K-Ar和40Ar/39Ar定年数据质量评价与Q值提出

Abstract

K-Ar和40Ar/39Ar的定年测试质量的评价是正确运用测试结果的前提。过去的研究,多通过仪器测试的偏差和误差传递来评价测试结果可靠性和精度。MSWD和Probability的提出,给出测试的内外误差概念,因考虑了仪器和样品二者的匹配性而得到广泛应用。这也说明,影响K-Ar和40Ar/39Ar的定年测试结果的因素可以是来自仪器设备,也可以来自样品自身的特性。本文由K-Ar和40Ar/39Ar的定年技术的原理、流程为出发点,通过对各个测试项的误差传递和对结果精度影响的数学方法评估,提出了影响测试精度的Q1和Q2参数,分别代表与样品有关的属性。Q1是样品钾含量、囚禁36Ar的含量、以及样品40Ar/36Ar的初始比值的综合参数,是决定仪器测试中误差传递系数大小的重要影响因子。Q2是样品钾含量、囚禁36Ar的含量、以及样品40Ar/36Ar的初始比值误差的综合参数,用来评价样品等时线年龄精度。在地质意义上,Q2是评价样品是否满足"同源、同时、封闭"特性的重要量化指标。根据这两个参数,可以判别测试数据质量优劣是源于测试仪器,还是样品属性。由Q1和Q2的分析可知,任何一项K-Ar和40Ar/39Ar的定年测试都应该充分考虑仪器性能和样品属性,设计合理的测试流程是K-Ar和40Ar/39Ar的定年获得较高质量数据的关键。

Reasonable application of K-Ar and 40Ar/39 Ar dating result should be based on a proper assessment of dating precision. To assess the reliability and accuracy of final results, researchers used to calculate statistic errors and error propagation. MSWD and Probability are proposed to involve systematic (external) and statistic (instrumental) errors at the same time, thus are widely applied for considering the relation of instrument and sample. This fact indicates that K-Ar and Ar/Ar dating results could be affected by both instrument and sample. Based on the theory and process of K-Ar and 40Ar/39Ar dating, this paper assesses error propagation of each testing step and their effect to the final results numerically. Parameters Q1 and Q2 are proposed to represent related properties of samples that may affect the final results. Q1 defines the relativity of K content, 36Ar content and initial Ar/Ar value of sample. Q 1 is crucial factor to affect the value of error propagation index. Q2 defines the relativity of K content, Ar content and error of initial 40Ar/36 Ar of sample. Q2 is proposed to assess the accuracy of isochron age and estimate whether samples started isochron clock in the exactly same geological time and on the same initial 40Ar/36Ar ratio without isotope diffusion and exchange after isotope system closure. According to parameter Q1 and Q 2, we can tell whether errors of final results are caused mostly by instruments or by samples. Obviously, properties of instruments and samples should be assessed from different aspects before dating as suggested here. Well designed testing process is the key to getting high precision K-Ar and 40Ar/39 Ar dating results.