Geochronology And Geochemical Characteristics Of The Paleoproterozoic Meta-sedimentary Rocks In The Jiaodong Peninsula And Its Tectonic Implication

The Jingshan and Fenzishan Groups are the most important parts of the Paleoproterozoic meta-sedimentary rocks in the Jiaodong peninsula,recording the meso to late Paleoproterozoic tectonic evolution history of the Jiao-Liao-Ji belt,eastern North China Craton.Accurate determination of their depositional and metamorphic timing,investigating their provenances and the geochemical characteristics of whole rock elements,is of great geological significance for rebuilding the tectonic setting of the Jiaobei terrane and the Jiao-Liao-Ji belt as well as the late-Paleoproterozoic orogenic process in the Jiao-Liao-Ji belt.Meanwhile,it also provides new constraints for further studying on the genetic relationship between the Jingshan Group and the Fenzishan Group.Based on the detailed 1:50000 reginal survey,through the systematic field work,and in-depth studying on the petrology,geochemical analysis and isotope geochronology,the following new achievements were achieved:The meta-sedimentary rocks were collected from the Jingshan and Fenzishan groups for detrital zircon LA-ICMPS U-Pb dating,we obtained the maximum sedimentary and metamorphic ages for the both groups,which were 2080 and 2170 Ma,1920 and 1916 Ma,respectively,we assume that the depositional timing of the Jingshan and Fenzishan groups ranges from 2146 Ma to 1920 Ma and 2178 Ma to 1916 Ma,respectively.The detrital zircon U-Pb dating and provenance analysis indicate that the Jingshan group and the Fenzishan group have similar age distributions.The main peak age is 2500 Ma and the sub-peak age is 2700 Ma,it is consistent with the Archean to Paleoproterozoic magmatic events in the Jiaodong peninsula.And all the detrital zircons have the characteristics of magmatic zircon.Therefore,the ArcheanPaleoproterozoic metamorphic basement of the Jiaodong peninsula is an important provenance of the Jingshan and Fenzishan groups.Most of the samples have obvious negative Eu anomaly.LA-ICMPS U-Pb dating of metamorphic zircons from the both groups revealed two metamorphic age peaks: 1)1.95 Ga,representing the prograde metamorphism;2)1.85 Ga,representing the retrograde metamorphism.According to the comprehensive study of the detrital composition,rock assemblages,depositional age,provenance feature and geochemical characteristics of the major and trace elements of the meta-sedimentary rocks from the Jingshan and Fenzishan groups indicate that the deposition of the two groups was related to the back-arc basin.The provenance has an obvious binary structure,it includes 2200?2100Ma intermediate acid igneous rocks from the juvenile arc and a stable Archean metamorphic basement(>2500Ma).In addition,the Jingshan and Fenzishan groups are different in bottom rock assemblages,metamorphim,ore bearing and structure features,indicating the two groups deposited the different sides of the back-arc basin.