西藏岗讲斑岩铜钼矿床黑云母二长花岗斑岩的成因和构造背景  

PETROGENESIS AND TECTONIC SETTING OF THE BIOTITE MONZONITIC PORPHYRY FROM THE GANGJIANG PORPHYRY Cu-Mo DEPOSIT,TIBET,CHINA

作　　者：赵长歌 邹光富[2] 毛英 张庆松[4] 郑立波[4] ZHAO Changge;ZOU Guangfu;MAO Ying;ZHANG Qingsong;ZHENG Libo(Henan Institute of Engineering,Zhengzhou,Henan 450000,China;Chengdu Institute of Geology and Mineral Resources,Chengdu,Sichuan 610082,China;Chengdu Comprehensive Rock and Mineral Testing Center,Chengdu,Sichuan 610081,China;Sichuan Institute of Metalallurgical Geology and Exloration,Chengdu,Sichuan 610051,China)

机构地区：[1]河南工程学院,河南郑州450000 [2]中国地质调查局成都地质调查中心,四川成都610081 [3]成都岩矿分析测试中心,四川成都610081 [4]四川省冶金地质勘查院,四川成都610051

出　　处：《矿物岩石》2023年第1期96-105,共10页Mineralogy and Petrology

基　　金：中国地质调查局项目(编号:12120114080701)。

摘　　要：西藏岗讲斑岩铜钼矿床位于冈底斯斑岩铜矿带尼木斑岩铜矿田中。该区中-酸性岩浆活动较为发育,形成以黑云母二长花岗斑岩为主的含矿斑岩体。为限定冈底斯斑岩铜矿带岗讲铜钼矿床含矿斑岩体的形成时代及成因背景,本次研究对成矿黑云母二长花岗斑岩进行了LA-ICP-MS锆石U-Pb定年和地球化学研究。锆石U-Pb年代学分析揭示,岗讲黑云母二长花岗斑岩形成于中新世(14.47±0.19 Ma)。岩石地球化学研究表明,岗讲黑云母二长花岗斑岩的w(SiO_(2))为69.12%~72.62%,w(Al_(2)O_(3))为13.31%~15.57%、K_(2)O/Na_(2)O为0.76~1.66。属于钾玄岩系列-高钾钙碱性系列,为过铝质花岗岩。岩石的ΣREE为83.19×10^(-6)~154.28×10^(-6),轻、重稀土分异明显,(LREE/HREE)=3.57~14.73,(La/Yb)N值为31.4~39.5,δEu为0.83~1.29,具有较弱的负Eu异常;稀土元素配分曲线呈右倾型,显示轻稀土元素相对重稀土元素富集。大离子亲石元素Rb,Sr相对富集,高场强元素Nb,Nd,Zr等相对亏损。岩石具有较高的Al_(2)O_(3)含量,w(MgO)含量低(0.82%~1.13%);具有较高的Sr含量(265×10^(-6)~572×10^(-6))和低的Y(4.96×10^(-6)~8.12×10^(-6))、Yb(0.35×10^(-6)~0.68×10^(-6))含量,Sr/Y比值为53.43~70.44,(La/Yb)N比值为31.4~39.5,显示出埃达克岩的性质。根据岩石地球化学特征和微量元素构造判别图解判别结果,表明岗讲黑云母二长花岗斑岩可能起源于新生下地壳角闪岩相,源区内有幔源物质参与。岗讲黑云母二长花岗斑岩为新生增厚下地壳部分熔融的产物,起源于含石榴子石角闪岩相下地壳的部分熔融。岗讲黑云母二长花岗斑岩形成于喜马拉雅期印度板块与拉萨板块碰撞后期下地壳加厚的伸展构造阶段,为加厚下地壳部分熔融的产物,是印度与亚洲大陆碰撞期后伸展构造背景下的岩浆活动响应。The Gangjiang porphyry Cu-Mo deposit is located in Nimu porphyry copper field of Gangdise porphyry copper belt in Tibet,which is characterized by Intermediate-acid magmatic activity and forms a mineralized porphyry body dominated by biotite monzonite granite porphyry.In this paper,LA-ICP-MS zircon U-Pb dating and geochemistry of biotite monzonite granite porphyry have been studied to define the age and genetic background of ore-bearing porphyry in the Gangjiang Cu molybdenum deposit.Zircon UPb chronology analysis reveals that the Gangjiang biotite monzonite granite porphyry was formed during the Miocene(14.47±0.19 Ma).The geochemical study shows that the contents of zw(SiO_(2)),w(Al_(2)O_(3))and K_(2)O/Na_(2)O are 69.12%to 72.62%,13.31%to 15.57%and 0.76 to 1.66 respectively,characteristic of potassic basalt series-high potassic calc-alkaline series,and belongs to peraluminous granite.The ZREE of the rocks is 83.19×10^(-6)to 154.28X10^(-6),and the difference between the light and heavy rare earths is obvious,(LREE/HREE)=3.57-14.73,(La/Yb)n value is 31.4 to 39.5,Eu is 0.83 to 1.29,showing a weak negative Eu anomaly.The distribution curve of rare earth elements is right-leaning,indicating that light rare earth elements are enriched compared to heavy rare earth elements.Large ion lithophile elements Rb and Sr are relatively enriched,while high field strength elements Nb,Nd and Zr are relatively deple-ted.The rock has high Al,O:content and low MgO content(0.82%~1.13%),with high Sr content(265×10^(-6)to 572×10^(-6))and low Y content(4.96×10^(-6)to 8.12×10^(-6))and Yb content(0.35×10^(-6)to 0.68×10^(-6)).The Sr/Y ratio is 53.43 to 70.44 and the N ratio of(La/Yb)n is 31.4 to 39.5,characteristic of Adakite.According to the geochemical features of the rocks and the tectonic discrimination diagram of trace elements,the biotite monzonite granite porphyry was likely to be originated from the amphibolite facies of the new lower crust,with addition of mantle materials in the source area.It is considered that the biotite

关 键 词：黑云母二长花岗斑岩 锆石U-PB定年 岩石成因 岗讲斑岩铜钼矿床 西藏 

分 类 号：P548[天文地球—构造地质学] P597[天文地球—地质学]