摘要
碳酸盐矿物的同位素年代学研究具有广阔的应用前景,但理想样品少、定年难度大(尤其是低铀样品)等因素限制了该方法的发展.本研究利用激光剥蚀多接收电感耦合等离子体质谱技术(LA-MC-ICPMS),建立了针对低铀碳酸盐矿物的微区原位U-Pb同位素定年方法.通过LA-ICPMS预扫描,可以快速筛选出适合定年的样品和最佳剥蚀点,再借助为实现低铀含量的精确测量而对接收器配置优化设计的Nu Plasma Ⅱ MC-ICPMS进行碳酸盐矿物的U-Pb年龄测定.此外,通过两种已报道的碳酸盐矿物标样ASH15和WC-1,标定出一种更加均一且适用对象更广的实验室内部标样AHX-1a,其与国际标样长期对比测量获得的年龄加权平均值为209.8±1.3Ma(2S总,n=21,MSWD=2.7).此年龄结果是在半年内不同时期对样品靶不同部位21次独立标定的年龄结果的加权平均值,每一次对测约有50~150组数据点,总共2000多组数据点.与此同时,为了继续寻找其他理想碳酸盐矿物标样,更进一步的同位素稀释法标定工作还有待开展.
The in-situ U-Pb isotopic geochronology of carbonate minerals has some broad application prospects, not only for the recording of paleoclimate, paleoenvironment, paleoecology, ancient human caverns, calcium plate and marine coral, but also in carbonate vein dating associated with fault activity, neotectonics, paleoearthquake and hydrocarbon reservoirs. However, the development of this method is limited by many factors, such as, very few samples satisfying essential dating conditions, low-uranium carbonates having ultra-low concentrations;and lack of ideal mineral standards. Currently, this technology is still in development in both China and Australia, with only four laboratories in the world having reported results which are mostly for high-uranium(>0.1 ppm) carbonate samples. In this study, Nu Plasma Ⅱ multi-collector inductively coupled plasma mass spectrometry(MC-ICPMS) with ASI RESOlution SE laser ablation system(LA) is used to refine an in-situ U-Pb isotopic dating method for low-uranium carbonate minerals. Here, NIST614 international glass standard is used for 207Pb/206Pb isotopic fractionation calibration, and carbonate mineral standard is used for 238U/206Pb element fractionation calibration. The age of the lower intersection obtained by using the Tera-Wassenburg(TW) 238U/206Pb-207Pb/206Pb diagram represents the U-Pb age of the carbonate mineral. The improvements made in this study are mainly completed on the following aspects. Firstly, pre-screening with LA-ICP-MS allows for rapid selection of suitable samples, which have large variations in 238U/206Pb and 207Pb/206Pb to construct a good TW reverse isochron or their common Pb is so low that measuring points can fall near the concordant line. Secondly, 1012? preamplifier at the highest quality end of the Nu Plasma Ⅱ MC-ICPMS(10 times more sensitive than a versatile 1011? preamplifier) and an ETP(electron multiplier) discrete dynode multiplier dedicated to static measurement of 238 U isotope were installed. The high sensitivity Faraday cup measurement
作者
程婷
Jianxin Zhao
Yuexing Feng
潘文庆
刘敦一
Ting Cheng;Jianxin Zhao;Yuexing Feng;Wenqing Pan;Dunyi Liu(Beijing SHRIMP Center,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;Radiogenic Isotope Facility,School of Earth and Environmental Sciences,the University of Queensland,Brisbane,Qld 4072,Australia;PetroChina Tarim Oilfield Company,Korla 841000,China)
出处
《科学通报》
EI
CAS
CSCD
北大核心
2020年第2期150-154,共5页
Chinese Science Bulletin
基金
国家自然科学基金(41703058)
中国地质科学院高级访问学者创新研究项目(A1403)
澳大利亚昆士兰大学MRFF项目(RM2016000555)
国家科技重大专项(2016zx05004-004)资助。
