Zircon U-Pb dating of Bolongke A-type granite on the margin of northern North China Plate and its geological significance

Bolongke granite, emplaced in the Upper Jurassic volcanic strata, is located on the north margin of the North China Craton (NCC).Detailed petrographical observation reveals that the granite occurs in the forms of euhedral and subeuhedral crystals and exhibits mymekitic and pegmatitic texture and massive structure.Sencitization and argillation exist in part of plagioclases caused by weathering. The LA-ICP-MS analysis of zircons yielded empkcement ages of 134.0±1.8Ma(MSWD=1.8) and 134.9±4.1Ma(MSWD=2.0), indicating that the Bolongke granite was fomied in the Early Cretaceous.A geochemical study of the intrusion suggests that it belongs to high-K calc-alkaline series and is characterized by depletion of Ba, Sr and enrichment of such elements as Rb, Th, Pb and Hf, with obviously negative Eu anomalies. To sum up, the intrusion shows the charactejstics of A-type granite. Tectonic discrimination diagrams indicate that Bolongke granite was fomed in an anorogenic extension environment. Combined with the achievements obtained by previous researchers, the authors tentatively hold that the emplacement of Bolongke granite belonged to the Mesozoic magmatic events in the North China Craton and was produced by lithospheric thinning.