第四纪洞穴次生碳酸盐激光及同位素稀释剂法U-Pb定年  

U-Pb DATING OF QUATERNARY SPELEOTHEMS USING LA & ID MC-ICPMS

作　　者：王健[1] 牛晓雯 康乐 张海伟 张普 宁有丰[1] 贾雪雪 梁峰 蔡演军[1] 储著银[4] 郭敬辉[4] 程海[1] WANG Jian;NIU Xiaowen;KANG Le;ZHANG Haiwei;ZHANG Pu;NING Youfeng;JIA Xuexue;LIANG Feng;CAI Yanjun;CHU Zhuyin;GUO Jinghui;CHENG Hai(Institute of Global Environmental Change,Xi'an Jiaotong University,Xi'an 712000,Shaanxi;Key Laboratory of Carbonate Reservoirs,China National Petroleum Corporation(CNPC),Hangzhou 310023,Zhejiang;PetroChina Hangzhou Research Institute of Geology(HIPG),Hangzhou 310023,Zhejiang;State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029)

机构地区：[1]西安交通大学全球环境变化研究院,陕西西安712000 [2]中国石油天然气集团有限公司碳酸盐岩储层重点实验室,浙江杭州310023 [3]中国石油杭州地质研究院,浙江杭州310023 [4]中国科学院地质与地球物理研究所,岩石圈演化国家重点实验室,北京100029

出　　处：《第四纪研究》2022年第5期1410-1419,共10页Quaternary Sciences

基　　金：国家自然科学基金项目(批准号:41888101和41973006)资助。

摘　　要：碳酸盐U-Pb年代学具有广阔的应用价值与潜力。近些年同位素稀释剂法和激光原位法碳酸盐U-Pb定年迅速发展,但国内尚未报道利用激光原位法测试的第四纪以来碳酸盐U-Pb年代,碳酸盐U-Pb定年的同位素稀释剂法也亟待开发,在此背景下西安交通大学同位素实验室针对第四纪洞穴次生碳酸盐开展了激光和稀释剂法(LA&ID MC-ICPMS)U-Pb定年方法研究。本研究利用激光法对不同碳酸盐标样进行了测试,获得的U-Pb年代结果与标准值在误差范围内一致;首次报道了三宝洞第四纪洞穴次生碳酸盐的高精度激光U-Pb定年结果,与国外实验室稀释法所得年代可相互印证;讨论了第四纪碳酸盐U-Pb定年初始U系非平衡分馏校正的有关问题,强调了稀释剂法对于δ^(234)U和Pb同位素高精度测试的重要价值;稀释剂法方面,本实验室全流程Pb本底目前能够达到世界一流水平(约10 pg);对于第四纪洞穴次生碳酸盐的初步测试结果(1.14±0.04 Ma, 2σ, n=5, MSWD=1)与国外稀释剂法及本实验室激光法在误差范围内一致,更进一步完善有望提高年代精度。本实验室建立了可靠的较高精度激光法和初步的稀释剂碳酸盐U-Pb定年方法,除了较老的碳酸盐样品以外,还能够对老于64万年的第四纪洞穴次生碳酸盐进行较高精度U-Pb年代学测试,对于早第四纪以来的众多科学问题的进一步研究具有重要意义。Carbonate U-Pb dating techniques have broad applications. Recently,the U-Pb isotope diluent( ID) and laser ablation( LA) dating of carbonate developed rapidly. Yet the U-Pb LA dating technique has not been used to obtain ages of carbonate formed in the Quaternary,and the U-Pb ID technique for dating carbonate remains unavailable in China. In this context,the U-Pb LA & ID MC-ICPMS dating tourniquets have been developed in the Isotope Laboratory of Xi’an Jiaotong University and applied to establish chronology for a set of speleothems across the Quaternary. We have tested different carbonate reference materials using our LA MC-ICPMS method,and the age results are consistent within the quoted uncertainties. Here,we report the first set of high-precision LA U-Pb ages of Quaternary speleothem samples from Sanbao cave, Central China. We discussed the U-series initial disequilibrium corrections which is critical to the Quaternary carbonate samples and then highlighted the importance of the ID methods for high-precision measurements of both δ^(234)U and Pb isotopes. Regarding the U-Pb ID method,the total Pb blank in our lab is now comparable to the world-class level( ca.10 pg). Our preliminary ID ages( e.g.,1. 14 ± 0. 04 Ma,2σ,n = 5,MSWD = 1) obtained from Quaternary speleothem samples are in agreement with the previous results from the U-Pb lab of Melbourne University,Australia. The age precisions maybe potentially improved substantially. In short,we have developed high-precision LA and ID U-Pb dating techniques in our lab,which are applicable to date carbonate samples formed in time period older than ca. 640 ka. This will effectively propel our scientific researches further back to the deep-time beyond the U-Th dating range.

关 键 词：碳酸盐U-Pb定年 LA&ID MC-ICPMS 第四纪洞穴次生碳酸盐 δ^(234)U非平衡校正 

分 类 号：P543.63[天文地球—构造地质学] P597.3[天文地球—地质学]