The Formation Age of the Neoarchean Zhuzhangzi and Dantazi Groups in the Qinglong Area, Eastern Hebei Province: Evidence from SHRIMP U-Pb Zircon Dating

In this paper are reported the SHRIMP U-Pb zircon ages of the Neoarchean Zhuzhangzi and Dantazi Groups in the Qinglong area, eastern Hebei Province. Weighted mean 207Pb/206Pb ages of magmatic zircons from TTG and granite pebbles and matrix of the Zhangjiagou Formation of the lowest Zhuzhangzi Group are 2515±9 Ma (MSWD=1.9), 2510±10 Ma (MSWD=1.6) and 2512±7 Ma (MSWD=1.0), respectively. Detrital zircons from biotite plagioclase gneiss of the Zhangjiagou Formation of the lowest Zhuzhangzi Group have a weighted mean 207Pb/206Pb age of 2540±6 Ma (MSWD=1.6). A weighted mean 207Pb/206Pb age for magmatic zircon from meta-felsic volcanic rock of the Buloutai Formation of the Zhuzhangzi Group is 2516±8 Ma (MSWD=1.1). The majority of detrital zircons from fine-grained biotite gneiss of the Luzhangzi Formation of the Dantazi Group have a weighted mean 207Pb/206Pb age of 2504±7 Ma (MSWD=1.8), with a spot being 3044 Ma in 207Pb/206Pb age. Based on data obtained in this study and by others, some conclusions can be drawn as follows: (1) The Zhuzhangzi and Dantazi Groups were formed in an arc environment at the end of Neoarchean; (2) The age gap between deposition of the Zhuzhangzi and Dantazi Groups was very short although there indeed was a unconformity between them; (3) The Zhuzhangzi and Dantazi Groups of greenschist—amphibolite facies and the Santunyun—Taipingzhai—Qianxi magmatic complex of amphibolite—granulite facies are different in metamorphic grade but were formed almost at the same time, being a result of late crustal movement which overthrust these deep-seated rocks to the same crustal level.