The Mesozoic Structural Style And Basin Evolution Of Jianchang Basin,Western Liaoning

Mesozoic basins are widely developed in western Liaoning province,represented by the Jianchang basin.Basin evolution is controlled by boundary faults and is closely related to volcanic eruption.However,due to the unclear division of structural styles and types and the divergent understanding of basin evolution in Jianchang basin.Therefore,the division of structural styles and the determination of basin properties are of great significance for the division of Yanshanian movement,the time limit,and the in-depth understanding of the Mesozoic tectonic evolution of the North China Craton and Western Liaoning.The Mesozoic strata of Jianchang basin in western Liaoning Province studied in this paper are relatively complete.The Mesozoic stratigraphic sequence and stratigraphic framework of Jianchang basin are established through field measurement and investigation of three geological sections,combined with zircon U-Pb dating analysis of Mesozoic volcanic and clastic rocks in the basin.Through the analysis of the characteristics and properties of Mesozoic faults in the basin margin,it is confirmed that the Hekanzi-Nangongyingzi thrust fault in the western margin of the basin controlled the Late Jurassic to Early Stage of Early Cretaceous strata,and the Majiadian normal fault in the eastern margin of the basin controlled the Late Early Cretaceous strata.Based on detailed field investigation and reinterpretation of some seismic sections,the main framework of Jianchang basin is determined to be composed of Tangshenmiao syncline and Jianchang monocline.The analysis of structural kinematics shows that the thrust nappe structure in the basin has a forward spreading thick-skinned structure combination.Based on structural analysis and geochronology analysis,combined with systematic measurement and data mapping of faults,folds,scratches and other occurrences,as well as the recovery of sub paleostress field state in each major tectonic period,the Mesozoic tectonic deformation of Jianchang basin is divided into four stages:N-S trending compression structure before Early Jurassic(D₁stage),NW-SE trending compression structure(D₂ stage,156-133Ma),NW-SE trending extensional structures(D₃stage,123-106Ma)and NE-SW trending weak extensional structures(D₄ stage,Late Cretaceous).Field investigation and seismic profile interpretation have proved that the angular unconformity interface between Tuchengzi Formation and Yixian formation is widespread in Jianchang basin,which not only marks the transition of tectonic system from NW-SE to extensional structure in Late Jurassic to Early Cretaceous,but also proves the existence of B episode of Yanshanian movement in Jianchang basin.The zircon U-Pb dating of the bottom of the Yixian formation is 122.8±2.2 Ma.Combined with the age of the top of the Tuchengzi Formation obtained by predecessors,the occurrence time of episode B of Yanshanian movement is roughly limited to 134-123 Ma,so the tectonic transition mainly occurred in the Early Cretaceous.According to the type of Mesozoic Jianchang basin,it can be divided into three major evolution stages:Jianchang basin is a residual craton basin in the Early and Middle Triassic,a compressional flexure basin from Late Jurassic to Early Stage of Early Cretaceous,and a half graben extensional basin from Late Early Cretaceous to Late Cretaceous.This is important for studying the structural development of the Yanshanian movement in western Liaoning.