Objectives:There are large-scale Linzizong Group volcanic rocks from east to west Gangdese belt.Different scholars have diverse view on the causes of its formation.The Chima Area is located in the western segment of the Gangdese belt.This paper aims to study the annual and geochemical characteristics of the Nianbo volcanic rocks in Chima Area,to supplemented relevant data andevidence of the Linzizong group volcanic rocks of the western segment of the Gangdise belt.Methods:A total of 10 samples were collected in the study area,numbered as BC2023-1,BC4022-1,BPM701-8-3,BC 1803-1,BC 1802-2,BC2031-1,BC 1208,BC3214-2,BC4031-1,BPM271-2-2,BPM701-8-3 are both geochemistry sample and LA-ICP-MS sample,while BC1803-1,BC1802-2,BC4022-1,BC3214-2,BC2031-1 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 1Sigma.We used ICP MS Data Cal9.2 software to analyze the data,Isoplot to calculate the weighted average age and draw U-Pb concordia ages graph.10 geochemical samples were completed by the Southwest Metallurgical Geology Testlnstitute.The PHILLIPSPW-2404 X-ray fluorescence spectrometer was used to measure theprincipal 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) =72.46％ ～ 81.4％,w (A12 O3) =11.39％ ～ 12.72％,Alk(K2O+Na2O) =3.33％ ～8.5％,w(K20)/w(Na2O) =1.09～ 46.48,A/CNK=1.4 ～3.4,Rittmann indexδ =0.27 ～2.15.These features indicate that the rock belongs to peraluminous,potassic and ultrapotassic,calcium—alkali and alkaline rocks.Total REE content varies from 118.38 × 10-6 ～ 343.65 × 10-6,LREE/HREE =2.13 ～ 10.99,δEu =0.07 ～0.38,which shows enrichment of LREE and loss of HREE.The REE patterns is right-dipping.the rock has obvious negative Eu anomaly.The rock is characterized by enrichment of K、Rb、LREE and etc.LILE.and loss of Nb、P、Ti and etc.HFSE.Zircon U-Pb dating results show that volcanic rocks of the Nianbo formations was about 65 ～45Ma.which belongs to Paleocene and the Eocene epoch.Conclusions:the volcanic rocks of the Nianbo formationes in the study area ages was between Paleocene and the Eocene epoch,time was about 65 ～45 Ma.The age is older than the middle and eastern segment of Gangdise,10Ma before the eastern segment of Gangdise.The magma activity lasts longer than the volcanic rocks in the central and eastern parts of the country.mainly material sources derived from crust remelting,And they have a mixture of the mantle source,has mantle material assimilation contamination,New over time,the earth's crust material contribution to the enhanced.The volcanic rocks of the Nianbo formation in Chima area,was formed in the later stages of arcs environment,which in the tectonic setting of syn-collision and post-collision.%西藏措勤县赤马地区年波组火山岩大地构造位置位于隆格尔—工布江达复合岛弧带,岩石w(SiO2)=72.46％ ～81.4％;w(A12O3)=11.39％ ～ 12.72％;Alk(K2O+ NaO) =3.33％ ～8.5％;w(K20)/w(NaO)=1.09～46.68;A/CNK=1.4～3.4;里特曼δ=0.27 ～2.15,属过铝质的钾质、超钾质钙碱性—亚碱性的中酸性火山岩.稀土总量ΣREE=118.38 × 10-6～343.65×10-6;LREE/HREE=2.13～10.99;δEu=0.07 ～0.38,轻稀土富集,重稀土亏损,配分曲线呈右倾型,较明显的铕负异常.富集K、Rb、LREE等大离子亲石元素,而亏损Nb、P、Ti等高场强元素的特征,岩石显示出岛弧火山岩相似特征.锆石U-Pb定年结果显示,年波组火山岩成岩年龄约65 ～ 45 Ma间,为古新世—始新世.年波组火山岩显示出物质来源主要为地壳物质重熔和地幔物质同化混染,由老到新,地壳物质贡献增强.
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