摘要
西藏拉萨地块阿翁错—盐湖岩浆弧的成因是解决班公湖—怒江特提斯洋俯冲极性和时限的关键。本文选取阿翁错北岩体中的二长花岗岩进行岩相学、锆石U-Pb年代学、岩石地球化学与Hf同位素研究。结果表明:阿翁错北二长花岗岩的锆石^(206)Pb/^(238)U加权平均年龄为(107.0±0.5)Ma,MSWD=2.6,属早白垩世晚期。样品表现为高硅、富钾的高钾钙碱性岩石系列,A/CNK值介于1.006~1.019之间,属弱过铝质;微量元素富集大离子亲石元素Rb、K、U、Th及轻稀土元素(LREE),亏损Nb、Ta、P、Ti等高场强元素,具中等至弱的负Eu异常(δEu=0.55~0.78),属弱过铝质未分异的I型花岗岩。二长花岗岩样品锆石初始Hf同位素_(εHf)(t)值除1颗锆石达11.1外,其他17颗锆石介于3.7~6.3之间,平均值5.0,Hf同位素二阶段模式年龄变化于928~765 Ma之间。基于同位素以及岩石地球化学数据,阿翁错北岩体很可能是新生地壳熔融产生的长英质岩浆与镁铁质岩浆发生不均一混合作用形成,并有少量幔源物质的参与。结合拉萨地块中北部岩浆岩Hf同位素研究分析,阿翁错—盐湖岩浆弧形成于班公湖—怒江特提斯洋后退式俯冲的构造体制下,阿翁错北岩体的形成时代(107~104 Ma)代表了由断离板片俯冲末期向碰撞环境转化的时限。
The Petrogenesis of the Awengcuo-Yanhu magmatic arc in Lhasa terrane is the key to solve the subduction polarity and time of the Bangong-Nujiang Tethy Ocean.In this paper,the monzonitic granite in the north Awengcuo was selected for petrography,geochemistry,zircon U-Pb geochronology and Hf isotopic studies.The zircon^(206)Pb/^(238)U weighted mean age of the monzonitic granite is(107.0±0.5)Ma,MSWD=2.6,belonging to the Late Early Cretaceous.The samples are a series of high-silicon and potassium-rich high-potassium calc-alkaline rocks with A/CNK values ranging from 1.006 to 1.019,belonging to weak peraluminum.The trace elements are enriched in large ion lithophile elements Rb,K,U,Th and LREE,depleted in high field strength elements such as Nb,Ta,P,Ti,with moderate to weak negative Eu anomalies(δEu=0.55-0.78),belonging to a weakly peralumious undifferentiated I-type granite.The monzonitic granite yields the zircons_(εHf)(t)values of 3.7-6.3 with a mean of 5.0,except for one characteristic value of 11.1,and the model ages(t_(DM2))range from 928 Ma to 765 Ma.Based on integrated isotopic and geochemical data,the north Awengcuo pluton is probably formed by the heterogeneous mixing of felsic magma and mafic magma generated by the melting of the juvenile crust,with the participation of a small amount of mantle-derived materials.Combined with Hf isotope analysis of magmatic rocks in the north-central Lhasa terrane,the Awengcuo-Yanhu magmatic arc was formed under the tectonic regime of the backward subduction of the Bangong-Nujiang Tethy Ocean,and the formation age of the pluton from the north Awengcuo(107-104 Ma)represents the time for the transformation from the end of slab break-off to the collision environment.
作者
彭勃
赵拓飞
李宝龙
史仲明
Peng Bo;Zhao Tuofei;Li Baolong;Shi Zhongming(MNR Key Laboratory of Metallogeny and Mineral Assessment,Institute of Mineral Resources,Chinese Academy ofGeological Science,Beijing 100037,China;Chinese Academy of Natural Resources Economics,Beijing 101149,China;School of Economics and Management,China University of Geosciences(Beijing),Beijing 100083,China;School of Earth Science and Mineral Resources,China University of Geosciences(Beijing),Beijing 100083,China)
出处
《吉林大学学报（地球科学版）》
CAS
CSCD
北大核心
2022年第5期1594-1609,共16页
Journal of Jilin University：Earth Science Edition
基金
国家重点研发计划项目(2021YFC2900100)
中国地质科学院矿产资源研究所基本科研业务费专项(KK2018,KK2017)
