MC-ICP-MS测定铀系定年标样的~(230)Th年龄

本研究利用Neptune Plus型多接收电感耦合等离子体质谱仪(MC-ICP-MS)测定了U和Th标准溶液的同位素比值及U系定年标样的~(230)Th年龄。结果显示:CRM 112A和Harwell Uraninite-1(HU-1)的234 U/238 U原子比值分别为(52.860±0.042)×10~(-6)(δ234 U=(-38.36±0.77)‰,n=17)和(54.911±0.007)×10-6(δ234 U=(-1.04±0.13)‰,n=27),实验数据在2σ不确定范围内与国际同类实验室一致;NBS Th标准,0.6pg ~(230)Th测试精度优于3‰;5个碳酸盐标准样品76001、GBW04412、RKM-6、RKM-5和RKM-4的230 Th年龄分别为(47 520±220)y、(86 880±340)y、(130 830±550)y、(129 380±480)y和(197 970±1 590)y,与美国明尼苏达大学、西安交通大学同类实验室测定的数据具有良好的重复性。上述数据表明,本实验建立的MC-ICP-MS法230 Th定年技术可应用于中晚更新世以来碳酸盐的U-Th定年与示踪研究。

Determination of 230Th Dating Age of Uranium-Series Standard Samples by Multiple Collector Inductively Coupled Plasma Mass Spectrometry

Five Quaternary standard samples were dated, and isotope ratios of U and Th contained in standard solutions were measured by Neptune Plus multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The results show that the ²³⁴U/²³⁸U atomic ratios of CRM 112A and Harwell Uraninite-1 (HU-1) are (52.860±0.042)×10^-6 (δ ²³⁴U=(-38.36±0.77)‰, n=17) and (54.911±0.007)×10^-6 (δ ²³⁴U=(-1.04±0.13)‰, n=27), respectively, which are in excellent agreement with the data previously reported by other laboratories within 2σ error; samples of 0.6 pg ²³⁰Th (NBS Th standard) give the precisions less than 3‰; the ages of five carbonate standards are (47520±220) y, (86880±340) y, (130 830±550) y, (129 380±480) y and (197970±1590) y for 76001, GBW04412, RKM-6, RKM-5 and RKM-4, respectively. These data are in accordance with the replicates measurements in the laboratories of Minnesota University and Xi’an Jiaotong University within uncertainties. All errors herein quote at the 2σ level, and all samples above are performed in the Uranium-series chronology laboratory of Institute of Geology and Geophysics, Chinese Academy of Sciences. This approach can be applied to dating various materials since late-middle Pleistocene, materials, such as speleothems, corals, deep-sea sulfides and so on.