崂山早白垩世高分异Ⅰ型花岗岩地球化学特征及岩石成因机制OA北大核心CSTPCD

Laoshan granites are widely distributed in Jiaodong area.Their typology,magma source and petrogenesis are still controversial,and the magmatic evolution and petrogenesis of highly fractionated Ⅰ-type granite have not been well constrained.In this study,the Laoshan Early Cretaceous granites are selected as the research theme.The granites are analyzed by petrology and petrography,whole rock major and trace elements,zircon U-Pb dating and Lu-Hf isotopes,plagioclase electron probe analysis.LA-MC-ICP-MS zircon U-Pb dating results show that the dia-genetic ages of quartz monzonite,monzogranite,syenogranite and granitic porphyry in Laoshan are 128.6±2.7 Ma,122.8±2.5 Ma～118.6±1.2 Ma,121.5±2.7 Ma～121.3±1.2 Ma and 114.5±1.2 Ma,respectively,indicating that they were all emplaced during the Early Cretaceous.The geochemical composition of Laoshan granites show high contents of silicon and alkali,low abundances of aluminum,magnesium and iron.They are also depleted in Rb,Th,U,Ba and Sr,with significant negative Eu anomaly.The zircons εH f(t)values of Laoshan granites range from-21.0 to-15.1,and Hf isotope second-stage model ages(tDM2)range from 2 482 to 2 149 Ma.Based on mineralogical,petrological and geochemical evidence,the quartz monzonite and monzogranite are Ⅰ-type granites,and the syenogranite and granitic porphyry are classified are high fractionated Ⅰ-type granites.Combined with the previous researches results in Jiaodong area,in the extensional tectonic setting generated by the subduction of the Paleo-pacific plate,magmas from the asthenosphere underplated into the lower crust,inducing partial melting of the lower crust material to form felsic magmas.After different degrees of fractional crystallization and evolution of felsic magmas,granites with varying degrees of differentiation in Laoshan area are formed ultimately.