Geochemical Characteristics And Geological Significance Of Gaixian In South Liaohe Group,Qingchengzi Region,Eastern Liaoning

A set of rocks composed of marble combination,schist combination,phyllite combination,metamorphic sandstone combination,granulite combination and gneiss combination is called Gaixian rock group in Qingchengzi area of eastern Liaoning.The lack of petrography,geochemistry,protolith recovery,tectonic setting,and chronology studies on the system in this area severely restricts the understanding of the genesis and tectonic significance of this area.The main lithological sillimanite diorite diorite schist and garnet-bearing biotite potash granite are the research objects.Through field investigations,systematic petrography,geochemistry and zircon were carried out.The chronological study,combined with the analysis data of the limited chronology and geochemical tests of the predecessors,discusses the formation age,metamorphic age and tectonic setting of the Nanliaohe Group in the Qingchengzi area.Mainly achieved the following results:（1）The main lithological sillimanite diorite and schists in the Gaixian Formation are rich in SiO₂（68.89%～64.14%）,Al₂O₃（19.65%～21.24%）and K₂O（3.88%～4.15%）,and are poor in iron,magnesium,and calcium,Sodium,etc.;the garnet-containing biotite-potassium long granulite is rich in SiO₂（70.15%～82.01%）,K₂O（3.95%～5.69%）,poor in aluminum,iron,magnesium,calcium,and sodium.Both show the relative enrichment of light rare earths and the relative loss of heavy rare earths.TheΣREE content of sillimanite and feldspar schists is248.12～335.32×10^-6,δEu is between 0.43～0.64,with obvious negative anomalies,δCe is between 0.87～0.97,with an average of 0.92,showing weak negative anomalies;The garnet-bearing biotite potassium plagioclaseΣREE content is61.84～168.09×10^-6,δEu is in the range of 0.71～1.68,the change is large,the average is 1.06,the performance is normal,δCe is in the range of 0.78～0.90,the average 0.84,showing weak negative anomalies.Trace element loss Ta,Nb,Ti（TNT abnormality）.（2）The zircon U-Pb isotope age of 1909±4.8Ma of the sillimanite diorite schists is obtained,which represents the metamorphic age of the sillimanite diorite schists.The zircon U-Pb isotope age of 2043±22Ma of the garnet-bearing biotite potassium plagioclase represents the formation age of the garnet-bearing biotite potassium plagioclase.（3）The sedimentation of the Gaixian Formation in the Qingchengzi area occurred between 2056 and 1920 Ma,and volcanic materials provided a large amount of provenance for the sedimentary rocks,followed by a strong metamorphism-deformation during the 1920-1901 Ma arc-continent collision.The time limit of sedimentation-metamorphism is 2056～1901Ma,and its evolution time is about 155Ma.（4）The formation environment of the South Liaohe Group is the active continental margin tectonic environment close to the continental island arc.The formation and evolution of the Jiao-Liao-Ji orogenic belt may be related to the arc-land collision.