基于LA-ICP-MS的磷灰石中铀、钍元素分布及其在（U-Th）/He定年中的影响研究

The(U-Th)/He chronology method isbased on the reaction that U and Thdecay and create 4He. The single particle methodis mainly used for the determination of U, Th and He, which is based on the presupposition that U and Th was homogenously distributed in rocks. However, in most mineral rocks that are suitable for (U-Th)/He dating, U and Th are heterogeneously distributed, bringing 30% relative error to the dating result. LA-ICP-MS technique is widely applied in the research of U, Th distribution because of its in suit and microcell analysis character.But the reference material for quantification used in LA-ICP-MS is not matrix-matched and will bring matrix effect that decreases the accuracy, which puts forward demands for the development of matrix matched reference material. Besides, the research of U, Thdistribution in domestic apatite is limited, and the data abroad may not be applicable on domestic apatite sample in spite of its abundance. Thus, this program is anticipated to fabricate matrix-matched reference materialfor LA-ICP-MS analysis to increase its accuracy, and to explore thecharacteristic and rule of U, Th distribution of various domestic apatite sample, as well as to explorethe influence of U, Th distribution on (U-Th)/Hedating through comparison with U-Pb dating.

利用U、Th衰变生成4He发展出的(U-Th)/He定年法，常用单颗粒法检测U、Th和He的含量进行定年，其基本前提是岩石中U、Th分布均匀。而大多数适于(U-Th)/He定年的天然矿物，其内U、Th分布都是不均匀的，导致定年结果相对误差达30%左右。LA-ICP-MS技术由于具有原位、微区等特点，在磷灰石中U、Th分布研究中获得广泛应用。但是LA-ICP-MS检测中常用的标准物质，都存在基体不匹配的问题，进而影响检测准确性，这就对基体匹配的标准物质的开发提出了需求。此外，国内对磷灰石中U、Th分布研究较少，国外研究数据丰富，但不一定适用于国内样品。因此本项目拟制备基体匹配的LA-ICP-MS标准物质，提高检测准确性，在此基础上对国内不同来源、不同类型磷灰石中U、Th分布特点、规律进行研究，并通过与U-Pb等定年法比对，探究其对(U-Th)/He定年准确度的影响。

LA-ICP-MS技术由于具有原位、微区等特点，在磷灰石中U、Th分布研究中获得广泛应用。但是LA-ICP-MS检测中常用的标准物质，都存在基体不匹配的问题，进而影响检测准确性，这就对基体匹配的标准物质的开发提出了需求。本文通过将磷灰石样品粉末和岩石成分分析标准物质粉末进行压片，获得了与磷灰石样品基体匹配的标准物质，并对其元素含量及分布均匀性进行表征，结果表明制作的标样分布均匀。同时，建立了He同位素丰度比和浓度的测量方法、U-Th元素分离和测量方法。并使用LA-ICP-MS对采集的磷灰石样品截面U、Th、Pb等元素分布进行测量和分析，并揭示了各元素含量的相关性。本工作为岩石LA-ICP-MS测量中基体匹配的标准物质制作方法提出了可行思路，并对岩石（U-Th）/He定年的准确性提供了测量方法上的支持。