The Sedimentary Characteristic And Tectonic Property Of Upper Neoproterozoic At Benxi,Liaoning

The Jiao-Liao Block which located in the northeastern of the North China Craton.The lithology of upper Neoproterozoic strata are clasitic rocks,and the lower are mainly carbonates,and also have seismites rocks along the Tanlu Fault Zone.The study of the biological stratigraphy show the biological combinations which belong to Sinia were found in the Neoproterozoic strata from the Jiao-Liao Block,but have never found tillites in the Jiao-Liao Block so far.So the focus of discussion is the age of the strata.Moreover,the method of corelate the Neoproterozoic strata between the Jiao-Liao Block and other blocks is litho-stratigraphy and bio-stratigraphy,but the geochronology of the Jiao-Liao Block is still a problem.Benxi area is a typical area which have the Neoproterozoic strata in the Jiao-Liao Block.On the bases of the former research results,the lithology,stratigraphy and geochronology of the Upper Neoproterozoic strata from Benxi area are studied in detail.First,all the three sections such as Xihe section,Lingxiacun section,Yangmugoucun section are measured and observed in detail,we find the relationship between the Qiaotou Formation and Kangjia Formation is conformity..So we update the division of the Xihe Group which divide into four formations.Besides,we find Molar Tooth structures in the Kangjia Formation at the first time.Because of the unique feature of Molar Tooth structures,the sedimentary environment of the Kangjia Formation is between the upper and lower intertidal zone.Second,the detrital zircons from the Qiaotou Formation and Kangjia Formation are analyzed by the method of LA-ICP-MS U-Pb and Hf isotope analysis.The results show the detrital zircons from the Kangjia Formation exist two peak ages which are 2.0?1.8Ga and 2.6Ga,and the Qiaotou Formation also exist two peak ages which arel.6Ga and 1.2Ga.The conclusion of the analysis is the provenance of the Kangjia Formation and the Qiaotou Formation came from the material of the North China Craton in the period of 2.6Ga-1.8Ga and 1.6Ga?1.2Ga.The result of Hf isotope show the elements of the bottom Kangjia Formation were magma,and the mid-upper were earth-crust,the elements of the Qiaotou Formation were earth-crust besides.By the analysis of geochemistry,the tectonic background of the study area is sea-facies basin in the passive continental margin.At last,considered the experiment results and former researches,we suggest the Kangjia Formation from Benxi area can correlate to the Nanguanling Formation from Dalian area and the lower Wanlong Formation form Tonghua area.This conclusion is benefit to the Precambrian research of the Jiao-Liao Block and provide a new thought and evidence for the correlation and evolution of the Neoproterozoic in the Jiao-Liao Block.