The Petrogenesis And Tectonic Implication Of Ca.2.5 Ga A-Type Granite In The Zanhuang Complex, North China Craton

The Zanhuang Complex,situated in the central of the North China Craton,retains abundance of Neoarchean-Paleoproterozoic volcanic-sedimentary rock records,and plays an important role in probing the evolutionary processes in the North China Craton.Petrogenesis and tectonic setting of the late Neoarchean TTG gneisses and granites is the key to unveiling the evolution of the Zanhuang Complex.In this paper,we choose the Huangcha granite which is located in western Xingtai of Hebei Province,and present petrologic,geochemical,zircon U-Pb and Lu-Hf isotopic data and discuss on the petrogenesis and tectonic background of this granite,and obtained following conclusions:1.This pluton is an irregular stock,and shows a structure contact with the surrounding strata locally intruding into the Guandu Group.The granite consists mainly of gneissic and porphyritic monzonite in which rare melanocratic enclaves are present.The phenocryst is mainly potassium feldspar and quartz.2.The granite is high in SiO₂,K₂O,Fe₂O₃^T and alkali,and low in Ca O,TiO₂ and MgO.It is high in total REE contents in which the differention of LREE and HREE is stronger and shows obvious negative Eu anomaly.In trace elements,the granite shows enrichment in Zr,Zn,Nb,Ga and Y and depletion in Sr,V,Cr,Co and Ni,with high Rb/Sr and Ga/Al ratios.Zircon saturation temperatures range from 780?to 877?,which is consistent with A-type granite presenting high temperature feature.3.Three granite samples yield zircon ²⁰⁷Pb/²⁰⁶Pb ages of 2488±6 Ma,2480±15 Ma and 2467±17 Ma,respectively.Based on the Huangcha granite intruding into the Guandu Group,we propose the Guandu Group formed in Archean,but not the Paleoproterozoic.4.Zircons in the Huangcha granite have?_Hf?t?values ranging from 0.94 to 6.18,and Hf model T_DM1 ages of 2553²747 Ma and T_DM2 ages of 2576²826 Ma.The Huangcha granite shows the features of post-orogenic A-type granite formed by anatexis of the Neoarchean TTG in an extensional setting after orogenic processes.5.The ca.2.5 Ga alkaline granites occur in different areas of the North China Craton and form in extensional tectonic setting,which further indicate the initial amalgamation of the North China Craton in the late Archean.