Geochronology,Geochemical Characteristics And Geological Significance Of The Nailinba Pluton In Bairin Left Banner,Inner Mongolia

Daxing'anling is an important Nonferrous metal ore concentration area in northern China,especially the large-scale Indosinian tectonic-magmatic activity in this area is closely related to large-scale mineralization at the same period.In this paper,the Nanlinba pluton is selected as the research object.Through the detailed petrography,zircon U-Pb chronology,geochemistry and Hf isotope composition study we discusse Nailinba pluton diagenetic age,petrogenic type,tectonic dynamics background,and source..The Late Permian-Early Triassic granites in the Nailinba mainly include biotite syenite and monzonitic granite.Zircon LA-ICP-MS U-Pb dating results show that the age of biotite syenite is 241.7�1.9 Ma,and 256.7�4.6 Ma,the age of monzonitic granite is 241.5�1.7 Ma.The main content of plaque-like biotite granite is characterized by high silicon?72.72-72.99 wt.%?,alkali-rich?7.26-8.32 wt.%?,high potassium?3.11-5.69 wt.%?and aluminum-rich?13.6-14.2 wt.%?,The monzonitic granite has the characteristics of relatively low SiO₂ content?67.78-69.53 wt.%?,alkali-rich?10.24-10.51 wt.%?,and aluminum-rich?16.01-16.19 wt.%?,all of which belong to the high-priced calc-alkaline-potassium series.The Litman index???ranges from 1.16 to 1.23,which belongs to the metaluminum-weak peraluminous range.According to the characteristics of the main elements,the spot of the main elements shows that the magma is derived from the mafic source The total content of rare earth elements in biotite granite is relatively low,?REE=140.41-144.88 ppm,and the total content of rare earth elements in monzonitic granite is high,?REE=325.7-328.39 ppm,the rock is relatively enriched with light rare earth elements,?La/Yb?_N=9.78-42.31,Eu is weak to moderate negative anomalies??Eu=0.2-0.58?,and the rock REE shows a right-inclined trend.The rocks are relatively enriched in elements such as Rb,Th,U,K,and Pb,and are depleted of Nb,Ta,Ti,etc.This characters similar to the characteristics of high-field strength elements in island arc magma.The mineralogical and geochemical characteristics show a high degree of crystallization differentiation.Both the plaque-like biotite syenite and the monzonitic granite of Nailinba have positive?_Hf?t?values,and the?_Hf?t?value of the plaque-like biotite syenite is+11.12-+11.84,and the?_Hf?t?of the quartz monzonite.The value is+9.97-+14.43.The zircon Hf isotope characteristics indicate that both acidic magma are derived from the young crust.The Late Permian granite in the Nanlinba pluton is an aluminum I-type granite,which is formed in the tectonic setting of the oceanic crust during the closed collision phase.