青藏高原拉萨地体中西段亚日二长花岗岩岩石成因及构造意义:年代学、地球化学及Hf同位素证据  

Petrogenesis and tectonic significance of the Yari granites in the west-middle segment of the Lhasa Terrane,Tibet:Evidences from geochronology,geochemistry and Hf isotope

作　　者：陶刚 杨远江[3] 杨文光 朱利东[2] 祁欣[4] 卢志友 何碧 TAO Gang;YANG Yuanjiang;YANG Wenguang;ZHU Lidong;QI Xin;LU Zhiyou;HE Bi(School of Environment and Resource,Southwest University of Science and Technology,Mianyang 621010,Sichuan,China;Institute of Sedimentary Geology,Chengdu University of Technology,Chengdu 610059,Sichuan,China;School of Civil and Architectural Engineering,East China University of Technology,Nanchang 330013,Jiangxi,China;Changsha Natural Resources Comprehensive Survey,China Geological Survey,Changsha 410600,Hunan,China;The Second Institute of Geology and Minerals Exploration Team,Gansu Provincial Bureau of Geology and Minerals Exploration and Development,Lanzhou 730020,Gansu,China)

机构地区：[1]西南科技大学环境与资源学院,四川绵阳621010 [2]成都理工大学沉积地质研究院,四川成都610059 [3]东华理工大学土木与建筑工程学院,江西南昌330013 [4]中国地质调查局长沙自然资源综合调查中心,湖南长沙410600 [5]甘肃省地质矿产勘查开发局第二地质矿产勘查院,甘肃兰州730020

出　　处：《地质通报》2021年第8期1344-1356,共13页Geological Bulletin of China

基　　金：中国地质调查局项目《西藏唐加地区15万区域地质调查》(编号:DD20160015);西南科技大学博士基金(编号:18zx7115)。

摘　　要：广泛分布在拉萨地体的中生代岩浆岩越来越受到地质学者的关注和研究,其研究成果对拉萨地体演化过程具有重要地质意义,而拉萨地体西段晚侏罗世亚日二长花岗岩体岩石成因、岩浆源区性质目前尚未得到很好地约束。对拉萨地体中西段亚日二长花岗岩体进行岩石学、锆石U-Pb年代学、地球化学及Lu-Hf同位素特征研究,结果显示岩体锆石U-Pb年龄为152.1±1.5 Ma,表明其形成于晚侏罗世。二长花岗岩SiO 2含量为73.55%~74.19%,P 2 O 5为0.12%~0.14%,铝饱和指数(A/CNK)为1.07~1.23,主要为一套过铝质高钾钙碱性系列。稀土元素总量(ΣREE)在104.12×10^(-6)~247.22×10^(-6)之间,(La/Yb)N值为32.14~51.03,明显富集轻稀土元素,具有明显的负Eu异常(δEu=0.54~0.68),稀土元素配分型式呈右倾特征;微量元素特征显示,样品具有富集大离子亲石元素(LILE)Rb、Th、U,亏损高场强元素(HFSE)Nb、Ti的特征,整体显示其为一套高钾钙碱性系列强过铝质S型花岗岩。岩石学、年代学及地球化学研究综合表明,新特提斯洋壳向北和班公湖-怒江洋壳向南的双向俯冲作用引起冈底斯微陆块与下察隅岩浆弧带发生陆-弧碰撞,而被板块俯冲作用卷入新生地壳的泥质岩夹杂砂岩在受热后抬升减压过程中发生部分熔融,形成晚侏罗世亚日S型二长花岗岩,同时研究区在晚侏罗世可能处于构造背景体制的转换阶段,即可能处于由俯冲向碰撞作用过渡的演化过程。More geological researchers are focusing on the Mesozoic magmatic activities of Lhasa terrane,which is significant for the evolution of the Lhasa terrane.But the petrogenesis and magmatic origin of the Late Jurassic Yari Granites(YRG)remain poorly constrained.This study presents petrology,zircon U-Pb ages,geochemistry,and Lu-Hf isotopic data of YRG.The zircon U-Pb age of the pluton is 152.1±1.5 Ma,indicating that it was formed in the Late Jurassic.The YRG are mainly adamellite characterized by high silicon(SiO 2=73.55%~74.19%),rich alkali,peraluminous and poor MgO,MnO and P 2 O 5(0.12%~0.14%).It belongs to the series of high potassium calc-alkaline with high degree of differentiation.It is characterized byΣREE of 104.12×10^(-6)~247.22×10^(-6),(La/Yb)N of 32.14~51.03,enrichment of light rare earth elements(ΣLREE),obvious negative Eu anomaly(δEu=0.54~0.68)and right-dipping distribution pattern of rare earth elements.It is enriched in Rb,Th,U and other large ion lithophile elements,and depleted in Nb,Ti.It belongs to highly differentiated S-type granite.Its petrology,geochronology and geochemistry indicate that the double subduction of the Neo-Tethys’northward subduction and Bangong-Nujiang Ocean’southward subduction led to the collision between the Gandese micro-continent and Chayu magmatic arc.The YRG were highly fractionated S-type adamellite and the source area might be related to the partial melting of mudstone with greywacke under the tectonic decompression settings.It is proposed that during the Late Jurassic,the Lhasa terrane area experienced a tectonic transformation from subduction to collision.

关 键 词：青藏高原 拉萨地体 锆石U-PB测年 地球化学 S型花岗岩 新特提斯洋 班公湖-怒江洋 

分 类 号：P534.52[天文地球—古生物学与地层学] P588.12[天文地球—地质学]