摘要
本文系统分析了目前确定云开群地质年代的同位素年龄数据和微古植物化石的可利用性和存在的问题,根据云开群牛辰坳组/兰坑组中化学沉积成因硅质岩测得的^(40)Ar/^(39)Ar坪年龄872.8±8.6 Ma,并结合云开群罗罅组变质英安斑岩中颗粒锆石分层蒸发法年龄922～940 Ma,确定了云开群的地质年代为新元古代青白口纪。按其时代和岩性序列特征将其与丹洲群和板溪群进行对比。文中指出前人建立并命名作为岩石地层单位的高州岩群和黄岭岩组不符合地层划分命名原则,因而是不恰当的。根据野外观察,对比研究岩性和追索构造展布,本文认为黄岭岩组中的沉积变质岩残留体可能就是云开群兰坑组地层。高州群其余两个组地层的地质年代和对比则还有待进一步的研究。
The present paper deals with the useability and remaining problems of the isotopic ages and microfossil plants used to determine the geologic age of the Yunkai Group. Based on the 40Ar/39Ar plateau age of 872. 8±8. 6 Ma newly obtained from chemical sedimentary silicalite of the Niushen'ao/Lankeng Formations of Yunkai Group and the 207Pb/206Pb ages of 922-940 Ma from zircon grains from porphyritic metadacite of the Luoxia Formation of Yunkai Group, the geologic age of the Yunkai Group is defined to be the Qingbaikou Period, Late Proterozoic. According to the geologic age and lithologic correlation, the Yunkai Group may correspond to the Danzhou and Banxi Groups. In the paper, it is pointed out that establishment and nomination of the Gaozhou Rock Group and Huangling Rock Formation as the lithostratigraphic units are unsuitable because it is not in keeping with principles of stratigraphic classification and nomination . On the basis of field investigations, lithologic correlation and structural tracing, the present paper considers that the metasedimentary relicts in the Huangling Rock Formation may actually be parts of the Lankeng Formation of Yunkai Group. As for the geologic ages and stratigraphic correlation of the remaining two formations of the Gaozhou Group, further study is required.
出处
《地质论评》
CAS
CSCD
北大核心
2000年第5期449-454,共6页
Geological Review
基金
国家自然科学基金 (编号49872024)
