THE ISOTOPIC AGES OF THE HONGQIYINGZI GROUP IN NORTHERN HEBEI AND ITS AGE ASSIGNMENT
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摘要: 冀北红旗营子群不整合于太古界褶皱变质基底岩系之上，对其时代归属尚存在不同认识。通过对使用不同方法和测定对象所获得的３０余件同位素年龄数据，结合产出的区域地质背景深入的分析研究，认为单颗粒碎屑锆石Ｕ－Ｐｂ法２４５０（２４３４±２３）Ｍａ，代表红旗营子群生成的最大下限年龄；而变质锆石及花岗岩中的锆石Ｕ－Ｐｂ年龄均在２０００（１９７８—２０２６）Ｍａ，是该群的上限年龄。根据以上结论，冀北红旗营子群形成的时限为２４５０—２０００Ｍａ，因此将其归属于早元古代。Abstract: The Hongqiyingzi Group in northern Hebei lies unconformably on the Archean folded metamorphosed basement rock series.Divergent views still exist as to its age assignment.Through an intensive analysis of more than 30 isotope age data obtainedby using different methods combined with a study of the geological setting,it is considered that the single grain detrital zirconU-Pb age of 2450（2434±23）Ma represents the maximum lower-limit age of formation of the Hongqiyingzi Group,while the UPb ages of metamorphosed zircon and zircon in granite are all about 2000（1978-2026）Ma,which is the upper-limit age of this group. Thus the authors hold that the time for the formation of the Hongqiyingzi Group in northern Hebei is in the range of 2450-2000 Ma;so the group should be assigned to the Lower Paleozoic.
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