Abstract: (U-Th)/He isotopic dating has been developed very quickly in recent years, due to the recognition that the thermal history of rock at low temperature can be effective revealed by such dating method. In particular, He closure temperature in apatite (40~80℃) is very low, so apatite (U-Th)/He ages can reflect the thermal history information of the low-temperature stage, and have a good application prospect in the field of low-temperature thermal chronology. However, because of many influence factors and complicated measurement procedures, the development of apatite He dating in China remains in its early stage. In this study, a measurement procedure was established at the (U-Th)/He dating laboratory of Institute of Geology, China Earthquake Administration. We measured the daughter isotopic helium by diode laser heating four batches of a total seventy-five grains of Durango apatite in an Alphachron helium mass spectrometry system. Then the apatite grains were dissolved to precisely measure the concentration of parent nuclides (U, Th)using the solution isotope dilution method through an automatic sampling ICP-MS (Agilent 7900). Results show that the Th/U values of Durango apatite grains were in the range of 17.23 to 23.60, while all the 75ages were in the range of 28.61 to 34.51Ma with an average of (31.71±1.55)Ma (1σ), which are consistent with the international calibrated ages.

Key words: (U-Th)/He dating, laser heating, isotope dilution method, Durango apatite

摘要： （U-Th）/He同位素定年是近几十年快速发展起来的1种能够对岩石低温冷却历史进行有效研究的新型放射性同位素定年方法。由于磷灰石的He封闭温度较低，所以它能反映低温阶段（40～80℃）的热历史信息，在低温热年代学领域具有很好的应用前景。但是，由于磷灰石（U-Th）/He测年的影响因素多且测试流程复杂，目前国内对于（U-Th）/He同位素定年方法和流程的研究还处于起步阶段。依托中国地震局地质研究所新建立的（U-Th）/He同位素年代学实验室，利用配备的Alphachron He同位素质谱仪对4批共75个国际标样Durango磷灰石单颗粒进行激光熔融和⁴ He的含量测量，随后应用自动进样安捷伦7900 ICP-MS和同位素稀释剂法测定母体同位素U、Th的含量，最后计算得到Durango磷灰石的Th/U同位素比值在17.23～23.60之间，全部年龄分布在28.61～34.51Ma，平均年龄为（31.71±1.55）Ma（1σ），与国际标定年龄在误差范围内一致。

关键词: (U-Th)/He定年, 激光熔融法, 同位素稀释剂法, Durango磷灰石