摘要
碳酸盐矿物特别是方解石分布广泛,作为原生和次生矿物在多种地质环境中形成,结合U-Pb同位素测年体系,能为地球科学应用提供直接的时间约束,具有广阔的应用前景。但方解石矿物的铀含量通常较低(小于5μg/g),测年难度大,限制了该方法的发展。激光剥蚀多接收电感耦合等离子体质谱仪(LA-MCICP-MS)具有高灵敏度和高精度的特点,已成功应用于锆石、方解石等副矿物的高空间分辨率U-Pb测年。本文针对LA-MC-ICP-MS的载气和氮气流速、屏蔽炬状态等实验参数进行了详细优化,建立了适用于低铀方解石矿物的高空间分辨率U-Pb测年方法。为提升仪器灵敏度和等离子体状态,详细讨论了锥组合、屏蔽炬接地状态、N_(2)引入量和Ar载气流速对U、Pb信号强度及氧化物产率(UO/U)的影响。结果表明,在Jet+X锥组合、屏蔽炬接地、8mL/min N_(2)引入量和0.9L/min载气Ar流速条件下,Pb灵敏度达到最高,同时氧化物产率(UO/U)低于1%。为验证该方法的准确性,采用三个低铀(0.04~0.63μg/g)方解石U-Pb定年参考物质进行测试,使用高铀含量的WC-1标准物质作为校正^(238)U/^(206)Pb的外标,同时减小束斑大小和剥蚀频率,保持标准物质和待测样品的剥蚀坑纵横比一致。实验结果表明,在44μm束斑条件下,LD-5、PTKD-2和TARIM的U-Pb年龄测试值分别为73.20±0.56Ma、152.7±2.5Ma和206.2±1.3Ma,与ID-TIMS/IDMC-ICP-MS的定值结果在误差范围内一致,验证了LA-MC-ICP-MS高空间分辨率测定低铀方解石U-Pb年龄的可靠性。
The combination of carbonate minerals with the U-Pb isotope dating system provides direct temporal constraints for geoscientific applications.LA-MC-ICP-MS with its high sensitivity and accuracy,has been successfully applied to the high spatial resolution U-Pb dating of zircon,calcite and other minerals.The experimental parameters of LA-MC-ICP-MS were optimized in detail,and a high spatial resolution U-Pb dating method was established for low-uranium calcite minerals.The effects of cone combination,GE mode,N_(2)introduction and Ar carrier gas flow rate on the U and Pb signal intensity and oxide yield(UO/U)were discussed in detail.The results showed that the highest sensitivity of Pb was achieved under the conditions of Jet+X cone combination,guard electrode(GE)grounded state,8mL/min N_(2)introduction and 0.9L/min Ar carrier gas flow rate,while the oxide yield(UO/U)was lower than 1%.Three low uranium(0.04−0.63μg/g),calcite U-Pb dating reference materials were used to validate the reliability of the method.Samples LD-5,PTKD-2 and TARIM yielded a lower intercept age of 73.20±0.56Ma,152.7±2.5Ma and 206.2±1.3Ma,respectively,under the condition of 44μm beam spot,which were in agreement with the calibrated results of ID-TIMS/ID-MC-ICP-MS within the error range.
作者
张晨西
熊玉新
付佳丽
赵伟
舒磊
李增胜
徐珺
周长祥
洪飞
ZHANG Chenxi;XIONG Yuxin;FU Jiali;ZHAO Wei;SHU Lei;LI Zengsheng;XU Jun;ZHOU Changxiang;HONG Fei(Key Laboratory of Gold Mineralization Processes and Resource Utilization,Ministry of Natural Resources,Shandong Provincial Key Laboratory of Metallogenic Geological Process and Resource Utilization,Shandong Institute of Geological Sciences,Jinan 250013,China;National Key Laboratory of Uranium Resource Exploration-Mining and Nuclear Remote Sensing,East China University of Technology,Nanchang 330013,China)
出处
《岩矿测试》
北大核心
2025年第3期369-383,共15页
Rock and Mineral Analysis
基金
山东省自然科学基金项目(ZR2022QD050)
自然资源部金矿成矿过程与资源利用重点实验室和山东省金属矿产成矿地质过程与资源利用重点实验室开放课题(Kfkt202118)
江西省自然科学基金项目(20232BAB213070)
国家自然科学基金项目(42203034)。
