西藏岗讲斑岩铜钼矿床花岗闪长斑岩锆石U-Pb年代学及地球化学特征  

The Zircon U-Pb Chronology and Geochemical Characteristics of Granodiorite Porphyry in the Gangjiang Porphyry Cu-Mo Deposit,Tibet,China

作　　者：姜华[1,2] 李文昌 张雄[4] 杨帆 JIANG Hua;LI Wen-chang;ZHANG Xiong;YANG Fan(Kunming University of Science and Technology,Kunming 650093,China;Yunnan Copper Co.Ltd.,Kunming 650000,China;Chengdu Center of China Geology Survey,Chengdu 610081,China;Beijing Institute of Geology for Mineral Resources,Beijing 100012,China;Yunnan Copper Industry Mineral Resources Exploration Development Co.Ltd.,Kunming 650000,China)

机构地区：[1]昆明理工大学,昆明650093 [2]云南铜业股份有限公司,昆明650000 [3]中国地质调查局成都地质调查中心,成都610081 [4]北京矿产地质研究院,北京100012 [5]云南铜业勘查开发有限公司,昆明650000

出　　处：《矿物岩石地球化学通报》2020年第5期961-972,共12页Bulletin of Mineralogy, Petrology and Geochemistry

基　　金：国家重点基础研究发展计划项目(2015CB452605);云南省科技领军人才培养计划项目(2013HA001)。

摘　　要：西藏岗讲斑岩铜钼矿是近年来在冈底斯斑岩铜矿带新发现的一个大型矿床,其主要含矿斑岩是花岗闪长斑岩。为探讨含矿斑岩的形成时代和起源演化,对其进行了岩石地球化学及锆石U-Pb年代学研究。结果显示,花岗闪长斑岩的锆石U-Pb年龄为(14.66±0.28)Ma,表明其形成于印亚大陆碰撞后的伸展阶段。花岗闪长斑岩的SiO2含量为66.11%~67.71%,属高钾钙碱性-钾玄岩系列,为准铝质-过铝质花岗岩;其ΣREE为84.92×10^-6~114.53×10^-6,轻重稀土分异明显,LaN/YbN值为14.93~23.67,Eu异常不明显(δEu为0.92~1.02);富集Rb、Th、U等大离子亲石元素,强烈亏损Nb、Ta、Nd等高场强元素,具有埃达克质岩的属性。研究表明,岗讲矿床花岗闪长斑岩起源于含石榴子石角闪岩相加厚下地壳的部分熔融,是中新世后碰撞构造环境中在板片断离作用下形成的。The Gangjiang porphyry Cu-Mo deposit in Tibet is a recently discovered large deposit in the Gangdese porphyry copper belt.In order to explore the formation age,origin,and evolution of the ore-bearing porphyry,a study on the zircon U-Pb chronology and petrogeochamistry of the ore-bearing granodiorite porphyry in the deposit has been carried out in this paper.The results show that the zircon U-Pb age of granodiorite porphyry is(14.66±0.28)Ma,indicating that it was formed in the extensional stage after the Indo-Asian continental collision.The granodiorite porphyry samples have contents of SiO2 varying from 66.11%to 67.71%,and belong to the high potassium calc-alkaline to shoshonite series and the aluminous to peraluminous granite.TheirΣREE vary from 84.92×10-6 to 114.53×10-6.Their LaN/YbN values vary from 14.93 to 23.67,showing strong fractionation between LREE and HREE.TheirδEu values range from 0.92 to 1.02,showing weak negative Eu anomaly.The rock is enriched in large-ion lithophile elements(LILE)such as Rb,Th,and U and strongly depleted in high field strength elements such as Nd,Nb,Ta,and is characterized with properties of the adakitic rock.Therefore,it is suggested that the ore-bearing granodiorite porphyry of the Gangjiang deposit,possibly formed by the magma derived from the partial melting of garnet-bearing amphibolite facies of the thickened lower crust,due to the heating by the upwelling asthenosphere related to the slab break-off in the post-collisional tectonic setting in Miocene.

关 键 词：成岩时代 岩石地球化学 花岗闪长斑岩 岗讲矿床 冈底斯斑岩铜矿带 

分 类 号：P588.12[天文地球—岩石学] P597[天文地球—地质学]