摘要
测定了张宣地区麻粒岩相退变到角闪岩相的岩石Rb—Sr等时线年龄,得到1629Ma的年代学数据。经研究认为它代表一次地质事件的年龄,是使麻粒岩相退变到角闪岩相的地质事件年龄。同时分析了这个年龄的可能偏差,最终认为它代表华北地台麻粒岩之后那次普遍的热事件的年龄。
Archean metamorphic rock series are distributed over Zhangjiakou- Xuanhua area in the north side of the North China platform (Fig. 1). Their metamorphism degree was up to granulite facies. Most of them retrograded to amphibolite facies by later event. In this paper, the author studied Rb-Sr isochron age in retrogressive metamorphic rocks in the above area. Samples were collected from Jiangouhe formation in Sanggan Group, in which the retrogressive metamorphism was very strong. After studied the author considers: 1. The age of C. 1629 Ma represents once geological event in this area, which caused granulite facies rocks to retrograde to amphibo- lite facies ones. We had gotten an age of C. 2800 Ma before. The two ages are so different as to show that there are two geological events in the seme area. 2. The age of C. 1629Ma is with slightly error. This due to that the temperature and pressure of retrogressive metamorphism were lower than granulite facies, so strontium isotope could not homoge- nety completely during the period of retrogressive metamorphism. 3. The age of C. 1629Ma has geological significance for reference. It is very similar to those ages that were determined by Bor-ming Jahn (1984) and Zhong Fudao (1978) in the Eastern Hebei. So the author consider that all the ages represent the same geological event. And the age of C. 1629Ma was very close to the age of Iuliang Movement or Zhongtiao Movement.