Zircon U-Pb geochronology,whole-rock geochemical,and Sr-Nd-Pb isotopic constraints on the timing and origin of Permian and Triassic mafic dykes from eastern North China Craton

作者：Shen Liu,Caixia Feng,Yan Fan,Xiaoqing Chen,Yuhong Yang,Huibo Zhao,Ian MCoulson

摘要：This work reports an important episode of extensional,mafic magmatism that impacted the North China Craton(NCC)during the Permo-Triassic and influenced the evolution of this Craton.We sampled 30 representative mafic dykes cropping out in eastern NCC,within the Hebei Province,China.New zircon LA-ICP-MS U-Pb ages,geochemical,and Sr-Nd-Pb isotopic data for these mafic dykes identified them as typical dolerites formed between 211.9±1.3 and 263.9±2.6 Ma.The mafic rocks fall into the alkaline and calc-alkaline series.They are enriched in light rare earth elements,some large ion lithophile elements(e.g.,Rb.Ba,and Sr),K,and Pb,and depleted in Nb,Ta,and Ti.The dykes have high initial 87Sr/86Sr ratios(0.7034-0.7178),negative eNd(t)values(—2.2 to—5.9),and relatively constant initial Pb isotopic ratios,that are EMI-like:(206Pb/204Pb)i=16.39-16.74,(207pb/204pb)j=15.22-15.24,and(208Pb/204Pb)i_=36.66-36.86,respectively.Our results indicate that the Hebei Province dolerites were likely derived from magma gen erated through low-medium degree partial melting(3.0-20%)of an EMI-like garnet-lherzolite mantle source.The parental magmas fractionated olivine,clinopyroxene,and Ti-bearing phases with obvious crustal contamination during rapid ascent and dyke emplacement.Since the possible influence of subduction of the Yangtze Plate has been excluded,we propose a model for the origin of the investigated mafic rocks,involving the Pennian collision between the Siberian Block and the NCC.The mafic dykes of eastern NCC within Hebei Province formed during a period of crustal thinning in response to extension after the early Permian collision.

发文机构：State Key Laboratory of Continental Dynamics and Department of Geology College of Earth Sciences Solid Earth Studies Laboratory

关键词：PERMO-TRIASSICDOLERITEORIGINNCCSiberianblock

分类号： F42[经济管理—产业经济]