LA-ICP-MS榍石U-Pb定年方法  

In situ U-Pb Dating of Titanite by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry

作　　者：崔玉荣 涂家润 李国占[1,2] 周红英 耿建珍[1,2] CUI Yu-rong;TU Jia-run;LI Guo-zhan;ZHOU Hong-ying;GENG Jian-zhen(Tianjin Center,China Geological Survey,Tianjin 300170,China;North China Center for Geoscience Innovation,Tianjin 300170,China)

机构地区：[1]中国地质调查局天津地质调查中心,天津300170 [2]华北科技创新中心,天津300170

出　　处：《华北地质》2022年第4期53-59,共7页North China Geology

基　　金：国家自然科学基金面上项目“铌铁矿微区原位U-Pb同位素定年标准物质的研制(41873066)”;“高钍低铀矿物高精确度同位素稀释-热电离质谱钍-铅年代学研究(42073055)”;国家自然科学基金青年基金项目“高铀矿物飞秒激光剥蚀-同位素稀释热电离质谱U-Pb定年研究(42103025)”。

摘　　要：榍石富含U、Th,贫Pb,是U-Pb定年较为理想的矿物。由于具有相对较高的U-Pb体系封闭温度,并普遍存在于多种岩石中,榍石U-Pb定年具有广阔的应用前景。利用193 nm准分子激光剥蚀系统(LA)与Agilent7900四级杆等离子体质谱仪(Q-ICP-MS)联用,对榍石标准物质MKED1、OLT1进行U-Pb年龄测定。系统对榍石LA-ICP-MS U-Pb定年中所涉及束斑直径、激光频率和能量密度等参数进行了优化,结果表明,利用LA-ICP-MS对榍石进行U-Pb定年时,束斑直径对年龄结果影响较低(~1%),激光频率和能量密度对年龄结果的影响低于3%。故在榍石LA-ICP-MS U-Pb定年过程中,选取的激光剥蚀测试条件为43μm、8 Hz、3 J/cm^(2)或51μm、8 Hz、3 J/cm^(2);进而建立了榍石LA-ICP-MS U-Pb定年技术,并成功应用于牟乳成矿带腊子沟金矿,验证了牟乳成矿带腊子沟金矿二长花岗岩的时代为晚侏罗纪。本研究结果进一步拓宽了榍石U-Pb定年方法适用性及优化潜力。Characterized by rich U,Th and low initial Pb content,titanite is an ideal object for U-Pb dating.For the relative high U-Pb system closure temperature and ubiquity in various rocks,titanite has enormous promise in U-Pb dating application.In this paper,combined use of 193nm excimer laser ablation system and Agilent7900quadrupole inductively coupled plasma mass spectrometer(Q-ICP-MS)was applied for dating of titanite standard samples including MKED1、OLT1.Through systematically optimizing the parameters of beam spot diameter,laser frequency and energy density involved in the dating of titanite,the results show that LA-ICP-MS U-Pb dating of titanite was insensitive to beam spot diameter(~1%),laser frequency and energy density(<3%).Therefore,in LA-ICP-MS U-Pb dating of titanite,the best laser ablation conditions are 43μm,8 Hz,3 J/cm^(2)or 51μm,8 Hz,3J/cm^(2).Furthermore,the LA-ICP-MS U-Pb dating technique of titanite was established and successfully applied to the Lazigou gold deposit in the Mouru metallogenic belt,verifying its age of late Jurassic.This research has shown the potentials of titanite U-Pb dating and further expanded the application of the method.

关 键 词：激光剥蚀-电感耦合等离子体质谱 榍石 U-PB测年 激光剥蚀参数 副矿物 

分 类 号：P597.3[天文地球—地球化学]