西藏则学地区俄穷瓦二长岩体的年代学、岩石地球化学特征及构造环境分析  

Chronology,Geochemical Characteristics and Tectonic Settings of the Late Yanshanian Granitoids in Zexue Area,Tibet

作　　者：丁鹏飞[1] 魏启荣[1] 王程[1] 张小强[1] 孙骥[1] 卜涛[1] 刘小念[1] 王敬元[1] 高满新 

机构地区：[1]中国地质大学资源学院,武汉430074

出　　处：《地质科技情报》2014年第4期37-45,59,共10页Geological Science and Technology Information

基　　金：中国地质调查局西藏则学地区矿产远景调查项目(1212011086040)

摘　　要：西藏则学地区在构造上属冈底斯弧背断隆带。以西藏则学地区俄穷瓦二长岩体为研究对象,从野外地质、岩石学、LAICP-MS锆石U-Pb定年、岩石地球化学特征等方面对其进行了研究。结果表明,俄穷瓦岩体的岩石类型主要为细粒黑云母石英二长岩,次为细粒黑云母二长岩。形成于晚白垩世(K2),其LA-ICP-MS锆石U-Pb年龄为(85.58±0.66)^(81.78±0.74)Ma。主量元素表现出低硅[w(SiO2)=62.31%~66.59%]、富Al[w(Al2O3)=14.96%~16.02%]、高K[w(K2O)=3.38%~4.33%]、低Ti[w(TiO2)=0.68%~0.99%]和高钾钙碱性系列的岩石地球化学成分特征;稀土元素配分模式为轻稀土元素强烈富集的右倾型,其(La/Yb)N为20.70~27.20,具中等程度的负铕异常(Eu/Eu*=0.64~0.74);微量元素显示出富Rb、Th、U元素和强烈亏损Nb、Ta、P、Ti元素的特点。俄穷瓦二长岩体形成于陆缘弧环境,是雅江洋板片北向俯冲于拉萨地体之下所形成的冈底斯弧背断隆带(GRUB)中燕山晚期构造-岩浆活动的岩浆产物。The late Yanshanian granitoids in Zexue area belongs to the Gangdese back-arc fault uplift belt,which is located in Xietongmen,Rikaze,Tibet.The Granitoids in that area mainly consists of fine grained biotite monzonlites.In order to investigate the age of formation,geochemical characteristics and tectonic settings,LA-ICP-MS U-Pb age dating,the major elements,REE elements and trace elements are reported in this paper.The LA-ICP-MS ages of zircon of two samples,B0537-1and B0989-1,formed in 81.78±0.74Ma and 85.58±0.66Ma,suggest that the granitoids formed in late Cretaceous.Petrogeochemically the Granitoids consists relatively low Si（SiO2=62.31%-66.59%）,high Al（Al2O3=14.96%-17.46%）,high K（K2O=2.63%-4.33%）,low Ti（TiO2=0.68%-0.99%）contents,and is mainly composed of high-K calcalkaline series.REE patterns show LREE enrichment of the rightist-type[（La/Yb）N=8.55-27.20]and the negative Eu anomalies are moderate（Eu/Eu＊=0.64-0.74）.Trace element primitivemantle-normalized spider diagram displays apparent enrichments of large ion lithophile elements（LILE）Rb,Th and U.High field strength elements（HFSE）Nb,Ta,P and Ti are sharply depleted.Granitoids occurred in continental marginal arc,which was part of the Gangdese back-arc fault uplift belt and magma product by the Yalung Zangbo neo-Tethyan Ocean northward subduct beneath Lhasa Terrane.

关 键 词：俄穷瓦岩体 锆石U-PB定年 岩石地球化学 构造环境 西藏则学地区 

分 类 号：P597[天文地球—地球化学]