| 基于多接收稀有气体质谱Argus Ⅵ的激光40Ar-39Ar测年方法及其地质应用 |
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| 引用本文： | 周波,董云鹏,杨钊,GenserJohann,柳小明.基于多接收稀有气体质谱Argus Ⅵ的激光40Ar-39Ar测年方法及其地质应用[J].地球科学,2020,45(3):804-814. |
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| 作者姓名： | 周波 董云鹏 杨钊 GenserJohann 柳小明 |
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| 作者单位： | 1.西北大学大陆动力学国家重点实验室, 陕西西安 710069 |
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| 基金项目： | 中国地质调查局项目DD20160012国家自然科学“创新群体”项目41421002 |
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| 摘 要： | 单接收稀有气体质谱仪由于效率、测试精度相对较低，制约了高精度40Ar-39Ar测年的进一步发展.近年来，新一代多接收稀有气体质谱仪在高精度40Ar-39Ar测年中显示出巨大的优势和潜力，并得到了日益广泛的应用.简要介绍了基于多接收稀有气体质谱仪Argus Ⅵ的激光全熔/阶段加热40Ar-39Ar测年实验技术，并对空气氩同位素、标准样品FCs和YBCs以及东昆仑开木其花岗岩体钾长石样品开展了测试研究.结果显示，连续4个月326次循环测试得到的空气氩同位素比值及对应的质量歧视因子（MDF）十分一致，显示了仪器系统良好的稳定性；FCs与YBCs单颗粒全熔“模式年龄”结果表明，仪器在单颗粒、微量样品测试中具有良好的测试精度，“模式年龄”精度可以达到1‰以下（不含衰变常数及标准样品年龄误差）；FCs的单颗粒全熔测试获得的J值及F值（40Ar*/39ArK）与萨尔茨堡大学ARGONAUT实验室结果具有相同的变化趋势，均反映了捷克LVR-15反应堆中子通量的梯度变化；对YBCs单颗粒全熔测试获得YBCs与FCs之间的内部校正系数RFCsYBCs=1.045 304±0.000 752（1σ），YBCs单颗粒全熔年龄为29.280±0.086（1σ），与前人结果在误差范围内一致.对东昆仑开木其花岗岩钾长石激光阶段加热测试，得到其坪年龄为229.9±0.2 Ma（1σ，MSWD=1.59），反等时线年龄为229.8±0.4 Ma（1σ，MSWD=1.71）.综合区域内已有锆石U-Pb年代学及黑云母、钾长石40Ar-39Ar年代学研究成果，认为开木其岩体钾长石40Ar-39Ar年龄反映了东昆仑晚三叠世的一次快速冷却-剥露过程.
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| 关 键 词： | Argus Ⅵ质谱仪 YBCs FCs 40Ar-39Ar测年 东昆仑 地质年代学 |
| 收稿时间： | 2019-01-04 |
Laser Fusion 40Ar-39Ar Dating Method Using Multi-Collector Noble Gas Mass Spectrometer Argus Ⅵ and Its Geological Application |
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| Abstract: | The single-collector noble gas mass spectrometer has constrained the further development of the high-precision 40Ar-39Ar dating, owing to its relatively low efficiency and precision of measurement. However, the multi-collector noble gas mass spectrometer has been increasingly widely applied in the high-precision 40Ar-39Ar dating in recent years, showing great advantage and potentiality. The method of 40Ar-39Ar dating by laser total fusion/stepwise heating using the multi-collector noble gas mass spectrometer Argus Ⅵ is reported briefly, and the measurements of air, standard mineral FCs and YBCs, and the K-feldspar from the Kaimuqi granitic pluton in the East Kunlun were performed. Concordant atmospheric 40Ar/36Ar ratio and the corresponding mass discrimination factor (MDF) were obtained from 326 air argon analyses during four successive months, indicative of the stability of the machine system. The "model ages" calculated from the laser fusion 40Ar-39Ar results of FCs and YBCs suggest that, the level of precision achievable using the Argus Ⅵ for single-grain or minor sample analysis is significantly high and is better than 1‰ (excluding the errors associated with the age of monitors and decay constants). J value and F value (40Ar*/39ArK) calculated from the total fusion results of the FCs show similar trend with those from ARGONAUT lab at the University of Salzburg, both suggesting a distinct gradient of the neutron flux of the LVR-15 reactor. The intercalibration factor between YBCs and FCs based on our total fusion analysis of YCs are calculated as: RFCsYBCs=1.045 304±0.000 752 (1σ), and the single-grain total fusion age of 29.280±0.086 (1σ) for YBCs is obtained as well. The results are in good agreement with those of previous studies within the range of uncertainty. Stepwise heating analyses of the K-feldspar from the Kaimuqi granitic pluton in the East Kunlun yield a plateau age of 229.9±0.2 Ma (1σ, MSWD=1.59), and an inverse isochron age of 229.8±0.4 Ma, MSWD=1.71). In combination with published geochronology data of zircon U-Pb, and biotite and K-feldspar 40Ar-39Ar in this area, it is suggested that the 40Ar-39Ar age of the K-feldspar from the Kaimuqi granitic pluton represents a rapid cooling-exhumation event in the East Kunlun during Late Triassic. |
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