Characteristics Of Middle And Late Jurassic Crustal Extension In Yiwulüshan Area, Western Of Liaoning Province

In recent years, lithosphere thinning and destruction of the North China Craton are intensively discussed. Extensional crustal detachment is the most important tectonic response of lithosphere thinning and Yiwulümetamorphic core complex is useful to research destruction of the North China Craton. Although a great many achievements about the geological structure and granite in Yiwulüshan area have been made, there are still some puzzles and arguments. This paper study the Mesozoic geological structure in Yiwulüshan area through field geological investigation, microstructure, lattice preferred orientations and SHEIMP geochronology. The results are as follows:①Extensional crenulation cleavage, rodding structure and"L"tectonite in the ductile shear zone and previous view show that its extensional shear zone. The ductile shear zone in Yiwulüshan area has composed with two department: Waziyu ductile shear zone and Yiwulüshan ductile shear zone. The former is dominated by low-temperature ductile deformation and the latter dominated by high-temperature tenacity deformation.②Yiwulüshan ductile shear zone deformed in the early and Waziyu ductile shear zone derormed in the late, the fabric deformed at low temperature transformed from the high-temperature fabric. Early extension is in the direction of 220°~136°, the direction of the late extension is 270°~290°. Angle between the direction of two stages extension is about 30°~60°.③Emplacement of Mesozoic granite in research area is controlled by C and S foliation of ductile shear zone and the mylonitic foliation in granite coordinates to it in wall rock, witch implies the granitic pluton and dikes emplacement as syn-tectonic granite. The pluton emplace along or parallel to ductile shear zone as a bedding-sill, based on the deformation character of granite and structure zone in Yiwulüshan region. SHRIMP geochronology of the syn-extensional granite dike provides it emplaced at 155±2Ma, combine with previous data shows crustal extension occurred in Yiwulü-shan region in middle-late Jurassic and early Cretaceous.④Microstructure and lattice preferred orientations of quartz in Yiwulüshan ductile shear zone implies that deformation temperature of early extension is 550℃~ 700℃, deformed at high temperature environment in the middle and lower crust. Analysis of dynamically recrystallised grain size shows the differential stress of early extension is 9.6~13.9Mpa, deformation of the rock mainly as mineral plastic flow under high temperature.⑤Redefinition of Yiwulüshan region middle-late Jurassic extension in implies that the Yanshan region and western Liaoning Province in the extension system from late Middle Jurassic to early Late Jurassic, destruction of the North China Craton has already begun at middle Jurassic, eastern of North China has become subject to the control of the Pacific tectonic domain and become the tectonic framework both compress and extension.