沉积岩中自生伊利石K-Ar定年研究——存在问题及原因讨论

Study on the K-Ar Dating of Diagenetic Illite in Sedimentary Rock Samples——Question and Discussion

在浙江长兴煤山全球二叠系-三叠系界线层型剖面中界线附近采集黏土岩样品,对其中的伊利石/蒙皂石成岩间层I/S进行K-Ar测年实验研究,来探讨沉积岩中自生伊利石K-Ar测年在确定沉积地层时代方面的可行性。结果表明,沉积岩中成岩间层I/S的K-Ar年龄在没有碎屑含钾矿物混入的情况下,比其对应的地层时代要年轻,其原因主要有两条,一是因为泥岩中的自生伊利石来自于蒙皂石的伊利石化,而蒙皂石的伊利石化受很多因素控制,需要一定的时间才能完成;另一原因是由于蒙皂石伊利石化过程中存在着放射性成因^(40)Ar的扩散丢失。

The diagenetic L/S of P-T boundary in Changxing, Zhejiang province was dated using K-Ar method. The results show that the K-Ar ages of pure diagenetic L/S is younger than the age of the P-T boundary. The reasons for this result are that （ 1 ） the diagenetic illite in mudstone is formed through the sluggish smectite illitization, and （2） the loss of the radiogenic ^40Ar exists in the fine clay minerals during the smectite illitization.