塔吉里霞隆花岗闪长岩体位于冈底斯构造岩浆岩带西段,拉萨地块中西部.岩石w(SiO2)=63.38％ ～72.56％;w(Al2O3)=13.85％～15.73％;Alk(K2O+ Na2O)=5.12％～6.79％;w(K2O)/w(Na2O) =0.67～ 1.32;A/CNK =0.90～ 1.02,属Ⅰ型弱过铝质高钾钙碱性系列.稀土总量∑REE=128.34×10-6～ 167.25×10-6,LREE/HREE=6.94 ～ 10.73,轻稀土富集,重稀土亏损,配分曲线呈右倾型;δEu =0.69～0.86,弱负铕异常.岩石具有富集Rb、Th、K等大离子亲石元素,而亏损Ba、U、Nb、P等高场强元素的特征,岩石显示出岛弧火山岩亲缘性.锆石U-Pb定年结果表明,塔吉里霞隆岩体主要侵位于126.3±1.1Ma,属早白垩世晚期.塔吉里霞隆花岗闪长岩显示出壳幔混合源特征,班公湖—怒江洋壳岩石圈的南向俯冲和随后发生的板片回转可以较好的解释岩体成因.%Objectives:There are large-scale Early Cretaceous magrnatite from east to west Gangdese belt.Different scholars have diverse view on the causes of its formation.Tajilixialong granodiorite is located in the west part of Gangdese tectonic magmatite belt,middle—western Lhasa block.This paper reports whole-rock geochemistry,zircon U-Pb age of Tajilixialong early Cretaceous granodiorite.Methods:A total of 4 granodiorite samples were collected in the study area,numbered as BN8201-1,BN6156-1,BN6157-1,BN4101-DY.BN6156-1,BN8201-1 are both geochemistry sample and LA-ICP-MS sample,while BN4101-DY,BN6157-1 are just geochemistry sample (3 other geochemistry data was cited).Zircon U-Pb isotope analysis was completed by Agilent 7500a ICP-MS instrument at the State Key Laboratory of ore deposit geochemistry,Institute of Geochemistry,Chinese Academy of Sciences.The diameter of analysis laser beam is 30μm.Standard zircon 91500 (age 1064Ma) and GJ1 (age 600Ma) are used as external calibration,NIST SRM 610 29Si as internal calibration.The standard error is ISigma.We used ICP MS Data Cal 9.2 software to analyze the data,Isoplot to calculate the weighted average age and draw U-Pb concordia ages graph.4 geochemical samples were completed by the Southwest Metallurgical Geology Test Institute.The PHILLIPSPW-2404 X-ray fluorescence spectrometer was used to measure the principal component,its accuracy was better than 1％.Trace elements and REE elements were determined by ELEMENT-2 MS,which was better than 2％ in accuracy.Results:Geochemistry analysis shows that:the rock is w (SiO2) =63.38 ％ ～ 72.56％,w (Al2 O3) =13.85 ％ ～ 15.73 ％,Alk (K2O + Na2 O) =5.12 ％ ～ 6.79 ％,w (K2 O)/w (Na2 O) =0.67 ～ 1.32,A/CNK =0.90 ～ 1.02.These features indicate that the rock belongs to weakly peraluminous calc-alkaline type Ⅰ series.Total REE content varies from 128.34 × 10-6 ～ 167.25 × 10-6,LREE/HREE =6.94 ～ 10.73,which shows enrichment of LREE and loss of HREE.The REE patterns is right-dipping.δEu =0.69 ～ 0.86 indicates that the rock has weak negative Eu anomaly.The rock is characterized by enrichment of Rb,Th,K and other LILE,and loss of Ba,U,Nb,P and etc.HFSE.Zircon U-Pb dating results show that Tajilixialong granodiorite mainly intruded at 126.3 ± 1.1Ma,which belongs to the late Early Cretaceous.Conclusions:The rock characteristic of enrichment of LILE and loss of HFSE shows the rock is island arcvolcanic affinity.Tajilixialong granodiorite mainly intruded at 126.3 ± 1.1Ma,this is consistent with the large-scale Cretaceous magmatism era of Lhasa block.The rock has strong fractionation between LREE and HREE,enriched in Rb,Th,K,Zr,Hf and depleted in Ba,U,Nb,Sr,P,Ti.These features are the effect of island arc magmatism.The rock-magma may originated from partial melting of ancient lower crust,and mixed with mantle derived magma.The weak negative Eu anomaly of rock indicates that the magma source region may also exist plagioclase residual phase.The genesis of Tajilixialong granodiorite can be attribute to southward subduction of Bangong Co—Nujiang River oceanic seafloor and plate rotary afterwards.Mixed magma upwelled along the plate tectonic window,intruded,subsequent formed the Tajilixialong granodiorite.
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