Characteristics Of Early Permian-middle Triassic Volcanic Rocks In Faku-Kaiyuan,Eastern Part Of The Northern Margin Of The North China Block And Their Tectonic Significance

The study area is located in Faku County and Kaiyuan City,northern Liaoning.The study area is located in the eastern section of the northern margin of the North China Block,south of the Solonker-Xar Moron-Changchun suture zone,across Yilan-Yitong fracture,Located on the southern margin of the Songliao Basin;Predecessors have carried out a lot of research work on the late Paleozoic-Early Mesozoic magmatism in the orogenic belt south of the Solonker-Xar MoronChangchun-Yanji suture zone.Research on volcanic rocks is relatively weak.The Faku-Kaiyuan area is located on the northern margin of the North China Black.Since the Paleozoic,it has experienced the evolutionary process of subduction,closure and collision of the Paleo-Asian Ocean.Its magmatic activity records the subductionsubtraction-closure process of the Paleo-Asian Ocean.Therefore,this article takes the Early Permian-Middle Triassic volcanic rocks in the Faku-Kaiyuan area in northern Liaoning Province as the research object.Using zircon LA-ICP-MS and SHRIMP dating techniques,combined with previous research results,determine the formation age of Early Permian-Middle Triassic magmatic rocks in the study area;Research the samples in petrography,petrogeochemistry and zircon Lu-Hf isotopes,discuss their petrogenesis and the tectonic background of their formation,and combine the research results of the study area and adjacent areas to discuss the evolution process and dynamics of the geotectonics Mechanism to establish a model for the evolution of geological structure since the Late Paleozoic.The Faku biotite andesite SHRIMP zircon U-Pb weighted average age is 287±2Ma,and the formation age belongs to the Early Permian;Kaiyuan metamorphic andesite and metamorphic dacite LA-ICP-MS zircon U-Pb weighted average ages are 253.3±3.7 Ma and 244.3±1.3 Ma,respectively,and their formation ages belong to the Late Permian and Middle Triassic,respectively.The geochemical characteristics of Faku biotite andesite are high silicon and alkali content,and low Mg O content.In terms of trace elements,large ion lithophile elements are enriched and high field strength elements are depleted.The distribution mode of rare earth elements is relatively enriched in light rare earth elements and relatively depleted in heavy rare earth elements.The ?Eu is 0.981~1.168,which is weak Eu.Negative anomaly and Eu positive anomaly,It belongs to the calc-alkaline-high potassium calcium-alkaline series,which is quasi-aluminum-peraluminum,The ages of ?Hf(t)and the second-stage model are 10.7~19.5 and 655~375 Ma,respectively.The magma originated from the depleted mantle wedge replaced by subducting fluids and formed on the active continental margin.The geochemical characteristics of Kaiyuan metamorphic andesite are moderate silicon and alkali content,rich in magnesium,and rich in aluminum.In terms of trace elements,it is enriched in large ion lithophile elements such as Sr and K,and depleted in high field strength elements such as Th,Nb,P,and Ti.The distribution mode of rare earth elements shows that light rare earth elements are relatively enriched and heavy rare earth elements are relatively depleted to the right.?Eu is 0.889~0.996,which is a weak negative Eu anomaly,belonging to the calc-alkaline-high potassium calc-alkaline series,with quasi-aluminum.Formed in the process of interaction between the melt formed by partial melting of subducted sediments and the mantle,the source rock magma was contaminated by crustal materials during the ascent process.Formed in the mantle wedge environment of the Black subduction zone,the study area is located at the edge of the Andean active continent.The geochemical characteristics of the Kaiyuan metamorphic dacite and I-type granite are similar: rich in silicon(Si O2=67.24%~68.07%),the ratio of Na2O/K2 O is greater than 1(1.45~1.48),and the A/CNK is less than 1.1(1.03~1.06);It is also similar to the geochemical characteristics of adakite: rich in silicon(Si O2=67.24%~68.07%),rich in aluminum(Al2O3=15.71%~15.94%),poor in magnesium(Mg O=1.22~1.41%),poor in Y and Yb(Y=10.8~11.2<18?g/g,Yb=0.86~0.89<1.9?g/g),Sr=424~478>400?g/g;In terms of trace elements,the large ion lithophile elements such as Sr,Zr,and K are enriched,and the high field strength elements such as Ba,Nb,P,and Ti are depleted.The distribution mode of rare earth elements shows that light rare earth elements are relatively enriched,and heavy rare earth elements are relatively depleted.Right-leaning,?Eu is 0.949~1.053,ranging from weak negative Eu anomaly to weak Eu anomaly.It belongs to the high potassium calc-alkaline series,with peraluminum.The magma originates from the crust with a small amount of mantle material.Formed in the environment where the North China Black collides with the northern land.In summary,during the Early Permian,the Paleo-Asian Ocean was undergoing subduction,and the eastern section of the northern margin of the North China Black was in an active continental margin;During the Middle Permian-Late Permian,the eastern section of the northern margin of the North China Black was in the Andean active continental margin,The Paleo-Asian Ocean continued to subduct and the Blackbroke off;During the Late Permian-Middle Triassic,the North China Black had collided with the northern land block,and a post-collision extension had occurred.