Provenance And Tectonic Setting Of The Paleoproterozoic Metasedimentary Rocks From The Liaohe Group In Gongchangling-Xiuyan Area,East Liaoning Province

The Liaohe Group in Liaodong peninsula is an important part of the Paleoproterozoic of Jiao-Liao-Ji orogenic belt.Former scholars divided it into the South Liaohe Group and the North Liaohe Group,but there are different ideas about their sedimentary environment and relationship.In terms of sedimentary environment,there are views of continental rift,active continental margin and different continental margins;There are three views on the relationship between the two groups,namely,they are contemporaneous heterotopic facies,successively deposited,and deposited on two different continental margins respectively.In this paper,we discuss the provenance and early tectonic setting of the South and North Liaohe Groups in Gongchangling-Xiuyan area of Eastern Liaoning Province by studying the geological characteristics and U-Pb geochronology of detrital zircon in the South and North Liaohe Groups and comparing the related data of the regional predecessors.The metamorphism degree of metasedimentary rocks in Gongchangling-Xiuyan area is relatively low.They are mainly metasandstone,mica schist and quartz marble.No high-grade metamorphic minerals are found in these rocks.The detrital zircons of six samples have been studied.Based on cathodoluminescence(CL)imaging and combining LA-ICP-MS U-Pb geochronology,these zircons show distinct oscillatory zoning,and high Th /U ratios(> 0.3),suggesting that its source rock is magmatic rock.Combining LA-ICP-MS U-Pb geochronology,detrital zircons of the Li'eryu,Gaojiayu,Dashiqiao and Gaixian Formations yield U-Pb age peaks at ~2159 Ma,~2500 Ma,~2189Ma/~2530 Ma,and ~2044/~2197 Ma.It is found that the same age distribution characteristics exist between the same groups of the South and North Liaohe groups,which shows that the South and North Liaohe groups are deposited at the same time,and their provenance is the same as well.Their sediments are derived from the Paleoproterozoic granitic rocks and the adjacent Archean complex.Based on the previous studies on the geochemistry and U-Pb geochronology of the basic rocks in this area,we found that the meta basic rocks and meta sedimentary rocks of the South and North Liaohe groups in this area have almost the same characteristics,indicating that the South and North Liaohe groups are the same one sedimentary strata,not deposited in two different continental margins or different facies at the same time.They may have been deposited in a same back-arc basin in the early stage and experienced the same structural evolution later.