全自动^40Ar/^39Ar激光探针定年系统空白本底与微量样品定年  

System Blank Level and Small Sample Dating in the All-Automatic ^40Ar/^39Ar Laser Probe Dating System

作　　者：高洪林[1] 

机构地区：[1]北京大学地球与空间科学学院“造山带与地壳演化”教育部重点实验室,北京100871

出　　处：《地球学报》2005年第B09期39-43,共5页Acta Geoscientica Sinica

摘　　要：氩-氩定年法中系统的空白本底是实现微区微量定年的关键条件。在北京大学“造山带与地壳演化教育部重点实验室全自动^40Ar／^39Ar激光探针定年系统”上以ZBH-25黑云母标样为试验样品进行了1个颗粒、3个颗粒和5个颗粒的全熔法定年以及7个颗粒的4步、9步、14步、19步和24步的分步释氩年龄谱测试。获得的5个氩同位素空白本底水平表明，本系统已经完全具备对中生代或更老的地质样品进行单颗粒全熔法等时线定年的能力。矿物或岩石光片原位全熔法定年的空白本底条件也已经具备。在适当增加样品量情况下（如10个颗粒），几个百万年的年轻样品全熔等时线定年也可以实现。去除干扰分子对^36Ar空白本底的影响，以及系统长期稳定运行后^36Ar空白本底的逐渐降低，实现微量样品的分步释氩年龄谱定年是必然的。The level of system blank is always the key point in ^40Ar/^39Ar dating of small samples and small area dating. Laboratory standard ZBH-25 biotite was dated on the all-automatic ^40Ar/^39Ar laser probe dating system in Key Laboratory of Orogenic Belts and Crustal Evolution （Peking University）, Ministry of Education. Total fuse of one, three and five small biotite gains by focused laser and step-heating with four, nine, fourteen, nineteen and twenty-four argon-release steps of seven grains by defocused laser were experimentally carried out. Signal intensity and system blank of five argon isotopes obtained indicate that the system blank level adopted by the authors is low enough to get a reasonable isochron age for single mineral grains from Mesozoic or older samples. The system blank level is also suitable for focused laser in-situ dating. Young samples of several million years old can be total-fuse dated if the number of grains is properly increased （for example, the number is 10 mineral grains）. The molecule of C3, a common interference to ^36At, can be eliminated after long time of operation. Under these conditions, the system is likely to be successful in step-heating dating of the single mineral grain.

关 键 词：北京大学 ^40Ar/^39Ar激光探针定年系统 空白本底 微量样品定年 ^40AR/^39AR 本底条件 微量样品 定年法 激光探针 全自动 

分 类 号：P318.44[天文地球—固体地球物理学] P426.616[天文地球—地球物理学]