西藏拉萨地块盐湖复式岩基中花岗斑岩的成因及其对班-怒洋闭合时限的制约  

The petrogenesis of the granite porphyry of Yanhu composite batholith in the Lhasa terrane,Tibet and its constraints on the time limit of Bangonghu-Nujiang Ocean closure

作　　者：史仲明 李宝龙[1] 彭勃 朱德全 范海滨 SHI Zhongming;LI Baolong;PENG Bo;ZHU Dequan;FAN Haibin(MNR Key Laboratory of Metallogeny and Mineral Assessment Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing 100037,China;Beijing Engineering Corporation Limited,POWERCHINA,Beijing 100024,China;248 Geological Brigade of Shandong Nuclear Industry,Qingdao 266041,Shandong,China;Shandong Provincial No.4 Institute of Geological and Mineral Survey,Weifang 261021,Shandong,China)

机构地区：[1]中国地质科学院矿产资源研究所自然资源部成矿作用与资源评价重点实验室,北京100037 [2]中国电建集团北京勘测设计研究院有限公司,北京100024 [3]山东省核工业二四八地质大队,山东青岛266041 [4]山东省地质矿产勘查开发局第四地质大队,山东潍坊261021

出　　处：《地质通报》2023年第5期788-801,共14页Geological Bulletin of China

基　　金：中国地质调查局项目《重点成矿区带铜金等矿产地质调查》(编号:DD20230033)、《战略性矿产重点远景区矿产地质调查》(编号:DD20221684);中国地质科学院矿产资源研究所基本科研业务费《西藏班戈县长给铅锌矿控矿因素与找矿方向研究》(编号:KK2107);国家自然科学青年基金项目《斑岩型矿床富Mo机制的矿物学制约--以班怒带荣嘎钼矿为例》(批准号:41802103)。

摘　　要：花岗质岩浆作用是大陆地壳演化、爆发式火山活动、稀有金属成矿等的关键过程。位于拉萨地块北部班公湖-怒江缝合带西段的盐湖复式岩基,是班公湖-怒江特提斯洋俯冲消减岩浆响应的重要组成部分。以西藏革吉县盐湖复式岩基中的花岗斑岩为研究对象,对其进行岩相学、锆石U-Pb年龄及岩石地球化学研究,探讨其成因。研究结果表明,盐湖复式岩基花岗斑岩的锆石U-Pb年龄为103.8±0.8 Ma(MSWD=3.0,n=25),侵位于早白垩世晚期。盐湖复式岩基花岗斑岩铝饱和指数(A/CNK)为1.05~1.08,显示弱过铝质特征,具有高K_(2)O、Na_(2)O含量,低Mg^(#)值(12.43~22.36)的特征,为高钾钙碱性I型花岗岩。盐湖复式岩基花岗斑岩富集K,亏损Ba、Nb、P、Zr、Ti,具有强的负Eu异常(δEu=0.20~0.48),稀土元素配分曲线呈轻稀土元素较陡、重稀土元素较平坦的右倾型,ΣREE=81.33×10^(-6)~121.61×10^(-6),LREE/HREE=5.75~6.74,具有较高的Y(20.14×10^(-6)~24.38×10^(-6),>18×10^(-6))和Yb(2.11×10^(-6)~2.62×10^(-6),>1.9×10^(-6))、较低的Sr/Y值(4.05~6.54,<20),La/Yb=6.79~8.94,Rb/Sr=0.50~1.12。锆石饱和温度计算结果为812~823℃,估算岩浆熔体形成深度为34~40 km,揭示盐湖复式岩基中花岗斑岩是玄武质下地壳于北拉萨地块与南羌塘地块碰撞阶段高温背景下部分熔融的产物,属于板片断离事件引起基性下地壳重熔,形成的高分异I型花岗岩。Granitic magmatism is one of the key processes of continental crust evolution,explosive volcanic activity,and rare metal mineralization.Yanhu composite batholith is located in the western section of Bangonghu-Nujiang suture zone in the north of Lhasa terrane,and is an important part of the response of Bangonghu-Nujiang Tethys Ocean subduction.In this paper,the petrography,zircon U-Pb chronology and petrogeochemistry of the granite porphyry in the Yanhu composite batholith from Geji County were studied,and its petrogenesis was discussed.The results show that the zircon U-Pb age of the Yanhu composite batholith granitic porphyry is 103.8±0.8 Ma(MSWD=3.0,n=25),and the intrusion occurred in the late Early Cretaceous.Aluminum saturation index(A/CNK)of Yanhu composite batholith granitic porphyry ranges from 1.05 to 1.08,showing weak peraluminous characteristics with high K_(2)O,Na_(2)O and low Mg^(#)(12.43~22.36),indicating the high K calc-alkaline type I-type granite.The Yanhu composite batholith granitic porphyry is enriched in K and depleted in Ba,Nb,P,Zr and Ti,and has strong negative Eu anomaly(δEu=0.20~0.48).The REE distribution curves are characterized by right-leaning type,ΣREE=81.33×10^(-6)~121.61×10^(-6),LREE/HREE=5.75~6.74,higher Y(20.14×10^(-6)~24.38×10^(-6),>18×10^(-6))and Yb(2.11×10^(-6)~2.62×10^(-6),>1.9×10^(-6)),lower Sr/Y ratio(4.05~6.54,<20),La/Yb=6.79~8.94.Rb/Sr=0.50~1.12.The calculated zircon saturation temperature is 812~823℃,and the formation depth of magmatic melt is estimated to be 34~40 km,indicating that the granitic porphyry formed in the Yanhu composite batholith was partially melted products of basaltic lower crust under the high temperature background of the collision between the North Lhasa terrane and the South Qiangtang terrane.It belongs to a set of highly differentiated I-type granites formed by remelting of the basic lower crust caused by plate fragmentation events.

关 键 词：盐湖复式岩基 锆石U-Pb年龄 岩石地球化学 班公湖-怒江缝合带 早白垩世 地质调查工程 

分 类 号：P588.121[天文地球—岩石学] P534.53[天文地球—地质学]