摘要
本文采用界线层型标定地层界线的方法，以河北滦平县井上－大店子和大北沟两界线层型剖面的生物地层研究结果，确定我国陆相侏罗系－白垩系界线在大北沟组与大店子组之间，对滦平县热河群下部及其下伏岩层中的火山岩层进行４０Ａｒ／３９Ａｒ法年代学研究，并推定侏罗系－白垩系界线年龄为１４０±１Ｍａ。
The Douling metamorphic complex (the Douling Group) , situated in Eastern Qinlin gorogenic belt, the joint zone between the North China and the Yangtze plate, consists mainly of gneisses, Di leptites and amphibolites. The ages of the metamorphic rocks of the Douling Group have been measured by single zircon stepwise evaporation deposition for 207 Pb/ 206 Pbage investigations, Sm Nd, Rb Sr and 40 Ar/ 39 Ar methods. The isotopic data show that the Douling Group was formed in early Proterozoic (about 2 000 Ma). After its formation, the Douling Group was subjected to several strong metamorphism and thermal events. The Sm Nd isochron age (1 878±256 Ma, ε Nd (t) =+2.8±2.6) of the gneisses may represent the time of the first strong metamorphism. The main period of metamorphism occurred in Jinningian, 833 ±17 Ma ( 40 Ar/ 39 Ar high temperature plateau age of hornblende). The Rb Sr isochron age of the gneisses, 422±16 Ma, represent a metamorphism of Late Caledonian . In addition, there are a thermal event in Variscan, 323±8 Ma ( 40 Ar/ 39 Ar low temperature plateau age of the hornblende). The isotopic characteristic of the Douling Group is similar to that of the Qingling Group of the North China Plate and probably one part of the Qingling Group.
