秦岭岩群和碧口岩群层序时代的重新厘定

REDEFINITION OF THE SEQUENCES AND AGES OF THE QINLING AND BIKOU GROUP COMPLEXES

秦岭岩群和碧口岩群因构造复杂、化石贫乏，多年来对其层序和时代的意见极不统一。笔者通过地层清理，并结合前人所获得的成果，对这两个岩群的层序和时代进行重新厘定。秦岭岩群包括云母石英片岩、大理岩、片麻岩三套岩石组合，据同位素年龄和区域地层对比定为早元古代；从原秦岭岩群中分解出峡河岩群，据同位素年龄定为中晚元古代。碧口岩群包括变火山岩和变沉积碎屑岩两套岩石组合，据同位素年龄和微古植物化石定为中晚元古代；从原碧口岩群中分解出鱼洞子杂岩，据同位素年龄和硅铁建造定为早元古一太古代。

For many years,views about the sequences and ages of the Qinling and Bikou Group Com-plexes have been very divergent owing to complex structures and scanty fossils therein. Through clarification of the strata coupled with new data obtained by predecessors,the authorshave redefined the sequences and ages of the two group complexes. The Qinling Group Complexincludes three rock associations,1.e。 mica-quartz schist,marble and gneiss. On the basis of theirisotppic ages and regional stratigraphic correlation,the age of the group complex was deter-mined to be Early Proterozoic.The Xiahe Group Complex divorced from the original QinlingGroup Complex is of Middle-Late Proterozoic age according to its isotopic age. The BikouGroup Complex comprises two rock associations,metavolcanic rocks and metasedimentary clas-tic rocks. According to the isotdpic ages and fossils of microfloras,its age is Middle-Late Pro-terozoic. The Yudongzi Group Complex divorced from the originaI Bikou Group Complex isEarly Proterozoic-Archean in age according to the isotopic ages and cherty iron formations。