摘要：
锆石原位微区U-Pb定年和微量元素分析已成为当前地球科学领域常规的分析手段。然而,锆石微区分析结果的解译受到分析点选取、仪器稳定性和采集信号校正等诸多因素的影响,定量揭示这些因素如何影响锆石微区分析结果是准确探讨该结果地质意义的重要前提。本文以来自青海野马泉铁多金属矿床晚三叠世二长花岗斑岩岩体中的锆石为研究对象,开展了LA-ICP-MS锆石原位U-Pb定年和微量元素分析,以探究副矿物包裹体和信号采集时间对锆石微区分析结果产生的影响。研究结果显示,尽管信号采集时间较短时会得到较大的U-Pb定年误差,但它的改变并不会对U-Pb年龄和微量元素分析结果产生明显影响。对比含矿物包裹体和不含矿物包裹体的分析点可知,矿物包裹体的存在同样不会对定年结果产生明显干扰。然而,若选择的锆石分析位置含有磷灰石等副矿物包裹体,得到的分析数据会具有“轻稀土富集”的假象,从而造成诸多误判,如推断出错误的岩浆氧逸度特征等。因此,锆石微区分析前必须首先查明所分析的位置是否存在副矿物包裹体,而在探讨锆石微量元素数据的地质意义前必须将受到矿物包裹体混染的锆石数据予以剔除。
关键词:
LA-ICP-MS,
锆石,
U-Pb定年,
副矿物包裹体,
信号采集时间
Abstract:
In-situ zircon micro-area U-Pb dating and trace element analysis have become routine techniques in Earth sciences. However, the interpretation of zircon micro-area analysis results is influenced by various factors, including the selection of analysis points, instrument stability, and signal correction. Quantitatively understanding how these factors affect zircon micro-area analysis results is a critical prerequisite for accurately interpreting the geological significance of such data. This study focuses on zircons from the Late Triassic monzogranite porphyry intrusion in the Yemaquan iron-polymetallic deposit in Qinghai Province. LA-ICP-MS zircon in-situ U-Pb dating and trace element analysis were performed to evaluate the effects of accessory mineral inclusions and signal acquisition time on zircon micro-area analysis results. The findings indicate that although shorter signal acquisition times lead to larger errors in U-Pb dating, they do not significantly affect U-Pb ages or trace element analysis results. A comparison of analysis points with and without mineral inclusions shows that the presence of mineral inclusions also does not significantly interfere with dating results. However, if the selected zircon analysis location contains accessory mineral inclusions (e.g., apatite), the resulting data may display a false “light rare earth element enrichment” signature. This can lead to misinterpretations, such as incorrectly inferring magmatic oxygen fugacity characteristics. Therefore, it is crucial to first identify whether accessory mineral inclusions are present at the analysis location before conducting zircon micro-area analysis. Additionally, zircon data contaminated by mineral inclusions must be excluded prior to interpreting the geological significance of zircon trace element data.
Key words:
LA-ICP-MS,
zircon,
U-Pb dating,
accessory mineral inclusions,
signal acquisition time
中图分类号:
P595
P597.3
引用本文
黄宇, 钟世华, 李三忠, 赵鸿, 薛梓萌, 郭广慧, 刘嘉情, 牛警徽. 副矿物包裹体和信号采集时间对锆石U-Pb年龄和微量元素分析结果的影响[J]. 地学前缘, 2025, 32(1): 388-400.
HUANG Yu, ZHONG Shihua, LI Sanzhong, ZHAO Hong, XUE Zimeng, GUO Guanghui, LIU Jiaqing, NIU Jinghui. Effects of accessory mineral inclusions and signal acquisition time on zircon U-Pb dating and trace element analysis results[J]. Earth Science Frontiers, 2025, 32(1): 388-400.
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链接本文:
https://www.earthsciencefrontiers.net.cn/CN/10.13745/j.esf.sf.2024.2.23
https://www.earthsciencefrontiers.net.cn/CN/Y2025/V32/I1/388