Chronology progress of the Guandaokou and Luoyu groups in the southern margin of North China Craton: Constraints on zircon U-Pb dating of tuff by means of the SHRIMP

Meso- to Neoproterozoic (1800 similar to 542Ma) sedimentary rocks crop out extensively along the southern margin of the North China Craton, where they locally overlie Archean-Paleoproterozoic crystalline basement. However, due to the lack of accurate isotope age data, the division and correlation of the strata have always been controversial. Two interbedded tuffite layers in the bottom and lower part of the Longjiayuan Formation have been obtained in Luanchuan County, Henan Province, by means of the SHRIMP zircon U-Pb dating, the ages are 1594 +/- 12Ma and 1541 +/- 8Ma. With these data, the depositional age of the Longjiayuan Formation can be calibrated accurately for the first time, which indicates that the bottom age of this formation should be most likely about 1600Ma. The Longjiayuan Formation should be the earliest strata in the Mesoproterozoic Jixian System. Four interbedded tuffite layers in the Luoyukou Formation have been obtained in Ruyang, Ruzhou, Lushan counties, Henan Province, by means of the SHRIMP zircon U-Pb dating, the ages are 1596 +/- 7Ma, 1596 +/- 15Ma, 1608 +/- 17Ma and 1620 +/- 16Ma, respectively. These further confirme the depositional time of the Luoyukou Formation. Combining with the results of detrital zircon U-Pb data from the Yunmengshan Formation of the Ruyang Group, the depositional time span of both the Luoyu Group and the Ruyang Group can be limited roughly into the period from 1700Ma to 1600Ma. The Guandaokou Group should be strata after the Ruyang Group.