Geochemical Characteristics And Petrogenesis Of Early Cretaceous Granites In Central Great Xing'an Range

This thesis focuses the Mesozoic granites in Zhalantun-Arxan area,central Great Xing'an Range,and we undertook geochronological,geochemical,zircon Hf isotopic analyses of these granites based on the field regional geological survey.Combined with previous research results,the formation age,petrogenesis and tectonic geological significance of granites in the study area are discussed.LA-ICP-MS zircon U-Pb dating shows that the granites in the study area were formed in the Early Cretaceous(140?130Ma).Whole rock geochemical data show that the Early Cretaceous granites in the study area are high in silica(Si O₂=74.00?77.29 wt.%),alkali(K₂O+Na₂O=8.52?8.90 wt.%),low in calcium(Ca O=0.21?0.71 wt.%),and low in magnesium(Mg O=0.06?0.48 wt.%),showing metaluminous to weak peraluminous(A/CNK=0.98?1.06)and high-K calc-alkaline series.In addition,the Early Cretaceous granites in the study area show a typical right-dipping REE distribution pattern,with significant negative Eu anomalies,enrichment of large ion lithophile elements(LILEs)and depletion of high field strength elements(HFSEs).Combined with the geochemical characteristics of Zr/Hf(14.58?30.46),Nb/Ta(7.46?11.47),high differentiation index(93.19?96.93)and depleted Hf isotopic composition of the Early Cretaceous granites in the study area,we suggested that the granites were highly differentiated I-type granites,and were derived from the partial melting of young crustal materials from the Mesoproterozoic to the Early Paleozoic.Based on the above research results and the spatio-temporal variation of late Mesozoic magmatism in Northeast China,we suggest that the Early Cretaceous granites in the Zhalantun-Arxan area of central Great Xing'an Range were formed in an extensional environment,which may be closely related to the rolling of the Paleo-Pacific plate.