIAN LABA FORMATION” OF THE CHANGNING-MENGLIAN BELT, WESTERN YUNNAN, CHINA AND ITS GEOLOGICAL SIGNIFICANCE

The U-Pb dating analysis of zircon was completed at Beijing Kehui Testing Technology Co., Ltd. The instrument used for zircon dating analysis is AnalyticJena PQMS type ICP-MS and the accompanying RESOlution 193nm excimer laser ablation system. The beam diameter used for laser ablation is 24 μ m. The frequency is 6 Hz, the energy density is about 5 J/cm2, and He is used as the carrier gas. LA-ICP-MS laser ablation sampling adopts a single point ablation method. Before testing, the instrument is adjusted using zircon standard GJ-1 to achieve the optimal state. Zircon U-Pb dating was performed using standard GJ-1 as the external standard, and trace element content was quantitatively calculated using NIST 610 as the external standard and Si as the internal standard. During the testing process, two zircon standard samples GJ-1 were repeatedly measured before and after every 10 samples to calibrate the samples, and one zircon Plesovice was measured. The status of the instrument was observed to ensure the accuracy of the test. The data processing was carried out using LADR_1.1.07 (Norris et al, 2018) software program. The zircon age harmony plot was obtained using the Isoplot 4.15 program. The detailed experimental testing process can be found in Hou Kejun et al. (2009). During the sample analysis process, the analysis result of Plesovice standard sample as an unknown sample was 336.6 ± 1.2 Ma (n=24,2 σ）， The recommended age value is 337.13 ± 0.37 Ma (2 σ） (Slama et al, 2008), the two are completely consistent within the error range.

锆石U-Pb定年分析工作由北京科汇测试技术有限公司（Beijing Kehui Testing Technology Co., Ltd.）完成。本次分析所用仪器为AnalyticJena PQMS型电感耦合等离子体质谱仪（Inductively Coupled Plasma Mass Spectrometry，ICP-MS），配套RESOlution 193nm准分子激光剥蚀系统。激光剥蚀的束斑直径为24 μm，激光频率为6 Hz，能量密度约为5 J/cm²，以氦气（He）作为载气。LA-ICP-MS激光剥蚀采样采用单点剥蚀方式。测试前，采用锆石标准物质GJ-1对仪器进行调试，使其达到最佳工作状态。本次锆石U-Pb定年以GJ-1作为外标进行校正，微量元素含量则以NIST 610为外标、硅（Si）作为内标进行定量计算。测试过程中，每间隔10个样品前后均重复测定2次锆石标准物质GJ-1以完成样品校正，并同步测定1次锆石标准物质Plesovice，以此监控仪器运行状态，确保测试准确性。数据处理采用LADR_1.1.07软件（Norris等，2018）完成。锆石年龄谐和图采用Isoplot 4.15软件绘制。详细的实验测试流程可参考侯可俊等（2009）的研究。样品分析过程中，作为未知样品测定的Plesovice标准物质的分析结果为336.6±1.2 Ma（n=24，2σ），其推荐年龄值为337.13±0.37 Ma（2σ）（Slama等，2008），二者在误差范围内完全一致。