Geochemistry And Zircon U-Pb Geochronology Of Xudapu Granitics In Xingcheng Area, Liaoning Province

The Xingcheng area of Liaoning is located in the eastern part of the northern margin of the North China Craton(NCC),at the transitional zonesin between the Shanhaiguan paleo-uplift and the Yanliao subsidence zone.It is a typical area to study the Mesozoic craton evolution and Yanshan movement tectonic activity Th Yanshan movement tectonic activity,with widely distributed Mesozoic granitic rocks and strongly magmatic activities.In this paper,the Mesozoic granitic rocks in the Xudapu area of Xingcheng,Liaoning were systematically studied by petrography,isotope chronology,and rock geochemistry.The genesis,source area properties,and tectonic background of the granitic rocks in different periods were discussed.Regional research data discusses the North China Craton destruction and the Yanshanian tectonic transformation system and time limit,and provides new evidence for Mesozoic tectonic evolution in western Liaoning.According to field geological survey and zircon U-Pb isotope dating,it is determined that the Mesozoic granitic rocks in Xudapu,Xingcheng are mainly divided into three stages: Early-Middle Triassic,Middle-Late Jurassic and Early Cretaceous.The Late Triassic rocks are mainly ocular-shaped granitic metamorphic mylonite and hornblende-bearing diorite gneisses,which are produced as rock walls or veins.The zircon isotope dating results are 248.4±2.1 Ma,238.0±4.4Ma;MiddleLate Jurassic rocks are mainly dolomite monzonite granite and garnet-bearing monzonite granite: the dolomite monzonite granite is exposed as a captive body in the garnet-bearing monzonite granite,with dark-colored minerals locally Enriched,light-colored bodies are developed in the form of reticulate veins,zircon isotope dating results are 172.4 ± 1.8Ma,168.2 ± 2.4Ma;garnet-bearing feldspar granites are produced in larger rock bases,and zircon isotope dating results are 153.9±3.9Ma,156.5 ± 5.6Ma;the Early Cretaceous rocks are mainly garnet granite fine-grained rocks,intruding into veins into the mid-late Jurassic granitic rocks.Rock geochemical analysis results show that the Si O2 content of the Early Triassic ocular granitic metamorphic mylonite and hornblende-bearing diorite gneisses is 60.83%-70.18%,the total alkali content(Na2O+K2O)is 6.79%-7.76% belongs to quasi-aluminum-peraluminous rock(A/CNK=0.89-1.02),high-potassium-calcium alkaline series.Enrichment of light rare earth elements(LREE),loss of heavy rare earth elements(HREE),obvious difference between light and heavy rare earth elements(LREE/HREE = 11.50-18.14),(La/Yb)N = 17.35-35.42,weak negative Eu anomaly(?Eu = 0.78-0.91),showing that the large ion lithophilic elements(LILE)Rb,Ba,Sr are relatively enriched,and the high field strength elements(HFS)such as Nb,Ta,Ti,Yb are relatively deficient;the mid-late Jurassic black cloud II The Si O2 content of the feldspar granite and the garnet-containing feldspar granite is 66.86%-75.55%,the total alkali content is 7.56%-8.71%,which belongs to quasi-aluminum-peraluminous rock(A/CNK=0.92-1.06),high potassium calcium calcium alkaline series.Enrichment of light rare earth elements,loss of heavy rare earth elements,medium and light rare earth differentiation(LREE/HREE=3.62-9.52),(La/Yb)N=3.30-12.20,medium negative Eu anomaly(?Eu = 0.55-0.86),large The ionic philophile elements Rb,K,Ba are relatively enriched,the high field strength elements Ta,Ti,Yb,etc.are relatively depleted,and the compatible element P is depleted;the Si O2 content of the Early Cretaceous garnet granite fine grains is 73.87%-75.05%,the total The alkali content is 8.13%-8.41%,which belongs to quasi-aluminum-peraluminous rock(A/CNK=0.89-1.04),high-calcium-calcium alkaline series.Enrichment of heavy rare earth elements,loss of light rare earth elements,no obvious difference between light and heavy rare earth elements(LREE/HREE = 0.59-0.77),(La/Yb)N = 0.37-0.60,obviously negative Eu anomaly(?Eu = 0.22-0.38),The large ionic stone affinity elements Ba and Sr are relatively depleted,Rb is enriched,the high field strength elements Hf,Nb,Th,U,etc.are relatively enriched,Ti is depleted,and the compatible element P is depleted.Combining with regional geological data and previous studies,the Early Triassic ocular granitic metamorphic mylonite and hornblende-bearing feldspar gneiss were formed at the base of the subduction orogenic stage of the ancient Asian Ocean plate toward the North China Craton The partial melting of the crust indicates that the ancient Asian ocean was completely closed at least after the Middle Triassic.The Middle-Late Jurassic biotite garnet and garnet-bearing feldspar granite were formed in the partial melting of the crust during the continuous subduction of the Paleo-Pacific plate toward the North China Craton.Destabilized the North China Craton,leading to thinning of the lithosphere and destruction of the Craton.The Early Cretaceous garnet granite has the characteristics of transition from type I granite to type A granite,formed in the partially depleted crustal melted in the extensional environment where the subduction from the ancient Pacific to the North China Craton ended,and experienced strong separation and crystallization The Yanshan Movement was transformed from an extruded structural system to an extended structural system.In terms of time,the initiation time of Yanshan Movement and the time of tectonic system transformation are both coupled with the time of the development of the two extensional structures of the North China Craton.The subduction of the Paleo-Pacific plate was the trigger for the Yanshan movement,and the tectonic evolution of the Yanshan movement further promoted the large-scale destruction of the North China Craton.