The Wulian-Qingdao-Yantai fault(WQYF)is one of the most important basin-controlling faults in the Jiaolai basin,where the fault dominates the formation and evolution of the basin.This fault is mainly com-posed of abundant NNE faults,such as Muping-Jimo fault and Taocun fault.The WQYF experienced sinistral strike-slip movement in Late Jurassic,extensional rift in EarlyCretaceous,and dextral strike-slip movement during Late Cretaceous-Paleocene.However,the most key question that the duration of the Cenozoic dextral strike-slip movement still remains unclear.Previous studies suggested that temperature of strike-slip movement in this region is about 550-650 ℃,which is higher than the closure temperature,350-550 ℃,of the apatite U-Pb system.Therefore,in this case apatite can be an ideal candidate to investigate the dextral strike-slip of the WQYF.In this study,we conducted U-Pb dating of apatite from the Early Cretaceous trachy-dacite in the Mashan area and obtained the U-Pb age of 64.1±3.7 Ma.The measured magmatic age of apatite is different from the crystallization age of the Mashan trachy-dacite,indicating that at least there was one geothermal event which reset the apatite U-Pb isotope system in Early Paleocene.Since Early Cretaceous,the collision between the Indian plate and Eurasian plate,and the switch of subduction direction of the paleo-Pacific plate from NWW to NW result in a north-south extension of the Jiaolai basin and the dextral strike-slip of the Muping-Jimo fault.Therefore,we propose that the apatite U-Pb age of the Mashan trachy-dacite documented the dextral strike-slip thermal event of the WQYF,and indicates that the dextral strike-slip may continue until Paleocene.
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