西藏驱龙铜钼矿床辉绿岩地球化学、锆石U-Pb年龄及地质意义  

Geochemistry and zircon U-Pb dating of diabase from Qulong coppermolybdenum deposit in Xizang and its geological significance

作　　者：孙悦 党飞鹏 黄勇[2] 吕川 SUN Yue;DANG Feipeng;HUANG Yong;LYU Chuan(Research Institute No.270,CNNC,Nanchang 330200,China;Civil Military Center of Geological Survey,China Geological Survey,Chengdu 610036,China)

机构地区：[1]核工业二七〇研究所,江西南昌330200 [2]中国地质调查局军民融合地质调查中心,四川成都610036

出　　处：《世界核地质科学》2024年第3期483-495,共13页World Nuclear Geoscience

基　　金：中国核工业地质局项目(编号:201930、202231、202348-7)资助。

摘　　要：冈底斯岩浆带位于西藏中部,是新特提斯洋形成、俯冲、消减以及印度大陆和欧亚大陆碰撞的产物,记录了中-新生代“构造-岩浆-成矿”过程和地质演变。驱龙铜钼矿床位于冈底斯岩浆带的东段,以超大规模斑岩型铜钼矿产而闻名。矿床内出露中侏罗统叶巴组火山岩,古近纪和中新世花岗岩类侵入岩,以及辉绿岩脉等脉岩。基性-中基性岩脉是探索地球深部动力学演变和幔源物质属性的重要窗口,是反演地幔物质化学组成和物理化学条件的直接研究对象。文章以冈底斯岩浆带东段驱龙铜钼矿床内辉绿岩为研究对象,在锆石U-Pb同位素年龄和全岩主量、微量及稀土元素特征分析的基础上,探讨辉绿岩的形成时代、源区属性和产出环境,浅析研究区古近纪构造背景,以期为冈底斯岩浆带古近纪基性岩浆活动和区域构造演化提供约束性数据支撑。锆石LA-ICP-MS U-Pb定年结果显示,辉绿岩成岩年龄为(58.9±1.1)Ma,属古新世晚期,与驱龙铜钼成矿作用(16.9~15.8 Ma)无成因联系。辉绿岩属钙碱性系列,高铝(Al_(2)O_(3)=15.43%~18.42%)、贫钾(K_(2)O=0.02%~1.39%)、低钛(TiO_(2)=0.74%~1.05%),相对富集Rb、Th、U、La、Sr和亏损Nb、P和Ti,稀土元素配分曲线呈弱右倾平环状,无负Eu异常,显示弧岩浆的特征。分析认为,研究区辉绿岩形成于冈底斯岩浆活动的第三阶段(65~41 Ma),是在印度大陆和欧亚大陆初始碰撞的背景下,俯冲的新特提斯洋板片发生断离折返,幔源岩浆底侵下地壳,使得岩石圈地幔部分熔融形成的基性岩浆快速上侵的产物。Gangdese magmatic belt is located in central Xizang,it is the product of the collision between India plate and Eurasia plate during the formation,subduction and subduction of the Neo-Tethys Ocean,which recorded Mesozoic-Cenozoic‘tectonic-magma-mineralization’process and geological evolution.In the eastern section of Gangdese magmatic belt,Qulong copper-molybdenum deposit was developed with super-large-scale porphyry and Middle Jurassic Yeba Formation volcanic rocks and Miocene granitic intrusive rocks and diabase dykes.To explore the dynamic evolution in the deep earth and the chemical composition of mantle materials in this area,diabase in the Qulong copper-molybdenum deposit was studied with zircon UPb dating,bulk rock major,trace and rare earth elements,so as to provide constrained data support for the Paleogene basic magmatic activity and regional tectonic evolution of the Gangdese magmatic belt.The analysis result indicated that the diabase formation age was(58.9±1.1)Ma,belong to Late Paleocene.It has no genetic relationship with Qulong copper-molybdenum mineralization(16.9~15.8 Ma).Diabase falls in calc-alkaline series with high-Al(Al_(2)O_(3)=15.43%~18.42%),poor-K(K_(2)O=0.02%~1.39%),low-Ti(TiO_(2)=0.74%~1.05%),relatively enriched in Rb,Th,U,La,Sr and depleted in Nb,P,Ti.The REE pattern is weakly right-leaning and with no negative Eu anomaly,showing the characteristics of arc magma.It was believed that the diabase was formed in the third stage(65~41Ma)of the Gangdese magmatic activity,which is the product of the rapid intrusion of the basic magma formed by the partial melting of the lithospheric mantle under the background of the initial collision between the Indian continent and the Eurasian continent.

关 键 词：冈底斯岩浆带 驱龙辉绿岩 新特提斯洋 弧岩浆 古新世 

分 类 号：P588.124[天文地球—岩石学] P595[天文地球—地质学]