Sm－Nd等时线年龄合理性的判别

JUDGEMENT ON THE RATIONALITY OF A Sm-Nd ISOCHRON

所有等时线年龄均要求样品具有相同或相近的同位素初始比值。为同源岩套的产物及岩石形成后分子体系统处于封闭状态。如果不能符合上述基本要求，则等时线可能是人为的或混合等时线，从而给出错误的年龄信息。为鉴别Ｓｍ－Ｎｄ等时线年龄的合理性，可利用同位素参数 、Ｔ＿（ＤＭ）和进行判别。文中利用这三个参数对已发表的Ｓｍ－Ｎｄ同位素资料进行了分析，提出密集点群和密集度的概念，介绍了判别方法、步骤和Ｂａｓｉｃ源程序。最后通过实例分析，介绍了几种类型的等时线，说明判别方法的有效性。

All isochron methods require that samples have the same or close initial isotopic ratio and arethe product of the comagmatic suite and that the parent-daughter system is in a sealed state afterrock formation。 If the samples could not conform to the above-mentioned requitements , theisochron might be a fictitious or mixed ore ,and an incorrect isotope age would be given, In orderto distinguish the reasonable Sm-Nd isochron from fictitious or mixed ones ,the isotopic parame-ters ,T_(DM) and are intrbduced as judging factors. In the paper the three parameters are usedin analyzing the published Sm-Nd isotopic data ,and then the concepts of the concentrated samplegroup and concentration degree are proposed and the discrimination method , steps and basicsource program are introduced. Finally five examples of reasonable Sm-Nd isochrons and incorrectones are given , which indicates that the discrimination method is effective.