摘要
对燕山地区蓟县剖面铁岭组条带状燧石进行Ar - Ar 阶段加热实验,获得一个马鞍形年龄谱。通过对各温度阶段K、Ca 、Cl 质量分数及Cl/K、Ca/K 比值变化特征的分析,笔者认为马鞍形谱线左侧视年龄的变化与燧石中流体包裹体含过剩Ar 有直接关系;而右侧的变化则与燧石晶格中过剩Ar 的释放有关。马鞍形谱线往往意味着样品含过剩Ar;但含过剩Ar 的样品不一定都呈马鞍形。当燧石纯度很高,加热阶段划分得很细时,马鞍形谱线中温区间最小视年龄具有某种年代学意义。
The striped chert from Tieling formation of Proterozoic Jixian section was measured by 40 Ar_ 39 Ar step_heating and,as a result,a saddle_shaped age spectrum was obtained.K,Ca,Cl content and changes in Cl/K and Ca/K ratios for each step indicate that the change on the left side of age spectrum is concerned with excess argon from fluid inclusions in chert,and the right one is related to the excess argon released from chert lattice.The saddle_shaped age spectrum often suggests that the sample contains excess argon,but the age spectrum of excess argon_bearing sample may not show the saddle shape.If chert does not contain impurities and the age spectrum is very precise,the minimum apparent age in middle temperature may have geochronological implication.
基金
国土资源部同位素地质研究开放实验室基金
