Deformations And Significance Of Middle Segment Of The Yanshan Belt In Early And Middle Jurassic

Differences on tectonic features of the northern part of North China in earlierMesozoic have still existed. The geochemical study of magmatic rocks shows it’smainly in the extensional state, but lack of support on related deformation. Noaccurate structural deformation and geochronology study in Yanshan central areasshows the early Mesozoic tectonic deformation properties.Jixian fault, oriented to NEE, is located in the northern part North China craton,southern margin of the middle Yanshan orogen, on both west and east sides ofPanshan pluton, and southern part of Fujunshan syncline and Zhuangguoyu syncline.The tectonic evolution of this area has been of much controversy. Our field work inthe south of Panshan pluton shows rock in the area which Jixian fault extend to don’texist fracture zone or fault activity indicate that the region’s rock intrusion is earlierthan the fault activity. We obtained195Ma by dating rocks in this region by zirconU-Pb LA-MC-ICPMS, indicating that the Jixian fault thrusted before195Ma. Sheet indolomite of Wumishan formation involved in deformation as footwall of Jixian faultin the west of Xujiatai. LA-MC-ICPMS zircon U-Pb dating result is204Ma, cloth tothe result of dating on northern part of Panshan pluton (203-207Ma, by SHRIMPzircon U-Pb). Field work and geochronology show that the Panshan pluton hasmulti-episode magmatic intrusion process. The earlier pluton and sheet in surroundingrock were involved in Jixian fault activity. Jixian fault was not activity after the laterintrusion. Jixian faults formed during204-195Ma.It’s kinematic properties andchronology suggest that shallow crust of North China craton was in compressionduring the early Mesozoic.Duanshuao-Jianbaoshan fault is oriented to EW, dips to north and makes Jixiansystem on top of Qingbaikou system, Cambrian system and lower Jurassic series.Eastern part of this fault is covered by Tiaojishan formation. Dating of VolcanicSample at the bottom of Kuanchang Basin shows Duanshuao-Jianbaoshan faultformed before152Ma, in early-middle Jurassic. Which indicate NS compression in Aperiod of Yanshan movement. After that, superimposed folds whose axis oriented toNE formed.