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常规的K-Ar法是基于~(40)K通过K-层电子捕获衰变成~(40)Ar~*这一机理,应用衰变定律而定年的。它具有测定对象广、测定年龄范围大等优点,是同位素地质定年的主要方法之一。但是,由于~(40)Ar~*是气体,当岩石、矿物形成以后受到搅动时(如岩浆的侵入、构造活动、宇宙物质的冲击等),~(40)Ar~*容易丢失,使年龄值偏低。1962年由Sigurgeirsson提出的,后经Merrihue、Turner等人逐步完善的~(40)Ar-~(39)Ar快中子活化定年技术,很好地克服了K-Ar法的局限性。~(40)Ar-~(39)Ar定年分为两种:一是全熔融法(total fusion),样品被快中子照射后一次加热熔融,然后计算年龄,此值与常规K-Ar法结果相当;另一种是阶段加热法(step-heating),被照射的样品从低温到高温被逐步加热,分别计算各温度阶段的~(40)Ar/~(39)Ar视年龄,并进而得到一条年龄谱和一个坪年龄(plateau age)。后一种方法对研
The conventional K-Ar method is based on the mechanism that ~ (40) K is decayed into ~ (40) Ar ~ * by K-layer electron capture using the decay law. It has the determination of a wide range of objects, the determination of a large range of ages, is one of the main methods of isotope geology dating. However, since ~ (40) Ar ~ * is a gas, ~ (40) Ar ~ * is easily lost when rocks and minerals are agitated (such as magma intrusion, tectonic activity, cosmic impact, etc.) Low value. The technique of ~ (40) Ar- ~ (39) Ar fast neutron activation dating by Sigurgeirsson in 1962 and later perfected by Merrihue and Turner et al. Overcomes the limitations of the K-Ar method well. ~ (40) Ar- ~ (39) Ar dating is divided into two types: one is the total fusion method, the sample is heated and melted by fast neutron irradiation, then the age is calculated, which is in agreement with the conventional K- The results were comparable. The other was step-heating. The irradiated samples were gradually heated from low temperature to high temperature. The age of ~ (40) Ar / ~ (39) Ar was calculated for each temperature and then Get an age spectrum and a plateau age. The latter method of research